Impact load flexible starting method for bidirectional off-grid and grid-connected energy storage inverter

Abstract

The invention discloses an impact load flexible starting method for a bidirectional off-grid and grid-connected energy storage inverter, and the method comprises the steps: collecting an output current of the bidirectional off-grid and grid-connected energy storage inverter to obtain a target current if a load connected with the bidirectional off-grid and grid-connected energy storage inverter is detected to be started; if the target current is greater than or equal to a preset current threshold value, taking a first preset PI controller as a target controller; obtaining a correction parameter of a modulation wave amplitude output by the target controller, and generating a control signal based on the correction parameter of the modulation wave amplitude; and controlling the bidirectional off-grid and grid-connected energy storage inverter based on the control signal so as to realize flexible starting. According to the invention, the output voltage can be reduced when the load is started, so that overcurrent and overpower are avoided, and overload or overcurrent protection can be avoided.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of inverters, in particular to a flexible starting method for an impact load of a bidirectional off-grid and grid-connected energy storage inverter. BACKGROUND

[0002] With the development of new energy technology, bidirectional off-grid and grid-connected energy storage inverters (hereinafter referred to as inverters) have been widely used due to their advantages such as peak clipping and valley filling and reduction of carbon emissions. When the load carried by the inverter is an inductive load, due to the contradiction between the energy time domain discontinuity of the load at the starting moment and the control strategy, transient overcurrent and overpower problems may occur, which may easily lead to damage of power devices or shutdown.

[0003] To solve the above problems, the commonly used solution is usually to adjust the maximum power threshold of the inverter, that is, to allow a short-time output of 2 times the rated power at the starting moment of the inductive load, so as to be compatible with the starting characteristics of the inductive load. However, increasing the maximum power threshold may easily lead to overload or overcurrent protection, resulting in failure to start. SUMMARY

[0004] The embodiments of the present application provide an impact load flexible starting method for a bidirectional off-grid and grid-connected energy storage inverter and an inverter, aiming to solve the problem that the current starting method for an inductive load is prone to overload or overcurrent protection.

[0005] In a first aspect, the embodiments of the present application provide an impact load flexible starting method for a bidirectional off-grid and grid-connected energy storage inverter, applied to a bidirectional off-grid and grid-connected energy storage inverter, and the method comprises:

[0006] If it is detected that the load connected to the bidirectional off-grid and grid-connected energy storage inverter is started, the output current of the bidirectional off-grid and grid-connected energy storage inverter is collected to obtain a target current;

[0007] If the target current is greater than or equal to a preset current threshold, a first preset PI controller is used as a target controller;

[0008] A correction parameter of a modulation wave amplitude output by the target controller is obtained, and a control signal is generated based on the correction parameter of the modulation wave amplitude;

[0009] The bidirectional off-grid and grid-connected energy storage inverter is controlled based on the control signal to realize flexible starting.

[0010] In a second aspect, the embodiments of the present application also provide a bidirectional off-grid and grid-connected energy storage inverter, which comprises a signal detection module, a power module and a control module, the control module is configured with the bidirectional off-grid and grid-connected energy storage inverter flexible starting method of any one of the above; the signal detection module is connected with the control module, and is used for collecting output current to obtain target current; the control module is connected with the power module, and is used for generating a control signal according to the target current, and controlling the power module through the control signal.

