CN117134595B - Comprehensive optimization method for loss distribution and capacitance ripple voltage of hybrid MMC device - Google Patents

Comprehensive optimization method for loss distribution and capacitance ripple voltage of hybrid MMC device Download PDF

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CN117134595B
CN117134595B CN202311124175.9A CN202311124175A CN117134595B CN 117134595 B CN117134595 B CN 117134595B CN 202311124175 A CN202311124175 A CN 202311124175A CN 117134595 B CN117134595 B CN 117134595B
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bridge
submodule
capacitor
submodules
voltage
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CN117134595A (en
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路茂增
苏田田
于丹
赵艳雷
杨金一
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Shandong University of Technology
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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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/14—Arrangements for reducing ripples from dc input or output
    • 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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/0048—Circuits or arrangements for reducing losses
    • H02M1/0054—Transistor switching losses
    • 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
    • H02M1/00—Details of apparatus for conversion
    • H02M1/32—Means for protecting converters other than automatic disconnection
    • 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
    • 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
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/60—Arrangements for transfer of electric power between AC networks or generators via a high voltage DC link [HVCD]

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

Abstract

A comprehensive optimization method for loss distribution and capacitance ripple voltage of a hybrid MMC device belongs to the technical field of power electronics. The maximum reduction of the capacitor ripple voltage of the half-bridge submodule is constrained to calculate the amplitude and the initial phase of the double frequency circulation injection; when the charge and discharge quantity of the traversing half-bridge submodule is minimum in a negative interval of bridge arm current, the output voltage command value of the half-bridge submodule in the bridge arm which meets the balance of the capacitor voltage of the submodule is calculated, the number of the corresponding maximum active bypass half-bridge submodule is calculated respectively, and the maximum value is selected; computing a full bridge T 2 Tube loss, half-bridge sub-module T 2 Tube loss, full bridge submodule capacitor ripple voltage deltau CF And Deltau CH The method comprises the steps of carrying out a first treatment on the surface of the At meeting DeltaP T2H >ΔP T2F And Deltau CH >Δu CF Number of active side sub-modules N sur Within the interval, select the best N sur . The invention gives consideration to the half-bridge sub-module T 2 The reduction of the tube loss and the reduction of the capacitor ripple voltage improve the reliability and the power density.

Description

Comprehensive optimization method for loss distribution and capacitance ripple voltage of hybrid MMC device
Technical Field
A comprehensive optimization method for loss distribution and capacitance ripple voltage of a hybrid MMC device belongs to the technical field of power electronics.
Background
The hybrid MMC has been applied to high-voltage and high-power occasions such as flexible direct-current transmission, direct-current distribution, offshore wind power grid connection and the like due to the direct-current fault ride-through capability, and the equipment reliability and the power density are important mattersAnd (5) pouring problems. In terms of reliability, temperature is the most important factor causing the failure of the converter, accounting for 55% of all failure factors of the equipment. Under the inversion condition, the lower IGBT of the half-bridge submodule (hereinafter referred to as T 2 Tube) losses are much greater than other devices, resulting in junction temperatures much higher than other devices. In terms of power density, the capacitance of the MMC sub-module accounts for more than 1/2 of the volume and weight of the sub-module, and the cost is about 1/3 of the cost. The submodule capacitor ripple voltage is inversely related to the capacitance value and the volume.
Aiming at the problem of optimizing the loss distribution of the mixed MMC, the technology is similar to the technology in that an active bypass control method is provided, and the circulation path of bridge arm current in a submodule during bypass is changed, namely the current flows through T 2 The pipe flows through SCR instead, and the half-bridge submodule T is reduced 2 Loss of the tube; decoupling control method, by flexibly distributing the output voltage command values of all full-bridge submodules in a bridge arm and the duty ratio of the output voltage command values of all half-bridge submodules in the output voltage command values of the bridge arm, the half-bridge submodule T is reduced 2 Loss of the tube. Aiming at improving the power density, the technology is similar to the technology in that third harmonic voltage injection, double frequency circulation injection and operation modulation ratio is changed to reduce the capacitive ripple voltage of the half-bridge submodule.
The above techniques focus on reliability or power density only. E.g. active bypass, which is implemented in a half-bridge submodule T 2 The total loss of the tube and the influence of the capacitor ripple voltage of the half-bridge submodule are shown in figure 2, and it can be seen from the figure that the active bypass technology reduces T 2 The total loss of the tube is increased, but the capacitance ripple voltage of the submodule is increased, and the power density is reduced; such as double frequency circulation injection technique, for T 2 The total loss of the tube and the influence of the capacitor ripple voltage are shown in fig. 3, and it can be seen from the graph that the capacitor ripple voltage of the half-bridge submodule is reduced and the half-bridge submodule T appears along with the injection of the double frequency circulation 2 The total loss of the tube is increased, and the running reliability of the mixed MMC is reduced due to the change of the current waveform of the bridge arm.
