Low-Voltage Ride-Through Control Method for Energy Storage Inverter and Energy Storage Inverter

Abstract

The present application provides a low-voltage ride-through control method and an energy storage converter for an energy storage converter, which relates to the field of low-voltage ride-through control. The method includes: obtaining the three-phase line voltages of the power grid; calculating the coordinate transformation angle by using the phase-locked loop method of a second-order generalized integrator based on the three-phase line voltages to obtain a first coordinate transformation angle; calculating the coordinate transformation angle by using the phase-locked loop method of detecting the zero-crossing point of the BC phase line voltage based on the three-phase line voltages to obtain a second coordinate transformation angle; calculating the absolute value of the difference between the first coordinate transformation angle and the second coordinate transformation angle to obtain a transformation angle difference; judging the power grid voltage sag condition; determining the target coordinate transformation angle, as well as the given values of the positive-sequence and negative-sequence components of the target reactive current according to the power grid voltage sag condition and the transformation angle difference. The method provided by the present application can meet the low-voltage ride-through requirements under different power grid voltage sag conditions, and improve the low-voltage ride-through ability and system stability of the energy storage converter.

Description

Technical Field

[0001] This application relates to the field of low voltage ride-through control, and in particular to a low voltage ride-through control method and an energy storage converter for an energy storage converter. Background Art

[0002] In related technologies, the phase-locked loop adopted by the energy storage converter will have sudden changes in the output frequency and phase when the grid voltage drops severely. Especially when the grid voltage drops to zero, the phase-locked loop can no longer lock the phase normally, resulting in phenomena such as overcurrent and inaccurate reactive power output during the low voltage ride-through period, especially during the zero voltage ride-through period, which affects the reliability of the low voltage ride-through. Summary of the Invention

[0003] This application provides a low voltage ride-through control method and an energy storage converter for an energy storage converter, which can meet the low voltage ride-through requirements under different grid voltage drop conditions and improve the low voltage ride-through ability and system stability of the energy storage converter.

[0004] In a first aspect, this application provides a low voltage ride-through control method for an energy storage converter, including:

[0005] Obtain the three-phase line voltage of the power grid;

[0006] Based on the three-phase line voltage, use the phase-locked loop method of the second-order generalized integrator to calculate the coordinate transformation angle to obtain the first coordinate transformation angle;

[0007] Based on the three-phase line voltage, use the phase-locked loop method of detecting the zero crossing point of the BC phase line voltage to calculate the coordinate transformation angle to obtain the second coordinate transformation angle; the coordinate transformation angle is the transformation angle from the three-phase stationary coordinate system to the two-phase rotating coordinate system or from the two-phase rotating coordinate system to the three-phase stationary coordinate system;

[0008] Calculate the absolute value of the difference between the first coordinate transformation angle and the second coordinate transformation angle to obtain the transformation angle difference;

[0009] Judge the grid voltage drop situation;

[0010] Determine the target coordinate transformation angle, as well as the positive and negative sequence component given values of the target reactive current according to the grid voltage drop situation and the transformation angle difference, and the target coordinate transformation angle is the first coordinate transformation angle or the second coordinate transformation angle.

[0011] In a second aspect, this application provides an energy storage converter, including: a processor and a memory, the memory is used to store a computer program; the processor is used to run the computer program to implement the low voltage ride-through control method of the energy storage converter as in the first aspect.

[0012] The beneficial effects of this application are:

[0013] The present application provides a low-voltage ride-through control method for an energy storage converter, which includes obtaining the three-phase line voltages of the power grid; based on the three-phase line voltages, calculating the coordinate transformation angle by using the phase-locked loop method of a second-order generalized integrator to obtain a first coordinate transformation angle; based on the three-phase line voltages, calculating the coordinate transformation angle by using the phase-locked loop method of detecting the zero-crossing point of the BC phase line voltage to obtain a second coordinate transformation angle; calculating the absolute value of the difference between the first coordinate transformation angle and the second coordinate transformation angle to obtain the transformation angle difference; judging the power grid voltage drop situation; and determining the target coordinate transformation angle, as well as the given values of the positive and negative sequence components of the target reactive current according to the power grid voltage drop situation and the transformation angle difference. The method provided by the present application comprehensively utilizes the advantages of the phase-locked loop based on the second-order generalized integrator and the phase-locked loop based on detecting the zero-crossing point of the BC phase line voltage. In the low-voltage ride-through interval, single-current-loop control is adopted, and according to the angle difference between the two phase-locked loops and the voltage drop situation, the target coordinate transformation angle, the given values of the positive and negative sequence components of the reactive current are determined for reactive current control. This method can meet the low-voltage ride-through requirements under different power grid voltage drop conditions. Even if the power grid voltage completely drops to zero, the low-voltage ride-through function can be successfully realized and the required reactive current can be output, improving the low-voltage ride-through ability and system stability of the energy storage converter. Description of the Drawings

[0014] Figure 1 It is a schematic flowchart of the low-voltage ride-through control method for the energy storage converter provided by the embodiment of the present application;

[0015] Figure 2 It is a schematic structural diagram of detecting the zero-crossing point of the BC phase line voltage provided by the embodiment of the present application;

[0016] Figure 3 It is a schematic structural diagram of the low-voltage ride-through control algorithm provided by the embodiment of the present application;

[0017] Figure 4 It is a schematic structural diagram of the energy storage converter provided by the embodiment of the present application. Detailed Embodiments

[0018] In the embodiments of the present application, unless otherwise specified, the character " / " indicates that the associated objects before and after are in an "or" relationship. For example, A / B can represent A or B. "And / or" describes the association relationship of the associated objects, indicating that three relationships can exist. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, and B exists alone.