[0011] The embodiments of the present application provide a bidirectional off-grid and grid-connected energy storage inverter flexible starting method and an inverter. The method comprises: if it is detected that a load connected with the bidirectional off-grid and grid-connected energy storage inverter is started, collecting output current of the bidirectional off-grid and grid-connected energy storage inverter to obtain target current; if the target current is greater than or equal to a preset current threshold, taking a first preset PI controller as a target controller; obtaining a correction parameter of a modulation wave amplitude value output by the target controller, and generating a control signal based on the correction parameter of the modulation wave amplitude value; and controlling the bidirectional off-grid and grid-connected energy storage inverter based on the control signal to realize flexible starting. The embodiments of the present application can collect output current of the bidirectional off-grid and grid-connected energy storage inverter to obtain target current when the load is started, take a first preset PI controller as a target controller when the target current is greater than or equal to a preset current threshold, generate a control signal according to a correction parameter of a modulation wave amplitude value output by the target controller, and then control the bidirectional off-grid and grid-connected energy storage inverter based on the generated control signal to realize flexible starting, which not only can reduce output voltage when the load is started to avoid overcurrent and over-power, but also can avoid overload or overcurrent protection. BRIEF DESCRIPTION OF DRAWINGS

[0012] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0013] Figure 1 is a flowchart of the bidirectional off-grid and grid-connected energy storage inverter flexible starting method provided by the embodiments of the present application;

[0014] Figure 2 is a first sub-flowchart of the bidirectional off-grid and grid-connected energy storage inverter flexible starting method provided by the embodiments of the present application;

[0015] Figure 3is a second sub-flow diagram of a flexible starting method of an impulse load of a bidirectional off-grid and grid-connected energy storage inverter provided by the embodiment of the present application;

[0016] Figure 4 is a third sub-flow diagram of a flexible starting method of an impulse load of a bidirectional off-grid and grid-connected energy storage inverter provided by the embodiment of the present application;

[0017] Figure 5 is a fourth sub-flow diagram of a flexible starting method of an impulse load of a bidirectional off-grid and grid-connected energy storage inverter provided by the embodiment of the present application;

[0018] Figure 6 is a fifth sub-flow diagram of a flexible starting method of an impulse load of a bidirectional off-grid and grid-connected energy storage inverter provided by the embodiment of the present application;

[0019] Figure 7 is a sixth sub-flow diagram of a flexible starting method of an impulse load of a bidirectional off-grid and grid-connected energy storage inverter provided by the embodiment of the present application;

[0020] Figure 8 is a block diagram of a bidirectional off-grid and grid-connected energy storage inverter provided by the embodiment of the present application;

[0021] Figure 9 is a topological structure diagram of a bidirectional off-grid and grid-connected energy storage inverter provided by the embodiment of the present application. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0023] It should be understood that when used in the specification and the appended claims, the terms "comprise" and "include" indicate the presence of the described features, integers, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, operations, elements, components, and / or groups thereof.

[0024] It should also be understood that the terminology used in this specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used in this specification and the appended claims, the singular forms “a,” “an,” and “the” are intended to include the plural forms unless the context clearly indicates otherwise. It should also be understood that the term “and / or” as used in this specification and the appended claims refers to any combination and all possible combinations of one or more of the associated listed items, and includes such combinations.

[0025] Please see Figure 1 , Figure 1 This is a flowchart illustrating the flexible start-up method for a bidirectional off-grid energy storage inverter under impulsive loads provided in an embodiment of the present invention. This method can be applied to bidirectional off-grid energy storage inverters to reduce the output voltage during load startup to avoid overcurrent and overpower situations. Figure 1 As shown, the method includes steps S100 to S130.

[0026] S100, if the load connected to the bidirectional off-grid energy storage inverter is detected to start, the output current of the bidirectional off-grid energy storage inverter is collected to obtain the target current.

[0027] In this embodiment of the invention, a bidirectional off-grid energy storage inverter is used to drive a load. It may include a signal detection module, a control module, and a power module. The signal detection module collects key electrical parameters of the bidirectional off-grid energy storage inverter, such as input / output current, voltage, and DC bus voltage, and outputs the sampling results to the control module to obtain the target current. The control module may be a DSP processing unit, which may include an ADC module and an EPWM module. The control module also incorporates SPWM and LLC algorithms to control the on / off state of the switching transistors in the power module.

