An output power fluctuation compensation control method of an energy storage photovoltaic power generation system

Abstract

The present application belongs to the technical field of photovoltaic power generation grid-connected control and energy storage power regulation, and relates to an output power fluctuation compensation control method of an energy storage photovoltaic power generation system. The present application acquires output power and sampling interval, and calculates the current power change rate; determines the voltage power response parameter according to the output power change and the voltage change; identifies the power overshoot overrun direction or the falling overrun direction and calculates the overrun amplitude; generates compensation instructions according to the overrun amplitude and the fast energy storage unit; and drives the slow energy storage unit to perform energy supplement or recovery on the fast energy storage unit. The present application solves the problems that the fixed power change rate limit value is difficult to adapt to the grid-connected point voltage response state and the state of charge of the fast energy storage unit continuously deviates in continuous compensation, and achieves the effects of reducing the influence of output power mutation of the grid-connected point, maintaining the continuous compensation capability of the fast energy storage unit, and improving the output power fluctuation compensation stability of the energy storage photovoltaic power generation system.

Description

Technical Field

[0001] This invention belongs to the field of photovoltaic power generation grid connection control and energy storage power regulation technology, and relates to a method for output power fluctuation compensation control of an energy storage photovoltaic power generation system. Background Technology

[0002] Photovoltaic power generation systems are affected by sunlight intensity, cloud cover, module temperature, and inverter operating status, resulting in significant randomness and fluctuations in their output power. When a photovoltaic power generation system is connected to a distribution network or microgrid, rapid increases or decreases in the output power at the grid connection point can cause changes in voltage, current, and power flow distribution at that point. To mitigate the impact of photovoltaic power fluctuations on grid stability, existing systems typically incorporate energy storage units. These units absorb and discharge power to smooth the output power at the grid connection point.

[0003] In existing power fluctuation compensation methods for energy storage photovoltaic power generation systems, the photovoltaic output power is typically compensated and controlled based on a fixed target output power, a fixed smoothing coefficient, or the grid connection interface's ramp-up requirements. These methods focus primarily on the deviation of the output power at the grid connection point itself, without fully considering the response of the grid connection point voltage to changes in output power. When the grid connection point is in a weak grid or operating condition where the voltage is highly sensitive to power disturbances, the same magnitude of power change may cause more significant voltage fluctuations. If a fixed power change rate limit or a fixed compensation intensity is still used, insufficient or excessive compensation is likely to occur, making it difficult to match the rate of change of the grid connection point's output power with the current grid-connected operating state.

[0004] Meanwhile, existing compensation methods mostly employ a single energy storage unit or control energy storage charging and discharging solely based on instantaneous power gaps. While fast energy storage units can quickly respond to power surges or drops, during continuous large-scale charging or discharging, their state of charge (SOC) will continuously shift towards increasing or decreasing, causing the fast energy storage unit to approach its charging and discharging capacity boundary, thereby reducing its subsequent power fluctuation compensation capability. If slow energy storage units cannot promptly perform energy recovery or replenishment based on the continuous shift in the SOC of fast energy storage units, it can easily cause the fast energy storage units to deviate from the suitable SOC range for extended periods, affecting the sustainability and reliability of the energy storage photovoltaic power generation system's compensation under continuous fluctuations. Summary of the Invention

[0005] In view of this, in order to solve the problems mentioned in the background technology, a method for output power fluctuation compensation control of energy storage photovoltaic power generation system is proposed.

[0006] The objective of this invention can be achieved through the following technical solution: a method for output power fluctuation compensation and control of an energy storage photovoltaic power generation system, comprising: S1, acquiring the output power at the grid connection point and the sampling interval, and calculating the current power change rate;

[0007] S2. Obtain the change in output power and the change in voltage at the grid connection point, calculate the ratio to determine the voltage and power response parameters, and generate the power change rate limit using the reciprocal of the voltage and power response parameters.

[0008] S3. Compare the current power change rate with the power change rate limit. If the current power change rate exceeds the power change rate limit, identify the direction of power overshoot or undershoot and calculate the overshoot magnitude. If the current power change rate does not exceed the power change rate limit, re-execute S1.

[0009] S4. Based on the excess amplitude, the current rechargeable power and current dischargeable power of the fast energy storage unit, generate an upward absorption compensation command or a downward support compensation command to drive the fast energy storage unit to charge or discharge.

[0010] S5. Monitor the fast energy storage unit during the current compensation cycle. If the state of charge continues to shift in the same direction, drive the slow energy storage unit to perform energy replenishment or recovery for the fast energy storage unit. If the state of charge shift stops or the shift direction reverses, stop the slow energy storage unit and re-execute S1.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The present invention obtains the change in output power and the change in voltage at the grid connection point, and generates a power change rate limit by using the reciprocal of the voltage power response parameter, so that the power change rate limit can dynamically change with the degree of response of the grid connection point voltage to power disturbance, thereby achieving the effect of tightening the power change rate limit and reducing the impact of sudden changes in output power at the grid connection point on the grid operation when the grid connection point voltage is more sensitive to power changes.

