General Low / High Voltage Ride-Through Control Method, System, Equipment and Control Strategy Parameter Identification Method for Battery Energy Storage Systems

Abstract

A general low / high voltage ride-through control method, system, device and control strategy parameter identification method for a battery energy storage system belong to the technical field of electromagnetic transient simulation modeling and control of energy storage systems in power systems. To solve the problem of poor generality of existing battery energy storage system models and their controls. The present invention uses a general low / high voltage ride-through control strategy for the battery energy storage system. The steady-state control in the strategy includes a power outer loop and a current inner loop. The output stage of the power outer loop is cascaded to the current inner loop, and after decoupling in the current inner loop, active and reactive powers are controlled separately. The general low voltage ride-through control strategy cuts off the power outer loop during active and reactive low voltage faults and only retains the current inner loop for single-loop control. The general high voltage ride-through control strategy disconnects the reactive power outer loop, and the active power loop maintains a steady-state grid-connected operation state. And the parameter identification of the control strategy is realized through test response data.

Description

Technical Field

[0001] The present invention belongs to the technical field of electromagnetic transient simulation modeling and control of energy storage systems in power systems, and specifically relates to a general low / high voltage ride-through control method, system, device, and parameter identification method for battery energy storage systems. Background Art

[0002] Establishing an accurate battery energy storage system model is an important basis for studying energy storage grid connection control and ensuring the normal and stable operation of power systems. However, currently, there are many manufacturers and models of energy storage units, with different characteristics and complex controls. The energy storage system models provided by manufacturers are mostly encapsulated models based on simulation platforms, and it is impossible to accurately obtain the control strategies and control parameters of the energy storage system. Therefore, modeling and analysis are very difficult.

[0003] Regarding the research on control strategies for battery energy storage, existing research mostly focuses on customized modeling for specific scenarios. For example:

[0004] 1. "Research on the General Energy Storage System Mathematical Model and Its PSASP Modeling" published by Li Yan et al., Power System Technology, 2012, 36(1): 51 - 57. This article proposed a general energy storage electromechanical transient model containing an outer loop control, an inner loop control, and a limiting link, and used PSASP to conduct experimental verification on the role of energy storage in suppressing the fluctuation of photovoltaic output. It did not involve the modeling of fault characteristics.

[0005] 2. "Multi-Scenario Simulation Modeling and Application of Electrochemical Energy Storage Power Stations Suitable for Large Power Grid Dynamic Simulation" published by Dai Hanyang et al., Power System Technology, 2023, 47(5): 1828 - 1836. Based on the actual operation parameters of energy storage power stations, this article constructed an energy storage power station model suitable for various typical scenarios such as steady-state operation, low voltage ride-through, frequency support, and secondary frequency modulation, but did not consider the high voltage fault ride-through scenario.

[0006] 3. "Electromagnetic Transient Modeling Method of Lithium-Ion Battery Energy Storage Suitable for Fault Characteristic Analysis" published by Zhang Jiaqi et al., Automation of Electric Power Systems, 2023, 47(07): 166 - 173. In addition to the positive sequence voltage ride-through control, the energy storage converter proposed in this article also introduced a negative sequence control link. The established electromagnetic transient model can be applied to symmetric and asymmetric low and high voltage ride-through scenarios and can accurately reflect the electromagnetic transient response characteristics of lithium-ion battery energy storage systems. This article also mentioned low and high voltage ride-through control strategies, but did not break through the limitations of traditional electromechanical control instructions and had low versatility.

[0007] In summary, the current modeling research on battery energy storage systems mostly focuses on customized modeling for single - model energy storage systems in steady - state or low - voltage scenarios, etc., and the constructed models cannot simultaneously adapt to low / high - voltage scenarios and different models of energy storage units. Therefore, it is very necessary to study a general low / high - voltage ride - through control model identification method for battery energy storage systems with a wide application range and high generality. Summary of the Invention

[0008] The present invention aims to solve the problem that the poor generality of the battery energy storage system model and its control is caused by the single applicable scenario and single applicable model in the existing battery energy storage system modeling research.

[0009] A general low / high - voltage ride - through control method for a battery energy storage system. The grid - connected structure of the battery energy storage system includes a battery bank, a grid - connected converter, a filter, a transformer, a collector network, and a control system; the battery bank, grid - connected converter, filter, and control system on the low - voltage side of the transformer form a bidirectional power conversion system of the energy storage system, namely the PCS; the high - voltage side of the converter is the collector network, which feeds energy into the grid; the battery energy storage system is controlled by using the general low / high - voltage ride - through control strategy in the controller; the general low / high - voltage ride - through control strategy of the battery energy storage system includes a steady - state operation control strategy and a general low / high - voltage ride - through control strategy of the battery energy storage system.

[0010] The steady - state operation control strategy of the battery energy storage system is as follows:

[0011] Use e d and e q to represent the d - axis component and q - axis component of the grid - connected point voltage in the dq coordinate system, and use v d , v q and i d , i q to represent the d - axis component and q - axis component of the output voltage and output current of the converter on the AC side in the dq coordinate system respectively; the energy storage PCS adopts a double - closed - loop decoupling control structure, and the steady - state control includes a power outer loop and a current inner loop. The current reference value output by the power outer loop is limited and then generates i dref and i qref cascaded to the current inner loop. i dref , i qref are the reference values of i d , i q ; the d - axis voltage component and q - axis voltage component obtained by adjusting through the PI controller of the current inner loop are then transformed by dq - abc transformation to generate the abc three - phase voltage required for pulse - width modulation and transmitted to the converter to realize the on - off of the converter valve - level switch; the current inner loop realizes the mutual cancellation of the controller and the coupling term through the feed - forward compensation method. After decoupling, the d - axis is only related to active power, and the q - axis control is only related to reactive power, realizing the independent control of active and reactive power.

[0012] The general control strategy for low / high voltage ride-through of the battery energy storage system is as follows:

[0013] 1) General control strategy for low voltage ride-through:

[0014] During active and reactive low voltage faults, the energy storage system enters the low voltage ride-through process, cuts off the power outer loop, and only retains the current inner loop for single-loop control; the d-axis and q-axis current commands for low voltage ride-through are controlled as shown in Equations (9) and (10) respectively:

[0015]

[0016] i qref =max[k qL1 (U Lin -u)+k qL2 I q0 +I qLset ,I qLmin (10)

[0017] In the formula, k dL1 , k dL2 , I dLset , k0 are the calculation coefficients of the active current during low voltage ride-through; u is the positive sequence voltage at the grid connection point; I d0 is the initial active current; P0 is the initial active power; I max is the maximum current; k qL1 , k qL2 , I qLset are the calculation coefficients of the reactive current during low voltage ride-through; U Lin is the voltage threshold for reactive power to enter low voltage ride-through; I q0 is the initial reactive current; I qLmin is the minimum value of the reactive current during low voltage ride-through;

[0018] During the recovery period of the active low voltage fault, the active current recovers to the value before the fault at a rate of r Id ;

[0019] 2) General control strategy for high voltage ride-through

[0020] During the high voltage fault, the reactive power outer loop is disconnected, and the d-axis and q-axis current commands for low voltage ride-through are controlled as shown in Equations (11) and (12) respectively;

[0021] i dref =k op (P ref -P)+k oi ∫(P ref -P)dt (11)

[0022] i qref =min[kqH1 (u - U Hin ) + k qH2 I q0 + I qHset ,I qHmax (12)

[0023] Wherein, k qH1 、k qH2 、I qHset are respectively the calculation coefficients of the high - penetration reactive current; U Hin is the voltage threshold for reactive power to enter high - penetration; I qHmax is the maximum value of the reactive current during high - penetration;

[0024] The active power loop maintains a steady - state grid - connected operation state.