[0028] like Figure 9 As shown, Figure 9 This is a topology diagram of a bidirectional grid-connected and off-grid energy storage inverter. Figure 9The power module includes a power factor correction circuit, an LLC resonant circuit, which contains a primary side full bridge, a resonant cavity and a secondary side full bridge circuit. AC is an alternating current end, which is a power grid input in charging mode and an inverter output in discharging mode, L1 is a boost inductor, C1 is an inverter output filter capacitor, QT1-QT4 are switch tubes of the PFC full bridge circuit, C2 is a bus circuit, QT5-QT8 are switch tubes of the LLC primary side full bridge circuit, the resonant cavity circuit includes a resonant inductor Lr, a resonant capacitor Cr, an excitation inductor Lm and a transformer T, QT9-QT12 are switch tubes of the LLC secondary side full bridge circuit, C2 is a filter capacitor on the DC battery side, and BAT is a DC battery.

[0029] The control module includes a signal detection module, a DSP processing unit and a drive circuit. The signal detection module collects key electrical parameters such as input / output current, voltage and DC bus voltage in real time through a high-precision sensor. After the signal detection module samples the output voltage and current, the signal is sent to the ADC module of the DSP processing unit. The ADC module converts the voltage value from 0 to 3.3V into an analog quantity from 0 to 4096. After the SPWM algorithm receives the analog quantity of the output voltage and current, the EPWM module of the DSP processing unit controls the switching sequence of the PFC full bridge circuit switch tube to make the system work at the rated output voltage. The front-stage LLC algorithm works in the same way. After the signal detection module samples the input current, voltage and bus voltage, the signal is sent to the DSP processing unit. The switching sequence of the primary side full bridge and the secondary side full bridge switch tube of the LLC resonant circuit is controlled through the algorithm to maintain the stability of the bus voltage.

[0030] The bidirectional off-grid and grid-connected energy storage inverter is used to drive a load, which can be connected to different types of loads, such as inductive loads, resistive loads and nonlinear loads. The current of the inductive load lags behind the voltage phase (power factor PF < 1), and the electromagnetic energy storage characteristic causes the current to surge suddenly at the start-up moment, such as the locked-rotor current 5-10 times the rated value. The current of the resistive load is in phase with the voltage (PF ≈ 1), and there is no start-up impact. The current waveform of the nonlinear load is distorted (contains high-order harmonics), the peak factor is high, but there is no phase delay.

[0031] When it is detected that the load connected to the bidirectional off-grid and grid-connected energy storage inverter starts, the output current of the bidirectional off-grid and grid-connected energy storage inverter is collected by the signal detection module to obtain a target current. For example, the output current can be collected first to obtain an output current analog quantity, and then the output current analog quantity is converted into a digital signal by the ADC module in the control module to obtain the target current.

[0032] In S110, if the target current is greater than or equal to a preset current threshold, a first preset PI controller is used as a target controller.

[0033] In the embodiment of the present application, the preset current threshold is an empirical value, which can be adjusted based on the rated current, for example, the preset current threshold is 150% of the rated current. After obtaining the target current, the size relationship between the target current and the preset current threshold can be compared to determine the load characteristics, for example, when the target current is greater than or equal to the preset current threshold, it can be confirmed that the load is an inductive load, and flexible starting is required, that is, the preset current threshold is the critical value of the inductive load, and when the target current is greater than or equal to the preset current threshold, it indicates that the load connected to the bidirectional off-grid energy storage inverter is an inductive load.

[0034] Based on the fact that the load connected to the bidirectional off-grid energy storage inverter is an inductive load, the first preset PI controller can be used as the target controller, and the first preset PI controller can be a high-gain current closed-loop PI controller. The high-gain current closed-loop PI controller can greatly attenuate the amplitude of the modulation wave in the SPWM algorithm, realize dynamic adjustment of the duty cycle of the switch tube of the full-bridge inverter circuit, and the mechanism causes the output voltage of the inverter to be actively reduced, thereby effectively suppressing the rising trend of the output current. Influenced by the inductance characteristics, the output current will continue to rise, and the output voltage will decrease exponentially. The proposed soft starting algorithm continues to run until the energy of the inductive impact load is exhausted or the output voltage is depressed to zero. The algorithm suppresses the sudden change of the output current by depressing the output voltage, and ensures that the system output current is always limited within the short-circuit protection current threshold range.