Therefore, a half-bridge sub-module T is proposed 2 Tube total loss and suppression of half-bridge submodule capacitor ripple voltage while improving reliabilityThe comprehensive optimization method of the performance and the power density becomes an urgent need.
Disclosure of Invention
The invention aims to solve the technical problems that: overcomes the defects of the prior art and provides a method for reducing the half-bridge submodule T 2 A method for comprehensively optimizing the total loss of a tube and the loss distribution and the capacitor ripple voltage of a mixed MMC device for inhibiting the capacitor ripple voltage of a half-bridge submodule.
The technical scheme adopted for solving the technical problems is as follows: the comprehensive optimization method for the loss distribution and the capacitor ripple voltage of the hybrid MMC device comprises the following steps:
s1, injecting amplitude value (2+m-m) into bridge arm current through a double frequency circulation controller 2 )I dc /(3*m (1+m)) double frequency circulation with an initial phase of-pi/2; wherein m is the modulation ratio and the value is 2U m /U dc ，U m Is the amplitude of alternating-current side-phase voltage, U dc For the rated voltage of the direct current side, I dc Rated current at the direct current side;
s2, taking the minimum charge amount discharged by the half-bridge submodule in the bridge arm current as a negative interval under the steady state as constraint, traversing the combination of the output voltage command value of all full-bridge submodules and the output voltage command value of all half-bridge submodules which meet the stability of the capacitance voltage of the submodule, calculating the number of the maximum active bypass half-bridge submodule under each condition, selecting the maximum value, and recording the value as N sur_max ；
S3 is according to N in S2 sur_max The voltage output command values of all full-bridge sub-modules and all half-bridge sub-modules in the corresponding bridge arm, and the number of bypass half-bridge sub-modules is 0, N sur_max ]In the interval, respectively calculating the full-bridge submodule T 2 Total loss of pipe P T2F Half-bridge sub-module T 2 Total loss of pipe P T2H Full bridge submodule capacitor ripple voltage deltau CF And the capacitive ripple voltage deltau of the half-bridge sub-module CH ；
The full-bridge submodule includes an Insulated Gate Bipolar Transistor (IGBT) T 1 -T 4 Diode D 1 -D 4 Capacitor C, insulated gate bipolar transistor T 1 、T 3 Collector and diode D of (c) 1 、D 3 Is commonly connected to the anode of the capacitor C; insulated gate bipolar transistor T 2 、T 4 Emitter and diode D of (c) 2 、D 4 Is commonly connected to the negative electrode of the capacitor C; insulated gate bipolar transistor T 1 Emitter, insulated gate bipolar transistor T of (2) 2 Collector, diode D of (c) 1 Anode of (D) and diode D 2 Is commonly connected to the upper input of the Quan Qiaozi module; t (T) 3 Emitter, T of (2) 4 Collector, diode D of (c) 3 Anode and diode D of (c) 4 Is commonly connected to the lower input of the Quan Qiaozi module;
the half-bridge submodule comprises two insulated gate bipolar transistors T 1 -T 2 Diode D 1 -D 2 Capacitor C and bidirectional thyristor SCR, insulated gate bipolar transistor T 1 Collector and diode D of (c) 1 Is commonly connected to the anode of the capacitor C; insulated gate bipolar transistor T 2 Emitter and diode D of (c) 2 Is commonly connected to the negative electrode of the capacitor C; insulated gate bipolar transistor T 1 Emitter, insulated gate bipolar transistor T of (2) 2 Collector, diode D of (c) 1 Anode of (D) and diode D 2 The cathodes of the half-bridge sub-modules are commonly connected to the upper input end of the half-bridge sub-modules; insulated gate bipolar transistor T 2 Emitter of (D) and diode D 2 The anodes of the two are commonly connected to the lower input end of the half-bridge sub-module; the bidirectional thyristor SCR is connected between the two input ends;
s4 to satisfy P at the same time T2H >P T2F And Deltau CH >Δu CF For constraint conditions, determining a comprehensive optimization interval of the number of the active bypass half-bridge submodules, and establishing a compromise for reducing the half-bridge submodules T in the interval 2 Comprehensive optimization objective function for total loss of tube and suppression of capacitor ripple voltage is obtained and simultaneously reduced half-bridge submodule T is satisfied 2 Number N of active bypass half-bridge submodules for total loss of tube and inhibiting capacitor ripple voltage sur Is the optimum value of (2);
s5, the stable operation of the mixed MMC is guaranteed through the power loop controller, the current loop controller and the double frequency circulation controller, the output angle of the phase-locked loop is combined, the bridge arm output voltage command value is distributed to the full-bridge submodule output voltage command value and the half-bridge submodule output voltage command value, and the comprehensive optimization target of the loss distribution and the capacitor ripple voltage of the mixed MMC device is achieved.
