Grid-connected control method and off-grid control method for energy storage inverter system and load thereof

Abstract

The present application relates to a grid-connected control method and an off-grid control method for an energy storage inverter system and a load thereof. The grid-connected control method comprises: controlling power grid side switches of a plurality of energy storage inverters to be all opened, and controlling energy storage side switches of the plurality of energy storage inverters to be all closed; controlling the phase angle of an alternating current output voltage of each energy storage inverter to be synchronized and ahead of the phase angle of a power grid voltage, and controlling the amplitude of the alternating current output voltage of each energy storage inverter to synchronously increase until the amplitude of the alternating current output voltage is higher than the amplitude of the power grid voltage; and controlling the power grid side switches of the plurality of energy storage inverters to be all closed, and after the power grid side switches of the plurality of energy storage inverters are all closed, controlling the energy storage side switches of the plurality of energy storage inverters to be all opened. By means of the present invention, the problem in the related art of low service life of power grid side switches and energy storage side switches of an energy storage inverter system in which a plurality of energy storage inverters are connected in parallel is solved, prolonging the service life of the power grid side switches and the energy storage side switches.

Description

Energy storage inverter system and grid-connected control method and off-grid control method of its load Technical Field

[0001] The present application relates to the technical field of energy storage inverters, and in particular to a grid-connected control method and an off-grid control method of an energy storage inverter system and its load. Background Art

[0002] Due to the maximum output power limitation of a single energy storage inverter, in order to meet the needs of high-power loads, the energy storage inverter system can use multiple energy storage inverters in parallel to increase the load capacity of the energy storage inverter system. However, when connecting the load powered by the energy storage inverter system to the grid to draw power from the grid, the relevant technology usually adopts the method of first disconnecting the energy storage side switch of each energy storage inverter and then closing the grid side switch of each energy storage inverter. During this process, it is necessary to strictly ensure that the energy storage side switch of each energy storage inverter is disconnected at the same time, and the grid side switch of each energy storage inverter is closed at the same time. Otherwise, excessive current will flow through the energy storage side switch that is disconnected last and the grid side switch that is closed first, causing damage to the switches or shortening their lifespan.

[0003] Summary of the Invention

[0004] The grid-connected control method and off-grid control method of the energy storage inverter system and its load provided in the embodiments of the present invention at least solve the problem of low life of the grid-side switch and energy storage-side switch of the energy storage inverter system with multiple energy storage inverters connected in parallel in the related art.

[0005] A method for controlling the grid connection of a load of an energy storage inverter system, wherein the energy storage inverter system comprises: a plurality of energy storage inverters arranged in parallel, each of the energy storage inverters being connected to a grid and a load, and each of the energy storage inverters comprising a grid-side switch and an energy storage-side switch; the method for controlling the grid connection of a load of the energy storage inverter system comprises:

[0006] Controlling the grid-side switches of the plurality of energy storage inverters to be disconnected, and controlling the energy storage-side switches of the plurality of energy storage inverters to be closed;

[0007] Controlling the phase angle of the AC output voltage of each of the energy storage inverters to be synchronous and ahead of the phase angle of the grid voltage, and controlling the amplitude of the AC output voltage of each of the energy storage inverters to increase synchronously until it is higher than the amplitude of the grid voltage;

[0008] The grid-side switches of the multiple energy storage inverters are controlled to be closed, and after the grid-side switches of the multiple energy storage inverters are closed, the energy storage-side switches of the multiple energy storage inverters are controlled to be opened.

[0009] In some embodiments, the method further includes: determining the number of the plurality of energy storage inverters in the energy storage inverter system according to the rated power of the load and the rated output power of the energy storage inverter.

[0010] In some embodiments, controlling the phase angle of the AC output voltage of each energy storage inverter to be synchronized and ahead of the phase angle of the grid voltage includes:

[0011] Obtaining a phase angle of the grid voltage by phase-locking the grid voltage;

[0012] Obtaining a tracking phase angle of the AC output voltage of the energy storage inverter based on the phase angle of the grid voltage and a set phase angle increment;

[0013] Based on the tracking phase angle and the initial amplitude, the AC output voltage of each of the energy storage inverters is modulated so that the phase angle of the AC output voltage of each of the energy storage inverters leads the phase angle of the grid voltage.

[0014] In some embodiments, controlling the amplitude of the AC output voltage of each energy storage inverter to increase synchronously until it is higher than the amplitude of the grid voltage includes:

[0015] collecting the amplitude of the grid voltage, and obtaining a target amplitude of the AC output voltage of the energy storage inverter based on the amplitude of the grid voltage and a set amplitude increment;

[0016] The initial amplitude is increased according to a set amplitude increase rate, and the AC output voltage of each energy storage inverter is modulated based on the tracking phase angle and the increased initial amplitude until the target amplitude is reached.