[0025] Furthermore, the construction process of the steady - state operation control strategy of the battery energy storage system includes:

[0026] Based on the bidirectional power conversion system, the mathematical model of the PCS converter in the dq rotating coordinate system with a synchronous speed of ω is:

[0027]

[0028] Wherein, e d 、e q are the d - axis component and q - axis component of the grid - connection point voltage in the dq coordinate system; v d 、v q and i d 、i q are respectively the d - axis component and q - axis component of the converter AC - side output voltage and output current in the dq coordinate system; R0 and L0 represent the resistance and inductance in the three - phase filter;

[0029] Converting the mathematical model described in Equation (1) to the frequency domain gives:

[0030]

[0031] Wherein, s is the Laplace operator;

[0032] Adopting a double - closed - loop feed - forward decoupling control form; let

[0033]

[0034] Wherein, v' d and v' q are set as equivalent control variables; t represents time;

[0035] v' d and v' q are realized by introducing a current - loop PI regulator:

[0036]

[0037] Wherein, k p and k i are respectively the proportional coefficient and integral coefficient of the current loop PI regulator; i dref and i qref are respectively the reference values of i d and i q ;

[0038] Substituting Equation (3) into Equation (1), we get:

[0039]

[0040] Under the two-phase rotating coordinate system, the active power P and reactive power Q output by the PCS are deduced as:

[0041]

[0042] Under the three-phase balanced condition, the d-axis is defined to coincide with the grid connection point voltage vector in the Park transformation. At this time, the expressions (6) of the active power P and reactive power Q output by the PCS become:

[0043]

[0044] The active power output by the PCS is proportional to the active current i d , and the reactive power is proportional to the reactive current i q . The power outer loop PI regulator is introduced to generate i dref and i qref :

[0045]

[0046] Wherein, P ref and Q ref are respectively the reference values of the active power and reactive power; k op and k oi are respectively the proportional coefficient and integral coefficient of the power outer loop PI regulator;

[0047] The reference value P ref of the active power is subtracted from the active power P after being limited by the active power change rate r P , and then regulated by the outer loop PI controller. The output is limited by the maximum value I dmax and minimum value I dmin of the d-axis current to obtain i dref . The difference between i dref and i d is regulated by the PI controller, and the output introduces the feed-forward compensation terms ωL0i q and e dObtain the d-axis component of the converter AC-side voltage; ωL0i as the feedforward compensation term q is the q-axis current coupling term, where ω is the angular frequency, L0 represents the inductor in the three-phase filter; i dref is for i d reference value;

[0048] Reactive power reference value Q ref After being limited by the reactive power change rate r Q and then subtracted from the reactive power Q, it is adjusted by the outer-loop PI controller. The output is limited by the maximum value I qmax and the minimum value I qmin to obtain i qref , i qref is subtracted from i q and then adjusted by the PI controller. The output feedforward compensation term ωL0i d and e q are used to obtain the q-axis component of the converter AC-side voltage; i qref is for i q reference value; ωL0i as the feedforward compensation term d is the d-axis current coupling term;

[0049] Furthermore, determine the steady-state operation control strategy of the battery energy storage system.

[0050] Furthermore, during the process of controlling the battery energy storage system using the low / high voltage ride-through general control strategy, the strategy switching for the entire process of fault ride-through is realized by judging the active fault flag bit and the reactive fault flag bit;

[0051] Determination of the active fault flag bit: The initial value of the active fault flag bit is 0, and the controller control state is the steady-state double closed-loop control at this time; if a low voltage fault occurs and the positive sequence voltage u at the grid connection point is lower than the voltage threshold for the active to enter the low ride-through, the active fault flag bit is set to 1. At this time, the controller enters the active low ride-through control, cuts off the active outer loop, and performs single-loop control of the current inner loop according to the active low ride-through current command. After the voltage recovers, the active current recovers to the value before the fault at the rate of r Id and then the active fault flag bit is set to 0, and the controller switches back to the steady-state double closed-loop control; if a high voltage fault occurs, the active fault flag bit remains 0, and the active control continues to use the steady-state double closed-loop control strategy;

[0052] Determination of reactive power fault flag bit: The initial value of the reactive power fault flag bit is 0. At this time, the idle state of the controller is the steady-state double-loop control. If a low-voltage fault occurs and the positive-sequence voltage u at the grid connection point is lower than the voltage threshold for reactive power to enter low-voltage ride-through, the reactive power fault flag bit is set to 1. At this time, the controller enters the reactive power low-voltage ride-through control, cuts off the reactive power outer loop, and performs single-loop control of the current inner loop according to the reactive power low-voltage ride-through current command. After the voltage recovers and the positive-sequence voltage u at the grid connection point is higher than the voltage threshold for reactive power to exit low-voltage ride-through, the reactive power fault flag bit is set to 0, and the controller switches back to the steady-state double-loop control. If a high-voltage fault occurs and the positive-sequence voltage u at the grid connection point is higher than the voltage threshold for reactive power to enter high-voltage ride-through, the reactive power fault flag bit is set to 2. At this time, the controller enters the reactive power high-voltage ride-through control, cuts off the reactive power outer loop, and performs single-loop control of the current inner loop according to the reactive power high-voltage ride-through current command. After the voltage recovers and the positive-sequence voltage u at the grid connection point is lower than the voltage threshold for reactive power to exit high-voltage ride-through, the reactive power fault flag bit is set to 0, and the controller switches back to the steady-state double-loop control.

[0053] A parameter identification method for a general low / high voltage ride-through control strategy of a battery energy storage system, which performs parameter identification on the general low / high voltage ride-through control strategy in the general low / high voltage ride-through control method of the battery energy storage system. The parameters to be identified include: k dL1 、k dL2 、I dLset 、k0、I max 、r Id 、k qL1 、k qL2 、I qLset 、U Lin 、I qLmin 、k qH1 、k qH2 、I qHset 、U Hin 、I qHmax ; The parameters are divided into three categories: threshold parameters: U Lin 、U Hin ,command parameters: k dL1 、k dL2 、I dLset 、k0、r Id 、k qL1 、k qL2 、I qLset 、k qH1 、k qH2 、I qHset ,limiting parameters: I qLmin 、I qHmax 、I max ; The specific parameter identification process includes the following steps:

[0054] 1) Obtain the manufacturer's test response data and voltage step test response data of the energy storage unit under the single low / high voltage fault test condition;

[0055] 2) Identify the threshold parameters based on the voltage step test response data:

[0056] The threshold parameters U Lin and U Hin are the grid connection point voltages at which reactive power enters the low and high voltage ride-through control states respectively. Taking the voltage step test response data of step-by-step downward / upward as the research object, judge whether the reactive power control of the energy storage system enters the fault ride-through control state according to the change of reactive power during the voltage step test; if the reactive power of the step-by-step downward and upward voltage step tests changes and is no longer the initial reactive power, it is determined that the system enters the fault ride-through control state, and record the grid connection voltage at this moment as U Lin and U Hin ;

[0057] 3) Identify the command parameters by fitting:

[0058] For the command parameters of active power low ride-through control, respectively use the grid connection voltage, active current, active power and current in the steady-state interval during the active low voltage ride-through fault under different initial charge and discharge powers and different fault voltages, and use the least squares method for k in formula (9) dL1 u + k dL2 I d0 + I dLset and Fit the parameters in the two formulas to obtain the specific values of the command parameters k dL1 , k dL2 , I dLset and k0; Use the active current during fault recovery to fit the active power recovery speed r Id by the least squares method;

[0059] For the command parameters of reactive power low ride-through control, use the grid connection voltage and reactive current during the reactive low voltage ride-through fault under different initial charge and discharge powers and different fault voltages, and use the least squares method for k in formula (10) qL1 (U Lin - u) + k qL2 I q0 + I qLset in the formula to fit the parameters, and obtain the specific values of the command parameters k qL1 , k qL2 and I qLset ; For active power high ride-through control, the active power high ride-through control strategy proposed by the present invention adopts the steady-state double closed-loop control strategy and control parameters, and parameter identification is no longer required here;

[0060] For the instruction parameters of the reactive power low-ride-through control, by using the grid-connected voltage and reactive current during the reactive power high-voltage ride-through fault under different initial charge and discharge powers and different fault voltages, the least squares method is used for k in Equation (12) qH1 (u - U Hin ) + k qH2 I q0 + I qHset to fit the parameters in it, and obtain the specific values of the instruction parameters k qH1 , k qH2 and I qHset ;

[0061] 4) Identify the clipping parameters I qLmin , I qHmax , I max according to the severe voltage dip / elevation fault. The severe voltage dip is that the grid voltage drops below 0.35 p.u., and the severe voltage elevation is that the grid voltage rises above 1.3 p.u.;

[0062] Obtain the threshold parameters, instruction parameters and clipping parameters according to the above steps.

[0063] Furthermore, the voltage fault test conditions at least include that the energy storage system operates in a steady state at high power or low power, and the operation mode is charging or discharging. The three-phase grid voltage drops to 90%, 80%, 75%, 70%, 60%, 50%, 40%, 35%, 30%, 20%, 10% and 0%, and the three-phase grid voltage rises to 110%, 115%, 120%, 125%, 130%, 135% and 140%. The combinations formed by various situations are used as a test condition; the high power is 0.9 p.u. to 1.0 p.u., and the low power is 0.1 p.u. to 0.3 p.u.

[0064] Furthermore, the voltage step test condition is: set the initial grid voltage of the energy storage system to 1 p.u., and perform a voltage step test with an interval value of 0.01 p.u. step by step up / down to obtain the voltage step test response data. The upper and lower limits of voltage adjustment are 1.15 p.u. and 0.75 p.u. respectively.

[0065] Furthermore, during the process of identifying the clipping parameters I qLmin , I qHmax , I max according to the severe voltage dip / elevation fault, I qLmin takes the minimum value of the reactive current in the manufacturer's test response data under the severe voltage dip condition, I qHmax takes the maximum value of the reactive current in the manufacturer's test response data under the severe voltage elevation condition, I maxTake the maximum value of the current in the manufacturer's test response data under the severe voltage dip condition.

[0066] Further, the method further includes the following steps:

[0067] Substitute the obtained threshold parameter, command parameter, and amplitude limiting parameter into the general low and high voltage ride-through control strategy to form a complete control model, and build a simulation model to verify whether the simulation accuracy of the whole process of the model voltage ride-through meets the requirements. When it meets the requirements, complete the parameter identification.