[0012] (2) The present invention prioritizes the fast energy storage unit to charge and absorb or discharge when the power surges or drops, and continuously monitors the offset direction of the state of charge of the fast energy storage unit. When the state of charge continues to shift in the same direction, the slow energy storage unit is driven to perform energy replenishment or recovery for the fast energy storage unit, thereby maintaining the subsequent compensation capability of the fast energy storage unit and improving the continuous fluctuation compensation stability of the energy storage photovoltaic power generation system. Attached Figure Description

[0013] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0014] Figure 1 This is a flowchart of an output power fluctuation compensation and control method for an energy storage photovoltaic power generation system according to the present invention;

[0015] Figure 2 This is a diagram showing the inverse correction relationship between the voltage power response parameters and the power change rate limit in this invention;

[0016] Figure 3 This is a comparison diagram of the power limiting compensation of the fast energy storage unit in this invention. Detailed Implementation

[0017] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0018] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0019] The specific scheme of the output power fluctuation compensation control method for an energy storage photovoltaic power generation system provided by the present invention will be described in detail below with reference to the accompanying drawings.

[0020] Please see Figure 1 As shown, the implementation of this invention includes S1 to S5: When the energy storage photovoltaic power generation system is connected to the grid, the photovoltaic output power is affected by changes in sunlight, cloud cover, and the inverter's operating status, and is prone to surges or drops within adjacent sampling periods. Existing methods mostly control the charging and discharging of the energy storage unit based on fixed ramp limits or fixed compensation strengths, which is difficult to adapt to the real-time response of the grid connection point voltage to power changes; at the same time, after the fast energy storage unit continuously performs charging absorption or discharging bottoming, the state of charge is prone to continuously shift in the same direction, resulting in a decrease in subsequent compensation capabilities.

[0021] Therefore, the rate of change of output power at the grid connection point is taken as the control object. The voltage and power response parameters are determined based on the change in output power and voltage at the grid connection point, and a power change rate limit is generated accordingly. When the current power change rate exceeds the power change rate limit, the fast energy storage unit is driven to perform overshoot absorption or undershoot support based on the magnitude of the overshoot. When the state of charge of the fast energy storage unit continues to deviate, the slow energy storage unit is driven to perform energy replenishment or energy recovery for the fast energy storage unit, thereby achieving suppression of output power fluctuations at the grid connection point and maintenance of the compensation capability of the fast energy storage unit.

[0022] S1. Obtain the output power and sampling interval at the grid connection point, and calculate the current power change rate;

[0023] Whether power fluctuation compensation is needed when a photovoltaic power storage system is connected to the grid depends not only on the output power at a specific moment, but also on the rate of change of that output power over adjacent sampling periods. If the output power at the grid connection point increases or decreases rapidly within a short period, even if the power value itself does not exceed the system's rated range, it can cause rapid changes in the grid connection point voltage and power flow distribution. Therefore, it is necessary to first calculate the current rate of power change based on the output power at the grid connection point in adjacent sampling periods to provide basic data for subsequently judging power surges or drops.

[0024] First, the historical output power value of the grid-connected point in the previous sampling period and the measured output power value of the grid-connected point in the current sampling period are obtained. The grid-connected point is the location where the AC output side of the photovoltaic inverter is connected to the common bus, the location where the AC side of the energy storage converter is connected to the common bus, or the common coupling point where the photovoltaic power generation unit and the energy storage unit are connected to the grid. The sampling period is the time period during which the control system continuously collects the output power of the grid-connected point. It is set according to the data refresh cycle of the grid-connected metering device, the acquisition cycle of the grid-connected point power acquisition device, or the reporting cycle of the inverter's grid-connected side detection unit. The time length corresponding to the sampling period is the sampling interval, and the acquisition frequency is the reciprocal of the sampling interval; that is, the shorter the time interval between two adjacent grid-connected point output power acquisitions, the higher the acquisition frequency. Furthermore, the historical output power value of the grid-connected point is the output power value collected and stored at the grid-connected point in the previous sampling period at the aforementioned acquisition frequency; the measured output power value of the grid-connected point is the output power value collected in the current sampling period at the same acquisition frequency by the grid-connected metering device, the grid-connected point power acquisition device, or the inverter's grid-connected side detection unit.

[0025] Secondly, the difference between the measured output power at the grid connection point and the historical output power at the grid connection point is used to obtain the output power deviation at the grid connection point. The output power deviation at the grid connection point indicates the direction and magnitude of the output power change in the current sampling period relative to the previous sampling period; a positive deviation indicates an increase in the output power at the grid connection point, while a negative deviation indicates a decrease in the output power at the grid connection point.

[0026] Finally, the current power change rate is obtained by dividing the grid-connected point output power deviation by the sampling interval. The sampling interval is derived from the time difference between the sampling time of the current sampling period and the sampling time of the previous sampling period. When the control system collects grid-connected point output power according to a fixed period, the sampling interval is the fixed time interval between two adjacent power samplings. Furthermore, the sampling interval corresponds to the same adjacent sampling period as the historical value and the measured value of the grid-connected point output power.

