CN111049201B - Coordination control method for AC/DC power grid hybrid high-power interface converter - Google Patents

Coordination control method for AC/DC power grid hybrid high-power interface converter Download PDF

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CN111049201B
CN111049201B CN201911157212.XA CN201911157212A CN111049201B CN 111049201 B CN111049201 B CN 111049201B CN 201911157212 A CN201911157212 A CN 201911157212A CN 111049201 B CN111049201 B CN 111049201B
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voltage
power grid
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CN111049201A (en
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张国澎
陶海军
王静
李斌
荆鹏辉
陈迪蕾
胡治国
郑征
徐冬冬
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Henan University of Technology
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    • 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
    • H02J5/00—Circuit arrangements for transfer of electric power between ac networks and dc networks
    • 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
    • H02M7/66—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal
    • H02M7/68—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters
    • H02M7/72—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output with possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • 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
    • H02M1/0067—Converter structures employing plural converter units, other than for parallel operation of the units on a single load
    • H02M1/007—Plural converter units in cascade

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Abstract

The invention discloses a coordination control method of an AC/DC power grid hybrid high-power interface converter, which comprises a power transmission level control method and a power buffer level control method, wherein the power transmission level and the power buffer level in the AC/DC power grid hybrid high-power interface converter are subjected to coordination control by adopting voltage loop and current loop double closed-loop control; the invention has the advantages that in an alternating current-direct current hybrid power grid, the influence of ripples and flicker in a direct current power grid on the alternating current power grid can be reduced, the dynamic performance of the direct current side of the high-power interface converter can be greatly improved on the premise of less increase of the loss of the interface converter, and the grid-connected waveform quality of the alternating current side of the interface converter can be improved.

Description

Coordination control method for AC/DC power grid hybrid high-power interface converter
Technical Field
The invention belongs to the technical field of power electronic control, and particularly relates to a coordination control method for an alternating current-direct current power grid hybrid high-power interface converter.
Background
The high-power AC/DC interface converter is a key device for constructing an AC/DC hybrid distribution network. In order to guarantee the operation efficiency of the interface converter, the switching frequency of the converter is in inverse proportion to the rated power of the converter. With the increase of the rated power of the converter, the switching frequency of the traditional three-phase fully-controlled rectifier structure is reduced, so that the dynamic operation performance of the interface converter is deteriorated, the operation requirements of the AC/DC network interface converter cannot be better met, and when flicker or ripple occurs in the DC power grid, the traditional interface converter does not have the capability of buffering flicker and inhibiting ripple, and flicker and ripple can be transferred to the AC power grid.
The traditional AC/DC interface converter and the control method thereof can cause disturbance coupling of an AC power grid and a DC power grid, a certain amount of DC ripples can appear on the bus voltage of the DC power grid under the action of various loads, and the DC ripples increase along with the reduction of the capacitance of a bus capacitor, and higher harmonics can be injected into the AC power grid through the coupling of the interface converter, so that the electric energy quality of the AC power grid is influenced.
Unlike an AC/DC power grid interface converter, a conventional hybrid AC/DC energy storage converter does not need to consider the fast response capability to the DC side because the DC side is connected with a battery. Currently, two schemes are generally adopted to improve the dynamic performance of the traditional interface converter: one scheme is that the switching frequency of the converter is greatly improved, the interface converter can be designed into a current loop and a voltage loop with larger bandwidth due to high switching frequency, the larger bandwidth means better dynamic performance, but the AC/DC power grid interface converter is used as an interface for connecting two power grids, the transmitted power is very high, and the operation loss of the interface converter is inevitably increased due to the improvement of the switching frequency; the other scheme is that a direct current feedforward control method is adopted, direct current or direct current side power of an interface converter is fed forward to a current loop of the interface converter, so that the direct current side response speed of the interface converter is improved, the unfavorable coupling between an alternating current network and a direct current network is enhanced through feedforward control, and when continuous power disturbance exists in the direct current network, the disturbance quantity is fed forward to the current loop through the feedforward control, so that the grid-connected current quality of the alternating current network side of the interface converter is poorer than the control performance of the interface converter without feedforward.
The essence of the two traditional schemes is that the rapid change of the power of the direct current network is transferred to the alternating current network, which has a certain effect on improving the response speed of the direct current side of the converter, but the faster the response speed is, the greater the adverse effect on the power quality of the alternating current network is caused when the direct current network is disturbed and flickers.
Disclosure of Invention
Aiming at the defects, the traditional three-phase fully-controlled rectifier is used as a power transmission stage of the interface converter, and the direct current converter with the super capacitor is used as a power buffer stage and integrated together to form a hybrid high-power interface converter; aiming at the operation characteristics of the high-power interface converter, the method for coordinately controlling the AC/DC power grid hybrid high-power interface converter is provided, and by the method, the influence of ripples and flicker in a DC power grid on the AC power grid can be reduced in the AC/DC hybrid power grid; on the premise of less increase of the loss of the interface converter, the direct-current side dynamic performance of the high-power interface converter is greatly improved, and the grid-connected waveform quality of the alternating-current side of the interface converter is improved.
The purpose of the invention can be realized by the following technical scheme:
a coordination control method for an AC/DC power grid hybrid high-power interface converter comprises a power transmission level control method and a power buffer level control method, wherein a voltage loop and current loop double closed loop control is adopted to carry out coordination control on a power transmission level and a power buffer level in the AC/DC power grid hybrid high-power interface converter;
the voltage loop of the power transmission stage controls the voltage of a super capacitor SC in the power buffer stage, and the power transmission stage comprises a three-phase fully-controlled bridge and a filter inductor L1And a first control system; by controlling a power switch tube of a three-phase full-control bridge in the power transmission stage, a current loop of the power transmission stage tracks the change of steady-state power at the side of a direct-current power grid in an alternating-current and direct-current power grid, and the steady-state power exchange among the alternating-current power grid, the direct-current power grid and a super capacitor SC is controlled;
the voltage loop of the power buffer stage controls the bus voltage of a direct current power grid, and the power buffer stage comprises a bidirectional boost circuit, a super capacitor SC, a filter capacitor C and an inductor L2And a second control system; the alternating current is realized by controlling a power switch tube of a bidirectional boost circuit in the power buffer stageAnd the input power of the AC power network side of the DC power network hybrid high-power interface converter is differed from the output power of the DC power network side to obtain a transient power difference, and the transient power difference is converted into a current feedforward instruction to be sent to a current loop of a power buffer level for current loop feedforward control of the power buffer level.