[0017] In some embodiments, the phase angle increment is determined based on the leading phase angle required to make the current value of the inductor connected in series at the AC end of the energy storage inverter less than the rated current of the energy storage inverter and approaching 0 under the current frequency and amplitude of the grid voltage.

[0018] In some embodiments, the phase angle increment has a value range of 0.5° to 3°.

[0019] In some embodiments, the amplitude increment range includes: 1V to 5V.

[0020] A method for controlling an off-grid load of an energy storage inverter system, the energy storage inverter system comprising: a plurality of energy storage inverters arranged in parallel, each of the energy storage inverters being connected to a grid and a load, and each of the energy storage inverters comprising a grid-side switch and an energy storage-side switch; the method for controlling an off-grid load of the energy storage inverter system comprising:

[0021] When the grid-side switches of the multiple energy storage inverters are closed and the load is powered by the grid, controlling the energy storage-side switches of the multiple energy storage inverters to be opened;

[0022] Controlling the phase angle of the AC output voltage of each of the energy storage inverters to be synchronized and ahead of the phase angle of the grid voltage, and controlling the amplitude of the AC output voltage of each of the energy storage inverters to be higher than the amplitude of the grid voltage;

[0023] Controlling the energy storage side switches of the multiple energy storage inverters to be closed, and after the energy storage side switches of the multiple energy storage inverters are closed, controlling the grid side switches of the multiple energy storage inverters to be opened;

[0024] The amplitude of the AC output voltage of each energy storage inverter is controlled to decrease according to a set amplitude reduction rate until the load stops working.

[0025] In some embodiments, the method further includes: determining the number of the plurality of energy storage inverters in the energy storage inverter system according to the rated power of the load and the rated output power of the energy storage inverter.

[0026] In some embodiments, controlling the phase angle of the AC output voltage of each energy storage inverter to be synchronized and ahead of the phase angle of the grid voltage, and controlling the amplitude of the AC output voltage of each energy storage inverter to be higher than the amplitude of the grid voltage includes:

[0027] By performing phase locking on the grid voltage, a phase angle of the grid voltage is obtained, and an amplitude of the grid voltage is collected;

[0028] Obtaining a tracking phase angle of the AC output voltage of the energy storage inverter based on the phase angle of the grid voltage and a set phase angle increment, and obtaining a tracking amplitude of the AC output voltage of the energy storage inverter based on the amplitude of the grid voltage and a set amplitude increment;

[0029] Based on the tracking phase angle and the tracking amplitude, the AC output voltage of each of the energy storage inverters is modulated so that the phase angle of the AC output voltage of each of the energy storage inverters leads the phase angle of the grid voltage, and the amplitude of the AC output voltage of each of the energy storage inverters is higher than the amplitude of the grid voltage.

[0030] In some embodiments, the phase angle increment is determined based on the leading phase angle required to make the current value of the inductor connected in series at the AC end of the energy storage inverter less than the rated current of the energy storage inverter and approaching 0 under the current frequency and amplitude of the grid voltage.

[0031] In some embodiments, the phase angle increment has a value range of 0.5° to 3°.

[0032] In some embodiments, the amplitude increment range includes: 1V to 5V.

[0033] An energy storage inverter system comprises: a plurality of energy storage inverters arranged in parallel, each of the energy storage inverters being connected to a power grid and a load, respectively, and each of the energy storage inverters comprising a grid-side switch and an energy storage-side switch; the energy storage inverter system is used to execute the above-mentioned method.

[0034] An electronic device includes: a processor and a memory storing a program, wherein the program includes instructions, and when the instructions are executed by the processor, the processor executes the above method.

[0035] A non-transitory machine-readable medium storing computer instructions, wherein the computer instructions are used to cause the computer to execute the above method.

[0036] The embodiments of the present invention provide a grid-connected control method and an off-grid control method for an energy storage inverter system and its load, which solves the problem of low service life of the grid-side switches and energy storage-side switches of an energy storage inverter system in which multiple energy storage inverters are connected in parallel in the related art by controlling the grid-side switches of multiple energy storage inverters to be disconnected and the energy storage-side switches of multiple energy storage inverters to be closed; controlling the phase angle of the AC output voltage of each energy storage inverter to be synchronized and ahead of the phase angle of the grid voltage, and controlling the amplitude of the AC output voltage of each energy storage inverter to be synchronously increased until it is higher than the amplitude of the grid voltage; controlling the grid-side switches of multiple energy storage inverters to be closed, and after the grid-side switches of multiple energy storage inverters are closed, controlling the energy storage-side switches of multiple energy storage inverters to be disconnected.

[0037] The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below so that other features, objects, and advantages of the invention are more readily apparent. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] To more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other embodiments can be derived from these drawings without inventive effort.

[0039] FIG1 is a schematic structural diagram of the energy storage inverter system of this embodiment.

[0040] FIG2 is a flow chart of a method for controlling grid connection of a load of the energy storage inverter system according to this embodiment.

[0041] FIG3 is a schematic diagram showing an increase in the amplitude of the AC output voltage of the energy storage inverter according to this embodiment.

