CN114785180A - Micro inverter magnetic element parameter optimization design method based on mode switching control - Google Patents

Micro inverter magnetic element parameter optimization design method based on mode switching control Download PDF

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CN114785180A
CN114785180A CN202210589560.XA CN202210589560A CN114785180A CN 114785180 A CN114785180 A CN 114785180A CN 202210589560 A CN202210589560 A CN 202210589560A CN 114785180 A CN114785180 A CN 114785180A
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transformer
micro
inverter
power
value
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CN114785180B (en
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杨骐箐
李睿
冯洋洋
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Shanghai Jiaotong University
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Shanghai Jiaotong University
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
    • H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
    • H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
    • H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/22—Conversion of dc power input into dc power output with intermediate conversion into ac
    • H02M3/24—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters
    • H02M3/28—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac
    • H02M3/325—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal
    • H02M3/335—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M3/33569—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements
    • H02M3/33576—Conversion of dc power input into dc power output with intermediate conversion into ac by static converters using discharge tubes with control electrode or semiconductor devices with control electrode to produce the intermediate ac using devices of a triode or a transistor type requiring continuous application of a control signal using semiconductor devices only having several active switching elements having at least one active switching element at the secondary side of an isolation transformer
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M5/00—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases
    • H02M5/02—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc
    • H02M5/04—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters
    • H02M5/10—Conversion of ac power input into ac power output, e.g. for change of voltage, for change of frequency, for change of number of phases without intermediate conversion into dc by static converters using transformers
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M7/219—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only in a bridge configuration

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  • Inverter Devices (AREA)

Abstract

The invention provides a micro-inverter magnetic element parameter optimization design method based on mode switching control, which is used for optimizing the turn ratio n and the leakage inductance L of a high-frequency transformer in a micro-inverter based on the characteristic that the micro-inverter is switched among a plurality of modulation modes in a power frequency periodkThe two coupled variables are subjected to mixed optimization design, so that the conduction loss of the converter under the same transmission power condition is minimized while the power transmission constraint is met. By the optimized design method, the conduction loss of the micro inverter under the full load condition can be minimized; by comprehensively considering the conduction losses at different power points, the European weighted efficiency of the micro inverter can be maximized; by synthesis ofThe influence of two design variables, namely turn ratio and leakage inductance of the high-frequency transformer on transmission power and efficiency of the micro inverter is considered, so that the designed parameters have higher practicability.

Description

Micro inverter magnetic element parameter optimization design method based on mode switching control
Technical Field
The invention relates to the technical field of photovoltaic micro-inverter magnetic element design, in particular to a double-active-bridge micro-inverter magnetic element parameter hybrid optimization design method based on mode switching control.
Background
The micro-inverter generally refers to an inverter which has power less than or equal to 1000W in a photovoltaic power generation system and has a module-level maximum power point tracking capability. Unlike centralized and string photovoltaic inversion systems, micro-inverters are directly connected to a single photovoltaic module. The MPPT control system has the advantages that independent MPPT control can be carried out on each module, the overall efficiency is greatly improved, and meanwhile, the direct-current high voltage, poor weak light effect, barrel effect and the like of a centralized inverter can be avoided.
According to the position and structural characteristics of the direct current bus, the micro-inverter can be divided into three categories: direct current bus structure, pseudo direct current bus structure and no direct current bus structure. The micro inverter with the direct-current bus structure is of a two-stage structure, a front-stage DC-DC conversion circuit is modulated by a fixed duty ratio, a rear-stage DC-AC circuit is modulated by SPWM, the two-stage DC-AC circuit is independently decoupled and controlled, but the loss of the rear-stage DC-AC conversion circuit is high; the micro inverter with the pseudo-direct current bus structure is also of a two-stage structure, wherein the front-stage DC-DC conversion circuit is modulated by SPWM, and the rear-stage DC-AC circuit is modulated by power frequency square waves, so that the defect that the control of the front-stage DC-DC circuit is complex and the distortion of alternating current output current is easily caused is overcome; the micro inverter without the direct-current bus structure is a single-stage circuit, matrix control is adopted, the number of used switching devices is small, and conversion efficiency is high, so that the micro inverter is more advantageous. In the micro-inverter without the direct-current bus structure, the number of switching devices used by a Dual Active Bridge (DAB) type micro-inverter is the least, and the problem of low efficiency of the DAB circuit under light load is solved on the basis of the characteristic of circuit wide-range soft switching.
The high-frequency transformer is an important component of the double-active-bridge micro-inverter and is also a junction of the energy interaction of a primary side circuit and a secondary side circuit. The magnetic element parameters in the high-frequency transformer not only can influence the transmission power boundary of the micro-inverter, but also can influence the primary and secondary side current effective values of the micro-inverter, so that the efficiency of the micro-inverter is influenced, and the optimal design of the magnetic element parameters is an important link for improving the efficiency of the micro-inverter. The existing high-frequency transformer magnetic element parameter design method is specific to a DAB type DC-DC converter, but is not suitable for an isolated DC-AC converter such as a single-stage half-bridge DAB type micro-inverter; in addition, the current transformer magnetic element design only designs the leakage inductance of the transformer, and ignores the fact that the turn ratio and the leakage inductance of the transformer both have influence on the transmission power and the transformer current. Therefore, a parameter mixing optimization design scheme suitable for an isolated DC-AC converter and comprehensively considering two magnetic element parameters, namely the turn ratio and the leakage inductance of the transformer, is urgently needed.
Through search, the following results are found:
the invention patent of China with the publication number of CN110138225B, a control method for a current source type double-transformer bidirectional DC-DC converter, obtains the duty ratio of zero level at the high-voltage side by giving output voltage, and realizes the matching of the voltage at the output side of the transformer; by determining the relationship between the high-level duty ratio and the phase shift angle of the low-voltage side, the zero-level duty ratio of the high-voltage side and the turns of the two transformers, the variables are controlled to enable the converter to work in a mode of minimizing peak current, the optimization of the peak value and the effective value of leakage inductance current is realized, wide-range soft switching of all switching tubes is realized, and the conversion efficiency of the converter is improved. The method still has the following technical problems: firstly, the method is only suitable for the optimal control of a current source type DC-DC converter, and the double-active bridge type micro inverter is a voltage source type DC-AC converter, so the method is not suitable any more; in addition, the method only improves the efficiency of the converter by optimizing the control of the current source type DC-DC converter, and does not carry out optimization design on parameters of the high-frequency transformer.
At present, no explanation or report of the similar technology of the invention is found, and similar data at home and abroad are not collected.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a micro-inverter magnetic element parameter optimization design method based on mode switching control, which is based on the modulation mode switching of a micro-inverter in a power frequency period and carries out mixed optimization design on the primary and secondary side turn ratio and the transformer leakage inductance of a high-frequency transformer of the micro-inverter, so that the efficiency is highest under the condition of full load of the micro-inverter; in addition, on the basis of the above, the microinverter european weighted efficiency is made the highest by combining the power points defined by the european weighted efficiency.
According to one aspect of the invention, a micro-inverter magnetic element parameter mixing optimization method based on mode switching is provided, and according to the modulation mode switching characteristics of a micro-inverter in a power frequency cycle, the primary and secondary side turn ratio and the transformer leakage inductance of a high-frequency transformer of the micro-inverter are subjected to mixing optimization design, so that the micro-inverter has the highest efficiency under the full-load condition; wherein:
the turn ratio of the primary side to the secondary side of the high-frequency transformer is 1: n, and the value converted from the leakage inductance of the transformer to the secondary side of the transformer is Lk；
The variable n to be optimized comprises s candidate values, and n is equal to { n ═ n1,n2,…,nj,…,ns}; variable L to be optimizedkThere are p candidates, Lk＝{L1,L2,…,Li,…,Lp}；
Pre-screening the candidate values of the two variables to be optimized to obtain a pre-screened candidate value (L)i,nj) As input variable, for the candidate value njAnd the candidate value LiScanning to obtain the candidate value (L)i,nj) The conduction loss of the micro inverter in the corresponding power frequency period;
repeating the steps, and carrying out optimization on the variable n to be optimized and the variable L to be optimizedkAnd scanning all the candidate values to obtain an input variable corresponding to the minimum conduction loss of the micro inverter in the power frequency period, wherein the input variable is the optimal magnetic element parameter.
Optionally, the pre-screening candidate values of two variables to be optimized includes:
if the candidate value (L)a,nb) Corresponding micro-inverter maximum transmission power Pmax(a, b) less than the nominal peak transmission power Pac,maxWhen b +1>s, take down a set of candidates (L)a+1,nb+1) Otherwise, take down a set of candidate values (L)a,nb+1) (ii) a Repeating the process until the maximum transmission power of the micro inverter corresponding to the candidate value is greater than or equal to the rated peak valueA transmission power;
if the candidate value (L)a,nb) Corresponding maximum transmission power P of micro invertermax(a, b) is equal to or greater than the rated peak transmission power Pac,maxOutputting the set of candidate values as input variables;
wherein the candidate value is the candidate value (L)a,nb) Corresponding micro-inverter maximum transmission power PmaxThe calculation method of (a, b), comprising:
Figure BDA0003664562530000031
in the formula, nbIs the turn ratio of the secondary side and the primary side of the high-frequency transformer in the candidate value, fswIs the switching frequency, L, of the micro-inverterkFor converting the leakage inductance of the transformer to the value of the leakage inductance of the secondary side, VdcIs the DC side bus capacitor voltage, VmAnd the rated voltage amplitude of the power grid.
Optionally, the pair of candidate values njAnd the candidate value LiPerforming a scan comprising:
for the input variable (L)i,nj) Judging the modulation mode of the micro inverter in each switching period in a power frequency period;
for the input variable (L)i,nj) Calculating the effective value of the secondary side current of the transformer under the corresponding modulation mode in each switching period in the power frequency period
Figure BDA0003664562530000032
And the effective value of the primary side current of the transformer
Figure BDA0003664562530000033
Repeating the modulation mode judgment and effective value calculation processes until all switching periods in the power frequency period are traversed;
for the input variable (L)i,nj) Secondary side electricity of transformer according to each switching period in power frequency periodStream valid value
Figure BDA0003664562530000034
And the effective value of the primary side current of the transformer
Figure BDA0003664562530000035
And calculating the conduction loss of the micro inverter in the power frequency period by the selected conduction resistance of the primary and secondary side switching tubes.
