阅读说明：本技术 一种电网模拟器拓扑结构及其控制方法 (Power grid simulator topological structure and control method thereof ) 是由 周连俊 汪诚 彭子琦 顾伟峰 应展烽 殷明慧 杨炯明 彭云 卜京 陈载宇 邹云 于 2021-01-13 设计创作，主要内容包括：本发明公开了一种电网模拟器拓扑结构及其控制方法。所述拓扑结构包括结构完全相同的A、B、C三相,A、B、C三相LC滤波器,A、B、C三相变压器及负载。模拟器可以四象限运行,实现电能向电网的回馈,可提供三相电网电压输出并模拟电网的电压跌落、频率偏移、三相不平衡、谐波畸变等各种电网故障情况。在设计控制器层面,将电网模拟器的控制方式分为基波控制和谐波控制,即分别控制低频大容量模块和高频小容量模块。此外,提出一种直流侧电压随动控制策略,以解决各模块间功率不匹配的问题。(The invention discloses a topological structure of a power grid simulator and a control method thereof. The topological structure comprises A, B, C three-phase, A, B, C three-phase LC filters, A, B, C three-phase transformers and loads which are identical in structure. The simulator can operate in four quadrants, realizes the feedback of electric energy to a power grid, can provide three-phase power grid voltage output and simulate various power grid fault conditions of power grid such as voltage drop, frequency offset, three-phase imbalance, harmonic distortion and the like. On the design controller level, the control mode of the power grid simulator is divided into fundamental wave control and harmonic wave control, namely a low-frequency large-capacity module and a high-frequency small-capacity module are respectively controlled. In addition, a direct current side voltage follow-up control strategy is provided to solve the problem of power mismatch among modules.)

1. A grid simulator topology, the topology comprising: A. b, C three-phase, A, B, C three-phase LC filter, A, B, C three-phase transformer, and load; A. b, C three phases respectively output fundamental wave, low harmonic wave and high harmonic wave, and then are respectively connected with a load through A, B, C three-phase LC filter and A, B, C three-phase transformer.

2. The grid simulator topology of claim 1, wherein the A, B, C three phases are identical in structure, each phase comprising a fundamental and low frequency large capacity converter module, a high frequency small capacity converter module;

the fundamental wave and low-frequency large-capacity converter module is used for outputting fundamental waves and low-order harmonics;

and the high-frequency small-capacity converter module is used for outputting higher harmonics.

3. The grid simulator topology of claim 2, wherein the fundamental and low frequency bulk converter module comprises n first gain-follower feedback modules (a)_a1～A_anOr B_a1～B_anOr C_a1～C_an) N first segmented wide gain inverter modules (H)_aa1～H_aanOr H_ba1～H_banOr H_ca1～H_can)；

The high frequency small capacity converter module includes n second gain follow-up feedback modules (A)_b1～A_bnOr B_b1～B_bnOr C_b1～C_bn) N second segmented wide gain inverter modules (H)_ab1～H_abnOr H_bb1～H_bbnOr H_cb1～H_cbn) Wherein n is more than or equal to 1;

the first gain follow-up feedback module (A)_aiOr B_aiOr C_ai) And a first segmented wide gain inverter module (H)_aaiOr H_baiOr H_cai) One-to-one connection, second gain follow-up feedback module (A)_biOr B_biOr C_bi) And a second sectional wide gain inversion module (H)_abiOr H_bbiOr H_cbi) Connecting in a one-to-one correspondence manner; n first segmented wide gain inversion modules (H)_aaiOr H_baiOr H_cai) N second segmented wide gain inversion modules (H) cascaded in sequence_abiOr H_bbiOr H_cbi) Sequentially cascading; at the same time, the first and second segmented wide gain inversion modules (H) are arranged in sequence_ab1Or H_bb1Or H_cb1) And the nth first segmented wide gain inversion module (H)_aanOr H_banOr H_can) Cascaded, sequentially first segment wideGain inversion module (H)_aa1Or H_ba1Or H_ca1) Is connected to an a-phase or B-phase or C-phase LC filter, which is then connected to an a-phase or B-phase or C-phase transformer (a1 or B1 or C1); A. b, C n-th segmented wide-gain inversion module in sequence in three phases_abnOr H_bbnOr H_cbn) Phase cascading; wherein i is more than or equal to 1 and less than or equal to n.

4. The grid simulator topology of claim 3, wherein the gain-follower feedback module has a hardware topology that is a three-phase pwm rectifier; the hardware topological structure of the sectional type wide-gain inversion module is an H-bridge inverter.

