LU102320B1

LU102320B1 - Control strategy of improving virtual synchronous generator of microgrid inverter

Info

Publication number: LU102320B1
Application number: LU102320A
Authority: LU
Inventors: Yanlei Zhao; Ke Zhao; Chengyang Wang
Original assignee: Univ Shandong Technology
Priority date: 2020-12-15
Filing date: 2020-12-15
Publication date: 2021-06-15

Abstract

The invention discloses a control strategy of improving virtual synchronous generator of microgrid inverter, comprising a VSG (Virtual Synchronous Generator) island parallel control strategy and a VSG active link control strategy, wherein it mainly refers to the synchronous control of each VSG based on the calculation of uPMU (Phase Measurement Unit) pulse per second to generate a uniform rotation phase angle in the microgrid, and measuring the output voltage phase angle and PCC (Point of Common Coupling) phase angle of each VSG through uPMU and calculating the difference and feed it back to each VSG, and combining the rated capacity ratio of each VSG to accurately distribute the output power.

Description

BL-5160 LU102320

CONTROL STRATEGY OF IMPROVING VIRTUAL SYNCHRONOUS GENERATOR OF MICROGRID INVERTER FIELD OF THE INVENTION

[0001] The invention relates to the field of microgrid and motor technology. in particular to a control strategy of improving virtual synchronous generator of microgrid inverter.

BACKGROUND OF THE RELATED ART

[0002] With the rapid development of the new energy industry. a large number of distributed power sources are connected to the power system in the form of microgrids, but the distributed power sources themselves do not have damping and moment of inertia. and it is difficult to participate in the regulation of the large power grid during grid-connected operation: the stability of the microgrid cannot be improved under the island mode. Some scholars have proposed a VSG control strategy to make distributed power sources have the external characteristics of synchronous generators. so that they can provide certain power support for large grids when they are connected to the grid; in the island mode. the damping and moment of inertia of the microgrid are increased to improve the anti-disturbance capability of the microgrid.

[0003] The traditional VSG control strategy controls the active power by adjusting the frequency. In the island operation state. frequent load mutations will cause frequency deviations and affect power quality. In the research of microgrid islanding control strategy. in order to avoid usine frequency as the amount of droop. the active-phase angle droop control method is adopted: since the frequency is no longer involved in the droop control, the frequency is stabilized at the rated value when the system is in steady state. but it is not considered how to measure the phase angle of the parallel DG in real time:

[0004] The synchrophasor phase measurement unit (PMU) is a phasor measurement device 1

BL-5180 LU102320 based on the global positioning system (GPS) for unified timing, which can accurately measure the voltage. current. phase angle and other phasor data of important nodes in the power system in real time. At present. the research and application of PMU are mainly concentrated in the transmission network. however. with the massive access of distributed power sources. the traditional distribution network has gradually transformed into an active distribution network, and the u PMU for the distribution network has also emerged. The use of uPMU can realize the rapid extraction and real-time transmission of phasor data in the distribution network. which provides new possibilities for the stable control and safe operation of the distribution network. The use of uPMU's synchronous fixed-frequency microgrid islanding operation control strategy can keep the frequency constant and svnchronouslv control each DG to achieve precise power distribution, but it cannot provide damping and inertia for the microgrid.

[0005] Aiming at the islanding state of microgrid. the invention proposes an unproved VSG control strategy based on the traditional VSG control strategy with the synchronous phasor measurement function of pPMU and combining the power angle characteristics of the svnchronous generator. which enables the system to keep the frequency constant during steady-state operation of the island on the basis of retaining damping and inertia. reduces the integral part of the control part. increases the response speed of the system when the load changes suddenly. and improves the power quality. The invention uses the uPMU pulse per second as the reference signal to caleulate the rotation phase angle of the synchronous reference coordinate system. and controls cach VSG synchronously in parallel. In the erid-connected mode. the traditional VSG control strategy is adopted to provide frequency and voltage support for the power grid: finally. the cffectiveness of the strategy proposed in the invention is verified by simulation.

SUMMARY OF THE INVENTION

[0006] The technical problem to be solved by the invention is to overcome the defects of the above technology and provide a control strategy of improving virtual synchronous generator of microgrid inverter.

2

BE-5180 LU102320

[0007] In order to solve the above technical problems. the technical solutions provided by the invention are: a control strategy of improving virtual synchronous generator of microgrid inverter. comprising a VSG (Virtual Synchronous Generator) island parallel control strategy and a VSG active link control strategy. wherein it mainly refers to the synchronous control of cach VSG based on the calculation of pPMU (Phase Measurement Unit) pulse per second to generate a uniform rotation phase angle in the microgrid. and measuring the output voltage phase angle and PCC (Point of Common Coupling) phase angle of cach VSG through pPMU and calculating the difference and feed it back 10 each VSG. and combining the rated capacity ratio of cach VSG to accurately distribute the output power.