Optionally, the modulation mode of the micro-inverter is dependent on the phase shift angle D of the micro-inverter1And an out-shifted phase angle D2Dividing the mode into a mode I, a mode II and a mode III; wherein:
said internally shifted phase angle D1Is defined as the staggered angle of the negative rising edge of the square wave voltage on the primary side of the transformer and the positive rising edge of the square wave voltage on the primary side of the transformer, and D is more than or equal to 01≤0.5；
Said phase angle D2Is defined as the staggered angle of the fundamental wave of the square wave voltage of the primary side of the transformer and the fundamental wave of the square wave voltage of the secondary side of the transformer, and D is more than or equal to-0.52≤0.5；
When the phase angle D is shifted outwards2Satisfy (1-D)1)/2＜D2Less than or equal to 0.5 or less than-0.5 < D2≤-(1-D1) When the voltage is in a first mode, the current of the transformer is close to a sine wave, and the effective value of the current of the transformer is the maximum;
when the phase angle D is shifted outwards2Satisfies D1/2＜D2≤(1-D1) [ 2 ] or- (1-D ]1)/2＜D2When the voltage is less than or equal to-D1/2, one part of the positive level of the primary side square wave voltage is superposed with the positive level of the secondary side square wave voltage, the other part of the positive level of the primary side square wave voltage is superposed with the negative level of the secondary side square wave voltage, the corresponding modulation mode is a mode II, the current of the transformer is close to trapezoidal wave at the moment, and the effective value of the current of the transformer is smaller than the effective value in the mode I and larger than the effective value in the mode III;
when the phase angle D is shifted outwards2D is more than or equal to 02≤D1/2 or-D1/2≤D2When the current is less than or equal to 0, the positive level part of the primary side square wave voltage and the positive level part of the secondary side square wave voltage are completely superposed, the corresponding modulation mode is a mode three, the current of the transformer is close to a triangular wave at the moment, and the effective value of the current of the transformer is minimum;
for the input variable (L)i,nj) And judging the modulation mode of the micro inverter in each switching period in the power frequency period, wherein the method comprises the following steps: if | M | is less than or equal to D1(1-2D1) If the modulation mode corresponds to the mode three; if M > D1(1-2D1) If the modulation mode corresponds to the second mode; wherein M is the micro-inverter transmission power ratio and is defined as
Figure BDA0003664562530000041
Wherein n is the turn ratio of the secondary side and the primary side of the high-frequency transformer, fswIs the switching frequency, L, of the micro-inverterkFor the transformer leakage inductance, sgn (v) is converted into the secondary leakage inductance valueg) As a sign function of the network-side voltage, VdcIs the DC side bus capacitor voltage, igrefAnd setting a grid-connected current value.
Optionally, the effective value of the secondary side current of the transformer in the corresponding modulation mode is calculated
Figure BDA0003664562530000042
And the effective value of the primary side current of the transformer
Figure BDA0003664562530000043
The method comprises the following steps:
secondary current effective value of transformer
Figure BDA0003664562530000044
The calculation method of (2) comprises:
Figure BDA0003664562530000045
wherein m is the number of power frequency period segments; i.e. is,rms,iThe effective value of the secondary side current of the transformer in the ith power frequency period is as followsAnd (3) calculating:
Figure BDA0003664562530000051
wherein, fswIs the switching frequency, L, of the micro-inverterkFor the transformer leakage inductance to the secondary value, njIs the turn ratio, V, of the secondary side and the primary side of the high-frequency transformerdcIs the DC side bus capacitor voltage, | vg,iL is the grid voltage at the beginning of the i-th power frequency period, mvFor voltage gain, satisfy mv＝|vg，i|/(njVdc)；
The primary side current effective value of the transformer
Figure BDA0003664562530000052
The calculation method of (2) comprises:
Figure BDA0003664562530000053
the method for calculating the conduction loss of the micro inverter in the power frequency period comprises the following steps: calculating the conduction loss P of the primary side switching tube of the micro-inverterloss,priAnd calculating the conduction loss P of the secondary side switching tube of the micro inverterloss,secAnd calculating the conduction loss P of the micro-inverter transformerloss,trWherein:
calculating the conduction loss P of the primary side switching tube of the micro inverterloss,priThe method comprises the following steps:
Figure BDA0003664562530000054
wherein R isds,on,priThe on-resistance of a single primary side switching tube;
calculating the conduction loss P of the primary side switching tube of the micro inverterloss,secThe method comprises the following steps:
Figure BDA0003664562530000055
wherein R isds,on,secThe on-resistance of a single secondary side switching tube;
the micro inverter transformer conduction loss Ploss,trThe method comprises the following steps:
Figure BDA0003664562530000056
wherein R istr,priAnd Rtr,secWinding resistors of primary and secondary sides of the transformer respectively;
in a power frequency period, the method for calculating the efficiency eta of the micro inverter under the full-load condition comprises the following steps:
Figure BDA0003664562530000057
wherein, Pac,NThe rated transmission power of the micro-inverter.
According to another aspect of the invention, a micro-inverter magnetic element parameter hybrid optimization design method based on mode switching is provided, according to the modulation mode switching characteristics of a micro-inverter in a power frequency period and in combination with a power point defined by European weighted efficiency, hybrid optimization design is carried out on the primary and secondary side turn ratio and the transformer leakage inductance of a high-frequency transformer of the micro-inverter, so that the European weighted efficiency of the micro-inverter is the highest; wherein:
the turn ratio of the primary side to the secondary side of the high-frequency transformer is 1: n, and the value converted from the leakage inductance of the transformer to the secondary side of the transformer is Lk；
The variable n to be optimized comprises s candidate values, and n is equal to { n ═ n1,n2,…,nj,…,ns}; variable L to be optimizedkThere are p candidates, Lk＝{L1,L2,…,Li,…,Lp}；
Pre-screening the candidate values of the two variables to be optimized to obtain a pre-screened candidate value (L)i,nj) As input variables, for the candidatesValue njAnd the candidate value LiScanning to obtain the candidate value (L)i,nj) Corresponding european weighted efficiency;
repeating the steps, and carrying out optimization on the variable n to be optimized and the variable L to be optimizedkAnd scanning all the candidate values to obtain an input variable corresponding to the maximum European weighted efficiency, namely the optimal magnetic element parameter.
Optionally, the method for calculating the european weighted efficiency includes:
calculating the micro-inverter efficiency eta (eta) corresponding to 5%, 10%, 20%, 30%, 50% and 100% power points5％，η10％，η20％，η30％，η50％，η100％And calculating the weighting efficiency to obtain European weighting efficiency;
the power points of 5%, 10%, 20%, 30%, 50%, and 100% are defined as power points defined by european weighted efficiency, and the corresponding weighting coefficients are W ═ 0.03,0.06,0.13,0.10,0.48, and 0.20, respectively.
Optionally, the pre-screening candidate values of two variables to be optimized includes:
calculate each set of candidate values (L)a,nb) Corresponding maximum transmission power P of micro inverter at 100% power pointmax(a,b)；
If the maximum transmission power P of the micro-invertermax(a, b) less than the rated peak transmission power Pac,maxWhen b +1>s, take down a set of candidate values (L)a+1,nb+1) Otherwise, take down a set of candidate values (L)a,nb+1) (ii) a Repeating the process until the maximum transmission power of the micro inverter at the 100% power point corresponding to the candidate value is greater than or equal to the rated peak transmission power;
if the maximum transmission power P of the micro-invertermax(a, b) is equal to or greater than the rated peak transmission power Pac,maxOutputting the set of candidate values as input variables;
wherein the candidate value is the candidate value (L)a,nb) Corresponding micro-inversion at 100% power pointMaximum transmission power PmaxThe calculation method of (a, b), comprising:
Figure BDA0003664562530000061
in the formula, nbIs the turn ratio of the secondary side and the primary side of the high-frequency transformer in the candidate value, fswIs the switching frequency, L, of the micro-inverterkFor converting the leakage inductance of the transformer to the value of the leakage inductance, V, of the secondary sidedcIs the DC side bus capacitor voltage, VmAnd the rated voltage amplitude of the power grid.
Optionally, the pair of candidate values njAnd the candidate value LiPerforming a scan comprising:
sequentially selecting working power points of the micro-inverter from the power points defined by the European weighted efficiency;
for the input variable (L)i,nj) Judging the modulation mode of the micro inverter in each switching period in the power frequency period by combining the selected working power point; (ii) a
For the input variable (L)i,nj) And calculating the effective value of the secondary side current of the transformer under the corresponding modulation mode in each switching period in the power frequency period by combining the selected working power point
Figure BDA0003664562530000071
And the effective value of the primary side current of the transformer
Figure BDA0003664562530000072
Repeating the processes of judging the modulation mode and calculating the current effective value until all switching periods in the power frequency period are traversed;
for the input variable (L)i,nj) Combining the selected working power point and the effective value of the secondary side current of the transformer in each switching period in the power frequency period
Figure BDA0003664562530000073
And the effective value of the primary side current of the transformer
Figure BDA0003664562530000074
And the conduction resistance of the selected primary and secondary side switching tubes is used for calculating the conduction loss and the efficiency of the micro-inverter in the power frequency period; if the selected operating power point is 100%, the input variable (L) is calculated according to a European weighted efficiency calculation methodi,nj) Corresponding european weighted efficiency; otherwise, the working power point of the next micro-inverter is reselected until the input variable (L) when the working power point is 100 percent is obtainedi,nj) Corresponding european weighted efficiencies.
Optionally, the modulation mode of the micro-inverter is dependent on the phase shift angle D of the micro-inverter1And an out-shifted phase angle D2Dividing the pattern into a first pattern, a second pattern and a third pattern; wherein:
said internally shifted phase angle D1Is defined as the staggered angle of the negative rising edge of the square wave voltage of the primary side of the transformer and the positive rising edge of the square wave voltage of the primary side of the transformer, and D is more than or equal to 01≤0.5；
Said out-shifted phase angle D2Is defined as the staggered angle of the fundamental wave of the square wave voltage of the primary side of the transformer and the fundamental wave of the square wave voltage of the secondary side of the transformer, and D is more than or equal to-0.52≤0.5；
When the phase angle D is shifted outwards2Satisfy (1-D)1)/2＜D2Less than or equal to 0.5 or less than-0.5 and less than D2≤-(1-D1) When the voltage is in a first mode, the current of the transformer is close to a sine wave, and the effective value of the current of the transformer is the maximum;
when the phase angle D is shifted outwards2Satisfy D1/2＜D2≤(1-D1) [ 2 ] or- (1-D ]1)/2＜D2≤-D1When the voltage of the transformer is in a second modulation mode, one part of the positive level of the primary side square wave voltage is superposed with the positive level of the secondary side square wave voltage, the other part of the positive level of the primary side square wave voltage is superposed with the negative level of the secondary side square wave voltage, and the corresponding modulation mode is the second modeThe current is close to trapezoidal wave, and the effective value of the transformer current is smaller than the effective value in the mode one and larger than the effective value in the mode three;
when the phase angle D is shifted outwards2D is more than or equal to 02≤D1/2 or-D1/2≤D2When the current is less than or equal to 0, the positive level part of the primary side square wave voltage and the positive level part of the secondary side square wave voltage are completely superposed, the corresponding modulation mode is a mode three, the current of the transformer is close to a triangular wave at the moment, and the effective value of the current of the transformer is minimum;
for the input variable (L)i,nj) And in combination with the selected working power point, judging the modulation mode of the micro inverter in each switching period in the power frequency period, wherein the method comprises the following steps:
if | M | is less than or equal to D1(1-2D1) If the modulation mode corresponds to the mode three; if M > D1(1-2D1) If the modulation mode corresponds to the second mode; in the formula D1For the phase angle, M is the transmission power ratio of the micro inverter, defined as
Figure BDA0003664562530000081
Where n is the turn ratio of the secondary side to the primary side of the high-frequency transformer, fswIs the switching frequency, L, of the micro-inverterkFor the transformer leakage inductance, sgn (v) is converted into the secondary leakage inductance valueg) As a function of the sign of the network-side voltage, VdcIs the DC side bus capacitor voltage igrefAnd setting the grid-connected current.