5. The grid simulator topology of claim 4, wherein the fundamental and low frequency large capacity converter modules and the high frequency small capacity converter modules have capacities selected from the group consisting of:

defining fundamental wave capacity as reference value 1, and obtaining harmonic wave capacity per unit value as S_h＝1.15-S(T_os) Where S (T) is a function of the fundamental output power over time, T_osIs the overshoot time of the total power output.

6. The method for controlling the topology of the grid simulator according to any of claims 1 to 5, wherein the method comprises a voltage outer loop control, a current inner loop control, a modulation wave distribution of a segmented wide gain inversion module, and a direct current side voltage follow-up control of a gain follow-up feedback module; wherein the content of the first and second substances,

the voltage outer ring control of the sectional type wide-gain inversion module specifically comprises the following steps: a, B, C three-phase voltage is sampled to obtain phase voltage U_A、U_B、U_CPhase voltage U_A、U_B、U_CObtaining U after converting abc _ dq coordinates_α、U_βA, B, C three-phase U_A、U_B、U_CVoltage command value U of_Aref、U_Bref、U_CrefBy abc _ dq coordinate changeObtaining a voltage instruction U of a dq axis after conversion_αrefAnd U_βrefWill U is_αrefAnd U_αObtaining an inner ring d-axis current reference signal I through a PR controller after difference making_αrefWill U is_βrefAnd U_βObtaining an inner ring q-axis current reference signal I through a PR controller after difference making_βref；

The segmented wide-gain inversion module current inner loop control specifically comprises the following steps: the current of A, B, C three phases is sampled to obtain phase current I_A、I_B、I_COf phase current I_A、I_B、I_CObtaining I after the coordinate transformation of abc _ dq_α、I_βIs shown by_αrefAnd I_αObtaining a d-axis modulated wave signal U through a PR controller after difference making_αrIs shown by_βrefAnd I_βObtaining a q-axis modulated wave signal U through a PR controller after difference making_βrModulating the wave signal U with d-axis_αrAnd q-axis modulated wave signal U_βrObtaining A, B, C three-phase modulating wave signal U after reverse Clack conversion_a、U_b、U_c；

The distribution of the modulation wave of the sectional type wide-gain inversion module is as follows: a, B, C three-phase modulated wave signal U_a、U_b、U_cObtaining U after Fourier transform_a、U_b、U_cFundamental component U of_af、U_bf、U_cfA fundamental component U_af、U_bf、U_cfAs a modulated wave of A, B, C three-phase fundamental wave and low-frequency large-capacity converter module, U is set_a-U_af、U_b-U_bf、U_c-U_cfThe modulation wave is used as an A, B, C three-phase high-frequency small-capacity converter module;

the gain follow-up feedback module direct-current side voltage follow-up control specifically comprises the following steps: voltage v at the DC side_dc1a...v_dcnaAnd the average value sigma v of all the modules of the system on the DC side voltage_dcjThe/3 n is compared, after the obtained error passes through the PI controller, the adjustment quantity of the output direct current side voltage is differed with the current direct current side voltage, and a new module direct current side voltage reference value v is generated^* _dc1a...v^* _dcnaWill modulate the wave v_r1a...v_rnaDivided by this value to obtain the control modulation ratio m_1a...m_naThe output voltage proportion of the module with higher power is increased, and the power of each module is matched.

Technical Field

The invention belongs to the field of power electronic converters and control thereof, and particularly relates to a topological structure of a power grid simulator and a control method thereof.

Background

In order to grid-connect a distributed power generation system such as photovoltaic and wind power, the power grid adaptability test needs to be carried out before grid connection, but the power grid is a huge system, so that the operation is difficult to carry out when the power grid adaptability test is carried out. And the main role of the grid is to provide standard three-phase sinusoidal voltage to the consumer, various forms of grid faults are not common. Therefore, special equipment is needed to simulate the grid fault, and the distributed power generation system is tested. The power grid simulator has the function of simulating and outputting various faults of a power grid, not only can output normal power grid voltage, but also can simulate common faults such as voltage drop, three-phase imbalance, frequency offset, harmonic contained voltage and the like. And four-quadrant operation is to be achieved so that energy flows in both directions. With the scale of distributed power generation systems, the requirements for power and functions of grid simulators are also increasing. The deep research on the topological structure and the control strategy of the power grid simulator has very important significance and value on the adaptability test of the distributed power system.

