Grid-connected power converter and power control method therefor, and energy storage system

Abstract

The present application provides a grid-connected power converter and a power control method therefor, and an energy storage system. In the grid-connected power converter, a controller is used for controlling, in response to the frequency of an alternating current grid being a first frequency, an output power of a power conversion circuit to be regulated to a first power from a preset reference power, wherein the first power is the sum of the preset reference power and a first inertia power. Furthermore, the controller is used for controlling, in response to the frequency of the alternating current grid being a second frequency, the output power of the power conversion circuit to be regulated to a second power from the first power, wherein the second power is the sum of the first power and a first frequency modulation frequency, and the absolute value of the difference between the second frequency and a power frequency of the alternating current grid is greater than the absolute value of the difference between the first frequency and the power frequency of the alternating current grid. By implementing the present application, more stable and accurate frequency support can be provided for an alternating current grid.

Description

Grid-connected power converter, power control method thereof, and energy storage system

[0001] This application claims priority to the Chinese patent application filed with the State Intellectual Property Office of China on June 13, 2023, with application number 202310702731.X, and priority to the Chinese patent application entitled “Grid-connected power converter, power control method thereof, and energy storage system”, all contents of which are incorporated by reference into this application. Technical Field

[0002] The present application relates to the field of photovoltaic energy storage technology, and in particular to a grid-connected power converter and a power control method thereof, as well as an energy storage system. Background Art

[0003] In photovoltaic or energy storage power generation, as the number of AC loads changes, the balance between the power output of the photovoltaic or energy storage generation and the power demand of the AC loads is disrupted, resulting in unstable AC frequency. For example, when this AC power is fed into the AC grid, when the AC frequency is less than 50Hz, the power output of the photovoltaic or energy storage generation is less than the power demand of the AC loads. When the AC frequency is greater than 50Hz, the power output of the photovoltaic or energy storage generation is greater than the power demand of the AC loads.

[0004] To maintain AC power frequency stability, current power converter control methods employ a grid forming (GFM) approach. This involves controlling the voltage amplitude and frequency output by the power converter to proactively provide frequency support for the AC grid. However, with current GFM methods, power converters are unable to provide stable frequency support for the AC grid.

[0005] Summary of the Invention

[0006] The present application provides a grid-connected power converter and a power control method thereof, as well as an energy storage system, which can enable the power grid to obtain more stable and accurate frequency support.

[0007] In a first aspect, the present application provides a grid-connected power converter, which includes a power conversion circuit and a controller, wherein a first end of the power conversion circuit is connected to a DC source through a DC bus, and a second end of the power conversion circuit is connected to an AC grid through an AC bus.

[0008] In a specific implementation, in response to the AC grid frequency being a first frequency, the controller controls the output power of the power conversion circuit to adjust from a preset reference power to a first power. The preset reference power is the output power of the power conversion circuit when the AC grid is stable, and the first power is the sum of the preset reference power and a first inertia power. The first inertia power is the power obtained by the power conversion circuit simulating the inertia characteristics of a synchronous generator. This first inertia power is generally related to the inherent properties of the grid-connected power converter and the degree of frequency fluctuation of the AC grid. Furthermore, in response to the AC grid frequency being a second frequency, the controller controls the output power of the power conversion circuit to adjust from the first power to a second power. The second power is the sum of the first power and the first frequency-modulated power, and the absolute value of the difference between the second frequency and the AC grid power frequency is greater than the absolute value of the difference between the first frequency and the AC grid power frequency. Furthermore, the first and second frequencies can be fixed values ​​or frequency ranges. Optionally, the AC grid power frequency is the frequency corresponding to the AC grid under normal operating conditions.

[0009] When the AC grid is underfrequency, the first frequency is less than the AC grid power frequency, and the first inertia power is positive. When the second frequency is less than the first frequency, the first frequency modulation power is positive. When the AC grid is overfrequency, the first frequency is greater than the AC grid power frequency, and the first inertia power is negative. When the second frequency is greater than the first frequency, the first frequency modulation power is negative.

[0010] When the frequency of the AC grid deviates from the AC grid working frequency, the AC grid can obtain rapid frequency support by preferentially superimposing the first inertia power on the basis of the preset reference power. When the frequency of the AC grid further deviates from the AC grid working frequency, the AC grid can obtain more stable and accurate frequency support by continuing to superimpose the first frequency modulation power on the basis of the preset reference power and the first inertia power.

[0011] In one possible implementation, when the AC grid is under-frequency, the second frequency is less than the AC grid power frequency. When the absolute value of the difference between the second frequency and the AC grid power frequency increases, the first frequency modulation power increases, that is, the value of the first frequency modulation power at this time increases. When the AC grid is over-frequency, the second frequency is greater than the AC grid power frequency. When the absolute value of the difference between the second frequency and the AC grid power frequency increases, the first frequency modulation power decreases, that is, the value of the first frequency modulation power at this time decreases. This configuration can provide dynamic frequency support for the AC grid when the degree of under-frequency or over-frequency of the AC grid gradually increases.

[0012] In one possible implementation, when the AC grid is underfrequency, the second frequency is less than the AC grid power frequency, and the second power is less than or equal to the maximum output power of the power conversion circuit. When the AC grid is overfrequency, the second frequency is greater than the AC grid power frequency, and the second power is greater than or equal to the minimum output power of the power conversion circuit. This configuration ensures that the output power of the power conversion circuit is within the rated safe power range, thereby improving the operational safety of the grid-connected power converter and the reliability of its support for the AC grid.

[0013] In one possible implementation, in response to the AC grid frequency being a third frequency, the controller controls the output power of the power conversion circuit to adjust from the second power to the third power. The third power is the difference between the second power and the first inertia power, and the absolute value of the difference between the third frequency and the AC grid power frequency is greater than the absolute value of the difference between the second frequency and the AC grid power frequency. When the AC grid is underfrequency, the third frequency is less than the AC grid power frequency and the third frequency is less than the second frequency. When the AC grid is overfrequency, the third frequency is greater than the AC grid power frequency and the third frequency is greater than the second frequency. It is understood that when the AC grid frequency is the third frequency, the first inertia power is withdrawn, thereby providing stable frequency support for the AC grid.