[0027] Therefore, the current power change rate is used to characterize the degree of change of the grid-connected point output power per unit time, and serves as the object for subsequent comparison with the power change rate limit to identify the direction of power overshoot or power undershoot.

[0028] S2. Obtain the change in output power and the change in voltage at the grid connection point, calculate the ratio to determine the voltage and power response parameters, and generate the power change rate limit using the reciprocal of the voltage and power response parameters.

[0029] Because the response of the grid connection point voltage to changes in output power varies under different grid connection conditions, a large change in the grid connection point voltage after a change in output power indicates that the current grid connection point is highly sensitive to power disturbances, and a fixed power change rate limit should not be used in this case. Conversely, a small change in the grid connection point voltage indicates that the current grid connection point has a strong ability to withstand the same power disturbance. Therefore, it is necessary to determine the voltage-power response parameter based on the changes in grid connection point output power and grid connection point voltage, and use this parameter to correct the allowable ramp rate of the grid connection interface to generate the power change rate limit for the current sampling period.

[0030] First, the grid-connected point output power for the current sampling period and the previous sampling period is read, and the difference between the current and previous sampling period's grid-connected point output power is calculated to obtain the change in grid-connected point output power. Simultaneously, the grid-connected point voltage for the current and previous sampling periods is read, and the difference between the current and previous sampling period's grid-connected point voltage is calculated to obtain the change in grid-connected point voltage. The change in grid-connected point output power represents the magnitude of output power change within adjacent sampling periods, and the change in grid-connected point voltage represents the magnitude of voltage response to power changes within adjacent sampling periods.

[0031] Secondly, since the voltage power response parameter is determined by the ratio of the change in grid connection voltage to the change in grid connection output power, if the change in grid connection output power is too small, the ratio is easily distorted by the acquisition error. Therefore, it is necessary to first determine whether the change in output power has reached the reliable resolution range.

[0032] Furthermore, if the absolute value of the change in output power at the grid connection point is lower than the minimum resolvable power change, it indicates that the change in output power within the current sampling period is insufficient to reliably characterize the voltage response to power changes. In this case, the voltage power response parameters from the previous sampling period are used to avoid fluctuations in the voltage power response parameters due to insufficient power detection resolution.

[0033] If the absolute value of the change in output power at the grid connection point is not lower than the minimum resolvable power change of the grid connection point power acquisition device, and this minimum resolvable power change is the power change dead zone threshold, the voltage-power response parameter for the current sampling period is obtained by calculating the ratio of the change in grid connection point voltage to the change in grid connection point output power. The voltage-power response parameter characterizes the degree of grid connection point voltage change caused by a unit change in output power; a larger voltage-power response parameter indicates that the current grid connection point is more sensitive to changes in output power.

[0034] Furthermore, after obtaining the voltage and power response parameters, it is necessary to combine the response sensitivity of the current grid connection point with the allowable power variation range of the grid connection interface itself to determine the feasible power variation rate limit for the current sampling period. Therefore, the allowable ramp rate of the grid connection interface is used as the basic limit, and the voltage and power response parameters are used to correct this basic limit.

[0035] Specifically, the grid-connected operation specification configuration is invoked to obtain the allowable ramp rate of the grid-connected interface. The grid-connected operation specification configuration includes the fields of grid-connected interface identifier, rated output power of the grid-connected interface, allowable power change ratio per unit time, and maximum allowable ramp rate. When the maximum allowable ramp rate is already written in the configuration, this field is directly read as the allowable ramp rate of the grid-connected interface. When the allowable power change ratio per unit time is written in the configuration, the allowable ramp rate of the grid-connected interface is determined by multiplying the rated output power of the grid-connected interface by the allowable power change ratio per unit time.

[0036] Finally, the voltage and power response parameters are normalized, and the reciprocal of the normalized voltage and power response parameters is taken as the limit correction ratio. The allowable ramp rate of the grid-connected interface is multiplied by the limit correction ratio to generate the power change rate limit for the current sampling period. Specifically, when the voltage and power response parameters increase, the limit correction ratio decreases, and the power change rate limit for the current sampling period decreases accordingly, narrowing the allowable change rate range between the positive overshoot threshold and the negative droop threshold. Conversely, when the voltage and power response parameters decrease, the limit correction ratio increases, and the power change rate limit for the current sampling period increases accordingly, widening the allowable change rate range between the positive overshoot threshold and the negative droop threshold.

[0037] like Figure 2As shown, the horizontal axis represents the normalized voltage-power response parameter, and the vertical axis represents the power change rate limit. As the normalized voltage-power response parameter increases, the limit correction ratio corresponding to its reciprocal decreases, thus lowering the power change rate limit generated by the grid-connected interface ramp rate. Conversely, as the normalized voltage-power response parameter decreases, the limit correction ratio corresponding to its reciprocal increases, thus raising the power change rate limit. The dots in the figure represent the power change rate limits generated under different sampling periods. The area of ​​each dot corresponds to the voltage change at the grid connection point, indicating that when the voltage change at the grid connection point is large, the power change rate limit decreases accordingly, serving as a comparison boundary for subsequent judgment of the direction of power overshoot or power undershoot.