The topological structure of the existing power grid simulator mostly adopts a front-stage uncontrollable rectification and rear-stage three-phase PWM inversion structure, but the topology structure can not realize four-quadrant operation, is only suitable for a medium-low voltage small-capacity system, and is not suitable for a large-capacity system. At present, a power grid simulator control strategy mainly comprises proportional-integral control, repetitive control, sliding mode variable control and the like, but a proportional-integral controller can only perform no-difference tracking on the amplitude of a power grid, and the tracking of given voltage has the problems of static difference, delay, oscillation and the like; the repetitive control has good steady-state output characteristics and robustness but has the problems of output delay of one fundamental wave period and poor dynamic performance; the sliding mode variable structure is nonlinear control, and has on and off control characteristics, so that a phenomenon of buffeting exists.

Disclosure of Invention

The invention aims to provide a power grid simulator topological structure and a control method thereof, aiming at the problems in the prior art.

The technical solution for realizing the purpose of the invention is as follows: a power grid simulator topology, the topology comprising: A. b, C three-phase, A, B, C three-phase LC filter, A, B, C three-phase transformer, and load; A. b, C three phases respectively output fundamental wave, low harmonic wave and high harmonic wave, and then are respectively connected with a load through A, B, C three-phase LC filter and A, B, C three-phase transformer.

Further, the A, B, C three phases have the same structure, and each phase comprises a fundamental wave and low-frequency large-capacity converter module and a high-frequency small-capacity converter module;

the fundamental wave and low-frequency large-capacity converter module is used for outputting fundamental waves and low-order harmonics;

and the high-frequency small-capacity converter module is used for outputting higher harmonics.

Furthermore, the fundamental wave and low-frequency large-capacity converter module comprises n first gain follow-up feedback modules and n first sectional wide-gain inversion modules;

the high-frequency small-capacity converter module comprises n second gain follow-up feedback modules and n second sectional wide-gain inversion modules, wherein n is more than or equal to 1;

the output end of the first gain follow-up feedback module is connected with the first sectional type wide gain inversion module in a one-to-one corresponding way, and the output end of the second gain follow-up feedback module is connected with the second sectional type wide gain inversion module in a one-to-one corresponding way; the n first sectional type wide gain inversion modules are sequentially cascaded, and the n second sectional type wide gain inversion modules are sequentially cascaded; meanwhile, a first second sectional type wide gain inversion module and an nth first sectional type wide gain inversion module which are arranged in sequence are cascaded, the output end of the first sectional type wide gain inversion module which is arranged in sequence is connected with an A-phase or B-phase or C-phase LC filter, and the LC filter is connected with an A-phase or B-phase or C-phase transformer; A. b, C the n second segmented wide gain inversion modules in sequence in the three phases are cascaded; wherein i is more than or equal to 1 and less than or equal to n.

Furthermore, the hardware topology structure of the gain follow-up feedback module is a three-phase pwm rectifier; the hardware topological structure of the sectional type wide-gain inversion module is an H-bridge inverter.

Further, the capacities of the fundamental wave and low frequency large-capacity converter module and the high frequency small-capacity converter module are selected as follows:

defining fundamental wave capacity as reference value 1, and obtaining harmonic wave capacity per unit value as S_h＝1.15-S(T_os) Where S (T) is a function of the fundamental output power over time, T_osIs the overshoot time of the total power output.

Furthermore, the method comprises the steps of voltage outer loop control, current inner loop control, modulation wave distribution of a sectional type wide gain inversion module and direct current side voltage follow-up control of a gain follow-up feedback module; wherein the content of the first and second substances,

the voltage outer ring control of the sectional type wide-gain inversion module specifically comprises the following steps: a, B, C three-phase voltage is sampled to obtain phase voltage U_A、U_B、U_CPhase voltage U_A、U_B、U_CObtaining U after converting abc _ dq coordinates_α、U_βWill beA. B, C three-phase U_A、U_B、U_CVoltage command value U of_Aref、U_Bref、U_CrefObtaining a voltage instruction U of a dq axis after abc _ dq coordinate transformation_αrefAnd U_βrefWill U is_αrefAnd U_αObtaining an inner ring d-axis current reference signal I through a PR controller after difference making_αrefWill U is_βrefAnd U_βObtaining an inner ring q-axis current reference signal I through a PR controller after difference making_βref；

