Multi-machine synchronous black-start control method for light-storage hybrid control system

Abstract

The application discloses a multi-machine synchronous black-start control method of a light storage hybrid control system, the light storage hybrid control system comprising an energy storage system adopting network construction type control and a photovoltaic power generation system adopting network following type control, the photovoltaic power generation system being connected to a grid through a phase-locked loop; wherein the multi-machine synchronous black-start control method comprises a step of analyzing the stability of multi-machine synchronous black-start; the stability analysis comprises dynamic stability analysis of the phase-locked loop in the black-start process and steady-state stability analysis of the phase-locked loop after the black-start is completed; wherein the active power outputted by the photovoltaic power generation system in the black-start process satisfies at a time t0 (0≤t0≤T s ) and the active power outputted by the photovoltaic power generation system after the black-start is completed, the light storage hybrid control system can be stable to complete the synchronous black-start. The application has the advantages of shortening the starting time and providing greater starting capacity.

Description

Technical Field

[0001] This invention relates to the field of microgrids, and more specifically to a multi-machine synchronous black-start control method for a photovoltaic-storage hybrid control system. Background Technology

[0002] With rapid economic development, the demand for electricity has increased dramatically. Traditional thermal power generation suffers from drawbacks such as high pollution and high cost. Distributed power generation, on the other hand, has gradually attracted widespread attention from scholars due to its advantages such as renewability and low pollution. Developing and utilizing distributed power sources to form microgrids for power supply, based on local geographical and resource conditions, is an important direction for the future utilization of distributed power sources.

[0003] A microgrid is a small power system composed of distributed power sources, energy storage systems, loads, power electronic converters, etc., and it has two operating modes: grid-connected operation and islanded operation. When operating in grid-connected mode, a microgrid can switch to islanded operation when the main grid experiences faults or poor power quality. When operating in islanded mode, a microgrid may experience power outages due to certain faults; to improve the reliability of the system's power supply, the microgrid should have black-start capability in islanded operation to quickly restore power supply to the loads.

[0004] Microgrid black start refers to the process by which a microgrid, after being shut down due to an external or internal fault and entering a completely dark state, restarts the entire microgrid without the assistance of the main grid or other microgrids. This is achieved by activating micro-sources within the microgrid that have black start capabilities, thereby enabling micro-sources without black start capabilities to gradually expand the recovery scope of the system and ultimately restart the entire microgrid.

[0005] Currently, existing research on microgrid black start technology focuses on asynchronous black start, such as... Figure 1 The asynchronous black-start two-unit system shown in the diagram starts the photovoltaic power generation system after the lithium battery energy storage system has fully started, reached its rated voltage, and provided stable frequency support. However, with asynchronous black-start, the black-start time is very long when there are many devices, which is not conducive to the recovery of subsequent loads and will have a significant impact on production and daily life. In addition, if it is a load-bearing black-start, if the energy storage capacity is insufficient to support the local load, the black-start will fail. Summary of the Invention

[0006] To at least partially address the shortcomings of the prior art, the main objective of this invention is to provide a multi-machine synchronous black-start control method for a photovoltaic-storage hybrid control system, which can shorten the start-up time and provide a larger start-up capacity.

[0007] In order to achieve the above-mentioned main purpose, the application discloses a multi-machine synchronous black start control method of a light storage hybrid control system, the light storage hybrid control system comprising an energy storage system adopting network-constructing type control and a photovoltaic power generation system adopting network-following type control, the photovoltaic power generation system being connected to the grid through a phase-locked loop; wherein the multi-machine synchronous black start control method comprises a step of analyzing the stability of multi-machine synchronous black start;

[0008] The stability analysis comprises:

[0009] Dynamic stability analysis of the phase-locked loop in the black start process;

[0010] And steady-state stability analysis of the phase-locked loop after the black start is completed;

[0011] Wherein, during the black start process, the photovoltaic power generation system sends active power that satisfies o ≤T s ) and And after the black start is completed, the photovoltaic power generation system sends active power , the light storage hybrid control system can be stable to complete the synchronous black start;

[0012] Wherein, P PV =3V VSG ·I PV , P PV is the active power instantaneous value output by the photovoltaic power generation system during the voltage rise process, V VSG is the effective value of the output phase voltage of the energy storage system during the voltage rise process, I PV is the effective value of the output current of the photovoltaic power generation system, the phase of the output current is from the output of the phase-locked loop, z line is the line impedance; P PVN =3U N ·I PVN , U N is the rated voltage of the photovoltaic power generation system, and I PVN is the rated output current of the photovoltaic power generation system.

