CN112003319B - Double-current feedback control method applied to bidirectional grid-connected converter - Google Patents

Double-current feedback control method applied to bidirectional grid-connected converter Download PDF

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CN112003319B
CN112003319B CN202010656695.4A CN202010656695A CN112003319B CN 112003319 B CN112003319 B CN 112003319B CN 202010656695 A CN202010656695 A CN 202010656695A CN 112003319 B CN112003319 B CN 112003319B
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converter
phase
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grid
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CN112003319A (en
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支娜
赵佳宝
明旭
李宁
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Xian 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
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
    • H02J3/381—Dispersed generators
    • 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
    • H02J1/00—Circuit arrangements for dc mains or dc distribution networks
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J3/00—Circuit arrangements for ac mains or ac distribution networks
    • H02J3/01—Arrangements for reducing harmonics or ripples
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • 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
    • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
    • H02J2203/00—Indexing scheme relating to details of circuit arrangements for AC mains or AC distribution networks
    • H02J2203/20—Simulating, e g planning, reliability check, modelling or computer assisted design [CAD]
    • 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
    • H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
    • H02J2300/20—The dispersed energy generation being of renewable origin
    • H02J2300/22—The renewable source being solar energy
    • H02J2300/24—The renewable source being solar energy of photovoltaic origin
    • H02J2300/26—The renewable source being solar energy of photovoltaic origin involving maximum power point tracking control for photovoltaic sources
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E10/00—Energy generation through renewable energy sources
    • Y02E10/50—Photovoltaic [PV] energy
    • Y02E10/56—Power conversion systems, e.g. maximum power point trackers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/40—Arrangements for reducing harmonics

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Abstract

The invention discloses a double-current feedback control method applied to a bidirectional grid-connected converter, which specifically comprises the following steps: firstly, according to the principle that the power on the two sides of the alternating current and the direct current of the three-phase AC/DC converter is equal, the direct current bus voltage U is establisheddcWith the AC side current i of the three-phase AC/DC converterLSubstituting the mathematical relation into a droop control equation to obtain the current i at the alternating current side of the three-phase AC/DC converterLCalculating an equation; and then, an active damping feedback loop is added in the control of the bidirectional grid-connected three-phase AC/DC converter, so that the resonance influence generated by the LCL filter is eliminated. The method provided by the invention optimizes the voltage control effect of the direct current bus by improving the traditional droop control. And the resonance is suppressed by adopting a grid-connected current feedback active damping method, so that the grid-connected current harmonic wave is reduced and the system robustness is improved. The droop control and the active damping feedback control are improved to be combined to form bidirectional control over the alternating current side and the direct current side of the grid-connected converter.

Description

Double-current feedback control method applied to bidirectional grid-connected converter
Technical Field
The invention belongs to the technical field of grid-connected current control, and particularly relates to a double-current feedback control method applied to a bidirectional grid-connected converter.
Background
With the exploitation and use of a large amount of primary energy, not only the earth environment is seriously polluted, but also conventional energy sources such as coal, petroleum, natural gas and the like are increasingly exhausted, so that various renewable clean energy sources such as solar energy, wind energy and the like as substitutes thereof are widely concerned. Based on the rapid development of the distributed power generation technology, important electric energy support is provided for a large power grid. However, distributed power sources present certain challenges in direct grid-tie processes due to the intermittent and fluctuating nature of renewable energy sources. The micro-grid is a small-sized power generation, distribution and utilization system which is formed by collecting a distributed power supply, an energy storage system, an energy conversion device, a monitoring and protecting device, a load and the like, can be connected with a large power grid to run in a grid-connected mode, can also run in an isolated mode, is favorable for improving the receptivity of the power distribution system to the distributed power supply, and improves the utilization rate of renewable energy. Compared with an alternating-current micro-grid, the direct-current micro-grid can more efficiently and reliably receive distributed renewable energy power generation systems such as wind and light, energy storage units, electric vehicles and other direct-current power loads, and is simple to control and stable to operate. According to the connection mode of the direct-current micro-grid and the alternating-current large grid, the working modes can be divided into a grid-connected mode and an island mode.
