A control method and device for a grid-type energy storage converter

Abstract

The present disclosure relates to a control method and device for a grid-type energy storage converter. The method comprises: analyzing the frequency and voltage regulation characteristics of the synchronous generator of a single energy storage converter PCS, and establishing a mathematical model of a single energy storage converter PCS; generating a mathematical model of a grid-type energy storage converter PCS in a multi-machine parallel manner, and achieving uniform power distribution of the grid-type energy storage converter PCS based on the droop characteristics of the virtual synchronous generator control VSG; establishing a voltage outer loop control based on virtual stator impedance for the grid-type energy storage converter PCS; and establishing a preset VSG control strategy based on power self-regulation for the grid-type energy storage converter PCS to achieve control of the grid-type energy storage converter. The present disclosure takes into account the large-capacity networking requirements of microgrids, so that the grid-type energy storage converter can automatically adjust the power output and operate reliably when the PCS with a smaller SOC value is connected in parallel.

Description

Technical Field

[0001] The present disclosure relates to the field of energy storage converter control, and in particular to a control method and device for a grid-type energy storage converter. Background Art

[0002] Some areas of my country with limited access to electricity cannot rely on centralized power supply, and distributed independent microgrids are generally used to power the loads. However, the integration of a large number of power electronic equipment and distributed energy resources into the microgrid reduces the microgrid's inertia support capacity, making it unable to provide voltage and frequency support for the loads. This necessitates a grid-forming converter device that simulates the external characteristics of synchronous generators, provides inertia support, and improves the grid's low inertia and weak damping characteristics. Furthermore, as the demand for microgrid capacity increases, energy storage converters must operate in parallel with multiple units to achieve high-capacity microgrid networking. This comes with the problem that multi-unit parallel systems are prone to power oscillations, resulting in uneven output power distribution and impacting the paralleling effect. Virtual synchronous generator (VSG) control can improve the low inertia and weak support capacity of microgrids, and leverages its own droop characteristics to achieve even power distribution across multiple converters.

[0003] In the existing technology, there is no research on VSG control strategy based on SOC level power self-regulation to address the large-capacity networking requirements of microgrids and the limited active output of low-level SOC converters in multi-machine parallel connection.

[0004] Therefore, one or more methods are needed to solve the above problems.

[0005] It should be noted that the information disclosed in the above background technology section is only used to enhance the understanding of the background of the present disclosure, and therefore may include information that does not constitute prior art known to ordinary technicians in the field. Summary of the Invention

[0006] The purpose of the present disclosure is to provide a control method and device for a grid-type energy storage converter, thereby overcoming one or more problems caused by limitations and defects of related technologies, at least to a certain extent.

[0007] According to one aspect of the present disclosure, a method for controlling a grid-type energy storage converter is provided, comprising:

[0008] Analyze the frequency and voltage regulation characteristics of the synchronous generator of a single energy storage converter PCS and establish a mathematical model of a single energy storage converter PCS;

[0009] Based on the mathematical model of the single energy storage converter PCS, a mathematical model of a grid-type energy storage converter PCS using multiple machines in parallel is generated, and based on the droop characteristics of the virtual synchronous generator (VSG), the power of the grid-type energy storage converter PCS is evenly distributed;

[0010] Establishing a voltage outer loop control based on virtual stator impedance for the grid-type energy storage converter PCS to achieve power decoupling and power oscillation suppression control for the grid-type energy storage converter PCS;

[0011] A preset VSG control strategy based on power self-regulation is established for the grid-type energy storage converter PCS to achieve control of the grid-type energy storage converter.

[0012] In an exemplary embodiment of the present disclosure, the method further includes:

[0013] Analyze the frequency and voltage regulation characteristics of the synchronous generator of a single energy storage converter PCS and establish a mathematical model of a single energy storage converter PCS;

[0014] Generate a virtual synchronous generator control (VSG) block diagram of a single energy storage converter PCS based on the mathematical model of the single energy storage converter PCS;

[0015] Based on the virtual synchronous generator control (VSG) control block diagram, an active small signal model of a single energy storage converter (PCS) is established.

[0016] In an exemplary embodiment of the present disclosure, the method further includes:

[0017] Based on preset constraints, inertia J and damping D control parameters are selected for the active small signal model of the single energy storage converter PCS.

[0018] In an exemplary embodiment of the present disclosure, the method further includes:

[0019] Based on a mathematical model of a grid-type energy storage converter PCS in a multi-machine parallel manner, voltage pre-synchronization processing and phase pre-synchronization processing are performed on a single energy storage converter PCS in the grid-type energy storage converter PCS.

[0020] In an exemplary embodiment of the present disclosure, the method further includes:

[0021] The power characteristics of the parallel system of the grid-type energy storage converter PCS are analyzed, and the influence relationships of the phase angle and voltage difference on the active power and reactive power of the inductive circuit are generated respectively.

[0022] In an exemplary embodiment of the present disclosure, the method further includes:

[0023] Based on the influence of the phase angle and voltage difference on the active power and reactive power of the inductive circuit, a relationship between the ratio of the droop coefficients of each single energy storage converter PCS in the parallel system of the grid-type energy storage converter PCS and the power distribution relationship is generated.

[0024] In an exemplary embodiment of the present disclosure, the method further includes:

[0025] Establishing a voltage outer loop control based on virtual stator impedance for the grid-type energy storage converter PCS, and generating an overall control block diagram of the virtual stator impedance of the grid-type energy storage converter PCS;

[0026] The overall control block diagram based on the virtual stator impedance realizes power decoupling and power oscillation suppression control of the grid-type energy storage converter PCS.