[0019] It should be noted that the terms "first", "second", etc. involved in the embodiments of the present application are only used for the purpose of distinguishing descriptions, and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features, nor can they be understood as indicating or implying order.

[0020] In the embodiments of the present application, "at least one" means one or more, and "a plurality" means two or more. In addition, "at least one of the following" or its similar expressions refer to any combination of these items, which can include any combination of single items or plural items. For example, at least one of A, B, or C can represent: A, B, C, A and B, A and C, B and C, or A, B, and C. Each of A, B, and C itself can be an element or a set containing one or more elements.

[0021] In the embodiments of the present application, "exemplary", "in some embodiments", "in another embodiment", etc. are used to give examples, illustrations, or explanations. Any embodiment or design described as "exemplary" in the present application should not be construed as more preferred or more advantageous than other embodiments or designs. Rather, the use of the word "exemplary" is intended to present concepts in a specific manner.

[0022] In the embodiments of the present application, "of", "corresponding", and "corresponding to" can sometimes be used interchangeably. It should be noted that when the difference is not emphasized, the intended meanings are the same. In the embodiments of the present application, communication and transmission can sometimes be used interchangeably. It should be noted that when the difference is not emphasized, the meanings expressed are the same. For example, transmission can include sending and / or receiving, and can be a noun or a verb.

[0023] In the embodiments of the present application, the equality involved can be used in combination with greater than, applicable to the technical solutions adopted when it is greater than, or can also be used in combination with less than, applicable to the technical solutions adopted when it is less than. It should be noted that when equality is used in combination with greater than, it cannot be used in combination with less than; when equality is used in combination with less than, it is not used in combination with greater than.

[0024] First, the nouns mentioned in the present application are explained.

[0025] Low Voltage Ride Through (LVRT): It means that when the power grid fails or is disturbed, resulting in a voltage dip, the power generation equipment can maintain its connection to the power grid and operate without disconnecting from the grid for a certain period of time, while providing a certain amount of reactive power to support the recovery of the grid voltage.

[0026] Zero Voltage Ride Through (ZVT): It is a special case of low voltage ride through, which means that when the grid voltage drops to zero, the power generation equipment can still maintain grid-connected operation and quickly return to normal operation after the voltage recovers.

[0027] Incremental and decremental counting method: It is a working mode of a counter. The value of the counter first increases within a cycle, starts to decrease after reaching the maximum value, and repeats this process after returning to the minimum value.

[0028] Triangular carrier wave: It is a periodic waveform that first linearly rises within each cycle and then linearly falls after reaching the peak value.

[0029] Clark transformation (also known as Clarke transformation): It is a mathematical transformation method that converts the current or voltage in the three-phase stationary coordinate system (ABC coordinate system) to the two-phase stationary coordinate system (αβ coordinate system).

[0030] Symmetrical dip: When the grid voltage drops, the amplitudes of the three-phase voltages drop simultaneously and the phases remain symmetrical.

[0031] Asymmetrical dip: When the grid voltage drops, the amplitudes and phases of the three-phase voltages are asymmetrical.

[0032] PWM (Pulse-Width Modulation) wave generation: It is a technology that controls the average level of the output signal by changing the width of the pulse signal.

[0033] In the related art, the phase-locked loop adopted by the energy storage converter (such as the traditional phase-locked loop based on the second-order generalized integrator) will have sudden changes in the output frequency and phase when the grid voltage drops severely. Especially when the grid voltage drops to zero, the phase-locked loop can no longer lock the phase normally, resulting in phenomena such as overcurrent and inaccurate reactive power output during the low-voltage ride-through period, especially during the zero-voltage ride-through period, which affects the reliability of the low-voltage ride-through.

[0034] Based on the above problems, the embodiments of the present application propose a low-voltage ride-through control method for an energy storage converter, which can meet the low-voltage ride-through requirements under different grid voltage drop conditions and improve the low-voltage ride-through ability and system stability of the energy storage converter.

[0035] Now in combination with Figures 1 - 3 Describe the low-voltage ride-through control method for the energy storage converter provided by the embodiments of the present application.

[0036] Figure 1 FIG. is a schematic flow chart of the low-voltage ride-through control method for the energy storage converter provided by the embodiments of the present application, which specifically includes the following steps:

[0037] Step S11, obtain the three-phase line voltages of the power grid.

[0038] Specifically, generate a triangular carrier wave by using the incremental and decremental counting method, and perform voltage sampling on the three-phase line voltages Uab, Ubc, and Uca of the power grid at the zero point of each triangular carrier wave to obtain the three-phase line voltages of the power grid, and further obtain the system carrier frequency fcarry , the system control period is 1 / f carry .