The segmented wide-gain inversion module current inner loop control specifically comprises the following steps: the current of A, B, C three phases is sampled to obtain phase current I_A、I_B、I_COf phase current I_A、I_B、I_CObtaining I after the coordinate transformation of abc _ dq_α、I_βIs shown by_αrefAnd I_αObtaining a d-axis modulated wave signal U through a PR controller after difference making_αrIs shown by_βrefAnd I_βObtaining a q-axis modulated wave signal U through a PR controller after difference making_βrModulating the wave signal U with d-axis_αrAnd q-axis modulated wave signal U_βrObtaining A, B, C three-phase modulating wave signal U after reverse Clack conversion_a、U_b、U_c；

The distribution of the modulation wave of the sectional type wide-gain inversion module is as follows: a, B, C three-phase modulated wave signal U_a、U_b、U_cObtaining U after Fourier transform_a、U_b、U_cFundamental component U of_af、U_bf、U_cfA fundamental component U_af、U_bf、U_cfAs a modulated wave of A, B, C three-phase fundamental wave and low-frequency large-capacity converter module, U is set_a-U_af、U_b-U_bf、U_c-U_cfThe modulation wave is used as an A, B, C three-phase high-frequency small-capacity converter module;

the gain follow-up feedback module direct-current side voltage follow-up control specifically comprises the following steps: voltage v at the DC side_dc1a...v_dcnaAnd the average value sigma v of all the modules of the system on the DC side voltage_dcjA/3 n comparison is made to obtain an errorAfter the difference passes through the PI controller, the adjustment quantity of the output direct current side voltage is differed with the current direct current side voltage to generate a new module direct current side voltage reference value v^* _dc1a...v^* _dcnaWill modulate the wave v_r1a...v_rnaDivided by this value to obtain the control modulation ratio m_1a...m_naThe output voltage proportion of the module with higher power is increased, and the power of each module is matched.

Compared with the prior art, the invention has the following remarkable advantages: aiming at the problem that the target performances of high capacity, high voltage dynamic response rate, high response precision, high reliability and the like of the current large-megawatt power grid simulator are difficult to consider, the invention provides a combined topological structure which can reasonably optimize and decompose the overall performance index to a subsystem, and avoids the bottleneck problem caused by excessive excavation of the performance of a single topological structure. Based on the thought, a power grid simulator topological structure with a fundamental wave and low-frequency large-capacity converter module and a high-frequency small-capacity converter module connected in series is provided, a sectional type wide-gain inversion module modulated wave distribution control strategy and a gain follow-up feedback module direct-current side voltage follow-up control strategy which correspond to the power grid simulator topological structure are provided, and a capacity matching principle of the low-frequency large-capacity converter module and the high-frequency small-capacity converter module is provided. The cost is reduced, the implementation complexity and the reliability risk are reduced, and meanwhile, a further breakthrough of the voltage dynamic response performance of the large-megawatt power grid simulator is obtained.

The present invention is described in further detail below with reference to the attached drawing figures.

Drawings

Fig. 1 is a schematic diagram of a topology of a power grid simulator in one embodiment.

Fig. 2 is a block diagram of voltage outer loop control, current inner loop control, and modulation wave distribution control of the power grid simulator topology in one embodiment.

Fig. 3 is a block diagram of dc side voltage follow-up control of a topology of a grid simulator in an embodiment.

Detailed Description

In order to make the objects, technical solutions and advantages of the present application more apparent, the present application is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the present application and are not intended to limit the present application.

In one embodiment, in conjunction with fig. 1, there is provided a grid simulator topology comprising: A. b, C three-phase, A, B, C three-phase LC filter, A, B, C three-phase transformer, and load; A. b, C three phases respectively output fundamental wave, low harmonic wave and high harmonic wave, and then are respectively connected with a load through A, B, C three-phase LC filter and A, B, C three-phase transformer.

The whole system is broken down into two parts: the topological structure comprises a fundamental wave rectifier module, a harmonic wave rectifier module, a fundamental wave inverter module, a harmonic wave inverter module, a filter and a fundamental wave harmonic wave connecting unit, wherein the fundamental wave rectifier module and the harmonic wave rectifier module adopt gain follow-up feedback modules and can generate respective required direct current voltages; the filter adopts an LC filter circuit; the fundamental wave harmonic wave connection unit adopts the transformer, not only plays a role in connecting fundamental wave harmonic waves, but also can play a role in isolating, and prevents the direct current side from generating a short circuit phenomenon.

Further, in one embodiment, the A, B, C three phases have the same structure, and each phase comprises a fundamental wave and low-frequency large-capacity converter module and a high-frequency small-capacity converter module;

the fundamental wave and low-frequency large-capacity converter module is used for outputting fundamental waves and low-order harmonics;

and the high-frequency small-capacity converter module is used for outputting higher harmonics.

