Off-grid working condition control system and control method of inverter

Abstract

The invention discloses an off-grid working condition control system and method for an inverter. The system comprises an inverter current feed-forward module, a first control loop, a second control loop and an inverter voltage feed-forward module which are connected in sequence. Wherein the inverter current feed-forward module is used for providing a current feed-forward signal for an inverter voltage output end of the inverter so as to generate an inverter voltage reference signal; the inverter voltage feed-forward module is used for providing a voltage feed-forward signal corresponding to an inverter voltage instantaneous value of the inverter; the first control loop is used for outputting an inversion current reference signal according to the inversion voltage reference signal and the voltage feed-forward signal; the second control loop is used for outputting a voltage adjusting signal according to the inverter current reference signal and the inverter current instantaneous value of the inverter, so that the adjusting signal and the voltage feed-forward signal are added to generate a PWM waveform signal for load power control, and therefore, an impact load can be driven with low rated inverter power; and the cost and the resource waste can be effectively reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of power electronics, and in particular to an off-grid operating condition control system and a control method for an inverter. Background Art

[0002] With the rapid promotion of household energy storage inverters in overseas markets, inverters face various types of load challenges when operating off-grid, especially impact loads such as refrigerators, air conditioners, water heaters, and water pumps. Such loads consume a lot of energy during the startup phase, which means that the inverter must have excellent dynamic performance to successfully start and stably operate these devices. However, existing inverter control strategies often focus on the stability of the inverter output voltage and ignore the effective management of the inverter output current. As a result, when starting impact loads, the inverter output voltage may drop significantly, the current rises sharply, triggering the current protection mechanism, and ultimately causing the inverter to be unable to drive these loads smoothly.

[0003] For example, when starting a high-impact load such as a water pump, the voltage will be significantly lowered and the current will increase rapidly, which can easily trigger the inverter's overcurrent protection mechanism, thereby preventing the inverter from working properly. This problem has become a pain point in the industry, and the usual solution is to use a larger rated power inverter to deal with the above situation, but this undoubtedly increases costs and wastes resources. 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, and to provide an off-grid operating control system and a control method for an inverter. By introducing two control loops and two feedforwards, the dynamic characteristics of the inverter voltage can be effectively improved, the inverter output current can be limited, and the current limiting time can be extended, so that impact loads can be driven with low rated inverter power, thereby effectively reducing costs and resource waste.

[0005] In a first aspect, an embodiment of the present invention provides an off-grid operating condition control system of an inverter, comprising: an inverter current feedforward module, a first control loop, a second control loop and an inverter voltage feedforward module connected in sequence; wherein the inverter current feedforward module is used to provide a current feedforward signal to the inverter voltage output terminal of the inverter to generate an inverter voltage reference signal; the inverter voltage feedforward module is used to provide a voltage feedforward signal corresponding to the instantaneous value of the inverter voltage of the inverter; the first control loop includes an inverter voltage instantaneous value PI controller, which is used to output an inverter current reference signal according to the inverter voltage reference signal and the voltage feedforward signal; the second control loop includes an inverter voltage instantaneous value PI controller, which is used to output a voltage adjustment signal according to the inverter current reference signal and the instantaneous value of the inverter current of the inverter, so that the adjustment signal and the voltage feedforward signal are added to generate a PWM waveform signal for load power control.

[0006] In some embodiments, the system also includes a third control loop, which is arranged between the inverter current feedforward module and the inverter voltage output terminal of the inverter, and the third control loop includes an inverter voltage effective value PI controller, which is used to output a first inverter voltage reference signal based on the difference signal between the inverter voltage reference signal of the inverter and the inverter voltage effective value.

[0007] In some embodiments, the system also includes an effective value given feedforward module, which is used to provide an inverter voltage effective signal to the input and output ends of the inverter voltage effective value PI controller, so that the first inverter voltage reference signal and the inverter voltage effective signal are added to generate a second inverter voltage reference signal; the second inverter voltage reference signal is used to be added to the current feedforward signal to generate the inverter voltage reference signal.

[0008] In some embodiments, the variable voltage instantaneous value PI controller is used to output an inverter current reference signal based on a first output limit and a first PI parameter according to a difference signal between the inverter voltage reference signal and the voltage feed-forward signal; the inverter voltage instantaneous value PI controller is used to output a voltage adjustment signal based on a second output limit and a second PI parameter according to the inverter current reference signal and the inverter current instantaneous value of the inverter; the inverter voltage effective value PI controller is used to output a first inverter voltage reference signal based on a third output limit and a third PI parameter according to a difference signal between the inverter voltage reference signal of the inverter and the inverter voltage effective value.

