Continuous high-low voltage ride-through control method and device and photovoltaic inverter

Abstract

This invention provides a continuous high and low voltage ride-through control method, device, and photovoltaic inverter, relating to the field of power equipment technology. The method includes: real-time acquisition of the DC bus voltage, three-phase voltage at the grid connection point, and three-phase current of the photovoltaic inverter; determining the current operating condition of the photovoltaic inverter based on the three-phase voltage; putting the dual compensation links into a standby ready state, wherein the dual compensation links include a dedicated low-voltage ride-through compensation link and a dedicated high-voltage ride-through compensation link; controlling the operating state of the dual compensation links according to the current operating condition; if in a low-voltage to high-voltage ride-through switching condition, stopping the output of the dedicated low-voltage ride-through compensation link and simultaneously starting the output of the dedicated high-voltage ride-through compensation link; dynamically calibrating the compensation amount of the currently operating compensation link output; generating a pulse width modulation signal based on the calibrated compensation amount to control the stable operation of the photovoltaic inverter. This invention can avoid high-voltage overshooting of the bus voltage caused by compensation delay during low-voltage to high-voltage ride-through switching, improving the stability and reliability of the photovoltaic inverter during continuous high and low voltage ride-through.

Description

Technical Field

[0001] This invention relates to the field of power equipment technology, and in particular to a continuous high and low voltage ride-through control method, device, and photovoltaic inverter. Background Technology

[0002] With the large-scale grid connection of new energy sources, the voltage fluctuation scenarios of the power grid are becoming increasingly complex. In addition to voltage drops and rises caused by single lightning strikes and temporary line faults, scenarios such as reclosing failures and multiple fault superpositions can lead to alternating or repeated voltage drops and rises at the grid connection point within a short period of time, with amplitudes exceeding the normal operating range. In such cases, the converters connected to the grid, such as photovoltaic inverters, are required to maintain stable grid-connected operation and quickly restore normal power output. This capability is called continuous high and low voltage ride-through.

[0003] In related technologies, when the grid connection point voltage rapidly rises from the rated voltage to 1.1 to 1.3 times the rated voltage due to factors such as reclosing failure or superimposed line faults, the converter initiates a high-voltage surge response. During this stage, to prevent the bus voltage from exceeding the upper limit of the voltage amplitude and causing the converter to disconnect from the grid, feedforward compensation is usually used to suppress the excessive rise of the bus voltage. When the grid connection point voltage rapidly drops from the rated voltage to 0 to 0.8 times the rated voltage due to factors such as multiple faults or lightning strikes, the converter initiates a low-voltage surge response. During this stage, to prevent the bus voltage from falling below the lower limit of the voltage amplitude and causing the converter to disconnect from the grid, feedforward compensation is usually used to suppress the continued drop in bus voltage.

[0004] However, the inventors discovered that before performing feedforward compensation, the collected voltage data needs to be filtered. Excessive filtering leads to a delay in feedforward compensation. When the response transitions from a low-voltage to a high-voltage stage, the feedforward compensation used to suppress further voltage drops in the low-voltage stage is applied to the high-voltage stage, causing a faster rise in bus voltage and resulting in high-voltage over-limit issues. Existing technologies using a single compensation link struggle to adapt to rapid operating condition switching, and the compensation response lacks specificity and synchronization, further exacerbating bus voltage fluctuations during operating condition switching and affecting the grid-connected stability of photovoltaic inverters. Summary of the Invention

[0005] This invention provides a continuous high and low voltage ride-through control method, device, and photovoltaic inverter to solve the problem of delay in feedforward compensation, where feedforward compensation at low voltage applies to the bus voltage at high voltage, causing the bus voltage to rise at an increased rate and resulting in high voltage over-limit. It also solves the problems of poor adaptability and insufficient synchronization of a single compensation link, thereby improving the stability of the photovoltaic inverter during continuous high and low voltage ride-through.

[0006] In a first aspect, embodiments of the present invention provide a continuous high and low voltage ride-through control method, comprising: Real-time acquisition of DC bus voltage of photovoltaic inverter and three-phase voltage at grid connection point, and synchronous acquisition of three-phase current at grid connection point; Based on the collected three-phase voltage, the current operating condition of the photovoltaic inverter is determined. The operating conditions include normal operation, low-voltage response, high-voltage response, and low-voltage to high-voltage switching. The dual compensation link is put into standby ready state. The dual compensation link includes a low-voltage dedicated compensation link and a high-voltage dedicated compensation link. The low-voltage dedicated compensation link is used to output the compensation amount to suppress the DC bus voltage drop, and the high-voltage dedicated compensation link is used to output the compensation amount to suppress the DC bus voltage rise. Based on the current operating conditions, control the working status of the dual compensation links. If it is in the low-passage to high-passage switching condition, stop the output of the low-passage dedicated compensation link and simultaneously start the output of the high-passage dedicated compensation link. The compensation amount output by the compensation link in the current operation is dynamically calibrated, and a pulse width modulation signal is generated based on the calibrated compensation amount to control the stable operation of the photovoltaic inverter.