[0068] A general low / high voltage ride-through control system for a battery energy storage system, the control system includes a steady-state control unit and a general low / high voltage ride-through control strategy unit;

[0069] The steady-state control unit controls the battery energy storage system by using a steady-state operation control strategy; the general low / high voltage ride-through control strategy unit controls the battery energy storage system by using a general low / high voltage ride-through control strategy;

[0070] The steady-state operation control strategy of the battery energy storage system is as follows:

[0071] Use e d 、e q to represent the d-axis component and q-axis component of the grid connection point voltage in the dq coordinate system, and use v d 、v q and i d 、i q to represent the d-axis component and q-axis component of the output voltage and output current of the converter on the AC side in the dq coordinate system respectively; the energy storage PCS adopts a double closed-loop decoupling control structure, and the steady-state control includes a power outer loop and a current inner loop. The current reference value output by the power outer loop is limited and then generates i dref and i qref cascaded to the current inner loop. i dref 、i qref are the reference values of i d 、i q ; the d-axis voltage component and q-axis voltage component obtained by adjusting through the current inner loop PI controller are then transformed by dq-abc to generate the abc three-phase voltage required for pulse width modulation and transmitted to the converter to realize the on and off of the converter valve level switch; the current inner loop realizes the cancellation of the controller and the coupling term through the feed-forward compensation method. After decoupling, the d-axis is only related to active power, and the q-axis control is only related to reactive power, realizing the separate control of active and reactive power;

[0072] The general low / high voltage ride-through control strategy of the battery energy storage system is as follows:

[0073] 1) General low voltage ride-through control strategy:

[0074] During active and reactive low-voltage faults, the energy storage system enters the low-voltage ride-through process, cuts off the power outer loop, and only retains the current inner loop for single-loop control; the d-axis and q-axis current command control equations during low-voltage ride-through are shown in Equations (9) and (10) respectively:

[0075]

[0076] i qref = max[k qL1 (U Lin - u)+ k qL2 I q0 + I qLset , I qLmin (10)

[0077] In the formula, k dL1 , k dL2 , I dLset , k0 are the calculation coefficients of the active current during low-voltage ride-through respectively; u is the positive-sequence voltage at the grid connection point; I d0 is the initial active current; P0 is the initial active power; I max is the maximum value of the current; k qL1 , k qL2 , I qLset are the calculation coefficients of the reactive current during low-voltage ride-through respectively; U Lin is the voltage threshold for reactive power to enter low-voltage ride-through; I q0 is the initial reactive current; I qLmin is the minimum value of the reactive current during low-voltage ride-through;

[0078] During the recovery period of the active low-voltage fault, the active current recovers to the value before the fault at a rate of r Id ;

[0079] 2) General control strategy for high-voltage ride-through

[0080] During high-voltage faults, the reactive power outer loop is disconnected, and the d-axis and q-axis current command control equations during low-voltage ride-through are shown in Equations (11) and (12) respectively;

[0081] i dref = k op (P ref - P)+ k oi ∫(P ref - P)dt (11)

[0082] i qref = min[k qH1 (u - U Hin )+ k qH2 I q0 + I qHset , I qHmax (12)

[0083] In the formula, k qH1 , k qH2 , I qHset are respectively the calculation coefficients of the high-penetration reactive current; U Hin is the voltage threshold for reactive power to enter high penetration; I qHmax is the maximum value of the reactive current during high penetration;

[0084] The active power loop maintains a steady-state grid-connected operation state.

[0085] A general low / high voltage ride-through control device for a battery energy storage system, the device includes a processor and a memory, and at least one instruction is stored in the memory, and the at least one instruction is loaded and run by the processor to implement the general low / high voltage ride-through control system of a battery energy storage system.

[0086] Beneficial effects:

[0087] Aiming at solving the problems of poor generality and difficult modeling of the existing battery energy storage system models and their controls, the present invention proposes a general low / high voltage ride-through control strategy and control method for a battery energy storage system, as well as a parameter identification method for the control strategy. The control strategy can simultaneously meet the simulation requirements of the low voltage fault and high voltage fault of the energy storage system, and has a wide generality, and can be applied to energy storage units with different initial powers, different fault degrees and different models. Therefore, the control model and control method have very good generality. At the same time, the method of the present invention has good simulation accuracy in simulating the low / high voltage fault ride-through characteristics of the energy storage system, and can provide a research basis for the grid-connected control research of the battery energy storage system. Description of the drawings

[0088] Figure 1 It is a schematic diagram of the equivalent circuit of the energy storage PCS.

[0089] Figure 2 It is a schematic diagram of the equivalent structure of the energy storage PCS circuit.

[0090] Figure 3 It is a schematic diagram of the PCS control structure with current loop control introduced.

[0091] Figure 4 It is a schematic diagram of the double closed-loop decoupling control structure of the energy storage PCS.

[0092] Figure 5 It is a logic diagram of the general voltage fault ride-through control method for a battery energy storage system.

[0093] Figure 6 It is the weighted average deviation of each electrical quantity under all discharge conditions of a certain model of energy storage unit with a large power voltage dip of 0-0.9 p.u.

[0094] Figure 7is the weighted average deviation of each electrical quantity under all discharge conditions of a certain type of energy storage unit for large-power voltage dips of 1.1 - 1.4 p.u.

[0095] Figure 8 is the weighted average deviation of each electrical quantity under all discharge conditions of a certain type of energy storage unit for small-power voltage dips of 0 - 0.9 p.u.

[0096] Figure 9 is the weighted average deviation of each electrical quantity under all discharge conditions of a certain type of energy storage unit for small-power voltage dips of 1.1 - 1.4 p.u.

[0097] Figure 10 is the weighted average deviation of each electrical quantity under all charge conditions of a certain type of energy storage unit for large-power voltage dips of 0 - 0.9 p.u.

[0098] Figure 11 is the weighted average deviation of each electrical quantity under all charge conditions of a certain type of energy storage unit for large-power voltage dips of 1.1 - 1.4 p.u.

[0099] Figure 12 is the weighted average deviation of each electrical quantity under all charge conditions of a certain type of energy storage unit for small-power voltage dips of 0 - 0.9 p.u.

[0100] Figure 13 is the weighted average deviation of each electrical quantity under all charge conditions of a certain type of energy storage unit for small-power voltage dips of 1.1 - 1.4 p.u. Detailed implementation manners

[0101] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention.

[0102] In order to solve the problem of difficult modeling of the voltage ride-through control model of the battery energy storage system, the present invention provides a general low / high voltage ride-through control model identification method for the electromagnetic transient model of the battery energy storage system. The present invention mainly focuses on the control identification of the entire process of voltage fault ride-through of the energy storage model, obtains the control structure of the energy storage model by designing a generally applicable general control strategy, and proposes a parameter identification method based on the control structure. Detailed implementation manner one:

[0104] This implementation manner is a general low / high voltage ride-through control strategy and control method for the battery energy storage system, wherein the control method is to control the battery energy storage system by using the general low / high voltage ride-through control strategy in the controller; the construction process of the general low / high voltage ride-through control strategy of the battery energy storage system includes the following steps:

[0105] S1. Construct the steady-state operation control strategy of the battery energy storage system

[0106] The typical grid-connected structure of a battery energy storage system mainly includes a battery bank, a grid-connected inverter, a filter, a transformer, a collector network, and a control system. The battery bank, grid-connected inverter, filter, and control system on the low-voltage side of the transformer constitute the bidirectional power conversion system of the energy storage system, namely the PCS (Power Conversion System); the high-voltage side of the inverter is the collector network, which feeds the energy into the grid.

[0107] Through active and reactive power control, the PCS maintains voltage stability and reduces grid-connected fluctuations. From the perspective of the grid, the power external characteristics of the energy storage system are mainly determined by the control strategy of the PCS. The equivalent circuit of the PCS is as Figure 1 shown, and the equivalent circuit includes: the three-phase voltage on the low-voltage side of the transformer, the filter resistance and filter inductance, the detailed topology of the inverter, the DC-side support capacitor, and the battery bank. The three-phase voltages on the low-voltage side of the transformer are e a 、e b 、e c (i.e., the three-phase voltages at the grid connection point of the energy storage PCS); the filter composed of the three-phase filter resistance R0 and the series filter inductance L0; in the detailed topology of the inverter (two-level topology), v a 、v b 、v c and i a 、i b 、i c are the three-phase output voltages and three-phase output currents on the AC side of the inverter respectively. S a 、S b 、S c are the three-phase bridge arm switching functions respectively. S k =1(k=a,b,c) indicates that the upper transistor of the corresponding bridge arm is conducting and the lower transistor is off. S k =0(k=a,b,c) indicates that the upper transistor of the corresponding bridge arm is off and the lower transistor is conducting; the DC-side support capacitor C dc , where i dc is the current flowing through the capacitor, and u dc is the DC-side bus voltage; the battery bank, where i load is the DC-side load current.