[0039] Step S12, based on the three-phase line voltage, use the phase-locked loop method of the second-order generalized integrator to calculate the coordinate transformation angle, and obtain the first coordinate transformation angle.

[0040] Specifically, perform Clark transformation on the three-phase line voltages Uab, Ubc, and Uca to obtain the voltages Uα and Uβ in the two-phase stationary coordinate system; use the second-order generalized integrator to extract the positive-sequence and negative-sequence components of the voltages Uα and Uβ in the two-phase stationary coordinate system to obtain the positive-sequence components Uα+, Uβ+ and the negative-sequence components Uα-, Uβ-; perform two-phase rotation transformation on the positive-sequence components Uα+, Uβ+ and the negative-sequence components Uα-, Uβ- to obtain the positive-sequence components Ud+, Uq+ and the negative-sequence components Ud-, Uq- in the rotating coordinate system; perform PI regulation and integral operation on the positive-sequence component Uq+ to obtain the first coordinate transformation angle.

[0041] In some alternative embodiments, performing PI regulation and integral operation on the positive-sequence component Uq+ to obtain the first coordinate transformation angle includes: adjusting the positive-sequence component Uq+ to zero through a PI regulator to obtain the angular frequency of the positive-sequence component of the grid voltage; performing integral operation on the angular frequency of the positive-sequence component of the grid voltage to obtain the two-phase positive-sequence voltage rotation transformation angle; subtracting π / 6 from the two-phase positive-sequence voltage rotation transformation angle and integrating the calculation result within 0 to 2π to obtain the first coordinate transformation angle θ1.

[0042] Among them, the role of the PI regulator is to make Uq+ approach zero, so as to ensure that the d-axis of the rotating coordinate system is aligned with the phase of the positive-sequence component of the grid voltage. Through two-phase rotation transformation and the PI regulator, the positive-sequence component of the grid voltage is converted to the rotating coordinate system, and phase locking is achieved by adjusting Uq+ to zero, and finally the rotation angle θ1 is obtained.

[0043] Subtracting π / 6 from the two-phase positive-sequence voltage rotation transformation angle is to convert the line voltage into the phase voltage (the phase voltage lags behind the line voltage by 30°), and it is also to compare with the second coordinate transformation angle calculated in the following step S13. At the same time, integrating the calculation result within a fixed range (such as 0 to 2π) is for convenient comparison and to simplify the subsequent control logic.

[0044] In other embodiments, the method provided by the present application may further include: obtaining the grid rated voltage E n ; based on the positive-sequence components Ud+ and Uq+ and the grid rated voltage E nCalculate the positive-sequence component percentage d of the voltage; when d is less than 90% and the duration is greater than 2 ms, enter the low-voltage ride-through control mode; or when d is greater than 92% and the duration is greater than 2 ms, exit the low-voltage ride-through control mode; calculate the effective value U of the negative-sequence component of the grid voltage based on the negative-sequence components Ud- and Uq- 负 。

[0045] Among them, when d is less than 90% and the duration is greater than 2 ms, it means that the d value is less than 90% within a time above 2 ms (such as 3 ms, 4 ms). Similarly, when d is greater than 92% and the duration is greater than 2 ms, it means that the d value is greater than 92% within a time above 2 ms (such as 3 ms, 4 ms).

[0046] Specifically, the positive-sequence component percentage d of the voltage is calculated by the following formula:

[0047]

[0048] The effective value U of the negative-sequence component of the grid voltage 负 is calculated by the following formula:

[0049]

[0050] By judging the magnitude and duration of the positive-sequence component percentage d value of the voltage, it can be judged whether the system enters the low-voltage ride-through control mode or exits the low-voltage ride-through control mode. Setting the duration is to prevent the rapid change of the d value caused by the short-term fluctuation of the power grid, thus causing misjudgment, and playing a role in anti-jitter and anti-misjudgment. If the duration is set too short, the role of anti-misjudgment cannot be played. If the duration is set too long, the response speed of the system is slow, and it cannot quickly enter or exit the low-voltage ride-through control mode, which is not conducive to ensuring the stability of the grid voltage. Therefore, in this application, the duration is set to 2 ms, which can not only prevent misjudgment but also take into account the rapidity.

[0051] Step S13, based on the three-phase line voltage, use the phase-locked loop method for detecting the zero-crossing point of the BC phase line voltage to calculate the coordinate transformation angle, and obtain the second coordinate transformation angle.

[0052] Among them, the coordinate transformation angle (including the first coordinate transformation angle θ1 and the second coordinate transformation angle θ2) is the transformation angle from the three-phase stationary coordinate system to the two-phase rotating coordinate system or from the two-phase rotating coordinate system to the three-phase stationary coordinate system.

[0053] Specifically, start the counter to begin counting, incrementing by 1 for each control period; convert the signal of the zero-crossing point where the BC phase line voltage changes from negative to positive into a rising edge signal; when not in the low-voltage ride-through control mode, trigger a controller software interrupt in response to the rising edge signal, and perform grid frequency update and counter clearing; when in the low-voltage ride-through control mode, stop the grid frequency update, the counter continuously counts until exiting the low-voltage ride-through control mode, then resume responding to the rising edge signal to perform grid frequency update and counter clearing; obtain the last grid frequency updated before entering the low-voltage ride-through control mode, the count value of the counter during the process of entering the low-voltage ride-through control mode, and the carrier frequency; calculate the second coordinate transformation angle θ2 based on the last updated grid frequency, the count value of the counter, and the carrier frequency.