[0007] In one possible implementation, determining the current operating condition of the photovoltaic inverter based on the collected three-phase voltage includes: Calculate the effective value and instantaneous rate of change of the three-phase voltage. The instantaneous rate of change is the ratio of the difference between the effective value of the three-phase voltage at the current moment and the effective value of the three-phase voltage at the previous acquisition moment to the acquisition interval. If the effective value of the three-phase voltage is between 0.9 and 1.1 times the rated voltage, and the absolute value of the instantaneous rate of change is less than the preset stability threshold, it is determined to be a normal operating condition. If the effective value of the three-phase voltage is less than 0.9 times the rated voltage and the instantaneous rate of change is less than 0, it is determined to be a low-voltage response condition. If the effective value of the three-phase voltage is higher than 1.1 times the rated voltage and the instantaneous rate of change is greater than 0, it is determined to be a high-voltage response condition. If the previous moment was under low-voltage response condition, and the effective value of the three-phase voltage rises at the current moment and the instantaneous rate of change is greater than the first preset switching threshold, then it is determined to be under low-voltage to high-voltage switching condition.

[0008] The preset stability threshold and the first preset switching threshold can be flexibly set according to the rated parameters of the photovoltaic inverter and the grid operation requirements. For example, the preset stability threshold can be set to 5V / ms, and the first preset switching threshold can be set to 60V / ms. No specific limitation is made here. The data acquisition interval can be set to 1ms~10ms to ensure the real-time performance of the operating condition judgment.

[0009] In one possible implementation, the output calculation process of the low-voltage dedicated compensation link includes: The DC bus voltage is compared with the DC bus voltage reference value to calculate the bus voltage drop deviation. Based on the bus voltage drop deviation, the base undervoltage compensation is calculated using a proportional-integral-derivative (PID) controller. By combining the effective value of the three-phase current at the grid connection point, the base undervoltage compensation amount is corrected to obtain the final undervoltage compensation amount. The final undervoltage compensation amount is positively correlated with the bus voltage drop deviation and negatively correlated with the effective value of the three-phase current.

[0010] Specifically, the bus voltage sag deviation is the difference between the DC bus voltage reference value and the current DC bus voltage. The larger the difference, the more severe the bus voltage sag, and the greater the foundation undervoltage compensation. A larger effective value of the three-phase current at the grid connection point indicates a larger grid load, requiring a suitable reduction in compensation to avoid current surges caused by over-compensation, ensuring the rationality and stability of the compensation. The proportional gain, integral time constant, and derivative time constant of the PID controller can be determined through on-site commissioning to adapt to different specifications of photovoltaic inverters.

[0011] In one possible implementation, the output calculation process of the high-speed penetration dedicated compensation link includes: The DC bus voltage is compared with the rated DC bus voltage, and the bus voltage rise deviation is calculated. The bus voltage rise deviation is the difference between the current DC bus voltage and the rated DC bus voltage. Based on the bus voltage rise deviation, the high-voltage compensation amount is calculated by a fuzzy control algorithm. The fuzzy control algorithm takes the bus voltage rise deviation and voltage change rate as input and the high-voltage compensation amount as output, and achieves adaptive adjustment through a preset fuzzy rule table. By combining the instantaneous rate of change of the three-phase voltage, the high-voltage compensation amount of the foundation is dynamically adjusted to obtain the final high-voltage compensation amount. The final high-voltage compensation amount is positively correlated with the deviation of the bus voltage rise and positively correlated with the instantaneous rate of change.

[0012] The upper limit of the DC bus voltage can be set to 1.3 times the rated DC bus voltage. The greater the deviation of the bus voltage rise, the closer the voltage is to the upper limit, and the higher the high voltage risk. The fuzzy control algorithm can output the corresponding basic high voltage compensation amount according to the magnitude and trend of the bus voltage rise deviation, and has strong anti-interference ability. The greater the instantaneous change rate of the three-phase voltage, the faster the voltage rises, and the greater the final high voltage compensation amount needs to be to quickly suppress the rise of the bus voltage and avoid high voltage exceeding the limit.

[0013] In one possible implementation, the step of stopping the output of the low-level penetration dedicated compensation link and simultaneously starting the output of the high-level penetration dedicated compensation link when in a low-level penetration to high-level penetration switching condition includes: When it is determined that the low-passage to high-passage switching condition is in progress, the low-passage dedicated compensation link is immediately triggered to stop the output of any compensation amount; The high-voltage transmission dedicated compensation link is started synchronously. Based on the currently collected DC bus voltage and three-phase voltage, the initial high-voltage transmission compensation amount is calculated. The initial high-voltage transmission compensation amount is output in a gradient start-up mode. The gradient start-up mode is to gradually increase the initial high-voltage transmission compensation amount from 0 to the target value within a preset start-up period.

[0014] The preset start-up period can be set to 10ms~50ms, and the step size of the gradient increase can be adjusted according to the actual working conditions. The gradient start-up method can avoid the drastic fluctuation of bus voltage caused by the sudden activation of high-voltage compensation, and ensure the smoothness of the working condition switching. The pulse blocking operation can stop the output of the pulse signal corresponding to the low-voltage compensation amount by controlling the pulse width modulator (PWM), so as to realize the rapid stop of the low-voltage dedicated compensation link.