[0035] In the embodiment of the present application, after confirming the target controller, the correction parameter of the modulation wave amplitude output by the target controller can be used as the parameter of the SPWM algorithm, and the control signal can be generated according to the SPWM algorithm. The control signal can be a PWM wave.

[0036] In the embodiment of the present application, after confirming the target controller, the correction parameter of the modulation wave amplitude output by the target controller can be used as the parameter of the SPWM algorithm, and the control signal can be generated according to the SPWM algorithm. The control signal can be a PWM wave.

[0037] In the embodiment of the present application, after confirming the target controller, the correction parameter of the modulation wave amplitude output by the target controller can be used as the parameter of the SPWM algorithm, and the control signal can be generated according to the SPWM algorithm. The control signal can be a PWM wave.

[0038] In the embodiment of the present application, after obtaining the control signal, the power module of the bidirectional off-grid energy storage inverter can be controlled based on the control signal, for example, the conduction and cutoff of the switch tube in the power module can be controlled, so that the output voltage can be reduced, and flexible starting can be realized.

[0039] For example, assuming that the inductive load is a 3kW three-phase asynchronous motor, the locked-rotor current = 6x rated current, and the starting time is 500ms, then at the starting moment of the motor, the signal detection module starts to collect the output current, assuming that the output current is 30A, and the preset current is 4.5A, then at this time, the high-gain current closed-loop PI controller can be used as the target controller, and the PI controller outputs ΔV m <0, that is, the amplitude of the greatly attenuated modulation wave is greatly attenuated, and the SPWM algorithm generates a control signal according to the value output by the PI controller. Due to the sharp drop in the amplitude of the modulation wave, the control signal compresses the duty cycle of the switching tube, so that the output voltage is actively recessed, for example, from 220V to 80V, thereby suppressing the current rise.

[0040] Referring to Figure 2 In some embodiments, such as the present embodiment, the flexible starting method of the bidirectional off-grid and grid-connected energy storage inverter for impact load further includes steps S140-S142.

[0041] S140, obtaining the target current and the preset current threshold value;

[0042] S141, if the target current threshold value is greater than or equal to the preset current threshold value, controlling the bidirectional off-grid and grid-connected energy storage inverter to enter the flexible starting working mode;

[0043] S142, if the target current threshold value is less than the preset current threshold value, controlling the bidirectional off-grid and grid-connected energy storage inverter to enter the steady-state normal working mode.

[0044] In the embodiment of the present application, the bidirectional off-grid and grid-connected energy storage inverter can be preset with two working modes, one of which is the flexible starting working mode, and the other of which is the steady-state normal working mode. The flexible starting working mode corresponds to the inductive load, and the steady-state normal working mode corresponds to the conventional load. The identification of the inductive load and the conventional load can be realized by the target current and the preset current threshold value. For example, when the target current is greater than or equal to the preset current threshold value, it indicates that the load type is an inductive load, and the flexible starting working mode can be entered to reduce the output voltage. When the target current is less than the preset current threshold value, it indicates that the load type is a conventional load, and the steady-state normal working mode can be entered.

[0045] Referring to Figure 3 In some embodiments, such as the present embodiment, the flexible starting method of the bidirectional off-grid and grid-connected energy storage inverter for impact load further includes step S143.

[0046] S143, in the steady-state normal working mode, a second preset PI controller is used as a target controller.