The direct-current bus voltage is an important index for reflecting the stable operation of the direct-current micro-grid, and is also a basic variable for maintaining the energy balance of the power supply end and the load end. The control mode of the dc bus voltage can be roughly divided into two types, i.e., master-slave control and peer-to-peer control. The master control unit in the microgrid only maintains the stability of the voltage of the direct-current bus, other units need to realize rapid communication with the master control unit, the control mode is simple and easy to realize, but the master control unit and interconnection communication are excessively depended on, and the system operation reliability is low; the peer-to-peer control realizes that each unit controls the direct current bus voltage at the same time, does not need communication, has the advantage of 'plug and play', improves the running stability of the system, and has better research value. Under the equivalent control, the power generation unit, the energy storage unit, the bidirectional grid-connected converter and other modules in the direct-current microgrid are mainly controlled by traditional voltage and current double closed loops, and the balance adjustment of power is realized through droop control. The traditional control method applied to the bidirectional grid-connected converter needs two PI controllers to respectively regulate voltage and current, so that the problems of complex PI parameter regulation, low control response speed and the like exist.
When the direct-current micro-grid is connected with a large power grid, an L filter or an LC filter is generally adopted to filter grid-connected current, so that the harmonic content of the grid-connected current is reduced. Compared with an L, LC filter, the LCL filter is small in size and good in high-frequency filtering effect, cost can be reduced in practical application, but the high-order characteristic of the LCL filter can generate a resonance phenomenon, harmonic amplitude under specific frequency of grid-connected current is increased, and stable operation of a system is affected. Therefore, whether the LCL filter can be well combined with the direct-current bus voltage control to be applied to the bidirectional grid-connected converter needs further research.
Disclosure of Invention
The invention aims to provide a double-current feedback control method applied to a bidirectional grid-connected converter.
The technical scheme adopted by the invention is a double-current feedback control method applied to a bidirectional grid-connected converter, which is specifically carried out according to the following steps:
step 1, establishing a direct-current bus voltage U according to the principle that power on two sides of alternating current and direct current of a three-phase AC/DC converter is equaldcWith the AC side current i of the three-phase AC/DC converterLSubstituting the mathematical relation into a droop control equation to obtain the current i at the alternating current side of the three-phase AC/DC converterLCalculating an equation;
and 2, adding an active damping feedback loop in the control of the bidirectional grid-connected three-phase AC/DC converter.
The present invention is also characterized in that,
in the step 1, the method specifically comprises the following steps:
step 1.1, direct current bus voltage reference value
Figure BDA0002577014450000031
And the input current i of the DC busdcThe equation (2) is shown as the formula (1);
Figure BDA0002577014450000032
in the formula (1), UNFor DC bus voltage rating, kdcIs the slope;
step 1.2, when the bidirectional grid-connected three-phase AC/DC converter works stably, the input power and the output power of the three-phase AC/DC converter are equal, and the following equation is established according to the input power and the output power, wherein the equation is shown in the formula (2);
Figure BDA0002577014450000033
in the formula (2), UacFor AC line voltage, iLFor alternating side currents of three-phase AC/DC converters, UdcThe actual value of the voltage of the direct current bus is obtained;
step 1.3, elimination of i by the combination of formula (1) and formula (2)dcTo obtain the DC bus voltage UdcWith the AC side current i of the three-phase AC/DC converterLThe formula (2) is shown as a formula (3);
Figure BDA0002577014450000034
step 1.4, neglecting the voltage reference value of the direct current bus
Figure BDA0002577014450000041
And DC bus voltage UdcTo obtain the AC side current i of the three-phase AC/DC converterLAs shown in formula (4);
Figure BDA0002577014450000042
after the formula (4) is simplified, the formula (5) is obtained;
Figure BDA0002577014450000043
step 1.5, extracting the actual value U of the voltage of the direct current bus from the topological circuit of the three-phase AC/DC converterdcCarrying out improved droop control calculation;
step 1.6, improving an output value obtained by droop control calculation to be used as a current reference value i on the alternating current side of the three-phase AC/DC converterLrefActual value i of alternating current side current of three-phase AC/DC converter extracted from topological circuit of three-phase AC/DC converterLComparing to obtain a current difference value delta I as shown in a formula (6);
iLref-iL＝ΔI (6)；
step 1.7, the compared current difference value delta I generates a modulation signal through a current regulator, and the equivalent transfer function G of the modulation signali(s) is represented by formula (7);
Figure BDA0002577014450000044
in the formula (7), KpIs a proportionality coefficient; krIs the resonance coefficient; omegaiIs the cut-off frequency; omega0Is the fundamental angular frequency.