[0009] In some embodiments, the first PI parameter is greater than the third PI parameter, and the second PI parameter is greater than the first PI parameter.

[0010] In some embodiments, the first output limit is greater than the third output limit, the second output limit is greater than the first output limit, the first output limit is determined according to a preset standard limit and a preset difference, and the second output limit is determined according to the preset standard limit and a preset multiple.

[0011] In some embodiments, the preset standard limit is -1 to 1, the preset difference is 0.1, the preset multiple is 2, the first output limit is -1.1 to 1.1, the first output limit is -2 to 2, and the third output limit is -0.3 to 0.3.

[0012] In some embodiments, the current feed-forward signal is 0.8 times the effective value of the inverter current of the inverter, and the inverter voltage effective signal is 0.8 times the effective value of the inverter voltage of the inverter.

[0013] In some embodiments, the system further comprises a sampling terminal for acquiring an instantaneous value of an inverter current, an instantaneous value of an inverter voltage and an effective value of an inverter voltage, and the system is connected to a DC bus of the inverter via the sampling terminal.

[0014] In a second aspect, an embodiment of the present invention provides an off-grid operating condition control method for an inverter, characterized in that the method is applied to an off-grid operating condition control system of an inverter as described in any one of the first aspects, and the method includes: using the inverter current feedforward module to provide a current feedforward signal for the inverter voltage output terminal of the inverter to generate an inverter voltage reference signal; using the inverter voltage feedforward module to provide a voltage feedforward signal corresponding to the instantaneous value of the inverter voltage of the inverter; outputting an inverter current reference signal according to the inverter voltage reference signal and the voltage feedforward signal; outputting a voltage adjustment signal according to the inverter current reference signal and the instantaneous value of the inverter current of the inverter, so that the adjustment signal and the voltage feedforward signal are added to generate a PWM waveform signal for load power control.

[0015] According to an embodiment of the present invention, an off-grid operating condition control system and a control method of an inverter are provided, which have at least the following beneficial effects: the present application includes an inverter current feedforward module, a first control loop, a second control loop and an inverter voltage feedforward module connected in sequence; wherein the inverter current feedforward module is used to provide a current feedforward signal to the inverter voltage output terminal of the inverter to generate an inverter voltage reference signal; the inverter voltage feedforward module is used to provide a voltage feedforward signal corresponding to the instantaneous value of the inverter voltage of the inverter; the first control loop includes an inverter voltage instantaneous value PI controller, which is used to output an inverter current reference signal according to the inverter voltage reference signal and the voltage feedforward signal; the second control loop is used to generate an inverter voltage reference signal according to the inverter voltage reference signal and the voltage feedforward signal; The control loop includes an inverter voltage instantaneous value PI controller, which is used to output a voltage adjustment signal according to an inverter current reference signal and an inverter current instantaneous value, so that the adjustment signal and the voltage feedforward signal are added to generate a PWM waveform signal for load power control; wherein, the present application can quickly respond when the load is instantaneously put into operation by adjusting the parameters and the amplitude limit value of the inverter voltage instantaneous value PI loop, reduce the voltage drop, and improve the dynamic response speed of the voltage; and by increasing the amplitude limit value and parameters of the inverter current instantaneous value PI loop, the current peak value can be more effectively limited to avoid triggering the protection mechanism due to excessive current, and ensure the stability of the inverter when facing an impact load. It can be understood that, under the premise of not affecting the steady-state performance, by introducing the inverter voltage instantaneous value feedforward and the inverter current effective value feedforward, the present invention can maintain voltage stability during the load unloading process and avoid the negative impact caused by voltage fluctuations, so that the present invention allows the use of a smaller rated power inverter to drive a larger load, thereby reducing the demand for high-cost inverters, reducing the overall system cost, and improving the inverter performance while improving its energy utilization efficiency.

[0016] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the description, claims and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings are used to provide a further understanding of the technical solution of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the technical solution of the present invention and do not constitute a limitation on the technical solution of the present invention.

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

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

[0020] Figure 2 It is a module schematic diagram of an off-grid working condition control system of an inverter provided by an embodiment of the present invention;

[0021] Figure 3 This is another optional module schematic diagram of an off-grid operating condition control system of an inverter provided by an embodiment of the present invention;

[0022] Figure 4 It is a circuit diagram of an off-grid operating condition control system of an inverter provided by an embodiment of the present invention;

[0023] Figure 5 It is a flow chart of an off-grid working condition control method of an inverter provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0024] This section 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 purpose of the accompanying drawings is to supplement the description of the text part of the specification with graphics, so that people can 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 scope of protection of the present invention.