[0015] In one possible implementation, the dynamic calibration of the compensation amount output by the currently operating compensation link includes: Real-time acquisition of output power and bus voltage fluctuation values ​​of photovoltaic inverters; A calibration coefficient is calculated based on the output power and bus voltage fluctuation. The calibration coefficient increases with the increase of output power and bus voltage fluctuation. An upper limit threshold is set for the calibration coefficient to avoid overcompensation that could lead to system oscillation. Multiply the compensation amount output by the compensation link currently in operation by the calibration coefficient to obtain the calibrated compensation amount, ensuring that the bus voltage fluctuation value is controlled within the preset allowable range.

[0016] The bus voltage fluctuation value is the absolute value of the difference between the current DC bus voltage and the rated DC bus voltage. The preset allowable range can be set to ±5% of the rated DC bus voltage. The calibration coefficient can be calculated using linear fitting or piecewise functions. For example, when the output power is 50% of the rated power and the bus voltage fluctuation value is 2% of the rated voltage, the calibration coefficient is set to 1.0. When the output power rises to 100% of the rated power and the bus voltage fluctuation value rises to 4% of the rated voltage, the calibration coefficient is set to 1.2 to ensure that the compensation amount can adapt to different operating conditions and improve the compensation accuracy.

[0017] In one possible implementation, the method further includes a link synchronization calibration step: The inherent delay of the low-voltage dedicated compensation link and the high-voltage dedicated compensation link is periodically tested, and the inherent delay is calibrated by the step signal response method; Based on the detected inherent delay, adjust the start and stop timing of the dual links to ensure that the stop of the low-voltage dedicated compensation link and the start of the high-voltage dedicated compensation link are synchronized when switching operating conditions, thus eliminating compensation lag caused by timing deviation.

[0018] Specifically, the step signal response method refers to inputting a step signal into the compensation link and recording the time difference from signal input to compensation output, which is the inherent delay. The periodic detection cycle can be set to 1 hour to 24 hours. Based on the detected inherent delay, the start and stop trigger times of the dual links are adjusted. For example, if the inherent delay of the low-voltage dedicated compensation link is 2ms and the inherent delay of the high-voltage dedicated compensation link is 3ms, then when the trigger condition switch is triggered, the high-voltage dedicated compensation link is started 1ms in advance to ensure that the dual links operate synchronously and avoid bus voltage fluctuations caused by compensation lag or superposition.

[0019] In a second aspect, embodiments of the present invention provide a continuous high and low voltage ride-through control device, comprising: The data acquisition module is used to collect the DC bus voltage, three-phase voltage at the grid connection point, and three-phase current at the grid connection point of the photovoltaic inverter in real time. The operating condition judgment module is used to determine the current operating condition of the photovoltaic inverter based on the collected three-phase voltage. A dual-link standby module is used to put the low-voltage dedicated compensation link and the high-voltage dedicated compensation link into a standby ready state. The low-voltage dedicated compensation link is used to output a compensation amount to suppress DC bus voltage drop, and the high-voltage dedicated compensation link is used to output a compensation amount to suppress DC bus voltage rise. The collaborative control module is used to coordinate and control the working status of the dual compensation links according to the current operating conditions. If it is in the low-passage to high-passage switching condition, the output of the low-passage dedicated compensation link is stopped and the output of the high-passage dedicated compensation link is started synchronously. The calibration module is used to dynamically calibrate the compensation amount output by the compensation link currently in operation. The PWM generation module is used to generate pulse width modulation signals based on the calibrated compensation amount to control the stable operation of the photovoltaic inverter.

[0020] In one possible implementation, the operating condition judgment module has a built-in voltage calculation unit and a threshold comparison unit. The voltage calculation unit is used to calculate the effective value and instantaneous rate of change of the three-phase voltage, and the threshold comparison unit is used to compare the calculation result with a preset threshold to complete the operating condition judgment. The calibration module has a built-in calibration coefficient calculation unit and a compensation amount correction unit to realize the dynamic calibration of the compensation amount.

[0021] The voltage calculation unit can use a DSP chip to calculate the effective value and instantaneous rate of change of the three-phase voltage in real time. The threshold comparison unit can compare thresholds through hardware comparators or software logic. The calibration coefficient calculation unit calculates the calibration coefficient in real time based on the collected output power and bus voltage fluctuation value. The compensation correction unit multiplies the compensation amount by the calibration coefficient to complete the dynamic correction of the compensation amount.

[0022] Thirdly, embodiments of the present invention provide a photovoltaic inverter, including a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the method described in the first aspect or any possible implementation of the first aspect.

