CN111245004A - Composite robust control method for high-frequency SiC photovoltaic grid-connected inverter under weak grid - Google Patents

Composite robust control method for high-frequency SiC photovoltaic grid-connected inverter under weak grid Download PDF

Info

Publication number
CN111245004A
CN111245004A CN201811469199.7A CN201811469199A CN111245004A CN 111245004 A CN111245004 A CN 111245004A CN 201811469199 A CN201811469199 A CN 201811469199A CN 111245004 A CN111245004 A CN 111245004A
Authority
CN
China
Prior art keywords
grid
frequency
sic
current
connected inverter
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Granted
Application number
CN201811469199.7A
Other languages
Chinese (zh)
Other versions
CN111245004B (en
Inventor
刘桂花
王卫
郭磊
朱凯
李芬
荆弈翔
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Harbin Institute of Technology
Original Assignee
Harbin Institute of Technology
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Harbin Institute of Technology filed Critical Harbin Institute of Technology
Priority to CN201811469199.7A priority Critical patent/CN111245004B/en
Publication of CN111245004A publication Critical patent/CN111245004A/en
Application granted granted Critical
Publication of CN111245004B publication Critical patent/CN111245004B/en
Active legal-status Critical Current
Anticipated expiration legal-status Critical

Links

Images

Classifications

    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/01—Arrangements for reducing harmonics or ripples
    • 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
    • H02M7/53871—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 with automatic control of output voltage or current
    • H02M7/53875—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 with automatic control of output voltage or current with analogue control of three-phase output
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B70/00—Technologies for an efficient end-user side electric power management and consumption
    • Y02B70/10—Technologies improving the efficiency by using switched-mode power supplies [SMPS], i.e. efficient power electronics conversion e.g. power factor correction or reduction of losses in power supplies or efficient standby modes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/40—Arrangements for reducing harmonics

Landscapes

  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Inverter Devices (AREA)

Abstract

The invention relates to a composite robust control method of a high-frequency SiC photovoltaic grid-connected inverter under a weak grid. Calculating to obtain a reference value of a current loop by designing parameters of an LCL filter; the power density of the high-frequency SiC photovoltaic grid-connected inverter is improved, grid-connected current is fed back, and an active damping feedback function H is designedad(s) determining an open loop transfer function G of the high-frequency SiC photovoltaic grid-connected inverteropen(s); the feed-forward function of the power grid voltage is improved, a first-order low-pass filter is configured, and a new power grid voltage transfer function G is obtainedv(s) suppressing each harmonic by using an odd-order repeated quasi-PR current controller to obtain a modulated wave uαβ *And the SVPWM module obtains a switch driving signal to drive the SiC switch tube. The invention does not need additional sensors and adopts a second-order differential link and a proportional linkAnd meanwhile, the voltage feedforward of the power grid is realized to eliminate the influence of weak power grid impedance on the stability of the high-frequency inverter.