Optionally, the effective value of the secondary side current of the transformer in the corresponding modulation mode is calculated
Figure BDA0003664562530000082
And the effective value of the primary side current of the transformer
Figure BDA0003664562530000083
The method comprises the following steps:
secondary side current effective value of transformer corresponding to h-th power point
Figure BDA0003664562530000084
Is calculated byA method, comprising:
Figure BDA0003664562530000085
wherein m is the number of power frequency period segments; i.e. is,rms,iCalculating the effective value of the secondary side current of the transformer in the ith section of power frequency period at the h-th power point according to the following mode:
Figure BDA0003664562530000086
wherein f isswIs the switching frequency, L, of the micro-inverterkFor converting the leakage inductance of the transformer to the value of the leakage inductance of the secondary side, njIs the turn ratio, V, of the secondary side and the primary side of the high-frequency transformerdcIs the DC side bus capacitor voltage, | vg,i,hL is the grid voltage at the start of the ith power frequency cycle at the h power point, mvFor voltage gain, satisfy mv＝|vg，i，h|/(njVdc)；
The primary side current effective value of the transformer
Figure BDA0003664562530000091
The calculation method of (2) comprises:
Figure BDA0003664562530000092
the method for calculating the conduction loss of the micro inverter in the power frequency period comprises the following steps: calculating the conduction loss P of the primary side switching tube of the micro-inverterloss,pri,hAnd calculating the conduction loss P of the secondary side switching tube of the micro inverterloss,sec,hAnd calculating the conduction loss P of the micro-inverter transformerloss,tr,hWherein:
at the h power point, the conduction loss P of the primary side switching tube of the micro inverter is calculatedloss,pri,hThe method comprises the following steps:
Figure BDA0003664562530000093
wherein R isds,on,priThe switch is the on-resistance of a single primary side switch tube;
at the h-th power point, the conduction loss P of the primary side switching tube of the micro inverter is calculatedloss,sec,hThe method comprises the following steps:
Figure BDA0003664562530000094
wherein R isds,on,secThe on-resistance of a single secondary side switching tube;
at the h power point, the calculation of the conduction loss P of the micro-inverter transformerloss,tr,hThe method comprises the following steps:
Figure BDA0003664562530000095
wherein R istr,priAnd Rtr,secWinding resistors of primary and secondary sides of the transformer respectively;
in a power frequency period at the h-th power point, the calculation method of the European weighted efficiency of the micro-inverter comprises the following steps:
calculating the efficiency eta of the micro inverter in the power frequency period at the h-th power pointhThe method comprises the following steps:
Figure BDA0003664562530000096
respectively calculating the efficiency of the h power points to obtain an efficiency matrix eta of 1 multiplied by h;
calculating the microinverter European weighted efficiency etaeuThe method comprises the following steps:
ηeu＝η×WT
wherein, WTIs a transpose of the weighting coefficient matrix.
Due to the adoption of the technical scheme, compared with the prior art, the invention has the following beneficial effects:
according to the method for optimally designing the parameters of the magnetic elements of the micro inverter based on mode switching control, the full-load efficiency of the micro inverter can be highest under the optimally designed parameters of the magnetic elements of the high-frequency transformer based on mode switching; meanwhile, the primary and secondary side turn ratio of the transformer and the leakage inductance parameter of the transformer are subjected to mixed optimization design, so that the primary and secondary side currents of the transformer under the optimized parameters are reduced while the power transmission constraint of the micro-inverter is met.
According to the method for optimally designing the parameters of the magnetic elements of the micro inverter based on the mode switching control, based on the mode switching, the efficiency of the micro inverter at six power points is comprehensively considered, so that the light load efficiency of the micro inverter under the optimally designed parameters of the high-frequency transformer is greatly improved, the European weighted efficiency is favorably improved, and the micro inverter still has higher efficiency when a photovoltaic panel is shielded, the illumination intensity is insufficient or the environment temperature is not suitable.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
FIG. 1 is a schematic circuit diagram of a dual active bridge micro-inverter of the present invention;
FIG. 2 is a schematic diagram of waveforms of driving signals of the switching tubes S1-S8, primary voltage of the transformer, secondary voltage of the transformer, and secondary current of the transformer in three modulation modes according to a preferred embodiment of the present invention;
FIG. 3 is a schematic diagram of the ranges of the internally shifted phase angle and the externally shifted phase angle corresponding to three modulation modes in a preferred embodiment of the present invention;
FIG. 4 is a flow chart of a dual active bridge micro-inverter magnetic element parameter hybrid optimization design method based on mode switching and maximizing full-load efficiency in a preferred embodiment of the present invention;
FIG. 5 is a schematic diagram of the square sum of the primary and secondary side currents of the micro-inverter varying with the leakage inductance of the transformer and the turn ratio of the transformer according to a preferred embodiment of the present invention;
fig. 6 is a flow chart of a dual active bridge micro-inverter magnetic element parameter hybrid optimization design method based on mode switching and maximizing european weighting efficiency in accordance with an embodiment of the present invention;
fig. 7 is a curved surface diagram of the european weighted efficiency of the micro-inverter as a function of the transformer leakage inductance and the transformer turn ratio in a preferred embodiment of the present invention.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the spirit of the invention, which falls within the scope of the invention. The following portions not described may refer to the description of the contents of the invention or the prior art.
The invention provides a micro-inverter magnetic element parameter hybrid optimization method based on mode switching, which performs hybrid optimization design on the primary and secondary turn ratio of a high-frequency transformer and the leakage inductance of the transformer according to the working characteristics of switching among a plurality of modulation modes of a micro-inverter in a power frequency period, so that the efficiency is highest under the full load condition.
Further, the embodiment provides a mode switching based micro-inverter magnetic element parameter hybrid optimization involving a method, which may include the steps of:
the turn ratio of the primary side to the secondary side of the high-frequency transformer is 1: n, and the value converted from the leakage inductance of the transformer to the secondary side of the transformer is Lk；
The variable n to be optimized comprises s candidate values, and n is equal to { n ═ n1,n2,…,nj,…,ns}; variable L to be optimizedkThere are p candidates, Lk＝{L1,L2,…,Li,…,Lp}；
Pre-screening the candidate values of the two variables to be optimized to obtain a pre-screened candidate value (L)i,nj) As input variable, for the candidate value njAnd the candidate value LiScanning to obtain the candidate value (L)i,nj) The conduction loss of the micro inverter in the corresponding power frequency period;
repeating the steps to the variable n to be optimized and the variable L to be optimizedkAnd scanning all the candidate values to obtain an input variable corresponding to the minimum conduction loss of the micro inverter in the power frequency period, wherein the input variable is the optimal magnetic element parameter.
In a preferred embodiment, the pre-screening candidate values of two variables to be optimized includes:
if the candidate value (L)a,nb) Corresponding micro-inverter maximum transmission power Pmax(a, b) less than the nominal peak transmission power Pac,maxWhen b +1>s, take down a set of candidates (L)a+1,nb+1) Otherwise, take down a set of candidate values (L)a,nb+1) (ii) a Repeating the comparison process until the maximum transmission power of the micro inverter corresponding to the candidate value is greater than or equal to the rated peak transmission power;
if the candidate value (L)a,nb) Corresponding maximum transmission power P of micro invertermax(a, b) is equal to or greater than the rated peak transmission power Pac,maxThe set of candidate values is output as input variables.
Wherein the candidate value (L) is a candidate valuea,nb) Corresponding micro-inverter maximum transmission power Pmax(a, b) is calculated as follows:
Figure BDA0003664562530000111
in the formula, nbIs the turn ratio of the secondary side and the primary side of the high-frequency transformer in the candidate value, fswIs the switching frequency, L, of the micro-inverterkFor converting the leakage inductance of the transformer to the value of the leakage inductance, V, of the secondary sidedcIs the DC side bus capacitor voltage, VmAnd the rated voltage amplitude of the power grid.
In a preferred embodiment, the pair of candidate values njAnd the candidate value LiPerforming a scan comprising:
for the input variable (L)i,nj) Judging the modulation mode of the micro inverter in each switching period in a power frequency period;
for the input variable (L)i,nj) Calculating the effective value of the secondary side current of the transformer under the corresponding modulation mode in each switching period in the power frequency period
Figure BDA0003664562530000112
And the effective value of the primary side current of the transformer
Figure BDA0003664562530000113
Repeating the modulation mode judging process and the effective value calculating process until traversing all switching periods in the power frequency period;
for the input variable (L)i,nj) According to the effective value of the secondary side current of the transformer in each switching period in the power frequency period
Figure BDA0003664562530000114
And the effective value of the primary side current of the transformer
Figure BDA0003664562530000115
And calculating the conduction loss of the micro inverter in the power frequency period by the selected conduction resistance of the primary and secondary side switching tubes.
In a preferred embodiment, the modulation modes of the micro-inverter are three in number, according to the phase angle D of the micro-inverter1And an out-shifted phase angle D2Dividing the value range of (a); wherein:
said phase angle D1Is defined as the staggered angle of the negative rising edge of the square wave voltage of the primary side of the transformer and the positive rising edge of the square wave voltage of the primary side of the transformer, and D is more than or equal to 01≤0.5；
Said out-shifted phase angle D2Is defined as the staggered angle of the fundamental wave of the square wave voltage of the primary side of the transformer and the fundamental wave of the square wave voltage of the secondary side of the transformer, and D is more than or equal to-0.52≤0.5；
When the phase angle D is shifted outwards2Satisfy (1-D)1)/2＜D2Less than or equal to 0.5 or less than-0.5 and less than D2≤-(1-D1) When the voltage is in a first mode, the current of the transformer is close to a sine wave, the effective value of the current of the transformer is the maximum, but the zero-voltage soft switching of the original secondary switching tube is most easily realized;
when the phase angle D is shifted outwards2Satisfies D1/2＜D2≤(1-D1) [ 2 ] or- (1-D ]1)/2＜D2≤-D1When the voltage of the transformer is higher than the zero voltage of the primary side switching tube, the current of the transformer is close to a trapezoidal wave, the effective value of the current of the transformer is moderate, and the zero voltage soft switching of the primary side switching tube is easy to realize;
when the phase angle D is shifted outwards2Satisfies 0. ltoreq. D2≤D1/2 or-D1/2≤D2When the voltage is less than or equal to 0, the positive level part of the primary voltage and the positive level part of the secondary voltage are completely superposed, the corresponding modulation mode is a mode three, the current of the transformer is close to a triangular wave at the moment, and in the three modulation modes, the effective value of the current of the transformer in the mode three is minimum, but the zero-voltage soft switching of the original secondary switching tube is difficult to realize.
Further, for the input variable (L)i,nj) And judging the modulation mode of the micro inverter in each switching period in the power frequency period, wherein the method comprises the following steps: if | M | is less than or equal to D1(1-2D1) If the modulation mode corresponds to the mode three; m > D1(1-2D1) If the modulation mode corresponds to the second mode; in the formula, D1For the phase shift angle, M is the transmission power ratio of the micro inverter and is defined as
Figure BDA0003664562530000121
Where n is the turn ratio of the secondary side to the primary side of the high-frequency transformer, fswIs the switching frequency, L, of the micro-inverterkThe leakage inductance value of the secondary side is converted for the leakage inductance of the transformer,sgn(vg) As a function of the sign of the network-side voltage, VdcIs the DC side bus capacitor voltage, igrefAnd setting a grid-connected current value.