[0042] FIG4 is a flow chart of the off-grid load control method of the energy storage inverter system of this embodiment. DETAILED DESCRIPTION

[0043] The following describes embodiments of the present invention in more detail with reference to the accompanying drawings. Although certain embodiments of the present invention are shown in the accompanying drawings, it should be understood that the present invention can be implemented in various forms and should not be construed as being limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and complete understanding of the present invention. It should be understood that the accompanying drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0044] In the power system, power loads (also known as power loads) are divided into multiple levels according to their importance, such as important loads and general loads. Compared with general loads, the power system needs to ensure stable and reliable power supply for important loads to avoid significant economic losses. Important loads are powered by two or more independent power sources to ensure that in the event of a power failure, they can switch to another power source to maintain power supply to the important loads. In the case of a large power load, a single energy storage inverter cannot provide sufficient power, and multiple energy storage inverters need to be used in parallel to power the important loads.

[0045] Figure 1 is a structural schematic diagram of the energy storage inverter system of this embodiment. As shown in Figure 1, the energy storage inverter system includes a plurality of energy storage inverters 10 arranged in parallel. Each energy storage inverter 10 is connected to a power grid 20 and a load 30, respectively. Each energy storage inverter 10 includes a grid-side switch 11 and an energy storage-side switch 12.

[0046] When grid 20 fails, the energy storage inverter system operates in an off-grid state. The grid-side switches 11 of multiple energy storage inverters 10 are disconnected, while the energy storage-side switches 12 are closed. Each of the multiple energy storage inverters 10 outputs power to load 30, and load 30 operates normally. When grid 20 returns to normal, the energy storage inverter system switches from off-grid to on-grid operation. First, the energy storage-side switch 12 is disconnected, halting load 30 operation. Then, the grid-side switch 11 is closed. When grid-side switch 11 is closed, a transient high current surge, which should be evenly shared by all grid-side switches 11, is generated on the first switch closed, causing damage to the switch or shortening its lifespan.

[0047] To this end, this embodiment provides a method for controlling the grid connection of a load of an energy storage inverter system. FIG2 is a flow chart of the method for controlling the grid connection of a load of an energy storage inverter system according to this embodiment. As shown in FIG2 , the flow chart includes the following steps:

[0048] Step S201 : Controlling the grid-side switches of a plurality of energy storage inverters to be disconnected, and controlling the energy storage-side switches of a plurality of energy storage inverters to be closed.

[0049] Step S202 , controlling the phase angle of the AC output voltage of each energy storage inverter to be synchronized and ahead of the phase angle of the grid voltage, and controlling the amplitude of the AC output voltage of each energy storage inverter to be synchronously increased until it is higher than the amplitude of the grid voltage.

[0050] Step S203 : Controlling the grid-side switches of the plurality of energy storage inverters to be closed, and after the grid-side switches of the plurality of energy storage inverters are closed, controlling the energy storage-side switches of the plurality of energy storage inverters to be opened.

[0051] Through the above steps, multiple energy storage inverters are first connected in parallel to power the load. After the phase angle of the AC output voltage of each energy storage inverter leads the phase angle of the grid voltage and the amplitude is higher than the amplitude of the grid voltage, the load is started and begins stable operation. Thereafter, the grid-side switch of the energy storage inverter is controlled to close. When the grid-side switch is closed, because the phase angle of the AC output voltage of the energy storage inverter leads the grid voltage and the amplitude is higher than the grid voltage, its output power is slightly greater than the output power provided by the grid at each grid-side switch. Even if all grid-side switches are not closed at the same time, the current change generated by the grid-side switch at the moment of closing will not exceed the current provided to the load by a single energy storage inverter before grid connection. After that, when the energy storage side switch of the energy storage inverter is controlled to be disconnected, even if all the energy storage side switches are not disconnected at the same time, at the moment the energy storage side switch is disconnected, the current change generated on the grid side switch will not exceed the current provided to the load by a single energy storage inverter before being connected to the grid, thereby avoiding large current shocks on the grid side switch and avoiding damage to the grid side switch or reduction in life.

[0052] Since the phase angle of the AC output voltage of each energy storage inverter is ahead of the grid voltage and the amplitude is higher than the grid voltage, at the moment the grid-side switch is closed, it can also prevent the grid energy from flowing back into the energy storage inverter and causing damage to the energy storage inverter.

[0053] FIG3 is a schematic diagram illustrating the increase in the amplitude of the AC output voltage of the energy storage inverter of this embodiment. As shown in FIG3 , in step S202, the amplitude of the AC output voltage of each energy storage inverter is synchronously increased from small to large, rather than directly controlling the energy storage inverter to output at an amplitude higher than the grid voltage. This avoids the problem of unsynchronized output of different energy storage inverters, which could cause energy from the first output energy storage inverter to flow back into the later output energy storage inverter, thereby damaging the later output energy storage inverter.