[0025] In the description of the present invention, "several" means one or more, "more" means more than two, "greater than", "less than", "exceed", etc. are understood to exclude the number itself, "above", "below", "within", etc. are understood to include the number itself, "any one" means one or more, "at least one of the following" and similar expressions refer to any combination of these items, including any combination of single or plural items. If there is a description of the first and the second, it is only used for the purpose of distinguishing the technical features, and cannot be understood as indicating or implying the relative importance or implicitly indicating the number of the indicated technical features or implicitly indicating the order of the indicated technical features.

[0026] It should be noted that the terms such as setting, installing, and connecting in the embodiments of the present invention should be understood in a broad sense, and 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 "connection" can be a mechanical connection, an electrical connection, or mutual communication; it can be directly connected or indirectly connected through an intermediate medium.

[0027] 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.

[0028] With the rapid promotion of household energy storage inverters in overseas markets, inverters face various types of load challenges when operating off-grid, especially impact loads such as refrigerators, air conditioners, water heaters, and water pumps. Such loads consume a lot of energy during the startup phase, which means that the inverter must have excellent dynamic performance to successfully start and stably operate these devices. However, existing inverter control strategies often focus on the stability of the inverter output voltage and ignore the effective management of the inverter output current. This results in the inverter output voltage may drop sharply and the current rises sharply when starting impact loads, triggering the current protection mechanism, and ultimately causing the inverter to fail to drive these loads smoothly. For example, when starting high impact loads such as water pumps, the voltage will be significantly lowered and the current will increase rapidly, which can easily trigger the inverter's overcurrent protection mechanism, thereby preventing the inverter from working properly. This problem has become a pain point in the industry. The usual solution is to use inverters with larger rated power to deal with the above situation, but this undoubtedly increases costs and wastes resources.

[0029] Based on this, the purpose of the present invention is to solve at least one of the technical problems existing in the prior art, and to provide an off-grid operating control system and a control method for an inverter. By introducing two control loops and two feedforwards, the dynamic characteristics of the inverter voltage can be effectively improved, the inverter output current can be limited, and the current limiting time can be extended, so that impact loads can be driven with low rated inverter power, thereby effectively reducing costs and resource waste.

[0030] The present application scheme is further described below with reference to the accompanying drawings.

[0031] refer to Figure 1 , Figure 1 is a schematic diagram of an inverter provided by an embodiment of the present invention; Figure 1 The basic circuit structure of the inverter is shown, including the DC bus (Ubus), capacitor C1, inverter bridge, filter inductor L1, capacitor C2 and load. On this basis, this application can realize the off-grid working condition control system of the inverter by adding specific functional modules. Figure 1 On the basis of the above, an inverter current feedforward module and an inverter voltage feedforward module are added. These two modules are responsible for providing current feedforward signals and voltage feedforward signals respectively to improve the dynamic response performance of the system, and construct a first control loop and a second control loop. The first control loop is composed of an inverter voltage instantaneous value PI controller, which receives the voltage feedforward signal and the inverter voltage reference signal from the inverter voltage feedforward module, and then outputs an inverter current reference signal. The second control loop is composed of another inverter voltage instantaneous value PI controller, which receives the inverter current reference signal and the actual inverter current instantaneous value, and then outputs a voltage adjustment signal. Furthermore, the voltage adjustment signal is added to the voltage feedforward signal to obtain a PWM waveform signal, which is used to control the switching action of the inverter bridge, and then adjust the output voltage and current of the inverter. Through the above method, it can be achieved in Figure 1 The off-grid operating condition control system of the inverter described in this application is applied to the basic inverter structure shown, thereby improving the load capacity and dynamic response performance of the inverter in the off-grid state.

[0032] Figure 1 InvVoltReal and InvCurrReal represent the inverter voltage instantaneous value signal and the inverter current instantaneous value signal of the inverter respectively, both of which can be detected by sensors. InvCurrRms represents the effective value of the inverter current of the inverter, which can be calculated based on the inverter current instantaneous value signal. Ubus and iInv represent the bus voltage and current respectively.

[0033] refer to Figure 2 , Figure 2 It is a module schematic diagram of an off-grid operating condition control system of an inverter provided by an embodiment of the present invention; in the first aspect, an embodiment of the present invention provides an off-grid operating condition control system of an inverter, comprising: an inverter current feedforward module, a first control loop, a second control loop and an inverter voltage feedforward module connected in sequence; wherein the inverter current feedforward module is used to provide a current feedforward signal to the inverter voltage output end of the inverter to generate an inverter voltage reference signal; the inverter voltage feedforward module is used to provide a voltage feedforward signal corresponding to the instantaneous value of the inverter voltage of the inverter; the first control loop includes an inverter voltage instantaneous value PI controller, which is used to output an inverter current reference signal according to the inverter voltage reference signal and the voltage feedforward signal; the second control loop includes an inverter voltage instantaneous value PI controller, which is used to output a voltage adjustment signal according to the inverter current reference signal and the instantaneous value of the inverter current of the inverter, so that the adjustment signal and the voltage feedforward signal are added to generate a PWM waveform signal for load power control.