[0047] In the embodiment of the present application, when the working mode is the steady normal working mode, it indicates that the load type is a regular load, and the second preset PI controller can be used as the target controller. The control module can be provided with a threshold comparison module, a first preset PI controller and a second preset PI controller. The threshold comparison module is used to compare the target current with a preset current threshold, and select the first preset PI controller or the second preset PI controller based on the comparison result. The first preset PI controller can be a high-gain current closed-loop controller, and the second preset PI controller can be a low-gain voltage closed-loop controller. The PI controller obtains the amplitude of the modulation wave in the sinusoidal pulse width modulation (SPWM) algorithm by comparing the error between the actual value and the target value, and then obtains the switching time sequence of the switching tube of the full-bridge inverter circuit by comparing the modulation wave with the carrier wave.

[0048] Referring to Figure 4 In some embodiments, such as the present embodiment, the flexible starting method of the bidirectional off-grid and grid-connected energy storage inverter for impact load further includes step S144.

[0049] S144, in the flexible starting working mode, if it is detected that the target current is less than the preset current threshold, the working mode of the bidirectional off-grid and grid-connected energy storage inverter is switched to the steady normal working mode.

[0050] In the embodiment of the present application, in the flexible starting working mode, when the target current decreases to be less than the preset current threshold, the working mode can be switched to the steady normal working mode, that is, the high-gain current closed-loop controller is adjusted to the low-gain voltage closed-loop controller, and then the modulation wave amplitude is gradually increased to a set value by the SPWM algorithm until the system stably operates at the rated working voltage.

[0051] Referring to Figure 5 In some embodiments, such as the present embodiment, the step S130 further includes steps S131-S133.

[0052] S131, confirming the working mode in which the bidirectional off-grid and grid-connected energy storage inverter currently locates;

[0053] S132, if the bidirectional off-grid and grid-connected energy storage inverter is in the flexible starting working mode, obtaining the modulation wave amplitude attenuation amount output by the first preset PI controller, and generating the control signal based on the modulation wave amplitude attenuation amount;

[0054] S133, if the bidirectional off-grid and grid-connected energy storage inverter is in the steady normal working mode, obtaining the modulation wave amplitude increment output by the second preset PI controller, and generating the control signal based on the modulation wave amplitude increment.

[0055] In the embodiment of the present application, the first preset PI controller is a high-gain current closed-loop controller, and the output thereof is a modulation wave amplitude attenuation amount; the second preset PI controller is a low-gain voltage closed-loop controller, and the output thereof is a modulation wave amplitude increment. The working mode of the modulation wave amplitude increment is a steady-state normal working mode, that is, the output current is less than a preset current threshold, which is output by the low-gain voltage closed-loop PI controller, and is used for allowing the output voltage to be smoothly raised to a rated value (220 V), and the formula is as follows:

[0056] ΔV m = K p_v · (V ref -V actual ) + K i_v ·∫(V ref -V actual )dt (1)

[0057] Wherein, K p_v is a proportional gain, K i_v is an integral gain, V ref is a reference voltage, and V actual is an actual voltage. The modulation wave amplitude Vm is gradually increased from an initial value (for example, 0% to 100%). The inverter output voltage V out is smoothly raised from 0 V to the rated value, and the output current is synchronously increased with the voltage, without overshoot or oscillation.

[0058] The working mode of the modulation wave amplitude attenuation amount is a flexible starting working mode, that is, the output current is greater than or equal to the preset current threshold, which is output by the high-gain current closed-loop PI controller, and is used for suppressing overcurrent by actively reducing the output voltage, and the formula is as follows:

[0059] ΔV m = K p_i · (I ref -I actual ) + K i_i ·∫(I ref -I actual )dt (2)

[0060] Wherein, K p_i is a proportional gain, K i_i is an integral gain, I ref is a reference current, and I actual is an actual current. The modulation wave amplitude V m is greatly attenuated (for example, 100% to 40%), the inverter output voltage V out is actively reduced, and the voltage is dented, for example, from 220 V to 80 V, and the rising trend of the inductive load current is forcibly suppressed.