[0008] As an improvement. the VSG island parallel control strategy comprises two VSGs and a load: all VSGs and loads are connected 10 a same PCC: in the island mode. the VSG controls the active power by adjusting the phase angle difference between the output voltage and the voltage at the PCC point: take one as an example. measure the output voltage phase angle 8, and the PCC voltage phase angle 0, through the uPMU device: measure the output voltage and output current. and calculate the actual output active power Py and the reactive power Qi: input the above parameters into the VSG control link to obtain the phase angle reference value 6, and the voltage amplitude reference value Use. which are calculated through the following formula: L'an = en COS Og U act =U, SIN On

[0009] to obtain the reference values Ugren and Ug of the voltage in the dq coordinate; then pass the voltage and current controller to calculate the synchronous rotation phase angle with uPMU pulse per second to perform Park inverse transformation. and obtain the three-phase modulation waveform used by PWM (Pulse Width Modulation) . so as to complete the entire control process.

[0010] As an improvement. the VSG active link control strategy inputs the difference between the active power reference value Poy and the output active power Pa into the first-order integration fink to obtain the reference value 8 or of the phase angle difference between the

BI.-5180 LU102320 VSGi and the PCC voltage. and adds S'ief and the PCC voltage phase angle 0; 10 obtain the phase angle reference value Ong: at the same time. 8 eri 1s compared with the difference 8,05 between the actual VSGi output voltage phase angle 0, and the PCC voltage phase angle 0, . to enable that after negative feedback . the values of 6,4 and 8" tend 10 be consistent: at this time. VSGi outputs active power according to the rated capacity ratio thereof. and the active link control equation thereof is as follows: 3 Os =P, RD (Si - Sr) dr ! On =O) Or

[0011] according to the above formula. by using the VSG controlled by active-phase angle. the phase angle reference value can be directly obtained. and the integration link from frequency to phase angle is reduced on the premise of retaming damping and inertia. and frequency is no longer used as the amount of droop. which avoids frequency fluctuations when the load changes suddenly: the fixed frequency rotating phase angle gencrated by the HPMU pulse per second signal is used to synchronously control the parallel VSGs, and the synchronous phasor measurement function is used to feed the phase angle to the control link in real time to ensure that each VSG always accurately distributes power according to the design capacity ratio.

[0012] The advantages of the invention compared with the prior art are: the invention controls the active power by adjusting the phase angle difference between the output voltage and the PCC voltage. which simplifies the control link. stabilizes the frequency at 50 Hz, and improves the power quality of the island microgrid. The invention combines the functions of HPMU pulse per second and synchronous phasor measurement to synchronously control each parallel VSG 10 quickly follow load changes in real time. and accurately distribute power according to the ratio of rated capacity.

BRIEF DESCRIPTION OF THE DRAWINGS 10013] FIG. | is a schematic diagram of an improved VSG microgrid island operation 4

BL-5180 LU102320 control diagram for the control strategy of improving virtual synchronous generator of microgrid inverter of the invention.

[0014] FIG. 2 is a schematic diagram of an improved VSG active link control diagram for the control strategy of improving virtual synchronous generator of microgrid inverter of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[6015] The control strategy of improving virtual synchronous generator of microgrid inverter of the invention will be further described in detail hereinalier with reference 10 the drawings.

[0016] With reference to FIG. 1-2. a control strategy of improving virtual synchronous generator of microgrid inverter. comprising a VSG (Virtual Synchronous Generator) island parallel control strategy and a VSG active tink control strategy, wherein it mainly refers to the synchronous control of each VSG based on the calculation of uPMU (Phase Mcasurement Unit) pulse per second to generate a uniform rotation phase angle in the microgrid. and measuring the output voltage phase angle and PCC (Point of Common Coupling) phase angle of cach VSG through pPMU and calculating the difference and feed it back to cach VSG. and combining the rated capacity ratio of each VSG to accurately distribute the output power.

[0017] Preferably. the VSG island parallel control strategy comprises two VSGs and a load: all VSGs and loads are connected to a same PCC: in the island mode. the VSG controls the active power by adjusting the phase angle difference between the output voltage and the voltage at the PCC point: take one as an example. measure the output voltage phase angle 6, and the PCC voltage phase angle ( through the pPMU device: measure the output voltage and output current. and calculate the actual output active power Py and the reactive power Qui: input the above parameters into the VSG control link to obtain the phase angle reference value Oren and the voltage amplitude reference value Un. which are calculated through the following formula: Cen = Ui COS Ge Uo = Ur SIN On 3

BL.-5180 LU102320 10018] to obtain the reference values Ugren and Ugsen of the voltage in the dg coordinate; then pass the voltage and current controller to calculate the synchronous rotation phase angle with uPMU pulse per second to perform Park inverse transformation. and obtain the three-phase modulation waveform used by PWM (Pulse Width Modulation} . so as to complete the entire control process.