Further, in one embodiment, the fundamental wave and low frequency large capacity converter module of phase a includes n first gain follow-up feedback modules a_a1～A_anN first segmented wide-gain inverter modules H_aa1～H_aan

The high-frequency small-capacity converter module comprises n second gain follow-up feedback modules A_b1～A_bnN second segmented wide gain inverter modules H_ab1～H_abnWherein n is more than or equal to 1;

the first gain follow-up feedback module A_aiOutput end and first sectional type wide gain inversion module H_aaiOne-to-one connection, second gain follow-up feedback module A_biAnd a second sectional wide gain inversion module H_abiConnecting in a one-to-one correspondence manner; n first sectional type wide gain inversion modules H_aaiN second sectional wide gain inversion modules H cascaded in sequence_abiSequentially cascading; at the same time, the first and second sectional wide-gain inversion modules H are arranged in sequence_ab1And the nth first segmented wide-gain inversion module H_aanCascaded, sequentially arranged first segmented wide-gain inversion module H_aa1Is connected with an a-phase or B-phase or C-phase LC filter, which is then connected with an a-phase or B-phase or C-phase transformer a 1; A. b, C n-th second segmented wide-gain inversion module H in sequence in three phases_abnPhase cascading; wherein i is more than or equal to 1 and less than or equal to n.

Further, in one embodiment, the B-phase fundamental wave and low-frequency bulk transformer module includes n first gain follow-up feedback modules B_a1～B_anN first segmented wide-gain inverter modules H_ba1～H_ban；

The high-frequency small-capacity converter module comprises n second gain follow-up feedback modules B_b1～B_bnN second segmented wide gain inverter modules H_bb1～H_bbnWherein n is more than or equal to 1;

the first gain follow-up feedback module B_aiOutput end and first sectional type wide gain inversion module H_baiOne-to-one connection, second gain follow-up feedback module B_biAnd a second sectional wide gain inversion module H_bbiConnecting in a one-to-one correspondence manner; n first sectional type wide gain inversion modules H_baiN second sectional wide gain inversion modules H cascaded in sequence_bbiSequentially cascading; at the same time, the first and second sectional wide-gain inversion modules H are arranged in sequence_bb1And a firstn first sectional type wide gain inversion modules H_banCascaded, sequentially arranged first segmented wide-gain inversion module H_ba1Is connected with an a-phase or B-phase or C-phase LC filter, which is then connected with an a-phase or B-phase or C-phase transformer B1; A. b, C n-th second segmented wide-gain inversion module H in sequence in three phases_bbnPhase cascading; wherein i is more than or equal to 1 and less than or equal to n.

Further, in one embodiment, the C-phase fundamental wave and low-frequency bulk transformer module includes n first gain follow-up feedback modules C_a1～C_anN first segmented wide-gain inverter modules H_ca1～H_can；

The high-frequency small-capacity converter module comprises n second gain follow-up feedback modules C_b1～C_bnN second segmented wide gain inverter modules H_cb1～H_cbnWherein n is more than or equal to 1;

the first gain follow-up feedback module C_aiOutput end and first sectional type wide gain inversion module H_caiOne-to-one connection, second gain follow-up feedback module C_biAnd a second sectional wide gain inversion module H_cbiConnecting in a one-to-one correspondence manner; n first sectional type wide gain inversion modules H_caiN second sectional wide gain inversion modules H cascaded in sequence_cbiSequentially cascading; at the same time, the first and second sectional wide-gain inversion modules H are arranged in sequence_cb1And the nth first segmented wide-gain inversion module H_canCascaded, sequentially arranged first segmented wide-gain inversion module H_ca1Is connected with an a-phase or B-phase or C-phase LC filter, which is then connected with an a-phase or B-phase or C-phase transformer C1; A. b, C n-th second segmented wide-gain inversion module H in sequence in three phases_cbnPhase cascading; wherein i is more than or equal to 1 and less than or equal to n.

Further, in one embodiment, the hardware topology of the gain follow-up feedback module is a three-phase pwm rectifier; the hardware topological structure of the sectional type wide-gain inversion module is an H-bridge inverter.