[0061] Referring to Figure 6In some embodiments, such as the present embodiment, the method further comprises steps S150-S151.

[0062] S150, obtaining the target current, and identifying the load characteristic of the load based on the target current;

[0063] S151, adjusting the preset current threshold based on the identified load characteristic.

[0064] In the embodiments of the present application, different loads have different load characteristics, for example, inductive loads have different impact forces according to their different load characteristics. The load characteristic of the inductive load can be identified according to the target current, and the preset current threshold is adjusted based on the identified load characteristic to adapt to the load characteristic of the inductive load, thereby avoiding false triggering caused by a fixed threshold.

[0065] Referring to Figure 7 In some embodiments, such as the present embodiment, the step S151 further comprises steps S1511-S1513.

[0066] S1511, if the load characteristic is strong impact, the preset current threshold is increased according to a first preset percentage;

[0067] S1512, if the load characteristic is medium impact, the preset current threshold is increased according to a second preset percentage;

[0068] S1513, if the load characteristic is weak impact, the preset current threshold is maintained unchanged.

[0069] In the embodiments of the present application, the load characteristic can include weak impact, medium impact and strong impact, and the load characteristic of the load can be identified according to the target current. For example, the load characteristic of the load can be identified by calculating the second derivative of the target current. When the second derivative is greater than or equal to 1000A / ms 2 , the load characteristic is strong impact, when the second derivative is less than 1000A / ms 2 and greater than 200A / ms 2 , the load characteristic is medium impact, and when the second derivative is less than or equal to 200A / ms 2 , the load characteristic is weak impact.

[0070] The preset current threshold corresponding to weak impact is a reference value, so when the load characteristic is medium impact, the preset current threshold can be increased by 20%, and when the load characteristic is strong impact, the preset current threshold can be increased by 50%.

[0071] Referring to Figure 8The application also provides a bidirectional off-grid and grid-connected energy storage inverter, which comprises a signal detection module 10, a power module 30 and a control module 20, wherein the control module 20 is configured with the bidirectional off-grid and grid-connected energy storage inverter impact load flexible starting method in any one of the above embodiments; the signal detection module 10 is connected with the control module 20 and used for collecting output current to obtain target current; and the control module 20 is connected with the power module 30 and used for generating a control signal according to the target current and controlling the power module 30 through the control signal.

[0072] Specifically, the bidirectional off-grid and grid-connected energy storage inverter is used for driving load operation, which can comprise a signal detection module 10, a control module 20 and a power module 30, wherein the signal detection module 10 is used for collecting input / output current, voltage and DC bus voltage and other key electrical parameters of the bidirectional off-grid and grid-connected energy storage inverter and outputting sampling results to the control module 20, so as to obtain target current. The control module 20 can be a DSP processing unit, which can comprise an ADC module and an EPWM module, and the control module 20 is built-in with SPWM and LLC algorithms, which are used for controlling the conduction and cutoff of the switching tubes in the power module 30.

[0073] As shown in Figure 9 , Figure 9 , a topology structure diagram of the bidirectional off-grid and grid-connected energy storage inverter, Figure 9 which comprises a power module 30 and a control module 20, wherein the power module 30 comprises a power factor correction circuit, an LLC resonant circuit, which comprises a primary side full bridge, a resonant cavity and a secondary side full bridge circuit. AC is an alternating current end, which is a grid input in charging mode and an inverter output in discharging mode, L1 is a boost inductor, C1 is an inverter output filter capacitor, QT1-QT4 are switching tubes of the PFC full bridge circuit, C2 is a bus circuit, QT5-QT8 are switching tubes of the LLC primary side full bridge circuit, the resonant cavity circuit comprises a resonant inductor Lr, a resonant capacitor Cr, an excitation inductor Lm and a transformer T, QT9-QT12 are switching tubes of the LLC secondary side full bridge circuit, C2 is a filter capacitor on the DC battery side, and BAT is a DC battery.

