Alternating current coupling control system and control method of hybrid energy storage inverter

Abstract

The invention discloses an alternating current coupling control system and control method of a hybrid energy storage inverter. The system comprises a first control module, an inverter current feed-forward module, a frequency adjustment module, a second control module, a third control module and an inverter voltage feed-forward module which are connected in sequence. Wherein the first control module is connected with an inverter voltage output end of the hybrid energy storage inverter, and can output an adjustment signal according to a difference signal between an inverter voltage reference signal and an inverter voltage effective value; the inverter current feed-forward module can adaptively provide current feed-forward compensation for the adjustment signal based on the power direction; the frequency adjustment module can provide voltage frequency compensation for an adjustment signal according to a battery current signal of the hybrid energy storage inverter and dynamically generate a voltage instantaneous value reference signal, so that the second control module and the third control module obtain a modulation signal under voltage feed-forward compensation of the inverter voltage feed-forward module, and the modulation signal is output to the hybrid energy storage inverter. AC coupling control of the hybrid energy storage inverter is realized, so that the system stability is improved.

Description

Technical Field

[0001] The present invention relates to the field of power electronics technology, and in particular to an AC coupling control system and a control method for a hybrid energy storage inverter. Background Art

[0002] Existing hybrid energy storage inverters often face the problem of power mismatch in AC coupling applications. Especially when the output power of a micro photovoltaic inverter exceeds the battery acceptance capacity of the energy storage system, the system is likely to trigger a protection mechanism, resulting in frequent shutdown and restart.

[0003] Traditional control strategies mostly rely on single-loop regulation, such as RMS voltage PI control, but its dynamic response speed is insufficient and it is difficult to cope with voltage instability caused by sudden changes in light or drastic fluctuations in load power. In addition, the existing technology also lacks direct closed-loop control of battery current. When the power of the micro-inverter suddenly increases or the load changes suddenly, the battery current may exceed the safety threshold, resulting in an increase in the bus voltage, forced shutdown of the system, and even damage to equipment. Summary of the Invention

[0004] The purpose of the present invention is to solve at least one of the technical problems existing in the prior art. It can dynamically adjust the feedforward compensation according to the power direction through the inverter current feedforward module, reduce the bus voltage fluctuation, and combine with the frequency adjustment module to monitor the battery current in real time. Avoid battery overload through frequency compensation, and dynamically generate a reference signal for the instantaneous value of the voltage for control, thereby improving the system stability.

[0005] In a first aspect, the present invention provides an AC coupling control system for a hybrid energy storage inverter. The system includes: a first control module, an inverter current feedforward module, a frequency adjustment module, a second control module, a third control module, and an inverter voltage feedforward module connected in sequence. Among them, the first control module is connected to the inverter voltage output terminal of the hybrid energy storage inverter, and is used to output a first adjustment signal according to the difference signal between the inverter voltage reference signal and the RMS value of the inverter voltage; the inverter current feedforward module is used to provide current feedforward compensation for the first adjustment signal according to the inverter power output by the hybrid energy storage inverter to obtain a second adjustment signal; the frequency adjustment module is used to provide voltage frequency compensation for the second adjustment signal according to the battery current signal of the hybrid energy storage inverter to obtain a reference signal for the instantaneous value of the inverter voltage; the second control module is used to output an inverter current reference signal according to the reference signal for the instantaneous value of the inverter voltage and the voltage feedforward signal provided by the inverter voltage feedforward module; the third control module is used to output a third adjustment signal according to the inverter current reference signal and the instantaneous value of the inverter current, and in combination with the voltage feedforward signal provided by the inverter voltage feedforward module, so as to obtain a modulation signal for generating a PWM waveform signal according to the third adjustment signal.

[0006] In some embodiments, the first control module includes an inverter voltage effective value PI loop, and the inverter voltage effective value PI loop is configured to output a first PI loop signal based on an output limit of ±1 according to the difference signal, and the first PI loop signal is added to the inverter voltage reference signal to obtain a first adjustment signal.

[0007] In some embodiments, the inverter current feedforward module is configured to, when the inverter power is greater than 0, output 80% of the effective value of the inverter current as a positive forward feed compensation; when the inverter power is less than 0, output 80% of the effective value of the inverter current as a negative forward feed compensation.

[0008] In some embodiments, the frequency adjustment module includes a voltage-frequency PI loop, and the voltage-frequency PI loop is configured to, by comparing the battery current signal with a preset maximum allowable current, perform voltage-frequency compensation on the reference voltage frequency of the hybrid energy storage inverter when the battery current signal is greater than the maximum allowable current, and the output range of the voltage-frequency compensation is from 0 Hz to 5 Hz, and the reference voltage frequency is 50 Hz.

[0009] In some embodiments, the system further includes a first calculation unit; in the process of providing voltage-frequency compensation for the second adjustment signal to obtain a reference signal of the instantaneous value of the inverter voltage, the first calculation unit is configured to execute the following calculation formula: wherein, InvVoltRealRef is the reference signal of the instantaneous value of the inverter voltage, S is the second adjustment signal, f base is the reference voltage frequency, and Δf is the voltage-frequency compensation.

[0010] In some embodiments, the second control module includes an inverter voltage instantaneous value PI loop, and the inverter voltage instantaneous value PI loop is configured to output a second PI loop signal based on an output limit of ±1 according to the reference signal of the instantaneous value of the inverter voltage and the voltage feedforward signal provided by the inverter voltage feedforward module, and the second PI loop signal is added to the signal of the instantaneous value of the inverter voltage of the hybrid energy storage inverter to obtain a reference signal of the inverter current.