[0054] Prior to step S201, the number of energy storage inverters in the energy storage inverter system is determined based on the rated power of the loads and the rated output power of the energy storage inverters. The sum of the rated output powers of the multiple energy storage inverters is not less than the rated power of the loads. The loads may be all loads or loads operating in the current time period determined based on load operating patterns.

[0055] In the related art, the number of energy storage inverters to be connected in parallel is determined by real-time detection of load power. However, since the output power of the energy storage inverter gradually increases in step S202, the real-time detection during this process is not the actual load power (some loads are not yet operating due to insufficient power). When the actual power demand of the loads exceeds the sum of the maximum output powers of the currently connected energy storage inverters, additional energy storage inverters need to be added. These newly added energy storage inverters cannot be directly connected in parallel but must maintain phase and amplitude synchronization with the other energy storage inverters, resulting in complex control. In comparison, the above embodiment determines the number of multiple energy storage inverters from the energy storage inverter system based on the rated power of all loads or loads operating in the current time period and the rated output power of the energy storage inverters to ensure that the sum of the output power of the multiple energy storage inverters can meet the power demand of the loads. This avoids the complex and time-consuming control issues caused by adding new energy storage inverters in parallel during the grid connection process and also avoids real-time estimation of load power.

[0056] For example, if the rated power of the load running in the current time period is 50kW and the rated output power of a single energy storage inverter is 5kW, at least 10 energy storage inverters should be selected for parallel operation to meet the load's power requirements. The current time period must be no less than the total time required for the load to be connected to the grid.

[0057] The AC output voltage of the energy storage inverter has the same frequency as the grid voltage, for example, both are 50 Hz or 60 Hz.

[0058] In some embodiments, the energy storage inverter operates in voltage source mode, and the energy storage inverter outputs a sinusoidal voltage with a certain frequency and amplitude. In voltage source mode, each AC terminal of the energy storage inverter is connected in series with an inductor that acts as a buffer.

[0059] In this embodiment, the phase angle of the AC output voltage of the energy storage inverter is achieved by phase-locking the grid voltage and modulating the AC output voltage of the energy storage inverter. In step S202, controlling the phase angle of the AC output voltage of each energy storage inverter to be synchronized and ahead of the phase angle of the grid voltage includes: obtaining the phase angle of the grid voltage by phase-locking the grid voltage; obtaining a tracking phase angle of the AC output voltage of the energy storage inverter based on the phase angle of the grid voltage and a set phase angle increment; and modulating the AC output voltage of each energy storage inverter based on the tracking phase angle and the initial amplitude, so that the phase angle of the AC output voltage of each energy storage inverter leads the phase angle of the grid voltage.

[0060] The phase angle of the grid voltage is obtained by phase-locking the grid voltage. The phase-locked angle obtained by the phase-locked loop is the phase angle of the grid voltage. The initial amplitude of the grid voltage can be set to 1V to 5V, for example.

[0061] In order to make the phase angle of the AC output voltage of the energy storage inverter lead the grid voltage, in this embodiment, the phase angle increment is increased above the phase angle of the grid voltage. Obtain a tracking phase angle of the AC output voltage of the energy storage inverter. Based on the tracking phase angle and the initial amplitude, modulate the AC output voltage of the energy storage inverter so that the phase angle of the AC output voltage of the energy storage inverter leads the phase angle of the grid voltage. At this time, the amplitude of the AC output voltage of the energy storage inverter is the initial amplitude, which is much smaller than the amplitude of the grid voltage.

[0062] For example, the modulation process of the AC output voltage of the energy storage inverter of this embodiment includes the following steps:

[0063] Step 1: Sample the grid voltage and phase-lock to obtain the phase angle cos(wt) of the grid voltage, where w is the grid frequency and t is time.

[0064] Step 2: Add the phase angle increment to the grid voltage phase angle cos(wt) Get the tracking phase angle Get the initial amplitude E0.

[0065] Step 3: Use the modulated signal The AC output voltage of the energy storage inverter is modulated, and the AC output voltage of the energy storage inverter reaches the initial amplitude E0 by changing the amplitude M of the modulation signal.

[0066] Through the above steps, the phase angle of the AC output voltage of the energy storage inverter is ahead of the phase angle of the grid voltage. At the same time, the AC output current is much smaller than the amplitude of the grid voltage, so as to avoid energy backflow between the energy storage inverters due to excessively high voltage amplitude and asynchronous modulation.

[0067] After the phase angles and amplitudes of the AC output voltages of the multiple energy storage inverters are modulated to the same value, amplitude modulation is further performed. In some embodiments, in step S202, controlling the amplitude of the AC output voltage of each energy storage inverter to increase synchronously until it exceeds the amplitude of the grid voltage includes: collecting the amplitude of the grid voltage, and obtaining a target amplitude of the AC output voltage of the energy storage inverter based on the amplitude of the grid voltage and a set amplitude increment; increasing the initial amplitude according to a set amplitude increase rate, and modulating the AC output voltage of each energy storage inverter based on the tracked phase angle and the increased initial amplitude until the target amplitude is reached.