[0038] Therefore, the power change rate limit for the current sampling period is no longer determined solely by the fixed ramp requirement, but is dynamically adjusted according to the response of the grid connection point voltage to changes in output power. This is used to compare with the current power change rate to determine whether a power surge or power drop has occurred.

[0039] S3. Compare the current power change rate with the power change rate limit. If the current power change rate exceeds the power change rate limit, identify the direction of power overshoot or undershoot and calculate the overshoot magnitude. If the current power change rate does not exceed the power change rate limit, re-execute S1.

[0040] After obtaining the current power change rate and the power change rate limit, it is necessary to determine whether the change in the grid-connected point output power within the current sampling period has exceeded the allowable range of change under the current grid-connected state. Since the current power change rate has positive and negative directions, with positive values ​​indicating an increase in grid-connected point output power and negative values ​​indicating a decrease in grid-connected point output power, it is necessary to determine the positive upward surge judgment boundary and the negative downward surge judgment boundary based on the power change rate limit.

[0041] First, the power change rate limit is used as the positive overshoot threshold, and the opposite of the power change rate limit is used as the negative fall threshold. The allowable change rate range is constructed from the negative fall threshold to the positive overshoot threshold. Here, the allowable change rate range represents the range of allowable changes in the grid-connected point output power within the current sampling period.

[0042] Secondly, the current power change rate is compared with the allowable change rate range. If the current power change rate is greater than the positive overshoot threshold, it indicates that the grid connection point output power is rising too fast, and it is identified as a power overshoot direction. The difference between the current power change rate and the positive overshoot threshold is taken as the excess amplitude.

[0043] Conversely, if the current power change rate is less than the negative decline threshold, it indicates that the grid-connected point's output power is decreasing too rapidly, and this is identified as an excessive power decline direction. The difference between the negative decline threshold and the current power change rate is taken as the excess magnitude. Therefore, regardless of whether the power surges or falls, the calculated excess magnitude is always a positive value, used to indicate the degree to which the current power change rate exceeds the allowable change rate range.

[0044] Finally, if the current power change rate is within the allowable change rate range, it is determined that the power change rate has not exceeded the limit in the current sampling period, no energy storage compensation command is generated, and S1 is re-executed to enter the grid connection point output power monitoring of the next sampling period.

[0045] S4. Based on the excess amplitude, the current rechargeable power and current dischargeable power of the fast energy storage unit, generate an upward absorption compensation command or a downward support compensation command to drive the fast energy storage unit to charge or discharge.

[0046] After identifying the direction of power overshoot or power drop overshoot, the excess amplitude needs to be converted into a charging / discharging compensation action that the fast energy storage unit can execute. Since the excess amplitude represents the degree to which the current power change rate exceeds the allowable change rate range, it cannot be directly used as a charging / discharging command for the converter. Therefore, it is necessary to determine the power to be absorbed or released within the current sampling period by combining the sampling interval, and further limit the amplitude by combining the current chargeable power and current dischargeable power of the fast energy storage unit to avoid generating compensation commands that exceed the current capacity of the fast energy storage unit.

[0047] First, the current rechargeable power and current dischargeable power of the fast energy storage unit are read. Since the charging absorption capacity and discharge support capacity of the fast energy storage unit are not fixed under different states of charge, terminal voltage, and current limiting conditions, the rated power cannot be directly used as the compensation upper limit for the current sampling period. Instead, the current rechargeable power and current dischargeable power need to be determined based on the current operating state of the fast energy storage unit.

[0048] Specifically, the terminal voltage, maximum permissible charging current limit, and maximum permissible discharging current limit of the fast energy storage unit are collected. The terminal voltage reflects the current voltage state of the DC side of the fast energy storage unit; the maximum permissible charging current limit restricts the maximum charging current the fast energy storage unit can withstand under the current conditions; and the maximum permissible discharging current limit restricts the maximum discharging current the fast energy storage unit can output under the current conditions. Furthermore, the maximum permissible charging current limit and the maximum permissible discharging current limit can be output by the battery management unit or energy storage converter control unit of the fast energy storage unit based on the state of charge, operating temperature, and protection status.

[0049] After obtaining the terminal voltage and the maximum allowable charging current limit, the theoretical maximum charging power is determined based on these two limits. The terminal voltage is the voltage value detected at the DC-side port of the fast energy storage unit during the current sampling period. The maximum allowable charging current limit is the upper limit of the current rechargeable current output by the battery management unit or energy storage converter control unit of the fast energy storage unit based on the state of charge, operating temperature, and protection status. Multiplying the terminal voltage by the maximum allowable charging current limit yields the theoretical maximum charging power of the fast energy storage unit under the current DC-side conditions. When the fast energy storage unit reaches or exceeds the upper limit, the current rechargeable power is reset to zero or charging absorption is stopped; when it reaches or falls below the lower limit, the current dischargeable power is reset to zero or discharging is stopped. Slow energy storage units, when performing energy replenishment or recovery, should also be subject to their own upper and lower limits. Furthermore, since the fast energy storage unit exchanges power with the grid side through the converter, the converter has real-time conversion losses during the power conversion process. Therefore, it is necessary to subtract the real-time conversion loss power of the converter from the theoretical maximum charging power to obtain the current rechargeable power that the fast energy storage unit can actually perform in the current sampling period.