[0011] In some embodiments, the third control module includes an inverter current instantaneous value PI loop, and the inverter current instantaneous value PI loop is configured to output a third PI loop signal based on an output limit of ±0.3 according to the difference between the reference signal of the inverter current and the instantaneous value of the inverter current, and the third PI loop signal is added to the voltage feedforward signal provided by the inverter voltage feedforward module to obtain a third adjustment signal.

[0012] In some embodiments, the system further includes a second calculation unit; in the process of obtaining a modulation signal for generating a PWM waveform signal according to the third adjustment signal, the second calculation unit is configured to execute the following calculation formula: the voltage modulation signal = the third adjustment signal * (1 / Ubus); where Ubus is the bus voltage of the hybrid energy storage inverter.

[0013] In some embodiments, the system further includes a sampling terminal for obtaining an instantaneous inverter voltage signal, an instantaneous inverter current signal, and the effective value of the inverter current, and the system is connected to the DC bus of the hybrid energy storage inverter through the sampling terminal.

[0014] In a second aspect, the present invention provides an AC coupling control method for a hybrid energy storage inverter, and the method is applied to the AC coupling control system of the hybrid energy storage inverter as described in any one of the first aspect. The method includes: outputting a first adjustment signal by the first control module according to the difference signal between the inverter voltage reference signal and the effective value of the inverter voltage; providing current feedforward compensation for the first adjustment signal by the inverter current feedforward module according to the power flow direction of AC coupling to obtain a second adjustment signal; providing voltage-frequency compensation for the second adjustment signal by the frequency adjustment module according to the battery current signal of the hybrid energy storage inverter to obtain an instantaneous inverter voltage reference signal; outputting an inverter current reference signal by the second control module according to the instantaneous inverter voltage reference signal and the voltage feedforward signal provided by the inverter voltage feedforward module; outputting a third adjustment signal by the third control module according to the inverter current reference signal and the instantaneous inverter current, and in combination with the voltage feedforward signal provided by the inverter voltage feedforward module, so as to obtain a modulation signal for generating a PWM waveform signal according to the third adjustment signal.

[0015] According to an embodiment of the present invention, an AC coupling control system and a control method for a hybrid energy storage inverter are provided, which have at least the following beneficial effects: The present invention realizes the AC coupling control of the hybrid energy storage inverter by setting a first control module, an inverter current feedforward module, a frequency adjustment module, a second control module, a third control module, and an inverter voltage feedforward module connected in sequence. Among them, the first control module is connected to the inverter voltage output end of the hybrid energy storage inverter and is used to output a first adjustment signal according to the difference signal between the inverter voltage reference signal and the effective value of the inverter voltage. The inverter current feedforward module is used to provide current feedforward compensation for the first adjustment signal according to the inverter power output by the hybrid energy storage inverter to obtain a second adjustment signal. The frequency adjustment module is used to provide voltage frequency compensation for the second adjustment signal according to the battery current signal of the hybrid energy storage inverter to obtain an instantaneous value reference signal of the inverter voltage. The second control module is used to output an inverter current reference signal according to the instantaneous value reference signal of the inverter voltage and the voltage feedforward signal provided by the inverter voltage feedforward module. The third control module is used to output a third adjustment signal according to the inverter current reference signal and the instantaneous value of the inverter current, and in combination with the voltage feedforward signal provided by the inverter voltage feedforward module, so as to obtain a modulation signal for generating a PWM waveform signal according to the third adjustment signal. It can be understood that the first control module can perform closed-loop regulation based on the effective value of the inverter voltage to ensure the stability of the basic voltage. The inverter current feedforward module can dynamically adjust the feedforward compensation according to the power direction, enhance energy absorption when flowing forward, and optimize power supply stability when flowing backward, significantly reducing the bus voltage fluctuation. The frequency adjustment module can monitor the battery current in real time, trigger the micro-inverter derating by increasing the frequency when exceeding the limit through frequency compensation to avoid battery overload, and at the same time, combined with the dynamic generation mechanism of the instantaneous value reference signal of the voltage, improve the response speed of the system to power mutations. Based on the above-mentioned modules, the present invention can still operate stably when the micro-inverter power exceeds the limit, the load changes suddenly, or the light fluctuates, so as to eliminate the "hiccup" shutdown problem. By introducing direct closed-loop control of the battery current and power direction adaptive compensation, the robustness of the system in complex energy flow scenarios is significantly enhanced, and the battery life is extended, thereby improving the system stability.

[0016] Other features and advantages of the present invention will be described in the following specification, and part of them will become obvious from the specification, or will be understood by implementing the present invention. The objectives and other advantages of the present invention can be realized and obtained through the structures specifically pointed out in the specification, the claims, and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings are used to provide a further understanding of the technical solutions of the present invention, and constitute a part of the specification. They are used together with the embodiments of the present invention to explain the technical solutions of the present invention, and do not constitute a limitation to the technical solutions of the present invention.