[0023] In this embodiment of the invention, multiple sets of electrical parameters are collected in real time to accurately determine the operating conditions of the photovoltaic inverter. A dedicated dual-compensation link for low-voltage and high-voltage ride-through is adopted. The dual-compensation link is an independent parallel link that completes initialization after system power-on and is in a standby ready state. It can be quickly switched to operation according to the operating conditions, outputting targeted compensation amounts to avoid the problem of poor adaptability of a single link. During the low-voltage to high-voltage ride-through switching condition, the stop and start of the dual links are synchronously controlled. Combined with gradient start and pulse blocking operation, high-voltage bus voltage exceeding limits caused by residual low-voltage compensation is prevented. Through dynamic calibration of the compensation amount and synchronous calibration of the links, the compensation accuracy and synchronization are further improved, eliminating the impact of compensation delay and timing deviation, ensuring stable grid-connected operation of the photovoltaic inverter during continuous high and low voltage ride-through. Attached Figure Description

[0024] Figure 1 This is a comparison diagram of the ideal bus voltage and the actual bus voltage during the continuous high and low voltage ride-through response stage provided in the embodiments of the present invention; Figure 2 This is a flowchart illustrating the implementation of the continuous high and low voltage ride-through control method provided in this embodiment of the invention. Figure 3 This is a flowchart illustrating the compensation strategy implementation of the continuous high and low voltage ride-through control method provided in this embodiment of the invention. Figure 4 This is a schematic diagram of the continuous high and low pressure crossing control device provided in an embodiment of the present invention. Detailed Implementation

[0025] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0026] Figure 1 This is a comparison chart of the ideal bus voltage and the actual bus voltage during the continuous high and low voltage ride-through response stage provided in the embodiments of the present invention. The following is a summary of the comparison. Figure 1 The causes of the technical problems solved by the embodiments of the present invention will be explained in detail: Taking a bus voltage with a rated voltage of 1000V as an example, the upper limit of its voltage amplitude is set to 1.3 times the rated value, which is 1300V, and the lower limit of its voltage amplitude is set to 0.2 times the rated value, which is 200V.

[0027] The 0-t1 stage is the high penetration response stage, the t1-t3 stage is the low penetration response stage, and after t3, it re-enters the high penetration response stage.

[0028] During the high-voltage response phase, the bus voltage of the photovoltaic inverter rises to 1300V and then drops. In order to ensure that the voltage does not exceed the limit, the controller of the photovoltaic inverter will try to suppress the rise of the bus voltage and eventually restore the bus voltage to the rated voltage in coordination with the grid voltage. In this case, the compensation amount of the photovoltaic inverter is used to compensate the bus voltage so that the bus voltage drops from 1300V to the rated voltage value, which is 1000V.

[0029] After time t1, the system switches from the high-throughput response phase to the low-throughput response phase. Theoretically, the voltage drop rate from 1300V to 1000V during this phase is higher than the voltage drop rate at the end of the high-throughput phase and the return to normal operation. In this case, the feedforward compensation has a delay, and the compensation amount from the high-throughput response phase is applied to the low-throughput response phase, increasing the rate of voltage drop at the bus. That is, the voltage change rate during the t1-t2 phase is greater than the voltage change rate without delay.

[0030] Because the lower limit of the voltage amplitude is relatively low, even if the compensation amount used to suppress the rise of the bus voltage in the high-through response stage is applied to the low-through response stage to increase the rate of bus voltage drop, the low-voltage over-limit of the bus voltage can still be prevented through feedforward compensation in this stage.

[0031] However, after time t3, the response switches from low-through-time response to high-through-time response. Due to the time delay, the compensation amount used to compensate the bus voltage to rise to 1000V at time t3 or before t3 will be applied to the high-through-time response stage, causing the bus voltage to rise instantaneously and exceed the upper limit of the voltage amplitude.

[0032] Therefore, due to the delay, there will be a problem of bus voltage exceeding the limit when switching from low-through-response to high-through-response. However, since the difference between the upper limit and the rated voltage is much smaller than the difference between the lower limit and the rated voltage, there will be no problem of bus voltage exceeding the limit when switching from high-through-response to low-through-response.

[0033] To address the aforementioned problems, this invention provides a continuous high and low voltage ride-through control method, the implementation process of which is as follows: Figure 2 As shown, the method may include: Step 110: Real-time acquisition of DC bus voltage of photovoltaic inverter and three-phase voltage at grid connection point, and synchronous acquisition of three-phase current at grid connection point.

[0034] A Hall effect voltage sensor can be connected in parallel across the DC bus capacitor of a photovoltaic inverter to directly acquire the DC bus voltage of the photovoltaic inverter in each acquisition cycle. Correspondingly, the three-phase voltage and three-phase current at the grid connection point can also be acquired by voltage transformers and current transformers installed at the grid connection point.

[0035] During data acquisition, data can be collected according to a set acquisition cycle, with data acquisition occurring every preset time interval. In this embodiment, the acquisition interval can be set to 1ms~10ms, preferably 2ms, to ensure the real-time acquisition of electrical parameters and provide an accurate data foundation for subsequent operating condition judgment and compensation calculation.

[0036] Step 120: Based on the collected three-phase voltage, determine the current operating condition of the photovoltaic inverter. The operating conditions include normal operation, low-voltage response, high-voltage response, and low-voltage to high-voltage switching.

[0037] The prerequisite for determining the low-to-high-transmission switching condition is that the previous moment was in the low-transmission response condition.

[0038] Step 130: Put the dual compensation link into standby ready state. The dual compensation link includes a low-voltage dedicated compensation link and a high-voltage dedicated compensation link. The low-voltage dedicated compensation link is used to output a compensation amount to suppress DC bus voltage drop, and the high-voltage dedicated compensation link is used to output a compensation amount to suppress DC bus voltage rise.