In a preferred embodiment, the effective value of the secondary side current of the transformer in the corresponding modulation mode is calculated
Figure BDA0003664562530000122
And the effective value of the primary side current of the transformer
Figure BDA0003664562530000123
The method comprises the following steps:
the secondary side current effective value of the transformer is calculated according to the following mode:
Figure BDA0003664562530000131
wherein m is the number of power frequency period segments; i all right angles,rms,iCalculating the effective value of the secondary side current of the transformer in the ith power frequency period according to the following mode:
Figure BDA0003664562530000132
wherein, fswIs the switching frequency, L, of the micro-inverterkFor converting the leakage inductance of the transformer to the value of the leakage inductance of the secondary side, njIs the turn ratio, V, of the secondary side and the primary side of the high-frequency transformerdcIs the DC side bus capacitor voltage, | vg,iL is the grid voltage at the beginning of the i-th power frequency period, mvFor voltage gain, satisfy mv＝|vg，i|/(njVdc)。
The effective value of the primary side current of the transformer is calculated according to the following mode:
Figure BDA0003664562530000133
calculating the conduction loss of the micro inverter in the power frequency periodLoss, including conduction loss P of primary side switching tube of micro-inverterloss,priConduction loss P of secondary side switching tube of micro inverterloss,secAnd micro inverter transformer conduction loss Ploss,trWherein:
conduction loss P of primary side switching tube of micro inverterloss,priThe calculation is performed as follows:
Figure BDA0003664562530000134
wherein R isds,on,priIs the on-resistance of a single primary side switching tube.
Conduction loss P of primary side switching tube of micro-inverterloss,secThe calculation is performed as follows:
Figure BDA0003664562530000135
wherein R isds,on,secIs the on-resistance of a single secondary side switch tube.
Micro inverter transformer conduction loss Ploss,trThe calculation is performed as follows:
Figure BDA0003664562530000136
wherein R istr,priAnd Rtr,secAre respectively the winding resistors of the primary side and the secondary side of the transformer.
The efficiency eta of the micro inverter in the power frequency period is calculated according to the following mode:
Figure BDA0003664562530000141
wherein P isac,NThe rated transmission power of the micro-inverter.
The method provided by the embodiment of the invention is a double-active bridge type micro-inverter magnetic element parameter hybrid optimization design method based on mode switching and enabling full load efficiency to be highest. Wherein:
the turn ratio of the primary side to the secondary side of the high-frequency transformer of the double-active-bridge micro-inverter is 1: n, and the value converted from the leakage inductance of the transformer to the secondary side of the transformer is LkThe transformer is not provided with an air gap, so that the excitation inductance L of the transformer is ensuredmAs large as possible.
The micro-inverter has three modulation modes, and the modulation modes are according to the internal phase shift angle D of the micro-inverter1And an out-shifted phase angle D2The value range of the primary side square wave voltage is divided, wherein the internal phase shift angle is defined as the staggered angle of the negative rising edge of the primary side square wave voltage and the positive rising edge of the primary side square wave voltage; the out-shift phase angle is defined as the angle of the offset between the fundamental wave of the square wave voltage on the primary side of the transformer and the fundamental wave of the square wave voltage on the secondary side of the transformer. When shifting out the phase angle D2Satisfy (1-D)1)/2＜D2Less than or equal to 0.5 or less than-0.5 and less than D2≤-(1-D1) When the modulation mode is a first mode, the modulation mode is a second mode; when phase angle is shifted outwards D2Satisfies D1/2＜D2≤(1-D1) [ 2 ] or- (1-D ]1)/2＜D2≤-D1When the modulation mode is the second mode, the modulation mode is the second mode; when phase angle is shifted outwards D2D is more than or equal to 02≤D1/2 or-D1/2≤D2When the modulation mode is less than or equal to 0, the corresponding modulation mode is a mode three.
The mode I is defined as a modulation mode in which a positive level part of primary side square wave voltage and a negative level part of secondary side square wave voltage are completely superposed, at the moment, the current of the transformer is close to a sine wave, the effective value of the current of the transformer is the largest, but the zero-voltage soft switching of an original secondary side switching tube is most easily realized; the mode II is defined as a modulation mode that one part of the positive level of the primary side voltage is superposed with the positive level of the secondary side voltage, and the other part of the positive level of the primary side voltage is superposed with the negative level of the secondary side voltage, at the moment, the current of the transformer is close to a trapezoidal wave, the effective value of the current of the transformer is moderate, and the zero-voltage soft switching of the original secondary side switching tube is easy to realize; and the third mode is defined as a modulation mode in which the positive level part of the primary voltage and the positive level part of the secondary voltage are completely superposed, the current of the transformer is close to triangular waves at the moment, and in the three modulation modes, the effective value of the current of the transformer in the third mode is minimum, but the zero-voltage soft switching of the original secondary switching tube is difficult to realize.
The variable n to be optimized has s candidate values, n is { n ═ n1,n2,…,nj,…,ns}; variable L to be optimizedkThere are p candidates, Lk＝{L1,L2,…,Li,…,Lp}。
The method provided by the embodiment of the invention mainly comprises two links, namely a pre-screening link and a formal optimization design link.
Wherein the pre-screening principle is as follows:
if the candidate variable group (L)a,nb) Corresponding maximum transmission power P of micro invertermax(i, j) less than the nominal peak transmission power Pac,maxThen take down a set of candidate variables (L)a+1,nb+1) Or (L)a,nb+1) Repeating the judging process;
if the candidate variable group (L)a,nb) Corresponding micro-inverter maximum transmission power Pmax(i, j) is equal to or greater than the rated peak transmission power Pac,maxAnd outputting the candidate variable group and entering a formal optimization design link.
Wherein the design flow is formally optimized with a pre-screened output (L)i,nj) The method is used as input and comprises three parts of modulation mode selection, primary and secondary side current effective value calculation of a transformer and conduction loss calculation in a power frequency period, and the specific process is as follows:
selecting a modulation mode: for the input variable (L)i,nj) And judging the modulation mode of the micro inverter in each switching period in the power frequency period. If | M | is less than or equal to D1(1-2D1) If the working mode corresponds to the mode III; if M > D1(1-2D1) The operating mode corresponds to mode two. In the above expression, M is the micro-inverter transmission power ratio, defined as
Figure BDA0003664562530000151
Where n is the turn ratio of the secondary side to the primary side of the high-frequency transformer, vpvIs the DC side bus capacitor voltage, fswIs the switching frequency, L, of the micro-inverterkFor the transformer, sgn (v) is converted into the value of the leakage inductance to the secondary sideg) As a function of the sign of the net side voltage.
Secondly, calculating the effective value of the primary and secondary side currents of the transformer: for the input variable (L)i,nj) Calculating the effective value of the secondary side current of the transformer under the corresponding modulation mode in each switching period in the power frequency period
Figure BDA0003664562530000152
And the effective value of the primary side current of the transformer
Figure BDA0003664562530000153
And repeating the first process and the second process until all the switching periods in the power frequency period are traversed.
Thirdly, calculating the conduction loss in the power frequency period: for the input variable (L)i,nj) According to the effective value of the secondary side current of the transformer in each switching period in the power frequency period
Figure BDA0003664562530000154
And the effective value of the primary side current of the transformer
Figure BDA0003664562530000155
And the conduction resistance of the selected primary and secondary side switching tubes is used for calculating and recording the conduction loss of the micro inverter in the power frequency period.
Repeat the prescreening and the three above-described procedures (i.e., scanning procedure) for all n and LkThe candidate value of (L) is scanned, and the minimum corresponding conduction loss (L) of the micro inverter in the power frequency period after scanning is finishedi,nj) I.e. the optimal magnetic element parameters.
The embodiment of the invention provides a micro-inverter magnetic element parameter hybrid optimization design method based on mode switching, which is used for performing hybrid optimization design on the primary and secondary side turn ratio and transformer leakage inductance of a high-frequency transformer of a micro-inverter according to the working characteristics of switching among a plurality of modulation modes of the micro-inverter in a power frequency period and by combining power points defined by European weighted efficiency, so that the European weighted efficiency of the micro-inverter is highest.
Further, the method for designing a micro-inverter magnetic element parameter hybrid optimization based on mode switching according to this embodiment may include the following steps:
the turn ratio of the primary side to the secondary side of the high-frequency transformer is 1: n, and the value converted from the leakage inductance of the transformer to the secondary side of the transformer is LkThe value of the transformer excitation inductance converted to the primary side of the transformer is Lm；
The variable n to be optimized comprises s candidate values, and n is equal to { n ═ n1,n2,…,nj,…,ns}; variable L to be optimizedkThere are p candidates, Lk＝{L1,L2,…,Li,…,Lp}；
Pre-screening the candidate values of the two variables to be optimized to obtain a pre-screened candidate value (L)i,nj) As input variable, for the candidate value njAnd the candidate value LiScanning to obtain the candidate value (L)i,nj) Corresponding european weighted efficiency;
repeating the steps to the variable n to be optimized and the variable L to be optimizedkAnd scanning all the candidate values to obtain an input variable corresponding to the European maximum weighted efficiency value, namely the optimal magnetic element parameter.
In a preferred embodiment, the method for calculating the european weighted efficiency includes:
calculating the micro-inverter efficiency eta (eta) corresponding to 5%, 10%, 20%, 30%, 50% and 100% power points5％，η10％，η20％，η30％，η50％，η100％And calculating the weighting efficiency to obtain European weighting efficiency;
the 5%, 10%, 20%, 30%, 50%, and 100% power points are defined as power points defined by european weighted efficiency, and their corresponding weighting coefficients are W ═ 0.03,0.06,0.13,0.10,0.48, and 0.20, respectively.
In a preferred embodiment, the pre-screening candidate values of two variables to be optimized includes:
calculate each set of candidate values (L)a,nb) Corresponding maximum transmission power P of micro inverter at 100% power pointmax(a,b)；
If the maximum transmission power P of the micro-invertermax(a, b) less than the rated peak transmission power Pac,maxWhen b +1>s, take down a set of candidate variables (L)a+1,nb+1) Otherwise, take down a set of candidate values (L)a,nb+1) (ii) a Re-performing the pre-screening process until the maximum transmission power of the micro inverter at a 100% power point corresponding to the candidate value is greater than or equal to the rated peak transmission power;
if the maximum transmission power P of the micro-invertermax(a, b) is equal to or greater than the rated peak transmission power Pac,maxThe set of candidate values is output as input variables.
Wherein the candidate value (L) is a candidate valuea,nb) Corresponding maximum transmission power P of micro inverter at 100% power pointmax(a, b) is calculated as follows:
Figure BDA0003664562530000161
in the formula, nbIs the turn ratio of the secondary side and the primary side of the high-frequency transformer in the candidate value, fswIs the switching frequency, L, of the micro-inverterkFor converting the leakage inductance of the transformer to the value of the leakage inductance of the secondary side, VdcIs the DC side bus capacitor voltage, VmAnd the rated voltage amplitude of the power grid.