[0014] In one possible implementation, in response to the AC grid frequency changing from a third frequency to a fourth frequency, the controller controls the output power of the power conversion circuit to adjust from the third power to a fourth power. The fourth power is the power obtained by superimposing the second inertia power and the second frequency-modulated power on the third power, and the absolute value of the difference between the fourth frequency and the AC grid power frequency is less than the absolute value of the difference between the third frequency and the AC grid power frequency. The fourth frequency can be either a fixed value or a frequency range. When the AC grid is underfrequency, the fourth frequency is greater than the third frequency and less than the AC grid power frequency. In this case, the value of the second inertia power is negative, and the value of the second frequency-modulated power is positive. When the AC grid is overfrequency, the fourth frequency is less than the third frequency and greater than the AC grid power frequency. In this case, the value of the second inertia power is positive, and the value of the second frequency-modulated power is negative. Based on the same principle, such an arrangement can enable the grid-connected power converter to provide stable and accurate frequency support for the AC grid.

[0015] In one possible implementation, when the AC grid is under-frequency, the fourth frequency is less than the AC grid power frequency. When the absolute value of the difference between the fourth frequency and the AC grid power frequency decreases, the second frequency modulation power decreases, that is, the value of the second frequency modulation power decreases at this time. When the AC grid is over-frequency, the fourth frequency is greater than the AC grid power frequency. When the absolute value of the difference between the fourth frequency and the AC grid power frequency decreases, the second frequency modulation power increases, that is, the value of the second frequency modulation power increases at this time. This setting can provide dynamic frequency support for the AC grid when the degree of under-frequency or over-frequency of the AC grid gradually decreases.

[0016] In one possible implementation, when the AC grid is underfrequency, the fourth frequency is less than the AC grid power frequency, and the fourth power is greater than or equal to the minimum output power of the power conversion circuit. When the AC grid is overfrequency, the fourth frequency is greater than the AC grid power frequency, and the fourth power is less than or equal to the maximum output power of the power conversion circuit. This configuration ensures that the output power of the power conversion circuit is within the rated safe power range, thereby improving the operational safety of the grid-connected power converter and the reliability of its support for the AC grid.

[0017] In one possible implementation, in response to the AC grid frequency changing from the fourth frequency to the AC grid power frequency, the controller controls the output power of the power conversion circuit to adjust from the fourth power to a preset reference power. This configuration can provide dynamic frequency support for the AC grid as the AC grid frequency gradually recovers to the AC grid power frequency.

[0018] In one possible implementation, the first frequency modulation power is determined by the controller based on a preset power-frequency droop curve, including a preset reference power, the output power of the power conversion circuit, the frequency of the AC power grid, and a preset lower frequency limit, where the preset lower frequency limit is the minimum value of the first frequency. This configuration can improve the accuracy of the primary frequency modulation power.

[0019] In a second aspect, the present application provides an energy storage system, comprising an energy storage battery and a grid-connected power converter in combination with the first aspect or in combination with any one of the possible implementations of the first aspect. The energy storage battery is connected to a first end of a power conversion circuit via a DC bus. The power conversion circuit outputs DC power based on the DC power provided by the energy storage battery, or the power conversion circuit outputs DC power to the energy storage battery. It is understandable that the grid-connected power converter can provide more stable and accurate frequency support for the AC power grid when the AC power grid is under-frequency or over-frequency, thereby improving the power supply reliability and stability of the energy storage system and having strong applicability.

[0020] In a third aspect, the present application provides a power control method for a grid-connected power converter, the method comprising: in response to the frequency of the AC power grid being a first frequency, controlling the output power of the grid-connected power converter to adjust from a preset reference power to a first power; wherein the preset reference power is the output power of the grid-connected power converter when the AC power grid is stable, the first power is the sum of the preset reference power and a first inertia power, and the first inertia power is the power obtained by the grid-connected power converter simulating the inertia characteristics of a synchronous generator. Furthermore, in response to the frequency of the AC power grid being a second frequency, controlling the output power of the grid-connected power converter to adjust from the first power to a second power, wherein the second power is the sum of the first power and the first frequency-modulated power, and the absolute value of the difference between the second frequency and the AC power grid frequency is greater than the absolute value of the difference between the first frequency and the AC power grid frequency. The first frequency and the second frequency can be either fixed values ​​or frequency ranges. Optionally, the AC power grid frequency is the frequency corresponding to the normal operation of the power grid.

[0021] When the frequency of the AC grid deviates from the AC grid working frequency, the AC grid can obtain rapid frequency support by preferentially superimposing the first inertia power on the basis of the preset reference power. When the frequency of the AC grid further deviates from the AC grid working frequency, the AC grid can obtain more stable and accurate frequency support by continuing to superimpose the first frequency modulation power on the basis of the preset reference power and the first inertia power.

[0022] In one possible implementation, in response to the second frequency being less than the AC grid power frequency and the absolute value of the difference between the second frequency and the AC grid power frequency increasing, the first frequency modulation power is increased, i.e., the value of the first frequency modulation power is increased. In response to the second frequency being greater than the AC grid power frequency and the absolute value of the difference between the second frequency and the AC grid power frequency increasing, the first frequency modulation power is decreased, i.e., the value of the first frequency modulation power is decreased. This configuration can provide dynamic frequency support for the AC grid as the level of underfrequency or overfrequency of the AC grid gradually increases.

[0023] In one possible implementation, in response to the second frequency being less than the AC grid power frequency, the second power is controlled to be less than or equal to the maximum output power of the grid-connected power converter. In response to the second frequency being greater than the AC grid power frequency, the second power is controlled to be greater than or equal to the minimum output power of the grid-connected power converter. This arrangement ensures that the output power of the grid-connected power converter is within the rated safe power range, thereby improving the operational safety of the grid-connected power converter and the reliability of its support for the AC grid.

[0024] In one possible implementation, in response to the AC grid frequency reaching a third frequency, the output power of the grid-connected power converter is controlled to be adjusted from the second power to a third power. The third power is the difference between the second power and the first inertia power, and the absolute value of the difference between the third frequency and the AC grid power frequency is greater than the absolute value of the difference between the second frequency and the AC grid power frequency. It is understood that when the AC grid frequency reaches the third frequency, the first inertia power is withdrawn, thereby providing stable frequency support for the AC grid.

[0025] In one possible implementation, in response to the frequency of the AC power grid changing from a third frequency to a fourth frequency, the output power of the grid-connected power converter is controlled to be adjusted from the third power to the fourth power. The fourth power is the superposition of the third power, the second inertia power, and the second frequency-modulated power. The absolute value of the difference between the fourth frequency and the AC power grid frequency is less than the absolute value of the difference between the third frequency and the AC power grid frequency. The fourth frequency here can be either a fixed value or a frequency range. Based on the same principle, such a setting can enable the grid-connected power converter to provide stable and accurate frequency support for the AC power grid.