[0027] In an exemplary embodiment of the present disclosure, the preset VSG control strategy based on power self-regulation further includes:

[0028] When the preset SOC value of the first single energy storage converter PCS1 in the grid-type energy storage converter PCS is lower than 20%, a trigger signal is generated;

[0029] The DSP controller sets the flag bit Flag_PCS1 of PCS1 to 1 based on the trigger signal, and determines whether the flag bit Flag_PCS2 of the second single energy storage converter PCS2 is 1;

[0030] If Flag_PCS2 is not 1, PCS2 can increase the power;

[0031] If Flag_PCS2 is 1, PCS2 cannot increase power, and PCS1 operates at the original set power.

[0032] When the conditions for PCS2 to increase power are met, PCS1 uploads the output voltage of PCS1 and the current value of PCS1 to the preset control system, and the preset control system calculates and updates the power value of PCS1. PCS2 uploads the output voltage of PCS2 and the current value of PCS2 to the preset control system, and the preset control system calculates and updates the power value of PCS2.

[0033] In one aspect of the present disclosure, a grid-type energy storage converter control device is provided, comprising:

[0034] A single PCS model building module is used to analyze the frequency and voltage regulation characteristics of the synchronous generator of a single energy storage converter PCS and establish a mathematical model of the single energy storage converter PCS;

[0035] A grid-type PCS model establishment module is used to generate a grid-type energy storage converter PCS mathematical model using multiple machines in parallel based on the mathematical model of the single energy storage converter PCS, and to achieve uniform power distribution of the grid-type energy storage converter PCS based on the droop characteristics of the virtual synchronous generator control VSG;

[0036] A virtual stator impedance control module is used to establish a voltage outer loop control based on virtual stator impedance for the grid-type energy storage converter PCS, thereby realizing power decoupling and power oscillation suppression control for the grid-type energy storage converter PCS;

[0037] The power self-regulating VSG control module is used to establish a preset VSG control strategy based on power self-regulation for the grid-type energy storage converter PCS to realize the control of the grid-type energy storage converter.

[0038] In an exemplary embodiment of the present disclosure, a control method for a grid-type energy storage converter is disclosed, wherein the method includes: analyzing the frequency and voltage regulation characteristics of the synchronous generator of a single energy storage converter (PCS) to establish a mathematical model of the single energy storage converter (PCS); generating a mathematical model of the grid-type energy storage converter (PCS) using multiple machines in parallel, and achieving uniform power distribution of the grid-type energy storage converter (PCS) based on the droop characteristics of the virtual synchronous generator (VSG); establishing a voltage outer loop control based on virtual stator impedance for the grid-type energy storage converter (PCS); and establishing a preset VSG control strategy based on power self-regulation for the grid-type energy storage converter (PCS) to achieve control of the grid-type energy storage converter. The present disclosure takes into account the large-capacity networking requirements of microgrids, enabling grid-type energy storage converters with smaller SOC values ​​to automatically adjust power output and operate reliably when connected in parallel.

[0039] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The above and other features and advantages of the present disclosure will become more apparent by describing in detail example embodiments thereof with reference to the accompanying drawings.

[0041] Figure 1 A flow chart of a method for controlling a grid-type energy storage converter according to an exemplary embodiment of the present disclosure is shown;

[0042] Figure 2 A mathematical model diagram of an NPC type PCS in a dq coordinate system of a control method for a grid-type energy storage converter according to an exemplary embodiment of the present disclosure is shown;

[0043] Figure 3 A diagram showing an active power small signal model of a grid-type energy storage converter control method according to an exemplary embodiment of the present disclosure is shown;

[0044] Figure 4 A simulation diagram showing the influence of J and D on active output of a grid-type energy storage converter control method according to an exemplary embodiment of the present disclosure is shown;

[0045] Figure 5 A schematic diagram of a parallel PCS main circuit of a grid-type energy storage converter control method according to an exemplary embodiment of the present disclosure is shown;

[0046] Figure 6 A schematic diagram of parallel pre-synchronization of a grid-type energy storage converter according to a control method of a grid-type energy storage converter according to an exemplary embodiment of the present disclosure is shown;

[0047] Figure 7 A flowchart of a pre-synchronization process of a grid-type energy storage converter control method according to an exemplary embodiment of the present disclosure is shown;

[0048] Figure 8 A physical model diagram of two energy storage converters connected in parallel according to a control method for a grid-type energy storage converter according to an exemplary embodiment of the present disclosure is shown;

[0049] Figure 9 A control block diagram of a grid-type energy storage converter control method without adding virtual stator impedance according to an exemplary embodiment of the present disclosure is shown;

[0050] Figure 10 A control block diagram of a grid-type energy storage converter control method after adding virtual stator impedance according to an exemplary embodiment of the present disclosure is shown;

[0051] Figure 11 A VSG overall control block diagram of a virtual stator impedance of a grid-type energy storage converter control method according to an exemplary embodiment of the present disclosure is shown;

[0052] Figure 12 A graph showing the relationship between the SOC level of a battery cell and the open circuit voltage of a port according to a control method for a grid-type energy storage converter according to an exemplary embodiment of the present disclosure is shown;

[0053] Figure 13 A power self-regulation flow chart of a grid-type energy storage converter control method according to an exemplary embodiment of the present disclosure is shown;

[0054] Figure 14 A schematic block diagram of a grid-type energy storage converter control device according to an exemplary embodiment of the present disclosure is shown. DETAILED DESCRIPTION

[0055] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be embodied in many forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concepts of the example embodiments to those skilled in the art. Like reference numerals in the drawings represent like or similar parts, and thus repetitive description thereof will be omitted.