In step 1.4, k is a proportionality coefficient;
Figure BDA0002577014450000045
in the step 2, the method specifically comprises the following steps:
step 2.1, extracting grid-connected current i from a three-phase AC/DC converter topological circuitgIs transmitted to an active damping controller Gh(s)；
Step 2.2, the output quantity of the active damping controller is compared with the output value of the current regulator and then transmitted to a PWM pulse signal generator, and pulses are generated to control the three-phase AC/DC converter;
and 2.3, controlling an IGBT switching tube of the three-phase AC/DC converter by the pulse signal generated by PWM to form closed-loop control of the grid-connected three-phase AC/DC converter.
In step 2.1, active damping controller Gh(s) the expression is shown as formula (8);
Figure BDA0002577014450000051
in the formula (8), khIs an active damping coefficient, omegadIs the cut-off angular frequency; s is the laplace operator.
The invention has the beneficial effects that:
the method reduces PI regulation of the voltage loop and improves control response speed. The control strategy establishes a quadratic function relation between the direct current bus voltage and the alternating current side current of the converter according to the power conservation principle, and improves the traditional droop control, so that the direct current bus voltage control effect is optimized. On the other hand, in order to improve the harmonic suppression capability of the grid-connected current, an LCL filter is adopted between the grid-connected converter and the power grid. When the LCL filter is in grid-connected operation, the LCL filter has better high-frequency harmonic suppression capability compared with an L filter and an LC filter, but the structure of the LCL filter belongs to a third-order system, and an unstable resonance phenomenon can be generated to influence the normal operation of the system. And the resonance is suppressed by adopting a grid-connected current feedback active damping method, so that the grid-connected current harmonic wave is reduced and the system robustness is improved. The droop control and the active damping feedback control are improved to be combined to form bidirectional control over the alternating current side and the direct current side of the grid-connected converter.
Drawings
Fig. 1 is a structure and control block diagram of a dual current feedback control system applied to a bidirectional grid-connected converter according to the present invention;
FIG. 2 is a control block diagram of a dual current feedback control method applied to a bi-directional grid-connected converter according to the present invention;
fig. 3 is a control block diagram of a simplified direct-current microgrid simulation system in the method of the present invention;
FIG. 4 is a DC bus voltage U before and after droop control improvement in accordance with the present invention method when load power changesdcComparing simulation waveforms;
FIG. 5 is a simulation waveform of grid-connected A-phase voltage current in the method of the present invention;
FIG. 6 is a DC bus voltage U before and after droop control improvement at pulsed disturbance in accordance with the method of the present inventiondcComparing simulation waveforms;
FIG. 7 is a graph of the grid-connected current waveform and THD analysis without the active damping method;
FIG. 8 is a diagram of analysis of the grid-connected current waveform and THD after the active damping feedback loop is added in the method of the present invention.
Detailed Description
The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.
The invention discloses a double-current feedback control system applied to a bidirectional grid-connected converter, which comprises a converter topology circuit and a control circuit as shown in figure 1, wherein the topology circuit has the following specific structure: the three-phase AC/DC converter is built by 6 IGBTs and 6 anti-parallel diodes, and the direct current side of the three-phase AC/DC converter passes through a voltage stabilizing capacitor CdcConnected with a DC bus and passing through the AC side of the three-phase AC/DC converterThe LCL filter is connected to an AC power supply system, wherein the LCL filter comprises an inductance L connected to the three-phase AC/DC converter side1Filter capacitor C and inductor L connected to the AC power supply side2；
The control circuit includes: the droop control calculation is improved, and the input end of the droop control calculation is the actual value U of the direct current bus voltagedcRated value U of DC bus voltageNThe output end is an output quantity iLrefCurrent i at the AC side of the three-phase AC/DC converterLAnd comparing, adjusting the comparison result through a current regulator, comparing the comparison result with the output value of the active damping controller, transmitting the comparison result to a PWM pulse signal generator, and controlling the on-off of the IGBT tube by the generated pulse signal.