[0108] The mathematical model of the PCS inverter in the dq rotating coordinate system with a synchronous speed of ω is:

[0109]

[0110] In the formula, e d 、e q are the d-axis component and q-axis component of the grid connection point voltage in the dq coordinate system; v d 、v q and i d 、i qThey are respectively the d-axis component and q-axis component of the output voltage and output current on the AC side of the converter in the dq coordinate system.

[0111] Converting the mathematical model described in Equation (1) to the frequency domain gives:

[0112]

[0113] In the formula, s is the Laplace operator.

[0114] It can be seen from this that the equivalent structure of the energy storage PCS circuit is as Figure 2 shown. The d-axis component i of the current on the low-voltage side of the transformer d is related not only to the d-axis component v of the voltage on the AC side of the inverter d , the filter resistance R0 and the filter inductance L0, but also affected by the d-axis component e of the grid connection point voltage d and the q-axis current coupling term ωL0i q . The q-axis component i of the current on the low-voltage side of the transformer q is related not only to the q-axis component v of the voltage on the AC side of the inverter q , the filter resistance R0 and the filter inductance L0, but also affected by the q-axis component e of the grid connection point voltage q and the d-axis current coupling term ωL0i d . It can be seen that the mutual coupling between the d-axis and q-axis in the PCS equivalent circuit will affect the control performance of active and reactive power. Therefore, the commonly used double closed-loop feedforward decoupling control form is adopted.

[0115] Let

[0116]

[0117] In the formula, v' d and v' q are set as equivalent control variables; t represents time.

[0118] It can be seen that at this time, the d-axis current is only affected by the d-axis equivalent control variable v' d , and the q-axis current is only affected by the q-axis equivalent control variable v' q . The circuit can be equivalent to a decoupled and independent first-order linear system. v' d and v' q can be realized by introducing a current loop PI regulator:

[0119]

[0120] In the formula, k p , k i are respectively the proportional coefficient and integral coefficient of the current loop PI regulator; i dref , i qref are respectively i d, i q The reference value of

[0121] Substituting Equation (3) into Equation (1) gives:

[0122]

[0123] From this, the PCS control structure with current loop control is obtained, as Figure 3 shown. The inner current loop control introduces a feedforward compensation term ωL0i q , ωL0i d and e d , e q which effectively cancels the influence of the cross-coupling term and the grid connection point voltage disturbance, is beneficial to achieving independent control of d-axis and q-axis currents, and effectively enhances the dynamic control performance of the PCS.

[0124] Under the two-phase rotating coordinate system, the active power P and reactive power Q output by the PCS can be derived as:

[0125]

[0126] Under the three-phase balanced condition, in the Park transformation, the d-axis is defined to coincide with the grid connection point voltage vector. At this time, e q = 0, v q ≈0, and the expressions (6) for the active power P and reactive power Q output by the PCS become:

[0127]

[0128] It can be seen that the active power output by the PCS is proportional to the active current i d , and the reactive power is proportional to the reactive current i q . Therefore, a power outer loop PI regulator is introduced to generate i dref and i qref :

[0129]

[0130] where P ref and Q ref are the reference values of the active power and reactive power respectively; k op , k oi are the proportional coefficient and integral coefficient of the power outer loop PI regulator respectively.

[0131] In summary, the double closed-loop decoupling control structure of the energy storage PCS is as Figure 4 shown. The reference value P ref of the active power is restricted by the rate of change r P of the active power, then subtracted from the active power P, and adjusted by the outer loop PI controller. The output is passed through the maximum value I dmax of the d-axis current.and the minimum value I dmin After being limited, i is obtained dref , i dref Subtracted from i d After the difference is adjusted by a PI controller, the output is introduced with a feed-forward compensation term ωL0i q and e d The required d-axis component of the converter AC-side voltage is obtained; the reactive power reference value Q ref After passing through the reactive power change rate r Q After being limited and subtracted from the reactive power Q, it is adjusted by an outer-loop PI controller, and the output is passed through the maximum value I of the q-axis current qmax and the minimum value I qmin After being limited, i is obtained qref , i qref Subtracted from i q After the difference is adjusted by a PI controller, the output is introduced with a feed-forward compensation term ωL0i d and e q The required q-axis component of the converter AC-side voltage is obtained.

[0132] In summary, the steady-state control includes a power outer loop and a current inner loop. The current reference value output by the power outer loop is limited to generate i dref and i qref Cascaded to the current inner loop, the d-axis voltage component and q-axis voltage component obtained by adjusting through the current inner loop PI controller are then transformed by dq-abc to generate the required abc three-phase voltage for pulse width modulation and transmitted to the converter to realize the on and off of the converter valve-level switch. The current inner loop realizes the mutual cancellation of the controller and the coupling term through feed-forward compensation. After decoupling, the d-axis is only related to active power, and the q-axis control is only related to reactive power, realizing the separate control of active and reactive power.

[0133] S2. Propose a low / high voltage ride-through general control strategy applicable to multiple models of battery energy storage systems

[0134] According to the low and high voltage fault ride-through characteristics of mainstream model energy storage systems, the low / high voltage ride-through general control strategy proposed by the present invention is as follows:

[0135] 1) Low voltage ride-through general control strategy

[0136] The present invention divides the low voltage ride-through process of the energy storage system into stages according to active and reactive power. Active power can be divided into four stages: before fault occurrence, during low voltage fault, during low voltage fault recovery, and after fault clearance. Reactive power is divided into three stages: before fault occurrence, during low voltage fault, and after fault clearance. In the two intervals of before fault occurrence and after fault clearance, the energy storage system is in the steady-state operation stage, and the active and reactive power are both controlled by the steady-state operation control method mentioned in step S1 to realize active power and reactive power control. The control strategies during the low voltage fault of active and reactive power and the control strategy during the low voltage ride-through recovery of active power are introduced below respectively.

[0137] During the active and reactive low - voltage faults, the energy storage system enters the low - voltage ride - through process, cuts off the power outer loop, and only retains the current inner loop for single - loop control. To simultaneously meet the requirements of reactive power support, initial power limit, and current limit of the grid for the energy storage converter during the fault, the d - axis and q - axis current command control methods proposed in the present invention are shown in Equations (9) and (10) respectively:

[0138]

[0139] i qref = max[k qL1 (U Lin - u)+ k qL2 I q0 + I qLset , I qLmin (10)

[0140] In the formula, k dL1 , k dL2 , I dLset , k0 are respectively the calculation coefficients of the active current during low - voltage ride - through; u is the positive - sequence voltage at the grid connection point; I d0 is the initial active current; P0 is the initial active power; I max is the maximum current; k qL1 , k qL2 , I qLset are respectively the calculation coefficients of the reactive current during low - voltage ride - through; U Lin is the voltage threshold for reactive power to enter low - voltage ride - through; I q0 is the initial reactive current; I qLmin is the minimum value of the reactive current during low - voltage ride - through.

[0141] It can be seen from Equations (9) and (10) that to simulate the low - voltage fault ride - through control strategies of different types of units, the present invention is based on the control strategies proposed in the "Modeling Guidelines for Electrochemical Energy Storage Power Stations" (i.e., i dref = k dL1 u + k dL2 I d0 + I dLset , i qref = k qL1 (U Lin - u)+ k qL2 I q0 + I qLset ), and an active - current control instruction related to the initial active power is added to the active - power link, considering the active - current limit instruction with reactive - power priority (i.e., ), and a reactive - current limit instruction (i.e., I qLmin ) is added to the reactive - power link.

[0142] During the recovery from the active low-voltage fault, the active current generally recovers to the pre-fault value at a certain slope. Therefore, the present invention adds an active current speed limit command r to the active low-voltage fault ride-through control. Id During the recovery period, the active power recovers at a rate of r Id to the pre-fault value.

[0143] 2) General control strategy for high-voltage ride-through

[0144] The whole process of high-voltage ride-through of the energy storage system can be divided into three stages: before the fault occurs, during the high-voltage fault, and after the fault is cleared. Different from the low-voltage fault stage division, the active power is not separately divided into a fault recovery stage, because after the high-voltage fault ends, the active power generally directly recovers to the pre-fault value and there is no special recovery process. In the two intervals of before the fault occurs and after the fault is cleared, the energy storage system is in the steady-state operation stage, and the active power and reactive power control are realized by using the steady-state operation control method mentioned in step S1.

[0145] During the high-voltage fault, the energy storage system enters the high-voltage ride-through process. The d-axis and q-axis current command control formulas for low-voltage ride-through proposed by the present invention are shown in formulas (11) and (12) respectively.

[0146] i dref = k op (P ref - P) + k oi ∫(P ref - P)dt (11)

[0147] i qref = min[k qH1 (u - U Hin ) + k qH2 I q0 + I qHset , I qHmax (12)

[0148] In the formulas, k qH1 , k qH2 , I qHset are the calculation coefficients of the high-ride reactive current respectively; U Hin is the voltage threshold for reactive power to enter high-ride; I qHmax is the maximum value of the reactive current during high-ride.