Further, the three-phase fully-controlled bridge adopts a two-level three-phase fully-controlled bridge topological structure and comprises a first bridge arm (A phase), a second bridge arm (B phase) and a third bridge arm (C phase), wherein the first bridge arm comprises power switching tubes VT1 and VT4, the second bridge arm comprises power switching tubes VT3 and VT6, the third bridge arm comprises power switching tubes VT5 and VT2, and a power switching tube VT1 emitter and a VT4 collector are respectively connected with a filter inductor L1One end of the A phase is connected, and the emitter of the power switching tube VT3 and the collector of the power switching tube VT6 are respectively connected with the filter inductor L1One end of the B phase is connected, and the emitter of the power switching tube VT5 and the collector of the power switching tube VT2 are respectively connected with the filter inductor L1C phase is connected with the filter inductor L1The other end of the phase A, the other end of the phase B and the other end of the phase C are respectively connected to an alternating current power grid; the first control system comprises a first voltage loop controller Gv1Low pass filter GLFFirst current loop controller Gi11A second current loop controller Gi12And a first PWM generator GPWM-1(ii) a The bidirectional boost circuit comprises a fourth bridge arm, the fourth bridge arm comprises power switching tubes VT7 and VT8, and an emitter of the power switching tube VT7 and a collector of the power switching tube VT8 are respectively connected with an inductor L2One end is connected with the inductor L2The other end is connected with one end of a super capacitor SC, and the second control system comprises a second voltage loop controller Gv2A third current loop controller Gi2And a second PWM generator GPWM-2(ii) a The collector electrodes of the power switching tubes VT1, VT3, VT5 and VT7 are connected with one end of a filter capacitor C and then connected to a direct current power grid, and the emitter electrodes of the power switching tubes VT4, VT6, VT2 and VT8 are connected with the other end of the filter capacitor C and then connected to the direct current power grid.
Further, the power transmission stage control method specifically includes the steps of:
the method comprises the following steps: setting a super capacitor voltageIs given by the instruction value VSC,refAnd acquiring real-time current and voltage signals of the AC/DC power grid hybrid high-power interface converter, including a real-time sampling value u of the voltage of a bus of the DC power gridDCReal-time sampling value u of super capacitor voltage SCscThe real-time sampling value i of the current flowing to the DC power grid by the interface converterdcReal-time sampling value u of AC network voltagea、ub、ucAnd a real-time sampling value i of the current flowing into the AC/DC power grid hybrid high-power interface converter from the AC power grida、ib、ic；
Step two: calculating a power instruction P for maintaining the voltage stability of the super capacitor SCref-1Will VSC,refSquare of minus uSCAfter squaring, the voltage is fed to a first voltage loop controller Gv1To obtain Pref-1Said first voltage loop controller Gv1A standard PI controller is adopted, and the expression of a controller transfer function is shown as a formula (1);
Figure GDA0003099666820000041
in the formula (1), ksc,vp，ksc,viProportional coefficient and integral coefficient of the first voltage loop controller respectively;
step three: calculating steady-state power P to be transmitted to direct-current power grid by alternating-current power gridref-2Let u stand forDCAnd idcAfter multiplication, the signal is sent to a low-pass filter GLFTo obtain Pref-2The low-pass filter may be a first-order low-pass filter, and a transfer function expression of the first-order low-pass filter is shown in formula (2):
Figure GDA0003099666820000042
in the formula (2) < omega >1Controls the low-pass filter GLFFilter bandwidth of, set ω1≤31.4rad/s；
Step four: calculating the power transfer level requirement from an AC grid to a DC gridTotal power of transmission Pref-tThe calculation formula is shown in formula (3):
Pref-t＝Pref-1+Pref-2 (3)
step five: calculating an active component u of the alternating current network side voltage in a dq rotation coordinate systemdAnd a reactive component uqWill ua、ub、ucThrough a first transformation matrix Gabc-dq1The calculation formula is shown as formula (4):
Figure GDA0003099666820000051
in the formula, theta is a real-time angle of an A phase of the voltage of the alternating current network;
step six: calculating the transfer function G from the active power to the active current to be transferred by the power transfer stagef1U calculated in the step fivedInto equation (5):
Figure GDA0003099666820000052
step seven: calculating an active current instruction value i of a current loop of a power transmission stage under a dq rotation coordinate systemref-dAnd a reactive current command value iref-qP calculated in the fourth stepref-tMultiplying by G calculated in step sixf1To obtain iref-dLet iref-q＝0；
Step eight: calculating the active component i of the alternating current side current of the power transmission stage under the dq rotation coordinate systemdAnd a reactive component iqI is toa、ib、icThrough a second transformation matrix Gabc-dq2The calculation formula is shown as formula (6):
Figure GDA0003099666820000053
in the formula (6), theta is the real-time angle of the voltage phase A of the alternating current network;
step nine: filter inductance L on alternating current network side of calculation power transmission stage1Active component u of voltage under dq rotation coordinate systemL-dAnd a reactive component uL-qI obtained in the seventh stepref-dSubtracting i obtained in step eightdThe difference thus obtained is fed to a first current loop controller G of the power transfer stagei11To obtain uL-dI obtained in the seventh stepref-qSubtracting i obtained in step eightqThe difference thus obtained is fed to a second current loop controller G of the power transfer stagei12Then u can be obtainedL-qSaid first current loop controller Gi11And a second current loop controller Gi12All adopt standard PI controllers, the first current loop controller Gi11Transfer function and second current loop controller Gi12Is the same as shown in equation (7):
Figure GDA0003099666820000061
k in formula (7)cp，kciThe proportional coefficient and the integral coefficient of the first current loop controller and the second current loop controller of the power transmission stage respectively;
step ten: calculating active component u of power transmission level alternating current network side modulation wave in dq rotation coordinate systemc-dAnd a reactive component uc-qThe calculation formula is shown in formula (8):
Figure GDA0003099666820000062
step eleven: calculating three-phase modulation wave u of power transmission level alternating current power grid side under abc coordinate systemc-a、uc-b、uc-cU in step tenc-d、uc-qThrough a third transformation matrix Gdq-abcTo obtain uc-a、uc-b、uc-cThe calculation formula is shown in formula (9):
Figure GDA0003099666820000063
in the formula (9), theta is the real-time angle of the voltage phase A of the alternating current network;
step twelve: obtaining a power switch action instruction of a power transmission stage, and converting u into uc-a、uc-b、uc-cSent to a first PWM generator GPWM-1Modulating the modulated wave u by SPWMc-a、uc-b、uc-cThe three-phase fully-controlled bridge power switching tube is converted into action signals of power switching tubes VT1, VT2, VT3, VT4, VT5 and VT6, and controls actions of VT1, VT2, VT3, VT4, VT5 and VT6, so that the control of a power transmission stage is finished.