Preferably, the output voltage command values of all half-bridge sub-modules which meet the capacitance-voltage balance of the sub-modules meet the following conditions:
wherein: x is a, b, c phase in three phases, u pxref For the x-phase upper bridge arm to output voltage command value, u pxhref The output voltage command value of all the half-bridge submodules in the upper bridge arm of the x phase is F, the number of the full-bridge submodules in the bridge arm is U C For submodule capacitor voltage rating, i px Is the current of the upper bridge arm of the x phase, theta i1 、θ i2 Is the zero crossing point of bridge arm current;
output voltage command value u of all full-bridge submodules in x-phase upper bridge arm pxfref The method meets the following conditions:
u pxfref ＝u pxref -u pxhref 。
preferably, N in step S2 sur_max The calculation formula is as follows:
wherein: floor is a downward rounding function, U o_pos Maximum bridge arm output voltage with bridge arm current as positive, U C Rated for the submodule capacitor voltage.
Preferably, the full bridge submodule T 2 Tube on-state loss P cond,T2F The calculation formula is as follows:
half-bridge sub-module T 2 Tube on-state loss P cond,T2H The calculation formula is as follows:
full bridge submodule capacitor ripple voltage deltau CF The calculation formula is as follows:
half-bridge submodule capacitor ripple voltage deltau CH The calculation formula is as follows:
wherein: c is capacitance value of submodule, H is number of half-bridge submodule in bridge arm, T is power frequency period, U CE Is IGBT threshold voltage, r CE Is IGBT on-state resistance, Q Filling material Charge of the half-bridge submodule in the positive range of bridge arm current, Q Put and put Is the discharge charge of the half-bridge submodule in the interval that the bridge arm current is negative, S pxh An average switch function of the half-bridge sub-module of the upper bridge arm of the x phase, and the value of the average switch function is u pxhref /(HU C )，S pxf An average switching function of the module Quan Qiaozi of the upper bridge arm of the x phase, and the value of the average switching function is u pxfref /(FU C )。
Preferably, a half-bridge sub-module T is established 2 And (3) a comprehensive objective function of the total loss of the tube and the ripple voltage of the capacitor, wherein the comprehensive objective function is defined as follows:
M＝k·Δu CH，k +ΔP T2H，k ；
wherein: ΔP T2H,k Is a half-bridge sub-module T 2 Per unit value of total loss of pipe, its reference value is P T2F ，Δu CH,k Is the per unit value of the half-bridge submodule capacitor ripple voltage, and the reference value is deltau CF K is the sum of reducing the half-bridge submodule T 2 Total loss of pipeThe weight coefficient of the ripple voltage of the capacitor of the sub-module of the half bridge;
fixing k, calculating M minimum value, and corresponding N sur I.e. the best.
Preferably, the selection principle of k in the comprehensive objective function is as follows:
if half-bridge submodule T is desired 2 The total loss reduction effect of the tube is the same as the suppression effect of the capacitor ripple voltage of the half-bridge submodule, and the value of k is 1;
if the half-bridge submodule capacitor ripple voltage inhibition effect is expected to be superior to that of the half-bridge submodule T 2 The total loss of the tube is reduced, the value of k is larger than 1, and the larger the degree of k larger than 1 is, the better the suppression effect on the capacitor ripple voltage of the half-bridge submodule is;
if half-bridge submodule T is desired 2 The total loss reduction effect of the tube is better than the suppression effect of the capacitor ripple voltage of the half-bridge submodule, the k value is smaller than 1 and is more approaching to 0, and the half-bridge submodule T 2 The better the total loss reduction effect of the pipe;
preferably, the step S5 further includes the steps of:
s5.1, obtaining a bridge arm output voltage instruction through a power loop controller, a current loop controller and a double frequency circulation controller;
s5.2, dividing a power frequency period into different sections, and distributing bridge arm output voltage command values in the different sections by combining an output angle theta of a phase-locked loop to obtain output voltage command values of all half-bridge submodules and output voltage command values of all full-bridge submodules in the bridge arm;
s5.3, calculating the number of full-bridge and half-bridge submodules to be input and the number of half-bridge submodules to be actively bypassed according to the output voltage command values of all full-bridge submodules and the output voltage command values of all half-bridge submodules in the bridge arm, judging the triggering time of the thyristor by the half-bridge submodules through positive and negative bridge arm currents, and sending T to the half-bridge submodules which have been actively bypassed 2 A tube lock signal; full-bridge submodule T is reduced by means of alternate conduction of full-bridge submodule 2 On-state loss of the tube;
s5.4, sequencing all full-bridge submodules and all half-bridge submodules according to the sequence from high to low of the submodule capacitor voltage, and inputting the number of required submodules with the lowest capacitor voltage when the bridge arm current is positive; when the bridge arm current is negative, the number of the required submodules with the highest bypass capacitor voltage is increased, and the balance of capacitor voltage among different submodules is realized. Compared with the prior art, the invention has the following beneficial effects:
the comprehensive optimization method for the loss distribution and the capacitor ripple voltage of the hybrid MMC device obtains N by distributing the output voltage instruction values of all the half-bridge submodules and all the full-bridge submodules in the bridge arm on the basis of double frequency circulation injection sur_max Half-bridge sub-module T is enlarged 2 Room for improvement of total loss of tube according to N sur_max Output voltage command values of all half-bridge submodules and all full-bridge submodules in corresponding bridge arms are calculated to obtain P T2H 、P T2F 、Δu CH 、Δu CF Determining to reduce half-bridge submodule T according to constraint 2 N of total loss of tube and half-bridge submodule capacitor ripple voltage sur A comprehensive optimization interval, a comprehensive optimization objective function is established in the interval, and the optimal N is determined sur The reliability of the device is enhanced while the power density is increased.