[0013] According to a specific embodiment of the application, the network-constructing type energy storage system has voltage support and active inertia characteristics through virtual synchronous generator control and has the ability to run under load without external grid support, and externally behaves as a voltage source; the network-following type photovoltaic power generation system injects or absorbs active and reactive power by tracking the voltage amplitude and angle of the energy storage, and externally behaves as a current source; wherein when the microgrid enters a full black state, the network-constructing type energy storage system is started through virtual synchronous generator control to provide voltage and frequency support, thereby driving the synchronous start of the network-following type photovoltaic power generation system, to control the multi-machine synchronous black start.

[0014] According to an embodiment of the present application, the light storage hybrid control system further comprises a line module, a filter inductor and a load module, wherein the energy storage system directly supplies power to the load module through the line module, the output voltage of the photovoltaic power generation system is converted into alternating current and then supplied to the load module after being processed by the filter inductor; the phase-locked loop collects the grid point voltage and outputs angle information, and generates a PWM driving signal through closed-loop control of the inductor current.

[0015] According to an embodiment of the present application, the energy storage system comprises an electromotive force generation layer, a virtual impedance control layer, a voltage-current double closed-loop control layer, a d-q inverse transformer and a PWM modulator; wherein the electromotive force generation layer is used to generate the potential amplitude E and phase θ of the virtual synchronous generator, the electromotive force E ∠ θ generated thereby is processed by the virtual impedance control layer to obtain an output voltage, the output voltage is processed by the voltage-current double closed-loop control layer and the d-q inverse transformer to obtain an inverter output voltage modulation wave, and then the PWM modulator is used to generate a driving signal for the inverter.

[0016] According to an embodiment of the present application, the energy storage system is provided with a zero-rise voltage boosting module for suppressing the magnetizing inrush current of the distribution transformer in the microgrid during the black start of the micro source, wherein the zero-rise voltage boosting control of the electromotive force amplitude is set in the following manner:

[0017]

[0018] wherein E o is the voltage amplitude when the virtual synchronous generator is in no-load state; k is the slope of the increase of the output electromotive force amplitude with time, k = E0 / T s ; T s is the time required for the output electromotive force amplitude to increase from 0 to E o .

[0019] According to an embodiment of the present application, during the black start of the microgrid, the energy storage system establishes a voltage reference by using the zero-rise voltage boosting module, generates an energy storage output active power reference value through primary frequency regulation and secondary frequency regulation, eliminates the frequency difference through an integral element, and then generates the phase of the electromotive force of the virtual synchronous generator through a rotor motion equation.

[0020] According to an embodiment of the present application, the primary frequency regulation is a differential frequency regulation, which can be realized through a proportional element; the secondary frequency regulation is a non-differential frequency regulation, which eliminates the frequency difference through an integral element.

[0021] According to an embodiment of the present application, the photovoltaic power generation system realizes the frequency regulation function through a PI regulator, and then generates a current instruction through a power ring to realize the closed-loop control of the inductor current.

[0022] According to one specific embodiment of the present application, the phase-locked loop transforms the voltage from a three-phase stationary coordinate system to a synchronous rotating dq coordinate system through d-q transformation to obtain the transformed voltage V q = V m sin(θ-θ'), wherein V m is a grid-connected point voltage amplitude, θ is an actual voltage angle, and θ' is an output estimation angle of the phase-locked loop;

[0023] Through PI regulation control, V q is 0, i.e., the output estimation angle θ' of the phase-locked loop is equal to the actual angle θ of the load voltage, so as to realize phase locking.