When the power of the direct current side is excessive and the voltage of a bus is increased, the three-phase AC/DC converter converts the direct current into the alternating current, namely works in an inversion mode, and realizes the output of the excessive power of the direct current side; when the power of the direct current side is insufficient and the voltage of the bus drops, the three-phase AC/DC converter converts the alternating current into the direct current, namely, the three-phase AC/DC converter works in a rectification mode, so that the supplement of the insufficient power of the direct current side is realized.
The DC bus provides stable DC voltage U for the DC side of the three-phase AC/DC converterdc(ii) a Voltage-stabilizing capacitor CdcThe device is used for stabilizing the voltage of the direct current bus and filtering partial voltage harmonic waves; the LCL filter is used for filtering high-frequency harmonic waves generated by the PWM control switch tube in the alternating current;
the improved droop control calculation is that the actual value U of the DC bus voltage extracted from the topological circuit is calculateddcWith a given DC bus voltage rating UNSubstituting formula (5) to obtain the AC side current reference value i of the three-phase AC/DC converterLref；
Extracting actual value i of alternating current side current of three-phase AC/DC converter in topological circuitLTransmitted to a control circuit and calculated to obtain a reference value i of the current at the AC side of the three-phase AC/DC converterLrefAfter comparison, adjusting through a current regulator; extracting grid-connected current actual value i from topological circuitgIs transmitted to a control circuit igAnd the output value of the current regulator is compared with the output value of the active damping controller, and the obtained result is sent to the PWM module to generate a pulse signal to control an IGBT switching tube.
The invention relates to a double-current feedback control method applied to a bidirectional grid-connected converter, which is specifically carried out according to the following steps:
step 1, establishing a direct-current bus voltage U according to the principle that power on two sides of alternating current and direct current of a three-phase AC/DC converter is equaldcWith the AC side current i of the three-phase AC/DC converterLSubstituting the mathematical relation into the traditional droop control equation to obtain the current i at the alternating current side of the three-phase AC/DC converterLThe calculation equation is specifically as follows:
step 1.1, knowing that in the traditional droop control of the DC bus voltage, a DC bus voltage reference value exists
Figure BDA0002577014450000081
And the input current i of the DC busdcThe equation (2) is shown as the formula (1);
Figure BDA0002577014450000082
in the formula (1), UNFor DC bus voltage rating, kdcIs the slope;
step 1.2, when the bidirectional grid-connected three-phase AC/DC converter works stably, the input power and the output power of the three-phase AC/DC converter are equal, all switches are set to be ideal switches, and the following equation is established according to the ideal switches, wherein the equation is shown in the formula (2);
Figure BDA0002577014450000083
in the formula (2), UacFor AC line voltage, iLFor alternating side currents of three-phase AC/DC converters, UdcThe actual value of the voltage of the direct current bus is obtained;
step 1.3, elimination of i by the combination of formula (1) and formula (2)dcTo obtain the DC bus voltage UdcTo a three-phase AC/DC converterCurrent i on the current sideLThe formula (2) is shown as a formula (3);
Figure BDA0002577014450000084
step 1.4, neglecting the voltage reference value of the direct current bus
Figure BDA0002577014450000085
And DC bus voltage UdcTo obtain the AC side current i of the three-phase AC/DC converterLAs shown in formula (4);
Figure BDA0002577014450000091
after the formula (4) is simplified, the formula (5) is obtained;
Figure BDA0002577014450000092
in the formula (5), k is a proportionality coefficient,
Figure BDA0002577014450000093
step 1.5, extracting the actual value U of the voltage of the direct current bus from the topological circuit of the three-phase AC/DC converterdcAs shown in fig. 2, droop control calculation is performed;
step 1.6, improving an output value obtained by droop control calculation to be used as a current reference value i on the alternating current side of the three-phase AC/DC converterLrefActual value i of alternating current side current of three-phase AC/DC converter extracted from topological circuit of three-phase AC/DC converterLComparing to obtain a current difference value delta I as shown in a formula (6);
iLref-iL＝ΔI (6)；
step 1.7, the compared current difference value delta I is used for generating a modulation signal through a current regulator, the current regulator adopts a quasi-PR regulator, and the equivalent transfer function G of the quasi-PR regulatori(s) is represented by formula (7);
Figure BDA0002577014450000094
in the formula (7), KpIs a proportionality coefficient; krIs the resonance coefficient; omegaiIs the cut-off frequency; omega0Is the fundamental angular frequency;
step 2, adding an active damping feedback loop in the control of the bidirectional grid-connected three-phase AC/DC converter, specifically:
step 2.1, extracting grid-connected current i from a three-phase AC/DC converter topological circuitgIs transmitted to an active damping controller Gh(s) wherein the active damping controller Gh(s) the expression is shown as formula (8);
Figure BDA0002577014450000101
in the formula (8), khIs an active damping coefficient, omegadIs the cut-off angular frequency; s is a laplace operator;
and 2.2, comparing the output quantity of the active damping controller with the output value of the current regulator, and transmitting the output quantity to a PWM pulse signal generator to generate pulses to control the three-phase AC/DC converter.