[0026] In one possible implementation, in response to the fourth frequency being less than the AC grid power frequency and the absolute value of the difference between the fourth frequency and the AC grid power frequency decreasing, the second frequency modulation power is reduced, i.e., the value of the second frequency modulation power is reduced. In response to the fourth frequency being greater than the AC grid power frequency and the absolute value of the difference between the fourth frequency and the AC grid power frequency decreasing, the second frequency modulation power is increased, i.e., the value of the second frequency modulation power is increased. This configuration can provide dynamic frequency support for the AC grid as the degree of underfrequency or overfrequency of the AC grid gradually decreases.

[0027] In one possible implementation, in response to the fourth frequency being less than the AC grid power frequency, the fourth power is controlled to be greater than or equal to the minimum output power of the grid-connected power converter. In response to the fourth frequency being greater than the AC grid power frequency, the fourth power is controlled to be less than or equal to the maximum output power of the grid-connected power converter. This arrangement ensures that the output power of the grid-connected power converter is within the rated safe power range, thereby improving the operational safety of the grid-connected power converter and the reliability of its support for the AC grid.

[0028] In one possible implementation, in response to the AC grid frequency changing from the fourth frequency to the AC grid power frequency, the output power of the grid-connected power converter is controlled to be adjusted from the fourth power to a preset reference power. This configuration can provide dynamic frequency support for the AC grid as the AC grid frequency gradually recovers to the AC grid power frequency.

[0029] In one possible implementation, the first frequency modulation power is determined based on a preset power-frequency droop curve, including a preset reference power, the output power of the grid-connected power converter, the frequency of the AC grid, and a preset lower frequency limit, where the preset lower frequency limit is the minimum value of the first frequency. This configuration can improve the accuracy of the primary frequency modulation power.

[0030] The specific implementation and beneficial effects of the above-mentioned aspects and possible implementation methods of each aspect can be referenced to each other. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] FIG1 is a structural block diagram of an energy storage system provided in an embodiment of the present application;

[0032] FIG2 is a schematic diagram of a waveform of the output power of a grid-connected power converter provided in an embodiment of the present application;

[0033] FIG3 is a control block diagram of a controller provided in an embodiment of the present application;

[0034] FIG4 is a schematic diagram of a control signal flow of a controller provided by an embodiment of the present application;

[0035] FIG5 is a schematic diagram of a waveform of the output power of a grid-connected power converter in the prior art;

[0036] FIG6 is another waveform diagram of the output power of a grid-connected power converter in the prior art;

[0037] 7 to 15 are further waveform diagrams of the output power of the grid-connected power converter provided in an embodiment of the present application;

[0038] FIG16 is a flow chart of a power control method for a grid-connected power converter provided in an embodiment of the present application. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are part of the embodiments of this application, not all of them. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0040] The implementation of the technical solution of the present application is further described in detail below with reference to the accompanying drawings.

[0041] Referring to Figure 1 , which is a block diagram of the energy storage system according to an embodiment of the present application, the energy storage system includes an energy storage battery 101 and a grid-connected power converter 102 . The grid-connected power converter 102 includes a power conversion circuit 1021 and a controller 1022 .

[0042] The energy storage battery 101 is connected to the first terminal of the power conversion circuit 1021 via a DC bus. When the energy storage battery 101 is discharging, the energy storage battery 101 outputs DC power to the power conversion circuit 1021; when the energy storage battery 101 is charging, the energy storage battery 101 receives the DC power output by the power conversion circuit 1021. Similarly, the energy storage system shown in Figure 1 may include multiple energy storage batteries, which may be connected in series, in parallel, or in series and parallel to the first terminal of the power conversion circuit 1021. In other words, the embodiments of the present application do not limit the number of energy storage batteries included in the energy storage system.

[0043] The second end of the power conversion circuit 1021 is connected to a common connection point (PCC) 1 through an AC bus. The PCC 1 can be connected to an AC grid 11 or an AC load.

[0044] The third terminal of the power conversion circuit 1021 is connected to the controller 1022. The controller 1022 can control the power conversion circuit 1021 to convert the DC power output by the energy storage battery 101 into AC power output to the AC power grid 11, and can also convert the AC power on the AC power grid 11 into DC power output to the energy storage battery 101. In this case, the controller 1022 specifically controls the voltage amplitude and voltage frequency output by the power conversion circuit 1021, that is, the controller 1022 can control the output power of the power conversion circuit 1021. Exemplarily, the controller 1022 can be specifically implemented as a microcontroller (MCU), a central processing unit (CPU), other general-purpose processors, a digital signal processor (DSP), an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc.

[0045] In this application, the controller in the grid-connected power converter changes the control method of the power conversion circuit. In the grid control method, it can provide more stable and accurate frequency support for the AC power grid when the AC power grid is underfrequency or overfrequency, thereby improving the power supply reliability and stability of the energy storage system, and has strong applicability.

[0046] The specific control method of the power conversion circuit is described in detail below with reference to the accompanying drawings.

[0047] In response to the AC grid frequency being a first frequency, the controller controls the output power of the power conversion circuit to adjust from a preset reference power to a first power. The preset reference power is the output power of the power conversion circuit when the AC grid is stable. The first power is the sum of the preset reference power and a first inertia power. The first inertia power is the power obtained by the power conversion circuit simulating the inertia characteristics of a synchronous generator. This first inertia power is generally related to the properties of the grid-connected power converter and the frequency fluctuation of the AC grid. Furthermore, in response to the AC grid frequency being a second frequency, the controller controls the output power of the power conversion circuit to adjust from the first power to a second power. The second power is the sum of the first power and the first frequency-modulated power, and the absolute value of the difference between the second frequency and the AC grid power frequency is greater than the absolute value of the difference between the first frequency and the AC grid power frequency. The first and second frequencies can be fixed values ​​or frequency ranges. Optionally, the AC grid power frequency is the frequency corresponding to the AC grid operating under normal operating conditions. Exemplarily, the AC grid power frequency can be 50 Hz or 60 Hz.

[0048] When the AC grid is underfrequency, the first frequency is less than the AC grid power frequency, and the first inertia power is positive. When the second frequency is less than the first frequency, the first frequency modulation power is positive. When the AC grid is overfrequency, the first frequency is greater than the AC grid power frequency, and the first inertia power is negative. When the second frequency is greater than the first frequency, the first frequency modulation power is negative.

[0049] It can be understood that when the frequency of the AC power grid deviates from the AC power grid working frequency, the AC power grid can obtain rapid frequency support by preferentially superimposing the first inertia power on the basis of the preset reference power. When the frequency of the AC power grid further deviates from the AC power grid working frequency, the AC power grid can obtain more stable and accurate frequency support by continuing to superimpose the first frequency modulation power on the basis of the preset reference power and the first inertia power.