Drawings
FIG. 1 is a prior art full-half bridge 1:1 hybrid MMC topology;
FIG. 2 is a half-bridge sub-module T in the active bypass technique 2 Tube loss and capacitance ripple voltage versus discharge charge;
FIG. 3 shows a half-bridge sub-module T of the double frequency loop injection technique 2 Tube loss and capacitance ripple voltage versus discharge charge;
FIG. 4 is a general flow chart of a method for optimizing the loss distribution and the capacitor voltage ripple of the hybrid MMC device according to the present invention;
FIG. 5 is a control block diagram of a hybrid MMC device loss distribution and capacitive voltage ripple comprehensive optimization method according to the present invention;
fig. 6 is a schematic diagram of an output voltage command of the a-phase upper bridge arm Quan Qiaozi module and the half-bridge submodule according to an embodiment of the present invention;
FIG. 7 is a schematic illustration of an optimization interval of an embodiment of the present invention;
FIG. 8 is a schematic diagram of capacitance and voltage simulations of a full-bridge sub-module and a half-bridge sub-module before comprehensive optimization in accordance with an embodiment of the present invention;
fig. 9 is a schematic diagram of capacitance-voltage simulation of a fully-bridge sub-module and a half-bridge sub-module after comprehensive optimization according to an embodiment of the present invention.
Detailed Description
The present invention will be further described with reference to specific embodiments, however, it will be appreciated by those skilled in the art that the detailed description herein with reference to the accompanying drawings is for better illustration, and that the invention is not necessarily limited to such embodiments, but rather is intended to cover various equivalent alternatives or modifications, as may be readily apparent to those skilled in the art.
FIGS. 1-9 illustrate preferred embodiments of the present invention, and the present invention will be further described with reference to FIGS. 1-9.
In this embodiment, as shown in fig. 1, a full-half-bridge 1:1 hybrid MMC (hereinafter referred to as hybrid MMC) topology is used as an example under the inversion condition.
As shown in fig. 4, the method for comprehensively optimizing the loss distribution and the capacitor ripple voltage of the hybrid MMC device includes the following steps:
s1 injecting amplitude value (2+m-m) into bridge arm current through a loop controller 2 )I dc /(3*m (1+m)) double frequency circulation with an initial phase of-pi/2; wherein m is the modulation ratio and the value is 2U m /U dc ，U m Is the amplitude of alternating-current side-phase voltage, U dc For the rated voltage of the direct current side, I dc Rated current at the direct current side;
s2, taking the minimum charge amount discharged by the half-bridge submodule in the bridge arm current as a negative interval under the steady state as constraint, traversing the combination of the output voltage command values of all full-bridge submodules and the output voltage command values of all half-bridge submodules which meet the stability of the capacitance voltage of the submodule, calculating the number of the maximum active bypass half-bridge submodule under each condition, selecting the maximum value, and marking the maximum value as N sur_max ；
S3 is according to N in S2 sur_max The voltage output command values of all full-bridge sub-modules and all half-bridge sub-modules in the corresponding bridge arm, and the number of bypass half-bridge sub-modules is 0, N sur_max ]In the interval, respectively calculating the full-bridge submodule T 2 Pipe loss P T2F Half-bridge sub-module T 2 Pipe loss P T2H Full bridge submodule capacitor ripple voltage deltau CF And the capacitive ripple voltage deltau of the half-bridge sub-module CH ；
S4 to satisfy P at the same time T2H >P T2F And Deltau CH >Δu CF For constraint conditions, a comprehensive optimization interval is determined, a comprehensive optimization objective function is established in the interval, and the sub-module T of the half-bridge is solved and simultaneously meets the requirement of reduction 2 Number N of active bypass half-bridge submodules for reducing tube loss and inhibiting capacitor ripple voltage sur Is the optimum value of (2);
s5, the stable operation of the mixed MMC is guaranteed through the power loop controller, the current loop controller and the double frequency circulation controller, the bridge arm output voltage command value is distributed to the full-bridge submodule output voltage command value and the half-bridge submodule output voltage command value according to the output angle of the S2 combined phase-locked loop, and the comprehensive optimization target of the loss distribution and the capacitor ripple voltage of the mixed MMC device is achieved.