Further, the operation mode of the power transmission stage is as follows: in order to guarantee the operating efficiency of the interface converter, the power transmission stage works at a low switching frequency and serves as a main channel for energy exchange between an alternating current power grid and a direct current power grid, the power transmission stage tracks the change of active power of the direct current power grid, the steady-state requirement of the active power of the direct current power grid is met, and the operating efficiency of the interface converter is guaranteed. The voltage loop of the power transmission stage controls the voltage of the super capacitor in the power buffer stage, and the super capacitor is a large inertia link and can be regarded as a constant voltage source, so that the power transmission stage with low switching frequency can well realize the voltage control of the super capacitor. The power transmission stage does not control the bus voltage of the direct current network any more, and a current loop of the power transmission stage tracks the change of the steady-state power of the direct current network and controls the steady-state power exchange among the alternating current network, the direct current network and the super capacitor. In order to block the exchange of the transient power by the power transmission stage, the invention firstly carries out low-pass filtering on the collected power of the direct current network, then converts the power into a steady-state current instruction which is required to be provided by the direct current network, and finally sends the steady-state current instruction into a current loop of the power transmission stage to control the power transmission stage to track the steady-state power.
Further, the power buffer stage control method specifically includes the steps of:
the method comprises the following steps: setting a command value V for a DC network bus voltageDC,refAnd obtaining the AC/DC power grid hybrid type large power gridReal-time current and voltage signals of power interface converter, including real-time sampling value u of DC power grid bus voltageDCReal-time sampling value u of super capacitor voltage SCscReal-time sampling value i of output current of super capacitorscThe real-time sampling value i of the current flowing to the DC power grid by the interface converterdcReal-time sampling value u of AC network voltagea、ub、ucAnd a real-time sampling value i of the current flowing into the AC/DC power grid hybrid high-power interface converter from the AC power grida、ib、ic；
Step two: calculating a current instruction i for maintaining the voltage of a direct-current power grid bus in a steady stateref-1Will VDC,refSquare of minus uDCAfter squaring, enter a second voltage loop controller Gv2To obtain iref-1Said second voltage loop controller Gv2A standard PI controller is adopted, and the transfer function expression of the PI controller is shown as a formula (10):
Figure GDA0003099666820000081
in the formula kv,p，kv,iThe proportional coefficient and the integral coefficient of the second voltage loop voltage controller are respectively;
step three: calculating transient power difference P between AC power grid input power and DC power grid output power of AC/DC power grid hybrid high-power interface convertererroThe calculation method is shown in formula (11):
Perro＝UaIa+UbIb+UcIc-uDCidc (11)
in the formula of Ua、Ub、UcRespectively, effective values, I, of the three-phase voltage of the ac network A, B, Ca、Ib、IcThe effective values of three phases of current flowing into the AC/DC power grid hybrid high-power interface converter A, B, C from the AC power grid respectively;
step four: calculating input work of AC power networkTransient power difference P between rate and output power of direct current power griderroConversion function G to feed-forward current command of power buffer stagef2The expression is shown as formula (12):
Figure GDA0003099666820000082
step five: calculating a feed-forward current command i of a power buffer stageref-2P obtained in the third steperroG obtained by multiplying by step fourf2To obtain iref-2The calculation formula is shown as formula (13):
iref-2＝Perro·Gf2 (13)
step six: calculating a current loop instruction i of a power buffer stageref-scThe calculation method is shown as formula (14):
iref-sc＝iref-1-iref-2 (14)
step seven: obtaining a modulated wave signal u of a power buffer stageref-pbLet the current loop command i of the power buffer stageref-scSubtract iscInto a third current loop controller Gi2To obtain uref-pbSaid third current loop controller Gi2A standard PI controller is adopted, and the transfer function expression of the PI controller is shown as the formula (15):
Figure GDA0003099666820000091
in the formula ksc,cp，ksc,ciAre respectively a third current loop controller Gi2The proportionality coefficient and the integral coefficient of (a);
step eight: acquiring a power switch action instruction of a power buffer stage; u. ofref-pbSent to a second PWM generator GPWM-2Modulating the modulated wave u by SPWMref-pbThe signals are converted into action signals of power switching tubes VT7 and VT8 in the bidirectional boost circuit to control the actions of VT7 and VT8, and the control of the power buffer stage is finished.
Further, the operation mode of the power buffer stage is as follows: the power buffer stage operates at a high switching frequency, and exchanges energy with the power grid when a direct-current grid voltage ripple or flicker occurs, wherein the exchange energy is related to the power causing the direct-current grid ripple or flicker. The voltage loop of the power buffer stage controls the bus voltage of the direct current power grid, and the switching frequency of the power buffer stage is high, so that the control bandwidth of the bus voltage of the direct current power grid is obviously increased compared with that of a traditional method, and the dynamic performance of the interface converter for controlling the direct current power grid can be effectively improved. When transient power exchange occurs between the alternating current and direct current power networks through the interface converter, in order to reduce the transient coupling between the alternating current and direct current power networks and improve the response speed of the power buffer stage to transient energy, the invention differentiates the inflow power at the alternating current side of the interface converter and the output power at the direct current side to obtain a transient power difference, and converts the transient power difference into a current feedforward instruction to be sent to a current loop of the power buffer stage.
The invention has the following advantages:
the invention provides a coordination control method for an AC/DC power grid hybrid high-power interface converter, which can be realized by coordinating the two-stage control of the hybrid high-power interface converter:
(1) on the premise of less increase of the loss of the interface converter, the direct-current side dynamic performance of the high-power interface converter is greatly improved;
(2) the coupling influence of flicker and disturbance of the direct current network on the alternating current network is reduced, and simultaneously the grid-connected waveform quality of the alternating current side and the direct current side of the interface converter is improved.