In a preferred embodiment, the pair of candidate values njAnd the candidate value LiPerforming a scan comprising:
sequentially selecting working power points of the micro-inverter from power points defined by the European weighted efficiency;
for the saidInput variable (L)i,nj) In combination with the selected working power point, judging the modulation mode of the micro inverter in each switching period in the power frequency period;
for the input variable (L)i,nj) And calculating the effective value of the secondary side current of the transformer under the corresponding modulation mode in each switching period in the power frequency period by combining the selected working power point
Figure BDA0003664562530000171
And the effective value of the primary side current of the transformer
Figure BDA0003664562530000172
Repeating the modulation mode judgment process and the current effective value calculation process until all the switching periods in the power frequency period are traversed;
for the input variable (L)i,nj) Combining the selected working power point, and according to the secondary current effective value of the transformer in each switching period in the power frequency period
Figure BDA0003664562530000173
And the effective value of the primary side current of the transformer
Figure BDA0003664562530000174
And the conduction resistance of the selected primary and secondary side switch tubes is used for calculating the conduction loss and the efficiency of the micro-inverter in the power frequency period; if the operating power point selected at this time is 100%, the input variable (L) is calculated according to a European weighted efficiency calculation methodi,nj) Corresponding european weighted efficiency; otherwise, the working power point of the next micro-inverter is reselected until the input variable (L) when the working power point is 100 percent is obtainedi,nj) Corresponding european weighted efficiencies.
In a preferred embodiment, the modulation modes of the micro-inverter are three in total, according to the internal phase shift angle D of the micro-inverter1And an out-shifted phase angle D2Dividing the value range of (A); wherein:
said phase angle D1Is defined as the staggered angle of the negative rising edge of the square wave voltage of the primary side of the transformer and the positive rising edge of the square wave voltage of the primary side of the transformer, and D is more than or equal to 01≤0.5；
Said phase angle D2Is defined as the staggered angle of the fundamental wave of the square wave voltage of the primary side of the transformer and the fundamental wave of the square wave voltage of the secondary side of the transformer, and D is more than or equal to-0.52≤0.5；
When the phase angle D is shifted outwards2Satisfy (1-D)1)/2＜D2Less than or equal to 0.5 or less than-0.5 and less than D2≤-(1-D1) When the voltage is in a first mode, the current of the transformer is close to a sine wave, the effective value of the current of the transformer is the maximum, but the zero-voltage soft switching of the original secondary switching tube is most easily realized;
when the phase angle D is shifted outwards2Satisfies D1/2＜D2≤(1-D1) [ 2 ] or- (1-D ]1)/2＜D2≤-D1When the voltage is higher than the primary side voltage, the current of the transformer is close to a trapezoidal wave, the effective value of the current of the transformer is moderate, and the zero-voltage soft switching of the original secondary side switching tube is easy to realize;
when the phase angle D is shifted outwards2Satisfies 0. ltoreq. D2≤D1/2 or-D1/2≤D2When the voltage is less than or equal to 0, the positive level part of the primary voltage and the positive level part of the secondary voltage are completely superposed, the corresponding modulation mode is a mode three, the current of the transformer is close to a triangular wave at the moment, and in the three modulation modes, the effective value of the current of the transformer in the mode three is minimum, but the zero-voltage soft switching of the original secondary switching tube is difficult to realize.
Further, for the input variable (L)i,nj) And in combination with the selected working power point, judging the modulation mode of the micro inverter in each switching period in the power frequency period, wherein the method comprises the following steps:
if | M | is less than or equal to D1(1-2D1) Then modulateThe mode corresponds to a mode III; if M > D1(1-2D1) If so, the modulation mode corresponds to the second mode; in the formula D1For the phase shift angle, M is the transmission power ratio of the micro inverter and is defined as
Figure BDA0003664562530000181
Wherein n is the turn ratio of the secondary side and the primary side of the high-frequency transformer, fswIs the switching frequency, L, of the micro-inverterkFor the transformer leakage inductance, sgn (v) is converted into the secondary leakage inductance valueg) As a sign function of the network-side voltage, VdcIs the DC side bus capacitor voltage igrefAnd setting a grid-connected current value.
In a preferred embodiment, the effective value of the secondary side current of the transformer in the corresponding modulation mode is calculated
Figure BDA0003664562530000182
And the effective value of the primary side current of the transformer
Figure BDA0003664562530000183
The method comprises the following steps:
the secondary side current effective value of the transformer corresponding to the h (h is less than or equal to 6) th power point is calculated according to the following mode:
Figure BDA0003664562530000184
wherein m is the number of power frequency period segments; i all right angles,rms,iCalculating the effective value of the secondary side current of the transformer in the ith section of power frequency period at the h power point according to the following mode:
Figure BDA0003664562530000185
wherein f isswIs the switching frequency, L, of the micro-inverterkFor converting the leakage inductance of the transformer to the value of the leakage inductance of the secondary side, njIs the turn ratio, V, of the secondary side and the primary side of the high-frequency transformerdcIs the DC side bus capacitor voltage, | vg,i,hL is the power grid voltage at the beginning of the ith power frequency period at the h power point, mvFor voltage gain, satisfy mv＝|vg，i，h|/(njVdc)。
The primary side current effective value of the transformer is calculated according to the following mode:
Figure BDA0003664562530000186
calculating the conduction loss of the micro inverter in the power frequency period comprises the conduction loss P of the primary side switching tube of the micro inverterloss,pri,hConduction loss P of secondary side switching tube of micro inverterloss,sec,hAnd micro inverter transformer conduction loss Ploss,tr,hWherein:
at the h power point, the conduction loss P of the primary side switching tube of the micro inverterloss,pri,hThe calculation is performed as follows:
Figure BDA0003664562530000191
wherein R isds,on,priIs the on-resistance of a single primary side switching tube.
At the h power point, the conduction loss P of the primary side switching tube of the micro inverterloss,sec,hThe calculation is performed as follows:
Figure BDA0003664562530000192
wherein R isds,on,secThe on-resistance of the single secondary side switching tube.
Micro inverter transformer conduction loss Ploss,tr,hThe calculation is performed as follows:
Figure BDA0003664562530000193
wherein R istr,priAnd Rtr,secAnd respectively calculating the efficiency of the micro-inverter in the power frequency period at the h-th power point of the winding resistors on the primary side and the secondary side of the transformer according to the following modes:
Figure BDA0003664562530000194
after the efficiencies are respectively calculated for the 6 power points, an efficiency matrix eta of 1 multiplied by 6 can be obtained.
European weighted efficiency eta of the micro-invertereuThe calculation is performed as follows:
ηeu＝η×WT
wherein WTIs a transpose of the weighting coefficient matrix described in claim 7. .
The method provided by the embodiment of the invention is a dual-active bridge type micro-inverter magnetic element parameter hybrid optimization design method based on mode switching and enabling European weighting efficiency to be highest. Wherein:
the circuit structure of the double-active-bridge micro-inverter, the parameters of the high-frequency transformer and the modulation mode of the micro-inverter are consistent with those in the embodiment of the invention;
the European weighted efficiency calculation method comprises the following steps: calculating the micro-inverter efficiency eta (eta) corresponding to 5%, 10%, 20%, 30%, 50% and 100% power points5％，η10％，η20％，η30％，η50％，η100％Calculating weighting efficiency, wherein the weighting coefficients corresponding to the six power points are W ═ 0.03,0.06,0.13,0.10,0.48 and 0.20, respectively;
the variable n to be optimized has s candidate values, n is { n ═ n1,n2,…,nj,…,ns}; variable L to be optimizedkThere are p candidates, Lk＝{L1,L2,…,Li,…,Lp}。
The method provided by the embodiment of the invention mainly comprises two links, namely a pre-screening link and a formal optimization design link.
Wherein the pre-screening principle is as follows:
calculating each set of candidate variables (L)a,nb) Corresponding maximum transmission power P of micro inverter at 100% power pointmax(a,b)；
If Pmax(a, b) less than the nominal peak transmission power Pac,maxWhen b +1>s time takes down a set of candidate variables (L)a+I,nb+1) Performing a pre-screening, otherwise taking down a set of candidate values (L)a,nb+1) Re-performing pre-screening;
if Pmax(a, b) is equal to or greater than the rated peak transmission power Pac,maxAnd outputting the candidate variable group and entering a formal optimization design link. Wherein the maximum transmission power Pmax(a, b) is calculated as follows:
Figure BDA0003664562530000201
wherein n isbIs the turn ratio of the secondary side and the primary side of the high-frequency transformer in the candidate value fswIs the switching frequency, L, of the micro-inverterkFor converting the leakage inductance of the transformer to the value of the leakage inductance, V, of the secondary sidedcIs the DC side bus capacitor voltage, VmAnd the rated voltage amplitude of the power grid.
Wherein the design step is formally optimized with a pre-screened output (L)i,nj) The method comprises four parts of (1) micro-inverter transmission power point selection, (2) modulation mode selection, (iii) transformer primary and secondary side current effective value calculation, and (iv) conduction loss calculation within a power frequency period, wherein the specific process comprises the following steps:
selecting transmission power points of a micro-inverter: the working power points of the micro-inverter are sequentially selected from six power points of 5%, 10%, 20%, 30%, 50% and 100%, and then the micro-inverter enters a process (II).
Modulation mode selection: for the input variable (L)i,nj) And for the selected working power point, judging the modulation mode of the micro inverter in each switching period in the power frequency period. If | M | is less than or equal to D1(1-2D1) If the working mode corresponds to the mode III; if | M | is less than or equal to D1(1-2D1) The working mode corresponds to the mode two and enters the flow process three.
Thirdly, calculating the effective value of the primary and secondary side currents of the transformer: for the input variable (L)i,nj) For the selected working power point, calculating the effective value of the secondary side current of the transformer under the corresponding modulation mode in each switching period in the power frequency period
Figure BDA0003664562530000202
And the effective value of the primary side current of the transformer
Figure BDA0003664562530000203
And repeating the flow II and the flow III until all the switching periods in the power frequency period are traversed, and then entering the flow IV.
Fourthly, conducting loss calculation in the power frequency period: for the input variable (L)i,nj) For the selected working power point, the effective value of the secondary side current of the transformer in each switching period in the power frequency period is determined
Figure BDA0003664562530000204
And the effective value of the primary side current of the transformer
Figure BDA0003664562530000205
And the conduction resistance of the selected primary and secondary side switching tubes is used for calculating the conduction loss and efficiency of the micro inverter in the power frequency period and recording the conduction loss and efficiency. If the selected operating power point is 100%, the input variable (L) is calculated according to the European weighted efficiency calculation methodi,nj) Recording the corresponding European weighted efficiency and returning the efficiency to the pre-screening process; otherwise, returning to the flow I, and selecting the working power point of the next micro inverter.
Repeat the prescreening and the four above-described procedures (i.e., sweeps)Description flow path) for all n and LkIs scanned, and the European weighted efficiency maximum value after scanning is finished corresponds to (L)i,nj) I.e. the optimal magnetic element parameters.
The technical solutions provided by the above embodiments of the present invention are further described below with reference to the drawings and a specific application example.