[0018] The present invention will be further described below in conjunction with the accompanying drawings and embodiments;

[0019] Figure 1 It is a schematic diagram of a hybrid energy storage inverter provided by an embodiment of the present invention;

[0020] Figure 2 It is a module schematic diagram of an AC coupling control system of a hybrid energy storage inverter provided by an embodiment of the present invention;

[0021] Figure 3 It is a circuit schematic diagram of an AC coupling control system of a hybrid energy storage inverter provided by an embodiment of the present invention;

[0022] Figure 4 It is a flowchart of an AC coupling control method of a hybrid energy storage inverter provided by an embodiment of the present invention. Specific Embodiments

[0023] This part will describe in detail the specific embodiments of the present invention. The preferred embodiments of the present invention are shown in the accompanying drawings. The role of the drawings is to supplement the description in the text part of the specification, enabling people to intuitively and vividly understand each technical feature and the overall technical solution of the present invention, but it cannot be understood as a limitation on the protection scope of the present invention.

[0024] In the description of the present invention, the meaning of several is one or more, the meaning of multiple is more than two, understand greater than, less than, exceeding, etc. as not including the number, understand above, below, within, etc. as including the number, "any one" means one or more, "at least one of the following" and its similar expressions mean any combination of these items, including any combination of single items or plural items. If there is a description of first and second, it is only for the purpose of distinguishing technical features and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features or implicitly indicating the sequence relationship of the indicated technical features.

[0025] It should be noted that the terms such as set, installed, and connected in the embodiments of the present invention should be understood in a broad sense. Those skilled in the art can reasonably determine the specific meanings of the above terms in the embodiments of the present invention in combination with the specific content of the technical solution. For example, the term "connected" can be a mechanical connection, an electrical connection, or a connection that can communicate with each other; it can be directly connected or indirectly connected through an intermediate medium.

[0026] It should be noted that the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0027] Existing hybrid energy storage inverters often face the problem of power mismatch in AC coupling applications. Especially when the output power of a micro PV inverter exceeds the battery acceptance capacity of the energy storage system, the system is prone to trigger the protection mechanism, resulting in frequent shutdown and restart. Traditional control strategies mostly rely on single-loop regulation, such as the PI control of the effective voltage value. However, its dynamic response speed is insufficient and it is difficult to cope with the voltage instability caused by sudden changes in light or drastic fluctuations in load power. In addition, the existing technology also lacks direct closed-loop control of the battery current. When the power of the micro-inverter suddenly increases or the load changes suddenly, the battery current may exceed the safety threshold, leading to an increase in the bus voltage, forced shutdown of the system, and even equipment damage.

[0028] Based on this, the purpose of the present invention is to solve at least one of the technical problems existing in the prior art. It can dynamically adjust the feedforward compensation according to the power direction through the inverter current feedforward module, reduce the bus voltage fluctuation, and combine with the frequency adjustment module to monitor the battery current in real time. Avoid battery overload through frequency compensation, and dynamically generate a reference signal for the instantaneous value of the voltage to control, thereby improving the system stability.

[0029] The following further illustrates the solution of the present application with reference to the accompanying drawings.

[0030] Refer to Figure 1 , Figure 1 FIG. is a schematic diagram of a hybrid energy storage inverter provided by an embodiment of the present invention; wherein, the battery (Bat) is the energy storage unit of the hybrid energy storage inverter and is connected to the bus (Vbus) through the BuckBoost topology; the BuckBoost topology is a DC-DC converter used to adjust the battery voltage to match the bus voltage; the bus (Vbus) is a DC bus used to connect the battery and the inverter bridge and provide a DC voltage; the inverter bridge is used to convert direct current into alternating current and can include a one-line three-level or a T-shaped three-level. The input end of the inverter bridge is connected to the bus (Vbus), and the output end is connected to the load and the power grid through the inductor L1 and the capacitor C2. The inductor L1 and the capacitor C2 are used to filter out the high-frequency harmonics output by the inverter and output a smooth AC voltage; the load (Load) is the load port connected to the hybrid storage and can be other electrical appliances; the power grid (GridPort) is the output port of the inverter and is used to output alternating current to the external power grid or load; the instantaneous value of the inverter voltage (InvVoltReal) refers to the instantaneous value of the voltage output by the inverter, and the effective value of the inverter voltage (InvVoltRms) refers to the effective value of the voltage output by the inverter. The instantaneous value of the inverter current (InvCurrReal) refers to the instantaneous value of the current output by the inverter. These signals are collected from the output end of the inverter bridge and are used for the feedback of the control loop; the battery current (Ibat) refers to the charging and discharging current of the battery, and the signal is collected from the output end of the battery and is used for the feedback of the control loop.

[0031] It can be understood that the AC coupling control system in the present invention can be connected to the hybrid energy storage inverter through a sampling interface to achieve sampling of various signals, and connected to the hybrid energy storage inverter through a control interface to achieve modulation of the hybrid energy storage inverter.

[0032] Reference Figure 2 , Figure 2 FIG. is a schematic diagram of the modules of an AC coupling control system for a hybrid energy storage inverter provided by an embodiment of the present invention; in a first aspect, the present invention provides an AC coupling control system for a hybrid energy storage inverter, the system comprising: a first control module, an inverter current feedforward module, a frequency adjustment module, a second control module, a third control module, and an inverter voltage feedforward module connected in sequence; wherein, the first control module is connected to the inverter voltage output terminal of the hybrid energy storage inverter, and is configured to output a first adjustment signal according to the difference signal between the inverter voltage reference signal and the effective value of the inverter voltage; the inverter current feedforward module is configured to provide current feedforward compensation for the first adjustment signal according to the inverter power output by the hybrid energy storage inverter to obtain a second adjustment signal; the frequency adjustment module is configured to provide voltage-frequency compensation for the second adjustment signal according to the battery current signal of the hybrid energy storage inverter to obtain an instantaneous value reference signal of the inverter voltage; the second control module is configured to output an inverter current reference signal according to the instantaneous value reference signal of the inverter voltage and the voltage feedforward signal provided by the inverter voltage feedforward module; the third control module is configured to output a third adjustment signal according to the inverter current reference signal and the instantaneous value of the inverter current, and in combination with the voltage feedforward signal provided by the inverter voltage feedforward module, and obtain a modulation signal for generating a PWM waveform signal according to the third adjustment signal.