[0050] Exemplarily, when the AC power grid is in a normal operating state, the frequency of the AC power grid is the AC power grid working frequency, and at this time, the output power of the power conversion circuit is the preset reference power.

[0051] When the AC power grid is under-frequency, the waveform diagram of the output power of the power conversion circuit can be shown in Figure 2. n is the AC power grid frequency, f set- is the preset lower limit frequency, f g is the frequency of the AC grid; P out is the output power of the power conversion circuit, P ref is the AC power grid frequency. The preset lower limit frequency is the minimum value of the first frequency. It can be seen that at t 40 Time to t 41At this moment, the frequency of the AC grid is less than the AC grid power frequency f n , greater than the preset lower limit frequency f set- , then the controller is at t 40 Time to t 41 The frequency of the AC power grid detected at the moment is the first frequency, that is, the first frequency represents t 40 Time to t 41 The frequency interval at time t 41 After the time, the frequency of the AC power grid is less than the preset lower limit frequency f set- , then the controller is at t 41 The frequency of the AC power grid detected after the time is the second frequency.

[0052] In a specific implementation, when the controller detects that the frequency of the AC power grid is the first frequency, as the first frequency is equal to the AC power grid power frequency f n The absolute value of the difference between the first and second inertia powers increases, and the first inertia power increases until the output power of the power conversion circuit increases from the preset reference power P ref Increase to the first power P 41 , the first power P 41 is the preset reference power P ref The sum of the first inertia power and the first inertia power. Among them, the first inertia power increases as the value of the first inertia power increases. In the process of decreasing the frequency of the AC power grid, the value of the first inertia power is a positive number, expressed as ΔP j Then the first power P 41 =P ref +ΔP j The first inertia power at t 41 Always respond.

[0053] When the controller detects that the frequency of the AC grid is the second frequency, as the second frequency is equal to the AC grid power frequency f n The absolute value of the difference between the first and second frequency modulation powers increases, that is, the first frequency modulation power increases until the output power of the power conversion circuit increases from the first power P 41 Adjust to the second power, so as to provide dynamic frequency support for the AC grid when the under-frequency degree of the AC grid gradually increases. The second power is the first power P 41 The sum of the first FM power and the first FM power increases so that the value of the first FM power increases.

[0054] As can be seen from Figure 2 above, the output power of the power conversion circuit is 41 At the first power P 41In a specific implementation, the controller may monitor the output power of the power conversion circuit and send a control signal to the power conversion circuit when the output power of the power conversion circuit reaches the first power. Optionally, the controller may detect that the frequency of the AC power grid begins to change from the AC power grid power frequency to the first frequency, i.e., t in FIG2 40 At this moment, a first preset time is pre-set, within which the first inertia power can respond in place, and then from t 40 After waiting for the first preset time, the control signal is sent to the power conversion circuit. The control signal is used to control the output power of the power conversion circuit to be within the first power P 41 The first FM power is superimposed on the basis of .

[0055] The controller controls the power conversion circuit to prioritize the first inertia power and then quickly respond to the first frequency modulation power. In a specific implementation, the controller can control the output power of the power conversion circuit according to the control block diagram shown in Figure 3. As shown in Figure 3, the controller 501 includes a virtual inertia and power angle control module 5011, an additional power adjustment module 5012, a primary frequency modulation module 5013, and an internal potential control module 5014.

[0056] When the frequency of the AC power grid is greater than the preset lower limit frequency and less than the preset upper limit frequency, the virtual inertia and power angle control module 5011 controls the power supply according to the preset reference power P ref And the output power P of the power conversion circuit out The power angle θ is calculated. The preset upper limit frequency is the maximum value of the first frequency. The internal potential control module 5014 is based on the power angle θ and the output voltage amplitude U of the power conversion circuit. e Generate the output voltage vector of the power conversion circuit The power angle θ represents the output voltage vector of the power conversion circuit Voltage vector with alternating current At this time, the virtual inertia and power angle control module 5011 controls the output power P of the power conversion circuit. out It can be expressed as:

[0057] Wherein, X is the impedance value between the power conversion circuit and the AC grid or AC load.

[0058] It can be seen that when the frequency of the AC power grid is greater than the preset lower frequency limit and less than the preset upper frequency limit, both the additional power regulation module 5012 and the primary frequency regulation module 5013 may not work.

[0059] When the frequency of the AC grid decreases to a preset lower limit frequency or increases to a preset upper limit frequency, the power angle θ between the output voltage of the power conversion circuit and the voltage of the AC power increases or decreases, and the output power P of the power conversion circuit increases or decreases. out The power demanded by the AC grid or the AC load is unbalanced. In this case, the virtual inertia and power angle control module 5011 first generates inertia power (e.g., first inertia power, second inertia power). The inertia power is negatively correlated with the frequency change of the AC grid, and the formula can be expressed as:

[0060] Among them, K j is the preset value of inertia power gain, Represents the change in the frequency of the AC power grid. When the frequency of the AC power grid decreases, If the value is negative, the value of the first inertia power is positive.

[0061] When the frequency of the AC grid drops to the preset lower limit frequency, the output power P of the power conversion circuit out The power increases from the preset reference power to the first power within the first preset time period, and the specific waveform is as shown in FIG3 . 40 Time to t 41 Waveform at the moment.

[0062] When the frequency of the AC grid decreases to a preset lower frequency limit or the frequency of the AC grid increases to a preset upper frequency limit, the primary frequency modulation module 5013 calculates the active power variation ΔP of the primary frequency modulation module 5013 based on the preset frequency and power droop curve according to the frequency of the AC grid and the preset frequency range. f , the formula can be expressed as:

[0063] Among them, K f is the slope of the preset frequency and power droop curve, f set+ is the preset upper limit frequency, f aet- is the preset lower frequency limit.

[0064] It can be seen from Formula 3 that when the frequency of the AC grid is lower than the preset lower frequency limit, the active power variation is increased, and when the frequency of the AC grid is higher than the preset upper frequency limit, the active power variation is reduced.

[0065] The additional power regulation module 5012 adjusts the active power variation ΔP of the primary frequency modulation module 5013 according to the f , preset reference power P ref , the output power P of the power conversion circuit out and the frequency f of the AC grid g , the active power regulation and power angle control are calculated, and the formula can be expressed as:

[0066] Where ΔP fo is the active power adjustment amount, that is, the first frequency modulation power.

[0067] The power angle control amount and the active power adjustment amount have a preset functional relationship, so the additional power adjustment module 5012 can obtain the power angle control amount according to the active power adjustment amount, and the formula is expressed as:

[0068] Where Δf c is the power angle control quantity, g(x) is ΔP fo function, and g(x)∝ΔP fo , g(x) according to Δf c The position of the superposition is determined.