[0039] The dual-compensation links are independent parallel links. After the system is powered on, it completes initialization and is in a standby ready state. It can be quickly switched to operation according to the working conditions, avoiding the initialization delay when switching a single link.

[0040] Step 140: Based on the current operating conditions, control the working status of the dual compensation links. If it is in the low-passage to high-passage switching condition, stop the output of the low-passage dedicated compensation link and simultaneously start the output of the high-passage dedicated compensation link.

[0041] Step 150: Dynamically calibrate the compensation amount output by the compensation link in the current operation.

[0042] Step 160: Generate a pulse width modulation signal based on the calibrated compensation amount to control the stable operation of the photovoltaic inverter.

[0043] Step 170: Perform link synchronization calibration periodically.

[0044] In summary, the embodiments of the present invention accurately determine the operating conditions of the photovoltaic inverter by collecting multiple sets of electrical parameters in real time, and adopt dedicated dual compensation links for low-voltage and high-voltage ride-through to output compensation amounts in a targeted manner, avoiding the problem of poor adaptability of a single link. During the low-voltage to high-voltage ride-through switching condition, the stopping and starting of the dual links are controlled synchronously to prevent the high voltage of the bus voltage from exceeding the limit due to the residual low-voltage compensation amount. Through dynamic calibration of the compensation amount and synchronous calibration of the links, the compensation accuracy and synchronization are further improved, eliminating the influence of compensation delay and timing deviation, and ensuring that the photovoltaic inverter operates stably in grid connection during continuous high and low voltage ride-through.

[0045] In an optional embodiment, step 120, which determines the current operating condition of the photovoltaic inverter based on the collected three-phase voltages, may include: Calculate the effective value and instantaneous rate of change of the three-phase voltage. The instantaneous rate of change is the ratio of the difference between the effective value of the three-phase voltage at the current moment and the effective value of the three-phase voltage at the previous acquisition moment to the acquisition interval.

[0046] If the effective value of the three-phase voltage is between 0.9 and 1.1 times the rated voltage, and the absolute value of the instantaneous rate of change is less than the preset stability threshold, it is determined to be a normal operating condition.

[0047] If the effective value of the three-phase voltage is less than 0.9 times the rated voltage and the instantaneous rate of change is less than 0, it is determined to be a low-voltage response condition.

[0048] If the effective value of the three-phase voltage is higher than 1.1 times the rated voltage and the instantaneous rate of change is greater than 0, it is determined to be a high-voltage response condition.

[0049] If the previous moment was under low-voltage response condition, and the effective value of the three-phase voltage rises at the current moment and the instantaneous rate of change is greater than the first preset switching threshold, then it is determined to be under low-voltage to high-voltage switching condition.

[0050] The preset stability threshold and the first preset switching threshold can be flexibly set according to the rated parameters of the photovoltaic inverter and the grid operation requirements. For example, the preset stability threshold can be set to 5V / ms and the first preset switching threshold can be set to 60V / ms. No specific limitation is made here.

[0051] In an optional embodiment, the output calculation process of the low-voltage dedicated compensation link in step 130 includes: The DC bus voltage is compared with the DC bus voltage reference value to calculate the bus voltage drop deviation.

[0052] Based on the bus voltage drop deviation, the foundation undervoltage compensation is calculated using a proportional-integral-derivative controller.

[0053] By combining the effective value of the three-phase current at the grid connection point, the base undervoltage compensation amount is corrected to obtain the final undervoltage compensation amount. The final undervoltage compensation amount is positively correlated with the bus voltage drop deviation and negatively correlated with the effective value of the three-phase current.

[0054] Specifically, the bus voltage sag deviation is the difference between the DC bus voltage reference value and the current DC bus voltage. The larger the difference, the more severe the bus voltage sag, and the greater the foundation undervoltage compensation. A larger effective value of the three-phase current at the grid connection point indicates a larger grid load, requiring a suitable reduction in compensation to avoid current surges caused by over-compensation, ensuring the rationality and stability of the compensation. The proportional gain, integral time constant, and derivative time constant of the PID controller can be determined through on-site commissioning to adapt to different specifications of photovoltaic inverters.

[0055] In an optional embodiment, the output calculation process of the high-speed penetration dedicated compensation link in step 130 includes: The DC bus voltage is compared with the rated DC bus voltage, and the bus voltage rise deviation is calculated. The bus voltage rise deviation is the difference between the current DC bus voltage and the rated DC bus voltage.

[0056] Based on the bus voltage rise deviation, the high-voltage compensation amount is calculated using a fuzzy control algorithm. The fuzzy control algorithm takes the bus voltage rise deviation and voltage change rate as input and the high-voltage compensation amount as output, and achieves adaptive adjustment through a preset fuzzy rule table.

[0057] By combining the instantaneous rate of change of the three-phase voltage, the high-voltage compensation amount of the foundation is dynamically adjusted to obtain the final high-voltage compensation amount. The final high-voltage compensation amount is positively correlated with the deviation of the bus voltage rise and positively correlated with the instantaneous rate of change.