Drawings
FIG. 1 is a topological structure diagram of a hybrid high-power interface converter;
FIG. 2 is a schematic diagram of the coordination control of the power transmission stage and the power buffer stage;
in fig. 1: 1: power transmission stage, 2: power buffer stage
In fig. 2:
3：VSC,refthe command value is the voltage of the super capacitor SC;
4：uscfor real-time sampling of supercapacitor voltageA value;
5：Gsqu1a first squarer for squaring the input signal;
6：Gsqu2a second squarer for squaring the input signal;
7：Gv1a first voltage loop controller;
8：uDCthe real-time sampling value of the bus voltage of the direct current network is obtained;
9：idcthe current real-time sampling value of the interface converter flowing to the direct current power grid is shown in the direction of figure 1;
10：GLFa low-pass filter:
11：Gf1a transfer function from active power to active current to be transferred for the power transfer stage 1;
12：ia、ib、icis a real-time sampling value of the current flowing into the interface converter of the alternating current network, the direction of which is shown in figure 1;
13：ua、ub、ucis a real-time sampling value of the AC grid voltage;
14：Gabc-dq1a first transformation matrix from a three-phase stationary coordinate system to a two-phase rotating coordinate system;
15：Gabc-dq2a second transformation matrix from the three-phase stationary coordinate system to the two-phase rotating coordinate system;
16：Gi11a first current loop controller being a power transfer stage;
17：Gi12a second current loop controller being a power transfer stage;
18：Gdq-abca third transformation matrix from the two-phase rotating coordinate system to the three-phase stationary coordinate system;
19：GPWM-1a first PWM generator that is a power transfer stage;
20：VDC,refthe command value is the bus voltage of the direct current network;
21：Perrothe transient state power difference between the input power of the AC power grid and the output power of the DC power grid of the interface converter is obtained;
22：Gf2the conversion function from the transient power difference between the input power of the alternating current power grid and the output power of the direct current power grid to a feed-forward current instruction of a power buffer level is obtained;
23：Gsqu3a third squarer for squaring the input signal;
24：Gsqu4a fourth squarer for squaring the input signal;
25：Gv2a second voltage loop controller;
26：iscoutputting a real-time sampling value of the current for the super capacitor SC, wherein the current direction is shown in figure 1;
27：Gi2a third current loop controller being a power buffer stage;
28：GPWM-2a second PWM generator that is a power buffer stage;
29：Pref-1the power instruction for maintaining the voltage stability of the super capacitor is a part of a power transmission stage current loop instruction signal;
30：Pref-tthe total power to be transmitted from the ac power supply system to the dc power supply system is required for the power transmission stage;
31：iref-dan active current instruction value of a current loop of the power transmission stage under a dq rotation coordinate system;
32：iref-qa reactive current instruction value of a current loop of the power transmission stage under a dq rotation coordinate system;
33：idthe active component of the alternating current side current of the power transmission stage under the dq rotation coordinate system is adopted;
34：iqthe reactive component of the alternating current side current of the power transmission stage under the dq rotation coordinate system is adopted;
35：uL-dthe active component of the alternating current side inductor voltage of the power transmission stage under a dq rotation coordinate system;
36：uL-qthe reactive component of the alternating current side inductance voltage of the power transmission stage under a dq rotation coordinate system;
37：udthe active component of the alternating current network voltage under the dq rotation coordinate system is shown;
38：uqthe reactive component of the voltage of the alternating current power grid under the dq rotation coordinate system is obtained;
39：uc-dactive components of the modulation waves on the alternating current side of the power transmission stage under a dq rotation coordinate system;
40：uc-qreactive components of the modulation waves on the alternating current side of the power transmission stage under a dq rotation coordinate system;
41：Pref-2the steady-state power which needs to be transmitted to the direct-current power grid for the alternating-current power grid is the other part of the power transmission level current loop instruction signal;
42：iref-1the current instruction for maintaining the voltage of the direct current network bus in a steady state is part of a power buffer level current loop instruction signal;
43：iref-2the feed-forward current command of the power buffer stage is another part of a current loop command signal of the power buffer stage;
44：uref-pba modulated wave that is a power buffer stage;
45：uc-a、uc-b、uc-cis a modulated wave of a power transfer stage.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived from the embodiments of the present invention by a person skilled in the art without any creative effort, should be included in the protection scope of the present invention.
The invention relates to a coordination control method of an AC/DC power grid hybrid high-power interface converter, which comprises a power transmission level control method and a power buffer level control method as shown in figure 1, wherein a voltage loop and current loop double closed loop control is adopted to coordinate and control a power transmission level 1 and a power buffer level 2 in the AC/DC power grid hybrid high-power interface converter;
the power isThe voltage loop of the transmission stage 1 controls the voltage of a super capacitor SC in the power buffer stage, and the power transmission stage 1 comprises a three-phase fully-controlled bridge and a filter inductor L1And a first control system; a current loop of the power transmission stage tracks the change of steady-state power at the side of a direct-current power grid in an alternating-current and direct-current power grid and controls the steady-state power exchange among the alternating-current power grid, the direct-current power grid and a super capacitor SC;
the voltage loop of the power buffer stage 2 controls the bus voltage of a direct current power grid, and the power buffer stage 2 comprises a bidirectional boost circuit, a super capacitor SC, a filter capacitor C and an inductor L2And a second control system; and the input power of the AC power grid side of the AC/DC power grid hybrid high-power interface converter is differenced with the output power of the DC power grid side to obtain a transient power difference, and the transient power difference is converted into a current feedforward instruction and is sent to a current loop of a power buffer stage to carry out current loop feedforward control of the power buffer stage.
The three-phase fully-controlled bridge adopts a two-level three-phase fully-controlled bridge topological structure and comprises a first bridge arm (A phase), a second bridge arm (B phase) and a third bridge arm (C phase), wherein the first bridge arm comprises power switching tubes VT1 and VT4, the second bridge arm comprises power switching tubes VT3 and VT6, the third bridge arm comprises power switching tubes VT5 and VT2, and a power switching tube VT1 emitter and a VT4 collector are respectively connected with a filter inductor L1One end of the A phase is connected, and the emitter of the power switching tube VT3 and the collector of the power switching tube VT6 are respectively connected with the filter inductor L1One end of the B phase is connected, and the emitter of the power switching tube VT5 and the collector of the power switching tube VT2 are respectively connected with the filter inductor L1C phase is connected with the filter inductor L1The other end of the phase A, the other end of the phase B and the other end of the phase C are respectively connected to an alternating current power grid; the first control system comprises a first voltage loop controller Gv17. Low pass filter G LF10. First current loop controller G i1116. Second current loop controller G i1217 and a first PWM generator G PWM-119; the bidirectional boost circuit comprises a fourth bridge arm, the fourth bridge arm comprises power switching tubes VT7 and VT8, and an emitter of the power switching tube VT7 and a collector of the power switching tube VT8 are respectively connected with an inductor L2One end is connected with the inductor L2The other end is connected with a super powerOne end of the capacitor SC is connected, and the second control system comprises a second voltage loop controller G v225. Third current loop controller Gi227 and a second PWM generator G PWM-228; the collector electrodes of the power switching tubes VT1, VT3, VT5 and VT7 are connected with one end of a filter capacitor C and then connected to a direct current power grid, and the emitter electrodes of the power switching tubes VT4, VT6, VT2 and VT8 are connected with the other end of the filter capacitor C and then connected to the direct current power grid.