[0056] In addition, the described features, structures or characteristics may be combined in any suitable manner in one or more embodiments. In the following description, many specific details are provided to provide a full understanding of the embodiments of the present disclosure. However, those skilled in the art will appreciate that the technical solutions of the present disclosure can be practiced without one or more of the specific details, or other methods, components, materials, devices, steps, etc. can be adopted. In other cases, well-known structures, methods and devices, implementations, materials or operations are not shown or described in detail to avoid obscuring various aspects of the present disclosure.

[0057] The blocks shown in the accompanying drawings are merely functional entities and do not necessarily correspond to physically separate entities. Specifically, these functional entities may be implemented in software, or in one or more software-hardened modules, or in different networks and / or processor devices and / or microcontroller devices.

[0058] In this exemplary embodiment, a control method for a grid-type energy storage converter is first provided; Figure 1 As shown in , the control method of a grid-type energy storage converter may include the following steps:

[0059] Step S110, analyzing the frequency and voltage regulation characteristics of the synchronous generator of a single energy storage converter PCS, and establishing a mathematical model of the single energy storage converter PCS;

[0060] Step S120: Based on the mathematical model of the single energy storage converter PCS, a mathematical model of a grid-type energy storage converter PCS using multiple machines in parallel is generated, and based on the droop characteristics of the virtual synchronous generator (VSG), the power of the grid-type energy storage converter PCS is evenly distributed.

[0061] Step S130, establishing a voltage outer loop control based on virtual stator impedance for the grid-type energy storage converter PCS to achieve power decoupling and power oscillation suppression control for the grid-type energy storage converter PCS;

[0062] Step S140 , establishing a preset VSG control strategy based on power self-regulation for the grid-type energy storage converter PCS to achieve control of the grid-type energy storage converter.

[0063] In an exemplary embodiment of the present disclosure, a control method for a grid-type energy storage converter is disclosed, wherein the method includes: analyzing the frequency and voltage regulation characteristics of the synchronous generator of a single energy storage converter (PCS) to establish a mathematical model of the single energy storage converter (PCS); generating a mathematical model of the grid-type energy storage converter (PCS) using multiple machines in parallel, and achieving uniform power distribution of the grid-type energy storage converter (PCS) based on the droop characteristics of the virtual synchronous generator (VSG); establishing a voltage outer loop control based on virtual stator impedance for the grid-type energy storage converter (PCS); and establishing a preset VSG control strategy based on power self-regulation for the grid-type energy storage converter (PCS) to achieve control of the grid-type energy storage converter. The present disclosure takes into account the large-capacity networking requirements of microgrids, enabling grid-type energy storage converters with smaller SOC values ​​to automatically adjust power output and operate reliably when connected in parallel.

[0064] Next, a control method for a grid-type energy storage converter in this exemplary embodiment will be further described.

[0065] Example 1:

[0066] In step S110 , the frequency and voltage regulation characteristics of the synchronous generator of a single energy storage converter PCS may be analyzed to establish a mathematical model of the single energy storage converter PCS.

[0067] In the embodiment of this example, the frequency and voltage regulation characteristics of the synchronous generator of a single energy storage converter PCS are analyzed, and a mathematical model of the single energy storage converter PCS is established;

[0068] Generate a virtual synchronous generator control (VSG) block diagram of a single energy storage converter PCS based on the mathematical model of the single energy storage converter PCS;

[0069] Based on the virtual synchronous generator control (VSG) control block diagram, an active small signal model of a single energy storage converter (PCS) is established.

[0070] In this exemplary embodiment, the method further includes:

[0071] Based on preset constraints, inertia J and damping D control parameters are selected for the active small signal model of the single energy storage converter PCS.

[0072] In step S120, a mathematical model of a grid-type energy storage converter PCS using multiple machines in parallel can be generated based on the mathematical model of the single energy storage converter PCS, and the power of the grid-type energy storage converter PCS can be evenly distributed based on the droop characteristics of the virtual synchronous generator control VSG.

[0073] In this exemplary embodiment, the method further includes:

[0074] Based on a mathematical model of a grid-type energy storage converter PCS in a multi-machine parallel manner, voltage pre-synchronization processing and phase pre-synchronization processing are performed on a single energy storage converter PCS in the grid-type energy storage converter PCS.

[0075] In this exemplary embodiment, the method further includes:

[0076] The power characteristics of the parallel system of the grid-type energy storage converter PCS are analyzed, and the influence relationships of the phase angle and voltage difference on the active power and reactive power of the inductive circuit are generated respectively.

[0077] In this exemplary embodiment, the method further includes:

[0078] Based on the influence of the phase angle and voltage difference on the active power and reactive power of the inductive circuit, a relationship between the ratio of the droop coefficients of each single energy storage converter PCS in the parallel system of the grid-type energy storage converter PCS and the power distribution relationship is generated.

[0079] In step S130, a voltage outer loop control based on virtual stator impedance may be established for the grid-type energy storage converter PCS to achieve power decoupling and power oscillation suppression control of the grid-type energy storage converter PCS.

[0080] In this exemplary embodiment, the method further includes:

[0081] Establishing a voltage outer loop control based on virtual stator impedance for the grid-type energy storage converter PCS, and generating an overall control block diagram of the virtual stator impedance of the grid-type energy storage converter PCS;

[0082] The overall control block diagram based on the virtual stator impedance realizes power decoupling and power oscillation suppression control of the grid-type energy storage converter PCS.

[0083] In step S140, a preset VSG control strategy based on power self-regulation may be established for the grid-type energy storage converter PCS to achieve control of the grid-type energy storage converter.