[0058] The upper limit of the DC bus voltage can be set to 1.3 times the rated DC bus voltage. The greater the deviation of the bus voltage rise, the closer the voltage is to the upper limit, and the higher the high voltage risk. The fuzzy control algorithm can output the corresponding basic high voltage compensation amount according to the magnitude and trend of the bus voltage rise deviation, and has strong anti-interference ability. The greater the instantaneous change rate of the three-phase voltage, the faster the voltage rises, and the greater the final high voltage compensation amount needs to be to quickly suppress the rise of the bus voltage and avoid high voltage exceeding the limit.

[0059] In an optional embodiment, step 140, which states that if the system is in a low-to-high penetration switching condition, the output of the low-penetration dedicated compensation link is stopped and the output of the high-penetration dedicated compensation link is simultaneously started, includes: When it is determined that the low-passage to high-passage switching condition is in progress, the pulse blocking operation of the low-passage dedicated compensation link is immediately triggered to stop the output of any compensation amount.

[0060] The high-voltage transmission dedicated compensation link is started synchronously. Based on the currently collected DC bus voltage and three-phase voltage, the initial high-voltage transmission compensation amount is calculated. The initial high-voltage transmission compensation amount is output in a gradient start-up mode. The gradient start-up mode is to gradually increase the initial high-voltage transmission compensation amount from 0 to the target value within a preset start-up period.

[0061] The preset start-up period can be set to 10ms~50ms, preferably 20ms. The step size of the gradient increase can be adjusted according to the actual working conditions. The gradient start-up method can avoid the drastic fluctuation of bus voltage caused by the sudden activation of high-voltage compensation and ensure the smoothness of the working condition switching. The pulse blocking operation can stop the output of the pulse signal corresponding to the low-voltage compensation amount by controlling the pulse width modulator (PWM), so as to realize the rapid stop of the low-voltage dedicated compensation link.

[0062] In an optional embodiment, the dynamic calibration of the compensation amount output by the currently operating compensation link in step 150 includes: Real-time acquisition of output power and bus voltage fluctuation values ​​of photovoltaic inverters.

[0063] The calibration coefficient is calculated based on the output power and bus voltage fluctuation. The calibration coefficient increases with the increase of output power and bus voltage fluctuation. An upper limit threshold is set for the calibration coefficient to avoid overcompensation that could cause system oscillation.

[0064] Multiply the compensation amount output by the compensation link currently in operation by the calibration coefficient to obtain the calibrated compensation amount, ensuring that the bus voltage fluctuation value is controlled within the preset allowable range.

[0065] The bus voltage fluctuation value is the absolute value of the difference between the current DC bus voltage and the rated DC bus voltage. The preset allowable range can be set to ±5% of the rated DC bus voltage. The calibration coefficient can be calculated using linear fitting or piecewise functions. For example, when the output power is 50% of the rated power and the bus voltage fluctuation value is 2% of the rated voltage, the calibration coefficient is set to 1.0. When the output power rises to 100% of the rated power and the bus voltage fluctuation value rises to 4% of the rated voltage, the calibration coefficient is set to 1.2 to ensure that the compensation amount can adapt to different operating conditions and improve the compensation accuracy.

[0066] In an optional embodiment, the link synchronization calibration step in step 170 includes: The inherent delay of the low-voltage dedicated compensation link and the high-voltage dedicated compensation link is periodically tested, and the inherent delay is calibrated by the step signal response method.

[0067] Based on the detected inherent delay, adjust the start and stop timing of the dual links to ensure that the stop of the low-voltage dedicated compensation link and the start of the high-voltage dedicated compensation link are synchronized when switching operating conditions, thus eliminating compensation lag caused by timing deviation.

[0068] Specifically, the step signal response method refers to inputting a step signal into the compensation link and recording the time difference from the signal input to the compensation output, which is the inherent delay. The periodic detection cycle can be set to 1 hour to 24 hours, preferably 12 hours. Based on the detected inherent delay, the start and stop trigger times of the dual links are adjusted. For example, if the inherent delay of the low-voltage dedicated compensation link is 2ms and the inherent delay of the high-voltage dedicated compensation link is 3ms, then when the trigger condition switch is triggered, the high-voltage dedicated compensation link is started 1ms in advance to ensure that the dual links operate synchronously and avoid bus voltage fluctuations caused by compensation lag or superposition.

[0069] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0070] Figure 4 A schematic diagram of the continuous high and low voltage ride-through control device provided in an embodiment of the present invention is shown. For ease of explanation, only the parts related to the embodiment of the present invention are shown, and are described in detail below: like Figure 4 As shown, the continuous high and low voltage ride control device 4 includes: The acquisition module 41 is used to acquire the DC bus voltage, three-phase voltage at the grid connection point, and three-phase current at the grid connection point of the photovoltaic inverter in real time.

[0071] The operating condition judgment module 42 is used to determine the current operating condition of the photovoltaic inverter based on the collected three-phase voltage.

[0072] The dual-link standby module 43 is used to put the low-voltage dedicated compensation link and the high-voltage dedicated compensation link into a standby ready state. The low-voltage dedicated compensation link is used to output a compensation amount to suppress DC bus voltage drop, and the high-voltage dedicated compensation link is used to output a compensation amount to suppress DC bus voltage rise.