[0024] According to one specific embodiment of the present application, the photovoltaic power generation system is equivalent to a current source and an equivalent circuit is obtained, and the load voltage can be obtained from the superposition theorem as follows:

[0025]

[0026] wherein,

[0027] The present application has the following advantages: a multi-machine synchronous black start control method for a light storage hybrid control system is provided, and compared with asynchronous black start, the present application mainly has the following advantages: 1) the starting time is accelerated, the energy storage system and the photovoltaic power generation system are started at the same time, which can greatly shorten the black start time and accelerate the load recovery; and 2) a larger starting capacity is provided, and the situation that the black start fails due to the fact that the energy storage cannot provide sufficient power under full load or heavy load when starting under load is avoided.

[0028] In order to more clearly illustrate the purpose, technical scheme and advantages of the present application, the present application will be further described in detail below with reference to the drawings and specific embodiments. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is a schematic diagram of a prior art asynchronous black start two-machine system;

[0030] Figure 2 is a topology diagram of the light storage hybrid control system of the present application;

[0031] Figure 3 is a framework diagram of the grid-forming energy storage control;

[0032] Figure 4 is a framework diagram of the active power control of the grid-forming energy storage;

[0033] Figure 5 is a framework diagram of the grid-following photovoltaic control;

[0034] Figure 6 is a framework diagram of the phase-locked loop control;

[0035] Figure 7 is a linearized model diagram of a phase-locked loop control structure;

[0036] Figure 8 is an equivalent circuit diagram of a photovoltaic power generation system;

[0037] Figure 9 is a synchronous stability analysis model diagram of a light-storage hybrid control system;

[0038] Figure 10 is a waveform diagram of an output voltage of an energy storage system;

[0039] Figure 11 is a frequency waveform diagram of an output voltage of an energy storage system;

[0040] Figure 12 is a waveform diagram of an output power of an energy storage system;

[0041] Figure 13 is a waveform diagram of an output power of a photovoltaic power generation system. DETAILED DESCRIPTION

[0042] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. It will be apparent, however, to one skilled in the art that the following embodiments and details can be practiced without limitation to the specific details set forth.

[0043] The embodiment of the present application provides a multi-machine synchronous black start control method of a light-storage hybrid control system, wherein the light-storage hybrid control system is a multi-machine system, and the following is specifically described by taking that the light-storage hybrid control system specifically comprises an energy storage system adopting network-constructing type control and a photovoltaic power generation system adopting network-following type control, and the photovoltaic power generation system is connected to a power grid through a phase-locked loop for grid-connected operation.

[0044] The energy storage system adopts network-constructing type control, specifically adopts virtual synchronous generator control and has voltage support and active inertia characteristics, has the ability of load operation without external power grid support, does not need a phase-locked loop, and externally behaves as a voltage source; the photovoltaic power generation system adopts network-following type control, depends on grid voltage, and must be connected to the power grid through a phase-locked loop for grid-connected operation, injects or absorbs active and reactive power by tracking the voltage amplitude and angle of the energy storage, and externally behaves as a current source. In the embodiment, when the microgrid enters a full black state, the network-constructing type energy storage system is started through virtual synchronous generator control to provide voltage and frequency support, and then drives the synchronous start of the network-following type photovoltaic, that is, the network-constructing type energy storage system and the network-following type photovoltaic power generation system are started at the same time, and finally the multi-machine synchronous black start control is realized.

[0045] The light storage hybrid control system further comprises a line module, a filter inductor and a load module, wherein the energy storage system directly supplies power to the load module through the line module, the output voltage of the photovoltaic power generation system outputs alternating current after inversion and supplies power to the load module after being processed by the filter inductor; the phase-locked loop (PLL) collects the grid point voltage and outputs angle information, and a PWM driving signal is generated through closed-loop control of the inductor current.

[0046] The topology diagram of the light storage hybrid control system is shown in Figure 2 ; wherein the energy storage system controlled by the virtual synchronous generator has stable output voltage and frequency, so that the alternating voltage source V VSG (θ1) can be used instead (wherein θ1 is the voltage source phase), and the energy storage system supplies power to the load z line through the line z L . The core of the embodiment is mainly the grid-connected operation of the photovoltaic power generation system, so the photovoltaic direct current side is equivalent to a direct current voltage source to simplify the analysis. The direct current voltage source U PV outputs alternating current i abc after inversion, and supplies power to the load z L through the filter inductor L f ; the PLL collects the grid point voltage V L and outputs angle information θ2, and a PWM driving signal is generated through closed-loop control of the inductor current.