In the prior art, the injection amplitude and the initial phase of the double frequency circulation satisfy the following steps: taking an a-phase upper bridge arm as an example, taking account of bridge arm current injected by double frequency circulation as follows:
wherein i is pa For the a-phase upper bridge arm current, I dc Is the rated current of the direct current side, I m For the ac side current amplitude,for the power factor angle, I 2m For doubling the circulation injection amplitude, theta 2 The initial phase of the double frequency circulation is-pi/2. The instantaneous capacitor voltage ripple of the submodule can be obtained according to the bridge arm current expression and the capacitor ripple voltage calculation formulaThe values are:
the optimum amplitude value obtained by deriving the above method is as follows:
the double frequency circulation injection can increase the charge and discharge charge quantity of the half-bridge submodule and the adjustment space of the number of the active bypass half-bridge submodule, and can be realized by a double frequency circulation controller.
The output voltage command values of all full-bridge submodules and the output voltage command values of all half-bridge submodules in the bridge arm meet the following conditions:
taking the a-phase upper bridge arm as an example, the bridge arm output current waveform is shown in fig. 6, and under the condition that the charge and discharge amounts of the half-bridge submodules are minimum, the output voltage command values of all the half-bridge submodules which meet the capacitance and voltage balance of the submodules are traversed:
wherein: u (u) paref For the a-phase upper bridge arm to output voltage command value, u pahref The output voltage command value of all the half-bridge submodules of the a-phase upper bridge arm is F, the number of the full-bridge submodules in the bridge arm is U C For submodule capacitor voltage rating, i pa For a phase upper arm current, θ i1 、θ i2 Is the zero crossing point of bridge arm current;
the number of the maximum active bypass half-bridge submodules is related to the maximum bridge arm output voltage with the bridge arm current being positive, and the maximum bridge arm output voltage with the bridge arm current being positive can be changed by distributing the output voltage command values of all the full-bridge submodules and the output voltage command values of all the half-bridge submodules in the bridge arm. According to the output voltage command values of all full-bridge submodules and the output voltage commands of all half-bridge submodules in the traversed bridge armThe values are respectively calculated, the number of the maximum active bypass half-bridge submodules is respectively calculated, the maximum value is selected and recorded as N sur_max The values thereof satisfy:
wherein: floor is a downward rounding function, U o_pos Maximum bridge arm output voltage with bridge arm current as positive, U C Rated value of capacitance voltage for the submodule;
in the present embodiment, N is satisfied sur_max The output voltage command values of all the half-bridge sub-modules and the output voltage command values of all the full-bridge sub-modules in the a-phase upper bridge arm are shown in fig. 5. The expression thereof satisfies:
u pafref ＝u paref -u pahref ；
wherein: mod is the remainder function, θ a Is the phase of the a-phase voltage.
θ i3 、θ i4 The method meets the following conditions:
the constant η can be derived from the capacitance-voltage balance:
the output voltage command values of all the half-bridge sub-modules of the a-phase upper bridge arm and the output voltage command value distribution modes of all the full-bridge sub-modules are not unique, and the balance of capacitance and voltage is met, and the embodiment is most favorable for reducing the half-bridge sub-modules T 2 Tube loss and distribution of capacitor ripple voltage.
And respectively calculating the on-state loss and the switching loss of the Quan Qiaozi module, the on-state loss and the switching loss of the half-bridge submodule, the capacitor ripple voltage of the full-bridge submodule and the capacitor ripple voltage of the half-bridge submodule under the output voltage command values of all the half-bridge submodules and the output voltage command values of all the full-bridge submodules in the bridge arm.
Full bridge submodule T 2 Tube on-state loss P cond,T2F The method meets the following conditions:
half-bridge sub-module T 2 Tube on-state loss P cond,T2H The method meets the following conditions:
full bridge submodule T 2 Tube switching loss and half-bridge submodule T 2 The switching loss of the tube satisfies the following conditions:
full bridge submodule capacitor ripple voltage deltau CF The method meets the following conditions:
half-bridge submodule capacitor ripple voltage deltau CH The method meets the following conditions:
wherein: n is the number of bridge arm neutron modules, T is the power frequency period, U CE Is IGBT threshold voltage, r CE Is IGBT on-state resistance, N sw The switching times of the device in a single period are shown; u (U) ref,sw Test voltage for switching loss of the device; i (k) is a flow-through deviceA piece of current; e (E) sw The method can be obtained by performing quadratic polynomial fitting on a switching loss curve; q (Q) Filling material Charge of the half-bridge submodule in the positive range of bridge arm current, Q Put and put Is the discharge charge of the half-bridge submodule in the interval that the bridge arm current is negative, S pah An average switching function of a phase a upper bridge arm half-bridge submodule with a value of 2u pxhref /(NU C )，S paf An average switching function of the a-phase upper bridge arm Quan Qiaozi module, the value of which is 2u pafref /(NU C )；θ i1 、θ i2 Is the zero crossing point of bridge arm current; n (N) sur The number of active bypass submodules.