Further, in one embodiment, the capacities of the fundamental wave and low frequency large-capacity converter module and the high frequency small-capacity converter module are selected as follows:

selecting different capacities, generally, the total overshoot does not exceed 15% of a steady state value, and the principle of minimum effective value is followed, namely, the fundamental wave is designed according to the control parameters of an optimal overshoot-free system, and the overshoot of a harmonic part is 15%;

defining fundamental wave capacity as reference value 1, and obtaining harmonic wave capacity per unit value as S_h＝1.15-S(T_os) Where S (T) is a function of the fundamental output power over time, T_osIs the overshoot time of the total power output.

In one embodiment, a control method for the power grid simulator topology is provided, and the method includes a segmented wide-gain inversion module voltage outer loop control, a current inner loop control, a modulation wave distribution, and a gain follow-up feedback module direct-current side voltage follow-up control; wherein, the voltage outer loop control, the current inner loop control and the modulation wave distribution are a sectional wide gain inversion module control strategy, as shown in fig. 2; the dc side voltage follow-up control is a gain follow-up feedback module control strategy, as shown in fig. 3.

The voltage outer ring control of the sectional type wide-gain inversion module specifically comprises the following steps: line voltage U after sampling line voltage of A, B, C three phases_AB、U_BCAnd U_CAAccording to the following formula:

phase voltage U is obtained through calculation_A、U_B、U_CPhase voltage U_A、U_B、U_CObtaining U after converting abc _ dq coordinates_α、U_βA, B, C three-phase U_A、U_B、U_CVoltage command value U of_Aref、U_Bref、U_CrefObtaining a voltage finger of a dq axis after abc _ dq coordinate transformationLet U_αrefAnd U_βrefWill U is_αrefAnd U_αObtaining an inner ring d-axis current reference signal I through a PR controller after difference making_αrefWill U is_βrefAnd U_βObtaining an inner ring q-axis current reference signal I through a PR controller after difference making_βref；

The segmented wide-gain inversion module current inner loop control specifically comprises the following steps: the current of A, B, C three phases is sampled to obtain phase current I_A、I_B、I_COf phase current I_A、I_B、I_CObtaining I after the coordinate transformation of abc _ dq_α、I_βIs shown by_αrefAnd I_αObtaining a d-axis modulated wave signal U through a PR controller after difference making_αrIs shown by_βrefAnd I_βObtaining a q-axis modulated wave signal U through a PR controller after difference making_βrModulating the wave signal U with d-axis_αrAnd q-axis modulated wave signal U_βrObtaining A, B, C three-phase modulating wave signal U after reverse Clack conversion_a、U_b、U_c；

The distribution of the modulation wave of the sectional type wide-gain inversion module is as follows: a, B, C three-phase modulated wave signal U_a、U_b、U_cObtaining U after Fourier transform_a、U_b、U_cFundamental component U of_af、U_bf、U_cfA fundamental component U_af、U_bf、U_cfAs a modulated wave of A, B, C three-phase fundamental wave and low-frequency large-capacity converter module, U is set_a-U_af、U_b-U_bf、U_c-U_cfThe modulation wave is used as an A, B, C three-phase high-frequency small-capacity converter module;

the gain follow-up feedback module direct-current side voltage follow-up control specifically comprises the following steps: voltage v at the DC side_dc1a...v_dcnaAnd the average value sigma v of all the modules of the system on the DC side voltage_dcjThe/3 n is compared, after the obtained error passes through the PI controller, the adjustment quantity of the output direct current side voltage is differed with the current direct current side voltage, and a new module direct current side voltage reference value v is generated^* _dc1a...v^* _dcnaWill modulate the wave v_r1a...v_rnaDivided by this value to obtain the control modulation ratio m_1a...m_naThe output voltage proportion of the module with higher power is increased, and the power of each module is matched.

In conclusion, the simulator can operate in four quadrants, realizes the feedback of electric energy to a power grid, can provide three-phase power grid voltage output and simulate various power grid fault conditions of power grid such as voltage drop, frequency offset, three-phase imbalance, harmonic distortion and the like. On the design controller level, the control mode of the power grid simulator is divided into fundamental wave control and harmonic wave control, namely a low-frequency large-capacity module and a high-frequency small-capacity module are respectively controlled. In addition, a direct current side voltage follow-up control strategy is provided to solve the problem of power mismatch among modules.

The embodiments described above are described to facilitate one of ordinary skill in the art to understand and use the invention patent. It will be readily apparent to those skilled in the art that various modifications to these embodiments may be made, and the generic principles described herein may be applied to other embodiments without the use of the inventive faculty. Therefore, the present invention is not limited to the above embodiments, and those skilled in the art should make improvements and modifications within the scope of the present invention based on the disclosure of the present invention.