[0068] For example, the amplitude modulation process of the AC output voltage of the energy storage inverter of this embodiment includes the following steps:

[0069] Step 1: Collect the amplitude of the grid voltage V G ; Get the amplitude increment ΔE.

[0070] Step 2: The amplitude of the grid voltage E G Increase the amplitude increment ΔE to obtain the target amplitude E G +ΔE.

[0071] Step 3: Obtain the amplitude increase rate e.

[0072] Step 4: Determine the tracking amplitude at time t as E0+et, and calculate the modulation amplitude M based on the tracking amplitude E0+et.

[0073] Step 5: Use the modulated signal The AC output voltage of the energy storage inverter is modulated so that the AC output voltage of the energy storage inverter reaches the tracking amplitude E0+et.

[0074] Step 6: Repeat steps 4 to 5 until the tracking amplitude E0+et reaches the target amplitude E G +ΔE.

[0075] The above steps ensure that the amplitude of the AC output voltage of the energy storage inverter is higher than the amplitude of the grid voltage.

[0076] The phase angle increment is determined based on the advanced phase angle required to make the current value of the inductor connected in series with the AC end of the energy storage inverter less than the rated current of the energy storage inverter and approaching 0 under the current frequency and amplitude of the grid voltage.

[0077] In this embodiment, ΔE is sufficiently small compared to the grid voltage E. To illustrate the relationship between the inductor's inductance and the phase angle increment, taking the example of a case where there is only a phase difference but no voltage difference between the energy storage inverter and the grid, the current flowing through the inductor connected in series with the AC end of the energy storage inverter, which acts as a buffer, is simplified to the following formula:

[0078] Where, E is the amplitude of the grid voltage, is the phase angle increment, w is the grid voltage frequency, and L is the inductor's inductance. The grid voltage amplitude and frequency are constants, so a larger inductor's inductance allows for a larger phase angle increment.

[0079] The minimum value of the phase angle increment is determined by the PWM interruption period of the energy storage inverter. For example, for an energy storage inverter with a PWM interruption period of 20 kHz, the minimum value of the phase angle increment is 0.9°.

[0080] In a power system with a grid voltage of 220V and a grid frequency of 50Hz, the aforementioned amplitude increment and phase angle increment ranges can be determined based on the selection of switching devices and snubber inductors used in the energy storage inverter. For example, in this embodiment, the amplitude increment ranges from 1V to 5V, and the phase angle increment ranges from 0.5° to 3°.

[0081] Taking the energy storage inverter with a buffer inductance of 2mH and a PWM interruption period of 20kHz as an example, the current flowing through the inductor calculated based on the above formula (1) is 5.5A, which is lower than the rated output current of the energy storage inverter.

[0082] Continuing with Figure 1 , after load 30 is connected to the grid and supplied by grid 20, if it is necessary to disconnect load 30, grid-side switch 11 is disconnected. When grid-side switch 11 is disconnected, a transient high current surge, which should be evenly shared by all grid-side switches 11, is generated on the last switch to be disconnected, potentially damaging the switch or reducing its lifespan.

[0083] To this end, this embodiment provides a method for controlling the off-grid load of an energy storage inverter system. FIG4 is a flow chart of the method for controlling the off-grid load of an energy storage inverter system of this embodiment. As shown in FIG4 , the flow chart includes the following steps:

[0084] Step S401 : When the grid-side switches of the plurality of energy storage inverters are closed and the load is powered by the grid, the energy storage-side switches of the plurality of energy storage inverters are controlled to be open.

[0085] Step S402 , controlling the phase angle of the AC output voltage of each energy storage inverter to be synchronized and ahead of the phase angle of the grid voltage, and controlling the amplitude of the AC output voltage of each energy storage inverter to be higher than the amplitude of the grid voltage.

[0086] Step S403 : Controlling the energy storage side switches of the multiple energy storage inverters to be closed, and after the energy storage side switches of the multiple energy storage inverters are closed, controlling the grid side switches of the multiple energy storage inverters to be opened.

[0087] Step S404 , controlling the amplitude of the AC output voltage of each energy storage inverter to decrease according to a set amplitude reduction rate until the load stops working.

[0088] Through the above steps, the phase angles of the AC output voltages of the multiple energy storage inverters are first controlled to lead the phase angle of the grid voltage and to have amplitudes greater than the amplitude of the grid voltage. The energy storage-side switches of the multiple energy storage inverters are then controlled to close. Even if all the energy storage-side switches are not closed at the same time, at the moment the energy storage-side switches are closed, the current change generated by the energy storage-side switches will not exceed the current provided by the grid to the load via the grid-side switches of the energy storage inverters. The grid-side switches of the multiple energy storage inverters are then controlled to open. Even if all the grid-side switches are not opened at the same time, at the moment the grid-side switches are opened, the current change generated by the energy storage-side switches will not exceed the current provided by the grid to the load via the grid-side switches of the energy storage inverters. Thereafter, the amplitudes of the AC output voltages of the energy storage inverters are synchronously reduced according to the set amplitude reduction rate, rather than directly shutting down the energy storage inverters. This avoids the problem of overload damage to some energy storage inverters due to asynchronous shutdown of multiple energy storage inverters, or damage or reduced lifespan of the corresponding energy storage-side inverters due to excessive current.

