High and low voltage ride-through control method for energy storage converter

Abstract

The invention relates to the technical field of energy storage converters, in particular to a high-low voltage ride-through control method for an energy storage converter. According to the method, the voltage change rate and the angular frequency change rate are calculated through real-time sampling of the grid-connected point voltage, and the voltage change rate and the angular frequency change rate are fused to serve as the criterion of the ride-through event. And when the voltage change rate and the angular frequency change rate exceed set thresholds, judging that high / low voltage ride-through occurs or ends. According to the method, the crossing identification time is less than 2ms, and the locking speed can be obviously faster than that of a traditional PLL (Phase Locked Loop). The control system is immediately switched to a pure current control loop at the moment of recognizing that crossing occurs or ends, and the output current is reduced to 0, so that the current over-limit and shutdown risks caused by PLL lag can be avoided. A coefficient on-line self-tuning mechanism is introduced, time delay is dynamically adjusted according to power grid operation characteristics, optimal waiting time under different working conditions is achieved, and the stability of the crossing process and the grid-connected friend performance are improved so as to deal with the voltage transient fault problem caused by lightning stroke and other extreme environments.

Description

Technical Field

[0001] This invention relates to the field of energy storage converter technology, and in particular to a high and low voltage ride-through control method for energy storage converters. Background Technology

[0002] The application of energy storage systems can effectively compensate for the inherent intermittency and instability of new energy power generation, making large-scale long-term grid connection of new energy possible. With the rapid development and widespread application of energy storage systems, energy storage converters are widely used in power systems. Transient voltage faults in the power grid (such as short circuits, lightning strikes, and load surges) can easily cause a sudden drop (low voltage) or surge (high voltage) in the voltage at the grid connection point. If the energy storage converter disconnects directly from the grid under such faults, it will exacerbate the power imbalance of the power grid and even trigger cascading faults. Therefore, countries have mandated that new energy equipment have high and low voltage ride-through (LVRT / HVRT) capabilities, that is, to maintain grid-connected operation during voltage anomalies and provide dynamic reactive power support to help the grid recover quickly. Current high and low voltage ride-through technology for energy storage converters relies on traditional phase-locked loops (PLLs). However, PLLs have limited bandwidth and lag in response to voltage surges (>10ms). This results in late switching of the control loop at the fault ride-through and fault recovery times, causing the energy storage converter output current to exceed the limit and triggering protection shutdown.

[0003] When a high-voltage ride-through (HVRT) or low-voltage ride-through (LVRT) occurs in the power grid, the existing energy storage converter relies on a traditional phase-locked loop (PLL) to relock before starting to output reactive power compensation current. However, the PLL has a lag in responding to voltage surges (≥10ms), which can lead to untimely switching of the control loop, resulting in excessive output current at the time of HVRT and LVRT occurrence and recovery, and triggering the risk of shutdown. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a high / low voltage ride-through control method for energy storage converters. It addresses issues such as delayed phase-locked loop (PLL) response, untimely control loop switching, and fixed adaptive delays that are not adapted to different grid conditions in existing energy storage converters during high / low voltage ride-through processes. The invention provides a method for rapid identification and adaptive delay control of high / low voltage ride-through.