[0074] The control module 20 comprises a signal detection module 10, a DSP processing unit and a driving circuit, wherein the signal detection module 10 collects key electrical parameters such as input / output current, voltage and DC bus voltage in real time through a high-precision sensor. After the signal detection module 10 samples the output voltage and current, the signal is sent to the ADC module of the DSP processing unit, the ADC module converts the voltage value of 0 to 3.3V into an analog quantity of 0 to 4096, and the SPWM algorithm receives the analog quantity of the output voltage and current, and controls the switching time sequence of the PFC full-bridge circuit switch tube through the EPWM module of the DSP processing unit to make the system work at the rated output voltage. The front-stage LLC algorithm is the same, the signal detection module 10 samples the input current, voltage and bus voltage, and sends the signal to the DSP processing unit, and controls the switching time sequence of the primary full-bridge and secondary full-bridge switch tubes of the LLC resonant circuit through the algorithm to maintain the stability of the bus voltage.

[0075] The bidirectional off-grid and grid-connected energy storage inverter is used to drive a load, which can be connected to different types of loads, such as inductive loads, resistive loads and nonlinear loads. The current of the inductive load lags behind the voltage phase (PF < 1), and the electromagnetic energy storage characteristic causes the current to suddenly surge at the start-up moment, such as 5-10 times the rated value of the locked-rotor current. The current of the resistive load is in phase with the voltage (PF ≈ 1), and there is no start-up impact. The current waveform of the nonlinear load is distorted (contains high-order harmonics), the peak factor is high, but there is no phase delay.

[0076] When it is detected that the load connected to the bidirectional off-grid and grid-connected energy storage inverter is started, the output current of the bidirectional off-grid and grid-connected energy storage inverter is collected by the signal detection module 10 to obtain a target current. For example, the output current can be collected first to obtain an output current analog quantity, and then the output current analog quantity is converted into a digital signal by the ADC module in the control module 20 to obtain the target current.

[0077] The control module 20 can be provided with a threshold comparison module, a first preset PI controller and a second preset PI controller. The threshold comparison module is used to compare the target current with a preset current threshold, and select the first preset PI controller or the second preset PI controller based on the comparison result. The first preset PI controller can be a high-gain current closed-loop controller, and the second preset PI controller can be a low-gain voltage closed-loop controller. The PI controller obtains the amplitude of the modulation wave in the sinusoidal pulse width modulation (SPWM) algorithm by comparing the error between the actual value and the target value, and then obtains the switching time sequence of the full-bridge inverter circuit switch tube by comparing the modulation wave with the carrier wave.

[0078] When the target current is greater than or equal to the preset current threshold, the control module 20 selects a high-gain current closed-loop controller as a target controller, generates a control signal according to a modulation wave amplitude attenuation amount, and controls the power module 30 based on the control signal.

[0079] The disclosed bidirectional off-grid energy storage inverter impact load flexible starting method and bidirectional off-grid energy storage inverter can collect the output current of the bidirectional off-grid energy storage inverter to obtain a target current when the load starts, and when the target current is greater than or equal to a preset current threshold, a first preset PI controller is selected as a target controller, a control signal is generated according to a correction parameter of a modulation wave amplitude output by the target controller, and then the bidirectional off-grid energy storage inverter is controlled based on the generated control signal to realize flexible starting, which not only can reduce the output voltage when the load starts to avoid overcurrent and over-power, but also can avoid overload or overcurrent protection.

[0080] It should be noted that those skilled in the art can clearly understand the specific implementation process of the bidirectional off-grid energy storage inverter and each unit, which can refer to the corresponding description in the foregoing method embodiments, and for the convenience and brevity of description, it will not be repeated here.

[0081] In the above embodiments, the description of each embodiment has its own emphasis, and the parts not described in detail in a certain embodiment can be referred to the related description of other embodiments.