[0034] Among them, the present application can quickly respond when the load is instantaneously put into operation, reduce voltage drop, and improve the dynamic response speed of voltage by adjusting the parameters and limit value of the PI loop of the instantaneous value of the inverter voltage; and by increasing the limit value and parameters of the PI loop of the instantaneous value of the inverter current, it can more effectively limit the current peak value, avoid triggering the protection mechanism due to excessive current, and ensure the stability of the inverter when facing impact loads. It can be understood that, under the premise of not affecting the steady-state performance, by introducing the instantaneous value feedforward of the inverter voltage and the effective value feedforward of the inverter current, the present invention can maintain voltage stability during the load unloading process and avoid the negative impact of voltage fluctuations, so that the present invention allows the use of inverters with smaller rated power to drive larger loads, thereby reducing the demand for high-cost inverters, reducing the overall system cost, and improving the inverter performance while improving its energy efficiency.

[0035] In some embodiments, Figure 2 The module schematic diagram of the off-grid operating control system of the inverter in the present application is shown. The system of the present application is mainly composed of four parts: an inverter current feedforward module, a first control loop, a second control loop and an inverter voltage feedforward module. Among them, the inverter current feedforward module is used to provide a current feedforward signal to the inverter voltage output terminal of the inverter. The purpose of the above signal is to predict and compensate for the current fluctuations caused by load changes in advance, so as to generate a more accurate inverter voltage reference signal. In this way, the system can make corresponding adjustments before the load changes, thereby improving the overall response speed and stability.

[0036] The first control loop includes an inverter voltage instantaneous value PI controller, which is used to calculate an inverter current reference signal based on an inverter voltage reference signal and a voltage feedforward signal. This process can be understood as a closed-loop control process, which continuously adjusts and corrects the actual output voltage of the inverter to be as close to the expected reference value as possible.

[0037] Among them, the second control loop includes an inverter voltage instantaneous value PI controller, which focuses on the instantaneous value of the inverter current. By comparing the inverter current reference signal with the actual measured instantaneous value of the inverter current, a voltage adjustment signal is output. This signal will be combined with the voltage feedforward signal to generate a PWM waveform signal that is ultimately used for load power control. The PWM waveform signal directly determines how the inverter distributes and regulates power.

[0038] Among them, the inverter voltage feedforward module is used to provide a voltage feedforward signal corresponding to the instantaneous value of the inverter voltage. The function of this signal is similar to the current feedforward signal mentioned above, both of which are to predict and compensate for possible changes in advance to ensure that the output voltage of the inverter is always in the best state.

[0039] It can be understood that the off-grid operating control system of the inverter in this application realizes precise control of the inverter output voltage and current through the coordinated work of multiple modules, so as to optimize the performance under static and dynamic conditions and improve the load capacity of the inverter. In addition, it can also reduce energy consumption and extend service life, making it suitable for use in off-grid environments.

[0040] In some embodiments, the inverter voltage instantaneous value PI controller in the first control loop is used to generate an inverter current reference signal according to the inverter voltage reference signal and the voltage feedforward signal, wherein the inverter voltage reference signal can be the target voltage value set by the system, and the voltage feedforward signal is the feedforward signal of the inverter voltage instantaneous value, which is provided by the inverter voltage feedforward module and is used to compensate for voltage changes in advance. The controller will first calculate the difference between the inverter voltage reference signal and the voltage feedforward signal, which reflects the deviation between the current inverter output voltage and the target voltage, and then control according to the proportional part of the error signal, quickly respond to the voltage deviation, reduce the error, control according to the integral part of the error signal, gradually accumulate the error, eliminate the steady-state error, and ensure voltage stability during long-term operation. The inverter current reference signal output by the PI controller will be used in a further control loop to adjust the output current of the inverter.

[0041] It can be understood that the proportional part of the inverter voltage instantaneous value PI controller ensures that the controller can respond quickly to voltage changes and reduce instantaneous voltage deviations, and the integral part ensures that the controller can eliminate steady-state errors and maintain voltage stability.

[0042] In some embodiments, the inverter voltage instantaneous value PI controller in the second control loop is used to output a voltage adjustment signal based on the inverter current reference signal and the inverter current instantaneous value of the inverter to generate a PWM waveform signal for load power control, wherein the inverter current reference signal is a signal output by the inverter voltage instantaneous value PI controller in the first control loop, which is used to indicate the current value that the inverter should output, and the inverter current instantaneous value is the instantaneous value of the current at the inverter output end detected by the sensor.