[0084] In the embodiment of this example, in the method, the preset VSG control strategy based on power self-regulation further includes:

[0085] When the preset SOC value of the first single energy storage converter PCS1 in the grid-type energy storage converter PCS is lower than 20%, a trigger signal is generated;

[0086] The DSP controller sets the flag bit Flag_PCS1 of PCS1 to 1 based on the trigger signal, and determines whether the flag bit Flag_PCS2 of the second single energy storage converter PCS2 is 1;

[0087] If Flag_PCS2 is not 1, PCS2 can increase the power;

[0088] If Flag_PCS2 is 1, PCS2 cannot increase power, and PCS1 operates at the original set power.

[0089] When the conditions for PCS2 to increase power are met, PCS1 uploads the output voltage of PCS1 and the current value of PCS1 to the preset control system, and the preset control system calculates and updates the power value of PCS1. PCS2 uploads the output voltage of PCS2 and the current value of PCS2 to the preset control system, and the preset control system calculates and updates the power value of PCS2.

[0090] Example 2:

[0091] In this example, through the circuit analysis of the neutral point clamped NPC three-level PCS, the meshed PCS needs to supply power to the load. Therefore, only the i A >0. With the inductor current i A 、i B 、i C As a reference to the positive direction, using Kirchhoff's law, the mathematical equation in the three-phase stationary coordinate system can be obtained as follows:

[0092]

[0093] In the formula

[0094]

[0095] Assuming that the three-phase output voltage is balanced and there is a three-phase balanced load, we can get

[0096]

[0097] Substituting formula (2) into formula (1), we can get

[0098]

[0099] Therefore, formula (1) can be simplified to

[0100]

[0101] To facilitate writing and analysis, some variables are defined as follows

[0102]

[0103] Substituting formula (5) into formula (4) we can get

[0104]

[0105] However, since all variables in Equation (6) are AC variables, they are not suitable for control strategy design. Therefore, Equation (6) can be transformed into coordinates. The transformation matrix from the three-phase stationary coordinate system to the two-phase rotating coordinate system is:

[0106]

[0107] The transformation matrix from the two-phase rotating coordinate system to the three-phase stationary coordinate system is:

[0108]

[0109] According to formula (8), we can get

[0110]

[0111] Substituting formula (9) into formula (6) we can get

[0112]

[0113] Where,

[0114] Multiplying both sides of formula (10) by formula (7) yields

[0115]

[0116] Where H 3s / 2r and H 2r / 3s Multiply

[0117]

[0118] Formula (11) can be simplified to

[0119]

[0120] Perform Laplace transform on Equation (13) and expand it into

[0121]

[0122] According to formula (14), the mathematical model of the neutral point clamped NPC three-level PCS can be obtained as follows: Figure 2 shown.

[0123] In the embodiment of this example, the analysis of the system's active frequency-rate characteristics is achieved with the help of the rotor mechanical motion equation, but in essence the rotor mechanical motion equation is a large signal model. In order to better analyze the dynamic characteristics of the system under small load disturbances and select parameters J and D, an active small signal model is established.

[0124] In inductive circuits, active and reactive power are approximately decoupled. When the system is in steady-state load, the power input to the load is at the static operating point. Small-signal perturbations are introduced near this point. The following lists the small-signal forms of various physical quantities in the VSG model.

[0125]

[0126] Substituting the above equation into equation (15) and removing the steady-state component and the high-order nonlinear component, we can obtain

[0127]

[0128] Performing Laplace transform on Equation (16) yields

[0129]

[0130] From formula (17), the active power small signal model diagram can be obtained as follows: Figure 3 shown.

[0131] Depend on Figure 3 It can be concluded that its active closed-loop transfer function is:

[0132]

[0133] It can be seen from Equation (18) that the closed-loop transfer function of the active small signal is a typical second-order system, so its characteristic equation root and attenuation frequency ω can be obtained b , damping ratio ζ.

[0134]

[0135] It can be seen from formula (19) that the attenuation frequency ω b It is only related to the inertia J, which means that the overshoot of active power is related to J. The damping ratio ζ is related to both J and D, which means that the dynamic adjustment capability of active power is related to J and D. The following simulation analysis of the control variables J and D is as follows: Figure 4As shown in the figure, the left diagram shows different J values ​​for D = 30, while the right diagram shows different D values ​​for J = 3. As can be seen from the left diagram, when D is 30, the larger the J, the greater the active power overshoot. In the right diagram, when J is constant, the larger the D, the slower the active power response time, and even overdamping may occur. Therefore, J and D must be adjusted in coordination to achieve optimal control results. Because damping D has a significant impact on system dynamic characteristics, it is generally not easily changed. Therefore, this article focuses solely on J to design the active power dynamic response.

[0136] The frequency loop transfer function is

[0137]

[0138] In formula (20), the droop characteristic is related to the damping coefficient D and the droop coefficient K f It is related to the PCS capacity and frequency deviation. The frequency loop is also a second-order system. Damping ratio ζ ω , attenuation frequency ω bω for

[0139]

[0140] From equations (19) and (21), it can be seen that the response speed of the active closed-loop transfer function is faster than that of the frequency loop transfer function. The frequency loop is designed as an overdamped system. Considering the PCS capacity, when the frequency changes by ±0.5Hz, K f The value is 120, and the active output is not less than 10%. According to the national standard "Virtual Synchronous Machine Technology-General Principles", the active closed loop requires the active frequency modulation response time to be no more than 500ms, the active frequency modulation adjustment time to be no more than 1s, and the power error to be controlled within 2%. Therefore, the active closed loop is designed as an underdamped system. The time of a typical underdamped system meets the national standard.