[0033] It can be understood that the first control module can perform closed-loop regulation based on the effective value of the inverter voltage to ensure the stability of the basic voltage; the inverter current feedforward module can dynamically adjust the feedforward compensation according to the power direction, enhance energy absorption during forward flow, optimize power supply stability during reverse flow, and significantly reduce bus voltage fluctuations; the frequency adjustment module can monitor the battery current in real time, through frequency compensation, raise the frequency to trigger micro-inverter derating when exceeding the limit to avoid battery overload, and at the same time, combined with the dynamic generation mechanism of the instantaneous value reference signal of the voltage, improve the response speed of the system to power mutations, so that the second control module and the third control module can obtain a modulation signal under the voltage feedforward compensation of the inverter voltage feedforward module to achieve AC coupling control of the hybrid energy storage inverter, thereby improving the system stability. Based on the above-mentioned modules, the present invention can still operate stably when the micro-inverter power exceeds the limit, the load changes suddenly, or the light fluctuates, so as to eliminate the "hiccup" shutdown problem. By introducing direct closed-loop control of the battery current and power direction adaptive compensation, the robustness of the system in complex energy flow scenarios is significantly enhanced, and the battery life is extended, thereby improving the system stability.

[0034] In some embodiments, the first control module includes an inverter voltage RMS PI loop. The inverter voltage RMS PI loop is configured to output a first PI loop signal based on an output limit of ±1 according to a difference signal. The first PI loop signal is added to an inverter voltage reference signal to obtain a first adjustment signal.

[0035] It can be understood that the first control module is connected to the inverter voltage output terminal of the hybrid energy storage inverter and is configured to output a first adjustment signal according to the difference signal between the inverter voltage reference signal and the inverter voltage RMS. This module is implemented through the inverter voltage RMS PI loop, which can output a first PI loop signal based on an output limit of ±1 according to the difference signal. This signal is added to the inverter voltage reference signal to obtain a first adjustment signal. The function of the first control module is to ensure that the output voltage of the inverter is close to the reference value and provide a basic signal for the subsequent control module.

[0036] In some embodiments, specifically, the core of the first control module is the inverter voltage RMS PI loop, whose proportional coefficient is set to 1.5, the integral coefficient is 0.03, and the output limit is ±1. This parameter combination can quickly respond when there is a deviation between the voltage RMS and the reference value, and at the same time avoid overshoot problems caused by integral accumulation. For example, when the inverter voltage RMS drops due to a sudden increase in load, the proportional coefficient of 1.5 can quickly amplify the error signal and drive the output adjustment; the integral coefficient of 0.03 gradually eliminates the steady-state error to ensure that the voltage returns to the set value. The first adjustment signal is obtained by superimposing the PI loop output and the reference voltage, which not only retains the stability of the reference voltage but also incorporates the dynamic correction amount.

[0037] In some embodiments, the inverter current feedforward module is configured to, when the inverter power is greater than 0, output 80% of the inverter current RMS as positive feedforward compensation; when the inverter power is less than 0, output 80% of the inverter current RMS as negative feedforward compensation. It can be understood that the inverter current feedforward module further includes a power direction judgment module, which is configured to detect the power flow direction. When the power flow direction is from the micro photovoltaic inverter to the hybrid energy storage inverter for power supply, the output feedforward signal polarity is +1; when the power flow direction is from the hybrid energy storage inverter to the load for power supply, the output feedforward signal polarity is -1.

[0038] It can be understood that the inverter current feedforward module receives the first adjustment signal and provides current feedforward compensation for the first adjustment signal according to the inverter power output by the hybrid energy storage inverter to obtain a second adjustment signal. This module can dynamically adjust the feedforward compensation according to the direction of the inverter power. When the inverter power is greater than 0, it outputs 80% of the inverter current RMS as positive feedforward compensation; when the inverter power is less than 0, it outputs 80% of the inverter current RMS as negative feedforward compensation. The function of the inverter current feedforward module is to reduce the bus voltage fluctuation and improve the dynamic response and stability of the system.

[0039] It can be understood that in the above inverter current feed-forward module, which dynamically adjusts the compensation strategy according to the inverter power direction, when the inverter power is greater than zero (micro-inverter supplies power to the hybrid energy storage), 80% of the effective value of the inverter current is output as the positive feed-forward compensation to accelerate energy absorption; when the inverter power is less than zero (hybrid energy storage supplies power to the load), 80% of the effective value of the output current is used as the negative compensation to suppress voltage dips; through the adaptive judgment of the power direction, the energy flow path is optimized. For example, in the scenario where the micro-inverter power suddenly increases due to sudden changes in light, the positive compensation can quickly offset the rising trend of the bus voltage; while when the load suddenly increases and the hybrid energy storage discharges, the negative compensation can effectively prevent voltage dips. The compensation ratio is selected as 80% instead of full compensation, which not only ensures the response speed but also avoids the oscillation risk caused by over-compensation.