[0149] It can be seen from formulas (11) and (12) that in order to simulate the high-voltage fault ride-through control strategies of different types of units, the present invention uses the control strategy in the "Modeling Guidelines for Electrochemical Energy Storage Power Stations" (i.e., i dref = k dH1 u + k dH2 I d0 + I dHset , iqref = k qH1 (u - U Hin ) + k qH2 I q0 + I qHset ) Based on this, the active power link retains the active outer loop, continues to use the steady-state control structure, and realizes the active high penetration control by changing P ref . The reactive power link adds a reactive current limit command I qHmax .

[0150] In summary, the low / high voltage ride-through general control strategy of the battery energy storage system designed by the present invention is as follows Figure 5 shown: When a voltage dip or rise fault occurs, the reactive power outer loop is disconnected, and a control method of cascading a reactive current generator and the inner loop is adopted. On the one hand, the reactive power response speed can be improved, and on the other hand, appropriate voltage support can be provided according to the amplitude of the voltage dip or rise. In terms of active power control, if a low voltage fault occurs in the power grid, the active power outer loop is disconnected, and a reactive power priority control strategy is adopted. After the fault ends, the active power recovers at a rate r Id . When a high voltage fault occurs, the active power loop maintains the steady-state grid-connected operation state, and the active power is kept constant during the fault by reducing the active current. This control strategy is applicable to different types of energy storage systems by configuring appropriate parameters for the control strategy, and the strategy switching during the whole process of fault ride-through is realized by judging the active fault flag bit and the reactive fault flag bit

[0151] It should be noted that the switching of the active and reactive power control strategies proposed by the present invention is controlled by two different signals, namely the active fault flag bit and the reactive fault flag bit. This feature is designed based on the investigation of the response characteristics of mainstream energy storage systems. Through investigation, it is found that there are differences in the nodes where the active and reactive power of the energy storage system enter and exit the fault ride-through state, and generally they cannot share one

[0152] The determination method of the active fault flag bit is as follows: The initial value of the active fault flag bit is 0, and at this time the controller control state is steady-state double closed-loop control; if a low voltage fault occurs and the positive sequence voltage u of the grid connection point is lower than the voltage threshold for the active power to enter low ride-through, the active fault flag bit is set to 1. At this time, the controller enters the active low ride-through control, cuts off the active outer loop, and performs single-loop control of the current inner loop according to the active low ride-through current command. After the voltage recovers, the active current recovers to the value before the fault at a rate of r Id , and then the active fault flag bit is set to 0, and the controller switches back to the steady-state double closed-loop control; if a high voltage fault occurs, the active fault flag bit remains 0, and the active power control continues to use the steady-state double closed-loop control strategy

[0153] The determination method of the reactive power fault flag bit is as follows: The initial value of the reactive power fault flag bit is 0. At this time, the idle state of the controller is the steady-state double closed-loop control. If a low-voltage fault occurs and the positive-sequence voltage u at the grid connection point is lower than the voltage threshold for reactive power to enter low-voltage ride-through, the reactive power fault flag bit is set to 1. At this time, the controller enters the reactive power low-voltage ride-through control, cuts off the reactive power outer loop, and performs single-loop control of the current inner loop according to the reactive power low-voltage ride-through current command. After the voltage recovers and the positive-sequence voltage u at the grid connection point is higher than the voltage threshold for reactive power to exit low-voltage ride-through, the reactive power fault flag bit is set to 0, and the controller switches back to the steady-state double closed-loop control. If a high-voltage fault occurs and the positive-sequence voltage u at the grid connection point is higher than the voltage threshold for reactive power to enter high-voltage ride-through, the reactive power fault flag bit is set to 2. At this time, the controller enters the reactive power high-voltage ride-through control, cuts off the reactive power outer loop, and performs single-loop control of the current inner loop according to the reactive power high-voltage ride-through current command. After the voltage recovers and the positive-sequence voltage u at the grid connection point is lower than the voltage threshold for reactive power to exit high-voltage ride-through, the reactive power fault flag bit is set to 0, and the controller switches back to the steady-state double closed-loop control. Specific Embodiment 2:

[0155] This embodiment is a parameter identification method for the general low / high voltage ride-through control strategy of a battery energy storage system. It is actually the parameter identification method of the general control strategy in Specific Embodiment 1. In Specific Embodiment 1, the control strategy for the entire process of voltage fault ride-through of the energy storage system has been constructed in steps S1 and S2. Based on the control strategy, the parameters to be identified are identified. The parameters to be identified include: k dL1 、k dL2 、I dLset 、k0、I max 、r Id 、k qL1 、k qL2 、I qLset 、U Lin 、I qLmin 、k qH1 、k qH2 、I qHset 、U Hin 、I qHmax . The above parameters can be divided into three categories: threshold parameters (U Lin 、U Hin ), command parameters (k dL1 、k dL2 、I dLset 、k0、r Id 、k qL1 、k qL2 、I qLset 、k qH1 、k qH2 、I qHset ), and limit parameters (I qLmin 、I qHmax 、I max ). The specific implementation steps of the parameter identification method are as follows:

[0156] 1) Obtain response data:

[0157] Use the battery energy storage unit instruction manual or the manufacturer's encapsulated model to obtain the manufacturer's test response data and voltage step test response data of the energy storage unit under the low / high voltage single fault test conditions specified in the "Draft for Comment on the Test Regulations for Electrochemical Energy Storage Power Station Model Parameters". Among them,

[0158] Voltage fault test conditions: Include the energy storage system operating in a steady state at high power (0.9 p.u. - 1.0 p.u.) or low power (0.1 p.u. - 0.3 p.u.), and the operating mode is charging or discharging. The three-phase grid voltage drops to 90%, 80%, 75%, 70%, 60%, 50%, 40%, 35%, 30%, 20%, 10% and 0%, and the three-phase grid voltage rises to 110%, 115%, 120%, 125%, 130%, 135% and 140%. The combinations formed by various situations are regarded as one test condition, with a total of at least 12 * 2 * 2 + 7 * 2 * 2 = 76 kinds;

[0159] The voltage step test conditions are as follows: Set the initial grid voltage of the energy storage system to 1 p.u., and perform voltage step tests with an interval value of 0.01 p.u. step by step up / down to obtain voltage step test response data. The upper and lower limits of voltage adjustment are 1.15 p.u. and 0.75 p.u. respectively.

[0160] It should be noted that the response data of this step includes the grid-connected positive sequence voltage, current, active current, reactive current, active power, and reactive power throughout the entire process of the manufacturer's test for fault ride-through. The response data specified in the standard "Draft for Comment on the Test Regulations for Electrochemical Energy Storage Power Station Model Parameters" includes the grid-connected positive sequence voltage, current, reactive current, active power, and reactive power. However, for the convenience of identification, the response data of the present invention adds active current. The active current data can be obtained by testing the manufacturer's encapsulated model or calculated using an arithmetic formula, which is the ratio of active power to voltage.

[0161] 2) Identify the threshold parameters based on the voltage step test response data:

[0162] The threshold parameters U Lin and U Hin are respectively the grid-connected voltages at which reactive power enters the low and high voltage ride-through control states. Therefore, taking the voltage step test response data step by step down / up as the research object, judge whether the reactive power control of the energy storage system enters the fault ride-through control state based on the change of reactive power during the voltage step test. If the reactive power of the voltage step test step by step down / up changes and is no longer the initial reactive power, it is determined that the system enters the fault ride-through control state, and the grid-connected voltage at this moment is recorded as U Lin, U Hin .

[0163] 3) Identify the instruction parameters by fitting:

[0164] For the instruction parameters of the active low voltage ride-through control, respectively use the grid-connected voltage, active current, active power and current in the steady-state interval during the active low voltage ride-through fault under different initial charge and discharge powers and different fault voltages, and use the least squares method for k in Equation (9) dL1 u + k dL2 I d0 + I dLset and Fit the parameters in the two equations to obtain the specific values of the instruction parameters k dL1 , k dL2 , I dLset and k0; Use the active current during the fault recovery period to fit the active recovery speed r Id by the least squares method;

[0165] For the instruction parameters of the reactive low voltage ride-through control, use the grid-connected voltage and reactive current during the reactive low voltage ride-through fault under different initial charge and discharge powers and different fault voltages, and use the least squares method for k in Equation (10) qL1 (U Lin - u) + k qL2 I q0 + I qLset in the equation to fit the parameters and obtain the specific values of the instruction parameters k qL1 , k qL2 and I qLset . For the active high voltage ride-through control, the active high voltage ride-through control strategy proposed by the present invention adopts the steady-state double closed-loop control strategy and control parameters, and there is no need to identify the parameters here.

[0166] For the instruction parameters of the reactive low voltage ride-through control, use the grid-connected voltage and reactive current during the reactive high voltage ride-through fault under different initial charge and discharge powers and different fault voltages, and use the least squares method for k in Equation (12) qH1 (u - U Hin ) + k qH2 I q0 + I qHset in the equation to fit the parameters and obtain the specific values of the instruction parameters k qH1 , k qH2 and I qHset .