Description

Composite robust control method for high-frequency SiC photovoltaic grid-connected inverter under weak grid
Technical Field
The invention relates to the technical field of control of high-frequency SiC photovoltaic grid-connected inverters, in particular to a composite robust control method of a high-frequency SiC photovoltaic grid-connected inverter under a weak power grid.
Background
With the increase of grid-connected power of the distributed power supply and the wide distribution of the positions of the connected power grids, the tail ends or local areas of the power grids show weak grid characteristics of low short-circuit capacity and high grid impedance, the grid impedance can change the loop gain of an inverter control system, and the system is possibly unstable; and grid voltage background harmonic can cause grid-connected current to be distorted. Therefore, when the photovoltaic grid-connected inverter is designed, the working state of a normal power grid is considered, and meanwhile, the inverter can be ensured to stably and reliably operate in a more complex weak power grid system.
With the development of the global energy internet, the performance requirements on power electronic equipment are higher and higher, and semiconductor power electronic devices manufactured by using a third-generation semiconductor material silicon carbide (SiC) are paid more and more attention and research on superior performances of high frequency, high temperature resistance and the like. The high-frequency photovoltaic inverter based on the SiC power device can have a smaller output filter, so that the volume and the weight of a passive device can be reduced, and the power density of the inverter can be improved; however, when such an inverter having a high frequency and a small filter is connected to a weak power grid having a high impedance, a serious stability problem is likely to occur. Aiming at the stability problem of interaction influence between an inverter based on a Si MOSFET/IGBT and a weak power grid, the stability problem is usually solved by adopting a power grid impedance measurement technology or a robust controller design at present, but the stability problem of the SiC MOSFET grid-connected inverter with higher frequency is not analyzed. In addition, in the aspects of suppressing the resonance of the LCL filter and improving the quality of the grid-connected current, the control loop usually adopts a capacitive current feedback method which requires an additional sensor.
Disclosure of Invention
The invention provides a composite robust control method of a high-frequency SiC photovoltaic grid-connected inverter, aiming at solving the stability problem caused by impedance mismatching of the high-frequency SiC photovoltaic inverter and a high power grid under a weak power grid, and the invention provides the following technical scheme:
a composite robust control method of a high-frequency SiC photovoltaic grid-connected inverter under a weak grid comprises the following steps:
the method comprises the following steps: designing parameters of an output LCL filter according to the power grade, switching frequency and current ripple required parameters of the high-frequency SiC photovoltaic grid-connected inverter;
step two: collecting output voltage u of high-frequency SiC photovoltaic grid-connected invertera、ubAnd ucAnd collecting output current i of the high-frequency SiC photovoltaic grid-connected invertera、ibAnd icAnd the output voltage u of the collected high-frequency SiC photovoltaic grid-connected inverter is converted by Clarkea、ub、ucAnd an output current ia、ib、icConversion to a two-phase stationary coordinate system αβ, according to the definition of instantaneous power and the active power reference value P*And a reactive power reference value Q*Calculating a reference value i of the current loopα *And iβ *；
Step three: the power density of the high-frequency SiC photovoltaic grid-connected inverter is improved, grid-connected current is selected to be fed back, and an active damping feedback function H is designed according to the active damping mechanismad(s) determining a stability constraint condition of the active damping inner ring according to a Laus criterion;
step four: taking into account the grid impedance LgAccording to the active damping feedback function Had(s) in combination with the full bridge gain kPWMFilter side inductor L1Filter capacitor C and electric network side inductor L2Feedforward voltage function Gf(s) and a current controller Gc(s) determining an open loop transfer function G of the high-frequency SiC photovoltaic grid-connected inverteropen(s)；
Step five: according to the open loop transfer function G of the high-frequency SiC photovoltaic grid-connected inverter obtained in the fourth stepopen(s) improving the feedforward function of the power grid voltage, and configuring a first-order low-pass filter to obtain a new power grid voltage transfer function Gv(s)；
Step six: the current controller adopts an odd-number-repetition quasi-PR controller, the odd-number-repetition quasi-PR current controller is used for carrying out rapid non-difference tracking on a fundamental wave signal, and the odd-number-repetition controller is used for inhibiting each harmonic wave;
step seven: i to be collectedα、iβRespectively corresponding to the reference current value iα *And iβ *After 0 comparison, the modulated wave u is obtained by combining a quasi-PR current controller with the grid voltage feedforward and the grid current feedback controlαβ *And then a switch driving signal is obtained through the SVPWM module and is used for driving the SiC switch tube.
Preferably, the parameters of the output LCL filter are designed by:
Figure BDA0001890509150000021
L2＝rL1(2)
Figure BDA0001890509150000022
wherein, UdcIs a DC side voltage irmaxFor maximum allowable current ripple, fsFor switching frequency, r is the ratio of the network side inductance to the inverter side inductance, P is the rated power of the inverter, λ is the ratio of the reactive power to the total power, EnIs the effective value of three-phase network phase voltage, f is the network fundamental frequency, L1Is a filter side inductor, C is a filter capacitor, L2Is the filter network side inductance.
Preferably, the second step is specifically:
the first step is as follows: collected output voltage u of high-frequency SiC photovoltaic grid-connected inverter by Clarke transformationa、ub、ucAnd an output current ia、ib、icConverting the voltage into a two-phase static coordinate system αβ to obtain a two-phase static voltage uα、uβTwo-phase stationary current iα、iβ；
The second step is that: with PQ outer loop control, according to the definition of instantaneous power and active power reference value P*And a reactive power reference value Q*Calculating to obtain a reference value i of the current loopα *And iβ *Calculating the reference value i of the current loop by the following formulaα *And iβ *：
Figure BDA0001890509150000023
Wherein u isα、uβIs a two-phase rest voltage iα、iβIs a two-phase quiescent current iα *And iβ *Is a reference value of the current loop, P*As active power reference value, Q*Is a reactive power reference value.
Preferably, the third step is specifically:
the first step is as follows: active damping feedback function H designed according to active damping mechanismad(s) expressed by the formula:
Figure BDA0001890509150000031
wherein Had(s) a feedback function in the form of a high-pass filter, kadIs the high pass filter gain, omegahIs the high pass filter corner frequency, kPWMFor the inverter full bridge gain, s is the laplace operator.
The second step is that: the active damping inner loop stability constraint is expressed by:
Figure BDA0001890509150000032
preferably, the open-loop transfer function G of the high-frequency SiC photovoltaic grid-connected inverter is determined by the following formulaopen(s)：
Figure BDA0001890509150000033
Gopen(s) is an open-loop transfer function of the high-frequency SiC photovoltaic grid-connected inverter, and A is L1(L2+Lg)C，B＝L1(L2+Lg)Cωh，D＝L1+L2+Lg-kPWMLgGf(s)，E＝(L1+L2+Lg)ωh-kPWMkad-kPWMLgωhGf(s), Lg is the network impedance, gc(s) is the current controller, and gf(s) is the feed forward voltage function.
Preferably, the step five specifically includes:
the first step is as follows: according to the open loop transfer function G of the high-frequency SiC photovoltaic grid-connected inverter obtained in the fourth stepopen(s) modifying the grid voltage feedforward function to a sum of a second order differential form and a proportional form;
the second step is that: configuring a first-order low-pass filter, and obtaining a new power grid voltage transfer function G through the expression of the following formulav(s)：
Figure BDA0001890509150000034
Wherein G isv(s) is the new grid voltage transfer function and τ is the low pass filter time constant.
Preferably, the repetitive quasi-PR controller is expressed by the following formula:
Figure BDA0001890509150000035
wherein G isQPR(s) is a repeating quasi-PR controller function, kpi，kriRespectively, the proportion and the resonance coefficient, omega, of the current loop quasi-PR controlcTo cut-off frequency, ωrIs the resonant frequency.
Preferably, the odd-numbered repetition controller is expressed by the following formula:
Figure BDA0001890509150000041
wherein G isRC(s) is an odd number of times the controller function is repeated, T is the sampling time, Q(s) is an integral attenuation coefficient less than 1, C(s) is a compensation function designed for the control object, krcIs the repetitive controller gain.
The invention has the following beneficial effects:
1. and adopting an active damping method of grid-connected current feedback to suppress the resonance peak of the output LCL filter. Compared with the traditional capacitance current feedback active damping method, the method has the advantages that no additional sensor is needed, and the advantage of high power density of the high-frequency SiC photovoltaic grid-connected inverter is fully exerted.
2. On the basis of a grid-connected current feedback active damping method, the stability problem of the traditional proportional voltage feedforward control generated under a weak power grid is considered, and a second-order differential link and a proportional link are adopted to jointly realize power grid voltage feedforward so as to completely eliminate the influence of impedance of the weak power grid on the stability of a high-frequency inverter.
3. In consideration of the problems of power grid background voltage harmonic waves and harmonic waves existing in a current reference command, current fundamental waves and the harmonic waves are independently controlled respectively, and the problem of output current distortion caused by the power grid background harmonic waves and the command reference harmonic waves together is solved by adopting a current controller based on repeated quasi-PR of an odd-order internal model.
Drawings
Fig. 1 is a topology structure diagram of a three-phase grid-connected inverter based on a SiC power device.
Fig. 2 is an overall control block diagram of a composite robust control method of the high-frequency SiC photovoltaic grid-connected inverter.
Fig. 3 is a block diagram of a grid-connected current active damping control structure with additional grid voltage feed-forward.
Fig. 4 is an odd-numbered repetitive quasi-PR current controller.
FIG. 5 is a simulation comparison diagram of a low-frequency Si and high-frequency SiC inverter when the grid impedance is 0, and FIG. 5(a) is the grid impedance LgThe grid-connected current waveform of the Si inverter at 0, and the grid impedance L in FIG. 5(b)gAnd (3) a grid-connected current waveform diagram of the SiC inverter when the grid-connected current is 0.
FIG. 6 is a simulation comparison graph of a low-frequency Si and high-frequency SiC inverter with a grid impedance of 2mH, and FIG. 6(a) is a grid impedance LgGrid-connected current waveform diagram of Si inverter at 2mH, and FIG. 6(b) is grid impedance LgAnd the grid-connected current waveform of the SiC inverter is 2 mH.
Fig. 7 is a simulation comparison diagram of the conventional control method and the composite robust control method under the condition of a grid having a grid impedance of 2mH, and fig. 7(a) is a grid-connected current waveform diagram of a Si inverter employing the conventional control method under the condition of a weak grid impedance of 2mH and a switching frequency of 10 kHz; fig. 7(b) is a grid-connected current waveform diagram of a SiC inverter employing a conventional control method with a weak grid impedance of 2mH and a switching frequency of 50 kHz; fig. 7(c) is a grid-connected current waveform diagram of the SiC inverter adopting the composite robust control method under the condition that the weak grid impedance is 2mH and the switching frequency is 50 kHz.
FIG. 8 shows the open-loop transfer function characteristics of the conventional control method and the robust control method under different grid impedances, and FIG. 8(a) shows the open-loop transfer function characteristics under the weak grid impedance LgFig. 8(b) is an open-loop transfer function characteristic diagram of the composite robust control strategy at different grid impedances for the open-loop transfer function characteristic diagram of the conventional grid voltage proportional feedforward control strategy at 2mH and the composite robust control strategy proposed herein.
Detailed Description
The present invention will be described in detail with reference to specific examples.
The first embodiment is as follows:
according to the illustration in fig. 1, the topology structure diagram of the three-phase grid-connected inverter based on the SiC power device mainly includes a direct-current side voltage UdcSwitching device SiC MOSFET, L1、L2LCL filter composed of C, LgIs a line equivalent impedance, ugFor a three-phase ac grid, PCC is the point of common coupling.
In order to solve the stability problem caused by impedance mismatching of a high-frequency SiC photovoltaic inverter and a high power grid under a weak power grid, a composite robust control method of the high-frequency SiC photovoltaic grid-connected inverter is provided, as shown in FIG. 2: the method mainly comprises PQ outer loop control, active damping control, fundamental wave and harmonic wave control and improved power grid voltage feedforward control.
