Microgrid system multi-machine parallel control method

Abstract

The invention discloses a multi-machine parallel control method for a micro-grid system, and the method comprises the steps: setting one of a plurality of PCSs without communication interconnection as a master PCS, setting the other PCSs as slave PCSs, and carrying out the start-stop control of the PCSs only through switching value IO ports; the main PCS operates in an improved PQ droop mode, and a micro-grid system can be established only by giving Uref and fref; the slave PCS also operates in the improved Pq droop mode, and in the off-network mode, the output of the slave PCS needs to be pre-synchronized at an angle omega before converging with the output of the master PCS; after the micro-grid of the master PCS is established, outputting a switching value Do to the slave PCS, after the slave PCS receives the Do of the master PCS, carrying out grid-connected operation, and after the operation is completed, feeding back a switching value Di to the master PCS; the rear stage of the energy storage converter PCS outputs u'd and u'q after being decoupled by a loop; and u 'alpha and u' beta are obtained after inverse PARK coordinate transformation and are sent to a PWM module control unit, and finally a power module is driven. The system stability can be improved, the load dynamic requirement is met, and the energy diversification development requirement is met.

Description

Technical Field

[0001] The present invention relates to the technical field of microgrid system control methods, and in particular to a microgrid system multi-machine parallel control method. Background Art

[0002] In order to meet the requirements of diversified energy development, the battery energy storage system needs to be able to supply power to the load in the microgrid when it is in an isolated operation state, and as the load of the microgrid increases, a control method for multiple energy storage systems to operate in parallel is required. When multiple energy storage systems are connected in parallel, the main control methods include master-slave control, droop control, and virtual synchronous machine (VSG) control. Master-slave control relies on system power distribution and high-speed interconnection and communication between each other. When the current grid is abnormal and the microgrid has not been established in the entire control system, the matching EMS dispatch has not been established. The entire control system cannot adapt to the unstable load power conditions. In addition, master-slave control also brings challenges to the communication rate and anti-interference ability of the system. Droop control provides voltage and frequency support for the microgrid through active frequency modulation and reactive amplitude modulation. There are serious limitations in the reactive power aspect in the multi-machine parallel system, which is mainly caused by feeder impedance mismatch and energy storage PCS parameter differences. Virtual synchronous machine (VSG) control simulates the motion equations of the stator and rotor of the synchronous machine, provides inertia for the parallel system on the basis of droop control, and improves the stability of the microgrid frequency. The premise is to establish an accurate mathematical model.

[0003] Therefore, it can be seen that the existing technology has the following deficiencies:

[0004] 1. The master-slave control relies on the communication between the master and slave PCS, and the system has weak anti-interference ability;

[0005] 2. Traditional droop control is based on system power distribution and cannot adapt to abnormalities in the previous power grid and unstable load conditions;

[0006] 3. The droop control strategy can only achieve differential regulation and cannot adjust the voltage amplitude and frequency of the multi-machine parallel system in real time;

[0007] 4. Droop control is subject to hardware parameter consistency and line impedance uncertainty, resulting in uneven power distribution and unstable system operation;

[0008] 5. The control of virtual synchronous machine (VSG) is relatively complex and depends on the moment of inertia J and damping D, and it is difficult to determine the exact parameters. Summary of the invention

[0009] The technical problem to be solved by the present invention is to provide a multi-machine parallel control method for a microgrid system, which can improve system stability, adapt to load dynamic requirements and meet the requirements of energy diversification development.