With P T2H ＝P T2F N of (2) sur As the upper bound of the optimization interval, Δu CH ＝Δu CF N of (2) sur As the lower bound of the optimization interval, when P is satisfied T2H >P T2F And Deltau CH >Δu CF N of (2) sur As shown in fig. 7. Establishing a half-bridge sub-module T 2 And (3) defining a comprehensive objective function of the on-state loss and the capacitor ripple voltage as follows:
M＝k·Δu CH，k +ΔP T2H，k ；
wherein: ΔP T2H,k Is a half-bridge sub-module T 2 Per unit value of total loss of pipe, its reference value is P T2F ，Δu CH,k Is the per unit value of the half-bridge submodule capacitor ripple voltage, and the reference value is deltau CF K is the half-bridge submodule T 2 The weight coefficient of the total loss of the tube and the capacitor ripple voltage of the half-bridge submodule;
solving M according to given k, and N corresponding to minimum value sur Namely, the half-bridge submodule T gives consideration to the current weight coefficient 2 Optimal N for reduced on-state loss of tube and reduced ripple of capacitor voltage sur ；
The selection principle of k in the comprehensive objective function is as follows:
if half-bridge submodule T is desired 2 The total loss reduction effect of the tube is the same as the suppression effect of the capacitor ripple voltage of the half-bridge submodule, and the value of k is 1;
if half-bridge submodule capacitance lines are expectedThe wave voltage inhibition effect is superior to that of the half-bridge submodule T 2 The total loss of the tube is reduced, the value of k is larger than 1, and the larger the degree of k larger than 1 is, the better the suppression effect on the capacitor ripple voltage of the half-bridge submodule is;
if half-bridge submodule T is desired 2 The total loss reduction effect of the tube is better than the suppression effect of the capacitor ripple voltage of the half-bridge submodule, the k value is smaller than 1 and is more approaching to 0, and the half-bridge submodule T 2 The better the total loss reduction effect of the pipe;
the specific control process of the method is shown in fig. 5. The concrete expression is as follows:
s5.1, obtaining a bridge arm output voltage instruction through a power loop controller, a current loop controller and a double frequency circulation controller;
s5.2, dividing a power frequency period into different intervals, and under the condition that the output voltage command values of all half-bridge submodules for realizing the capacitance and voltage balance of the submodules and the output voltage command values of all full-bridge submodules in an x-phase upper bridge arm meet the conditions, distributing the bridge arm output voltage command values in the different intervals by combining the output angle theta of the phase-locked loop to obtain the output voltage command values of all the half-bridge submodules and the output voltage command values of all the full-bridge submodules in the bridge arm;
s5.3, calculating the number of full-bridge and half-bridge submodules to be input and the number of half-bridge submodules to be actively bypassed according to the output voltage command values of all full-bridge submodules and the output voltage command values of all half-bridge submodules in the bridge arm, judging the triggering time of the thyristor by the half-bridge submodules through positive and negative bridge arm currents, and sending T to the half-bridge submodules which have been actively bypassed 2 A tube lock signal; full-bridge submodule T is reduced by means of alternate conduction of full-bridge submodule 2 On-state loss of the tube;
s5.4, sequencing all full-bridge submodules and all half-bridge submodules according to the sequence from high to low of the submodule capacitor voltage, and inputting the number of required submodules with the lowest capacitor voltage when the bridge arm current is positive; when the bridge arm current is negative, the number of the required submodules with the highest bypass capacitor voltage is increased, and the balance of capacitor voltage among different submodules is realized.
TABLE 1 parameters of a hybrid MMC main circuit in an embodiment of the invention
Better, in order to verify that the invention has the effect of reducing the half-bridge submodule T 2 Simulation verification is performed on the total loss of the tube and the effect of suppressing the half-bridge submodule capacitor voltage ripple, and in the embodiment, the optimal N is selected sur The reference value is 100 half-bridge submodules, the injection amplitude of the double frequency circulation is 247A, and the parameters of the mixed MMC main circuit are shown in table 1. Respectively observing the capacitor voltage u of the a-phase half-bridge submodule before and after comprehensive optimization cpah Capacitor voltage u of a-phase full-bridge submodule cpaf . FIG. 8 is u before comprehensive optimization cpah 、u cpaf FIG. 9 is a diagram of a complex optimized u cpah 、u cpaf . As can be seen from fig. 8 and 9, the capacitor ripple voltages of the two types of sub-modules after comprehensive optimization are lower than the respective capacitor ripple voltages before comprehensive optimization;
TABLE 2 comprehensive optimization of the front and rear sub-modules T in this embodiment 2 Total loss of pipe
Table 2 shows the capacitance ripple voltage and T of the sub-modules before and after the comprehensive optimization in this embodiment 2 Tube loss. It can be seen from the table that after the comprehensive optimization, the half-bridge submodule T 2 The total loss reduction of the pipe is 20.1%; the half-bridge submodule capacitor ripple voltage reduction is 27.77%. Proved by the method, the half-bridge submodule T can be reduced 2 Total tube loss and rejection of half-bridge submodule capacitive ripple voltage.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the invention in any way, and any person skilled in the art may make modifications or alterations to the disclosed technical content to the equivalent embodiments. However, any simple modification, equivalent variation and variation of the above embodiments according to the technical substance of the present invention still fall within the protection scope of the technical solution of the present invention.