[0082] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, these modifications and variations of the present application are intended to be included within the scope of the present application claims and their equivalent technologies. Therefore, the present application also intends to include these modifications and variations.

[0083] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited to this. Any skilled person in the art can easily think of various equivalent modifications or replacements within the technical range disclosed by the present application, and these modifications or replacements should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A method for flexible start-up of a bidirectional grid-connected and off-grid energy storage inverter under impact load, characterized in that, The method, applied to bidirectional off-grid and grid-connected energy storage inverters, includes: If the load connected to the bidirectional off-grid energy storage inverter is detected to start, the output current of the bidirectional off-grid energy storage inverter is collected to obtain the target current. If the target current is greater than or equal to a preset current threshold, then the first preset PI controller is used as the target controller. Obtain the correction parameter of the modulation wave amplitude value output by the target controller, and generate a control signal based on the correction parameter of the modulation wave amplitude value; The bidirectional off-grid and on-grid energy storage inverter is controlled based on the control signal to achieve flexible start-up.

2. The method as described in claim 1, characterized in that, The method further includes: Obtain the target current and the preset current threshold; If the target current threshold is greater than or equal to the preset current threshold, the bidirectional grid-connected and off-grid energy storage inverter is controlled to enter the flexible start-up working mode.

3. The method as described in claim 2, characterized in that, After the step of obtaining the target current and the preset current threshold, the method further includes: If the target current threshold is less than the preset current threshold, the bidirectional off-grid energy storage inverter is controlled to enter a steady-state normal operation mode.

4. The method as described in claim 3, characterized in that, The method further includes: In the steady-state normal operating mode, the second preset PI controller is used as the target controller.

5. The method as described in claim 4, characterized in that, The correction parameters for the modulation amplitude include the modulation amplitude increment and the modulation amplitude attenuation. The step of generating a control signal based on the correction parameters for the modulation amplitude includes: Confirm the current operating mode of the bidirectional grid-connected and off-grid energy storage inverter; If the bidirectional grid-connected and off-grid energy storage inverter is in the flexible start-up working mode, the modulation amplitude attenuation value output by the first preset PI controller is obtained, and the control signal is generated based on the modulation amplitude attenuation value.

6. The method as described in claim 5, characterized in that, After confirming the current operating mode of the bidirectional grid-connected and off-grid energy storage inverter, the method further includes: If the bidirectional grid-connected and off-grid energy storage inverter is in the steady-state normal operation mode, the modulation amplitude increment output by the second preset PI controller is obtained, and the control signal is generated based on the modulation amplitude increment.

7. The method as described in claim 1, characterized in that, The method further includes: Obtain the target current and identify the load characteristics of the load based on the target current; The preset current threshold is adjusted based on the identified load characteristics.

8. The method as described in claim 7, characterized in that, The step of adjusting the preset current threshold based on the identified load characteristics includes: If the load characteristic is a strong impact, then the preset current threshold is increased according to the first preset percentage; If the load characteristic is medium impact, then the preset current threshold is increased according to the second preset percentage; If the load characteristic is a weak impact, then the preset current threshold remains unchanged.

9. The method as described in claim 3, characterized in that, The method further includes: In the flexible start-up working mode, if the target current is detected to be less than the preset current threshold, the working mode of the bidirectional off-grid energy storage inverter is switched to the steady-state normal working mode.

10. A bidirectional grid-connected and off-grid energy storage inverter, characterized in that, The bidirectional off-grid energy storage inverter includes a signal detection module, a power module, and a control module. The control module is configured with the impact load flexible start-up method for the bidirectional off-grid energy storage inverter as described in any one of claims 1-9. The signal detection module is connected to the control module and is used to collect the output current to obtain the target current. The control module is connected to the power module and is used to generate a control signal based on the target current, and to control the power module through the control signal.

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