[0010] In order to solve the above technical problems, the present invention provides a multi-machine parallel control method for a microgrid system, including multiple energy storage converters PCS without communication interconnection, and the steps are as follows: S1: using one PCS as the main PCS and the other PCSs as slave PCSs, and only relying on the switch quantity IO port to transmit information between each other; S2: the main PCS operates in the PQ droop mode of the modified machine. Due to the uncertain load and no power given, as long as the given U ref and f ref , first establish the microgrid system; S3: In addition to controlling its own main disconnect switch S1, the main PCS also controls the system's microgrid master switch Sa; S4: The slave PCS controls its own main disconnect switch Sn; S5: The slave PCS also operates in the Pq droop mode, and before merging with the main PCS, it must perform angle ω pre-synchronization, and after the pre-synchronization is completed, the slave PCS main disconnect switch is closed; S6: After the main PCS microgrid is established, the switch value Do is output to the slave PCS. After the slave PCS receives the Do from the main PCS, it performs grid-connected operation. After the operation is completed, the switch value Di is fed back to the main PCS; S7: The front stage of the energy storage converter PCS operates in the improved PQ droop control mode. The droop control is based on the amplitude and p frequency of the microgrid voltage to achieve active frequency modulation and reactive amplitude modulation functions; S8: The rear stage of the energy storage converter PCS adopts a dual-loop control mode with the outer loop as the voltage loop and the inner loop as the current loop. After loop decoupling, the output u' d 、u' q ; S9: dual loop output u' d 、u' q After inverse PARK coordinate transformation, we get u' α 、u' β It is sent to the PWM module control unit and finally drives the power module.

[0011] Furthermore, the main PCS is equipped with a dedicated Vf regulator, which can achieve precise control of the amplitude and phase of the microgrid system. The control steps are as follows:

[0012] (1) The main PCS controls the voltage V at the PCC pcc Perform phase-locking processing to obtain V pcc The voltage amplitude Ud_ref and frequency F_fed at;

[0013] (2) The set voltage Uset and the feedback voltage amplitude Ud_ref are used as the reference and feedback of the voltage regulator, and the output voltage Uref is adjusted by the PI regulator;

[0014] (3) The set frequency Fset and the feedback voltage frequency F_fed are used as the reference and feedback of the frequency regulator, and the output frequency Fref is adjusted by the PI regulator;

[0015] (4) Send Uref and Fref to the droop control loop of the main PCS.

[0016] Further, the pre-synchronization step in step S5 is as follows:

[0017] (1) After receiving the Do signal from the master PCS, the slave PCS starts to enter the droop mode. At this time, the master disconnect switch of the slave PCS is disconnected;

[0018] (2) Voltage signal V from PCS to main circuit breaker Sa pcc Perform phase locking processing to obtain the phase locking angle θ pll ;

[0019] (3) From the PCS phase-locking angle θ pll Angle θ with self-wave ref After the PI regulator, the output adjusts the angular frequency Δω and adds it to ω ref ;

[0020] (4) When θ pll With θ ref If the angle difference is within the set threshold, it means that pre-synchronization is completed, and the main disconnect switch of the slave PCS is closed.

[0021] Further, the total load power of the entire system does not exceed the total output power of the master PCS and the slave PCS.

[0022] Furthermore, each PCS control system includes an AD sampling unit, a power calculation unit, an improved droop control unit, a voltage loop and current loop dual loop control unit, and a PWM wave generating unit.

[0023] Beneficial effects of the present invention:

[0024] 1. There is no communication connection in microgrid mode, which solves the communication interference problem of multi-machine master-slave control and improves system stability;

[0025] 2. In the absence of a given power, the output power changes with the load to adapt to the dynamic requirements of the load;

[0026] 3. Solve the problem of uneven active / reactive power distribution when multiple machines are connected in parallel in microgrid mode, so that the system can operate stably;

[0027] 4. Improve the output voltage amplitude / frequency control accuracy of multiple machines in microgrid mode to meet the requirements of diversified energy development. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the connection of a multi-machine parallel microgrid of the present invention (two connection modes of grid-connected switches: parallel and series).

[0029] Figure 2 It is the overall control block diagram of multiple machines in parallel of the present invention.

[0030] Figure 3 The improved droop control strategy diagram of the present invention is

[0031] Figure 4 It is a schematic diagram of the main PCS dedicated Vf regulator of the present invention.

[0032] Figure 5 It is a dual-loop control block diagram of the present invention.