[0050] Similarly, after obtaining the terminal voltage and the maximum allowable discharge current limit, the theoretical maximum discharge power is determined based on the terminal voltage and the maximum allowable discharge current limit. The real-time conversion loss power of the converter is then subtracted from the theoretical maximum discharge power to obtain the current discharge power that the fast energy storage unit can actually perform in the current sampling period.

[0051] Therefore, the current chargeable power and current dischargeable power are no longer fixed rated values, but real-time power capabilities obtained by combining the terminal voltage and current limits of the fast energy storage unit and the real-time conversion loss of the converter. These are then used to limit the power to be absorbed or released, so as to avoid generating compensation commands that exceed the current charging and discharging capabilities of the fast energy storage unit.

[0052] Secondly, when the power surge is identified as exceeding the limit, it indicates that the grid-connected point output power is rising too rapidly within the current sampling period, exceeding the allowable range of the power change rate limit. In this case, the fast energy storage unit needs to enter charging mode to absorb the excess power on the grid-connected point side, causing the rate of increase of the grid-connected point output power to fall back into the allowable change rate range.

[0053] Specifically, the excess amplitude is multiplied by the sampling interval to obtain the power change that needs to be absorbed within the current sampling period, and this power change is taken as the power to be absorbed. Here, the excess amplitude indicates the degree to which the current power change rate exceeds the positive overshoot threshold, and the sampling interval indicates the time span corresponding to this over-limit state. The combination of the two can reflect the power compensation demand that needs to be absorbed by the fast energy storage unit within the current sampling period.

[0054] After obtaining the power to be absorbed, it is compared with the current rechargeable power. The power to be absorbed represents the theoretical power required to suppress this power surge, while the current rechargeable power represents the maximum charging power that the fast energy storage unit can actually withstand under its current operating conditions. If the power to be absorbed is not greater than the current rechargeable power, it means the fast energy storage unit can fully absorb the power surge demand, and the power to be absorbed is used as the surge absorption compensation power. If the power to be absorbed is greater than the current rechargeable power, it means the fast energy storage unit's current charging capacity is insufficient to fully absorb the power surge demand, and the current rechargeable power is used as the surge absorption compensation power.

[0055] Therefore, the overshoot absorption compensation power is the smaller value between the power to be absorbed and the current rechargeable power, which corresponds to the absorption demand caused by the overshoot of this power and does not exceed the current charging capacity of the fast energy storage unit.

[0056] After determining the overshoot absorption compensation power, the control system binds the charging action identifier, the overshoot absorption compensation power, and the current sampling period identifier to form an overshoot absorption compensation command corresponding to the current sampling period. The overshoot absorption compensation command includes at least the charging action identifier and the overshoot absorption compensation power. The charging action identifier instructs the converter corresponding to the fast energy storage unit to enter the charging absorption state, and the overshoot absorption compensation power limits the charging absorption power of the converter within the current sampling period. This overshoot absorption compensation command is subsequently output to the converter of the fast energy storage unit, causing the fast energy storage unit to perform charging absorption according to the overshoot absorption compensation power.

[0057] Similarly, when a power drop exceeding the limit is identified, it indicates that the output power at the grid connection point is decreasing too rapidly within the current sampling period, exceeding the allowable range of the power change rate limit. In this case, it is necessary to release power to the grid connection point through the fast energy storage unit entering a discharge state, so that the rate of decrease of the output power at the grid connection point falls back into the allowable change rate range.

[0058] Specifically, the excess amplitude is multiplied by the sampling interval to obtain the power change that needs to be released within the current sampling period, and this power change is used as the power to be released. Here, the excess amplitude represents the degree to which the current power change rate exceeds the negative drop threshold, and the sampling interval represents the time span corresponding to this over-limit state. The combination of the two can reflect the power compensation demand that needs to be released by the fast energy storage unit within the current sampling period.

[0059] After obtaining the power to be released, it is compared with the current dischargeable power. If the power to be released is not greater than the current dischargeable power, the power to be released is used as the fallback compensation power; if the power to be released is greater than the current dischargeable power, the current dischargeable power is used as the fallback compensation power. Therefore, the fallback compensation power is the smaller value between the power to be released and the current dischargeable power, which corresponds to the discharge support demand caused by the current power drop exceeding the limit, and does not exceed the current executable discharge capacity of the fast energy storage unit.

[0060] After determining the fallback compensation power, a fallback compensation command is generated. This command includes at least a discharge action flag and a fallback compensation power. The discharge action flag instructs the converter corresponding to the fast energy storage unit to enter a discharge support state, and the fallback compensation power limits the discharge support power of the converter within the current sampling period. This fallback compensation command is subsequently output to the converter of the fast energy storage unit, causing the fast energy storage unit to perform discharge support according to the fallback compensation power.