[0005] To solve the aforementioned technical problem, the technical solution adopted by the present invention is: a high and low voltage ride-through control method for an energy storage converter, comprising the following steps: S01. Three-phase voltage amplitude acquisition: The amplitude of the three-phase voltage is sampled in real time, and the sampled data is restored to the real-time instantaneous value of the grid voltage. S02, Calculate the rate of change of voltage (ROCV). , in This represents the instantaneous value of the grid voltage at the current sampling moment. This refers to the sampled value at that sampling moment in the previous sampling period; S03. Obtain the voltage angular frequency. The angular frequency of the three-phase voltage is obtained by sampling the three-phase voltage values ​​and then using a PLL phase-locked loop. S04. Calculate the rate of change of angular frequency (ROCOF). ,in The voltage angular frequency at the current sampling time. This refers to the sampled value at that sampling moment in the previous sampling period; S05. Determine if a time travel event occurs, and if ROCV ≥ ROCV. th And ROCOF ≥ ROCOF th When a high / low pressure ride-through event is detected or resumed, the ROCV will... th ROCOF th These are the threshold values ​​for voltage change rate and angular frequency change rate, respectively. S06, Control loop switching: When S05 determines that a high- or low-voltage ride-through event has occurred or recovered, the control loop of the energy storage converter is switched to the positive and negative sequence current control loop, and the current command of the positive and negative sequence current control loop is set to 0. S07. Calculate the adaptive delay τ. The calculation process is as follows: Extract the ROCV and ROCOF at the moment of occurrence or recovery of high- and low-pressure cross-traverse events, and calculate the disturbance index D. ( ), The disturbance index D and adaptive delay τ corresponding to different high and low pressure crossing events were obtained by simulation, and the functional relationship F(τ, D) between the disturbance index D and the adaptive delay τ was fitted. By substituting the disturbance index at the moment of occurrence or recovery of the low-pressure ride-through event into the function F(τ, D), the adaptive delay τ is obtained; S08. After reaching the adaptive delay τ, output the positive and negative sequence components of the current grid voltage. If the grid voltage meets the high and low voltage ride-through criteria, calculate the reactive power compensation current and output it as the current command for the positive and negative sequence current control loop. If the grid voltage does not meet the high and low voltage ride-through criteria, switch back to the original control loop.

[0006] Furthermore, ROCV th The maximum value of the difference between two adjacent sampling points of the grid voltage, which is greater than or equal to the grid voltage.

[0007] Furthermore, the process for determining the maximum value of the difference between two adjacent sampling points of the grid voltage is as follows: The expression for grid voltage is: Set a straight line The maximum voltage point of the power grid is at Calculate the line at The y-value at point U is determined because the slope of line y is greater than or equal to U. s The maximum slope is determined by sampling the grid voltage and line y at the same sampling frequency. If the difference between two adjacent points on line y is greater than or equal to the difference between two adjacent points on the grid voltage, then ROCVth is taken as... ; in The amplitude of the grid voltage. The angular frequency of the grid voltage. Let be the initial phase of the grid voltage, k be the slope of the line y, T be the period of the grid voltage, and N be the number of sampling points for each period of the grid voltage.

[0008] Furthermore, ROCOF th Set to greater than or equal to π rad / s.

[0009] Furthermore, the calculation process for α and β is as follows: Calculate the energy contributions of ROCV and ROCOF within time t1 after the crossing event is identified. , Indicates the energy contribution of ROCV. Indicates the energy contribution of ROCOF; α and β are determined based on the energy ratio. .

[0010] Furthermore, t1 = 2ms.

[0011] Furthermore, ,in The A / D frequency of the sampling device, The frequency of the grid voltage.

[0012] Furthermore, the instantaneous values ​​of the collected grid voltage and voltage angular frequency are stored. Let the sampled values ​​of the three-phase voltage be Ua(n), Ub(n), and Uc(n), respectively. The method for storing the instantaneous grid voltage value for one cycle in the RAM of the sampling device is as follows: A1. Create three double-type arrays Ua, each with a length of N. array []、Ub array []、Uc array []; B1. Create an array index cnt_v; C1. In each sampling period, store the current sampled values ​​Ua(n), Ub(n), and Uc(n) into Uaarray[], Ubarray[], and Ucarray[] respectively, with the array index being cnt_v; D1. If cnt_v ≥ N-1, then cnt_v is set to 0; otherwise, cnt_v is incremented by 1. N is the number of sampling points in one period. E1. Repeat steps C1 and D1; The method for storing the voltage angular frequency of one cycle in the RAM of the sampling device is as follows: A2. Create three double-type arrays Phase[] of length N; B2. Create an array index cnt_p; C2. In each sampling period, store the current sampled value ω(n) into Phase[], with the array index being cnt_p; D2. If cnt_p ≥ N-1, then set cnt_p to 0; otherwise, increment cnt_p by 1. E2. Repeat steps C2 and D2.

[0013] Furthermore, this method is implemented using a DSP, which has analog-to-digital conversion capabilities. There is a proportional relationship k between the digital quantity after analog-to-digital conversion and the actual grid voltage. Based on the proportional relationship k, the sampled data is restored to the real-time instantaneous value of the grid voltage.