[0040] In some embodiments, the frequency adjustment module includes a voltage-frequency PI loop. The voltage-frequency PI loop is used to perform voltage-frequency compensation on the reference voltage frequency of the hybrid energy storage inverter by comparing the battery current signal with a preset maximum allowable current. When the battery current signal is greater than the maximum allowable current, the output range of the voltage-frequency compensation is 0 Hz to 5 Hz, and the reference voltage frequency is 50 Hz.

[0041] It can be understood that the frequency adjustment module receives the second adjustment signal and provides voltage-frequency compensation for the second adjustment signal according to the battery current signal of the hybrid energy storage inverter to obtain the reference signal of the instantaneous value of the inverter voltage. This module is implemented through a voltage-frequency PI loop, which can perform voltage-frequency compensation on the reference voltage frequency by comparing the battery current signal with a preset maximum allowable current. When the battery current signal is greater than the maximum allowable current, the compensation range is 0 Hz to 5 Hz, and the reference voltage frequency is 50 Hz. The function of the frequency adjustment module is to avoid battery overload, dynamically generate the reference signal of the instantaneous value of the inverter voltage, and improve the stability of the system.

[0042] In some embodiments, the frequency adjustment module further includes a battery current detection module. The battery current detection module is used to collect the battery charge and discharge current of the hybrid energy storage inverter in real time and convert it into a battery current signal. The frequency adjustment module further includes a voltage-frequency PI loop, whose input terminal is connected to the current feedback signal, and the output terminal generates a frequency adjustment signal; the output range of the frequency adjustment signal is 50 Hz to 55 Hz, and the frequency adjustment step size is 0.1 Hz.

[0043] Among them, the voltage-frequency PI loop of the frequency adjustment module takes the battery current as the control object. The proportional coefficient can be set to 0.8, the integral coefficient to 0.02, and the output limit to 0 - 5Hz. When it is detected that the battery current exceeds the preset maximum allowable value (such as 120% of the battery rated current), the PI loop outputs a frequency compensation value, which proportionally increases the reference frequency from 50Hz to a maximum of 55Hz. For example, if the battery current exceeds the limit by 20%, the frequency compensation value can reach 2Hz, and the inverter voltage frequency rises to 52Hz. After the micro-inverter senses the frequency increase, it automatically activates the over-frequency derating function and reduces the output power proportionally (such as derating 10% for every 1Hz increase), thereby reducing the input power to the battery and achieving a smooth transition when the power limit is exceeded.

[0044] In some embodiments, the system further includes a first calculation unit; in the process of providing voltage-frequency compensation for the second adjustment signal to obtain the instantaneous value reference signal of the inverter voltage, the first calculation unit is used to execute the following calculation formula: wherein, InvVoltRealRef is the instantaneous value reference signal of the inverter voltage, S is the second adjustment signal, f base is the reference voltage frequency, and Δf is the voltage-frequency compensation.

[0045] In some embodiments, the second control module includes an instantaneous value PI loop of the inverter voltage. The instantaneous value PI loop of the inverter voltage is used to output a second PI loop signal based on the output limit of ±1 according to the instantaneous value reference signal of the inverter voltage and the voltage feedforward signal provided by the inverter voltage feedforward module. The second PI loop signal is added to the instantaneous value signal of the inverter voltage of the hybrid energy storage inverter to obtain the reference signal of the inverter current.

[0046] It can be understood that the second control module receives the instantaneous value reference signal of the inverter voltage and the voltage feedforward signal provided by the inverter voltage feedforward module and outputs the reference signal of the inverter current. This module is implemented through the instantaneous value PI loop of the inverter voltage. It can output a second PI loop signal based on the output limit of ±1 according to the difference between the instantaneous value reference signal of the inverter voltage and the voltage feedforward signal. This signal is added to the instantaneous value signal of the inverter voltage to obtain the reference signal of the inverter current; the function of the second control module is to ensure that the output current of the inverter meets the expectations and improve the dynamic response and stability of the system.

[0047] Among them, the instantaneous value PI loop of the inverter voltage of the second control module can adopt a high proportional coefficient (2.0) and a medium integral coefficient (0.1), with an output limit of ±1. The high proportional coefficient ensures the rapid suppression of instantaneous voltage fluctuations. For example, when the voltage drops instantaneously due to a load mutation, the controller can quickly output a compensation signal; the integral coefficient of 0.1 takes into account the steady-state accuracy and avoids high-frequency noise interference. This module combines the instantaneous value reference signal generated by the frequency adjustment module with the feedforward voltage signal and outputs the reference value of the inverter current, providing an accurate target for downstream control.

[0048] In some embodiments, the third control module includes an instantaneous inverse current PI loop, which is configured to output a third PI loop signal based on the difference between the inverse current reference signal and the instantaneous inverse current with an output limit of ±0.3. The third PI loop signal is added to the voltage feedforward signal provided by the inverse voltage feedforward module to obtain a third adjustment signal.