[0043] It can be understood that the inverter voltage instantaneous value PI controller first calculates the difference between the inverter current reference signal and the inverter current instantaneous value. This difference reflects the deviation between the current inverter output current and the target current. It controls according to the proportional part of the error signal to quickly respond to the current deviation and reduce the error. It also controls according to the integral part of the error signal to gradually accumulate the error and eliminate the steady-state error to ensure current stability during long-term operation. The voltage adjustment signal output by the PI controller will be added to the voltage feedforward signal to generate a PWM waveform signal for load power control.

[0044] It can be understood that through proportional and integral control, a voltage adjustment signal is generated according to the inverter current reference signal and the instantaneous value of the inverter current, and finally a PWM waveform signal for load power control is generated to ensure the rapid response and long-term stability of the inverter output current. Under the joint action of the above two controllers, the inverter can efficiently and stably drive various loads, especially impact loads, in an off-grid state.

[0045] refer to Figure 3 , Figure 3 It is another optional module schematic diagram of an off-grid operating condition control system of an inverter provided in an embodiment of the present invention; in some embodiments, the system also includes a third control loop, the third control loop is arranged between the inverter current feedforward module and the inverter voltage output terminal of the inverter, and the third control loop includes an inverter voltage effective value PI controller, which is used to output a first inverter voltage reference signal based on the difference signal between the inverter voltage reference signal of the inverter and the inverter voltage effective value.

[0046] Among them, the input signal of the inverter voltage effective value PI controller: The inverter voltage effective value PI controller receives two input signals: inverter voltage reference signal: this is the target voltage value set by the system, which can be a constant reference value; inverter voltage effective value: the voltage instantaneous value signal at the inverter output end is detected by the sensor, and then the voltage effective value is calculated.

[0047] Among them, the output signal of the inverter voltage effective value PI controller: the inverter voltage effective value PI controller outputs a first inverter voltage reference signal according to the difference between the two input signals (ie, the error signal).

[0048] It can be understood that the inverter voltage effective value PI controller first calculates the difference between the inverter voltage reference signal and the inverter voltage effective value. This difference reflects the deviation between the current inverter output voltage and the target voltage. The PI controller performs proportional (P) and integral (I) control based on this error signal. The proportional part is used to quickly respond to errors, and the integral part is used to eliminate steady-state errors to ensure voltage stability when the system runs for a long time. The first inverter voltage reference signal output by the PI controller will be used in a further control loop to adjust the output voltage of the inverter.

[0049] In some embodiments, the main purpose of the third control loop is to ensure the stability of the inverter output voltage. By continuously adjusting the inverter output voltage to make it close to the set reference value, the impact of voltage fluctuations can be effectively avoided. When facing load changes, the third control loop can respond quickly to ensure that the voltage returns to the set value in a short time, thereby improving the dynamic performance of the system.

[0050] It can be understood that the inverter current feedforward module provides a current feedforward signal to help the system respond quickly when the load changes. The first control loop outputs an inverter current reference signal based on the inverter voltage reference signal and the voltage feedforward signal. The second control loop outputs a voltage adjustment signal based on the inverter current reference signal and the instantaneous value of the inverter current of the inverter. The third control loop ensures the stability of the inverter output voltage by adjusting the inverter voltage reference signal, thereby supporting the normal operation of the first and second control loops.

[0051] refer to Figure 4 , Figure 4 It is a circuit diagram of an off-grid operating condition control system of an inverter provided by an embodiment of the present invention; in some embodiments, a variable voltage instantaneous value PI controller is used to output an inverter current reference signal based on a first output limit and a first PI parameter according to a difference signal between an inverter voltage reference signal and a voltage feedforward signal; an inverter voltage instantaneous value PI controller is used to output a voltage adjustment signal based on a second output limit and a second PI parameter according to an inverter current reference signal and an instantaneous value of the inverter current of the inverter; an inverter voltage effective value PI controller is used to output a first inverter voltage reference signal based on a third output limit and a third PI parameter according to a difference signal between an inverter voltage reference signal of the inverter and an inverter voltage effective value.

[0052] Among them, corresponding to Figure 4 ,The figure shows the three main control loops of the inverter off-grid operating control system and their interrelationships. Each loop contains a PI controller, which is responsible for generating a corresponding output signal based on a specific input signal to achieve effective control of the inverter output voltage and current.