Fig. 1 is a schematic diagram of a dual active bridge micro-inverter circuit. Referring to fig. 1, the single-double active bridge type micro-inverter circuit is composed of a photovoltaic panel assembly, a direct current bus capacitor, a primary side full-bridge circuit, a high-frequency transformer, a secondary side half-bridge circuit and a network side low-pass filter. The primary side half-bridge circuit comprises switching tubes S1-S4, and the secondary side half-bridge circuit comprises switching tubes S5-S8 and a thin-film capacitor C1/C2; the turn ratio of the primary side to the secondary side of the high-frequency transformer is 1: n, and the excitation inductance converted to the primary side is LmThe leakage inductance of the transformer converted to the secondary side is Lk. The photovoltaic panel is connected with the DC side bus capacitor in parallel and then is connected with the DC port of the input end of the primary side square wave generating circuit, the output end of the primary side square wave generating circuit is connected with the primary side of the high-frequency transformer, the secondary side of the high-frequency transformer is connected with the AC port of the secondary side square wave generating circuit, the DC port of the secondary side square wave generating circuit is connected with the grid side low-pass filter, and the grid side low-pass filter is directly connected with an AC power grid; in the primary side square wave generating circuit, a source electrode of a switch tube S1 is connected with a drain electrode of a switch tube S2 and is connected with an anode of a primary side port of a high-frequency transformer, a source electrode of a switch tube S3 is connected with a drain electrode of a switch tube S4 and is connected with a cathode of the primary side port of the high-frequency transformer, a drain electrode of a switch tube S1 is connected with a drain electrode of a switch tube S3 and is connected with an anode of a direct-current side bus capacitor, and a source electrode of the switch tube S2 is connected with a source electrode of a switch tube S4 and is connected with a cathode of the direct-current side bus capacitor; in the secondary side square wave generating circuit, the drain electrode of a switch tube S5 is connected with the anode of a film capacitor C1, the source electrode of a switch tube S5 is connected with the source electrode of a switch tube S6, the drain electrode of a switch tube S6 is connected with the drain electrode of a switch tube S7 and is connected with the anode of a secondary side port of a transformer, the source electrode of the switch tube S7 is connected with the source electrode of a switch tube S8, and the drain electrode of the switch tube S8 is connected with a filmThe negative electrode of the capacitor C2 is connected, and the negative electrode of the thin-film capacitor C1 is connected with the positive electrode of the thin-film capacitor C2 and is connected with the negative electrode of the secondary side port of the transformer. The optimization design method in the above two embodiments of the invention can be applied to the parameters n and L of the magnetic element in the high-frequency transformer shown in fig. 1kAnd (5) designing.
Further, the variable n to be optimized has s candidate values, where n is { n ═ n1,n2,…,nj,…,ns}; variable L to be optimizedkThere are p candidates, Lk＝{L1,L2,…,Li,…,Lp}。
FIG. 2 is a schematic diagram of driving waveforms of switching tubes S1-S8 and primary and secondary side current and voltage waveforms of a transformer in three modulation modes of a double-active bridge type micro-inverter circuit. The modulation mode of the micro-inverter is based on the phase angle D of the micro-inverter1And an out-shifted phase angle D2Is divided, as shown in fig. 3 specifically:
when shifting out the phase angle D2Satisfy (1-D)1)/2＜D2Less than or equal to 0.5 or less than-0.5 and less than D2≤-(1-D1) When the modulation mode is a first mode, the modulation mode is a second mode;
when phase angle is shifted outwards D2Satisfies D1/2＜D2≤(1-D1) [ 2 ] or- (1-D ]1)/2＜D2≤-D1When the modulation mode is the second mode, the modulation mode is the second mode;
when shifting out the phase angle D2Satisfies 0. ltoreq. D2≤D1/2 or-D1/2≤D2And when the modulation mode is less than or equal to 0, the corresponding modulation mode is a mode three.
Wherein the phase shift angle is defined as the angle of the staggered driving pulse of the switch tube S4 and the driving pulse of the switch tube S1; the out-shifted phase angle is defined as the angle of the offset of the fundamental wave of the square wave voltage on the primary side of the transformer and the fundamental wave of the square wave voltage on the secondary side of the transformer.
Fig. 4 is a flow chart of a dual active bridge micro-inverter magnetic element parameter hybrid optimization design method based on mode switching and maximizing full-load efficiency. Referring to fig. 4, when designing, it is necessary to pre-screen candidate values of two variables to be optimized, and the pre-screening principle is as follows:
if the candidate variable group (L)i,nj) Corresponding micro-inverter maximum transmission power Pmax(i, j) less than the nominal peak transmission power Pac,maxThen take down a set of candidate variables (L)i+1,nj+1) Or (L)i,nj+1) Repeating the judging process;
if the candidate variable group (L)i,nj) Corresponding maximum transmission power P of micro invertermax(i, j) is greater than the nominal peak transmission power Pac,maxThen the set of candidate variables is output and enters the design flow below.
As shown in FIG. 4, the design flow is optimized to pre-filter the output (L)i,nj) The method is used as input and comprises three parts, namely modulation mode selection, primary and secondary side current effective value calculation of a transformer and conduction loss calculation in a power frequency period, and the specific process comprises the following steps:
selecting a modulation mode: for the input variable (L)i,nj) And judging the modulation mode of the micro inverter in each switching period in the power frequency period. If | M | is less than or equal to D1(1-2D1) If the working mode corresponds to the mode III; if M > D1(1-2D1) The operating mode corresponds to mode two. In the above expression, M is the micro-inverter transmission power ratio, defined as
Figure BDA0003664562530000221
Wherein n is the turn ratio of the secondary side and the primary side of the high-frequency transformer, vpvIs the DC side bus capacitor voltage, fswIs the switching frequency, L, of the micro-inverterkFor the transformer, sgn (v) is converted into the value of the leakage inductance to the secondary sideg) As a function of the sign of the net side voltage.
Secondly, calculating the effective value of the primary and secondary side currents of the transformer: for the input variable (L)i,nj) Calculating the effective value of the secondary side current of the transformer under the corresponding modulation mode in each switching period in the power frequency period
Figure BDA0003664562530000222
And the primary side of the transformerEffective value of current
Figure BDA0003664562530000223
And repeating the first flow and the second flow until all the switching periods in the power frequency period are traversed.
Thirdly, calculating the conduction loss in the power frequency period: for the input variable (L)i,nj) According to the effective value of the secondary side current of the transformer in each switching period in the power frequency period
Figure BDA0003664562530000224
And the effective value of the primary side current of the transformer
Figure BDA0003664562530000225
And the conduction resistance of the selected primary and secondary side switching tubes is used for calculating and recording the conduction loss of the micro inverter in the power frequency period.
Repeat the prescreening and three procedures described above for all n and LkThe candidate value of (L) is scanned, and the minimum corresponding conduction loss (L) of the micro inverter in the power frequency period after scanning is finishedi,nj) I.e. the optimal magnetic element parameters.
In fig. 4, i is a count value of the leakage inductance candidate values, and has a value range of 1 to p, where p is the number of the leakage inductance candidate values; j is the counting value of the turn ratio candidate value, and the value range is 1-s; s is the maximum counting value of the turn ratio candidate value; k is a counting value of the power frequency period segmentation, and the value range is 1-m; and m is the maximum segment number of the power frequency period.
Further, by the above-mentioned optimal design method based on mode switching and maximizing full-load efficiency, a specific example of the optimal design of the magnetic element parameters of the high-frequency transformer in the micro-inverter can be given under the micro-inverter parameter conditions shown in table 1. As shown in fig. 5, which is a schematic view of a curved surface of the micro-inverter where the sum of squares of the primary and secondary side currents varies with the leakage inductance of the transformer and the turn ratio of the transformer, the sum of squares of the primary and secondary side currents of the micro-inverter at the lowest point of the curved surface is the smallest, and the conduction loss is also the smallest, so that the optimal magnetic component parameter of the transformer is Lk＝12μH，n＝4。
TABLE 1
Parameter(s) Numerical value (Unit) Parameter(s) Numerical value (Unit)
Direct voltage 30V Frequency of mains voltage 50Hz
Network voltage 220Vrms Switching frequency 100kHz
Net side current set value 2.73Arms Angle of power factor 0°
Fig. 6 is a flow chart of a dual active bridge micro-inverter magnetic element parameter hybrid optimization design method based on mode switching and maximizing european weighting efficiency. Referring to fig. 6, on the basis of the above optimization method based on mode switching and maximizing full-load efficiency, the optimization method needs to combine six power points defined by european weighted efficiency to perform hybrid optimization design on the primary and secondary turn ratio of the high-frequency transformer and the transformer leakage inductance, so that european weighted efficiency is maximized.
Further, the european weighted efficiency calculation method is: calculating the micro-inverter efficiency eta of { eta ] corresponding to 5%, 10%, 20%, 30%, 50% and 100% power points5％，η10％，η20％，η30％，η50％，η100％And calculating weighting efficiencies, wherein the weighting coefficients corresponding to the six power points are W ═ 0.03,0.06,0.13,0.10,0.48 and 0.20, respectively.
Referring to fig. 6, when designing, it is necessary to pre-screen candidate values of two variables to be optimized. Specifically, the pre-screening principle is as follows:
calculating each set of candidate variables (L)i,nj) Corresponding maximum transmission power P of micro inverter at 100% power pointmax(i,j)；
If Pmax(i, j) less than the nominal peak transmission power Pac,maxThen take down a set of candidate variables (L)i+1,nj+1) Or (L)i,nj+1) Carrying out pre-screening;
if Pmax(i, j) is greater than the nominal peak transmission power Pac,maxThen the set of candidate variables is output and the design flow proceeds as follows.
Referring to FIG. 6, the design flow is optimized for pre-screened output (L)i,nj) The method comprises four parts of (1) micro-inverter transmission power point selection, (two) modulation mode selection, (three) transformer primary and secondary side current effective value calculation, and (four) conduction loss calculation in a power frequency period, wherein the specific process is as follows:
selecting transmission power points of a micro-inverter: and sequentially selecting working power points of the micro inverter from six power points of 5%, 10%, 20%, 30%, 50% and 100%, and entering a process II.
Modulation mode selection: for the input variable (L)i,nj) And for the selected working power point, judging the modulation mode of the micro inverter in each switching period in the power frequency period. If | M | is less than or equal to D1(1-2D1) If the working mode corresponds to the mode III; if M > D1(1-2D1) The working mode corresponds to the mode two and enters the flow process three.
Thirdly, calculating the effective value of the primary and secondary side currents of the transformer: for the input variable (L)i,nj) For the selected working power point, calculating the effective value of the secondary side current of the transformer in the corresponding modulation mode in each switching period in the power frequency period
Figure BDA0003664562530000241
And the effective value of the primary side current of the transformer
Figure BDA0003664562530000242
And repeating the flow II and the flow III until all the switching periods in the power frequency period are traversed, and then entering the flow IV.