As shown in fig. 2, the method for controlling the power transmission stage 1 specifically includes the following steps:
the method comprises the following steps: setting a command value V of a supercapacitor voltageSC,refAnd acquiring real-time current and voltage signals of the AC/DC power grid hybrid high-power interface converter, including a real-time sampling value u of the voltage of a bus of the DC power gridDCReal-time sampling value u of super capacitor voltage SCscThe real-time sampling value i of the current flowing to the DC power grid by the interface converterdcReal-time sampling value u of AC network voltagea、ub、ucAnd a real-time sampling value i of the current flowing into the AC/DC power grid hybrid high-power interface converter from the AC power grida、ib、ic；
Step two: calculating a power instruction P for maintaining the voltage stability of the super capacitor SCref-1Will VSC,refSquare of minus uSCAfter squaring, the voltage is fed to a first voltage loop controller Gv1To obtain Pref-1Said first voltage loop controller Gv1A standard PI controller is adopted, and the expression of a controller transfer function is shown as a formula (1);
Figure GDA0003099666820000141
in the formula (1), ksc,vp，ksc,viProportional coefficient and integral coefficient of the first voltage loop controller respectively;
step three: calculating steady-state power P to be transmitted to direct-current power grid by alternating-current power gridref-2Let u stand forDCAnd idcAfter multiplication, the product is sent to low-pass filterWave filter GLFTo obtain Pref-2The low-pass filter may be a first-order low-pass filter, and a transfer function expression of the first-order low-pass filter is shown in formula (2):
Figure GDA0003099666820000142
in the formula (2) < omega >1Controls the low-pass filter GLFFilter bandwidth of, set ω1≤31.4rad/s；
Step four: calculating the total power P to be transmitted from the AC power network to the DC power network by the power transmission stageref-tThe calculation formula is shown in formula (3):
Pref-t＝Pref-1+Pref-2 (3)
step five: calculating an active component u of the alternating current network side voltage in a dq rotation coordinate systemdAnd a reactive component uqWill ua、ub、ucThrough a first transformation matrix Gabc-dq1The calculation formula is shown as formula (4):
Figure GDA0003099666820000151
in the formula, theta is a real-time angle of an A phase of the voltage of the alternating current network;
step six: calculating the transfer function G from the active power to the active current to be transferred by the power transfer stagef1U calculated in the step fivedInto equation (5):
Figure GDA0003099666820000152
step seven: calculating an active current instruction value i of a current loop of a power transmission stage under a dq rotation coordinate systemref-dAnd a reactive current command value iref-qP calculated in the fourth stepref-tMultiplying by G calculated in step sixf1To obtain iref-dLet iref-q＝0；
Step eight: calculating the active component i of the alternating current side current of the power transmission stage under the dq rotation coordinate systemdAnd a reactive component iqI is toa、ib、icThrough a second transformation matrix Gabc-dq2The calculation formula is shown as formula (6):
Figure GDA0003099666820000153
in the formula (6), theta is the real-time angle of the voltage phase A of the alternating current network;
step nine: filter inductance L on alternating current network side of calculation power transmission stage1Active component u of voltage under dq rotation coordinate systemL-dAnd a reactive component uL-qI obtained in the seventh stepref-dSubtracting i obtained in step eightdThe difference thus obtained is fed to a first current loop controller G of the power transfer stagei11To obtain uL-dI obtained in the seventh stepref-qSubtracting i obtained in step eightqThe difference thus obtained is fed to a second current loop controller G of the power transfer stagei12Then u can be obtainedL-qSaid first current loop controller Gi11And a second current loop controller Gi12All adopt standard PI controllers, the first current loop controller Gi11Transfer function and second current loop controller Gi12Is the same as shown in equation (7):
Figure GDA0003099666820000161
k in formula (7)cp，kciThe proportional coefficient and the integral coefficient of the first current loop controller and the second current loop controller of the power transmission stage respectively;
step ten: calculating active component u of power transmission level alternating current network side modulation wave in dq rotation coordinate systemc-dAnd a reactive component uc-qThe calculation formula is shown in formula (8):
Figure GDA0003099666820000162
step eleven: calculating three-phase modulation wave u of power transmission level alternating current power grid side under abc coordinate systemc-a、uc-b、uc-cU in step tenc-d、uc-qThrough a third transformation matrix Gdq-abcTo obtain uc-a、uc-b、uc-cThe calculation formula is shown in formula (9):
Figure GDA0003099666820000163
in the formula (9), theta is the real-time angle of the voltage phase A of the alternating current network;
step twelve: obtaining a power switch action instruction of a power transmission stage, and converting u into uc-a、uc-b、uc-cSent to a first PWM generator GPWM-1Modulating the modulated wave u by SPWMc-a、uc-b、uc-cThe three-phase fully-controlled bridge power switching tube is converted into action signals of power switching tubes VT1, VT2, VT3, VT4, VT5 and VT6, and controls actions of VT1, VT2, VT3, VT4, VT5 and VT6, so that the control of a power transmission stage is finished.
The operating modes of the power transfer stage are: in order to guarantee the operating efficiency of the interface converter, the power transmission stage works at a low switching frequency and serves as a main channel for energy exchange between an alternating current power grid and a direct current power grid, the power transmission stage tracks the change of active power of the direct current power grid, the steady-state requirement of the active power of the direct current power grid is met, and the operating efficiency of the interface converter is guaranteed. The voltage loop of the power transmission stage controls the voltage of the super capacitor in the power buffer stage, and the super capacitor is a large inertia link and can be regarded as a constant voltage source, so that the power transmission stage with low switching frequency can well realize the voltage control of the super capacitor. The power transmission stage does not control the bus voltage of the direct current network any more, and a current loop of the power transmission stage tracks the change of the steady-state power of the direct current network and controls the steady-state power exchange among the alternating current network, the direct current network and the super capacitor. In order to block the exchange of the transient power by the power transmission stage, the invention firstly carries out low-pass filtering on the collected power of the direct current network, then converts the power into a steady-state current instruction which is required to be provided by the direct current network, and finally sends the steady-state current instruction into a current loop of the power transmission stage to control the power transmission stage to track the steady-state power.