[0054] Among them, converting the signal of the zero-crossing point where the BC phase line voltage changes from negative to positive into a rising edge signal can be achieved by using a hardware circuit (such as a zero-crossing detection circuit) to detect the zero-crossing point where the BC phase line voltage changes from negative to positive and convert it into a digital signal (such as a rising edge signal from 0 to 1). In this application, converting the zero-crossing point signal into a rising edge signal is to enable the controller to better capture the zero-crossing point signal, so that when not in the low-voltage ride-through control mode, a controller software interrupt can be triggered in response to the rising edge signal.

[0055] When not in the low-voltage ride-through control mode, trigger a controller software interrupt in response to the rising edge signal, read the current grid frequency value, record the grid frequency at the time of the previous controller software interrupt, and at the same time clear the counter, that is, when not in the low-voltage ride-through control mode, continuously perform grid frequency update and counter clearing.

[0056] When in the low-voltage ride-through control mode, stop the grid frequency update, and obtain the last grid frequency f updated before entering the low-voltage ride-through control mode grid-pre1 , the counter continuously counts until exiting the low-voltage ride-through control mode, then resume responding to the rising edge signal to perform grid frequency update and counter clearing, and obtain the count value N of the counter during the process of entering the low-voltage ride-through control mode.

[0057] Based on the last updated grid frequency f grid-pre1 , the count value N of the counter, and the carrier frequency f carry Calculate the second coordinate transformation angle θ2, which can be specifically obtained according to the following formula:

[0058]

[0059] Further, the second coordinate transformation angle θ2 is integrated into a fixed range (such as 0 to 2π). If θ2 exceeds the range of 0 to 2π, it can be adjusted by adding or subtracting multiples of 2π to integrate the second coordinate transformation angle θ2 into the fixed range, which is convenient for comparing with the first coordinate transformation angle θ1 and simplifies the control logic.

[0060] Figure 2 FIG. is a schematic structural diagram of the zero-crossing detection of the BC phase line voltage provided by the embodiment of the present application. As Figure 2 shown, the system enters the low-voltage ride-through control mode at time T1 and exits the low-voltage ride-through control mode at time T2. In the time period from 0 to T1, the number of zero-crossings of the BC phase line voltage changing from negative to positive is 2, namely S1 and S2, and the zero-crossing signal is converted into a rising-edge signal. In the time period from T1 to T2, the number of zero-crossings of the BC phase line voltage changing from negative to positive is multiple, including Figure 2 S3, S4, and S5 shown in, and the zero-crossing signal is converted into a rising-edge signal.

[0061] Step S14: Calculate the absolute value of the difference between the first coordinate transformation angle and the second coordinate transformation angle to obtain the transformation angle difference.

[0062] Specifically, according to the first coordinate transformation angle θ1 calculated in step S12 above and the second coordinate transformation angle θ2 calculated in step S13, calculate the absolute value of the difference between the two to obtain the transformation angle difference Δθ, that is, Δθ = |θ1 - θ2|.

[0063] Step S15: Judge the grid voltage drop situation.

[0064] Specifically, the grid voltage drop includes symmetric drop and asymmetric drop. When entering the low-voltage ride-through control mode, start timing. After 5 ms, calculate the percentage d of the positive-sequence voltage component and the effective value U of the negative-sequence voltage component of the grid voltage respectively 负 The sliding average value within 1 ms to obtain d ave and U 负ave ; when U 负ave is less than 10% of the rated grid voltage, it is determined that the grid voltage has a symmetric drop; or when U 负ave is greater than or equal to 10% of the rated grid voltage, it is determined that the grid voltage has an asymmetric drop. Among them, the sliding average value refers to calculating the average value by using the sliding window method, which is faster, more accurate than the general calculation of the average value, and is not prone to sudden changes.

[0065] Within a certain period of time (such as 5 ms) after the system enters the low-voltage ride-through control mode, the amplitude drop of the grid voltage is unstable. Therefore, the grid voltage drop situation is judged 5 ms after entering the low-voltage ride-through control mode to reduce the influence of grid fluctuations and make the judgment result more accurate. Moreover, in this application, the percentage d of the positive-sequence voltage component and the effective value U of the negative-sequence grid voltage 负 The sliding average within 1 ms is used to judge the grid voltage drop situation, which can more accurately evaluate the grid voltage drop situation.

[0066] In other embodiments, the method provided in this application further includes: when entering the low-voltage ride-through control mode, recording the given values of the positive-sequence and negative-sequence components of the initial reactive current; within 6 ms after entering the low-voltage ride-through control mode, setting the given values of the positive-sequence and negative-sequence components of the reactive current to 0.