[0141]

[0142] Substituting formula (19) into formula (22) we can get

[0143]

[0144] The damping ratio of the underdamped system is preferably 0.4<ξ<0.8. Combining formula (19), we can get

[0145]

[0146] The specific parameters are given below: U0=E0=380V, D=50, Z=1.289mH. The two PCS have the same parameters. According to equations (23) and (24), we can get

[0147]

[0148] If both boundary conditions are met at the same time, the value range of J is

[0149] 2.74≤J≤5.68 (26)

[0150] The system is designed according to the optimal damping ratio of the second-order system ξ = 0.707, so the final J is 3.5, and substituting it into formula (21) yields ζ ω =1.01, which satisfies both the active power response requirement and the frequency response requirement.

[0151] In the embodiment of this example, the grid-type storage PCS parallel topology is developed from the single topology, and its structure is as follows: Figure 5 As shown in Figure 2. The two PCS AC sides are connected to the AC bus after passing through the line impedance, and they jointly supply power to the load. Figure 5 It can be seen that the two PCSs are independently controlled and symmetrical to each other. S represents the relay switch. The output circuit at the AC bus is a three-phase symmetrical circuit. The filtering device uses an LC filter. In actual applications, the PCS has line impedance. In the main circuit model, the line impedance is uniformly written as Z. line .

[0152] In the embodiment of this example, the parallel pre-synchronization of the grid-type energy storage converter includes:

[0153] In the grid-type PCS parallel connection, one PCS is used as the "grid" and the other PCS is used as the device. During the "grid connection" process, the device needs to track and lock the voltage amplitude and phase of the grid. It can only be connected when the voltage and phase of the device are consistent with the grid. If the phase is not synchronized, it will cause a current shock at the moment of parallel connection. At this time, the system will trigger the overcurrent protection and the parallel connection will fail. In addition, due to the line impedance between the PCS and the load, when one of the PCSs is in grid operation, the voltage collected at this time includes the line impedance voltage drop, which will cause the voltage amplitude of the two PCSs to be inconsistent when in parallel, and the parallel connection will also fail. Therefore, pre-synchronization processing is performed on the phase and voltage. With PCS1 as the reference grid, PCS2 performs phase and voltage pre-synchronization processing on PCS1. The control block diagram is as follows Figure 6 shown. Figure 6 It can be seen that the realization of phase pre-synchronization is to improve the active power-frequency loop of PCS2. The specific idea is: the two PCSs obtain the output voltage angular frequency ω through the phase-locked loop pcs1 、ω pcs2 , Δω is compensated to the ω output by PCS2 through the PI controller, and the two PCSs autonomously adjust the angular frequency until the angular frequency and phase of the two PCSs are consistent. At this time, the phase pre-synchronization switch is disconnected; realizing voltage pre-synchronization is to improve the reactive-voltage loop of PCS2. The specific idea is: the two PCSs finally obtain U after 3r / 2s transformation and voltage amplitude calculation. m1 and Um2 , since PCS1 is used as the reference grid, U m1 As the voltage pre-synchronization reference voltage, when the voltage amplitudes of the two PCSs are similar, the switch is set to the reference voltage U of PCS2. ref , completing the voltage pre-synchronization process.

[0154] The pre-synchronization process flow diagram is as follows Figure 7 As shown. Figure 7 As can be seen from the figure, phase pre-synchronization and voltage pre-synchronization are performed simultaneously. During voltage pre-synchronization, the line impedance of each PCS may be inconsistent, and it is difficult for the voltage amplitudes of the two PCSs to be completely consistent when they are connected in parallel. The difference in the voltage amplitudes of the two PCSs satisfies |U m1 -U m2 |=(0.01~0.05)U N That is, a voltage amplitude difference of 6V is selected as the voltage pre-synchronization parallel condition. When the voltage pre-synchronization condition is met, the voltage pre-synchronization switch is opened and the voltage reference value of PCS2 is given. The voltage pre-synchronization flag is set to 1, and the phase pre-synchronization flag is checked. When the phases of the two PCSs are aligned, the phase pre-synchronization switch is opened and the phase pre-synchronization flag is set to 1. At this point, the voltage pre-synchronization receives the phase pre-synchronization flag, closes the switch of PCS2, and pre-synchronization is completed.

[0155] In this exemplary embodiment, the parallel system power characteristic analysis includes:

[0156] right Figure 5 The physical modeling analysis of the circuit model in the figure shows that the output voltage of each bridge arm of the grid-type energy storage converter can be equivalent to an ideal voltage source. Therefore, the parallel system that can be constructed is as follows: Figure 8 shown. Figure 8 In the parallel model shown, E1∠θ1 and E2∠θ2 are the output voltages of the PCS bridge arms, and U load ∠0 is the load voltage, Z1 and Z2 are the equivalent impedances of the LC filters of the two energy storage converters, and Z L For load.

[0157] In the parallel system, taking PCS1 as an example, when in steady state operation, the power it provides to the load is

[0158] S1=P1+jQ1 (27)

[0159] The power absorbed by the load side is

[0160]

[0161] Combining equations (27) and (28), the active and reactive power provided by PCS1 to the load can be obtained as

[0162]

[0163] Similarly, the active and reactive power provided by PCS2 to the load is

[0164]

[0165] When the parallel system is running, the phase difference between the output voltage E1∠θ1, E2∠θ2 on the AC side of the device and the voltage U∠0 on the load is very small, so it can be approximately obtained

[0166]

[0167] Substituting formula (31) into formula (29) and formula (30), we can get

[0168]

[0169] According to formula (32), the characteristics of the active power output of the device can be analyzed: taking the output voltage amplitude E1 and phase angle θ1 of PCS1 as variables and taking the derivative of P1, we can get

[0170]

[0171] It can be seen from formula (33) that the output voltage angle θ1 and the voltage amplitude E1 are both proportional to the active power. The following is a comparison of the two influencing factors, and we can get

[0172]

[0173] When the entire parallel system is in stable operation, the phase θ1 of the PCS output voltage is very small. If the output characteristic of the circuit is inductive, It can be approximated

[0174]

[0175] Similarly, the characteristics of the reactive power output of the device are analyzed: the output voltage phase angle θ1 and amplitude E1 of PCS1 are used as variables to derive the reactive power Q1, and we can get

[0176]

[0177] From the above analysis, we can see that since the circuit is inductive, r1θ1-X1<0, and dQ1 / dE1>0. Therefore, the reactive power output by the PCS is positively correlated with the output voltage and negatively correlated with the output voltage phase. The same processing as for the active power can be obtained.