As shown in fig. 2, the power buffer stage control method specifically includes the following steps:
the method comprises the following steps: setting a command value V for a DC network bus voltageDC,refAnd acquiring real-time current and voltage signals of the AC/DC power grid hybrid high-power interface converter, including a real-time sampling value u of the voltage of a bus of the DC power gridDCReal-time sampling value u of super capacitor voltage SCscReal-time sampling value i of output current of super capacitorscThe real-time sampling value i of the current flowing to the DC power grid by the interface converterdcReal-time sampling value u of AC network voltagea、ub、ucAnd a real-time sampling value i of the current flowing into the AC/DC power grid hybrid high-power interface converter from the AC power grida、ib、ic；
Step two: calculating a current instruction i for maintaining the voltage of a direct-current power grid bus in a steady stateref-1Will VDC,refSquare of minus uDCAfter squaring, enter a second voltage loop controller Gv2To obtain iref-1Said second voltage loop controller Gv2A standard PI controller is adopted, and the transfer function expression of the PI controller is shown as a formula (10):
Figure GDA0003099666820000181
in the formula kv,p，kv,iThe proportional coefficient and the integral coefficient of the second voltage loop voltage controller are respectively;
step three: calculating transient power difference P between AC power grid input power and DC power grid output power of AC/DC power grid hybrid high-power interface convertererroThe calculation method is as followsFormula (11):
Perro＝UaIa+UbIb+UcIc-uDCidc (11)
in the formula of Ua、Ub、UcRespectively, effective values, I, of the three-phase voltage of the ac network A, B, Ca、Ib、IcThe effective values of three phases of current flowing into the AC/DC power grid hybrid high-power interface converter A, B, C from the AC power grid respectively;
step four: calculating transient power difference P between input power of alternating current power grid and output power of direct current power griderroConversion function G to feed-forward current command of power buffer stagef2The expression is shown as formula (12):
Figure GDA0003099666820000182
step five: calculating a feed-forward current command i of a power buffer stageref-2P obtained in the third steperroG obtained by multiplying by step fourf2To obtain iref-2The calculation formula is shown as formula (13):
iref-2＝Perro·Gf2 (13)
step six: calculating a current loop instruction i of a power buffer stageref-scThe calculation method is shown as formula (14):
iref-sc＝iref-1-iref-2 (14)
step seven: obtaining a modulated wave signal u of a power buffer stageref-pbLet the current loop command i of the power buffer stageref-scSubtract iscInto a third current loop controller Gi2To obtain uref-pbSaid third current loop controller Gi2A standard PI controller is adopted, and the transfer function expression of the PI controller is shown as the formula (15):
Figure GDA0003099666820000191
in the formula ksc,cp，ksc,ciAre respectively a third current loop controller Gi2The proportionality coefficient and the integral coefficient of (a);
step eight: acquiring a power switch action instruction of a power buffer stage; u. ofref-pbSent to a second PWM generator GPWM-2Modulating the modulated wave u by SPWMref-pbThe signals are converted into action signals of power switching tubes VT7 and VT8 in the bidirectional boost circuit to control the actions of VT7 and VT8, and the control of the power buffer stage is finished.
The operation mode of the power buffer stage is as follows: the power buffer stage operates at a high switching frequency, and exchanges energy with the power grid when a direct-current grid voltage ripple or flicker occurs, wherein the exchange energy is related to the power causing the direct-current grid ripple or flicker. The voltage loop of the power buffer stage controls the bus voltage of the direct current power grid, and the switching frequency of the power buffer stage is high, so that the control bandwidth of the bus voltage of the direct current power grid is obviously increased compared with that of a traditional method, and the dynamic performance of the interface converter for controlling the direct current power grid can be effectively improved. When transient power exchange occurs between the alternating current and direct current power networks through the interface converter, in order to reduce the transient coupling between the alternating current and direct current power networks and improve the response speed of the power buffer stage to transient energy, the invention differentiates the inflow power at the alternating current side of the interface converter and the output power at the direct current side to obtain a transient power difference, and converts the transient power difference into a current feedforward instruction to be sent to a current loop of the power buffer stage.
Through the above coordination control:
and in a steady state, the bus voltage of the direct current network is stable. Because the main energy exchange between the AC and DC networks is completed by the power transmission stage, the power input by the AC network of the interface converter is equal to the power output by the DC network, and the transient power difference is zero, the current loop instruction current of the power buffer stage is small, although the frequency of the power buffer stage is high and has certain system loss, the energy exchange between the power buffer stage and the power network is small; when ripple occurs to the bus voltage of the direct current network, the power buffer stage controls the bus voltage of the direct current network, and compared with the power transmission stage with low switching frequency for controlling the bus voltage of the direct current network, the high bandwidth of the voltage loop of the power buffer stage has a better effect of suppressing the ripple of the bus voltage of the direct current network. In this case, power exchange takes place between the power buffer stage and the dc power grid, the magnitude of which is related to the dc ripple power causing the dc power grid bus voltage ripple, but generally the power causing the dc power grid voltage ripple is not too large.
Therefore, in a steady state, the coordinated control method provided by the invention can ensure the steady-state performance of the interface converter, and meanwhile, compared with the traditional high-power rectifier with low switching frequency, the loss of the coordinated control method provided by the invention is not greatly increased, and compared with the traditional high-power rectifier with high switching frequency, the loss of the coordinated control method provided by the invention is smaller.
In a transient state, the direct current load jumps, and the power transmission stage only controls the transmission of steady-state power, so that the power change caused by the load jump cannot be responded immediately, the energy transfer between the alternating current power grid and the direct current power grid cannot jump, and the coupling influence of the flickering of the direct current power grid on the alternating current power grid is reduced. At the moment, the transient power difference between the input power of the interface converter alternating current power grid and the output power of the direct current power grid is not zero, and the transient power difference controls the feed-forward of a current loop of the power buffer stage, so that the jump power of the direct current power grid is mostly provided by the power buffer stage. Due to the high switching frequency of the power buffer stage, the response speed to transient power is faster. At this time, power exchange occurs between the power buffer stage and the direct current power grid, and the size of the power exchange is related to the transient power difference. Due to the fact that the duration time of the transient power difference is short, the control of the power buffer level still cannot lead to the great increase of the loss of the interface converter.