[0067] Specifically, when entering the low-voltage ride-through control mode, use the variable I 0+ to record the given value I of the positive-sequence component of the reactive current at the moment of voltage drop 0+ = iq + , use the variable I 0- to record the given value I of the negative-sequence component of the reactive current at the moment of voltage drop 0- = iq - . Among them, I 0+ , I 0- are the initial values of the given values of the positive-sequence and negative-sequence components of the reactive current. When entering the low-voltage ride-through control mode, the low-voltage ride-through timer starts timing. Within 6 ms, set the given values of the positive-sequence and negative-sequence components of the reactive current to 0, that is, id + = 0, iq + = 0, id - = 0, iq - = 0.

[0068] Since within a certain period of time (such as 6 ms) after the system enters the low-voltage ride-through control mode, the voltage drop amplitude is unstable and the calculated given values of the positive-sequence and negative-sequence components of the reactive current are inaccurate, therefore, within 6 ms, set the given values of the positive-sequence and negative-sequence components of the reactive current to 0, and the system will stop controlling the positive-sequence and negative-sequence reactive currents to avoid further impact on the power grid.

[0069] This application records the given values of the reactive current at the moment of grid drop (including the given values of the positive-sequence and negative-sequence components), starts the timer, and sets the given value of the reactive current to zero within a certain time to ensure the stable operation of the system under low-voltage conditions.

[0070] Step S16, determine the target coordinate transformation angle, as well as the target given values of the positive-sequence and negative-sequence components of the reactive current according to the grid voltage drop situation and the transformation angle difference.

[0071] Among them, the target coordinate transformation angle θ is the first coordinate transformation angle θ1 or the second coordinate transformation angle θ2.

[0072] Specifically, 6 ms after entering the low-voltage ride-through control mode, when the grid voltage undergoes a symmetrical dip, the initial positive-sequence given value of the reactive current is compensated to obtain the target positive-sequence given value of the reactive current, and the target negative-sequence given value of the reactive current is the initial negative-sequence given value of the reactive current; if 10% ≤ d ave < 90%, then the target coordinate transformation angle is determined according to the comparison of the transformation angle difference with a preset value; or if d ave < 10%, then the target coordinate transformation angle is the second coordinate transformation angle;

[0073] 6 ms after entering the low-voltage ride-through control mode, when the grid voltage undergoes an asymmetrical dip, the initial positive-sequence given value of the reactive current is compensated to obtain the target positive-sequence given value of the reactive current; the initial negative-sequence given value of the reactive current is compensated to obtain the target negative-sequence given value of the reactive current; the target coordinate transformation angle is determined according to the comparison of the transformation angle difference with a preset value.

[0074] In this application, during symmetrical dips, the reactive power output is adjusted through the positive-sequence current given value to support the grid voltage. During asymmetrical dips, in addition to adjusting the positive-sequence current, negative-sequence current control is also required to suppress unbalanced current and ensure balanced three-phase currents.

[0075] This application can achieve precise control of the grid voltage and current and ensure stable operation of the system under low-voltage conditions by evaluating different grid voltage dip situations and determining the target coordinate transformation angle, as well as the target positive-sequence and negative-sequence component given values of the reactive current.

[0076] In one possible embodiment, determining the target coordinate transformation angle according to the comparison of the transformation angle difference with a preset value includes: if the transformation angle difference is greater than or equal to the preset value, then the target coordinate transformation angle is the second coordinate transformation angle; or if the transformation angle difference is less than the preset value, then the target transformation angle is the first coordinate transformation angle.

[0077] For example, if Δθ ≥ 0.25, then θ = θ2; if Δθ < 0.25, then θ = θ1.

[0078] During low voltage ride-through, by judging the value of Δθ, a suitable coordinate transformation angle is selected to ensure the stable operation of the system during voltage dips. The selection of the coordinate transformation angle plays a key role in low voltage ride-through control, which directly affects the extraction accuracy of the positive and negative sequence components of the grid voltage and the implementation of the low voltage ride-through control strategy. In low voltage ride-through control, a suitable coordinate transformation angle is not likely to cause overcurrent and overvoltage phenomena. Reasonable selection and dynamic adjustment of the coordinate transformation angle are the keys to ensuring the stable operation of the system.

[0079] The selection of the target coordinate transformation angle, as well as the given values of the positive and negative sequence components of the target reactive current, is shown in Table 1.

[0080] Table 1. Selection Table of Target Coordinate Transformation Angle and Given Values of Positive and Negative Sequence Components of Target Reactive Current

[0081]

[0082] Among them, I 0+ , I 0- are the initial values of the given values of the positive and negative sequence components of the reactive current, and I N , K1, K2 + , K2 - are calibration values. When d ave <10%, U 负ave <10% E n When this happens, it means that the grid voltage dip is relatively serious at this time. The coordinate transformation angle calculated by the phase-locked loop method based on the zero-crossing detection of the line voltage of phase BC (i.e., the second coordinate transformation angle) should be used to perform reactive power compensation on the grid voltage.