[0178]

[0179] It can be seen from equation (28) that when the circuit is inductive, the PCS output voltage amplitude E1 is much smaller than X1 / r1, so it can be considered that equation (37) is much smaller than 1.

[0180] Based on all the above assumptions, Equation (32) can be rewritten as

[0181]

[0182] From formula (38), we can see that when the circuit is inductive, the main factor affecting the active power is the phase angle, and the main factor affecting the reactive power is the voltage difference between the PCS and the load.

[0183] In this exemplary embodiment, the power sharing principle includes:

[0184] In meshed PCS parallel control, proper power distribution is crucial. Uneven power distribution among multiple PCSs can easily lead to power oscillations. Power sharing issues can be categorized into two main types: power sharing during load fluctuations and power distribution during system setpoint changes. Both types of power sharing are transient power sharing issues.

[0185] The total power output of multiple PCSs meets the load power.

[0186]

[0187] For example, assume two PCSs are both rated at 100kW, given the same power and a 200kW active load. The control target is for each PCS to output 100kW. If the load is reduced, the final steady-state output power is evenly distributed according to the reduced power.

[0188] When the given power of the two PCSs remains unchanged, the relationship between the active power and the droop coefficient is:

[0189]

[0190] During stable operation, the voltage amplitudes and phase angles of the two PCSs are not much different. Therefore, substituting equation (40) into equation (38) yields

[0191]

[0192] Equation (41) shows that the output impedance ratio of the two PCSs is proportional to the droop coefficient. When the droop coefficient ratio and output impedance ratio are the same, power can be evenly distributed. The output impedance includes the filter output impedance and the line impedance. Two PCSs with the same filter parameters generally have the same parameters, but because the two PCSs may have significantly different parameters, the line impedance may be different. This makes it difficult to evenly distribute the output power and may cause oscillation. Therefore, it is necessary to introduce virtual impedance to balance the line impedance, reduce power fluctuations, and solve the power sharing problem.

[0193] The second category is divided into changes in PCS setpoint power. Assuming the load remains constant, at a certain moment, the setpoint value of a PCS increases. Therefore, the power setpoint values ​​of the two PCSs at that moment are different. The PCS with the larger setpoint value increases its power. Due to the droop characteristic, the other PCS must reduce its power. This decreases the setpoint value and the output power target, but the total output power still satisfies Equation (39).

[0194] When the given value of PCS1 increases, the P output of VSG at rated frequency VSG1 Increase, but because the load power remains unchanged, the common bus frequency is forced to rise. At the same time, PCS2 detects the frequency increase and according to the droop characteristic P VSG2 Reduce. Offset the extra power. The increase or decrease in power of the two PCS is

[0195]

[0196] This shows that the key factor in achieving power sharing lies in the ratio of the droop coefficients of the two PCSs. If the droop coefficients of the two PCSs are the same, a 1:1 power distribution can be achieved. Therefore, this article is based on the assumption that the droop coefficients of the two PCSs are the same.

[0197] In the embodiment of this example, the virtual stator impedance control strategy includes:

[0198] Conventional VSG control is to give the output phase of the rotor's mechanical equation and the reactive-voltage loop output reference voltage to the voltage and current dual closed-loop control through dq transformation. However, it can be seen from the synchronous generator stator voltage equation that the stator output voltage should also consider the stator's own impedance voltage drop before giving it to the closed-loop control. In this way, the established model is more accurate and the output impedance can be adjusted. Therefore, it is necessary to add a virtual stator impedance. The function of the virtual stator impedance is to simulate the impedance voltage drop of the stator itself. It works as a virtual impedance controller. The virtual stator impedance controller multiplies the output current by the virtual stator impedance Z V to achieve.

[0199] First, the control block diagram without adding virtual stator impedance is as follows: Figure 9 shown. Figure 9 In, Kpwm is the three-phase gain, G u (s) and G i (s) is the voltage loop and current loop gain, which can be expressed as

[0200]

[0201] Therefore, the forward gain G(s) of the voltage and current loop is obtained as

[0202]

[0203] Without adding stator impedance regulator, the output impedance Z0(s) of the filter can be expressed as

[0204]

[0205] The control block diagram after adding virtual stator impedance is as follows: Figure 10 As shown. Figure 10 available

[0206]

[0207] Combining formula (46), we can get:

[0208]

[0209] It can be seen from formula (47) that the equivalent output impedance of the device after adding the virtual impedance is

[0210] Z v0 (s)=G(s)Z v (s)+Z0(s) (48)

[0211] It can be seen from formula (48) that after adding the virtual stator impedance, the equivalent output impedance of the PCS becomes the sum of the original filter output impedance and the virtual impedance.

[0212] The following is a modeling analysis of the virtual stator impedance. Assuming that the three-phase virtual impedance circuit is

[0213]

[0214] Since the algorithms used in this paper are all based on the dq coordinate system, the virtual impedance modeling is also implemented based on the dq coordinate system.

[0215]

[0216] Combining the above analysis, we can get the overall control block diagram of virtual stator impedance, as shown in Figure 11 shown.