[0047] The energy storage system comprises an electromotive force generation layer, a virtual impedance control layer, a voltage and current double closed-loop control layer, a d-q inverse transformer and a PWM modulator; wherein the electromotive force generation layer is used to generate the potential amplitude E and phase θ of the virtual synchronous generator, the generated electromotive force E∠θ is processed by the virtual impedance control layer to obtain the output voltage, the output voltage is processed by the voltage and current double closed-loop control layer and the d-q inverse transformer to obtain the inverter output voltage modulation wave, and then the PWM modulator is used to drive the inverter signal. Specifically, the grid-connected energy storage control structure is shown in Figure 3 , the purpose of the electromotive force generation layer is to generate the potential amplitude E and phase θ of the virtual synchronous generator, the generated electromotive force E∠θ is processed by the virtual impedance control to obtain the output voltage u oabc , and then the PWM modulator is used to drive the inverter signal after the inverter output voltage modulation wave is obtained through the voltage and current double closed-loop control and the d-q inverse transformation.

[0048] Further, the energy storage system is provided with a zero-rise voltage boosting module for inhibiting the excitation inrush current of the distribution transformer in the microgrid during the black start of the micro source, and the zero-rise voltage boosting module enables the energy storage system to have a zero-rise voltage boosting function; wherein the zero-rise voltage boosting control of the electromotive force amplitude is set in the following manner:

[0049]

[0050] wherein E o is the voltage amplitude of the virtual synchronous generator at no-load; k is the slope of the increase of the output potential amplitude with time, k = E0 / T s ; T s is the time required for the increase of the output potential amplitude from 0 to E o . In particular, to ensure the rapidity of the energy storage start-up and the unsaturation of the transformer magnetic flux at any time, the output potential amplitude rise time T s should generally be greater than 38.2 ms.

[0051] During the black start of the microgrid, the energy storage system uses the zero-rise voltage module to establish a voltage reference, and specifically establishes a stable frequency reference through the active control shown in Figure 4 ; this control generates an energy storage output power reference value through primary and secondary frequency modulation, eliminates the frequency difference through an integral element, and then generates the phase of the virtual synchronous generator electromotive force through the rotor motion equation. The primary frequency modulation is differential frequency modulation, which can be achieved through a proportional element; the secondary frequency modulation is differential frequency modulation, which eliminates the frequency difference through an integral element.

[0052] The grid-connected control framework of the photovoltaic power generation system is shown in Figure 5 ; this control enables the photovoltaic power generation system to have frequency modulation function; in Figure 5 , the frequency modulation function is achieved through a PI regulator, and then the current command I ref is generated through the power loop to achieve closed-loop control of the inductor current.

[0053] Further, the multi-machine synchronous black start control method includes the step of analyzing the stability of the multi-machine synchronous black start, and the stability analysis includes dynamic stability analysis of the phase-locked loop during the black start process and steady-state stability analysis of the phase-locked loop after the completion of the black start; the specific development is as follows:

[0054] The phase-locked loop control structure is shown in Figure 6 , which mainly extracts the phase of the grid-connected point voltage V L (θ) in Figure 2 . The phase-locked loop converts the voltage V L (θ) from the three-phase static abc coordinate system to the synchronous rotating dq coordinate system through d-q transformation, obtaining V q = V m sin(θ-θ′), wherein V m is the grid-connected point voltage amplitude, θ is the actual angle of the voltage, and θ′ is the estimated angle of the phase-locked loop output. Through PI regulation control, V q is 0, i.e. the estimated angle θ′ of the phase-locked loop output is equal to the actual angle θ of the load voltage, so as to achieve phase locking.

[0055] The linearized model of this structure is shown in Figure 7As shown, PD is a phase detector, and its output is V. q .

[0056] In this embodiment, the photovoltaic power generation system is equivalent to a current source, and an equivalent circuit is obtained. The obtained equivalent circuit is as follows: Figure 8 As shown, where I PV The effective value of the output current of the photovoltaic power generation system is given, and the phase θ2 of the current comes from the output of the phase-locked loop.