[0089] Since the phase angle of the AC output voltage of each energy storage inverter is ahead of the grid voltage and the amplitude is higher than the grid voltage, at the moment the energy storage side switch is closed, it can also avoid the problem of grid energy backflowing into the energy storage inverter and causing damage to the energy storage inverter.

[0090] Prior to step S401, the number of energy storage inverters in the energy storage inverter system is determined based on the rated power of the loads and the rated output power of the energy storage inverters. The sum of the rated output powers of the multiple energy storage inverters is not less than the rated power of the loads. The loads may be all loads or loads operating in the current time period determined based on load operating patterns.

[0091] In other embodiments, the number of multiple energy storage inverters in the energy storage inverter system may also be determined by detecting the output power of the grid to the load and the rated output power of the energy storage inverter when the load is powered by the grid.

[0092] For example, when it is detected that the grid's output power to the load is 50kW and the rated output power of a single energy storage inverter is 5kW, at least 10 energy storage inverters are selected for off-grid control so that when the energy storage inverters operate in parallel to supply power to the load, the load's power demand is met, thereby avoiding a large current shock on the energy storage side switch when the grid side switch is disconnected, or overload damage to the energy storage inverter.

[0093] The AC output voltage of the energy storage inverter has the same frequency as the grid voltage, for example, both are 50 Hz or 60 Hz.

[0094] In some embodiments, the energy storage inverter operates in voltage source mode, and the energy storage inverter outputs a sinusoidal voltage with a certain frequency and amplitude. In voltage source mode, each AC terminal of the energy storage inverter is connected in series with an inductor that acts as a buffer.

[0095] In this embodiment, by phase-locking the grid voltage and modulating the AC output voltage of the energy storage inverter, the phase angle of the AC output voltage of the energy storage inverter is advanced over the phase angle of the grid voltage, and the amplitude of the AC output voltage of the energy storage inverter is higher than the amplitude of the grid voltage.

[0096] The phase angle of the grid voltage is obtained by phase-locking the grid voltage. The phase angle obtained by the phase-locked loop is the phase angle of the grid voltage. The amplitude of the grid voltage is collected at the output end of the grid by the current sensor. In order to make the phase angle of the AC output voltage of the energy storage inverter lead the grid voltage, and the amplitude of the AC output voltage of the energy storage inverter higher than the grid voltage, in this embodiment, a phase angle increment is added to the phase angle of the grid voltage. The tracking phase angle of the AC output voltage of the energy storage inverter is obtained; the tracking amplitude of the AC output voltage of the energy storage inverter is obtained by adding an amplitude increment ΔV to the amplitude of the grid voltage. Finally, based on the tracking phase angle and the tracking amplitude, the AC output voltage of the energy storage inverter is modulated so that the phase angle of the AC output voltage of the energy storage inverter leads the phase angle of the grid voltage and the amplitude of the AC output voltage of the energy storage inverter is higher than the amplitude of the grid voltage.

[0097] For example, the modulation process of the AC output voltage of the energy storage inverter of this embodiment includes the following steps:

[0098] Step 1: Sample the grid voltage and phase-lock to obtain the grid voltage phase angle cos(wt), where w is the grid frequency and t is time; collect the grid voltage amplitude V G .

[0099] Step 2: Add the phase angle increment to the grid voltage phase angle cos(wt) Get the tracking phase angle The amplitude of the grid voltage E G Add the amplitude increment ΔE to obtain the tracking amplitude E G +ΔE.

[0100] Step 3: Use the modulated signal The AC output voltage of the energy storage inverter is modulated, and the AC output voltage of the energy storage inverter reaches the tracking amplitude E by changing the amplitude M of the modulation signal. G +ΔE.

[0101] Through the above steps, the phase angle of the AC output voltage of the energy storage inverter is ahead of the phase angle of the grid voltage, and the amplitude of the AC output voltage of the energy storage inverter is higher than the amplitude of the grid voltage.

[0102] The phase angle increment is determined based on the leading phase angle required to make the current value of the inductor connected in series with the AC end of the energy storage inverter, which acts as a buffer, less than the rated current of the energy storage inverter and approaching 0 under the current frequency and amplitude of the grid voltage.