[0073] The collaborative control module 44 is used to coordinate and control the working status of the dual compensation links according to the current operating conditions. If it is in the low-passage to high-passage switching condition, it stops the output of the low-passage dedicated compensation link and simultaneously starts the output of the high-passage dedicated compensation link.

[0074] The calibration module 45 is used to dynamically calibrate the compensation amount output by the compensation link currently in operation.

[0075] The PWM generation module 46 is used to generate a pulse width modulation signal based on the calibrated compensation amount to control the stable operation of the photovoltaic inverter.

[0076] In one possible implementation, the operating condition judgment module 42 has a built-in voltage calculation unit and a threshold comparison unit. The voltage calculation unit is used to calculate the effective value and instantaneous change rate of the three-phase voltage, and the threshold comparison unit is used to compare the calculation result with a preset threshold to complete the operating condition judgment. The calibration module 45 has a built-in calibration coefficient calculation unit and a compensation amount correction unit to realize the dynamic calibration of the compensation amount.

[0077] The voltage calculation unit can use a DSP chip to calculate the effective value and instantaneous rate of change of the three-phase voltage in real time. The threshold comparison unit can compare thresholds through hardware comparators or software logic. The calibration coefficient calculation unit calculates the calibration coefficient in real time based on the collected output power and bus voltage fluctuation value. The compensation correction unit multiplies the compensation amount by the calibration coefficient to complete the dynamic correction of the compensation amount.

[0078] In one possible implementation, the collaborative control module 44 is specifically used to: when it is determined that the low-voltage to high-voltage switching condition is in progress, immediately trigger the pulse blocking operation of the low-voltage dedicated compensation link to stop outputting any compensation amount; synchronously start the high-voltage dedicated compensation link, calculate the initial high-voltage compensation amount based on the currently collected DC bus voltage and three-phase voltage, and output the initial high-voltage compensation amount using a gradient start method.

[0079] In one possible implementation, the calibration module 45 is also used to periodically detect the inherent delay of the low-penetration dedicated compensation link and the high-penetration dedicated compensation link, and adjust the start and stop timing of the dual links according to the detected inherent delay to ensure that the dual links operate synchronously when switching operating conditions.

[0080] This invention also provides a photovoltaic inverter, including a memory and a processor. The memory stores a computer program, and the processor executes the computer program to implement the method described in the above method embodiments.

[0081] In the above embodiments, the descriptions of each embodiment have their own emphasis. Parts not described in detail or in a particular embodiment can be referred to in the relevant descriptions of other embodiments. Unless otherwise specified or in conflict with logic, the terminology and / or descriptions between different embodiments are consistent and can be referenced interchangeably. Technical features in different embodiments can be combined to form new embodiments based on their inherent logical relationships.

[0082] The above-described embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention, and should all be included within the protection scope of the present invention.

Claims

1. A continuous high and low voltage ride-through control method, characterized in that, include: Real-time acquisition of DC bus voltage of photovoltaic inverter and three-phase voltage at grid connection point, and synchronous acquisition of three-phase current at grid connection point; Based on the collected three-phase voltage, the current operating condition of the photovoltaic inverter is determined. The operating conditions include normal operation, low-voltage response, high-voltage response, and low-voltage to high-voltage switching. The dual compensation link is put into standby ready state. The dual compensation link includes a low-voltage dedicated compensation link and a high-voltage dedicated compensation link. The low-voltage dedicated compensation link is used to output the compensation amount to suppress the DC bus voltage drop, and the high-voltage dedicated compensation link is used to output the compensation amount to suppress the DC bus voltage rise. Based on the current operating conditions, control the working status of the dual compensation links. If it is in the low-passage to high-passage switching condition, stop the output of the low-passage dedicated compensation link and simultaneously start the output of the high-passage dedicated compensation link. The compensation amount output by the compensation link in the current operation is dynamically calibrated, and a pulse width modulation signal is generated based on the calibrated compensation amount to control the stable operation of the photovoltaic inverter.

2. The continuous high and low voltage ride-through control method according to claim 1, characterized in that, The determination of the current operating condition of the photovoltaic inverter based on the collected three-phase voltage includes: Calculate the effective value and instantaneous rate of change of the three-phase voltage. The instantaneous rate of change is the ratio of the difference between the effective value of the three-phase voltage at the current moment and the effective value of the three-phase voltage at the previous acquisition moment to the acquisition interval. If the effective value of the three-phase voltage is between 0.9 and 1.1 times the rated voltage, and the absolute value of the instantaneous rate of change is less than the preset stability threshold, it is determined to be a normal operating condition. If the effective value of the three-phase voltage is less than 0.9 times the rated voltage and the instantaneous rate of change is less than 0, it is determined to be a low-voltage response condition. If the effective value of the three-phase voltage is higher than 1.1 times the rated voltage and the instantaneous rate of change is greater than 0, it is determined to be a high-voltage response condition. If the previous moment was under low-voltage response condition, and the effective value of the three-phase voltage rises at the current moment and the instantaneous rate of change is greater than the first preset switching threshold, then it is determined to be under low-voltage to high-voltage switching condition.