[0057] The load voltage can be obtained by the superposition theorem:

[0058]

[0059] in,

[0060] In the embodiment, the phase-locked loop synchronization stability analysis model of the photovoltaic-storage hybrid control system is as follows: Figure 9 As shown, in Figure 9 middle:

[0061]

[0062]

[0063]

[0064] Therefore, the presence of the current source provides positive feedback to the phase-locked loop (PLL); to ensure the stability of the PLL, V must be guaranteed. q+ <V q- Due to the existence of the sine function, Therefore, for a phase-locked loop to be stable, the following must be satisfied:

[0065]

[0066] In this embodiment, the stability analysis of the multi-machine synchronous black start of the photovoltaic-storage hybrid control system includes dynamic stability analysis and steady-state stability analysis. Dynamic stability refers to the stability of the phase-locked loop during the black start process, while steady-state stability refers to the stability of the phase-locked loop after the black start is completed.

[0067] During black start, the output power P of the photovoltaic power generation system PV =3V VSG ·I PV , where P PV V represents the instantaneous value of the active power output by the photovoltaic power generation system during the zero-start-up voltage boost process. VSG This represents the effective value of the output phase voltage of the energy storage system during the zero-start-up voltage boost process. This applies when the hybrid photovoltaic-energy storage system meets the following conditions. At that time, the phase-locked loop can be relatively stable.

[0068] Since sin(p2) < 1, it can be approximated as...

[0069] At steady state, the output power and output current effective value of the photovoltaic power generation system are stable, and the output power and output voltage effective value of the energy storage system are stable; the photovoltaic output rated power is P PVN = 3U N ·I PVN , U N is the system rated voltage, I PVN is the photovoltaic system output rated current, and at this time, the phase-locked loop stability needs to meet

[0070] Based on the above, considering the dynamic stability condition and the steady state stability condition of the light-storage hybrid control system, it can be concluded that during the black start process, the photovoltaic power generation system outputs active power at t0(o≤t o ≤T s ) and after that, the light-storage hybrid control system can be stable to complete the synchronous black start of the light-storage hybrid control system. After the black start is completed, the photovoltaic power generation system outputs active power

[0071] Based on the above, a light-storage hybrid control system simulation model is built in Simulink, and the system parameters are shown in Table 1.

[0072] Table 1: Light-storage hybrid control system parameters

[0073]

[0074] The energy storage system output voltage waveform is shown in Figure 10 . It can be seen that the output voltage amplitude linearly increases, and the voltage amplitude reaches 311V at 1s, which can complete the zero-to-rise voltage.

[0075] The energy storage system output voltage frequency waveform controlled by the virtual synchronous machine is shown in Figure 11 . The frequency deviation is within 0.1Hz.

[0076] The energy storage system output power waveform is shown in Figure 12 . After the zero-to-rise voltage is completed, the output active power is controlled at 10KW, and the output reactive power is controlled at 0.

[0077] The photovoltaic system output power waveform is shown in Figure 13 . After the zero-to-rise voltage is completed, the output active power is controlled at 10KW, and the output reactive power is controlled at 0.

[0078] The above simulation results show that the embodiment of the present application can realize the multi-machine synchronous black start of the light-storage hybrid control system.

[0079] ​Although the present application has been described above with reference to the example embodiments, the above embodiments are merely intended for illustrative description of the implementable forms of the present application, but are not intended to limit the scope of protection of the present application, and equivalent substitutions or changes made by those skilled in the art based on the present application should be construed as falling within the scope of protection of the present application as defined by the claims.