[0167] Furthermore, for k in Equation (9) dL1 u + k dL2 I d0 + I dLsetThe fitting method is introduced by taking the parameters to be identified in the formula as an example: (1) Under the same initial active power, the active current values in the steady-state interval during the fault period under the low-break conditions of different fault voltages are recorded. Indicates that the positive sequence voltage of the grid connection point is recorded, and u is used in the following text. * Indicates that with u * For data with a linear relationship, we have the equation (2) The data recorded under the low-breakdown condition of different fault voltages are subtracted to obtain the active current increment Δi d * And the grid voltage increment Δu * , then we have the equation Established; (3) Δi d * With Δu * It is a linear relationship, and k is obtained by least squares fitting. dL1 ; (4) Record the active current value in the steady-state interval during the fault period under low-break conditions at different initial active powers Grid-connected point positive sequence voltage u * , initial active current (5) The data recorded under low-breakdown conditions with different initial active powers are subtracted from each other to obtain the active current increment Δi d * , grid connection point voltage increment Δu * and initial active current increment Then there is the equation Established; (6) With ΔI d0 It is a linear relationship, and k is obtained by least squares fitting. dL2 ; (7) According to equation The equation The instruction parameter k obtained through steps (1)-(6) is dL1 , k dL2 And test data u * , Substituting into the above formula, we get a set of I dLset , take the average value of this group of data as I dLset , the parameter identification is completed.

[0168] 4) Identify the limiting parameters based on severe voltage drop / rise faults:

[0169] In fact, there is a minimum / maximum limit on the reactive current of the energy storage system during the low / high voltage ride-through process, that is, the I qLmin ,I qHmax , the current has a maximum value limit, that is, the I mentioned in step S2 of the present inventionmax When a severe voltage dip occurs in the power grid (the grid voltage drops to 0.35 p.u. or below) or a severe voltage rise occurs (the grid voltage rises to 1.3 p.u. or above), the reactive current of the energy storage system will reach its limit when the degree of dip or rise is deep enough, and it will no longer have a linear relationship with the grid connection point voltage. The total value of the current will reach its limit when the degree of the dip fault is deep enough. I qLmin Take the minimum value of the reactive current in the manufacturer's test response data under the severe voltage dip condition. I qHmax Take the maximum value of the reactive current in the manufacturer's test response data under the severe voltage rise condition. I max Take the maximum value of the current in the manufacturer's test response data under the severe voltage dip condition.

[0170] 5) Substitute the threshold parameters (U Lin 、U Hin ), command parameters (k dL1 、k dL2 、I dLset 、k0、r Id 、k qL1 、k qL2 、I qLset 、k qH1 、k qH2 、I qHset ), and limit parameters (I qLmin 、I qHmax 、I max ) obtained from the above identification steps into the general low and high voltage ride-through control strategies to form a complete control model, and build a simulation model to verify that the simulation accuracy of the model during the entire voltage ride-through process meets the standard requirements, thus completing the parameter identification.

[0171] Embodiment

[0172] According to the specific implementation manner of the general low / high voltage ride-through control strategy and parameter identification method for the battery energy storage system of the present invention, a voltage ride-through control model is built and simulated for a battery energy storage system with a rated power of 200 kW of a certain manufacturer. The overall weighted average deviation of the response data of the simulation model under all discharge and charge conditions of this type of energy storage system from the response data tested by the manufacturer is as Figures 6 to 13 shown. The yellow square columns in the figure represent the maximum allowable deviation of the standard, and the cyan square columns represent the response deviation between the simulation model and the manufacturer's encapsulated model. From Figures 6 to 13 it can be seen that by using the control model construction and identification method proposed by the present invention, the simulation accuracy of the simulation model meets the standard requirements, and the response deviation is much smaller than the maximum allowable deviation of the standard, which proves the effectiveness of the method.

[0173] In summary, the present invention proposes a general low / high voltage ride-through control strategy and its parameter identification method for a battery energy storage system. Aiming at solving the problems of poor versatility and difficult modeling in the existing research on the modeling of battery energy storage systems, a general low / high voltage ride-through control strategy for battery energy storage systems is proposed. This strategy can simultaneously meet the simulation requirements of low voltage faults and high voltage faults of energy storage systems, and has wide versatility, and can be applied to energy storage units with different initial powers, different fault degrees and different models. The method of the present invention has good simulation accuracy in simulating the low / high voltage fault ride-through characteristics of energy storage systems, and can provide a research basis for the grid connection control research of battery energy storage systems. Specific Embodiment 3:

[0175] This embodiment is a general low / high voltage ride-through control system for a battery energy storage system, specifically the program instructions of the general low / high voltage ride-through control strategy for the battery energy storage system described in Specific Embodiment 1. It should be understood that the instructions include any computer program product, software or computerized method corresponding to the method described in the present invention; the instructions can be used to program a computer system or other electronic devices.

[0176] The general low / high voltage ride-through control system for a battery energy storage system described in this embodiment includes a steady-state control unit and a general low / high voltage ride-through control strategy unit;

[0177] The steady-state control unit controls the battery energy storage system by using a steady-state operation control strategy; the general low / high voltage ride-through control strategy unit controls the battery energy storage system by using a general low / high voltage ride-through control strategy;

[0178] The steady-state operation control strategy of the battery energy storage system is as follows:

[0179] Use e d and e q to represent the d-axis component and q-axis component of the grid connection point voltage in the dq coordinate system, and use v d , v q and i d , i q to represent the d-axis component and q-axis component of the output voltage and output current of the converter AC side in the dq coordinate system respectively; the energy storage PCS adopts a double closed-loop decoupling control structure, and the steady-state control includes a power outer loop and a current inner loop. The current reference value output by the power outer loop is limited and then generates i dref and i qref cascaded to the current inner loop, and i dref , i qref are i d , i qReference value; the d-axis voltage component and q-axis voltage component obtained by adjusting through the current inner-loop PI controller are then transformed by dq-abc to generate the abc three-phase voltages required for pulse width modulation and transmitted to the converter to realize the on and off of the converter valve-level switches; the current inner-loop cancels out the controller and the coupling term through feedforward compensation. After decoupling, the d-axis is only related to active power, and the q-axis control is only related to reactive power, realizing independent control of active and reactive power;

[0180] The low / high voltage ride-through general control strategy of the battery energy storage system is as follows:

[0181] 1) Low voltage ride-through general control strategy:

[0182] During the low voltage fault of active and reactive power, the energy storage system enters the low voltage ride-through process, cuts off the power outer-loop, and only retains the current inner-loop for single-loop control; the d-axis and q-axis current command control formulas for low voltage ride-through are shown in Formulas (9) and (10) respectively:

[0183]

[0184] i qref =max[k qL1 (U Lin -u)+k qL2 I q0 +I qLset ,I qLmin (10)

[0185] In the formula, k dL1 , k dL2 , I dLset , k0 are the calculation coefficients of the active current during low voltage ride-through respectively; u is the positive sequence voltage at the grid connection point; I d0 is the initial active current; P0 is the initial active power; I max is the maximum current; k qL1 , k qL2 , I qLset are the calculation coefficients of the reactive current during low voltage ride-through respectively; U Lin is the voltage threshold for reactive power to enter low voltage ride-through; I q0 is the initial reactive current; I qLmin is the minimum value of the reactive current during low voltage ride-through;

[0186] During the recovery period of the active low voltage fault, the active current recovers to the value before the fault at a rate of r Id ;

[0187] 2) High voltage ride-through general control strategy

[0188] During the high voltage fault, the reactive power outer-loop is disconnected, and the d-axis and q-axis current command control formulas for low voltage ride-through are shown in Formulas (11) and (12) respectively;

[0189] i dref = k op (P ref - P) + k oi ∫(P ref - P)dt (11)

[0190] i qref = min[k qH1 (u - U Hin ) + k qH2 I q0 + I qHset , I qHmax (12)

[0191] Wherein, k qH1 , k qH2 , I qHset are respectively the calculation coefficients of the high - penetration reactive current; U Hin is the voltage threshold for reactive power to enter high - penetration; I qHmax is the maximum value of the reactive current during high - penetration;

[0192] The active power loop maintains a steady - state grid - connected operation state. Specific Embodiment 4:

[0194] This embodiment is a general low / high - voltage ride - through control device for a battery energy storage system. The device includes a processor and a memory. It should be understood that any device including a processor and a memory described in the present invention, the device may also include other units and modules for display, interaction, processing, control, etc. through signals or instructions and other functions;

[0195] A general low / high - voltage ride - through control device for a battery energy storage system according to this embodiment includes a processor and a memory. At least one instruction is stored in the memory, and the at least one instruction is loaded and run by the processor to implement the general low / high - voltage ride - through control system for a battery energy storage system.

[0196] It should be understood that a computer memory may include a readable medium storing instructions, which may include but are not limited to magnetic memory, optical memory; magneto - optical memory includes read - only memory ROM, random access memory RAM, erasable programmable memory (e.g., EPROM and EEPROM), and flash memory layers, or other types of media suitable for storing electronic instructions.