3. The continuous high and low voltage ride-through control method according to claim 1, characterized in that, The calculation process for the output of the dedicated low-voltage compensation link includes: The DC bus voltage is compared with the DC bus voltage reference value to calculate the bus voltage drop deviation. Based on the bus voltage dip deviation, the foundation undervoltage compensation is calculated using a proportional-integral-derivative controller. By combining the effective value of the three-phase current at the grid connection point, the base undervoltage compensation amount is corrected to obtain the final undervoltage compensation amount. The final undervoltage compensation amount is positively correlated with the bus voltage drop deviation and negatively correlated with the effective value of the three-phase current.

4. The continuous high and low voltage ride-through control method according to claim 1, characterized in that, The calculation process for the output of the dedicated high-speed crossing compensation link includes: The DC bus voltage is compared with the rated DC bus voltage, and the bus voltage rise deviation is calculated. The bus voltage rise deviation is the difference between the current DC bus voltage and the rated DC bus voltage. Based on the bus voltage rise deviation, the high-voltage compensation amount is calculated by a fuzzy control algorithm. The fuzzy control algorithm takes the bus voltage rise deviation and voltage change rate as input and the high-voltage compensation amount as output, and achieves adaptive adjustment through a preset fuzzy rule table. By combining the instantaneous rate of change of the three-phase voltage, the high-voltage compensation amount of the foundation is dynamically adjusted to obtain the final high-voltage compensation amount. The final high-voltage compensation amount is positively correlated with the deviation of the bus voltage rise and positively correlated with the instantaneous rate of change.

5. The continuous high and low voltage ride-through control method according to claim 1, characterized in that, If the system is in a low-to-high penetration switching condition, the output of the low-penetration dedicated compensation link will be stopped, and the output of the high-penetration dedicated compensation link will be started simultaneously, including: When it is determined that the low-passage to high-passage switching condition is in progress, the pulse blocking operation of the low-passage dedicated compensation link is immediately triggered to stop the output of any compensation amount; The high-voltage transmission dedicated compensation link is started synchronously. Based on the currently collected DC bus voltage and three-phase voltage, the initial high-voltage transmission compensation amount is calculated. The initial high-voltage transmission compensation amount is output in a gradient start-up mode. The gradient start-up mode is to gradually increase the initial high-voltage transmission compensation amount from 0 to the target value within a preset start-up period.

6. The continuous high and low voltage ride-through control method according to claim 1, characterized in that, The dynamic calibration of the compensation amount output by the compensation link in the current operation includes: Real-time acquisition of output power and bus voltage fluctuation values ​​of photovoltaic inverters; A calibration coefficient is calculated based on the output power and bus voltage fluctuation. The calibration coefficient increases with the increase of output power and bus voltage fluctuation. An upper limit threshold is set for the calibration coefficient to avoid overcompensation that could lead to system oscillation. Multiply the compensation amount output by the compensation link currently in operation by the calibration coefficient to obtain the calibrated compensation amount, ensuring that the bus voltage fluctuation value is controlled within the preset allowable range.

7. The continuous high and low voltage ride-through control method according to claim 1, characterized in that, It also includes a link synchronization calibration step: The inherent delay of the low-voltage penetration dedicated compensation link and the high-voltage penetration dedicated compensation link is periodically tested, and the inherent delay is calibrated by the step signal response method; Based on the detected inherent delay, adjust the start and stop timing of the dual links to ensure that the stop of the low-voltage dedicated compensation link and the start of the high-voltage dedicated compensation link are synchronized when switching operating conditions, thus eliminating compensation lag caused by timing deviation.

8. A continuous high and low voltage ride-through control device, characterized in that, include: The data acquisition module is used to collect the DC bus voltage, three-phase voltage at the grid connection point, and three-phase current at the grid connection point of the photovoltaic inverter in real time. The operating condition judgment module is used to determine the current operating condition of the photovoltaic inverter based on the collected three-phase voltage. A dual-link standby module is used to put the low-voltage dedicated compensation link and the high-voltage dedicated compensation link into a standby ready state. The low-voltage dedicated compensation link is used to output a compensation amount to suppress DC bus voltage drop, and the high-voltage dedicated compensation link is used to output a compensation amount to suppress DC bus voltage rise. The collaborative control module is used to coordinate and control the working status of the dual compensation links according to the current operating conditions. If it is in the low-passage to high-passage switching condition, the output of the low-passage dedicated compensation link is stopped and the output of the high-passage dedicated compensation link is started synchronously. The calibration module is used to dynamically calibrate the compensation amount output by the compensation link currently in operation. The PWM generation module is used to generate pulse width modulation signals based on the calibrated compensation amount to control the stable operation of the photovoltaic inverter.

9. The continuous high and low voltage ride-through control device according to claim 8, characterized in that, The operating condition judgment module has a built-in voltage calculation unit and a threshold comparison unit. The voltage calculation unit is used to calculate the effective value and instantaneous rate of change of the three-phase voltage, and the threshold comparison unit is used to compare the calculation result with a preset threshold to complete the operating condition judgment. The calibration module has a built-in calibration coefficient calculation unit and a compensation amount correction unit to realize the dynamic calibration of the compensation amount.

10. A photovoltaic inverter, characterized in that, It includes a memory and a processor, the memory storing a computer program, and the processor executing the computer program to implement the continuous high and low voltage ride-through control method as described in any one of claims 1 to 7.

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