[0053] Among them, the input signal of the third control loop (inverter voltage effective value PI loop) is the inverter voltage effective value reference signal InvVoltRmsRef and the actually measured inverter voltage effective value InvVoltRms, and the output signal is the first inverter voltage reference signal after being processed by the PI controller. The system also includes an effective value given feedforward module, which is used to provide an inverter voltage effective signal to the input and output ends of the inverter voltage effective value PI controller, so that the first inverter voltage reference signal and the inverter voltage effective signal are added to generate a second inverter voltage reference signal; the second inverter voltage reference signal is used to be added to the current feedforward signal to generate an inverter voltage reference signal.

[0054] In some embodiments, the effective signal of the inverter voltage provided by the effective value given feedforward module is Figure 4 0.8 times the effective value of the inverter voltage of the inverter.

[0055] In some embodiments, the input signal of the first control loop (inverter voltage instantaneous value PI loop) is the inverter voltage instantaneous value reference signal InvVoltRealRef and the actually measured inverter voltage instantaneous value InvVoltReal. After being processed by the PI controller, the inverter current reference signal InvCurrRef is output; the input signal of the second control loop (inverter current instantaneous value PI loop) is the inverter current reference signal InvCurrRefˋ and the actually measured inverter current instantaneous value InvCurrRea. After being processed by the PI controller, it is output to 1 / Ubus, which is used to generate the PWM waveform signal.

[0056] In some embodiments, Figure 4 As shown in the figure, each PI controller has corresponding output limit and PI parameters, such as ±0.3, ±1.1, ±2, etc., as well as specific gain coefficients of each controller (such as 0.8, 1.1, 2, etc.). These parameters determine the response characteristics and stability of the controller.

[0057] In some embodiments, the first PI parameter is greater than the third PI parameter, and the second PI parameter is greater than the first PI parameter, wherein it can be understood that the gain of the inverter voltage instantaneous value PI controller (first control loop) is greater than the gain of the inverter voltage effective value PI controller (third control loop), because the inverter voltage instantaneous value controller needs to respond quickly to the instantaneous change of the voltage to ensure the dynamic characteristics of the voltage; the gain of the inverter current instantaneous value PI controller (second control loop) is greater than the gain of the inverter voltage instantaneous value PI controller (first control loop), because the inverter current instantaneous value controller needs to respond faster to the instantaneous change of the current to ensure the dynamic characteristics of the current. By setting different PI parameters, each control loop can achieve the best performance within its respective control range, and the high gain of the first control loop and the second control loop can quickly respond to the instantaneous changes of voltage and current to ensure the dynamic characteristics of the system.

[0058] In some embodiments, the first output limit is greater than the third output limit, the second output limit is greater than the first output limit, the first output limit is determined according to a preset standard limit and a preset difference, and the second output limit is determined according to a preset standard limit and a preset multiple, wherein the output limit of the inverter voltage instantaneous value PI controller (first control loop) is greater than the output limit of the inverter voltage effective value PI controller (third control loop). This is because the instantaneous value controller requires a larger adjustment range to cope with instantaneous changes. The output limit of the inverter current instantaneous value PI controller (second control loop) is greater than the output limit of the inverter voltage instantaneous value PI controller (first control loop). This is because the current instantaneous value controller requires a larger adjustment range to cope with instantaneous changes in current. By setting a reasonable output limit, the controller output can be prevented from exceeding a reasonable range, over-adjustment and under-adjustment can be avoided, and the stability and reliability of the system can be ensured.

[0059] In some embodiments, the preset standard limit is -1 to 1, the preset difference is 0.1, the preset multiple is 2, the first output limit is -1.1 to 1.1, the first output limit is -2 to 2, and the third output limit is -0.3 to 0.3.

[0060] In some embodiments, the current feedforward signal is 0.8 times the effective value of the inverter current of the inverter, and the inverter voltage effective signal is 0.8 times the effective value of the inverter voltage of the inverter, so as to compensate for the current change in advance and improve the dynamic response speed of the system.

[0061] It can be understood that the 0.8 times inverter voltage effective value is given as feed-forward, the purpose of which is to be able to quickly output the required effective value when carrying a heavy load.

[0062] In some embodiments, the system also includes a sampling terminal for obtaining the instantaneous value of the inverter current, the instantaneous value of the inverter voltage and the effective value of the inverter voltage. The system is connected to the DC bus of the inverter through the sampling terminal to ensure that the collected signal accurately reflects the working status of the inverter.