[0217] In the embodiment of this example, the power self-regulation strategy considering the SOC characteristics includes:

[0218] In parallel operation, PCS is used as the main power source. If the energy storage device still produces a large amount of active power when the SOC level is low, it is very likely that the PCS will shut down due to insufficient power. After the PCS shuts down, the entire microgrid will not be able to operate normally, which will have extremely serious consequences. Therefore, it is necessary to consider the physical properties of the energy storage medium, which will limit the freedom of VSG design. For example, the battery. The relationship between the SOC level of the battery cell and the port open circuit voltage is as follows: Figure 12 As shown. Figure 12 As can be seen, the open-circuit voltage of a battery cell is positively correlated with the SOC level, remaining relatively stable between 20% and 80%. The terminal voltage of a battery cell fluctuates within a range of 3.8V ± 0.1V. When the SOC level drops below 10%, the open-circuit voltage of the battery cell drops significantly. Energy storage systems require multiple battery cells connected in parallel to form a battery pack, where voltage drops are even more pronounced. If the battery pack voltage is too low, the PCS will continue to output significant active power for extended periods, resulting in insufficient system power and inoperability. Therefore, VSG control is constrained.

[0219] By analyzing the active closed-loop transfer function as a second-order underdamped system, the PCS output power changes with the power command ΔP m When , the expression of its active power output response in the time domain is

[0220]

[0221] Where,

[0222]

[0223] The maximum active power available is

[0224]

[0225] From formula (53), it can be concluded that the maximum active power is related to the change of power command and overshoot. When the SOC value is 20%, the overshoot should be as small as possible. Let ΔP m is 25kW, then |ΔP emax | is 30kW, and the overshoot σ% is 1.5%. Therefore, when two PCSs are operating in parallel, if the SOC of the battery pack of one PCS is lower than 20%, it will actively reduce its own active output by half. This requires the other PCS to have a higher SOC value and sufficient power to increase its active output.

[0226] The specific implementation flow chart is as follows Figure 13 As shown. Taking PCS1 as an example, Figure 13It can be seen that when the EMS detects that the SOC value of PCS1 is lower than 20%, it will transmit a trigger signal to the DSP of PCS1. After receiving the trigger signal, the DSP sets the PCS1 flag Flag_PCS1 to 1 and determines whether the PCS2 flag Flag_PCS2 is 1. If it is not 1, it means that PCS2 is currently at a higher SOC and can increase power. If the flag is 1, it means that PCS2 is also at a low SOC and cannot increase power. PCS1 still uses the original set power. After the conditions for PCS2 to increase power are met, PCS1 uploads the current output voltage and current values ​​to the EMS system. The EMS system calculates the current PCS1 power and resets the PCS1 power value. At the same time, the output voltage and current values ​​of PCS2 are also uploaded to the EMS system, and the PCS2 power value is reset.

[0227] In this example embodiment, the control of single and multiple meshed PCS virtual synchronous generators is introduced and analyzed. First, the principles of traditional generator frequency and voltage regulation are analyzed. A mechanical model of the synchronous generator rotor and an electrical model of the stator voltage are established, from which a single VSG control strategy is proposed, including the active power-frequency equation and the reactive power-voltage equation. An active small-signal model is established, and the optimal inertia is determined according to standard definitions. Based on the single PCS topology, a multi-machine parallel topology is derived, and a meshed PCS parallel pre-synchronization link is designed to reduce the instantaneous power and current impact of parallel connection. Power characteristics are analyzed. Considering the problem of low SOC when multiple machines are connected in parallel in a microgrid, which can cause the microgrid to malfunction, a design process for power self-regulation is presented.

[0228] It should be noted that although the steps of the method disclosed herein are depicted in a particular order in the accompanying drawings, this does not require or imply that the steps must be performed in that particular order, or that all steps must be performed to achieve the desired result. Additionally or alternatively, certain steps may be omitted, multiple steps may be combined into one, and / or one step may be decomposed into multiple steps.

[0229] In addition, in this exemplary embodiment, a grid-type energy storage converter control device is also provided. Figure 4 As shown, the grid-type energy storage converter control device 200 may include: a single PCS model establishment module 210, a grid-type PCS model establishment module 220, a virtual stator impedance control module 230, and a power self-regulating VSG control module 240.

[0230] A single PCS model building module 210 is used to analyze the frequency and voltage regulation characteristics of the synchronous generator of a single energy storage converter PCS and establish a mathematical model of the single energy storage converter PCS;

[0231] A grid-type PCS model establishment module 220 is used to generate a grid-type energy storage converter PCS mathematical model using multiple machines in parallel based on the mathematical model of the single energy storage converter PCS, and to achieve uniform power distribution of the grid-type energy storage converter PCS based on the droop characteristics of the virtual synchronous generator (VSG);

[0232] The virtual stator impedance control module 230 is used to establish a voltage outer loop control based on the virtual stator impedance for the grid-type energy storage converter PCS, thereby achieving power decoupling and power oscillation suppression control for the grid-type energy storage converter PCS;

[0233] The power self-regulation VSG control module 240 is used to establish a preset VSG control strategy based on power self-regulation for the grid-type energy storage converter PCS to achieve control of the grid-type energy storage converter.

[0234] The specific details of each of the above-mentioned grid-type energy storage converter control device modules have been described in detail in a corresponding grid-type energy storage converter control method, and therefore will not be repeated here.

[0235] It should be noted that although the detailed description above mentions several modules or units of a grid-type energy storage converter control device 200, this division is not mandatory. In fact, according to embodiments of the present disclosure, the features and functions of two or more modules or units described above can be embodied in a single module or unit. Conversely, the features and functions of a single module or unit described above can be further divided and embodied by multiple modules or units.