[0049] It can be understood that the third control module receives the inverse current reference signal and the instantaneous inverse current, and combines the voltage feedforward signal provided by the inverse voltage feedforward module to output a third adjustment signal. This module is implemented through the instantaneous inverse current PI loop, which can output a third PI loop signal based on the difference between the inverse current reference signal and the instantaneous inverse current with an output limit of ±0.3. This signal is added to the voltage feedforward signal to obtain a third adjustment signal. The function of the third control module is to further adjust the output voltage of the inverter to ensure it is within a reasonable range and improve the stability and dynamic response of the system.

[0050] Among them, the parameters of the instantaneous inverse current PI loop of the third control module can adopt more targeted numbers. For example, the proportional coefficient is set to 2.5, the integral coefficient is 0.15, and the output limit is ±0.3. The higher proportional coefficient can quickly track the change of the current reference value. For example, when the micro-inverter power suddenly drops, the controller can adjust the current output within milliseconds. The narrower output limit prevents the current overshoot from impacting the inverter bridge. The third adjustment signal generates the final modulation signal by superimposing the PI output and the feedforward voltage, and after being normalized by the bus voltage, it drives the generation of the PWM waveform. For example, when the bus voltage is 400V, the modulation signal is scaled proportionally to ensure the accuracy of the PWM duty cycle under different bus voltages.

[0051] In some embodiments, the inverse voltage feedforward module provides a voltage feedforward signal to improve the dynamic response and stability of the system. This module can provide feedforward compensation according to the instantaneous inverse voltage value to reduce errors and improve the response speed and stability of the system. The function of the inverse voltage feedforward module is an auxiliary control module to ensure that the output voltage and current of the inverter meet the expectations.

[0052] In some embodiments, the system further includes a second calculation unit. In the process of obtaining the modulation signal for generating the PWM waveform signal based on the third adjustment signal, the second calculation unit is configured to execute the following calculation formula: voltage modulation signal = third adjustment signal * (1 / Ubus); where Ubus is the bus voltage of the hybrid energy storage inverter.

[0053] In some embodiments, the system further includes a sampling terminal for acquiring the instantaneous inverse voltage signal, the instantaneous inverse current signal, and the effective value of the inverse current. The system is connected to the DC bus of the hybrid energy storage inverter through the sampling terminal.

[0054] It is understandable that the system obtains the instantaneous value of the inverter voltage, the instantaneous value of the current and the effective value signal in real time through the sampling terminal, and is directly connected to the DC bus. The sampling terminal can use a Hall sensor to ensure that the control loop responds in real time to the rapidly changing power state. As a result, in complex working conditions (such as frequent fluctuations in photovoltaic power caused by cloudy weather), multiple modules in the present invention can work together. The effective voltage loop maintains basic stability, the current feed-forward compensation cancels out the directional disturbance, the frequency adjustment module realizes battery protection, and the instantaneous value loop quickly tracks the dynamic changes. Finally, the system keeps the voltage deviation less than 2% within the power fluctuation range of ±20%, completely eliminating the "hiccup" shutdown problem.

[0055] In summary, through the linkage design of the battery current closed-loop and frequency compensation, the present invention converts the traditional protection mechanism into active regulation, prolonging the equipment life. Further, through the power direction adaptive feed-forward strategy, the compensation polarity is optimized for the energy flow path, enhancing the dynamic performance. Further, through the refined configuration of multi-level PI parameters, both the response speed and stability are taken into account. For example, the medium integral coefficient of the first control module prevents the voltage loop from saturation, and the high proportional coefficient of the third control module ensures the current tracking accuracy, so as to improve the system stability and system performance.

[0056] Reference Figure 3 , Figure 3 is the circuit schematic diagram of an AC coupling control system of a hybrid energy storage inverter provided by an embodiment of the present invention; in some embodiments, as Figure 3 shown, InvVoltRmsRef is the reference signal of the inverter voltage, InvVoltRms is the effective value of the inverter voltage, InvCurrRms is the effective value of the inverter current, Pinv is the inverter power, InvCurrRms*0.8 represents 80% of the effective value of the inverter current (positive forward feed compensation), InvCurrRms - 0.8* represents 80% of the effective value of the inverter current (negative forward feed compensation); in the frequency adjustment module, Ibat represents the battery current signal, Ibat_Max represents the preset maximum allowable current, and a PI loop can also be set in the frequency adjustment module. When the battery current signal is greater than the maximum allowable current, the voltage frequency compensation is performed on the reference voltage frequency of the hybrid energy storage inverter. The output range of the voltage frequency compensation is 0 Hz to 5 Hz, Δf is the voltage frequency compensation, fbase is the reference voltage frequency (50 Hz), "1.414" is the approximate value of, and InvVoltRealRef is the reference signal of the instantaneous value of the inverter voltage.

[0057] Further, a feedforward of the given instantaneous value of the inverter voltage is connected to both the input end of the PI loop of the instantaneous value of the inverter voltage and the output end of the PI loop of the instantaneous value of the inverter current. This feedforward of the given instantaneous value of the inverter voltage is the inverter voltage feedforward module, which is used to provide a voltage feedforward signal; InvVoltRealRef represents the reference signal of the instantaneous value of the inverter voltage, InvVoltReal represents the instantaneous value of the inverter voltage, InvCurrRef represents the reference signal of the inverter current, InvCurrReal represents the instantaneous value of the inverter current, and 1 / Ubus represents the reciprocal of the bus voltage.