[0083] Figure 3 is the structural schematic diagram of the low voltage ride-through control algorithm provided by the embodiment of the present application. As Figure 3 shown, according to the grid voltage u abc , the coordinate transformation angles are calculated respectively by using the phase-locked loop method of the second-order generalized integrator and the phase-locked loop method of the zero-crossing detection of the line voltage of phase BC, and the first coordinate transformation angle θ1 and the second coordinate transformation angle θ2 are obtained. According to the method shown in the above embodiment, the transformation angle difference is calculated and the grid voltage dip situation is judged. According to the grid voltage dip situation and the transformation angle difference, the target coordinate transformation angle (θ1 or θ2) is determined. According to the target coordinate transformation angle (θ1 or θ2), the positive and negative sequence separation of voltage and current is performed, and the given values of the positive and negative sequence components of the target reactive current are determined. Then, the grid voltage is regulated through the PI controller, the coordinate transformation module dq / abc, and the PWM wave generation module to meet the low voltage ride-through requirements under different grid voltage dip conditions, and improve the low voltage ride-through ability and system stability of the energy storage converter.

[0084] Optionally, during low voltage ride-through, the system dynamically adjusts the reactive power output through current loop control to maintain the stability of the grid voltage. After the voltage recovers, that is, after exiting the low voltage ride-through control mode, the system switches back to the dual-loop control of the power outer loop and current inner loop. The power outer loop is responsible for regulating the active power, and the current inner loop is responsible for regulating the current to ensure high efficiency and stability of the system under normal operating conditions.

[0085] The method provided in this application comprehensively utilizes the advantages of two phase-locked loops, namely the phase-locked loop based on the second-order generalized integrator and the phase-locked loop based on the zero-crossing detection of the BC phase line voltage. In the low voltage ride-through interval, single current loop control is adopted, and the target coordinate transformation angle, the given values of the positive and negative sequence components of the reactive current are determined according to the angle difference between the two phase-locked loops and the voltage dip situation, and reactive current control is carried out. This method can meet the low voltage ride-through requirements under different grid voltage dips. Even if the grid voltage drops completely to zero, it can successfully implement the low voltage ride-through function and output the required reactive current, improving the low voltage ride-through ability and system stability of the energy storage converter. At the same time, it can also reduce the inrush current during the grid voltage mutation process and improve the reactive power control accuracy during low voltage ride-through.

[0086] The following combines Figure 4 to further introduce the exemplary energy storage converter provided in the embodiments of this application. Figure 4 The structural schematic diagram of the energy storage converter 4000 is shown.

[0087] The above-mentioned energy storage converter 4000 may include: at least one processor; and at least one memory communicatively connected to the above-mentioned processor, wherein: the above-mentioned memory stores program instructions executable by the above-mentioned processor, and the processor can execute the energy storage converter low voltage ride-through control method provided by the embodiments shown in this application by calling the above-mentioned program instructions. Among them, the memory is used to store the programs and data required for the operation of the processor; the processor is one of the core components of the energy storage converter and is used to execute various control and management tasks, such as charge and discharge control, power regulation, grid synchronization, etc.; it can also process data from sensors (such as voltage, current, temperature sensors), perform fast calculations and decisions; interact with external devices (such as battery management systems, grid monitoring systems, energy management systems); monitor the system status, detect and handle faults in a timely manner to ensure the safe operation of the device. In this application, the processor in the energy storage converter is mainly used to execute the energy storage converter low voltage ride-through control method in the above-mentioned embodiments.

[0088] Figure 4 The block diagram of the exemplary energy storage converter 4000 suitable for implementing the embodiments of this application is shown. Figure 4The shown energy storage converter 4000 is merely an example and should not impose any limitation on the functions and usage scope of the embodiments of this application.

[0089] As Figure 4 shown, the energy storage converter 4000 is presented in the form of a general computing device. The components of the energy storage converter 4000 may include, but are not limited to: one or more processors 4010, a memory 4020, a communication bus 4040 connecting different system components (including the memory 4020 and the processor 4010), and a communication interface 4030.

[0090] The communication bus 4040 represents one or more of several types of bus structures, including a memory bus or a memory controller, a peripheral bus, a graphics acceleration port, a processor, or a local bus using any of the various bus structures. For example, these architectures include, but are not limited to, the Industry Standard Architecture (ISA) bus, the Micro Channel Architecture (MAC) bus, the Enhanced ISA bus, the Video Electronics Standards Association (VESA) local bus, and the Peripheral Component Interconnection (PCI) bus.

[0091] The memory 4020 may include computer system readable media in the form of volatile memory, such as random access memory (RAM) and / or cache memory. The energy storage converter may further include other removable / non-removable, volatile / non-volatile computer system storage media. Although Figure 4 not shown in the figure, a disk drive for reading and writing a removable non-volatile disk (such as a "floppy disk") and an optical disk drive for reading and writing a removable non-volatile optical disk (such as a Compact Disc Read Only Memory (CD-ROM), a Digital Video Disc Read Only Memory (DVD-ROM), or other optical media) may be provided. In these cases, each drive may be connected to the communication bus 4040 through one or more data media interfaces. The memory 4020 may include at least one program product having a set of (such as at least one) program modules configured to perform the functions of the embodiments of this application.

[0092] A program / util utility having a set (at least one) of program modules can be stored in the memory 4020. Such program modules include, but are not limited to, an operating system, one or more application programs, other program modules, and program data. Each or some combination of these examples may include the implementation of a network environment. The program modules generally perform the functions and / or methods in the embodiments described in the present application.