[0236] Furthermore, the above-described figures are merely illustrative of the processes included in the method according to exemplary embodiments of the present invention and are not intended to be limiting. It is readily understood that the processes illustrated in the above-described figures do not indicate or limit the temporal order of these processes. Furthermore, it is readily understood that these processes may be executed synchronously or asynchronously, for example, in multiple modules.

[0237] Other embodiments of the present disclosure will readily occur to those skilled in the art after considering the specification and practicing the invention disclosed herein. This application is intended to cover any variations, uses, or adaptations of the present disclosure that follow from the general principles of the present disclosure and include common knowledge or customary techniques in the art not disclosed herein. The description and examples are to be considered as exemplary only, with the true scope and spirit of the present disclosure being indicated by the claims.

[0238] It should be understood that the present disclosure is not limited to the exact structures that have been described above and shown in the drawings, and that various modifications and changes can be made without departing from the scope thereof. The scope of the present disclosure is limited only by the appended claims.

Claims

1. A control method for a grid-type energy storage converter, characterized in that: The method comprises: Analyze the frequency and voltage regulation characteristics of the synchronous generator of a single energy storage converter PCS and establish a mathematical model of a single energy storage converter PCS; Based on the mathematical model of the single energy storage converter PCS, a mathematical model of a grid-type energy storage converter PCS in a multi-machine parallel manner is generated, and based on the droop characteristics of the virtual synchronous generator control VSG, the power of the grid-type energy storage converter PCS is evenly distributed; based on the mathematical model of the grid-type energy storage converter PCS in a multi-machine parallel manner, voltage pre-synchronization processing and phase pre-synchronization processing are performed on each of the single energy storage converter PCS in the grid-type energy storage converter PCS; Establishing a voltage outer loop control based on virtual stator impedance for the grid-type energy storage converter PCS to achieve power decoupling and power oscillation suppression control for the grid-type energy storage converter PCS; A preset VSG control strategy based on power self-regulation is established for the grid-type energy storage converter PCS to achieve control of the grid-type energy storage converter.

2. The method according to claim 1, wherein The method further comprises: Analyze the frequency and voltage regulation characteristics of the synchronous generator of a single energy storage converter PCS and establish a mathematical model of a single energy storage converter PCS; Generate a virtual synchronous generator control (VSG) block diagram of a single energy storage converter PCS based on the mathematical model of the single energy storage converter PCS; Based on the virtual synchronous generator control (VSG) control block diagram, an active small signal model of a single energy storage converter (PCS) is established.

3. The method according to claim 2, wherein The method further comprises: Based on preset constraints, inertia J and damping D control parameters are selected for the active small signal model of the single energy storage converter PCS.

4. The method according to claim 3, wherein The method further comprises: The power characteristics of the parallel system of the grid-type energy storage converter PCS are analyzed, and the influence relationships of the phase angle and voltage difference on the active power and reactive power of the inductive circuit are generated respectively.

5. The method according to claim 4, wherein The method further comprises: Based on the influence of the phase angle and voltage difference on the active power and reactive power of the inductive circuit, a relationship between the ratio of the droop coefficients of each single energy storage converter PCS in the parallel system of the grid-type energy storage converter PCS and the power distribution is generated.

6. The method according to claim 1, wherein The method further comprises: Establishing a voltage outer loop control based on virtual stator impedance for the grid-type energy storage converter PCS, and generating an overall control block diagram of the virtual stator impedance of the grid-type energy storage converter PCS; The overall control block diagram based on the virtual stator impedance realizes power decoupling and power oscillation suppression control of the grid-type energy storage converter PCS.

7. The method according to claim 1, wherein In the method, the preset VSG control strategy based on power self-regulation further includes: When the preset SOC value of the first single energy storage converter PCS1 in the grid-type energy storage converter PCS is lower than 20%, a trigger signal is generated; The DSP controller sets the flag bit Flag_PCS1 of PCS1 to 1 based on the trigger signal, and determines whether the flag bit Flag_PCS2 of the second single energy storage converter PCS2 is 1; If Flag_PCS2 is not 1, PCS2 can increase the power; If Flag_PCS2 is 1, PCS2 cannot increase power, and PCS1 operates at the original set power. When the conditions for PCS2 to increase power are met, PCS1 uploads the output voltage of PCS1 and the current value of PCS1 to the preset control system, and the preset control system calculates and updates the power value of PCS1. PCS2 uploads the output voltage of PCS2 and the current value of PCS2 to the preset control system, and the preset control system calculates and updates the power value of PCS2.

8. A grid-type energy storage converter control device, characterized in that: The device comprises: A single PCS model building module is used to analyze the frequency and voltage regulation characteristics of the synchronous generator of a single energy storage converter PCS and establish a mathematical model of the single energy storage converter PCS; A grid-type PCS model establishment module is used to generate a grid-type energy storage converter PCS mathematical model using multiple machines in parallel based on the mathematical model of the single energy storage converter PCS, and to achieve uniform power distribution of the grid-type energy storage converter PCS based on the droop characteristics of the virtual synchronous generator control VSG; based on the grid-type energy storage converter PCS mathematical model using multiple machines in parallel, perform voltage pre-synchronization processing and phase pre-synchronization processing on a single energy storage converter PCS in the grid-type energy storage converter PCS; A virtual stator impedance control module is used to establish a voltage outer loop control based on virtual stator impedance for the grid-type energy storage converter PCS, thereby realizing power decoupling and power oscillation suppression control for the grid-type energy storage converter PCS; The power self-regulating VSG control module is used to establish a preset VSG control strategy based on power self-regulation for the grid-type energy storage converter PCS to realize the control of the grid-type energy storage converter.

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