[0069] At this time, the additional power regulation module 5012 transmits the active power regulation amount and the power angle control amount to the virtual inertia and power angle control module 5011. When the first inertia power output of the virtual inertia and power angle control module 5011 is in place, the signal flow in the virtual inertia and power angle control module 5011 is shown in FIG4 , and the active power regulation amount is consistent with the preset reference power P ref The superposition is performed and the superposition result is transmitted to the additional power regulation module 5012, and the superposition result is also transmitted to the virtual synchronous generator. In the virtual synchronous generator, D is the damping system, J is the s is the virtual moment of inertia, w n The superimposed result is calculated by the virtual synchronous generator to obtain the power angle change Δw c Power angle change Δw c and the power angle control variable Δf c Superposition is performed to obtain the power angle output Δw out , the virtual inertia and power angle control module 5011 controls the power angle output Δw out Performing an integral operation to obtain the power angle θ. At this time, the internal potential control module 5014 can calculate the output power of the power conversion circuit according to Formula 1. For example, the output power of the power conversion circuit can also be expressed as: out =K θp .sinθ Formula 6

[0070] Among them, K θp is the transfer gain from power angle to power. Combining formula 1 and formula 6, we can get

[0071] Unlike conventional power conversion circuit output power control, this embodiment of the present application adds an additional power regulation module 5012 between the primary frequency modulation module 5013 and the virtual inertia and power angle control module 5011. When the AC grid frequency drops to a preset lower frequency limit, the first inertia power is prioritized, and the additional power regulation module 5012 then quickly and accurately responds to the first frequency modulation power. As shown in FIG4 , the additional power regulation module outputs the calculated power angle control variable and active power control variable separately. The active power control variable passes through the virtual synchronous generator, while the power angle control variable does not.

[0072] The difference between the embodiment of the present application and the prior art in which the active power variation output by the primary frequency modulation module is directly superimposed on the preset reference power is that the virtual inertia exists in the virtual synchronous generator, and the active power variation output by the primary frequency modulation module responds slowly, resulting in the output power of the power conversion circuit being unable to quickly provide frequency support to the AC power grid or AC load. The output power of the power conversion circuit at this time can be seen in Figure 5, which is a waveform diagram of the output power of the power converter in the prior art. As shown in Figure 5, at t 70 At time t, the frequency of the AC grid drops to the preset lower limit frequency, but due to the existence of virtual inertia, the active power output of the primary frequency modulation module changes at t 71 The moment begins to overlap with P ref +ΔP j On t 70 Time to t 71 Only the inertia power supports the frequency of the AC grid during this time, that is, after the frequency of the AC grid drops to the preset lower limit frequency, Δt 71 The frequency modulation module outputs to the power conversion circuit after a certain time. 71 The duration is too long, Δt 71 The duration is much longer than the Δt shown in Figure 2 41 The primary frequency modulation module basically fails during this period, as shown in Figure 5. 71 Even if the active power variation is added to the power conversion circuit after the time, the slope of the output power of the power conversion circuit is still very small, which is smaller than the slope of the output power of the power conversion circuit shown in FIG2. 41 Therefore, in the embodiment of the present application, the power angle control value Δf calculated by the additional power adjustment module 5012 is c The first frequency modulation power of the embodiment of the present application responds quickly by directly participating in the calculation of the power angle without passing through the virtual synchronous generator.

[0073] In the prior art, there is also a method that directly uses the active power change output by the primary frequency modulation module without passing through the virtual synchronous generator and directly participates in the calculation of the power angle. In this case, the output power of the power conversion circuit can be seen in Figure 6, which is another waveform diagram of the output power of the power converter in the prior art. As shown in Figure 6, at t 80 At this moment, the frequency of the AC grid drops to the preset lower limit frequency, and the active power change output by the primary frequency modulation module responds quickly, making the frequency of the AC grid at t 80 Time to t 81 When frequency crossing occurs between the time instants, that is, when the frequency change of the AC power grid is very small, the active power change output by the primary frequency regulation module responds quickly and begins to be superimposed on the output power of the power conversion circuit, destroying the output of the virtual inertia, which is manifested as inertia power loss, resulting in insufficient support of the primary frequency regulation module for the initial stage of the AC power grid frequency being reduced to the preset lower limit frequency. Therefore, in the embodiment of the present application, the active power regulation amount ΔP calculated by the additional power regulation module 5012 is fo The virtual synchronous generator is also used to ensure that the response of the first frequency modulation power in the embodiment of the present application is accurate.

[0074] In the embodiment of the present application, an additional power regulation module is added to calculate the active power regulation amount and the power angle control amount according to the output of the primary frequency regulation module. The active power regulation amount needs to pass through the virtual synchronous generator, while the power angle control amount does not need to pass through the virtual synchronous generator. This takes into account the response speed and accuracy of the inertia power and the primary frequency regulation power, thereby enabling the AC power grid to obtain more stable and accurate frequency support.

[0075] Optionally, in some feasible embodiments, the controller controls the output power of the power conversion circuit to adjust from the second power to the third power in response to the frequency of the AC power grid being a third frequency. The absolute value of the difference between the third frequency and the AC power grid frequency is greater than the absolute value of the difference between the second frequency and the AC power grid frequency. When the AC power grid is underfrequency, the third frequency is less than the AC power grid frequency and the third frequency is less than the second frequency. When the AC power grid is overfrequency, the third frequency is greater than the AC power grid frequency and the third frequency is greater than the second frequency. It is understandable that when the frequency of the AC power grid is the third frequency, the first inertia power is withdrawn, thereby providing stable frequency support for the AC power grid.

[0076] For example, when the AC grid is under-frequency, the waveform diagram of the output power of the power conversion circuit may be as shown in FIG7 . 41 Time to t 44 The waveform between the moments. The controller is at t 41 Time to t 42 The frequency of the AC power grid detected at the moment is the second frequency, that is, the second frequency represents t 41 Time to t42 The frequency interval at time t 42 Time to t 44 The frequency of the AC power grid detected at any moment is the third frequency. It can be seen that the third frequency is a fixed value.

[0077] In the specific implementation, the output power of the power conversion circuit is 41 Time to t 42 The first frequency modulation power (i.e., the active power adjustment amount) is continuously superimposed between the moments. In the process of decreasing the frequency of the AC power grid, the value of the first frequency modulation power is a positive number, expressed as ΔP fo , then the output power of the power conversion circuit can be expressed as P ref +ΔP j +ΔP fo The output power of the power conversion circuit is at t 42 The second power P is reached at this moment 42 .