[0093] The energy storage converter 4000 can also communicate with one or more external devices (such as a battery management system BMS, an energy management system EMS, etc.), and can also communicate with one or more devices that enable a user to interact with the energy storage converter, and / or communicate with any device that enables the energy storage converter to communicate with one or more other computing devices (such as a network card, a modem, etc.). This communication can be carried out through the communication interface 4030. And, the energy storage converter 4000 can also communicate with one or more networks (such as a local area network (Local Area Network; hereinafter referred to as: LAN), a wide area network (Wide Area Network; hereinafter referred to as: WAN) and / or a public network, such as the Internet) through a network adapter ( Figure 4 not shown in the figure). The above network adapter can communicate with other modules of the energy storage converter through the communication bus 4040. It should be understood that although Figure 4 not shown in the figure, other hardware and / or software modules can be used in combination with the energy storage converter 4000, including but not limited to: microcode, device drivers, redundant processing units, external disk drive arrays, disk arrays (Redundant Arrays of Independent Drives; hereinafter referred to as: RAID) systems, tape drives, and data backup storage systems, etc.

[0094] The processor 4010 executes various functional applications and data processing by running the programs stored in the memory 4020, such as implementing the method provided in the embodiments of the present application.

[0095] It can be understood that the interface connection relationship between the modules schematically shown in the embodiments of the present application is only for illustrative purposes and does not constitute a structural limitation on the energy storage converter 4000. In other embodiments of the present application, the energy storage converter 4000 can also adopt different interface connection methods in the above embodiments, or a combination of multiple interface connection methods.

[0096] In the above embodiments, the processors involved may include, for example, a CPU (Central Processing Unit), a DSP (Digital Signal Processor), a microcontroller, and may also include a GPU (Graphics Processing Unit), an embedded neural network processor (Neural-network Process Units; hereinafter referred to as: NPU), and an image signal processor (Image Signal Processing; hereinafter referred to as: ISP). The processor may also include necessary hardware accelerators or logic processing hardware circuits, such as an ASIC (Application-Specific Integrated Circuit), or one or more integrated circuits for controlling the execution of the technical solution programs of the present application. In addition, the processor may have the function of operating one or more software programs, and the software programs may be stored in a storage medium.

[0097] Those of ordinary skill in the art can realize that the units and algorithm steps described in the embodiments disclosed herein can be implemented by a combination of electronic hardware, computer software, and electronic hardware. Whether these functions are executed in a hardware or software manner depends on the specific application and design constraints of the technical solution. Professional technicians can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of the present application.

[0098] Those skilled in the art can clearly understand that for the convenience and brevity of description, the specific working processes of the above-described systems, devices, and units can refer to the corresponding processes in the foregoing method embodiments, and will not be described herein again.

[0099] In several embodiments provided by the present application, if any function is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on such an understanding, the technical solution of the present application, in essence, or the part that contributes to the prior art or a part of this technical solution can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions for causing a computer device (which may be a personal computer, a server, or a network device, etc.) to execute all or part of the steps of the methods in various embodiments of the present application. The aforementioned storage medium includes: various media such as USB flash drives, mobile hard disks, read-only memories (ROM for short), random access memories (RAM for short), magnetic disks, or optical discs that can store program codes.

[0100] The above is only the specific implementation manner of the present application. Any person skilled in the art within the technical scope disclosed by the present application can easily think of changes or substitutions, which should all be covered by the protection scope of the present application. The protection scope of the present application shall be subject to the protection scope of the claimed rights.

Claims

1. A low voltage ride-through control method for an energy storage converter, characterized in that, The method includes: Obtaining the three-phase line voltage of the power grid; Based on the three-phase line voltage, calculating the coordinate transformation angle by using the phase-locked loop method of the second-order generalized integrator to obtain the first coordinate transformation angle; Based on the three-phase line voltage, calculating the coordinate transformation angle by using the phase-locked loop method of detecting the zero crossing of the BC phase line voltage to obtain the second coordinate transformation angle; the coordinate transformation angle is the transformation angle from the three-phase stationary coordinate system to the two-phase rotating coordinate system or from the two-phase rotating coordinate system to the three-phase stationary coordinate system; Calculating the absolute value of the difference between the first coordinate transformation angle and the second coordinate transformation angle to obtain the transformation angle difference; Judging the power grid voltage sag situation; Determining the target coordinate transformation angle, as well as the given value of the positive sequence component of the target reactive current and the given value of the negative sequence component of the target reactive current according to the power grid voltage sag situation and the transformation angle difference, and the target coordinate transformation angle is the first coordinate transformation angle or the second coordinate transformation angle; Based on the three-phase line voltage, calculating the coordinate transformation angle by using the phase-locked loop method of the second-order generalized integrator to obtain the first coordinate transformation angle, including: Performing Clark transformation on the three-phase line voltage to obtain the voltages Uα and Uβ in the two-phase stationary coordinate system; Using the second-order generalized integrator to extract the positive and negative sequence components of the voltages Uα and Uβ to obtain the positive sequence components Uα+, Uβ+ and the negative sequence components Uα-, Uβ-; Performing two-phase rotation transformation on the positive sequence components Uα+, Uβ+ and the negative sequence components Uα-, Uβ- to obtain the positive sequence components Ud+, Uq+ and the negative sequence components Ud-, Uq- in the rotating coordinate system; Performing PI regulation and integral operation on the positive sequence component Uq+ to obtain the first coordinate transformation angle; The method further includes: Obtaining the rated voltage of the power grid; Calculating the percentage d of the positive sequence voltage component based on the positive sequence components Ud+ and Uq+ and the rated voltage of the power grid; When d is less than 90% and the duration is greater than 2 ms, entering the low-voltage ride-through control mode; or When d is greater than 92% and the duration is greater than 2 ms, exiting the low-voltage ride-through control mode; Calculating the effective value U of the negative-sequence component of the grid voltage based on the negative-sequence components Ud- and Uq- 负 ; Based on the three-phase line voltage, calculating the coordinate transformation angle by using the phase-locked loop method of detecting the zero crossing of the BC phase line voltage to obtain the second coordinate transformation angle, including: Starting the counter to start counting, increasing by 1 in each control period; Converting the signal of the zero crossing of the BC phase line voltage from negative to positive into a rising edge signal; When not entering the low-voltage ride-through control mode, triggering the controller software interrupt in response to the rising edge signal and performing power grid frequency update and counter clearing; When entering the low-voltage ride-through control mode, stopping the power grid frequency update, continuously counting the counter, and resuming responding to the rising edge signal to perform power grid frequency update and counter clearing until exiting the low-voltage ride-through control mode; Obtaining the last power grid frequency updated before not entering the low-voltage ride-through control mode, the count value of the counter during the process of entering the low-voltage ride-through control mode, and the carrier frequency; Calculating the second coordinate transformation angle according to the last updated power grid frequency, the count value of the counter, and the carrier frequency.