Claims (5)

1. The comprehensive optimization method for the loss distribution and the capacitor ripple voltage of the hybrid MMC device is characterized by comprising the following steps of: the method comprises the following steps:
s1, injecting amplitude value (2+m-m) into bridge arm current through a double frequency circulation controller 2 )I dc /(3*m (1+m)) double frequency circulation with an initial phase of-pi/2; wherein m is the modulation ratio and the value is 2U m /U dc ，U m Is the amplitude of alternating-current side-phase voltage, U dc For the rated voltage of the direct current side, I dc Rated current at the direct current side;
s2, taking the minimum charge amount discharged by the half-bridge submodule in the bridge arm current as a negative interval under the steady state as constraint, traversing the combination of the output voltage command value of all full-bridge submodules and the output voltage command value of all half-bridge submodules which meet the stability of the capacitance voltage of the submodule, calculating the number of the maximum active bypass half-bridge submodule under each condition, selecting the maximum value, and recording the value as N sur_max ；
S3 is according to N in S2 sur_max The voltage output command values of all full-bridge sub-modules and all half-bridge sub-modules in the corresponding bridge arm, and the number of bypass half-bridge sub-modules is 0, N sur_max ]In the interval, respectively calculating the full-bridge submodule T 2 Total loss of pipe P T2F Half-bridge sub-module T 2 Total loss of pipe P T2H Full bridge submodule capacitor ripple voltage deltau CF And the capacitive ripple voltage deltau of the half-bridge sub-module CH ；
Wherein the full-bridge submodule comprises an Insulated Gate Bipolar Transistor (IGBT) T 1 -T 4 Diode D 1 -D 4 Capacitor C, insulated gate bipolar transistor T 1 、T 3 Collector and diode D of (c) 1 、D 3 Is commonly connected to the anode of the capacitor C; insulated gate bipolar transistor T 2 、T 4 Emitter and diode D of (c) 2 、D 4 Is commonly connected to the negative electrode of the capacitor C; insulated gate bipolar transistor T 1 Emitter, insulated gate bipolar transistor T of (2) 2 Collector, diode D of (c) 1 Anode of (D) and diode D 2 Is commonly connected to the upper input of the Quan Qiaozi module; t (T) 3 Emitter, T of (2) 4 Collector, diode D of (c) 3 Anode and diode D of (c) 4 Is commonly connected to the lower input of the Quan Qiaozi module;
the half-bridge submodule comprises two insulated gate bipolar transistors T 1 -T 2 Diode D 1 -D 2 Capacitor C and bidirectional thyristor SCR, insulated gate bipolar transistor T 1 Collector and diode D of (c) 1 Is commonly connected to the anode of the capacitor C; insulated gate bipolar transistor T 2 Emitter and diode D of (c) 2 Is commonly connected to the negative electrode of the capacitor C; insulated gate bipolar transistor T 1 Emitter, insulated gate bipolar transistor T of (2) 2 Collector, diode D of (c) 1 Anode of (D) and diode D 2 The cathodes of the half-bridge sub-modules are commonly connected to the upper input end of the half-bridge sub-modules; insulated gate bipolar transistor T 2 Emitter of (D) and diode D 2 The anodes of the two are commonly connected to the lower input end of the half-bridge sub-module; the bidirectional thyristor SCR is connected between the two input ends;
s4 to satisfy P at the same time T2H >P T2F And Deltau CH >Δu CF For constraint conditions, determining a comprehensive optimization interval of the number of the active bypass half-bridge submodules, and establishing a compromise for reducing the half-bridge submodules T in the interval 2 Comprehensive optimization objective function for total loss of tube and suppression of capacitor ripple voltage is obtained and simultaneously reduced half-bridge submodule T is satisfied 2 Number N of active bypass half-bridge submodules for total loss of tube and inhibiting capacitor ripple voltage sur Is the optimum value of (2);
establishing a half-bridge sub-module T 2 And (3) a comprehensive objective function of the total loss of the tube and the ripple voltage of the capacitor, wherein the comprehensive objective function is defined as follows:
M＝k·Δu CH，k +ΔP T2H，k ；
wherein: ΔP T2H,k Is a half-bridge sub-module T 2 Per unit value of total loss of pipe, its reference value is P T2F ，Δu CH,k Is the per unit value of the half-bridge submodule capacitor ripple voltage, and the reference value is deltau CF K is the sum of reducing the half-bridge submodule T 2 The weight coefficient of the total loss of the tube and the capacitor ripple voltage of the half-bridge submodule;
fixing k, calculating M minimum value, and corresponding N sur The method is the best;
the selection principle of k in the comprehensive objective function is as follows:
if half-bridge submodule T is desired 2 The total loss reduction effect of the tube is the same as the suppression effect of the capacitor ripple voltage of the half-bridge submodule, and the value of k is 1;
if the half-bridge submodule capacitor ripple voltage inhibition effect is expected to be superior to that of the half-bridge submodule T 2 The total loss of the tube is reduced, the value of k is larger than 1, and the larger the degree of k larger than 1 is, the better the suppression effect on the capacitor ripple voltage of the half-bridge submodule is;
if half-bridge submodule T is desired 2 The total loss reduction effect of the tube is better than the suppression effect of the capacitor ripple voltage of the half-bridge submodule, the k value is smaller than 1 and is more approaching to 0, and the half-bridge submodule T 2 The better the total loss reduction effect of the pipe;
s5, the stable operation of the mixed MMC is guaranteed through the power loop controller, the current loop controller and the double frequency circulation controller, the output angle of the phase-locked loop is combined, the bridge arm output voltage command value is distributed to the full-bridge submodule output voltage command value and the half-bridge submodule output voltage command value, and the comprehensive optimization target of the loss distribution and the capacitor ripple voltage of the mixed MMC device is achieved.