[0078] It can be seen that t 42 The moment is when the frequency of the AC grid changes from decreasing to constant, that is, the moment when the frequency change of the AC grid ends. At this time, the controller controls the output power of the power conversion circuit at t 42 It starts to decrease at time t 43 Reduce to the third power P 43 The third power P 43 The second power P 42 The difference between the first inertia power and the third power P 43 =P 42 -ΔP j That is, when the frequency of the AC grid remains unchanged, the first inertia power exits. When the frequency of the AC grid remains unchanged, the output power of the power conversion circuit also remains unchanged and is maintained at the third power P 43 .

[0079] Furthermore, in some feasible embodiments, in response to the frequency of the AC power grid changing from the third frequency to the fourth frequency, the controller controls the output power of the power conversion circuit to be adjusted from the third power to the fourth power. The fourth power is the power after the third power is superimposed on the second inertia power and the second frequency modulation power, and the absolute value of the difference between the fourth frequency and the AC power grid frequency is less than the absolute value of the difference between the third frequency and the AC power grid frequency. The fourth frequency can be a fixed value or a frequency range. When the AC power grid is under-frequency, the fourth frequency is greater than the third frequency and the fourth frequency is less than the AC power grid frequency. At this time, the value of the second inertia power is negative and the value of the second frequency modulation power is positive. When the AC power grid is over-frequency, the fourth frequency is less than the third frequency and the fourth frequency is greater than the AC power grid frequency. At this time, the value of the second inertia power is positive and the value of the second frequency modulation power is negative. Implementation of the embodiments of the present application can enable the grid-connected power converter to provide stable and accurate frequency support for the AC power grid.

[0080] For example, when the AC grid is under-frequency, the output waveform diagram of the power conversion circuit may be as shown in FIG7 . 44 Time to t 46 The waveform between the moments. It can be seen that at t 44 Time to t 46 At this moment, the frequency of the AC grid changes from constant to increasing. Although the frequency of the AC grid begins to increase at this time, the frequency of the AC grid is still lower than the AC grid power frequency f n The controller is at t 44 Time to t 46 The frequency of the AC power grid detected at the moment is the fourth frequency, that is, the fourth frequency represents t 44 Time to t 46 The frequency interval at the moment, and the fourth frequency is less than the AC grid power frequency f n .

[0081] t 44 The moment can be understood as the moment when the frequency of the AC power grid begins to recover. The output power of the power conversion circuit responds to the second inertia power. The value is a positive number. According to Formula 2, the value of the second inertia power is a negative number, expressed as -ΔP j The output power of the power conversion circuit is 44 The time starts to decrease.

[0082] The output power of the power conversion circuit is at t 45 At this moment, the second frequency modulation power is further superimposed on the basis of the response to the second inertia power. As the fourth frequency and the AC grid power frequency f n The absolute value of the difference between the two decreases, and the controller will reduce the second frequency modulation power, that is, the second frequency modulation power decreases until the output power of the power conversion circuit changes from the third power P43 Adjust to the fourth power P 44 , thereby providing dynamic frequency support for the AC power grid when the under-frequency degree of the AC power grid gradually decreases. Wherein, the second frequency modulation power is reduced to a value of the second frequency modulation power that is reduced.

[0083] Furthermore, according to Formula 3 and Formula 4, the value of the second frequency modulation power is a positive number, which is expressed as ΔP fo , then the fourth power P 44 =P ref -ΔP j +ΔP fo , where the fourth power P 44 is the power conversion circuit at t 46 The output power at the moment. It can be understood that at t 45 Time to t 46 At this moment, the output power of the power conversion circuit is the superposition of the preset reference power, the second inertia power, and the second frequency modulation power. Since the second inertia power is a negative number, even if the second frequency modulation power is a positive number, the absolute value of the second inertia power is greater than the second frequency modulation power. Therefore, at t 45 Time to t 46 At this moment, the output power of the power conversion circuit still decreases, but relative to t 44 Time to t 45 At this moment, the second frequency modulation power having a positive value is superimposed, and the speed at which the output power of the power conversion circuit decreases becomes slower.

[0084] Similarly, when the AC grid frequency increases from constant to constant, the controller controls the power conversion circuit to prioritize responding to the second inertia power and then quickly responding to the second frequency modulation power. Specifically, this can be implemented according to the control block diagram shown in FIG3 . For details, please refer to the description above in conjunction with FIG3 , and will not be repeated here.

[0085] Furthermore, in some feasible implementations, in response to the AC grid frequency changing from the fourth frequency to the AC grid power frequency, the controller controls the output power of the power conversion circuit to adjust from the fourth power to a preset reference power. Implementing this embodiment of the present application can provide dynamic frequency support for the AC grid as the AC grid frequency gradually recovers to the AC grid power frequency.

[0086] In a specific implementation, when the AC grid is under-frequency, the controller controls the output power of the power conversion circuit to increase from the fourth power to the preset reference power when detecting that the frequency of the AC grid increases from the fourth frequency to the AC grid power frequency. At this time, the output waveform diagram of the power conversion circuit can be as shown in FIG7. 46 The waveform after the moment t 46It is detected that the frequency of the AC grid increases to the AC grid power frequency f n , t 46 The second inertia power and the second frequency modulation power are at t 46 Start exiting at time t 47 The exit is completed at time t 47 At this moment, the output power of the power conversion circuit is the preset reference power P ref .

[0087] Optionally, in some feasible implementations, the power obtained by superimposing the first frequency modulation power after the power conversion circuit responds to the first inertia power is larger. For example, the upper limit of the output power of the power conversion circuit can be limited. Specifically, when the AC power grid is under-frequency, the second frequency is less than the AC power grid working frequency. At this time, the second power is less than or equal to the maximum output power of the power conversion circuit. At this time, the waveform diagram of the output power of the power conversion circuit is shown in Figure 8. As can be seen from Figure 8, at t 41 Time to t 42 At this moment, the output power of the power conversion circuit is expressed as P out ′, the maximum is the upper limit power P 42 ′.

[0088] Similarly, after the power conversion circuit responds to the second inertia power and then adds the second frequency modulation power, the power that can be obtained is relatively small. For example, the lower limit of the output power of the power conversion circuit can be limited. Specifically, when the AC grid is under-frequency, the fourth frequency is lower than the AC grid power frequency. At this time, the fourth power is greater than or equal to the minimum output power of the power conversion circuit. At this time, it can be seen from Figure 8 that at t 45 Time to t 46 At this moment, the output power of the power conversion circuit is at least the lower limit power P 45 ′.