[0197] The above calculation examples of the present invention are only for explaining in detail the calculation model and calculation process of the present invention, rather than limiting the implementation manners of the present invention. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is impossible to list all the implementation manners here. Any obvious changes or modifications derived from the technical solutions of the present invention still fall within the protection scope of the present invention.

Claims

1. A general low / high voltage ride-through control method for a battery energy storage system. The grid-connected structure of the battery energy storage system includes a battery pack, a grid-connected converter, a filter, a transformer, a collector network, and a control system. The battery pack, grid-connected converter, filter, and control system on the low-voltage side of the transformer constitute the bidirectional power conversion system of the energy storage system, i.e., the PCS. The high-voltage side of the converter is the collector network, which feeds the energy into the grid. The battery energy storage system is controlled by using the general low / high voltage ride-through control strategy in the controller. It is characterized in that The general low / high voltage ride-through control strategy of the battery energy storage system includes the steady-state operation control strategy and the general low / high voltage ride-through control strategy of the battery energy storage system. The steady-state operation control strategy of the battery energy storage system is as follows: Use e d and e q to represent the d-axis component and q-axis component of the grid connection point voltage in the dq coordinate system. Use v d and v q and i d and i q to represent the d-axis component and q-axis component of the converter AC side output voltage and output current in the dq coordinate system respectively; the energy storage PCS adopts a double closed-loop decoupling control structure, and the steady-state control includes a power outer loop and a current inner loop. The current reference value output by the power outer loop is limited and then generates i dref and i qref which are cascaded to the current inner loop. i dref and i qref are the reference values of i d and i q ; the d-axis voltage component and q-axis voltage component obtained by adjusting through the current inner loop PI controller are then transformed by dq-abc to generate the abc three-phase voltages required for pulse width modulation and transmitted to the converter to realize the opening and closing of the converter valve-level switches; the current inner loop realizes the cancellation of the current inner loop PI controller and the coupling term through the feedforward compensation method. After decoupling, the d-axis control is only related to the active power, and the q-axis control is only related to the reactive power, realizing the separate control of active and reactive power; The general low / high voltage ride-through control strategy of the battery energy storage system is as follows: 1) General low voltage ride-through control strategy: During the active and reactive low voltage faults, the energy storage system enters the low voltage ride-through process, cuts off the power outer loop, and only retains the current inner loop for single-loop control. The d-axis and q-axis current command control equations during low voltage ride-through are shown in equations (9) and (10) respectively: i qref = max[k qL1 (U Lin - u) + k qL2 I q0 + I qLset , I qLmin (In Equation (10), k dL1 , k dL2 , I dLset , and k0 are the calculation coefficients of the low - penetration active current respectively; u is the positive - sequence voltage at the grid - connection point; I d0 is the initial active current; P0 is the initial active power; I max is the maximum current; k qL1 , k qL2 , I qLset are the calculation coefficients of the low-voltage ride-through reactive current respectively; U Lin is the voltage threshold for reactive power to enter the low-voltage ride-through; I q0 is the initial reactive current; I qLmin is the minimum value of the reactive current during the low-voltage ride-through; During the active low-voltage fault recovery period, the active current recovers to the pre-fault value at a rate of r Id ; 2) General high voltage ride-through control strategy During the high voltage fault, the reactive power outer loop is disconnected, and the d-axis and q-axis current command control equations during high voltage ride-through are shown in equations (11) and (12) respectively; i dref = k op (P ref - P) + k oi ∫(P ref - P)dt(11) i qref =min[k qH1 (uU Hin )+k qH2 I q0 +I qHset ,I qHmax ](12)In the formula, k qH1 , k qH2 ,I qHset are the high-voltage reactive current calculation coefficients; U Hin I is the voltage threshold for reactive power to enter high voltage; qHmax is the maximum value of reactive current during high-voltage wear, k op Represents the proportional coefficient of the power outer loop PI regulator, k oi Represents the integral coefficient of the power outer loop PI regulator, P ref Represents the reference value of active power, P represents active power; The active power outer loop maintains the steady-state grid-connected operation state.

2. A general low / high voltage ride-through control method for a battery energy storage system according to claim 1, characterized in that, The construction process of the steady-state operation control strategy of the battery energy storage system includes: Based on the bidirectional power conversion system, the mathematical model of the PCS converter in the dq rotating coordinate system with a synchronous speed of ω is determined as: where, e d and e q are the d-axis component and q-axis component of the grid connection point voltage in the dq coordinate system; v d and v q and i d and i q are respectively the d-axis component and q-axis component of the converter AC side output voltage and output current in the dq coordinate system; R0 and L0 represent the resistance and inductance in the three-phase filter; Converting the mathematical model described in equation (1) to the frequency domain gives: where s is the Laplace operator; Adopt the double closed-loop feedforward decoupling control form; let wherein, v' d and v' q are set as equivalent control variables; t represents time; v' d and v' q is achieved by introducing a current loop PI regulator: where k p and k i are the proportional coefficient and integral coefficient of the current loop PI regulator respectively; i dref and i qref are the reference values of i d and i q respectively; Substituting equation (3) into equation (1) gives: Under the two-phase rotating coordinate system, the active power P and reactive power Q output by the PCS are deduced as: Under the three-phase balanced condition, it is defined in the Park transformation that the d-axis coincides with the grid connection point voltage vector. At this time, the expressions (6) of the active power P and reactive power Q output by the PCS become: The active power output by the PCS is proportional to the active current i d and the reactive power is proportional to the reactive current i q A power outer-loop PI regulator is introduced to generate i dref and i qref : Wherein, P ref and Q ref are respectively the reference values of the active power and the reactive power; k op , k oi are respectively the proportional coefficient and the integral coefficient of the power outer-loop PI regulator; Active power reference value P ref After being limited by the active power change rate r P The difference with the active power P is adjusted by the outer loop PI regulator, and the output is passed through the maximum value I of the d-axis current dmax And the minimum value I dmin After being limited, i is obtained dref , i dref The difference with i d Is adjusted by the PI controller, and the output introduces the feedforward compensation term ωL0i q And e d To obtain the d-axis component of the required converter AC side voltage; ωL0i as the feedforward compensation term q Is the q-axis current coupling term, where ω is the synchronous speed and L0 represents the inductance in the three-phase filter; i dref Is the reference value of i d ; Reactive power reference value Q ref After being limited by the reactive power change rate r Q The difference is made with the reactive power Q and then adjusted by the outer-loop PI regulator. The output is passed through the maximum value I of the q-axis current qmax And the minimum value I qmin After being limited, i is obtained qref , i qref The difference is made with i q And then adjusted by the PI controller. The output feedforward compensation term is ωL0i d And e q To obtain the q-axis component of the required converter AC-side voltage; i qref Is the reference value of i q The ωL0i as the feedforward compensation term d Is the d-axis current coupling term Furthermore, the steady-state operation control strategy of the battery energy storage system is determined.

3. A general low / high voltage ride-through control method for a battery energy storage system according to claim 1 or 2, characterized in that During the process of controlling the battery energy storage system by using the general low / high voltage ride-through control strategy, the strategy switching of the whole fault ride-through process is judged through the active fault flag bit and the reactive fault flag bit; Determination of active fault flag bit: The initial value of the active fault flag bit is 0, and the control state of the controller is the steady-state double closed-loop control at this time; if a low-voltage fault occurs and the positive-sequence voltage u at the grid connection point is lower than the voltage threshold for the active power to enter the low-ride-through, the active fault flag bit is set to 1. At this time, the controller enters the active power low-ride-through control, cuts off the active power outer loop, and performs single-loop control of the current inner loop according to the active power low-ride-through current command. After the voltage recovers, the active power current recovers to the value before the fault at a rate of r Id and then the active fault flag bit is set to 0. The controller switches back to the steady-state double closed-loop control; If a high voltage fault occurs, the active fault flag bit remains 0, and the active control continues to use the steady-state double closed-loop control strategy; Determination of reactive power fault flag bit: The initial value of the reactive power fault flag bit is 0. At this time, the idle state of the controller is the steady-state double-loop control. If a low-voltage fault occurs and the positive-sequence voltage u at the grid connection point is lower than the voltage threshold for reactive power to enter low-voltage ride-through, the reactive power fault flag bit is set to 1. At this time, the controller enters the reactive power low-voltage ride-through control, cuts off the reactive power outer loop, and performs single-loop control of the current inner loop according to the reactive power low-voltage ride-through current command. After the voltage recovers and the positive-sequence voltage u at the grid connection point is higher than the voltage threshold for reactive power to exit low-voltage ride-through, the reactive power fault flag bit is set to 0, and the controller switches back to the steady-state double-loop control. If a high-voltage fault occurs and the positive-sequence voltage u at the grid connection point is higher than the voltage threshold for reactive power to enter high-voltage ride-through, the reactive power fault flag bit is set to 2. At this time, the controller enters the reactive power high-voltage ride-through control, cuts off the reactive power outer loop, and performs single-loop control of the current inner loop according to the reactive power high-voltage ride-through current command. After the voltage recovers and the positive-sequence voltage u at the grid connection point is lower than the voltage threshold for reactive power to exit high-voltage ride-through, the reactive power fault flag bit is set to 0, and the controller switches back to the steady-state double-loop control.