Fourthly, conducting loss calculation in the power frequency period: for the input variable (L)i,nj) For the selected working power point, the effective value of the secondary side current of the transformer in each switching period in the power frequency period is determined
Figure BDA0003664562530000243
And the effective value of the primary side current of the transformer
Figure BDA0003664562530000244
And the conduction resistance of the selected primary and secondary side switching tubes is used for calculating the conduction loss and efficiency of the micro inverter in the power frequency period and recording the conduction loss and efficiency. If the operating power point selected at this time is 100%, the input variable (L) is calculated according to the European weighted efficiency calculation methodi,nj) Recording the corresponding European weighted efficiency and returning the efficiency to the pre-screening process; otherwise, returning to the flow I, and selecting the working power point of the next micro inverter.
Repeat the prescreening and the four above-described procedures for all n and LkIs scanned, and the European weighted maximum corresponds to (L) after scanning is finishedi,nj) I.e. the optimal magnetic element parameters.
In fig. 6, i is a count value of the leakage inductance candidate value, and the value range is 1 to p; p is the number of leakage inductance candidate values; j is the counting value of the turn ratio candidate value, and the value range is 1-s; p is the number of leakage inductance candidate values; s is the number of turn ratio candidate values; k is a counting value of the power frequency period segmentation, and the value range is 1-m; m is the number of power frequency period segments; h is a counting value of the power point, and the value range is 1-6.
Further, by the above-mentioned optimization design method based on mode switching and maximizing european weighted efficiency, a specific example of optimization design of magnetic element parameters of a high-frequency transformer in a micro-inverter can be given under the conditions of the micro-inverter parameters shown in table 2. As shown in fig. 7, which is a curved surface schematic diagram of the european weighting efficiency of the micro-inverter varying with the leakage inductance and the turn ratio of the transformer, the european weighting efficiency of the micro-inverter corresponding to the highest point of the curved surface is the highest, so that the magnetic component parameter value that maximizes the european weighting efficiency can be obtained as Lk＝19μH，n＝4.5。
TABLE 2
Figure BDA0003664562530000245
Figure BDA0003664562530000251
Of course, the specific circuit of the above embodiment is only a preferred embodiment of one implementation of the present invention, and is not limited to the present invention, and in other embodiments, other circuit forms may be used to implement the same function.
The method for optimally designing the double-active-bridge micro-inverter magnetic element parameter mixing based on mode switching and enabling the full-load efficiency to be highest provided by the embodiment of the invention can enable the full-load efficiency of the micro-inverter to be highest under the designed high-frequency transformer magnetic element parameter. Meanwhile, the turn ratio and the leakage inductance parameter of the transformer are subjected to mixed optimization design, so that the primary and secondary side currents of the transformer under the optimized parameters are reduced while the power transmission constraint of the micro inverter is met.
According to the double-active-bridge type micro-inverter magnetic element parameter hybrid optimization design method based on mode switching and enabling the European weighting efficiency to be highest, the efficiency of the micro-inverter at six power points is comprehensively considered, so that the light load efficiency of the micro-inverter under the designed high-frequency transformer parameters is greatly improved, the European weighting efficiency is favorably improved, and the micro-inverter still has high efficiency when a photovoltaic panel is shielded, the illumination intensity is insufficient or the environment temperature is not appropriate.
The method for optimally designing the magnetic element parameters of the micro-inverter based on the mode switching control provided by the embodiment of the invention is based on the characteristic that the micro-inverter is switched among a plurality of modulation modes in a power frequency period, and is used for adjusting the turn ratio n and the leakage inductance L of a high-frequency transformer in the micro-inverterkThe two coupled variables are subjected to hybrid optimization design, so that the conduction loss of the converter under the same transmission power condition is minimized while the power transmission constraint is met. By the optimal design method, the conduction loss of the micro inverter under the full load condition can be minimized; by comprehensively considering the conduction losses at different power points, the European weighted efficiency of the micro inverter can be maximized; the influence of two design variables, namely the turn ratio and the leakage inductance of the high-frequency transformer on the transmission power and the efficiency of the micro inverter is comprehensively considered, so that the designed parameters have higher practicability.
The above embodiments of the present invention are not exhaustive and are all known in the art.
The foregoing description has described specific embodiments of the present invention. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention.

Claims (11)

1. A micro-inverter magnetic element parameter hybrid optimization method based on mode switching is characterized in that according to the modulation mode switching characteristics of a micro-inverter in a power frequency period, the primary and secondary side turn ratio and the transformer leakage inductance of a high-frequency transformer of the micro-inverter are subjected to hybrid optimization design, so that the efficiency is highest under the condition of full load of the micro-inverter; wherein:
the turn ratio of the primary side to the secondary side of the high-frequency transformer is 1: n, and the value converted from the leakage inductance of the transformer to the secondary side of the transformer is Lk；
The variable n to be optimized comprises s candidate values, and n is equal to { n ═ n1，n2，…，nj，…，ns}; variable L to be optimizedkThere are p candidates, Lk＝{L1，L2，…，Li，…，Lp}；
Pre-screening the candidate values of the two variables to be optimized to obtain a pre-screened candidate value (L)i，nj) As input variable, for the candidate value njAnd the candidate value LiScanning to obtain the candidate value (L)i，nj) The conduction loss of the micro inverter in the corresponding power frequency period;
repeating the steps, and carrying out optimization on the variable n to be optimized and the variable L to be optimizedkAnd scanning all the candidate values to obtain an input variable corresponding to the minimum conduction loss of the micro inverter in the power frequency period, wherein the input variable is the optimal magnetic element parameter.
2. The method of claim 1, wherein the pre-screening candidate values for two variables to be optimized comprises:
if the candidate value (L)a，nb) Corresponding maximum transmission power P of micro invertermax(a, b) less than the nominal peak transmission power Pac，maxWhen b +1 > s, a set of candidate values (L) is takena+1，nb+1) Otherwise, take down a set of candidate values (L)a，nb+1) (ii) a Repeating the process until the maximum transmission power of the micro inverter corresponding to the candidate value is greater than or equal to the rated peak transmission power;
if the candidate value (L)a，nb) Corresponding micro-inverter maximum transmission power Pmax(a, b) is equal to or greater than the rated peak transmission power Pac，maxOutputting the set of candidate values as input variables;
wherein the candidate value is the candidate value (L)a，nb) Corresponding micro-inverter maximum transmission power PmaxThe calculation method of (a, b), comprising:
Figure FDA0003664562520000011
in the formula, nbIs the turn ratio of the secondary side and the primary side of the high-frequency transformer in the candidate value fswIs the switching frequency, L, of the micro-inverterkFor converting the leakage inductance of the transformer to the value of the leakage inductance, V, of the secondary sidedcIs the DC side bus capacitor voltage, VmAnd the rated voltage amplitude of the power grid.
3. The method as claimed in claim 1, wherein the pair of candidate values n is a value of njAnd the candidate value LiPerforming a scan comprising:
for the input variable (L)i，nj) Judging the modulation mode of the micro inverter in each switching period in a power frequency period;
for the input variable (L)i，nj) Calculating the effective value of the secondary side current of the transformer under the corresponding modulation mode in each switching period in the power frequency period
Figure FDA0003664562520000021
And the effective value of the primary side current of the transformer
Figure FDA0003664562520000022
Repeating the processes of the modulation mode judgment and the effective value calculation until all the switching periods in the power frequency period are traversed;
for the input variable (L)i，nj) According to the effective value of the secondary side current of the transformer in each switching period in the power frequency period
Figure FDA0003664562520000023
And the effective value of the primary side current of the transformer
Figure FDA0003664562520000024
And calculating the conduction loss of the micro inverter in the power frequency period by using the selected conduction resistance of the primary and secondary side switching tubes.
4. The method of claim 3, wherein the modulation pattern of the microinverter is based on the phase angle D of the microinverter1And an out-shifted phase angle D2Dividing the pattern into a first pattern, a second pattern and a third pattern; wherein:
said internally shifted phase angle D1Is defined as the staggered angle of the negative rising edge of the square wave voltage on the primary side of the transformer and the positive rising edge of the square wave voltage on the primary side of the transformer, and D is more than or equal to 01≤0.5；
Said phase angle D2Is defined as the staggered angle of the fundamental wave of the square wave voltage of the primary side of the transformer and the fundamental wave of the square wave voltage of the secondary side of the transformer, and D is more than or equal to-0.52≤0.5；
When the phase angle D is shifted outwards2Satisfy (1-D)1)/2＜D2Less than or equal to 0.5 or less than-0.5 < D2≤-(1-D1) When the voltage is in a first mode, the current of the transformer is close to a sine wave, and the effective value of the current of the transformer is the maximum;
when the phase angle D is shifted outwards2Satisfies D1/2＜D2Less than or equal to (1-D1)/2 or- (1-D)1)/2＜D2When the voltage is less than or equal to-D1/2, one part of the positive level of the primary side square wave voltage is superposed with the positive level of the secondary side square wave voltage, the other part of the positive level of the primary side square wave voltage is superposed with the negative level of the secondary side square wave voltage, the corresponding modulation mode is a mode II, the current of the transformer is close to a trapezoidal wave at the moment, and the effective value of the current of the transformer is smaller than the effective value in the mode I and larger than the effective value in the mode III;
when the phase angle is shifted outwardsD2D is more than or equal to 02≤D1/2 or-D1/2≤D2When the current is less than or equal to 0, the positive level part of the primary side square wave voltage and the positive level part of the secondary side square wave voltage are completely superposed, the corresponding modulation mode is a mode three, the current of the transformer is close to a triangular wave at the moment, and the effective value of the current of the transformer is minimum;
for the input variable (L)i，nj) And judging the modulation mode of the micro inverter in each switching period in a power frequency period, wherein the method comprises the following steps of: if | M | is less than or equal to D1(1-2D1) If so, the modulation mode corresponds to the mode three; if M > D1(1-2D1) If so, the modulation mode corresponds to the second mode; wherein M is the micro-inverter transmission power ratio and is defined as
Figure FDA0003664562520000025
Where n is the turn ratio of the secondary side to the primary side of the high-frequency transformer, fswIs the switching frequency, L, of the micro-inverterkFor the transformer leakage inductance, sgn (v) is converted into the secondary leakage inductance valueg) As a function of the sign of the network-side voltage, VdcIs the DC side bus capacitor voltage igrefAnd setting a grid-connected current value.