[0033] Figure 6 It is a schematic diagram of simulation of active and reactive power equalization of two PCS microgrid systems of the present invention.

[0034] Figure 7 It is a schematic diagram of the actual measured power sharing situation of three PCS microgrids of the present invention. DETAILED DESCRIPTION

[0035] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments so that those skilled in the art can better understand the present invention and implement it, but the embodiments are not intended to limit the present invention.

[0036] Reference Figures 1 to 7 As shown, an embodiment of a microgrid system multi-machine parallel control method of the present invention includes multiple energy storage converters PCS without communication interconnection, and the steps are as follows:

[0037] S1: Use one PCS as the master PCS and the rest as slave PCSs, and only use the switch IO ports to transmit information between them;

[0038] S2: The main PCS runs in the PQ droop mode of the modified machine. Due to the uncertain load, there is no power given. As long as U ref and f ref , first establish the microgrid system;

[0039] S3: In addition to controlling its own main disconnect switch S1, the main PCS also controls the system's microgrid master switch Sa;

[0040] S4: Control the respective main disconnect switches from PCS, such as S2 from PCS2, S3 from PCS3, and Sn from PCSn;

[0041] S5: The slave PCS also operates in the Pq droop mode. It needs to perform angle ω pre-synchronization before merging with the master PCS. After the pre-synchronization is completed, the slave PCS main disconnect switch is closed.

[0042] S6: After the master PCS microgrid is established, it outputs the switch value Do to the slave PCS. After the slave PCS receives the Do from the master PCS, it performs the grid connection operation. After the operation is completed, it feeds back the switch value Di to the master PCS.

[0043] S7: The PCS front stage of the energy storage converter operates in an improved PQ droop control mode. The droop control is based on the amplitude and frequency of the microgrid voltage to achieve active frequency modulation and reactive amplitude modulation functions;

[0044] S8: The PCS back stage of the energy storage converter adopts a dual-loop control mode with the outer loop as the voltage loop and the inner loop as the current loop. After loop decoupling, the output u' d 、u' q ;

[0045] S9: Dual loop output u' d 、u' q After the inverse PARK coordinate transformation, it is sent to the PWM module control unit and finally drives the power module.

[0046] It also includes a fault handling part. When one of the slave PCSs fails, it informs the master PCS through Di feedback; when the master PCS fails, the master PCS informs the slave PCS through Do; Sa controls the on-grid switch, and S_load controls the load switch.

[0047] The specific instructions are as follows:

[0048] The schematic diagram of multi-machine parallel connection in microgrid system is as follows: Figure 1 As shown, Sa controls the on-grid switch and S_load controls the load switch. PCS1 is set as the master and the other PCSs are slaves. The master and slaves are started and stopped and faults are handled only through the switch IO port. When the master PCS microgrid is established, the slave PCS is informed through the output switch Do. At this time, the slave PCS receives the master PCS signal and performs pre-synchronization processing. After the processing is completed, it is connected to the microgrid system through the main breaker Sn. The master PCS collects the front-stage voltage signal V of the main circuit breaker Sa on the grid side. p ' cc , other slave PCS collects the voltage signal after the main circuit breaker Sa, and the main PCS collects the voltage V p ' cc Confirm whether the system is in grid-connected or microgrid state, and collect V pcc It is used for pre-synchronization processing and is then integrated into the microgrid system. AC ELECTRONICLOAD is the system load and is connected to the rear end of the main disconnect switch Sa. The following are the specific steps for implementing this solution:

[0049] 1. The main PCS first establishes a microgrid and adopts a PQ-based droop control strategy, such as Figure 3 As shown, by collecting the PCS output voltage u o and the output current i o , after the relevant coordinate transformation, we get U od , U oq ,i od ,ioq ;

[0050] 2. According to the formula p = 1.5 (U od i od +U oq i oq ),q=1.5(U oq i od -U od i oq ) Calculate the instantaneous active power and reactive power of the system and perform a second-order low-pass filter (Lpf) on them;