[0061] like Figure 3 As shown, the right side represents charging absorption in the direction of power overshoot, and the left side represents discharging support in the direction of power drop overshoot. The light-colored bars represent the current rechargeable or dischargeable power of the fast energy storage unit within the current sampling period. The solid bars represent the overshoot absorption compensation power or drop support compensation power obtained after limiting. The diamond-shaped dots represent the power to be absorbed or released, determined by the exceedance amplitude and the sampling interval. When the diamond-shaped dot extends beyond the end of the light-colored bar, it indicates that the theoretical compensation requirement exceeds the current executable capacity of the fast energy storage unit, and the excess portion is not output as a compensation command. When the diamond-shaped dot does not extend beyond the end of the light-colored bar, it indicates that the fast energy storage unit can fully execute the current power to be absorbed or released. Therefore, the overshoot absorption compensation power or drop support compensation power is obtained by comparing the theoretical compensation requirement with the current executable capacity and taking the smaller value.

[0062] Finally, the overshoot absorption compensation command or the undershoot support compensation command is output to the converter of the fast energy storage unit. When the overshoot absorption compensation command is output, the converter enters the charging absorption state according to the charging action indicator and controls the fast energy storage unit to charge according to the overshoot absorption compensation power, so that the fast energy storage unit absorbs the excess power caused by the rapid rise of the grid connection point output power. When the undershoot support compensation command is output, the converter enters the discharging support state according to the discharging action indicator and controls the fast energy storage unit to discharge according to the undershoot support compensation power, so that the fast energy storage unit releases power to the grid connection point to compensate for the power gap caused by the rapid drop of the grid connection point output power. Thus, the overshoot absorption compensation command and the undershoot support compensation command correspond to the charging absorption action and the discharging support action of the fast energy storage unit, respectively, so that the rate of change of the grid connection point output power falls back to within the allowable rate of change range.

[0063] Furthermore, when the power drop exceeds the limit, the real-time conversion loss of the converter affects the effective supporting power actually reaching the grid connection point when the fast energy storage unit releases power to the grid connection point through the converter. To ensure that the power change rate limit in the next sampling period can accommodate the losses during this discharge support process, a dynamic loss compensation coefficient is determined by calculating the ratio of real-time conversion loss power to the power to be released within the current sampling period, and this dynamic loss compensation coefficient is stored in the next sampling period.

[0064] When generating the power change rate limit in the next sampling period, the dynamic loss compensation coefficient is superimposed on the reciprocal of the voltage and power response parameters in the next sampling period to form a corrected limit correction ratio. The power change rate limit for the next sampling period is then generated based on this corrected limit correction ratio, which can be specifically expressed as follows: ;in, This indicates the power change rate limit for the next sampling period; This indicates the allowable ramp rate of the grid-connected interface, which is obtained from the grid-connected operation specification configuration in the next sampling period; This represents the normalized voltage and power response parameter after the next sampling period, which is derived from the change in grid connection point voltage and the change in grid connection point output power during the next sampling period. This represents the real-time conversion loss power of the converter during the current sampling period, which is derived from converter operation monitoring data. This represents the power to be released within the current sampling period, based on the excess amplitude and sampling interval.

[0065] This indicates the voltage response side limit correction term, which is used to make the corresponding limit correction ratio smaller when the grid connection point voltage is more sensitive to changes in output power; This represents the dynamic loss compensation coefficient, used to characterize the proportion of the real-time conversion loss of the converter relative to the power to be released during the current discharge bottoming process; This indicates the overall limit correction ratio.

[0066] Therefore, the dynamic loss compensation coefficient is not stored in isolation, but participates in the generation of the power change rate limit as part of the limit correction ratio for the next sampling period. This allows the limit generation process for the next sampling period to simultaneously take into account the grid connection point voltage response state and the conversion loss situation during the discharge bottoming process of the fast energy storage unit in the previous sampling period.

[0067] S5. Monitor the fast energy storage unit during the current compensation cycle. If the state of charge continues to shift in the same direction, drive the slow energy storage unit to perform energy replenishment or recovery for the fast energy storage unit. If the state of charge shift stops or the shift direction reverses, stop the slow energy storage unit and re-execute S1.

[0068] After a fast energy storage unit performs an upward absorption or a downward support operation, its state of charge (SOC) will change with continuous charging or discharging. If the SOC of the fast energy storage unit continues to increase within the current compensation cycle, it indicates that the unit is continuously absorbing energy and may be approaching its charging capacity limit. Conversely, if the SOC of the fast energy storage unit continues to decrease, it indicates that it is continuously releasing energy and may be approaching its discharging capacity limit. Therefore, it is necessary to determine whether a slow energy storage unit needs to intervene to maintain the subsequent compensation capacity of the fast energy storage unit based on the changes in its SOC between adjacent sampling cycles.