2. The low-voltage ride-through control method for an energy storage converter according to claim 1, wherein, Performing PI regulation and integral operation on the positive sequence component Uq+ to obtain the first coordinate transformation angle, including: Adjusting the positive sequence component Uq+ to zero through a PI regulator to obtain the angular frequency of the positive sequence component of the grid voltage; Performing integral operation on the angular frequency of the positive sequence component of the grid voltage to obtain the rotation transformation angle of the two-phase positive sequence voltage; Subtracting π / 6 from the rotation transformation angle of the two-phase positive sequence voltage and integrating the calculation result within 0 to 2π to obtain the first coordinate transformation angle.

3. The low-voltage ride-through control method of the energy storage converter according to claim 1, characterized in that Judging the grid voltage sag situation, including: When entering the low-voltage ride-through control mode, start timing. After 5 ms, calculate the percentage d of the positive-sequence voltage component and the effective value U of the negative-sequence grid voltage respectively 负 The sliding average value within 1 ms to obtain d ave and U 负ave ; When U 负ave is less than 10% of the rated voltage of the power grid, it is determined that the power grid voltage has a symmetrical dip; or When U 负ave is greater than or equal to 10% of the rated voltage of the power grid, it is determined that an asymmetrical voltage dip occurs in the power grid.

4. The low-voltage ride-through control method for an energy storage converter according to claim 3, characterized in that The method further includes: When entering the low voltage ride-through control mode, recording the initial given value of the positive sequence component of the reactive current and the initial given value of the negative sequence component of the reactive current; Within 6 ms after entering the low voltage ride-through control mode, setting the given value of the positive sequence component of the reactive current and the given value of the negative sequence component of the reactive current to 0.

5. The low-voltage ride-through control method for an energy storage converter according to claim 4, wherein Determining the target coordinate transformation angle, as well as the target given value of the positive sequence component of the reactive current and the target given value of the negative sequence component of the reactive current according to the grid voltage sag situation and the transformation angle difference, including: After 6 ms of entering the low voltage ride-through control mode, when the grid voltage undergoes a symmetrical sag, compensating the initial given value of the positive sequence component of the reactive current to obtain the target given value of the positive sequence component of the reactive current, and the target given value of the negative sequence component of the reactive current is the initial given value of the negative sequence component of the reactive current; If 10% ≤ d ave < 90%, then determine the target coordinate transformation angle according to the comparison between the transformation angle difference and a preset value; or If d ave < 10%, then the target coordinate transformation angle is the second coordinate transformation angle; or After 6 ms of entering the low voltage ride-through control mode, when the grid voltage undergoes an asymmetrical sag, compensating the initial given value of the positive sequence component of the reactive current to obtain the target given value of the positive sequence component of the reactive current; compensating the initial given value of the negative sequence component of the reactive current to obtain the target given value of the negative sequence component of the reactive current; Determining the target coordinate transformation angle according to the comparison of the transformation angle difference with a preset value.

6. The low-voltage ride-through control method for an energy storage converter according to claim 5, characterized in that Determining the target coordinate transformation angle according to the comparison of the transformation angle difference with a preset value, including: If the transformation angle difference is greater than or equal to the preset value, the target coordinate transformation angle is the second coordinate transformation angle; or If the transformation angle difference is less than the preset value, the target transformation angle is the first coordinate transformation angle.

7. A energy storage converter, characterized in that, Including: A processor and a memory, the memory is used to store a computer program; the processor is used to run the computer program to implement the low voltage ride-through control method of the energy storage converter as described in any one of claims 1-6.

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