Claims

1. A multi-machine synchronous black start control method for a hybrid light and storage control system, the hybrid light and storage control system comprising a storage system adopting network-forming control and a photovoltaic power generation system adopting network-following control, the photovoltaic power generation system being connected to a grid through a phase-locked loop; characterized in that, The multi-machine synchronous black start control method comprises the step of analyzing the stability of multi-machine synchronous black start; The stability analysis comprises: Dynamic stability analysis of the phase-locked loop during the black start process; And, steady-state stability analysis of the phase-locked loop after the black start is completed; Wherein, the active power emitted by the photovoltaic power generation system in the black start process satisfies and the active power emitted by the photovoltaic power generation system after the black start is completed , the light storage hybrid control system can be stable to complete synchronous black start, wherein 0≤t0≤T s ; wherein P PV = 3V VSG ·I PV , P PV is the active power instantaneous value of the photovoltaic system output during the voltage rise from zero, V VSG is the effective value of the energy storage system output phase voltage during the voltage rise from zero, I PV is the effective value of the photovoltaic system output current, the phase of which comes from the output of the phase-locked loop, Z line is the line impedance; P PV N = 3U N ·I PV N , U N is the rated voltage of the photovoltaic system, I PV N is the rated current of the photovoltaic system; The grid-constructing energy storage system has voltage support and active inertia characteristics and the ability to run under the support of no external power grid through virtual synchronous generator control, and externally behaves as a voltage source; the grid-following photovoltaic power generation system injects or absorbs active and reactive power by tracking the voltage amplitude and angle of the energy storage, and externally behaves as a current source; wherein, when the microgrid enters a full black state, the grid-constructing energy storage system starts to provide voltage and frequency support through virtual synchronous generator control, thereby driving the synchronous start of the grid-following photovoltaic power generation system, to control multi-machine synchronous black start; The energy storage system is provided with a zero-rise voltage boosting module for suppressing the field current surge of the distribution transformer in the microgrid during the black start of the micro-source, wherein the zero-rise voltage boosting control of the electromotive force amplitude is set in the following manner: Wherein, E0 is the voltage amplitude when the virtual synchronous generator is at no load; k is the slope of the increase of the output potential amplitude with time, k = E0 / T s ; T s is the time required for the output potential amplitude to increase from 0 to E0.

2. The multi-machine synchronization black-start control method of the optical storage hybrid control system according to claim 1, characterized in that: The light-storage hybrid control system further comprises a line module, a filter inductor and a load module, wherein the energy storage system directly supplies power to the load module through the line module, the output voltage of the photovoltaic power generation system is inverted to output alternating current, and the alternating current is processed through the filter inductor to supply power to the load module; the phase-locked loop collects the grid-connected point voltage and outputs angle information, and generates a PWM driving signal through closed-loop control of the inductor current.

3. The multi-machine synchronization black-start control method of the optical storage hybrid control system according to claim 2, characterized in that: The energy storage system comprises an electromotive force generation layer, a virtual impedance control layer, a voltage and current double closed-loop control layer, a d-q inverse transformer and a PWM modulator; wherein the electromotive force generation layer is used to generate the electromotive force amplitude E and phase θ of the virtual synchronous generator, the generated electromotive force E ∠ θ is processed by the virtual impedance control layer to obtain the output voltage, the output voltage is processed by the voltage and current double closed-loop control layer and the d-q inverse transformer to obtain the inverter output voltage modulation wave, and then the PWM modulator is used to generate the inverter driving signal.

4. The method of claim 1, wherein the method further comprises: During the black start of the microgrid, the energy storage system establishes a voltage reference by using the zero-rise voltage boosting module, generates an energy storage output active power reference value through primary frequency modulation and secondary frequency modulation, eliminates the frequency difference through an integral element, and generates the phase of the virtual synchronous generator electromotive force through the rotor motion equation.

5. The multi-machine synchronization black-start control method of the optical storage hybrid control system according to claim 4, characterized in that: The primary frequency modulation is a differential frequency modulation, which can be realized through a proportional element; the secondary frequency modulation is a differential frequency modulation, which eliminates the frequency difference through an integral element.

6. The method of claim 2, wherein the method further comprises: The photovoltaic power generation system realizes the frequency modulation function through a PI regulator, and generates a current instruction through a power ring to realize closed-loop control of the inductor current.

7. The multi-machine synchronization black-start control method of the optical storage hybrid control system according to claim 6, characterized in that: The phase-locked loop transforms the voltage from three-phase stationary coordinate system to synchronous rotating dq coordinate system through d-q transformation to obtain the transformed voltage V q = V m sin(θ-θ'), wherein V m is grid-connected point voltage amplitude, θ is actual voltage angle, and θ' is output estimation angle of the phase-locked loop; By PI regulation control, V q is 0, i.e. the output estimated angle θ' of the phase-locked loop equals the actual angle θ of the load voltage, to achieve phase locking.

8. The multi-machine synchronization black-start control method of the optical storage hybrid control system according to claim 7, wherein: The photovoltaic power generation system is equivalent to a current source, and the equivalent circuit is obtained, and the load voltage is obtained by superposition theorem: wherein

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