The method comprises the following steps: designing parameters of an output LCL filter according to the power grade, switching frequency and current ripple required parameters of the high-frequency SiC photovoltaic grid-connected inverter;
step two: collecting output voltage u of high-frequency SiC photovoltaic grid-connected invertera、ubAnd ucAnd collecting output current i of the high-frequency SiC photovoltaic grid-connected invertera、ibAnd icAnd the output voltage u of the collected high-frequency SiC photovoltaic grid-connected inverter is converted by Clarkea、ub、ucAnd an output current ia、ib、icConversion to a two-phase stationary coordinate system αβ, according to the definition of instantaneous power and the active power reference value P*And a reactive power reference value Q*Calculating a reference value i of the current loopα *And iβ *；
Step three: in order to improve the power density of the high-frequency SiC photovoltaic grid-connected inverter, grid-connected current is selected to be fed back, and an active damping feedback function H is designed according to the active damping mechanismad(s) determining a stability constraint condition of the active damping inner ring according to a Laus criterion;
step four: taking into account the grid impedance LgAccording to the active damping feedback function Had(s) in combination with the full bridge gain kPWMFilter side inductor L1Filter capacitor C and electric network side inductor L2Feedforward voltage function Gf(s) and a current controller Gc(s) determining an open loop transfer function G of the high-frequency SiC photovoltaic grid-connected inverteropen(s)；
Step five: according to the open loop transfer function G of the high-frequency SiC photovoltaic grid-connected inverter obtained in the fourth stepopen(s) improving the feedforward function of the power grid voltage, and configuring a first-order low-pass filter to obtain a new power grid voltage transfer function Gv(s)；
Step six: the current controller adopts an odd-number repeated quasi-PR controller, the quasi-PR controller is used for carrying out rapid error-free tracking on fundamental wave signals, and the odd-number repeated controller is used for inhibiting each harmonic wave;
step seven: i to be collectedα、iβRespectively with a reference current value iα *、iβ *After 0 comparison, the modulated wave u is obtained by combining odd-number repeated quasi-PR current controller with power grid voltage feedforward and power grid current feedback controlαβ *And then a switch driving signal is obtained through the SVPWM module and is used for driving the SiC switch tube.
The parameters of the LCL filter are reasonably designed, and the specific formula is as follows:
Figure BDA0001890509150000061
L2＝rL1(2)
Figure BDA0001890509150000062
wherein, UdcIs a DC side voltage irmaxFor maximum allowable current ripple, fsFor switching frequency, r is the ratio of the network side inductance to the inverter side inductance, P is the rated power of the inverter, λ is the ratio of the reactive power to the total power, EnIs the effective value of three-phase network phase voltage, f is the network fundamental frequency, L1Is a filter side inductor, C is a filter capacitor, L2Is the filter network side inductance.
The overall control block diagram of the system is shown in fig. 2. The method mainly comprises PQ outer loop control, active damping control, fundamental wave and harmonic wave control and improved power grid voltage feedforward control. Sampling inverter output voltage u firsta、ub、ucAnd an output current ia、ib、icAnd the output voltage u of the collected high-frequency SiC photovoltaic grid-connected inverter is converted by Clarkea、ub、ucAnd an output current ia、ib、icConverting the voltage into a two-phase static coordinate system αβ to obtain a two-phase static voltage uα、uβTwo-phase stationary current iα、iβ。
With PQ outer-loop control, rootAccording to the definition of instantaneous power and active power reference value P*And a reactive power reference value Q*Calculating to obtain a reference value i of the current loopα *、iβ *The concrete formula is as follows:
Figure BDA0001890509150000063
wherein u isα、uβIs a two-phase rest voltage iα、iβIs a two-phase quiescent current iα *And iβ *Is a reference value of the current loop, P*As active power reference value, Q*Is a reactive power reference value.
On the basis of traditional PQ control and power grid voltage feedforward control, in order to realize that active damping suppresses LCL filter resonance peak, do not increase extra sensor simultaneously, promote inverter power density, select to feed back grid-connected current, combine the mechanism of active damping to design feedback function H of high pass filter formad(s) is represented by formula (5):
Figure BDA0001890509150000064
wherein Had(s) a feedback function in the form of a high-pass filter, kadIs the high pass filter gain, omegahIs the high pass filter corner frequency, kPWMFor the inverter full bridge gain, s is the laplace operator.
The stability constraint condition of the active damping inner ring under the scheme can be obtained according to the Laus criterion, and the formula (6) is as follows:
Figure BDA0001890509150000071
grid-connected current active damping control block diagram with additional grid voltage feed-forward shown in fig. 3, taking into account grid impedance LgAccording to the active damping feedback function Had(s) in combination with a full bridge gain kPWMFilter side circuitFeeling L1Filter capacitor C, network side inductor L2Voltage feedforward function Gf(s) and a current controller Gc(s) obtaining an open loop transfer function G of the grid-connected inverteropen(s) represented by formula (7):
Figure BDA0001890509150000072
gopen(s) is an open-loop transfer function of the high-frequency SiC photovoltaic grid-connected inverter, and A is L1(L2+Lg)C，B＝L1(L2+Lg)Cωh，D＝L1+L2+Lg-kPWMLgGf(s)，E＝(L1+L2+Lg)ωh-kPWMkad-kPWMLgωhGf(s), Lg is the network impedance, gc(s) is the current controller, and gf(s) is the feed forward voltage function.
In order to eliminate the influence of the power grid impedance on the grid-connected inverter, on the basis of an active damping method of single grid-connected current feedback, from the perspective of a system open-loop transfer function shown in a formula (7), considering the stability problem of the traditional proportional voltage feedforward generated under a weak power grid, the power grid voltage feedforward function is improved into the sum of a second-order differential form and a proportional form to completely eliminate the L in the system open-loop transfer functiongA component; meanwhile, in order to avoid the noise problem possibly brought by differential terms in the feedforward function, a first-order low-pass filter is configured for the feedforward function to obtain a new power grid voltage transfer function Gv(s) as shown in formula (8):
Figure BDA0001890509150000073
wherein G isv(s) is the new grid voltage transfer function and τ is the low pass filter time constant.