[0103] In this embodiment, ΔE is sufficiently small compared to the grid voltage E. To illustrate the relationship between the inductor's inductance and the phase angle increment, taking the example of a case where there is only a phase difference but no voltage difference between the energy storage inverter and the grid, the current flowing through the inductor connected in series with the AC end of the energy storage inverter, which acts as a buffer, is simplified to the following formula:

[0104] Where, E is the amplitude of the grid voltage, is the phase angle increment, w is the grid voltage frequency, and L is the inductor's inductance. The grid voltage amplitude and frequency are constants, so a larger inductor's inductance allows for a larger phase angle increment.

[0105] The minimum value of the phase angle increment is determined by the PWM interruption period of the energy storage inverter. For example, for an energy storage inverter with a PWM interruption period of 20 kHz, the minimum value of the phase angle increment is 0.9°.

[0106] In a power system with a grid voltage amplitude of 220V and a grid frequency of 50Hz, the aforementioned amplitude increment and phase angle increment ranges can be obtained based on the different selections of the switching devices and snubber inductors used in the energy storage inverter. For example, in this embodiment, the aforementioned amplitude increment ranges from 1V to 5V, and the aforementioned phase angle increment ranges from 0.5° to 3°.

[0107] Taking the energy storage inverter with a buffer inductance of 2mH and a PWM interruption period of 20kHz as an example, the current flowing through the inductor calculated based on the above formula (1) is 5.5A, which is lower than the rated output current of the energy storage inverter.

[0108] This embodiment also provides an energy storage inverter system, comprising: a plurality of energy storage inverters arranged in parallel, each energy storage inverter being connected to a grid and a load respectively, and each energy storage inverter comprising a grid-side switch and an energy storage-side switch; wherein the energy storage inverter system is used to execute the above-mentioned grid-connected control method and / or off-grid control method.

[0109] This embodiment further provides an electronic device, comprising: at least one processor; and a memory communicatively connected to the at least one processor. The memory stores a computer program executable by the at least one processor, wherein the computer program, when executed by the at least one processor, causes the electronic device to perform the grid-connected control method and / or the off-grid control method according to an embodiment of the present invention.

[0110] This embodiment further provides a non-transitory machine-readable medium storing a computer program, wherein the computer program, when executed by a processor of a computer, is used to enable the computer to execute the grid-connected control method and / or off-grid control method of the embodiments of the present invention.

[0111] It should be noted that the term "including" and its variations used in the embodiments of the present invention are open-ended, i.e., "including but not limited to." The term "based on" means "based at least in part on." The term "one embodiment" means "at least one embodiment"; the term "another embodiment" means "at least one other embodiment"; and the term "some embodiments" means "at least some embodiments." The modifications of "one" and "a plurality of" mentioned in the embodiments of the present invention are illustrative and non-restrictive. Those skilled in the art should understand that, unless the context clearly indicates otherwise, they should be understood as "one or more."

[0112] The various steps described in the method implementation scheme provided in the embodiments of the present invention may be performed in different orders and / or in parallel. In addition, the method implementation scheme may include additional steps and / or omit the steps shown. The scope of protection of the present invention is not limited in this respect.

[0113] The term "embodiment" in this specification refers to specific features, structures, or characteristics described in conjunction with the embodiment that can be included in at least one embodiment of the present invention. The appearance of this phrase in various places in the specification does not necessarily mean the same embodiment, nor does it mean that it is mutually exclusive with other embodiments and is independent or optional. The various embodiments in this specification are described in a related manner, and the same or similar parts between the various embodiments are referenced to each other. In particular, for the embodiments of the device, equipment, and system, since they are basically similar to the method embodiments, the description is relatively simple, and the relevant parts are referred to the partial description of the method embodiment.

[0114] The above-described embodiments merely illustrate several implementations of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of the present invention. Therefore, the scope of the present invention shall be determined by the appended claims.

Claims

1. A method for controlling grid connection of a load of an energy storage inverter system, the energy storage inverter system comprising: A plurality of energy storage inverters are arranged in parallel, each of which is connected to a power grid and a load respectively, and each of which includes a power grid side switch and an energy storage side switch; characterized in that the grid connection control method of the load of the energy storage inverter system includes: Controlling the grid-side switches of the multiple energy storage inverters to be disconnected, and controlling the energy storage-side switches of the multiple energy storage inverters to be closed; Controlling the phase angle of the AC output voltage of each of the energy storage inverters to be synchronous and ahead of the phase angle of the grid voltage, and controlling the amplitude of the AC output voltage of each of the energy storage inverters to increase synchronously until it is higher than the amplitude of the grid voltage; The grid-side switches of the multiple energy storage inverters are controlled to be closed, and after the grid-side switches of the multiple energy storage inverters are closed, the energy storage-side switches of the multiple energy storage inverters are controlled to be opened.

2. The method according to claim 1, characterized in that The method further comprises: The number of the plurality of energy storage inverters is determined from the energy storage inverter system according to the rated power of the load and the rated output power of the energy storage inverter.