[0014] Furthermore, the power commands for the positive and negative sequence current control loop include the d-axis positive sequence current command IdcmdP, the q-axis positive sequence current command IqcmdP, the d-axis negative sequence current command IdcmdN, and the q-axis negative sequence current command IqcmdN.

[0015] The beneficial effects of this invention: The high and low voltage ride-through control method for energy storage converters proposed in this invention has the following advantages compared with existing high and low voltage ride-through control methods: Fast ride-through mode recognition: In addition to using a PLL, it also introduces the rate of change of voltage vector amplitude (ROCV) or the rate of change of angular frequency (ROCOF) as auxiliary criteria, achieving high / low voltage ride-through recognition within 1~2ms, improving the speed and accuracy of ride-through recognition. Dynamic calculation of delay response time: It can avoid inaccurate reactive power compensation current output caused by slow PLL phase locking, resulting in premature or delayed recovery, leading to secondary grid impact, voltage overshoot, harmonic rise, and protection malfunction. Attached Figure Description

[0016] Figure 1 This is a flowchart of the method; Figure 2 A diagram showing the voltage waveform of the power grid and a schematic diagram of setting the straight line y; Figure 3 This is a schematic diagram of the positive and negative sequence current control loop. Detailed Implementation

[0017] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0018] Example 1 This embodiment discloses a high / low voltage ride-through identification method based on a fusion criterion of voltage change rate and angular frequency change rate. The identification time is <2ms. When a high / low voltage ride-through occurs or recovers, the control loop is switched to a pure current control loop and the output current is controlled to 0, effectively avoiding the shutdown of the energy storage converter. Furthermore, during the high / low voltage ride-through process, in order to calculate the accurate reactive power compensation current, an adaptive delay τ is required until the PLL relocks. However, under different high / low voltage ride-through amplitudes and change rates, the PLL lock-in time varies significantly. A fixed adaptive delay τ is prone to problems such as premature recovery or delayed recovery, leading to secondary impacts on the power grid, voltage overshoot, harmonic rise, and protection malfunctions. This invention introduces an online self-tuning mechanism to dynamically adjust the delay according to the power grid operating characteristics, achieving the optimal adaptive delay τ under different operating conditions, thereby improving the stability and grid-friendliness of the ride-through process to cope with voltage transient faults caused by extreme environments such as lightning strikes.

[0019] This method first calculates the rate of change of voltage (ROCV) and the rate of change of angular frequency (ROCOF) by real-time sampling of the grid connection point voltage, and then combines these two values ​​as the criterion for a ride-through event. When the voltage amplitude exceeds the high-voltage threshold or falls below the low-voltage threshold, it is determined that a high / low voltage ride-through has occurred or ended. This method has a ride-through identification time of less than 2ms, significantly faster than the locking speed of traditional PLLs. Upon detecting the occurrence or end of a ride-through, the control system immediately switches to a pure current control loop and reduces the output current to 0, avoiding the risk of current over-limit and shutdown caused by PLL lag.

[0020] like Figure 1 As shown, this method includes the following steps: S01: Three-phase voltage amplitude acquisition. The control of the energy storage converter is implemented using a DSP. The DSP has analog-to-digital conversion (A / D) functionality. The DSP samples the amplitude of the three-phase voltage in real time and restores the A / D data to the real-time instantaneous grid voltage value. Specifically, there is a proportional relationship k between the digital quantity after analog-to-digital conversion and the actual grid voltage. Based on the proportional relationship k, the sampled data is restored to the real-time instantaneous grid voltage value. The value of k is set according to the actual sensors and sampling circuits used.

[0021] S02: Storage of instantaneous three-phase voltage values. Assume the DSP's A / D frequency is... f s The frequency of the grid voltage is f grid The number of sampling points N for each cycle of the three-phase voltage is as shown in Formula 1: Formula 1 Assuming the sampled values ​​of the three-phase voltages are Ua(n), Ub(n), and Uc(n), the method for storing one cycle of sampled data in the DSP's RAM is as follows: A1. Create three double-type arrays Ua, each with a length of N. array []、Ub array []、Uc array []; B1. Create an array index cnt_v, of type 16-bit integer; C1. In each sampling period, store the current sampled values ​​Ua(n), Ub(n), and Uc(n) into Uaarray[], Ubarray[], and Ucarray[] respectively, with the array index being cnt_v; D1. If cnt_v ≥ N-1, then set cnt_v to 0; otherwise, increment cnt_v by 1. E1. Repeat steps C1 and D1.