Further, in order to solve the problem of inverter output current distortion possibly caused by weak grid background harmonics, an odd-number repeated quasi-PR controller shown in FIG. 4 is adopted, and the quasi-PR controller is utilized to realize fast and error-free tracking of fundamental wave signals, so that good dynamic performance of the system is ensured; because only odd harmonics exist in the three-phase power grid, the suppression of each odd harmonic is realized by using the repetitive controller based on the odd internal model, and the good steady-state performance of the system is ensured. The quasi-PR controller expression is shown as formula (9)
Figure BDA0001890509150000074
Wherein kpi, kri are respectively the proportion and the resonance coefficient of the current loop quasi-PR control, ω c is the cut-off frequency, and ω r is the resonance frequency.
The expression of the repetitive controller is shown in formula (10)
Figure BDA0001890509150000075
Wherein G isRC(s) is a repetitive controller function, T is a sampling time, Q(s) is an integral attenuation coefficient less than 1, C(s) is a compensation function designed for the control object, krcIs the repetitive controller gain.
I to be collectedα、iβRespectively with a reference current value iα *、iβ *After 0 comparison, the modulated wave u is obtained by the combination of the repeated quasi-PR current controller, the grid voltage feedforward and the grid current feedback controlαβ *And then, a switch driving signal is obtained through the SVPWM module and is used for driving the SiC switch tube.
The second embodiment is as follows:
in order to further illustrate the correctness and feasibility of the method of the invention in detail, the method of the invention is subjected to simulation verification by combining the specific example. The simulation parameters in this example are: DC voltage UdcThe voltage is 300V, the rated voltage effective value of the power grid is 110V, and the power level of the inverter is 1.5 kW. The working frequency of the Si inverter is selected to be 10kHz, and the parameter of the LCL filter is designed to be L1＝5mH，L21.25mH, 4.7 mu F, 50kHz of SiC inverter working frequency and L of LCL filter parameter design1＝1mH，L2＝0.2mH，C＝4.7μF。
In order to verify that the stability of the high-frequency SiC inverter is more easily influenced by weak grid impedance, the weak grid impedance L of the Si inverter and the SiC inverter is respectively usedgSimulations were performed at 0 and 2mH, respectively. FIGS. 5(a) and 5(b) are graphs showing the impedance L in the power grid, respectivelygThe grid-connected current waveform diagrams of the Si inverter and the SiC inverter at 0, and FIG. 6(a) and FIG. 6(b) are respectively the grid impedance LgAnd the grid-connected current waveform diagrams of the Si inverter and the SiC inverter are 2 mH.
As can be seen from fig. 5(a) and 5(b), when there is no grid impedance, the grid-connected current waveform quality of both the Si inverter and the SiC inverter is high, and the inverters can stably operate; as can be seen from fig. 6(a) and 6(b), when the grid impedance is 2mH, the grid-connected current waveform of the Si inverter is still stable, while the grid-connected current stability of the SiC inverter rapidly deteriorates, proving that the grid impedance L isgAnd filter net side impedance L2The stability of the system is more susceptible as the degree of mismatch is higher.
Fig. 7(a) is a grid-connected current waveform diagram of a Si inverter adopting a conventional control method under the condition that the weak grid impedance is 2mH and the switching frequency is 10kHz, and it can be seen that the grid-connected current waveform quality is good and the inverter operates stably; fig. 7(b) is a grid-connected current waveform diagram of the SiC inverter adopting the conventional control method under the condition that the weak grid impedance is 2mH and the switching frequency is 50kHz, and the grid-connected current waveform is seriously distorted, which greatly affects the stability of the inverter; fig. 7(c) is a grid-connected current waveform diagram of the SiC inverter adopting the composite robust control method under the condition that the weak grid impedance is 2mH and the switching frequency is 50kHz, the current waveform is recovered to be normal and the inverter operates stably.
Further, the effectiveness of the composite robust control method is demonstrated from the aspect of system stability.
FIG. 8(a) shows the impedance L at a weak gridgFig. 8(b) is an open-loop transfer function characteristic diagram of the composite robust control strategy at different grid impedances for the open-loop transfer function characteristic diagram of the conventional grid voltage proportional feedforward control strategy at 2mH and the composite robust control strategy proposed herein.
As can be seen from fig. 8(a), when the grid impedance is 2mH, the phase margin of the system under the conventional grid voltage proportional feedforward control is-5 °, and the system is unstable; and under the composite robust control, the phase margin of the system is 63 degrees, and the system stably operates. From fig. 8(b), it can be seen that the open-loop transfer function of the system under the composite robust control does not change with the grid impedance, that is, the phase margin of the system is not affected by the grid impedance, and the system can operate stably.
And adopting an active damping method of grid-connected current feedback to suppress the resonance peak of the output LCL filter. Compared with the traditional capacitance current feedback active damping method, the method has the advantages that no additional sensor is needed, and the advantage of high power density of the high-frequency SiC photovoltaic grid-connected inverter is fully exerted.
On the basis of a grid-connected current feedback active damping method, the stability problem of the traditional proportional voltage feedforward control generated under a weak power grid is considered, and a second-order differential link and a proportional link are adopted to jointly realize power grid voltage feedforward so as to completely eliminate the influence of impedance of the weak power grid on the stability of a high-frequency inverter.
In consideration of the problems of power grid background voltage harmonic waves and harmonic waves existing in a current reference command, current fundamental waves and the harmonic waves are independently controlled respectively, and the problem of output current distortion caused by the power grid background harmonic waves and the command reference harmonic waves together is solved by adopting a current controller based on repeated quasi-PR of an odd-order internal model.
The above description is only a preferred embodiment of the composite robust control method for the high-frequency SiC photovoltaic grid-connected inverter in the weak grid, and the protection range of the composite robust control method for the high-frequency SiC photovoltaic grid-connected inverter in the weak grid is not limited to the above embodiments, and all technical solutions belonging to the idea belong to the protection range of the invention. It should be noted that modifications and variations can be made by those skilled in the art without departing from the principles of the invention and these modifications and variations should also be considered as within the scope of the invention.