[0063] It is worth noting that, from the actual effect, although the existing inverter voltage effective value PI loop has added feedforward, its output is still not enough to quickly compensate for the voltage drop when the load is instantaneously put into operation, resulting in a serious voltage drop. In contrast, the inverter voltage instantaneous value feedforward is all added to the output, which can quickly generate an ideal PWM waveform at the load moment, and combined with the fine-tuning of the inverter current instantaneous value PI loop, the output voltage waveform can be quickly stabilized. This feature performs very well when the load is less than the rated power, so it is widely used. However, when carrying an impact load exceeding the rated power, since a lower voltage needs to be output at this time, the inverter voltage instantaneous value feedforward makes the output waveform exceed expectations, the current rises rapidly, triggering the inverter's overcurrent protection point, resulting in the inability to drive impact loads exceeding the rated power. This has become a pain point in the industry, and usually only inverters with larger rated power can be used to carry loads, resulting in a great waste of resources.

[0064] Therefore, in the present application, two control loops are used and two feedforward functions are added to ensure the dynamic characteristics of the inverter voltage and the limitation of the inverter output current, prolong the current output time, and thus realize the function of driving the maximum load with the minimum rated inverter power. The details are as follows:

[0065] Inverter voltage instantaneous value PI loop: Output limit: slightly enlarge the output limit; PI parameter: increase the PI parameter to improve the dynamic response speed.

[0066] Inverter current instantaneous value PI loop: Output limit: amplify the output limit by 1 times; PI parameter: increase the PI parameter by 1 times to further improve the dynamic response speed.

[0067] Feedforward function: Inverter voltage instantaneous value feedforward: Inverter voltage instantaneous value feedforward is used instead of the previous inverter voltage instantaneous value given feedforward; Inverter current feedforward: A 0.8 times inverter current feedforward signal is compensated at the effective value loop.

[0068] Among them, it can be understood that when an impact heavy load is instantaneously applied, the instantaneous value of the inverter voltage will be quickly pulled down, causing the output PWM to be unable to continue to increase. At this time, the output of the inverter voltage instantaneous value PI loop will quickly reach the maximum value and enter the saturation state, so that the entire control system actually only has one inverter current instantaneous value PI loop running. The inverter current instantaneous value PI loop will strictly limit the current to a given upper limit value, and the system will continue to run in this state for a period of time until the starting energy required by the impact load is met, and then it will slowly exit the saturation state. In this way, the ability to carry impact loads can be significantly improved.

[0069] However, this method will cause a serious voltage drop when the load is within the normal rated power because the instantaneous value of the inverter voltage will be pulled down. For this reason, we introduced a 0.8 times inverter current feedforward signal into the system. When the heavy load is instantaneously put into use, the effective value loop is quickly compensated by an amount so that the voltage does not drop. When the heavy load is instantaneously unloaded, the current will suddenly disappear, and the 0.8 times inverter current feedforward signal will also disappear instantly, thus perfectly solving the problem of load unloading under rated power.

[0070] In summary, with the support of two control loops and two feedforward functions, the system in the present application solution can not only ensure the dynamic characteristics of the voltage, but also effectively limit the current, thereby significantly improving the performance of the inverter.

[0071] refer to Figure 5 , Figure 5 is a flow chart of an off-grid operating condition control method of an inverter provided by an embodiment of the present invention; in a second aspect, an embodiment of the present invention provides an off-grid operating condition control method of an inverter, the method is applied to an off-grid operating condition control system of an inverter as in any embodiment of the first aspect, the method comprising:

[0072] Step S510, providing a current feedforward signal to an inverter voltage output terminal of the inverter through an inverter current feedforward module to generate an inverter voltage reference signal;

[0073] Step S520, providing a voltage feedforward signal corresponding to the instantaneous value of the inverter voltage of the inverter through the inverter voltage feedforward module;

[0074] Step S530, outputting an inverter current reference signal according to the inverter voltage reference signal and the voltage feed-forward signal;

[0075] Step S540: outputting a voltage adjustment signal according to the inverter current reference signal and the inverter current instantaneous value of the inverter, so as to add the adjustment signal and the voltage feedforward signal to generate a PWM waveform signal for load power control.

[0076] Through the above steps S510 to S540, the present application can generate a PWM waveform signal for load power control, so that impact loads can be driven with low rated inverter power, thereby effectively reducing costs and resource waste.

[0077] Among them, the PWM waveform signal is used to control the AC voltage output by the inverter. By adjusting the duty cycle of the PWM waveform, the amplitude and frequency of the inverter output voltage can be adjusted to ensure that the output voltage meets the load requirements; through the precise control of the PWM waveform signal, the inverter output current can be limited to prevent overcurrent. Especially when there is an impact load, the PWM waveform signal can effectively control the current peak and avoid triggering the inverter's overcurrent protection mechanism.

[0078] Among them, the PWM waveform signal directly acts on the switching devices (such as IGBT, MOSFET, etc.) inside the inverter, and accurately controls the output voltage and current of the inverter by controlling the on and off time of these switching devices. The inverter receives the PWM waveform signal, controls the working state of the switching devices, and converts the DC power supply into the required AC voltage for supplying the load.