Therefore, compared with the traditional high-power rectifier control, the coordination control method provided by the invention reduces the coupling influence of the flicker of the direct-current power grid on the alternating-current power grid in a transient state, and meanwhile, the system loss of the interface converter cannot be greatly improved.

Claims (6)

1. A coordination control method for an AC/DC power grid hybrid high-power interface converter is characterized by comprising a power transmission level control method and a power buffer level control method, wherein the power transmission level and the power buffer level in the AC/DC power grid hybrid high-power interface converter are subjected to coordination control by adopting voltage loop and current loop double closed-loop control;
the power transmission stage comprises a three-phase full-control bridge, a filter inductor L1 and a first control system, a power transmission stage voltage loop generates a power switch tube control signal of the three-phase full-control bridge in the power transmission stage by acquiring voltages at two ends of a super capacitor SC in the power buffer stage, controls the voltage of the super capacitor SC in the power buffer stage, realizes that a current loop of the power transmission stage tracks the change of steady-state power at the side of a direct-current power grid in an alternating-current and direct-current power grid, and controls the steady-state power exchange among the alternating-current power grid, the direct-current power grid and the super capacitor SC;
the power buffer stage comprises a bidirectional boost circuit, a super capacitor SC, a filter capacitor C, an inductor L2 and a second control system, a power buffer stage voltage loop generates a power switch tube control signal of the bidirectional boost circuit in the power buffer stage by collecting bus voltage of a direct current power grid in the power transmission stage, the bus voltage of the direct current power grid in the power transmission stage is controlled, the input power of an alternating current power grid side and the output power of the direct current power grid side of the alternating current and direct current power grid hybrid high-power interface converter are differentiated to obtain a transient power difference, and the transient power difference is converted into a current feedforward instruction to be sent to a current loop of the power buffer stage for current loop feedforward control of the power buffer stage.
2. The AC-DC grid hybrid high-power interface converter coordination control method as claimed in claim 1, wherein the three-phase fully-controlled bridge adopts a two-level three-phase fully-controlled bridge topology structure and comprises a first bridge arm A phase, a second bridge arm B phase and a third bridge arm C phase, the first bridge arm comprises power switching tubes VT1 and VT4, the second bridge arm comprises power switching tubes VT3 and VT6, the third bridge arm comprises power switching tubes VT5 and VT2, and VT1 emitter electrodes and VT4 collector electrodes of the power switching tubes are respectively connected with a filter inductor L41One end of A phase is connected with the power switch tubeVT3 emitter and VT6 collector are respectively connected with filter inductor L1One end of the B phase is connected, and the emitter of the power switching tube VT5 and the collector of the power switching tube VT2 are respectively connected with the filter inductor L1C phase is connected with the filter inductor L1The other end of the phase A, the other end of the phase B and the other end of the phase C are respectively connected to an alternating current power grid; the first control system comprises a first voltage loop controller Gv1Low pass filter GLFFirst current loop controller Gi11A second current loop controller Gi12And a first PWM generator GPWM-1(ii) a The bidirectional boost circuit comprises a fourth bridge arm, the fourth bridge arm comprises power switching tubes VT7 and VT8, and an emitter of the power switching tube VT7 and a collector of the power switching tube VT8 are respectively connected with an inductor L2One end is connected with the inductor L2The other end is connected with one end of a super capacitor SC, and the second control system comprises a second voltage loop controller Gv2A third current loop controller Gi2And a second PWM generator GPWM-2(ii) a The collector electrodes of the power switching tubes VT1, VT3, VT5 and VT7 are connected with one end of a filter capacitor C and then connected to a direct current power grid, and the emitter electrodes of the power switching tubes VT4, VT6, VT2 and VT8 are connected with the other end of the filter capacitor C and then connected to the direct current power grid.
3. The AC/DC/power grid hybrid high-power interface converter coordination control method according to claim 2, wherein the power transmission stage control method specifically comprises the following steps:
the method comprises the following steps: setting a command value V of a supercapacitor voltageSC,refAnd acquiring real-time current and voltage signals of the AC/DC power grid hybrid high-power interface converter, including a real-time sampling value u of the voltage of a bus of the DC power gridDCReal-time sampling value u of super capacitor voltage SCscThe real-time sampling value i of the current flowing to the DC power grid by the interface converterdcReal-time sampling value u of AC network voltagea、ub、ucAnd a real-time sampling value i of the current flowing into the AC/DC power grid hybrid high-power interface converter from the AC power grida、ib、ic；
Step two: calculating a power instruction P for maintaining the voltage stability of the super capacitor SCref-1Will VSC,refSquare of minus uSCAfter squaring, the voltage is fed to a first voltage loop controller Gv1To obtain Pref-1Said first voltage loop controller Gv1A standard PI controller is adopted, and the expression of a controller transfer function is shown as a formula (1);
Figure FDA0003101185250000031
in the formula (1), ksc,vp，ksc,viProportional coefficient and integral coefficient of the first voltage loop controller respectively;
step three: calculating steady-state power P to be transmitted to direct-current power grid by alternating-current power gridref-2Let u stand forDCAnd idcAfter multiplication, the signal is sent to a low-pass filter GLFTo obtain Pref-2The low-pass filter may be a first-order low-pass filter, and a transfer function expression of the first-order low-pass filter is shown in formula (2):
Figure FDA0003101185250000032
in the formula (2) < omega >1Controls the low-pass filter GLFFilter bandwidth of, set ω1≤31.4rad/s；
Step four: calculating the total power P to be transmitted from the AC power network to the DC power network by the power transmission stageref-tThe calculation formula is shown in formula (3):
Pref-t＝Pref-1+Pref-2 (3)
step five: calculating an active component u of the alternating current network side voltage in a dq rotation coordinate systemdAnd a reactive component uqWill ua、ub、ucThrough a first transformation matrix Gabc-dq1The calculation formula is shown as formula (4):
Figure FDA0003101185250000033
in the formula, theta is a real-time angle of an A phase of the voltage of the alternating current network;
step six: calculating the transfer function G from the active power to the active current to be transferred by the power transfer stagef1U calculated in the step fivedInto equation (5):
Figure FDA0003101185250000041