[0019] Preferably. the VSG active link control strategy inputs the difference between the active power reference value Pau and the output active power P into the first-order integration link to obtain the reference value 8 ony Of the phase angle difference between the VSGi and the PCC voltage. and adds & and the PCC voltage phase angle 8, to obtain the phase angle reference value Brent at the same time. 8 en 18 compared with the différence 8.5 between the actual VSGi output voltage phase angle 0, and the PCC voltage phase angle 0. to enable that after negative feedback . the values of dun and 8 ers tend to be consistent: at this time. VSGi outputs active power according to the rated capacity ratio thereof. and the active link control equation thereof is as follows: Jw _p wD (Se = 6) d 7 fe p A Gein 7 Oa Bree = 0) +d

[0020] according to the above formula. by using the VSG controlled by active-phase angle. the phase angle reference value can be directly obtained. and the integration link from frequency to phase angle is reduced on the premise of retaining damping and inertia. and frequency is no longer used as the amount of droop. which avoids frequency fluctuations when the load changes suddenly: the fixed frequency rotating phase angle generated by the uPMU pulse per second signal is used 10 synchronously control the parallel VSGs. and the synchronous phasor measurement function is used to feed the phase angle to the control link in reat time 10 ensure that each VSG always accurately distributes power according to the design capacity ratio.

[0021] The invention and the embodiments thereof have been described hereinabove. and the description is not restrictive. What is shown in the drawings is only one of the embodiments 6

BI.-5180

LU102320 of the invention. and the actual structure is not limited thereto.

All in all, structural modes and embodiments similar to the technical solutions without departing from the inventive purpose of the invention made by those of ordinary skill in the art without creative efforts shall all fall within the protection scope of the invention.

Claims

BL-5180 LU102320 Claims

1. A control strategy of improving virtual synchronous generator of microgrid inverter. comprising a VSG (Virtual Synchronous Generator) istand parallel control strategy and a VSG active link control strategy. wherein it mainly refers to the synchronous control of each VSG based on the calculation of pPMU (Phase Measurement Unit) pulse per second to gencrate a uniform rotation phase angle in the microgrid, and measuring the output voltage phase angle and PCC (Point of Common Coupling) phase angle of each VSG through pPMU and calculating the difference and feed it back to each VSG. and combining the rated capacity ratio of each VSG to accurately distribute the output power.

2. The control strategy of improving virtual synchronous generator of microgrid inverter according to claim |. wherein the VSG island parallel control strategy comprises two VSGs and a load: all VSGs and loads are connected lo a same PCC: in the island mode. the VSG controls the active power by adjusting the phase angle difference between the output voltage and the voltage at the PCC point: take one as an example. measure the output voltage phase angle 0; and the PCC voltage phase angle 0, through the (PMU device; measure the output voltage and output current. and calculate the actual output active power Pay and the reactive power Q.1: input the above parameters into the VSG control link to obtain the phase angle reference value Ben and the voltage amplitude reference value Ur. which are calculated through the following formula: Lun = Up COS Org U ets = UC sin Or to obtain the reference values Ugen and Uyen of the voltage in the dq coordinate: then pass the voltage and current controller to calculate the synchronous rotation phase angle with uPMU pulse per second to perform Park inverse transformation. and obtain the three-phase modulation waveform used by PWM (Pulse Width Modulation) . so as to complete the entire control process,

[31-5180 LU102320

3. The control strategy of improving virtual synchronous generator of microgrid inverter according to claim !. wherein the VSG active link control strategy inputs the difference between the active power reference value Pa and the output active power Pg into the first-order integration link to obtain the reference value 8 ren Of the phase angle difference between the VSGi and the PCC voltage. and adds S'en and the PCC voltage phase angle 6, to obtain the phase angle reference value On: at the same time. 8 eri is compared with the difference ôren between the actual VSGi output voltage phase angie 0; and the PCC voltage phase angle 6,. to enable that after negative feedback | the values of 8, and Sen tend to be consistent: at this time. VSGi outputs active power according to the rated capacity ratio thereof. and the active link control equation thereof is as follows: J La =P =D (On Sr) 6, = 0 +65 bv using the VSG controlled by active-phase angle. the phase angle reference value can be directly obtained. and the integration link from frequency te phase angle is reduced on the premise of retaining damping and inertia. and frequency is no longer used as the amount of droop. which avoids frequency fluctuations when the load changes suddenly: the fixed frequency rotating phase angle generated by the uPMU pulse per second signal is used to synchronously control the parallel VSGs. and the synchronous phasor measurement function is used to feed the phase angle to the control link in real time to ensure that each VSG always accurately distributes power according to the design capacity ratio.