[0058] It can be understood that the specific explanations of each signal are as follows:

[0059] Inverter voltage reference signal (InvVoltRmsRef): The reference signal of the inverter voltage of the inverter, that is, the expected effective value of the inverter voltage, which is used to compare with the actual effective value of the inverter voltage to generate an error signal, and then adjust the output voltage of the inverter;

[0060] Effective value of inverter voltage (InvVoltRms); The actual effective value of the output voltage of the inverter, which is used to compare with the inverter voltage reference signal to generate an error signal for controlling the output voltage of the inverter;

[0061] Effective value of inverter current (InvCurrRms); The actual effective value of the output current of the inverter, which is used to calculate the inverter power and provide feedforward compensation according to the power direction;

[0062] Inverter power (Pinv), the output power of the inverter, which is used to judge the power direction and determine the positive and negative directions of the feedforward compensation;

[0063] Battery current signal (Ibat): The charging and discharging current of the battery, which is used to monitor the charging and discharging state of the battery, avoid overcurrent or undercurrent, and ensure the safety of the battery;

[0064] Voltage frequency compensation (Δf): The compensation value for the reference voltage frequency, which is used to compensate the reference voltage frequency when the battery current exceeds the preset maximum allowable current to avoid battery overload;

[0065] Reference voltage frequency (fbase); The reference voltage frequency of the inverter, usually 50Hz, which is used as the reference value for frequency compensation to ensure the stability of the output frequency of the inverter;

[0066] Reference signal of the instantaneous value of the inverter voltage (InvVoltRealRef): The reference signal of the instantaneous value of the output voltage of the inverter; It is used to compare with the actual instantaneous value of the inverter voltage to generate an error signal, and then adjust the output voltage of the inverter;

[0067] Instantaneous value of inverter voltage (InvVoltReal): The actual instantaneous value of the inverter output voltage, which is used to compare with the reference signal of the instantaneous value of the inverter voltage to generate an error signal for controlling the output voltage of the inverter;

[0068] Reference signal of inverter current (InvCurrRef): The reference signal of the inverter output current, which is used to compare with the actual instantaneous value of the inverter current to generate an error signal and then adjust the output current of the inverter;

[0069] Instantaneous value of inverter current (InvCurrReal): The actual instantaneous value of the inverter output current, which is used to compare with the reference signal of the inverter current to generate an error signal for controlling the output current of the inverter;

[0070] Bus voltage (Ubus): The DC bus voltage of the inverter, which is used to calculate the voltage modulation signal to ensure that the output voltage of the inverter is within a reasonable range;

[0071] Voltage feedforward signal: A voltage feedforward signal used to improve the dynamic response and stability of the system. It provides feedforward compensation in the control loop to reduce errors and improve the response speed and stability of the system;

[0072] Modulation signal: A modulation signal used to generate a PWM waveform signal. It controls the switching devices of the inverter through the modulation signal to achieve precise control of the output voltage of the inverter.

[0073] Reference Figure 4 , Figure 4 is the flowchart of an AC coupling control method for a hybrid energy storage inverter provided by an embodiment of the present invention; Second, the present invention provides an AC coupling control method for a hybrid energy storage inverter. The method is applied to the AC coupling control system of the hybrid energy storage inverter as described in any one of the first aspects. The method includes the following steps;

[0074] Step S410: Output a first adjustment signal by the first control module according to the difference signal between the reference signal of the inverter voltage and the effective value of the inverter voltage;

[0075] Step S420: Provide current feedforward compensation for the first adjustment signal by the inverter current feedforward module according to the power flow direction of the AC coupling to obtain a second adjustment signal; Provide voltage-frequency compensation for the second adjustment signal by the frequency adjustment module according to the battery current signal of the hybrid energy storage inverter to obtain the reference signal of the instantaneous value of the inverter voltage;

[0076] Step S430: Output the reference signal of the inverter current by the second control module according to the reference signal of the instantaneous value of the inverter voltage and the voltage feedforward signal provided by the inverter voltage feedforward module;

[0077] Step S440: The third control module outputs a third adjustment signal according to the inverter current reference signal and the instantaneous value of the inverter current, and in combination with the voltage feedforward signal provided by the inverter voltage feedforward module, so as to obtain a modulation signal for generating a PWM waveform signal according to the third adjustment signal.

[0078] It can be understood that the first control module generates a first adjustment signal by comparing the inverter voltage reference signal and the effective value of the inverter voltage. This signal can be used to preliminarily adjust the output voltage of the inverter to ensure that it is close to the reference value; the inverter current feedforward module provides current feedforward compensation for the first adjustment signal according to the direction of the inverter power; the frequency adjustment module provides voltage-frequency compensation for the second adjustment signal according to the battery current signal to ensure the stability of the output frequency of the inverter; the second control module generates an inverter current reference signal according to the inverter voltage instantaneous value reference signal and the voltage feedforward signal. This signal can be used to adjust the output current of the inverter to ensure that it meets the expectations; the third control module generates a third adjustment signal according to the inverter current reference signal and the instantaneous value of the inverter current. This signal can be added to the voltage feedforward signal to generate a modulation signal for generating a PWM waveform signal, and this modulation signal can be used to control the switching devices of the inverter to achieve precise control of the output voltage of the inverter, so as to improve the system.

[0079] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the gist of the present invention.