[0069] It is important to note that fast and slow energy storage units are distinguished based on their rated charge / discharge rates. First, the device nameplate parameters, energy storage management system registration parameters, or factory technical parameters of the candidate energy storage media are read to obtain the rated charge / discharge rate for each candidate medium. Second, the rated charge / discharge rates of each candidate medium are compared numerically. The rated charge / discharge rate with the highest value is designated as the first charge / discharge rate, and the energy storage medium corresponding to the first charge / discharge rate is designated as the power-type energy storage medium. Among the remaining candidate energy storage media, those with a rated charge / discharge rate lower than the first charge / discharge rate are selected as energy-type energy storage media, and their rated charge / discharge rate is designated as the second charge / discharge rate. Further, a fast energy storage unit is constructed using a power-type energy storage medium with the first charge / discharge rate, and a slow energy storage unit is constructed using an energy-type energy storage medium with the second charge / discharge rate, with the first charge / discharge rate being greater than the second charge / discharge rate. Therefore, fast energy storage units can undertake short-term rapid power compensation, while slow energy storage units can undertake subsequent energy balancing, enabling the energy storage photovoltaic power generation system to maintain its compensation capability under continuous fluctuating operating conditions.

[0070] First, within the current compensation period, the state of charge (SOC) value of the fast energy storage unit in the current sampling period and the SOC value in the previous sampling period are read, and the difference between the two is calculated as the SOC change in the current sampling period. The SOC change is the difference between the SOC values. A positive SOC change indicates an increase in the SOC of the fast energy storage unit; a negative SOC change indicates a decrease in the SOC; and a zero SOC change indicates that the SOC offset has stopped.

[0071] To determine whether the state of charge continues to shift in the same direction, the following determination method is used: ;in, This indicates the result of the charge state offset determination for the current sampling period; Indicates the current sampling period; This represents the change in state of charge during the current sampling period, which is derived from the difference between the state of charge value of the fast energy storage unit in the current sampling period and the state of charge value of the fast energy storage unit in the previous sampling period. This represents the change in the state of charge in the previous sampling period; This is used to determine whether the direction of the state of charge change is consistent between two adjacent sampling periods. When it is greater than zero, it means that the change in the state of charge of the two sampling periods has the same sign, and the state of charge of the fast energy storage unit continues to shift in the same direction. When it is less than zero, it means that the shift direction of the current sampling period is reversed relative to the previous sampling period. When it is equal to zero, it means that there was no shift in the state of charge of the previous sampling period, and the current sampling period has not yet formed a continuous shift trend, so the slow energy storage unit is not triggered to operate.

[0072] In the above judgment results, This indicates that the state of charge of the fast energy storage unit continues to shift in the direction of increase; This indicates that the state of charge of the fast energy storage unit continues to shift in the direction of decrease; This indicates that the state of charge offset of the fast energy storage unit has stopped or the offset direction has reversed.

[0073] Secondly, when it is determined that the state of charge of the fast energy storage unit continues to shift in the direction of decrease, it indicates that the fast energy storage unit is continuously discharging within the current compensation cycle, and its subsequent discharge support capability may decrease. At this time, the slow energy storage unit is driven to discharge to the fast energy storage unit to replenish the energy of the fast energy storage unit.

[0074] Similarly, when it is determined that the state of charge of the fast energy storage unit continues to shift in the direction of increasing, it indicates that the fast energy storage unit is continuously charging in the current compensation cycle, and its subsequent charging absorption capacity may decrease. At this time, the slow energy storage unit is driven to absorb the energy of the fast energy storage unit in order to perform energy recovery on the fast energy storage unit.

[0075] Finally, if the change in state of charge (SOC) in the current sampling period is zero, the SOC offset of the fast energy storage unit is determined to have stopped; if the change in SOC in the current sampling period is opposite in sign to the change in SOC in the previous sampling period, the SOC offset direction of the fast energy storage unit is determined to have reversed. When the SOC offset stops or the offset direction reverses, the slow energy storage unit stops operating, and S1 is re-executed to enter the grid-connected point output power monitoring for the next sampling period.

[0076] The above embodiments can be implemented, in whole or in part, by software, hardware, firmware, or any other combination thereof. When implemented using software, the above embodiments can be implemented, in whole or in part, in the form of a computer program product.

[0077] Those skilled in the art will recognize that the algorithmic steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementations should not be considered beyond the scope of this application.

[0078] In addition, the functional modules in the various embodiments of this application can be integrated into one processing module, or each module can exist physically separately, or two or more modules can be integrated into one module.