Claims (8)

1. A composite robust control method of a high-frequency SiC photovoltaic grid-connected inverter under a weak grid is characterized by comprising the following steps: the method comprises the following steps:
the method comprises the following steps: designing parameters of an output LCL filter according to the power grade, switching frequency and current ripple required parameters of the high-frequency SiC photovoltaic grid-connected inverter;
step two: collecting output voltage u of high-frequency SiC photovoltaic grid-connected invertera、ubAnd ucAnd collecting output current i of the high-frequency SiC photovoltaic grid-connected invertera、ibAnd icAnd the output voltage u of the collected high-frequency SiC photovoltaic grid-connected inverter is converted by Clarkea、ub、ucAnd an output current ia、ib、icConversion to a two-phase stationary coordinate system αβ, according to the definition of instantaneous power and the active power reference value P*And a reactive power reference value Q*Calculating a reference value i of the current loopα *And iβ *；
Step three: the power density of the high-frequency SiC photovoltaic grid-connected inverter is improved, grid-connected current is selected to be fed back, and an active damping feedback function H is designed according to the active damping mechanismad(s) determining a stability constraint condition of the active damping inner ring according to a Laus criterion;
step four: taking into account the grid impedance LgAccording to the active damping feedback function Had(s) in combination with the full bridge gain kPWMFilter side inductor L1Filter capacitor C and electric network side inductor L2Feedforward voltage function Gf(s) and a current controller Gc(s) determining an open loop transfer function G of the high-frequency SiC photovoltaic grid-connected inverteropen(s)；
Step five: according to the open loop transfer function G of the high-frequency SiC photovoltaic grid-connected inverter obtained in the fourth stepopen(s) improving the feedforward function of the power grid voltage, and configuring a first-order low-pass filter to obtain a new power grid voltage transfer function Gv(s)；
Step six: the current controller adopts an odd-number repeated quasi-PR controller, the quasi-PR controller is used for carrying out rapid error-free tracking on fundamental wave signals, and the odd-number repeated controller is used for inhibiting each harmonic wave;
step seven: will be provided withCollected iα、iβRespectively corresponding to the reference current value iα *、iβ *After 0 comparison, the modulated wave u is obtained by combining odd-number repeated quasi-PR current controller with power grid voltage feedforward and power grid current feedback controlαβ *And then a switch driving signal is obtained through the SVPWM module and is used for driving the SiC switch tube.
2. The composite robust control method of the high-frequency SiC photovoltaic grid-connected inverter under the weak grid as claimed in claim 1, wherein the composite robust control method comprises the following steps: the parameters of the output LCL filter are designed by:
Figure RE-FDA0001911100310000011
L2＝rL1(2)
Figure RE-FDA0001911100310000012
wherein, UdcIs a DC side voltage irmaxFor maximum allowable current ripple, fsFor switching frequency, r is the ratio of the network side inductance to the inverter side inductance, P is the rated power of the inverter, λ is the ratio of the reactive power to the total power, EnIs the effective value of three-phase network phase voltage, f is the network fundamental frequency, L1Is a filter side inductor, C is a filter capacitor, L2Is the filter network side inductance.
3. The composite robust control method of the high-frequency SiC photovoltaic grid-connected inverter under the weak grid as claimed in claim 1, wherein the composite robust control method comprises the following steps: the second step is specifically as follows:
the first step is as follows: collected output voltage u of high-frequency SiC photovoltaic grid-connected inverter by Clarke transformationa、ub、ucAnd an output current ia、ib、icConverting the voltage into a two-phase static coordinate system αβ to obtain a two-phase static voltage uα、uβTwo-phase stationary current iα、iβ；
The second step is that: with PQ outer loop control, according to the definition of instantaneous power and active power reference value P*And a reactive power reference value Q*Calculating to obtain a reference value i of the current loopα *And iβ *Calculating the reference value i of the current loop by the following formulaα *And iβ *：
Figure RE-FDA0001911100310000021
Wherein u isα、uβIs a two-phase rest voltage iα、iβIs a two-phase quiescent current iα *And iβ *Is a reference value of the current loop, P*As active power reference value, Q*Is a reactive power reference value.
4. The composite robust control method of the high-frequency SiC photovoltaic grid-connected inverter under the weak grid as claimed in claim 1, wherein the composite robust control method comprises the following steps: the third step is specifically as follows:
the first step is as follows: active damping feedback function H designed according to active damping mechanismad(s) expressed by the formula:
Figure RE-FDA0001911100310000022
wherein Had(s) a feedback function in the form of a high-pass filter, kadIs the high pass filter gain, omegahIs the high pass filter corner frequency, kPWMIs the inverter full-bridge gain, s is the Laplace operator;
the second step is that: the active damping inner loop stability constraint is expressed by:
Figure RE-FDA0001911100310000023
5. the composite robust control method of the high-frequency SiC photovoltaic grid-connected inverter under the weak grid as claimed in claim 1, wherein the composite robust control method comprises the following steps: determining an open-loop transfer function G of a high-frequency SiC photovoltaic grid-connected inverter by the following formulaopen(s)：
Figure RE-FDA0001911100310000024
Gopen(s) is an open-loop transfer function of the high-frequency SiC photovoltaic grid-connected inverter, and A is L1(L2+Lg)C，B＝L1(L2+Lg)Cωh，D＝L1+L2+Lg-kPWMLgGf(s)，E＝(L1+L2+Lg)ωh-kPWMkad-kPWMLgωhGf(s), Lg is the network impedance, gc(s) is the current controller, and gf(s) is the feed forward voltage function.
6. The composite robust control method of the high-frequency SiC photovoltaic grid-connected inverter under the weak grid as claimed in claim 1, wherein the composite robust control method comprises the following steps: the fifth step is specifically as follows:
the first step is as follows: according to the open loop transfer function G of the high-frequency SiC photovoltaic grid-connected inverter obtained in the fourth stepopen(s) modifying the grid voltage feedforward function to a sum of a second order differential form and a proportional form;
the second step is that: configuring a first-order low-pass filter, and obtaining a new power grid voltage transfer function G through the expression of the following formulav(s)：
Figure RE-FDA0001911100310000031
Wherein G isv(s) is the new grid voltage transfer function and τ is the low pass filter time constant.
7. The composite robust control method of the high-frequency SiC photovoltaic grid-connected inverter under the weak grid as claimed in claim 1, wherein the composite robust control method comprises the following steps: the repetitive quasi-PR controller is expressed by the following equation:
Figure RE-FDA0001911100310000032
wherein G isQPR(s) is a repeating quasi-PR controller function, kpi，kriRespectively, the proportion and the resonance coefficient, omega, of the current loop quasi-PR controlcTo cut-off frequency, ωrIs the resonant frequency.
8. The composite robust control method of the high-frequency SiC photovoltaic grid-connected inverter under the weak grid as claimed in claim 7, wherein the composite robust control method comprises the following steps: the odd-numbered repetitive controller is expressed by the following formula:
Figure RE-FDA0001911100310000033
wherein G isRC(s) is an odd number of times the controller function is repeated, T is the sampling time, Q(s) is an integral attenuation coefficient less than 1, C(s) is a compensation function designed for the control object, krcIs the repetitive controller gain.
CN201811469199.7A 2018-11-28 2018-11-28 Composite robust control method of high-frequency SiC photovoltaic grid-connected inverter under weak current network Active CN111245004B (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
CN201811469199.7A CN111245004B (en) 2018-11-28 2018-11-28 Composite robust control method of high-frequency SiC photovoltaic grid-connected inverter under weak current network