3. The method according to claim 1, characterized in that Controlling the phase angle of the AC output voltage of each of the energy storage inverters to be synchronized and ahead of the phase angle of the grid voltage includes: Obtaining a phase angle of the grid voltage by phase-locking the grid voltage; Based on the phase angle of the grid voltage and the set phase angle increment, obtaining a tracking phase angle of the AC output voltage of the energy storage inverter; Based on the tracking phase angle and the initial amplitude, the AC output voltage of each of the energy storage inverters is modulated so that the phase angle of the AC output voltage of each of the energy storage inverters leads the phase angle of the grid voltage.

4. The method according to claim 3, characterized in that Controlling the amplitude of the AC output voltage of each energy storage inverter to increase synchronously until it is higher than the amplitude of the grid voltage includes: Collecting the amplitude of the grid voltage, and obtaining the target amplitude of the AC output voltage of the energy storage inverter based on the amplitude of the grid voltage and a set amplitude increment; The initial amplitude is increased according to a set amplitude increase rate, and the AC output voltage of each energy storage inverter is modulated based on the tracking phase angle and the increased initial amplitude until the target amplitude is reached.

5. The method according to claim 3, characterized in that: The phase angle increment is determined based on the leading phase angle required to make the current value of the inductor connected in series at the AC end of the energy storage inverter less than the rated current of the energy storage inverter and approaching 0 under the current frequency and amplitude of the grid voltage.

6. The method according to claim 3, characterized in that The phase angle increment has a value range of 0.5° to 3°.

7. The method according to claim 4, characterized in that The value range of the amplitude increment includes: 1V~5V.

8. A method for controlling an off-grid load of an energy storage inverter system, the energy storage inverter system comprising: A plurality of energy storage inverters are arranged in parallel, each of which is connected to a power grid and a load respectively, and each of which includes a power grid side switch and an energy storage side switch; characterized in that the off-grid control method of the load of the energy storage inverter system includes: When the grid-side switches of the multiple energy storage inverters are closed and the load is powered by the grid, the multiple energy storage inverters are controlled. The energy storage side switches of the energy inverter are all disconnected; Controlling the phase angle of the AC output voltage of each of the energy storage inverters to be synchronized and ahead of the phase angle of the grid voltage, and controlling the amplitude of the AC output voltage of each of the energy storage inverters to be higher than the amplitude of the grid voltage; Controlling the energy storage side switches of the multiple energy storage inverters to be closed, and after the energy storage side switches of the multiple energy storage inverters are closed, controlling the grid side switches of the multiple energy storage inverters to be opened; The amplitude of the AC output voltage of each of the energy storage inverters is controlled to decrease according to a set amplitude reduction rate until the load stops working.

9. The method according to claim 8, characterized in that The method further comprises: The number of the plurality of energy storage inverters is determined from the energy storage inverter system according to the rated power of the load and the rated output power of the energy storage inverter.

10. The method according to claim 8, characterized in that Controlling the phase angle of the AC output voltage of each of the energy storage inverters to be synchronized and ahead of the phase angle of the grid voltage, and controlling the amplitude of the AC output voltage of each of the energy storage inverters to be higher than the amplitude of the grid voltage includes: By performing phase locking on the grid voltage, a phase angle of the grid voltage is obtained, and an amplitude of the grid voltage is collected; Based on the phase angle of the grid voltage and the set phase angle increment, a tracking phase angle of the AC output voltage of the energy storage inverter is obtained, and based on the amplitude of the grid voltage and the set amplitude increment, a tracking amplitude of the AC output voltage of the energy storage inverter is obtained; Based on the tracking phase angle and the tracking amplitude, the AC output voltage of each of the energy storage inverters is modulated so that the phase angle of the AC output voltage of each of the energy storage inverters leads the phase angle of the grid voltage, and the amplitude of the AC output voltage of each of the energy storage inverters is higher than the amplitude of the grid voltage.

11. The method according to claim 10, characterized in that The phase angle increment is determined based on the leading phase angle required to make the current value of the inductor connected in series at the AC end of the energy storage inverter less than the rated current of the energy storage inverter and approaching 0 under the current frequency and amplitude of the grid voltage.

12. The method according to claim 10, characterized in that The phase angle increment has a value range of 0.5° to 3°.

13. The method according to claim 10, characterized in that The value range of the amplitude increment includes: 1V~5V.

14. An energy storage inverter system, comprising: A plurality of energy storage inverters arranged in parallel, each of the energy storage inverters being connected to a grid and a load respectively, and each of the energy storage inverters comprising a grid-side switch and an energy storage-side switch; characterized in that the energy storage inverter system is used to execute the method described in any one of claims 1 to 7, and / or claims 8 to 13.

15. An electronic device, comprising: A processor, and a memory storing a program, characterized in that the program includes instructions, which, when executed by the processor, cause the processor to execute the method of any one of claims 1 to 7 and / or claims 8 to 13.

16. A non-transitory machine-readable medium storing computer instructions, characterized in that: The computer instructions are used to cause the computer to execute the method according to any one of claims 1 to 7 and / or claims 8 to 13.

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