[0079] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

[0080] Finally, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for compensating and controlling output power fluctuations in an energy storage photovoltaic power generation system, characterized in that, include: S1. Obtain the output power and sampling interval at the grid connection point, and calculate the current power change rate; S2. Read the difference between the grid-connected point output power of the current sampling period and the previous sampling period as the change in grid-connected point output power, and read the difference between the grid-connected point voltage of the current sampling period and the previous sampling period as the change in grid-connected point voltage. The voltage-power response parameter is obtained by calculating the ratio of the change in grid connection point voltage to the change in grid connection point output power. The system calls the locally stored grid-connected operation specification configuration, reads the grid-connected interface ramp rate, and multiplies the grid-connected interface ramp rate by the reciprocal of the voltage and power response parameters to generate the power change rate limit for the current sampling period. S3. Compare the current power change rate with the power change rate limit. If the current power change rate exceeds the power change rate limit, identify the direction of power overshoot or undershoot and calculate the overshoot magnitude. If the current power change rate does not exceed the power change rate limit, re-execute S1. S4. Read the current rechargeable power and current dischargeable power of the fast energy storage unit; When the direction of power overshoot is identified, the excess amplitude is multiplied by the sampling interval to calculate the power to be absorbed, and the smaller value between the power to be absorbed and the current rechargeable power is used as the overshoot absorption compensation power to generate an overshoot absorption compensation command. When the direction of power drop exceeding the limit is identified, the excess amplitude is multiplied by the sampling interval to calculate the power to be released, and the smaller value between the power to be released and the current dischargeable power is used as the power to support the drop and generate a power to support the drop. The overshoot absorption compensation command or the undershoot support compensation command is output to the converter of the fast energy storage unit to drive the fast energy storage unit to charge according to the overshoot absorption compensation power or discharge according to the undershoot support compensation power. The dynamic loss compensation coefficient is determined by calculating the ratio of the real-time conversion loss power of the converter to the power to be released. The dynamic loss compensation coefficient is stored and superimposed on the reciprocal of the voltage power response parameter in the next sampling period to correct the power change rate limit in the next sampling period. S5. Monitor the fast energy storage unit during the current compensation cycle. If the state of charge continues to shift in the same direction, drive the slow energy storage unit to perform energy replenishment or recovery for the fast energy storage unit. If the state of charge shift stops or the shift direction reverses, stop the slow energy storage unit and re-execute S1.

2. The output power fluctuation compensation and control method for an energy storage photovoltaic power generation system as described in claim 1, characterized in that, S1 specifically includes: Obtain the historical value of the grid-connected point output power in the previous sampling period, and the measured value of the grid-connected point output power in the current sampling period; The difference between the measured output power at the grid connection point and the historical output power at the grid connection point is used to obtain the output power deviation at the grid connection point. Divide the output power deviation at the grid connection point by the sampling interval to obtain the current power change rate.

3. The output power fluctuation compensation and control method for an energy storage photovoltaic power generation system as described in claim 1, characterized in that, When the absolute value of the output power change at the grid connection point is lower than the minimum resolvable power change of the grid connection point power acquisition device, the voltage and power response parameters of the previous sampling period are used to generate the power change rate limit for the current sampling period.

4. The output power fluctuation compensation and control method for an energy storage photovoltaic power generation system as described in claim 1, characterized in that, S3 specifically includes: The power change rate limit is used as the positive upward threshold, and the opposite of the power change rate limit is used as the negative downward threshold to construct the allowable change rate range, and it is determined whether the current power change rate falls into the allowable change rate range. If the current power change rate is greater than the positive overshoot threshold, it is identified as the direction of power overshoot exceeding the limit, and the difference between the current power change rate and the positive overshoot threshold is calculated as the overshoot amplitude. If the current power change rate is less than the negative decline threshold, it is identified as the direction of power decline exceeding the limit, and the difference between the negative decline threshold and the current power change rate is calculated as the excess amplitude. If the current power change rate is within the allowable change rate range, it is determined that the limit has not been exceeded and S1 is re-executed.

5. The output power fluctuation compensation and control method for an energy storage photovoltaic power generation system as described in claim 1, characterized in that, The method for obtaining the current rechargeable power and the current dischargeable power is as follows: Collect the terminal voltage, maximum allowable charging current limit, and maximum allowable discharging current limit of the fast energy storage unit; Multiply the terminal voltage by the maximum allowable charging current limit to obtain the theoretical maximum charging power, and subtract the real-time conversion loss power of the converter to obtain the current chargeable power; Multiply the terminal voltage by the maximum allowable discharge current limit to obtain the theoretical maximum discharge power, and subtract the real-time conversion loss power of the converter to obtain the current dischargeable power.

6. The output power fluctuation compensation and control method for an energy storage photovoltaic power generation system as described in claim 1, characterized in that, S5 specifically includes: Within the current compensation period, calculate the difference in state of charge of the fast energy storage unit between adjacent sampling periods, and determine the offset direction of the state of charge by the positive or negative sign of the difference in state of charge. If the sign of the difference in state of charge between adjacent sampling periods remains consistent, it is determined that the state of charge continues to shift in the same direction within the current compensation period. When the state of charge of the fast energy storage unit continues to shift in the direction of decreasing state of charge, it drives the slow energy storage unit to discharge to the fast energy storage unit to perform energy replenishment; when it continues to shift in the direction of increasing state of charge, it drives the slow energy storage unit to absorb energy from the fast energy storage unit to perform energy recovery. If the state of charge difference in the current sampling period is zero, it is determined that the state of charge offset has stopped; if the sign of the state of charge difference in the current sampling period is opposite to that of the previous sampling period, it is determined that the offset direction has reversed, the slow energy storage unit stops operating, and S1 is re-executed.

7. The output power fluctuation compensation and control method for an energy storage photovoltaic power generation system as described in claim 1, characterized in that, The method for determining the fast energy storage unit and the slow energy storage unit is as follows: The fast energy storage unit includes a power-type energy storage medium with a first charge-discharge rate, and the slow energy storage unit includes an energy-type energy storage medium with a second charge-discharge rate, wherein the first charge-discharge rate is greater than the second charge-discharge rate.

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