[0051] 3. The filtered active power P is passed through the controller f=f ref -mP, get the normalized angular frequency f pu , we calculate ω=2πf pu After that, the angle θ is obtained by integrating ω ref ; Reactive power Q through U = U ref -nQ, get the normalized voltage amplitude U;

[0052] 4. From the voltage amplitude U and θ ref The three-phase voltage u can be calculated aref =U∠θ ref 、u bref =U∠(θ ref -2 / 3π)、u bref =U∠(θ ref +2 / 3π);

[0053] 5. After coordinate transformation of the three-phase voltage, the voltage u is obtained dref 、u qref , through dual-loop control with the outer loop being the voltage loop and the inner loop being the current loop, such as Figure 5 As shown, the specific steps are as follows:

[0054] a. Set the voltage u dref It is sent to the voltage loop and after PI regulation, the active current given i' is obtained d =(u dref -u d )(K p +K i / s)-u q ωC, -u q ωC is the coupling term;

[0055] b. Set the voltage u qref It is sent to the voltage loop and after PI regulation, the reactive current given i' is obtained q =(u qref -u q )(K p +K i / s)+u d ωC,u d ωC is the coupling term;

[0056] c. Set the current i' d It is sent into the current loop and the voltage u' is obtained after PI regulation d =u d +(i' d -i d )(K p +K i / s)-i q ωL, -i q ωL is the coupling term, u d It is voltage feed forward;

[0057] d. The current i' q It is sent into the current loop and the voltage u' is obtained after PI regulation q =u q +(i' q -i q )(K p +K i / s)+i d ωL,i d ωL is the coupling term, u q It is voltage feed forward;

[0058] 6. For u' d 、u' q After inverse PARK coordinate transformation, we get u' α 、u' β It is sent to the PWM module control unit and finally drives the power module;

[0059] 7. The slave performs the same operation as the master, except that it needs to be pre-synchronized before being incorporated into the microgrid system. The specific steps are as follows:

[0060] a. After the slave receives the Do signal from the master, it starts the PCS and enters the droop mode. At this time, the slave master disconnect switch S2 (other slaves are numbered in sequence) is disconnected;

[0061] b. Figure 3 As shown, the voltage signal V after the slave to the main circuit breaker Sa pcc Perform phase locking processing to obtain the phase locking angle θ pll ;

[0062] c. Slave phase lock angle θ pll Angle θ with self-wave ref After the PI regulator, the output adjusts the angular frequency Δω and adds it to ω ref ;

[0063] d. When θ pllWith θ ref If the angle difference is within the set threshold, it means that pre-synchronization is completed, and the slave master disconnect switch S2 is closed (other slaves are numbered in sequence);

[0064] 8. Since the droop control is a differential adjustment, if no special treatment is performed, the voltage amplitude and frequency output by the microgrid system will not achieve the expected effect. A Vf controller is added to the main PCS. The specific steps are as follows;

[0065] a. Figure 4 As shown, the main PCS controls the voltage V at the PCC pcc Perform phase-locking processing to obtain V pcc The voltage amplitude Ud_ref and frequency F_fed at;

[0066] b. The set voltage Uset and the feedback voltage amplitude Ud_ref are used as the reference and feedback of the voltage regulator, and the output voltage Uref is adjusted by the PI regulator;

[0067] c. The set frequency Fset and the feedback voltage frequency F_fed are used as the given and feedback of the frequency regulator, and the output frequency Fref is adjusted by the PI regulator;

[0068] d. Send Uref and Fref to the droop control loop of the main PCS (such as Figure 5 shown);

[0069] 9. Figure 6 The simulation waveform of two 100KW-PCS microgrid systems in parallel is shown below. Figure 7 The power waveform of a microgrid multi-machine parallel system (three 100KW-PCS) was measured. From the simulation and measured results, the feasibility of the control method of the microgrid system was verified;

[0070] 10. Figure 2 This is the overall control block diagram of PCS. The system mainly includes AD sampling unit, power calculation unit, improved droop control unit: droop control implementation, voltage loop + current loop dual loop control unit and PWM wave generating unit.