2. The method for comprehensively optimizing loss distribution and capacitor ripple voltage of a hybrid MMC device according to claim 1, characterized by: the output voltage command values of all the half-bridge sub-modules which meet the capacitance and voltage balance of the sub-modules meet the following conditions:
wherein: x is a, b, c phase in three phases, u pxref For the x-phase upper bridge arm to output voltage command value, u pxhref The output voltage command value of all the half-bridge submodules in the upper bridge arm of the x phase is F, the number of the full-bridge submodules in the bridge arm is U C For submodule capacitor voltage rating, i px Is the current of the upper bridge arm of the x phase, theta i1 、θ i2 Is the zero crossing point of bridge arm current;
output voltage command value u of all full-bridge submodules in x-phase upper bridge arm pxfref The method meets the following conditions:
u pxfref ＝u pxref -u pxhref 。
3. the method for comprehensively optimizing loss distribution and capacitor ripple voltage of a hybrid MMC device according to claim 2, characterized by: n in step S2 sur_max The calculation formula is as follows:
wherein: floor is a downward rounding function, U o_pos And the maximum bridge arm output voltage with the bridge arm current being positive.
4. The method for comprehensively optimizing loss distribution and capacitor ripple voltage of a hybrid MMC device according to claim 2, characterized by:
full bridge submodule T 2 Tube on-state loss P cond,T2F The calculation formula is as follows:
half-bridge sub-module T 2 Tube on-state loss P cond,T2H The calculation formula is as follows:
full bridge submodule capacitor ripple voltage deltau CF The calculation formula is as follows:
half-bridge submodule capacitor ripple voltage deltau CH The calculation formula is as follows:
wherein: c is capacitance value of submodule, H is number of half-bridge submodule in bridge arm, T is power frequency period, U CE Is IGBT threshold voltage, r CE Is IGBT on-state resistance, Q Filling material Charge of the half-bridge submodule in the positive range of bridge arm current, Q Put and put Is the discharge charge of the half-bridge submodule in the interval that the bridge arm current is negative, S pxh An average switch function of the half-bridge sub-module of the upper bridge arm of the x phase, and the value of the average switch function is u pxhref /(HU C )，S pxf An average switching function of the module Quan Qiaozi of the upper bridge arm of the x phase, and the value of the average switching function is u pxfref /(FU C )。
5. The method for comprehensively optimizing loss distribution and capacitor ripple voltage of a hybrid MMC device according to claim 1, characterized by: step S5 further comprises the steps of:
s5.1, obtaining a bridge arm output voltage instruction through a power loop controller, a current loop controller and a double frequency circulation controller;
s5.2, dividing a power frequency period into different sections, and distributing bridge arm output voltage command values in the different sections by combining an output angle theta of a phase-locked loop to obtain output voltage command values of all half-bridge submodules and output voltage command values of all full-bridge submodules in the bridge arm;
s5.3, according to the output voltage command values of all the full-bridge submodules and the output voltage commands of all the half-bridge submodules in the bridge armCalculating the number of full-bridge and half-bridge submodules required to be input and the number of half-bridge submodules required to be actively bypassed, judging the triggering time of the thyristor by the half-bridge submodules through the positive and negative of bridge arm current, and sending T to the half-bridge submodules which are already actively bypassed 2 A tube lock signal; full-bridge submodule T is reduced by means of alternate conduction of full-bridge submodule 2 On-state loss of the tube;
s5.4, sequencing all full-bridge submodules and all half-bridge submodules according to the sequence from high to low of the submodule capacitor voltage, and inputting the number of required submodules with the lowest capacitor voltage when the bridge arm current is positive; when the bridge arm current is negative, the number of the required submodules with the highest bypass capacitor voltage is increased, and the balance of capacitor voltage among different submodules is realized.
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