5. The method as claimed in claim 3, wherein the calculating the effective secondary current value of the transformer in the corresponding modulation mode is based on the optimal mixed design method of magnetic parameters of micro-inverter based on mode switching
Figure FDA0003664562520000031
And the effective value of the primary side current of the transformer
Figure FDA0003664562520000032
The method comprises the following steps:
secondary current effective value of transformer
Figure FDA0003664562520000033
The method comprises the following steps:
Figure FDA0003664562520000034
wherein m is the number of power frequency period segments; i.e. is，rms，iCalculating the effective value of the secondary side current of the transformer in the ith power frequency period according to the following mode:
Figure FDA0003664562520000035
wherein f isswIs the switching frequency, L, of the micro-inverterkFor the transformer leakage inductance to the secondary value, njIs the turn ratio, V, of the secondary side and the primary side of the high-frequency transformerdcIs the DC side bus capacitor voltage, | vg，iL is the grid voltage at the beginning of the i-th power frequency period, mvFor voltage gain, satisfy mv＝|vg，i|/(njVdc)；
Effective value of primary side current of transformer
Figure FDA0003664562520000036
The calculation method of (2) comprises:
Figure FDA0003664562520000037
the method for calculating the conduction loss of the micro inverter in the power frequency period comprises the following steps: calculating conduction loss P of primary side switching tube of micro inverterloss，priCalculating the conduction loss P of the secondary side switching tube of the micro inverterloss，secAnd calculating the conduction loss P of the micro-inverter transformerloss，trWherein:
calculating the conduction loss P of the primary side switching tube of the micro inverterloss，priThe method comprises the following steps:
Figure FDA0003664562520000041
wherein R isds，on，priThe on-resistance of a single primary side switching tube;
calculating the conduction loss P of the primary side switching tube of the micro inverterloss，secThe method comprises the following steps:
Figure FDA0003664562520000042
wherein R isds，on，secThe on-resistance of a single secondary side switching tube;
the micro inverter transformer has conduction loss Ploss，trThe method comprises the following steps:
Figure FDA0003664562520000043
wherein R istr，priAnd Rtr，secWinding resistors of primary and secondary sides of the transformer respectively;
in a power frequency period, the method for calculating the efficiency eta of the micro inverter under the full-load condition comprises the following steps:
Figure FDA0003664562520000044
wherein, Pac，NThe rated transmission power of the micro-inverter.
6. A micro-inverter magnetic element parameter hybrid optimization design method based on mode switching is characterized in that according to modulation mode switching characteristics of a micro-inverter in a power frequency period, and power points defined by European weighted efficiency are combined, hybrid optimization design is carried out on the primary and secondary side turn ratio of a high-frequency transformer and transformer leakage inductance of the micro-inverter, and the European weighted efficiency of the micro-inverter is enabled to be highest; wherein:
the turn ratio of the primary side to the secondary side of the high-frequency transformer is 1: n, and the value of the leakage inductance of the transformer converted to the secondary side of the transformer is Lk；
The variable n to be optimized comprises s candidate values, and n is equal to { n ═ n1，n2，…，nj，…，ns}; variable L to be optimizedkThere are p candidates, Lk＝{L1，L2，…，Li，…，Lp}；
Pre-screening the candidate values of the two variables to be optimized to obtain a pre-screened candidate value (L)i，nj) As input variable, for the candidate value njAnd the candidate value LiScanning to obtain the candidate value (L)i，nj) Corresponding european weighted efficiency;
repeating the steps, and carrying out optimization on the variable n to be optimized and the variable L to be optimizedkAnd scanning all the candidate values to obtain an input variable corresponding to the maximum European weighted efficiency, namely the optimal magnetic element parameter.
7. The method of claim 6, wherein the method of calculating the European weighted efficiency comprises:
calculating the micro-inverter efficiency eta (eta) corresponding to 5%, 10%, 20%, 30%, 50% and 100% power points5％，η10％，η20％，η30％，η50％，η100％Calculating the weighting efficiency to obtain European weighting efficiency;
the power points of 5%, 10%, 20%, 30%, 50%, and 100% are defined as power points defined by european weighted efficiency, and the corresponding weighting coefficients are W ═ 0.03,0.06,0.13,0.10,0.48, and 0.20, respectively.
8. The method of claim 7, wherein the pre-screening candidate values for two variables to be optimized comprises:
calculate each set of candidate values (L)a，nb) Corresponding 100% powerMaximum transmission power P of point micro invertermax(a，b)；
If the maximum transmission power P of the micro-invertermax(a, b) less than the rated peak transmission power Pac，maxWhen b +1 > s, a set of candidate values (L) is takena+1，nb+1) Otherwise, take down a set of candidate values (L)a，nb+1) (ii) a Repeating the process until the maximum transmission power of the micro inverter at the 100% power point corresponding to the candidate value is greater than or equal to the rated peak transmission power;
if the maximum transmission power P of the micro-invertermax(a, b) is equal to or greater than the rated peak transmission power Pac，maxOutputting the set of candidate values as input variables;
wherein the candidate value is the candidate value (L)a，nb) Corresponding maximum transmission power P of micro inverter at 100% power pointmaxThe calculation method of (a, b), comprising:
Figure FDA0003664562520000051
in the formula, nbIs the turn ratio of the secondary side and the primary side of the high-frequency transformer in the candidate value, fswIs the switching frequency, L, of the micro-inverterkFor converting the leakage inductance of the transformer to the value of the leakage inductance of the secondary side, VdcIs the DC side bus capacitor voltage, VmAnd the rated voltage amplitude of the power grid.
9. The method of claim 7, wherein the pair of candidate values n is a function of a parameter of the microinverterjAnd the candidate value LiPerforming a scan comprising:
sequentially selecting working power points of the micro-inverter from the power points defined by the European weighted efficiency;
for the input variable (L)i，nj) In combination with the selected working power point, judging the modulation mode of the micro inverter in each switching period in the power frequency period; (ii) a
For the input variable (L)i，nj) And calculating the effective value of the secondary side current of the transformer under the corresponding modulation mode in each switching period in the power frequency period by combining the selected working power point
Figure FDA0003664562520000052
And the effective value of the primary side current of the transformer
Figure FDA0003664562520000053
Repeating the processes of the modulation mode judgment and the current effective value calculation until all the switching periods in the power frequency period are traversed;
for the input variable (L)i，nj) Combining the selected working power point and the effective value of the secondary side current of the transformer in each switching period in the power frequency period
Figure FDA0003664562520000054
And the effective value of the primary side current of the transformer
Figure FDA0003664562520000055
And the conduction resistance of the selected primary and secondary side switch tubes is used for calculating the conduction loss and the efficiency of the micro-inverter in the power frequency period; if the selected operating power point is 100%, the input variable (L) is calculated according to a European weighted efficiency calculation methodi，nj) Corresponding european weighted efficiency; otherwise, the working power point of the next micro-inverter is reselected until the input variable (L) when the working power point is 100 percent is obtainedi，nj) Corresponding european weighted efficiency.
10. The method of claim 9, wherein the modulation pattern of the microinverter is based on the phase angle D of the microinverter1And an out-shifted phase angle D2Divided into mode one and modeII and mode III; wherein:
said phase angle D1Is defined as the staggered angle of the negative rising edge of the square wave voltage on the primary side of the transformer and the positive rising edge of the square wave voltage on the primary side of the transformer, and D is more than or equal to 01≤0.5；
Said phase angle D2Is defined as the staggered angle of the fundamental wave of the square wave voltage of the primary side of the transformer and the fundamental wave of the square wave voltage of the secondary side of the transformer, and D is more than or equal to-0.52≤0.5；
When the phase angle D is shifted outwards2Satisfy (1-D)1)/2＜D2Less than or equal to 0.5 or less than-0.5 and less than D2≤-(1-D1) When the voltage is in a first mode, the current of the transformer is close to a sine wave, and the effective value of the current of the transformer is maximum;
when the phase angle D is shifted outwards2Satisfy D1/2＜D2Less than or equal to (1-D1)/2 or- (1-D)1)/2＜D2≤-D1When the voltage is in a second mode, the current of the transformer is close to a trapezoidal wave, and the effective value of the current of the transformer is smaller than the effective value in the first mode and larger than the effective value in the third mode;
when the phase angle D is shifted outwards2Satisfies 0. ltoreq. D2≤D1/2 or-D1/2≤D2When the current is less than or equal to 0, the positive level part of the primary side square wave voltage and the positive level part of the secondary side square wave voltage are completely superposed, the corresponding modulation mode is a mode three, the current of the transformer is close to a triangular wave at the moment, and the effective value of the current of the transformer is minimum;
for the input variable (L)i，nj) And in combination with the selected working power point, judging the modulation mode of the micro inverter in each switching period in the power frequency period, wherein the method comprises the following steps:
if | M | is less than or equal to D1(1-2D1) If so, the modulation mode corresponds to the mode three; if M > D1(1-2D1) Then the modulation mode corresponds to the modeII, performing secondary filtration; in the formula D1For the phase angle, M is the transmission power ratio of the micro inverter, defined as
Figure FDA0003664562520000061
Where n is the turn ratio of the secondary side to the primary side of the high-frequency transformer, fswIs the switching frequency, L, of the micro-inverterkFor the transformer leakage inductance, sgn (v) is converted into the value of the secondary side leakage inductanceg) As a function of the sign of the network-side voltage, VdcIs the DC side bus capacitor voltage igrefAnd setting a grid-connected current value.
11. The method as claimed in claim 9, wherein the calculating the effective secondary current value of the transformer in the corresponding modulation mode is performed by using a hybrid optimization design method of magnetic parameters of micro-inverter based on mode switching
Figure FDA0003664562520000062
And the effective value of the primary side current of the transformer
Figure FDA0003664562520000063
The method comprises the following steps:
secondary side current effective value of transformer corresponding to h-th power point
Figure FDA0003664562520000071
The calculation method of (2) comprises:
Figure FDA0003664562520000072
wherein m is the number of power frequency period segments; i.e. is，rms，iCalculating the effective value of the secondary side current of the transformer in the ith section of power frequency period at the h-th power point according to the following mode:
Figure FDA0003664562520000073
wherein f isswIs the switching frequency, L, of the micro-inverterkFor the transformer leakage inductance to the secondary value, njIs the turn ratio, V, of the secondary side and the primary side of the high-frequency transformerdcIs the DC side bus capacitor voltage, | vg，i，hL is the grid voltage at the start of the ith power frequency cycle at the h power point, mvFor voltage gain, satisfy mv＝|vg，i，h|/(njVdc)；
Effective value of primary side current of transformer
Figure FDA0003664562520000074
The calculation method of (2) comprises:
Figure FDA0003664562520000075
the method for calculating the conduction loss of the micro inverter in the power frequency period comprises the following steps: calculating conduction loss P of primary side switching tube of micro inverterloss，pri，hCalculating the conduction loss P of the secondary side switching tube of the micro inverterloss，sec，hAnd calculating the conduction loss P of the micro-inverter transformerloss，tr，hWherein:
at the h-th power point, the conduction loss P of the primary side switching tube of the micro inverter is calculatedloss，pri，hThe method comprises the following steps:
Figure FDA0003664562520000076
wherein R isds，on，priThe on-resistance of a single primary side switching tube;
at the h power point, the conduction loss P of the primary side switching tube of the micro inverter is calculatedloss，sec，hThe method comprises the following steps:
Figure FDA0003664562520000077
wherein R isds，on，secThe on-resistance of a single secondary side switching tube;
at the h power point, the calculation of the conduction loss P of the micro-inverter transformerloss，tr，hThe method comprises the following steps:
Figure FDA0003664562520000081
wherein R istr，priAnd Rtr，secWinding resistors of primary and secondary sides of the transformer respectively;
in a power frequency cycle at the h-th power point, the calculation method of the European weighted efficiency of the micro-inverter comprises the following steps: calculating the efficiency eta of the micro inverter in the power frequency period at the h-th power pointhThe method comprises the following steps:
Figure FDA0003664562520000082
respectively calculating the efficiency of the h power points to obtain an efficiency matrix eta of 1 multiplied by h;
calculating the microinverter European weighted efficiency etaeuThe method comprises the following steps:
ηeu＝η×WT
wherein, WTIs a transpose of the weighting coefficient matrix.
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