[0071] The above-described embodiments are only preferred embodiments for fully illustrating the present invention, and the protection scope of the present invention is not limited thereto. Equivalent substitutions or changes made by those skilled in the art based on the present invention are within the protection scope of the present invention. The protection scope of the present invention shall be subject to the claims.

Claims

1. A multi-machine parallel control method for a microgrid system, characterized in that: Including multiple energy storage converter PCSs without communication interconnection, the steps are as follows: S1: Use one PCS as the master PCS and the rest as slave PCSs, and only rely on the switch IO port to start and stop each other; S2: The main PCS operates in the improved PQ droop mode. Since the load is uncertain, no power setting is required. As long as U ref and f ref , a microgrid system can be established; S3: In addition to controlling its own main disconnect switch S1, the main PCS also controls the system's microgrid master switch Sa; S4: Control the respective main disconnect switches Sn from the PCS; S5: The slave PCS also operates in the Pq droop mode. It needs to perform angle ω pre-synchronization before merging with the master PCS. After the pre-synchronization is completed, the slave PCS main disconnect switch is closed. S6: After the master PCS microgrid is established, it outputs the switch value Do to the slave PCS. After the slave PCS receives the Do from the master PCS, it performs the grid connection operation. After the operation is completed, it feeds back the switch value Di to the master PCS. S7: The PCS front stage of the energy storage converter operates in an improved PQ droop control mode. The droop control is based on the amplitude and frequency of the given microgrid voltage to achieve active frequency modulation and reactive amplitude modulation functions; S8: The PCS back stage of the energy storage converter adopts a dual-loop control mode with the outer loop as the voltage loop and the inner loop as the current loop. After decoupling, the output u' d 、u' q ; S9: Dual-loop output u' d 、u' q After inverse PARK coordinate transformation, we get u' α 、u' β It is sent to the PWM module control unit and finally drives the power module.

2. The microgrid system multi-machine parallel control method according to claim 1, characterized in that: The main PCS is equipped with a dedicated Vf regulator, which can achieve precise control of the amplitude and frequency of the microgrid system. The control steps are as follows: (1) The main PCS controls the voltage V at the PCC pcc Perform phase-locking processing to obtain V pcc The voltage amplitude Ud_ref and frequency F_fed at; (2) The set voltage Uset and the feedback voltage amplitude Ud_ref are used as the reference and feedback of the voltage regulator, and the output voltage Uref is adjusted by the PI regulator; (3) The set frequency Fset and the feedback voltage frequency F_fed are used as the reference and feedback of the frequency regulator, and the output frequency Fref is adjusted by the PI regulator; (4) Send Uref and Fref to the droop control loop of the main PCS.

3. The microgrid system multi-machine parallel control method according to claim 1, characterized in that: The pre-synchronization step in step S5 is as follows: (1) After receiving the Do signal from the master PCS, the slave PCS starts to enter the droop mode. At this time, the master disconnect switch of the slave PCS is disconnected; (2) Voltage signal V from PCS to main circuit breaker Sa pcc Perform phase locking processing to obtain the phase locking angle θ pll ; (3) From the PCS phase locking angle θ pll Angle θ with self-wave ref After the PI regulator, the output adjusts the angular frequency Δω and adds it to ω ref ; (4) When θ pll With θ ref If the angle difference is within the set threshold, it means that pre-synchronization is completed, and the main disconnect switch of the slave PCS is closed.

4. The microgrid system multi-machine parallel control method according to claim 1, characterized in that: The total load power of the entire system shall not exceed the total output power of the master PCS and the slave PCS.

5. The microgrid system multi-machine parallel control method according to claim 1, characterized in that: Each PCS control system includes an AD sampling unit, a power calculation unit, an improved droop control unit, a voltage loop and current loop dual loop control unit and a PWM wave generating unit.

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