Pulse Width Modulation (PWM) basic principle: the control mode is to control the on-off of the circuit switch device to make the output end obtain a series of pulses with equal amplitude, and the pulses are used to replace sine wave or required waveform. That is, a plurality of pulses are generated in a half cycle of an output waveform, and the equivalent voltage of each pulse is a sine waveform, so that the obtained output is smooth and has few low-order harmonics. The width of each pulse is modulated according to a certain rule, so that the magnitude of the output voltage of the inverter circuit can be changed.
And 2.3, controlling an IGBT switching tube of the three-phase AC/DC converter by the pulse signal generated by PWM to form closed-loop control of the grid-connected three-phase AC/DC converter.
The embodiment and the simulation verification of the control method of the invention are explained in detail aiming at a simplified direct current microgrid model.
Fig. 3 is a control block diagram of a simplified direct-current microgrid simulation system. The bidirectional grid-connected converter adopts a control method combining improved droop control and grid-connected current feedback active damping, the photovoltaic module adopts Maximum Power Point Tracking (MPPT) control, and when the photovoltaic output Power P is obtainedPVGreater than the load power PLoadWhen the grid-connected converter works in an inversion state; when P is presentPVLess than PLoadIn time, the grid-connected converter operates in a rectification state.
Simulation initial state photovoltaic output power PPVIs 10 kW. Load power PLoadThe initial value was 6 kW. To verify the correctness and feasibility of the proposed control method, the load power P is varied at 0.5s of simulationLoadIncreasing it from the initial 6kW to 14 kW. Due to the fact that photovoltaic output power is insufficient, bus voltage drops, and the grid-connected converter is changed from an inversion state to a rectification state. FIG. 4 shows U before and after droop control improvementdcBy contrast, it can be seen that the U under droop control is improved when the load power changesdcThe response speed is faster, and the time for reaching the steady state value is shorter. Fig. 5 is a simulation waveform of the grid-connected a-phase voltage current of the present invention. Therefore, under the condition that the working state of the bidirectional grid-connected converter changes, the alternating-current side voltage and current waveforms are smooth, and the switching is stable.
In order to further verify the performance of improving droop control, load pulse disturbance is added when the DC bus voltage is 400V in operation, so that the load power is restored to an initial value after being suddenly increased by 5kW, and the voltage waveform change of the DC bus is shown in FIG. 6, which shows that U under the condition of improving droop controldcThe change amplitude of the droop control is smaller, the recovery time is shorter, and the stability is obviously superior to that of the traditional droop control.
Fig. 7 shows the simulation waveform of the grid-connected current and the analysis result of the waveform distortion rate THD of the a-phase current when the active damping method is not adopted. It can be seen from the figure that the three-phase grid-connected current has poor waveform effect in an inversion or rectification state, the harmonic amplitude reaches 3.7% of the fundamental frequency amplitude under specific frequency, and the waveform distortion rate is over 7%. Fig. 8 shows that the grid-connected current waveform adopting the active damping method is obviously improved, the maximum amplitude of the harmonic wave is reduced to be less than 0.5% of the amplitude of the fundamental frequency, and the waveform distortion rate is kept to be about 2.5%, so that the method is proved to be capable of reducing the harmonic distortion rate of the grid-connected current, effectively inhibiting the resonance phenomenon of the LCL and optimizing the grid-connected current.