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
CN201811469199.7A CN111245004B (en) 2018-11-28 2018-11-28 Composite robust control method of high-frequency SiC photovoltaic grid-connected inverter under weak current network

Publications (2)

Publication Number Publication Date
CN111245004A true CN111245004A (en) 2020-06-05
CN111245004B CN111245004B (en) 2023-06-16

Family

ID=70865780

Family Applications (1)

Application Number Title Priority Date Filing Date
CN201811469199.7A Active CN111245004B (en) 2018-11-28 2018-11-28 Composite robust control method of high-frequency SiC photovoltaic grid-connected inverter under weak current network

Country Status (1)

Country Link
CN (1) CN111245004B (en)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112398319A (en) * 2020-12-05 2021-02-23 南京理工大学 Feedforward strategy for inhibiting inverter current harmonic caused by power grid harmonic voltage
CN113258615A (en) * 2021-06-08 2021-08-13 西南石油大学 Grid-connected inverter frequency self-adaptive control method, device, equipment and storage medium
CN113489357A (en) * 2021-05-26 2021-10-08 国电南瑞科技股份有限公司 Microgrid inverter control method and system, storage medium and computing equipment
CN113517720A (en) * 2021-09-10 2021-10-19 四川大学 Fractional phase compensation control method and device for LCL grid-connected inverter under weak grid
CN113595430A (en) * 2021-08-05 2021-11-02 上海交通大学 Three-loop controller of LCL type grid-connected inverter and parameter design method thereof
CN113839421A (en) * 2021-11-16 2021-12-24 四川大学 Stability combination control method for LCL type grid-connected inverter under weak grid
CN114884125A (en) * 2022-05-23 2022-08-09 中赟国际工程有限公司 High-stability control method for LCL type grid-connected inverter system under weak power grid
CN115207968A (en) * 2022-06-22 2022-10-18 湖南工业大学 Method for improving stability margin of photovoltaic grid-connected inverter under weak grid

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103545838A (en) * 2013-09-17 2014-01-29 南京航空航天大学 Method for adaptively controlling hybrid damping of grid-connection inverter applicable to weak grid access conditions
CN105591400A (en) * 2016-01-15 2016-05-18 湖南大学 Rapid robustness single-current feedback control method of LCL type grid-connected inverter
CN105915094A (en) * 2016-04-22 2016-08-31 哈尔滨工业大学 LCL type grid-connected inverter control method based on power grid current single sensor
CN106712099A (en) * 2017-02-27 2017-05-24 重庆大学 Multi-parallel photovoltaic grid-connected inverter design method
TWI599134B (en) * 2016-06-21 2017-09-11 Synchronization method for two separate areas in independent microgrid
CN108429281A (en) * 2018-03-15 2018-08-21 上海电力学院 A kind of LCL type gird-connected inverter parallel virtual impedance adjustment
CN108448583A (en) * 2018-05-02 2018-08-24 燕山大学 A kind of modified adjuster applied to light current gird-connected inverter off the net