[0022] S03. Calculate ROCV. This step should precede step C1 in S02. The calculation method is shown in Formula 2: Formula 2, in This represents the instantaneous value of the grid voltage at the current sampling moment. This is the sampled value at the current sampling time in the previous sampling period.

[0023] S04. Obtain the voltage angular frequency. The angular frequency of the three-phase voltage is obtained by sampling the three-phase voltage values ​​and then using a PLL phase-locked loop.

[0024] S05. Voltage angular frequency storage: Assuming the phase of the grid voltage at the current moment is ω(n), the method for storing the phase of one cycle in the DSP's RAM is as follows: A2. Create three double-type arrays Phase[] of length N; B2. Create an array index cnt_p, of type 16-bit integer; C2. In each sampling period, store the current sampled value ω(n) into Phase[], with the array index being cnt_p; D2. If cnt_p ≥ N-1, then set cnt_p to 0; otherwise, increment cnt_p by 1. E2. Repeat steps C2 and D2.

[0025] S06. Calculate the rate of change of angular frequency (ROCOF). ,in The voltage angular frequency at the current sampling time. This is the sampled value at the current sampling time in the previous sampling period.

[0026] S07. Determine the crossing event based on the fusion criterion: when ROCV ≥ ROCV th And ROCOF ≥ ROCOF th When a high / low pressure ride-through event is detected or resumed, the ROCV will... th ROCOF th These are the threshold values ​​for voltage change rate and angular frequency change rate, respectively.

[0027] S08. Control loop switching: When S05 determines that a high or low voltage ride-through event has occurred or recovered, immediately switch to the positive and negative sequence current control loop (IdcmdP, IqcmdP, IdcmdN, and IqcmdN are all set to zero) to control the output current to zero in order to avoid current surges and protection actions caused by PLL lag.

[0028] S09. Calculate the adaptive delay τ for the positive and negative sequence current control loop to reach the control target. After reaching the adaptive delay τ, output the positive and negative sequence components of the current grid voltage. If the grid voltage meets the high and low voltage ride-through criteria, calculate the reactive power compensation current and use it as the current command output for the positive and negative sequence current control loop. If the grid voltage does not meet the high and low voltage ride-through criteria, switch back to the original control loop. This step determines whether the grid voltage meets the high and low voltage ride-through criteria according to the standard GB_T 34120-2023 "Technical Requirements for Energy Storage Converters in Electrochemical Energy Storage Systems".

[0029] In this embodiment, ROCV th The determination method is as follows: when the grid voltage is normal, the difference between the sampling point of the previous cycle and the sampling point at the current moment must be less than the difference between two adjacent sampling points. Therefore, ROCV th The value is taken as the maximum value of the difference between two adjacent sampling points of the grid voltage, which is greater than or equal to the grid voltage.

[0030] like Figure 2 As shown, the process for determining the maximum value of the difference between two adjacent sampling points of the grid voltage is as follows: Grid voltage ( Figure 2 The expression for the (as shown by the star-shaped curve) is: Set a straight line ( Figure 2 (As shown by the dashed line) The maximum voltage point of the power grid is at Calculate the line at The y-value at point U is determined because the slope of line y is greater than or equal to U. s The maximum slope is determined by sampling the grid voltage and line y at the same sampling frequency. If the difference between two adjacent points on line y is greater than or equal to the difference between two adjacent points on the grid voltage, then ROCVth is taken as... ,in The amplitude of the grid voltage. The angular frequency of the grid voltage. Let be the initial phase of the grid voltage, k be the slope of the line y, T be the period of the grid voltage, and N be the number of sampling points for each period of the grid voltage.