[0089] The maximum output power or minimum output power of the power conversion circuit may be a preset value or a value determined based on the components used in the grid-connected power converter. Exemplarily, the maximum output power or minimum output power of the power conversion circuit is the maximum output power or minimum output power of the grid-connected power converter.

[0090] By implementing the embodiments of the present application, the output power of the power conversion circuit can be placed within the rated safe power range, thereby improving the safety of the grid-connected power converter and the reliability of its support for the AC power grid.

[0091] The embodiments described above in conjunction with Figures 2 to 8 are based on the example of the grid-connected power converter outputting power to the AC grid when the AC grid is under-frequency. It is defined that the direction in which the grid-connected power converter outputs power to the AC grid is a positive direction, and the output power curves of the grid-connected power converter, i.e., the power conversion circuit, are all above the 0 axis.

[0092] Optionally, in some feasible implementations, when the AC power grid is under-frequency, the grid-connected power converter can be used in a charging scenario, that is, the AC power grid outputs power to the grid-connected power converter, and the direction in which the grid-connected power converter outputs power to the AC power grid is still the positive direction. At this time, the output power curve of the power conversion circuit is all below the 0 axis. For specific waveform diagrams, please refer to Figures 9 to 10.

[0093] Referring to FIG9 , FIG9 is another waveform diagram of the output power of a grid-connected power converter provided in an embodiment of the present application. As shown in FIG9 , the waveform diagram of the output power of the power conversion circuit differs from the waveform diagram shown in FIG7 in that the output power of the power conversion circuit is less than 0. In a specific implementation, the controller's control of the output power of the power conversion circuit can refer to the embodiment described in FIG7 .

[0094] Similarly, the waveform diagram shown in FIG10 differs from the waveform diagram shown in FIG8 in that the output power of the power conversion circuit is less than 0. In a specific implementation, the controller can control the output power of the power conversion circuit with reference to the embodiment described in FIG8.

[0095] Optionally, in some feasible implementations, when the AC power grid is over-frequency, the waveform diagram of the output power of the power conversion circuit may be as shown in FIG11. n is the AC power grid frequency, f set+ is the preset upper limit frequency, f g1 is the frequency of the AC grid; P out1 is the output power of the power conversion circuit, P ref is the AC power frequency. It can be seen that at t 130 Time to t 131 At this moment, the frequency of the AC grid is greater than the AC grid power frequency f n , which is less than the preset upper limit frequency f set+ , then the controller is at t 130 Time to t 131 The frequency of the AC power grid detected at the moment is the first frequency, that is, the first frequency represents t 130 Time to t 131 The frequency interval at time t 131 After the time, the frequency of the AC power grid is greater than the preset upper limit frequency f set+ , then the controller is at t 131The frequency of the AC power grid detected after the time is the second frequency.

[0096] In a specific implementation, when the controller detects that the frequency of the AC power grid is the first frequency, as the first frequency is equal to the AC power grid power frequency f n The absolute value of the difference increases to control the first inertia power to decrease until the output power of the power conversion circuit decreases from the preset reference power P ref Reduce to the first power P 131 Among them, the first power P 131 is the preset reference power P ref The sum of the first inertia power and the first inertia power can be understood as the decrease in the value of the first inertia power. According to Formula 2, when the frequency of the AC power grid increases, the value of the first inertia power is negative, expressed as -ΔP j Then the first power P 131 =P ref -ΔP j The first inertia power at t 131 Always respond.

[0097] Moreover, when the controller detects that the frequency of the AC power grid is the second frequency, as the second frequency is equal to the AC power grid frequency f n The absolute value of the difference between the first and second frequency modulation powers increases, and the first frequency modulation power decreases, that is, the first frequency modulation power decreases until the output power of the power conversion circuit decreases from the first power P 131 Adjust to the second power, so that when the over-frequency degree of the AC grid gradually increases, dynamic frequency support can be provided for the AC grid. The second power is the first power P 131 The sum of the first FM power and the second FM power, the reduction of the first FM power can be understood as a reduction in the value of the second FM power.

[0098] In some feasible implementations, it can be seen from FIG11 that the output power of the power conversion circuit is 131 At the first power P 131 In a specific implementation, the controller can monitor the output power of the power conversion circuit, and when the output power of the power conversion circuit reaches the first power, send a control signal to the power conversion circuit. Optionally, the controller can detect that the frequency of the AC power grid begins to change from the AC power grid power frequency to the first frequency, that is, t in FIG11. 130 At this moment, a second preset time is pre-set, within which the first inertia power can respond in place, and then from t 130 After waiting for the second preset time, the control signal is sent to the power conversion circuit. The control signal is used to control the output power of the power conversion circuit to be within the first power P 131 The first FM power is superimposed on the basis of .

[0099] The controller still controls the power conversion circuit to respond to the first inertia power first, and then quickly respond to the first frequency modulation power. For specific implementation, please refer to the embodiment described above in conjunction with Figures 3 and 4, which will not be repeated here.

[0100] Furthermore, in some feasible embodiments, the controller controls the output power of the power conversion circuit to adjust from the second power to the third power in response to the frequency of the AC power grid being the third frequency. For example, when the AC power grid is over-frequency, the waveform diagram of the output power of the power conversion circuit may be as shown in FIG11. 131 Time to t 134 Waveform between moments.

[0101] The controller is at t 131 Time to t 132 The frequency of the AC power grid detected at the moment is the second frequency, that is, the second frequency represents t 131 Time to t 132 The frequency interval at time t 132 Time to t 134 The frequency of the AC power grid detected at any moment is the third frequency. It can be seen that the third frequency is a fixed value.

[0102] In the specific implementation, the output power of the power conversion circuit is 131 Time to t 132 The first frequency modulation power (i.e., the active power adjustment amount) is continuously superimposed between the moments. In the process of increasing the frequency of the AC power grid, the value of the first frequency modulation power is a negative number, expressed as -ΔP fo , then the output power of the power conversion circuit can be expressed as P ref -ΔP j -ΔP fo The output power of the power conversion circuit is at t 132 The second power P is reached at this moment 132 .

[0103] It can be seen that t 132 The moment is when the frequency of the AC grid changes from increasing to constant, that is, the moment when the AC power change ends. At this time, the output power of the power conversion circuit is at t 132 It starts to increase at time t 133 The power increases to the third power P 133 The third power P 133 The second power P 132 The difference between the first inertia power and the third power P 133 =P 132 +ΔP jThat is, when the frequency of the AC grid remains unchanged, the first inertia power exits. When the frequency of the AC grid remains unchanged, the output power of the power conversion circuit also remains unchanged and is maintained at the third power P 133 .