4. A parameter identification method for a general low / high voltage ride-through control strategy of a battery energy storage system, characterized in that, Parameter identification is performed on the general low / high voltage ride-through control strategy of a battery energy storage system in the general low / high voltage ride-through control method for a battery energy storage system according to any one of claims 1 to 3. The parameters to be identified include: k dL1 、k dL2 、I dLset 、k0、I max 、r Id 、k qL1 、k qL2 、I qLset 、U Lin 、I qLmin 、k qH1 、k qH2 、I qHset 、U Hin 、I qHmax ;The parameters are divided into three categories, threshold parameters: U Lin 、U Hin ,command parameters: k dL1 、k dL2 、I dLset 、k0、r Id 、k qL1 、k qL2 、I qLset 、k qH1 、k qH2 、I qHset ,limiting parameters: I qLmin 、I qHmax 、I max ;The specific parameter identification process includes the following steps: 1) Obtain the manufacturer's test response data and voltage step test response data of the energy storage unit under low / high voltage single fault test conditions; 2) Identify the threshold parameters according to the voltage step test response data; Threshold parameter U Lin , U Hin are the grid connection point voltages at which reactive power enters the low and high voltage ride-through control states respectively. Taking the response data of the voltage step test in a step-by-step downward / upward manner as the research object, it is judged whether the reactive power control of the energy storage system enters the fault ride-through control state based on the change of reactive power during the voltage step test. If the reactive power changes during the step-by-step downward and upward voltage step tests and is no longer the initial reactive power, it is determined that the system enters the fault ride-through control state, and the grid connection point voltage at this moment is recorded as U Lin , U Hin ; 3) Identify the command parameters by fitting; For the command parameters of the active low voltage ride-through control, the grid connection point voltage, active current, active power, and current during the steady-state interval of the active low voltage ride-through fault under different initial charge and discharge powers and different fault voltages are respectively used. The least squares method is used for k in Equation (9). dL1 u + k dL2 I d0 + I dLset 、 The parameters in the two equations are fitted to obtain the specific values of the command parameters k dL1 、k dL2 、I dLset and k0; the least squares method is used to fit the active power recovery rate r Id using the active current during the fault recovery period. For the instruction parameters of the reactive low-ride-through control, using the grid connection point voltage and reactive current during the reactive low-voltage ride-through fault under different initial charge and discharge powers and different fault voltages, the least squares method is used for k in Equation (10) qL1 (U Lin -u)+k qL2 I q0 +I qLset to fit the parameters in, and obtain the specific values of the instruction parameters k qL1 、k qL2 and I qLset ; for the active high-ride-through control, the proposed active high-ride-through control strategy continues to use the steady-state double closed-loop control strategy and control parameters, and parameter identification is no longer required here; For the command parameters of the reactive power high penetration control, using the grid connection point voltage and reactive current during the reactive power high voltage crossing fault under different initial charge and discharge powers and different fault voltages, the least squares method is used for k in Equation (12) qH1 (u - U Hin ) + k qH2 I q0 + I qHset to fit the parameters in, and obtain the specific values of the command parameters k qH1 、k qH2 and I qHset ; 4) Identify the limiting parameters I qLmin , I qHmax , I max according to severe voltage sag / swell faults. A severe voltage sag is when the grid voltage drops below 0.35 p.u., and a severe voltage swell is when the grid voltage rises above 1.3 p.u.; Obtain the threshold parameters, command parameters, and limit parameters according to the above steps.

5. A parameter identification method for a general low / high voltage ride-through control strategy of a battery energy storage system according to claim 4, characterized in that, The low / high voltage single fault test conditions at least include that the energy storage system operates in a steady state at high power or low power, and the operation mode is charging or discharging. The grid voltage undergoes three-phase voltage dips to 90%, 80%, 75%, 70%, 60%, 50%, 40%, 35%, 30%, 20%, 10%, and 0%, and the grid voltage undergoes three-phase voltage rises to 110%, 115%, 120%, 125%, 130%, 135%, and 140%. The combinations formed by various situations are used as a test condition; the high power is 0.9 p.u. - 1.0 p.u., and the low power is 0.1 p.u. - 0.3 p.u.

6. A parameter identification method for a general low / high voltage ride-through control strategy of a battery energy storage system according to claim 4, characterized in that The voltage step test condition is: Set the initial grid voltage of the energy storage system to 1 p.u., and perform voltage step tests with an interval of 0.01 p.u. step by step up / down to obtain the voltage step test response data. The upper and lower limits of voltage adjustment are 1.15 p.u. and 0.75 p.u. respectively.

7. A parameter identification method for a general low / high voltage ride-through control strategy of a battery energy storage system according to claim 4, characterized in that, According to the severe voltage dip / rise fault, the clipping parameters I qLmin , I qHmax , I max are identified. During the identification process, I qLmin takes the minimum value of the reactive current in the manufacturer's test response data under the severe voltage dip condition, I qHmax takes the maximum value of the reactive current in the manufacturer's test response data under the severe voltage rise condition, I max takes the maximum value of the current in the manufacturer's test response data under the severe voltage dip condition.

8. A parameter identification method for a general low / high voltage ride-through control strategy of a battery energy storage system according to any one of claims 4 to 7, characterized in that The method further includes the following steps: Substitute the obtained threshold parameters, command parameters, and limit parameters into the general low / high voltage ride-through control strategy to form a complete control model, and build a simulation model to verify whether the simulation accuracy of the entire voltage ride-through process meets the requirements. When it meets the requirements, the parameter identification is completed.

9. A general low / high voltage ride-through control system for a battery energy storage system, characterized in that, The control system includes a steady-state control unit and a general low / high voltage ride-through control strategy unit; The steady-state control unit controls the battery energy storage system using a steady-state operation control strategy; the general low / high voltage ride-through control strategy unit controls the battery energy storage system using a general low / high voltage ride-through control strategy; The steady-state operation control strategy of the battery energy storage system is as follows: Use e d and e q to represent the d-axis component and q-axis component of the grid connection point voltage in the dq coordinate system. Use v d and v q and i d and i q to represent the d-axis component and q-axis component of the converter AC side output voltage and output current in the dq coordinate system respectively; the energy storage PCS adopts a double closed-loop decoupling control structure, and the steady-state control includes a power outer loop and a current inner loop. The current reference value output by the power outer loop is limited and then generates i dref and i qref which are cascaded to the current inner loop. i dref and i qref are the reference values of i d and i q ; the d-axis voltage component and q-axis voltage component obtained by adjusting through the current inner loop PI controller are then transformed by dq-abc to generate the abc three-phase voltage required for pulse width modulation and transmitted to the converter to realize the on and off of the converter valve-level switch; the current inner loop realizes the cancellation of the PI controller and the coupling term through the feedforward compensation method. After decoupling, the d-axis control is only related to active power, and the q-axis control is only related to reactive power, realizing the independent control of active and reactive power; The general low / high voltage ride-through control strategy of the battery energy storage system is as follows: 1) General low-voltage ride-through control strategy: During the active and reactive low-voltage faults, the energy storage system enters the low-voltage ride-through process, cuts off the power outer loop, and only retains the current inner loop for single-loop control; the d-axis and q-axis current command control equations during the low-voltage ride-through are shown in Equations (9) and (10) respectively: i qref = max[k qL1 (U Lin - u)+ k qL2 I q0 + I qLset , I qLmin (10) where k dL1 , k dL2 , I dLset , k0 are the calculation coefficients of the low-through active current; u is the positive-sequence voltage at the grid connection point; I d0 is the initial active current; P0 is the initial active power; I max is the maximum current; k qL1 , k qL2 , I qLset are respectively the low-ride reactive current calculation coefficients; U Lin is the voltage threshold for reactive power to enter low-ride; I q0 is the initial reactive current; I qLmin is the minimum value of the reactive current during low-ride; During the recovery from an active low-voltage fault, the active current recovers to its pre-fault value at a rate of r Id ; 2) General control strategy for high-voltage ride-through During the high-voltage fault, the reactive power outer loop is disconnected, and the d-axis and q-axis current command control equations during the high-voltage ride-through are shown in Equations (11) and (12) respectively; i dref = k op (P ref - P) + k oi ∫(P ref - P)dt (11) i qref = min[k qH1 (u - U Hin ) + k qH2 I q0 + I qHset , I qHmax (12) where k qH1 , k qH2 , I qHset are respectively the calculation coefficients of the high-penetration reactive current; U Hin is the voltage threshold for reactive power to enter high penetration; I qHmax is the maximum value of the reactive current during high penetration, k op represents the proportional coefficient of the power outer-loop PI regulator, k oi represents the integral coefficient of the power outer-loop PI regulator, P ref represents the reference value of the active power, and P represents the active power; The active power outer loop maintains the steady-state grid-connected operation state.

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