[0031] ROCOF th The determination method is as follows: According to GB / T 34120-2023 Technical Requirements for Energy Storage Converters in Electrochemical Energy Storage Systems, when the grid frequency change exceeds 0.5Hz, the energy storage converter needs to change its operating state. Therefore, ROCOF... th Set to greater than or equal to π rad / s.

[0032] After a pass-through event is identified, the PLL cannot accurately calculate the reactive power compensation current due to its delayed response to voltage surges. Therefore, it is necessary to maintain the current control state for a period of time, i.e., to control the current to zero within time τ. To ensure PLL stability and accurate calculation of the reactive power compensation current, an adaptive delay strategy based on disturbance energy weighting is introduced. The calculation process for the adaptive delay τ is as follows: Extract the ROCV and ROCOF at the moment of occurrence or recovery of high- and low-pressure cross-traverse events, and calculate the disturbance index D. ( ), The disturbance index D and adaptive delay τ corresponding to different high and low voltage crossing events were obtained by Simulink simulation, and the functional relationship F(τ, D) between the disturbance index D and the adaptive delay τ was fitted. By substituting the disturbance index at the time of occurrence or recovery of the low-pressure ride-through event into the function F(τ, D), the adaptive delay τ is obtained.

[0033] α and β are determined using a weighted approach based on perturbation energy, treating ROCV and ROCOF as two orthogonal components of the perturbation energy weighted according to their relative intensity. The calculation process for α and β is as follows: Calculate the energy contributions of ROCV and ROCOF within time t1 (2ms) after the crossing event is identified. , Indicates the energy contribution of ROCV. Indicates the energy contribution of ROCOF; α and β are determined based on the energy ratio. .

[0034] like Figure 3 As shown, the current commands of the positive and negative sequence current control loop include the d-axis positive sequence current command IdcmdP, the q-axis positive sequence current command IqcmdP, the d-axis negative sequence current command IdcmdN, and the q-axis negative sequence current command IqcmdN.

[0035] This embodiment can complete the ride-through event identification within 1~2ms. By using an adaptive delay mechanism to match the locking characteristics of the PLL under different grid disturbances, it avoids the risk of early or late recovery caused by fixed delay, and improves the stability and grid-friendliness of the energy storage converter during high / low voltage ride-through.

[0036] The above description is merely the basic principle and preferred embodiment of the present invention. Improvements and substitutions made by those skilled in the art based on the present invention are within the scope of protection of the present invention.

Claims

1. A high- and low-voltage ride-through control method for an energy storage converter, characterized in that: Includes the following steps: S01. Three-phase voltage amplitude acquisition: The amplitude of the three-phase voltage is sampled in real time, and the sampled data is restored to the real-time instantaneous value of the grid voltage. S02, Calculate the rate of change of voltage (ROCV). , in This represents the instantaneous value of the grid voltage at the current sampling moment. This refers to the sampled value at that sampling moment in the previous sampling period; S03. Obtain the voltage angular frequency. The angular frequency of the three-phase voltage is obtained by sampling the three-phase voltage values ​​and then using a PLL phase-locked loop. S04. Calculate the rate of change of angular frequency (ROCOF). ,in The voltage angular frequency at the current sampling time. This refers to the sampled value at that sampling moment in the previous sampling period; S05. Determine if a time travel event occurs, and if ROCV ≥ ROCV. th And ROCOF ≥ ROCOF th When a high / low pressure ride-through event is detected or resumed, the ROCV will... th ROCOF th These are the threshold values ​​for voltage change rate and angular frequency change rate, respectively. S06, Control loop switching: When S05 determines that a high- or low-voltage ride-through event has occurred or recovered, the control loop of the energy storage converter is switched to the positive and negative sequence current control loop, and the current command of the positive and negative sequence current control loop is set to 0. S07. Calculate the adaptive delay τ. The calculation process is as follows: Extract the ROCV and ROCOF at the moment of occurrence or recovery of high- and low-pressure cross-traverse events, and calculate the disturbance index D. ( ), The disturbance index D and adaptive delay τ corresponding to different high and low pressure crossing events were obtained by simulation, and the functional relationship F(τ, D) between the disturbance index D and the adaptive delay τ was fitted. By substituting the disturbance index at the moment of occurrence or recovery of the low-pressure ride-through event into the function F(τ, D), the adaptive delay τ is obtained; S08. After the adaptive delay τ is reached, the PLL outputs the positive and negative sequence components of the current grid voltage. If the grid voltage meets the high and low voltage ride-through criteria, the reactive power compensation current is calculated and used as the current command output of the positive and negative sequence current control loop. If the grid voltage does not meet the high and low voltage ride-through criteria, the original control loop is switched back.