Claims (3)

1. A double-current feedback control method applied to a bidirectional grid-connected converter is characterized by comprising the following steps:
step 1, establishing a direct-current bus voltage U according to the principle that power on two sides of alternating current and direct current of a three-phase AC/DC converter is equaldcWith the AC side current i of the three-phase AC/DC converterLSubstituting the mathematical relation into a droop control equation to obtain the current i at the alternating current side of the three-phase AC/DC converterLCalculating an equation; the method specifically comprises the following steps:
step 1.1, direct current bus voltage reference value
Figure FDA0003250832940000011
And the input current i of the DC busdcThe equation (2) is shown as the formula (1);
Figure FDA0003250832940000012
in the formula (1), UNFor DC bus voltage rating, kdcIs the slope;
step 1.2, when the bidirectional grid-connected three-phase AC/DC converter works stably, the input power and the output power of the three-phase AC/DC converter are equal, and the following equation is established according to the input power and the output power, wherein the equation is shown in the formula (2);
Figure FDA0003250832940000013
in the formula (2), UacFor AC line voltage, iLFor alternating side currents of three-phase AC/DC converters, UdcThe actual value of the voltage of the direct current bus is obtained;
step 1.3, simultaneousFormula (1) and formula (2) eliminate idcTo obtain the DC bus voltage UdcWith the AC side current i of the three-phase AC/DC converterLThe formula (2) is shown as a formula (3);
Figure FDA0003250832940000014
step 1.4, neglecting the voltage reference value of the direct current bus
Figure FDA0003250832940000015
And DC bus voltage UdcTo obtain the AC side current i of the three-phase AC/DC converterLAs shown in formula (4);
Figure FDA0003250832940000021
after the formula (4) is simplified, the formula (5) is obtained;
Figure FDA0003250832940000022
step 1.5, extracting the actual value U of the voltage of the direct current bus from the topological circuit of the three-phase AC/DC converterdcCarrying out improved droop control calculation;
step 1.6, improving an output value obtained by droop control calculation to be used as a current reference value i on the alternating current side of the three-phase AC/DC converterLrefActual value i of alternating current side current of three-phase AC/DC converter extracted from topological circuit of three-phase AC/DC converterLComparing to obtain a current difference value delta I as shown in a formula (6);
iLref-iL＝ΔI (6)；
step 1.7, the compared current difference value delta I generates a modulation signal through a current regulator, and the equivalent transfer function G of the modulation signali(s) is represented by formula (7);
Figure FDA0003250832940000023
in the formula (7), KpIs a proportionality coefficient; krIs the resonance coefficient; omegaiIs the cut-off frequency; omega0Is the fundamental angular frequency;
step 2, adding an active damping feedback loop in the control of the bidirectional grid-connected three-phase AC/DC converter; the method specifically comprises the following steps:
step 2.1, extracting grid-connected current i from a three-phase AC/DC converter topological circuitgIs transmitted to an active damping controller Gh(s)；
Step 2.2, the output quantity of the active damping controller is compared with the output value of the current regulator and then transmitted to a PWM pulse signal generator, and pulses are generated to control the three-phase AC/DC converter;
and 2.3, controlling an IGBT switching tube of the three-phase AC/DC converter by the pulse signal generated by PWM to form closed-loop control of the grid-connected three-phase AC/DC converter.
2. The dual-current feedback control method applied to the bidirectional grid-connected converter according to claim 1, wherein in step 1.4, k is a proportionality coefficient;
Figure FDA0003250832940000031
3. the method according to claim 1, wherein in step 2.1, the active damping controller G is used for controlling the feedback of the double current in the bidirectional grid-connected converterh(s) the expression is shown as formula (8);
Figure FDA0003250832940000032
in the formula (8), khIs an active damping coefficient, omegadIs the cut-off angular frequency; s is the laplace operator.
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