[0079] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments, and various changes can be made within the knowledge scope of ordinary technicians in the technical field without departing from the purpose of the present invention.

Claims

1. An off-grid operating control system for an inverter, characterized in that: include: An inverter current feedforward module, a first control loop, a second control loop and an inverter voltage feedforward module connected in sequence; The inverter current feedforward module is used to provide a current feedforward signal to the inverter voltage output terminal of the inverter to generate an inverter voltage reference signal; the inverter voltage feedforward module is used to provide a voltage feedforward signal corresponding to the instantaneous value of the inverter voltage of the inverter; The first control loop includes an inverter voltage instantaneous value PI controller, which is used to output an inverter current reference signal according to the inverter voltage reference signal and the voltage feedforward signal; The second control loop includes an inverter voltage instantaneous value PI controller, which is used to output a voltage adjustment signal based on the inverter current reference signal and the inverter current instantaneous value of the inverter, so that the adjustment signal and the voltage feedforward signal are added to generate a PWM waveform signal for load power control.

2. The off-grid operating control system of the inverter according to claim 1, characterized in that: The system also includes a third control loop, which is arranged between the inverter current feedforward module and the inverter voltage output terminal of the inverter. The third control loop includes an inverter voltage effective value PI controller, which is used to output a first inverter voltage reference signal based on the difference signal between the inverter voltage reference signal of the inverter and the inverter voltage effective value.

3. The off-grid operating control system of the inverter according to claim 2, characterized in that: The system also includes an effective value given feedforward module, which is used to provide an inverter voltage effective signal for the input and output ends of the inverter voltage effective value PI controller, so that the first inverter voltage reference signal and the inverter voltage effective signal are added to generate a second inverter voltage reference signal; the second inverter voltage reference signal is used to be added to the current feedforward signal to generate the inverter voltage reference signal.

4. The off-grid operating control system of the inverter according to claim 2, characterized in that: The variable voltage instantaneous value PI controller is used to output an inverter current reference signal based on a first output limit and a first PI parameter according to a difference signal between the inverter voltage reference signal and the voltage feed-forward signal; the inverter voltage instantaneous value PI controller is used to output a voltage adjustment signal based on a second output limit and a second PI parameter according to the inverter current reference signal and the inverter current instantaneous value of the inverter; the inverter voltage effective value PI controller is used to output a first inverter voltage reference signal based on a third output limit and a third PI parameter according to a difference signal between the inverter voltage reference signal of the inverter and the inverter voltage effective value.

5. The off-grid operating control system of the inverter according to claim 4, characterized in that: The first PI parameter is greater than the third PI parameter, and the second PI parameter is greater than the first PI parameter.

6. The off-grid operating control system of the inverter according to claim 4, characterized in that: The first output limit is greater than the third output limit, the second output limit is greater than the first output limit, the first output limit is determined according to a preset standard limit and a preset difference, and the second output limit is determined according to the preset standard limit and a preset multiple.

7. The off-grid operating control system of the inverter according to claim 6, characterized in that: The preset standard limit is -1 to 1, the preset difference is 0.1, the preset multiple is 2, the first output limit is -1.1 to 1.1, the first output limit is -2 to 2, and the third output limit is -0.3 to 0.

3.

8. The off-grid operating control system of the inverter according to claim 3, characterized in that: The current feed-forward signal is 0.8 times the effective value of the inverter current of the inverter, and the inverter voltage effective signal is 0.8 times the effective value of the inverter voltage of the inverter.

9. The off-grid operating control system of the inverter according to claim 3, characterized in that: The system also includes a sampling terminal for obtaining an instantaneous value of an inverter current, an instantaneous value of an inverter voltage and an effective value of an inverter voltage, and the system is connected to a DC bus of the inverter via the sampling terminal.

10. A method for controlling an inverter in an off-grid condition, characterized in that: The method is applied to an off-grid operating condition control system of an inverter according to any one of claims 1 to 9, and the method comprises: The inverter current feedforward module is used to provide a current feedforward signal to the inverter voltage output terminal of the inverter to generate an inverter voltage reference signal; Providing a voltage feedforward signal corresponding to the instantaneous value of the inverter voltage of the inverter through the inverter voltage feedforward module; Outputting an inverter current reference signal according to the inverter voltage reference signal and the voltage feed-forward signal; A voltage adjustment signal is output according to the inverter current reference signal and the inverter current instantaneous value of the inverter, so that the adjustment signal and the voltage feedforward signal are added to generate a PWM waveform signal for load power control.

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