2. The high and low voltage ride-through control method for energy storage converters according to claim 1, characterized in that: ROCV th The maximum value of the difference between two adjacent sampling points of the grid voltage, which is greater than or equal to the grid voltage.

3. The high and low voltage ride-through control method for energy storage converters according to claim 2, characterized in that: The process for determining the maximum value of the difference between two adjacent sampling points of the power grid voltage is as follows: The expression for grid voltage is: Set a straight line The maximum voltage point of the power grid is at Calculate the line at The y-value at point U is determined because the slope of line y is greater than or equal to U. s The maximum slope is determined by sampling the grid voltage and line y at the same sampling frequency. If the difference between two adjacent points on line y is greater than or equal to the difference between two adjacent points on the grid voltage, then ROCVth is taken as... ; in The amplitude of the grid voltage. The angular frequency of the grid voltage. Let be the initial phase of the grid voltage, k be the slope of the line y, T be the period of the grid voltage, and N be the number of sampling points for each period of the grid voltage.

4. The high and low voltage ride-through control method for energy storage converters according to claim 1, characterized in that: ROCOF th Set to greater than or equal to π rad / s.

5. The high and low voltage ride-through control method for energy storage converters according to claim 1, characterized in that: The calculation process for α and β is as follows: Calculate the energy contributions of ROCV and ROCOF within time t1 after the crossing event is identified. ， Indicates the energy contribution of ROCV. Indicates the energy contribution of ROCOF; α and β are determined based on the energy ratio. .

6. The high and low voltage ride-through control method for energy storage converters according to claim 5, characterized in that: t1=2ms.

7. The high and low voltage ride-through control method for energy storage converters according to claim 3, characterized in that: ,in The A / D frequency of the sampling device, The frequency of the grid voltage.

8. The high and low voltage ride-through control method for energy storage converters according to claim 1, characterized in that: The instantaneous values ​​of the collected grid voltage and voltage angular frequency are stored. Let the sampled values ​​of the three-phase voltage be Ua(n), Ub(n), and Uc(n), respectively. The method for storing the instantaneous grid voltage value for one cycle in the RAM of the sampling device is as follows: A1. Create three double-type arrays Ua, each with a length of N. array []、Ub array []、Uc array []; B1. Create an array index cnt_v; C1. In each sampling period, store the current sampled values ​​Ua(n), Ub(n), and Uc(n) into Uaarray[], Ubarray[], and Ucarray[] respectively, with the array index being cnt_v; D1. If cnt_v ≥ N-1, then cnt_v is set to 0; otherwise, cnt_v is incremented by 1. N is the number of sampling points in one period. E1. Repeat steps C1 and D1; The method for storing the voltage angular frequency of one cycle in the RAM of the sampling device is as follows: A2. Create three double-type arrays Phase[] of length N; B2. Create an array index cnt_p; C2. In each sampling period, store the current sampled value ω(n) into Phase[], with the array index being cnt_p; D2. If cnt_p ≥ N-1, then set cnt_p to 0; otherwise, increment cnt_p by 1. E2. Repeat steps C2 and D2.

9. The high and low voltage ride-through control method for energy storage converters according to claim 1, characterized in that: This method is implemented using a DSP, which has analog-to-digital conversion capabilities. There is a proportional relationship k between the digital quantity after analog-to-digital conversion and the actual grid voltage. Based on the proportional relationship k, the sampled data is restored to the real-time instantaneous value of the grid voltage.

10. The high and low voltage ride-through control method for energy storage converters according to claim 1, characterized in that: The current commands for the positive and negative sequence current control loop include the d-axis positive sequence current command IdcmdP, the q-axis positive sequence current command IqcmdP, the d-axis negative sequence current command IdcmdN, and the q-axis negative sequence current command IqcmdN.

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