step seven: calculating an active current instruction value i of a current loop of a power transmission stage under a dq rotation coordinate systemref-dAnd a reactive current command value iref-qP calculated in the fourth stepref-tMultiplying by G calculated in step sixf1To obtain iref-dLet iref-q＝0；
Step eight: calculating the active component i of the alternating current side current of the power transmission stage under the dq rotation coordinate systemdAnd a reactive component iqI is toa、ib、icThrough a second transformation matrix Gabc-dq2The calculation formula is shown as formula (6):
Figure FDA0003101185250000042
in the formula (6), theta is the real-time angle of the voltage phase A of the alternating current network;
step nine: filter inductance L on alternating current network side of calculation power transmission stage1Active component u of voltage under dq rotation coordinate systemL-dAnd a reactive component uL-qI obtained in the seventh stepref-dSubtracting i obtained in step eightdThe difference thus obtained is fed to a first current loop controller G of the power transfer stagei11To obtain uL-dI obtained in the seventh stepref-qSubtracting i obtained in step eightqThe obtained difference is sent to a second current of the power transmission stageRing controller Gi12Then u can be obtainedL-qSaid first current loop controller Gi11And a second current loop controller Gi12All adopt standard PI controllers, the first current loop controller Gi11Transfer function and second current loop controller Gi12Is the same as shown in equation (7):
Figure FDA0003101185250000043
k in formula (7)cp，kciThe proportional coefficient and the integral coefficient of the first current loop controller and the second current loop controller of the power transmission stage respectively;
step ten: calculating active component u of power transmission level alternating current network side modulation wave in dq rotation coordinate systemc-dAnd a reactive component uc-qThe calculation formula is shown in formula (8):
Figure FDA0003101185250000051
step eleven: calculating three-phase modulation wave u of power transmission level alternating current power grid side under abc coordinate systemc-a、uc-b、uc-cU in step tenc-d、uc-qThrough a third transformation matrix Gdq-abcTo obtain uc-a、uc-b、uc-cThe calculation formula is shown in formula (9):
Figure FDA0003101185250000052
in the formula (9), theta is the real-time angle of the voltage phase A of the alternating current network;
step twelve: obtaining a power switch action instruction of a power transmission stage, and converting u into uc-a、uc-b、uc-cSent to a first PWM generator GPWM-1Modulating the modulated wave u by SPWMc-a、uc-b、uc-cThe three-phase fully-controlled bridge power switching tube is converted into action signals of power switching tubes VT1, VT2, VT3, VT4, VT5 and VT6, and controls actions of VT1, VT2, VT3, VT4, VT5 and VT6, so that the control of a power transmission stage is finished.
4. The AC/DC/power grid hybrid high-power interface converter coordination control method according to claim 3, wherein the operation modes of the power transmission stage are as follows: in order to guarantee the operating efficiency of the interface converter, the power transmission stage works at a low switching frequency and is used as a main channel for energy exchange of an alternating current power grid and a direct current power grid; the power transmission stage tracks the change of the active power of the direct-current power grid and meets the steady-state requirement of the active energy of the direct-current power grid.
5. The AC/DC/power grid hybrid high-power interface converter coordination control method according to claim 2, wherein the power buffer stage control method specifically comprises the following steps:
the method comprises the following steps: setting a command value V for a DC network bus voltageDC,refAnd acquiring real-time current and voltage signals of the AC/DC power grid hybrid high-power interface converter, including a real-time sampling value u of the voltage of a bus of the DC power gridDCReal-time sampling value u of super capacitor voltage SCscReal-time sampling value i of output current of super capacitorscThe real-time sampling value i of the current flowing to the DC power grid by the interface converterdcReal-time sampling value u of AC network voltagea、ub、ucAnd a real-time sampling value i of the current flowing into the AC/DC power grid hybrid high-power interface converter from the AC power grida、ib、ic；
Step two: calculating a current instruction i for maintaining the voltage of a direct-current power grid bus in a steady stateref-1Will VDC,refSquare of minus uDCAfter squaring, enter a second voltage loop controller Gv2To obtain iref-1Said second voltage loop controller Gv2A standard PI controller is adopted, and the transfer function expression of the PI controller is shown as a formula (10):
Figure FDA0003101185250000061
in the formula kv,p，kv,iThe proportional coefficient and the integral coefficient of the second voltage loop voltage controller are respectively;
step three: calculating transient power difference P between AC power grid input power and DC power grid output power of AC/DC power grid hybrid high-power interface convertererroThe calculation method is shown in formula (11):
Perro＝UaIa+UbIb+UcIc-uDCidc (11)
in the formula of Ua、Ub、UcRespectively, effective values, I, of the three-phase voltage of the ac network A, B, Ca、Ib、IcThe effective values of three phases of current flowing into the AC/DC power grid hybrid high-power interface converter A, B, C from the AC power grid respectively;
step four: calculating transient power difference P between input power of alternating current power grid and output power of direct current power griderroConversion function G to feed-forward current command of power buffer stagef2The expression is shown as formula (12):
Figure FDA0003101185250000071
step five: calculating a feed-forward current command i of a power buffer stageref-2P obtained in the third steperroG obtained by multiplying by step fourf2To obtain iref-2The calculation formula is shown as formula (13):
iref-2＝Perro·Gf2 (13)
step six: calculating a current loop instruction i of a power buffer stageref-scThe calculation method is shown as formula (14):
iref-sc＝iref-1-iref-2 (14)
step seven: obtaining a modulated wave signal u of a power buffer stageref-pbLet the current loop command i of the power buffer stageref-scSubtract iscInto a third current loop controller Gi2To obtain uref-pbSaid third current loop controller Gi2A standard PI controller is adopted, and the transfer function expression of the PI controller is shown as the formula (15):
Figure FDA0003101185250000072
in the formula ksc,cp，ksc,ciAre respectively a third current loop controller Gi2The proportionality coefficient and the integral coefficient of (a);
step eight: acquiring a power switch action instruction of a power buffer stage; u. ofref-pbSent to a second PWM generator GPWM-2Modulating the modulated wave u by SPWMref-pbThe signals are converted into action signals of power switching tubes VT7 and VT8 in the bidirectional boost circuit to control the actions of VT7 and VT8, and the control of the power buffer stage is finished.
6. The AC/DC/power grid hybrid high-power interface converter coordination control method according to claim 5, wherein the operation mode of the power buffer stage is as follows: the power buffer stage operates at a high switching frequency, and exchanges energy with the power grid when a direct-current grid voltage ripple or flicker occurs, wherein the exchange energy is related to the power causing the direct-current grid ripple or flicker.
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