Claims

1. An AC coupling control system for a hybrid energy storage inverter, characterized in that, The system includes: a first control module, an inverter current feedforward module, a frequency adjustment module, a second control module, a third control module, and an inverter voltage feedforward module connected in sequence; wherein, The first control module is connected to the inverter voltage output terminal of the hybrid energy storage inverter, and is configured to output a first adjustment signal according to the difference signal between the inverter voltage reference signal and the effective value of the inverter voltage; The inverter current feedforward module is configured to provide current feedforward compensation for the first adjustment signal according to the inverter power output by the hybrid energy storage inverter, and obtain a second adjustment signal; The frequency adjustment module is configured to provide voltage-frequency compensation for the second adjustment signal according to the battery current signal of the hybrid energy storage inverter, and obtain an instantaneous value reference signal of the inverter voltage; The second control module is configured to output an inverter current reference signal according to the instantaneous value reference signal of the inverter voltage and the voltage feedforward signal provided by the inverter voltage feedforward module; The third control module is configured to output a third adjustment signal according to the inverter current reference signal and the instantaneous value of the inverter current, and in combination with the voltage feedforward signal provided by the inverter voltage feedforward module, and obtain a modulation signal for generating a PWM waveform signal according to the third adjustment signal.

2. The AC coupling control system of the hybrid energy storage inverter according to claim 1, wherein The first control module includes an effective value PI loop of the inverter voltage, and the effective value PI loop of the inverter voltage is configured to output a first PI loop signal based on an output limit of ±1 according to the difference signal, and the first PI loop signal is added to the inverter voltage reference signal to obtain a first adjustment signal.

3. The AC coupling control system of the hybrid energy storage inverter according to claim 2, wherein, The inverter current feedforward module is configured to, when the inverter power is greater than 0, output 80% of the effective value of the inverter current as positive forward feed compensation; when the inverter power is less than 0, output 80% of the effective value of the inverter current as negative forward feed compensation.

4. The AC coupling control system of the hybrid energy storage inverter according to claim 3, characterized in that, The frequency adjustment module includes a voltage-frequency PI loop, and the voltage-frequency PI loop is configured to perform voltage-frequency compensation on the reference voltage frequency of the hybrid energy storage inverter when the battery current signal is greater than the preset maximum allowable current by comparing the battery current signal with the preset maximum allowable current. The output range of the voltage-frequency compensation is 0 Hz to 5 Hz, and the reference voltage frequency is 50 Hz.

5. The AC coupling control system of the hybrid energy storage inverter according to claim 4, wherein The system further includes a first calculation unit; in the process of providing voltage-frequency compensation for the second adjustment signal to obtain an instantaneous value reference signal of the inverter voltage, the first calculation unit is configured to execute the following calculation formula: Among them, InvVoltRealRef is the instantaneous value reference signal of the inverter voltage, S is the second adjustment signal, f base is the reference voltage frequency, and Δf is the voltage frequency compensation.

6. The AC coupling control system of the hybrid energy storage inverter according to claim 1, wherein The second control module includes an instantaneous value PI loop of the inverter voltage, and the instantaneous value PI loop of the inverter voltage is configured to output a second PI loop signal based on an output limit of ±1 according to the instantaneous value reference signal of the inverter voltage and the voltage feedforward signal provided by the inverter voltage feedforward module, and the second PI loop signal is added to the instantaneous value signal of the inverter voltage of the hybrid energy storage inverter to obtain an inverter current reference signal.

7. The AC coupling control system of the hybrid energy storage inverter according to claim 1, characterized in that, The third control module includes an instantaneous inverter current PI loop, which is configured to output a third PI loop signal based on the difference between the inverter current reference signal and the instantaneous inverter current according to the output limit of ±0.

3. The third PI loop signal is added to the voltage feedforward signal provided by the inverter voltage feedforward module to obtain a third adjustment signal.

8. The AC coupling control system of the hybrid energy storage inverter according to claim 1, characterized in that The system further includes a second calculation unit; in the process of obtaining the modulation signal for generating the PWM waveform signal according to the third adjustment signal, the second calculation unit is configured to execute the following calculation formula: The voltage modulation signal = the third adjustment signal * (1 / Ubus); wherein, Ubus is the bus voltage of the hybrid energy storage inverter.

9. The AC coupling control system of the hybrid energy storage inverter according to any one of claims 1 to 8, characterized in that The system further includes a sampling terminal for acquiring the instantaneous inverter voltage signal, the instantaneous inverter current signal, and the effective value of the inverter current. The system is connected to the DC bus of the hybrid energy storage inverter through the sampling terminal.

10. An AC coupling control method for a hybrid energy storage inverter, characterized in that, The method is applied to the AC-coupled control system of the hybrid energy storage inverter as described in any one of claims 1 to 9, and the method includes: outputting a first adjustment signal by the first control module according to the difference signal between the inverter voltage reference signal and the effective value of the inverter voltage; providing a current feedforward compensation for the first adjustment signal by the inverter current feedforward module according to the power flow direction of the AC coupling to obtain a second adjustment signal; providing a voltage frequency compensation for the second adjustment signal by the frequency adjustment module according to the battery current signal of the hybrid energy storage inverter to obtain an instantaneous inverter voltage reference signal; outputting an inverter current reference signal by the second control module according to the instantaneous inverter voltage reference signal and the voltage feedforward signal provided by the inverter voltage feedforward module; outputting a third adjustment signal by the third control module according to the inverter current reference signal and the instantaneous inverter current, in combination with the voltage feedforward signal provided by the inverter voltage feedforward module, so as to obtain a modulation signal for generating the PWM waveform signal according to the third adjustment signal.

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