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103545838A (en) * 2013-09-17 2014-01-29 南京航空航天大学 Method for adaptively controlling hybrid damping of grid-connection inverter applicable to weak grid access conditions
CN105591400A (en) * 2016-01-15 2016-05-18 湖南大学 Rapid robustness single-current feedback control method of LCL type grid-connected inverter
CN105915094A (en) * 2016-04-22 2016-08-31 哈尔滨工业大学 LCL type grid-connected inverter control method based on power grid current single sensor
TWI599134B (en) * 2016-06-21 2017-09-11 Synchronization method for two separate areas in independent microgrid
CN106712099A (en) * 2017-02-27 2017-05-24 重庆大学 Multi-parallel photovoltaic grid-connected inverter design method
CN108429281A (en) * 2018-03-15 2018-08-21 上海电力学院 A kind of LCL type gird-connected inverter parallel virtual impedance adjustment
CN108448583A (en) * 2018-05-02 2018-08-24 燕山大学 A kind of modified adjuster applied to light current gird-connected inverter off the net

Non-Patent Citations (3)

* Cited by examiner, † Cited by third party
Title
刘桂花;曹小娇;王卫;: "弱电网下单相光伏并网逆变器锁频环同步方法", no. 19, pages 5022 - 5029 *
刘湘宁: "弱电网下LCL型并网逆变器控制策略研究刘", pages 042 - 325 *
张雪: "基于有源阻尼的LCL并网逆变器控制策略研究", pages 042 - 325 *

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN112398319A (en) * 2020-12-05 2021-02-23 南京理工大学 Feedforward strategy for inhibiting inverter current harmonic caused by power grid harmonic voltage
CN113489357A (en) * 2021-05-26 2021-10-08 国电南瑞科技股份有限公司 Microgrid inverter control method and system, storage medium and computing equipment
CN113258615A (en) * 2021-06-08 2021-08-13 西南石油大学 Grid-connected inverter frequency self-adaptive control method, device, equipment and storage medium
CN113258615B (en) * 2021-06-08 2021-10-08 西南石油大学 Grid-connected inverter frequency self-adaptive control method, device, equipment and storage medium
CN113595430A (en) * 2021-08-05 2021-11-02 上海交通大学 Three-loop controller of LCL type grid-connected inverter and parameter design method thereof
CN113595430B (en) * 2021-08-05 2022-12-20 上海交通大学 Three-loop controller of LCL type grid-connected inverter and parameter design method thereof
CN113517720A (en) * 2021-09-10 2021-10-19 四川大学 Fractional phase compensation control method and device for LCL grid-connected inverter under weak grid
CN113517720B (en) * 2021-09-10 2022-02-11 四川大学 Fractional phase compensation control method and device for LCL grid-connected inverter under weak grid
CN113839421A (en) * 2021-11-16 2021-12-24 四川大学 Stability combination control method for LCL type grid-connected inverter under weak grid
CN114884125A (en) * 2022-05-23 2022-08-09 中赟国际工程有限公司 High-stability control method for LCL type grid-connected inverter system under weak power grid
CN115207968A (en) * 2022-06-22 2022-10-18 湖南工业大学 Method for improving stability margin of photovoltaic grid-connected inverter under weak grid
CN115207968B (en) * 2022-06-22 2024-05-03 湖南工业大学 Method for improving stability margin of photovoltaic grid-connected inverter under weak current network

Also Published As

Publication number Publication date
CN111245004B (en) 2023-06-16

Similar Documents

Publication Publication Date Title
CN111245004B (en) Composite robust control method of high-frequency SiC photovoltaic grid-connected inverter under weak current network
CN111245017B (en) Capacitive voltage feedforward control method for grid-connected inverter under weak current network
CN108173288B (en) Voltage type impedance adapter control method for inhibiting multi-inverter grid-connected system resonance
CN108988343B (en) Global high-frequency oscillation suppression method for multi-inverter grid-connected system under weak grid
CN106684918A (en) Low damping resonant suppression and rapid power adjustment method of LCL inverter
CN106253646B (en) Improve the gird-connected inverter LCL filter Parameters design of light current net adaptability
CN106208142A (en) A kind of LCL type combining inverter repeats double-closed-loop control method
CN108448629B (en) Multi-inverter parallel resonance suppression method and device based on virtual impedance
CN105743123A (en) LCL-LC based active damping parameter design method for grid-connected system
CN111463785A (en) Active damper self-adaptive control method for restraining cluster resonance of photovoltaic inverter
CN109327048B (en) Robust phase locking system and method for grid-connected converter
CN113285625B (en) Photovoltaic inverter cluster resonance suppression method based on improved active damping method
CN110233494A (en) A kind of control method of grid-connected inverter of the specific component of degree n n feedforward of network voltage
CN108767873B (en) High-reliability damping remodeling method for large new energy power station
CN113489049A (en) Grid-connected inverter grid-side current control method
CN112803416A (en) Grid-connected inverter topology structure for inhibiting power grid background harmonic waves and control method
CN114421494B (en) High-frequency oscillation suppression method and system for enhanced flexible direct current transmission system
CN111814102A (en) Harmonic parameter optimization method suitable for offshore wind power transmission system through alternating current submarine cable network
CN111064380A (en) Grid-connected inverter system
CN114844383A (en) Voltage control method, system and device based on load current feedforward
CN107919682B (en) Control method suitable for three-phase double-resonant-filter grid-connected inverter system
CN113067372A (en) Active damping method and circuit for improving LCL filtering grid-connected control performance
CN117155089A (en) Input ripple suppression method for three-phase voltage type inverter under nonlinear load
CN105978018B (en) A kind of LC types control method of grid-connected inverter
CN117498354A (en) VSG-based LCL grid-connected inverter harmonic current suppression method

Legal Events

Date Code Title Description
PB01 Publication
PB01 Publication
SE01 Entry into force of request for substantive examination
SE01 Entry into force of request for substantive examination
GR01 Patent grant
GR01 Patent grant