[0104] Furthermore, in some feasible embodiments, the controller controls the output power of the power conversion circuit to adjust from the third power to the fourth power in response to the frequency of the AC power grid changing from the third frequency to the fourth frequency. For example, when the AC power grid is over-frequency, the output waveform diagram of the power conversion circuit may be as shown in FIG12. 134 Time to t 136 The waveform between the moments. It can be seen that at t 134 Time to t 136 At this moment, the frequency of the AC grid changes from constant to decreasing. Although the frequency of the AC grid begins to decrease at this time, the frequency of the AC grid is still higher than the AC grid power frequency fn n The controller is at t 134 Time to t 136 The frequency of the AC power grid detected at the moment is the fourth frequency, that is, the fourth frequency represents t 134 Time to t 136 The frequency interval of the moment.

[0105] t 134 The moment can be understood as the moment when the frequency of the AC power grid begins to recover. The output power of the power conversion circuit responds to the second inertia power. The value is a negative number. According to Formula 2, the value of the second inertia power is a positive number, expressed as ΔP j The output power of the power conversion circuit is 134 The time begins to increase.

[0106] The output power of the power conversion circuit is at t 135 The second frequency modulation power is further superimposed on the second inertia power at the beginning of the moment, and as the fourth frequency and the AC grid power frequency f n The absolute value of the difference between the two gradually decreases, and the controller increases the second frequency modulation power, that is, the second frequency modulation power increases until the output power of the power conversion circuit increases from the third power P 133 Adjust to the fourth power P 134 , thereby providing dynamic frequency support for the AC power grid when the overfrequency degree of the AC power grid gradually decreases. Wherein, the second frequency modulation power is increased so that the value of the second frequency modulation power is increased.

[0107] Furthermore, according to Formula 3 and Formula 4, the value of the second FM power is a negative number, expressed as -ΔP fo , then the fourth power P 134 =P ref +ΔPj -ΔP fo , where the fourth power P 134 is the power conversion circuit at t 136 The output power at the moment. It can be understood that at t 135 Time to t 136 At the moment t, the output power of the power conversion circuit is the superposition of the preset reference power, the second inertia power and the second frequency modulation power. Since the second inertia power is a positive number, even if the second frequency modulation power is a negative number, the absolute value of the second inertia power is greater than the absolute value of the second frequency modulation power. Therefore, at t 135 Time to t 136 At this moment, the output power of the power conversion circuit still increases, but relative to t 134 Time to t 135 At this moment, the second frequency modulation power having a negative value is superimposed, and the speed at which the output power of the power conversion circuit increases becomes slower.

[0108] Similarly, when the AC grid frequency decreases from constant to decreasing, the controller controls the power conversion circuit to prioritize responding to the second inertia power and then quickly responding to the second frequency modulation power. Specifically, this can be implemented according to the control block diagram shown in FIG3 . For details, please refer to the description above in conjunction with FIG3 , and will not be repeated here.

[0109] Furthermore, in some feasible implementations, the controller controls the output power of the power conversion circuit to be adjusted from the fourth power to the preset reference power in response to the frequency of the AC grid changing from the fourth frequency to the AC grid power frequency. In a specific implementation, when the AC grid is over-frequencyed, the controller controls the output power of the power conversion circuit to be reduced from the fourth power to the preset reference power when detecting that the frequency of the AC grid decreases from the fourth frequency to the AC grid power frequency. At this time, the output waveform diagram of the power conversion circuit can be as shown in FIG13. 136 The waveform after the moment t 136 It is detected at all times that the frequency of the AC grid decreases to the AC grid power frequency f n , t 136 The second inertia power and the second frequency modulation power are at t 136 Start exiting at time t 137 The exit is completed at time t 137 At this moment, the output power of the power conversion circuit is the preset reference power P ref .

[0110] Optionally, in some feasible implementations, the power obtained by superimposing the first frequency modulation power after the power conversion circuit responds to the first inertia power is relatively small. For example, the lower limit of the output power of the power conversion circuit can be limited. Specifically, when the AC power grid is over-frequency, the second frequency is greater than the AC power grid operating frequency. At this time, the second power is greater than or equal to the minimum output power of the power conversion circuit. At this time, the waveform diagram of the output power of the power conversion circuit is shown in Figure 13. As can be seen from Figure 13, at t 131 Time to t 132 At this moment, the output power of the power conversion circuit is expressed as P out1 ′, the minimum is the lower limit power P 132 ′.

[0111] Similarly, after the power conversion circuit responds to the second inertia power and then adds the second frequency modulation power, the power that can be obtained is relatively large. For example, the upper limit of the output power of the power conversion circuit can be limited. Specifically, when the AC power grid is over-frequency, the fourth frequency is greater than the AC power grid working frequency. At this time, the fourth power is less than or equal to the maximum output power of the power conversion circuit. At this time, it can be seen from Figure 13 that at t 135 Time to t 136 At this moment, the maximum output power of the power conversion circuit is the lower limit power P 135 ′.

[0112] By implementing the embodiments of the present application, the output power of the power conversion circuit can be placed within the rated safe power range, thereby improving the safety of the grid-connected power converter and the reliability of its support for the AC power grid.

[0113] The embodiments described above in conjunction with Figures 11 to 13 are based on the example of the grid-connected power converter outputting power to the AC grid when the AC grid is over-frequency. It is defined that the direction in which the grid-connected power converter outputs power to the AC grid is a positive direction, and the output power curves of the grid-connected power converter, i.e., the power conversion circuit, are all above the 0 axis.

[0114] Optionally, in some feasible implementations, when the AC power grid is over-frequency, the grid-connected power converter can be used in a charging scenario, that is, the AC power grid outputs power to the grid-connected power converter, and the direction in which the grid-connected power converter outputs power to the AC power grid is still the positive direction. At this time, the output power curve of the power conversion circuit is all below the 0 axis. For specific waveform diagrams, please refer to Figures 14 to 15.

[0115] Referring to Figure 14, Figure 14 is another waveform diagram of the output power of the grid-connected power converter provided in an embodiment of the present application. As shown in Figure 14, the waveform diagram of the output power of the power conversion circuit differs from the waveform diagram shown in Figure 12 in that the output power of the power conversion circuit is less than 0. In a specific implementation, the controller's control of the output power of the power conversion circuit can refer to the embodiment described in Figure 12.

[0116] Similarly, the waveform diagram shown in FIG15 differs from the waveform diagram shown in FIG13 in that the output power of the power conversion circuit is less than 0. In a specific implementation, the controller can control the output power of the power conversion circuit with reference to the embodiment described in FIG13 .

[0117] Referring to Figure 16, Figure 16 is a flow chart of a power control method for a grid-connected power converter according to an embodiment of the present application. As shown in Figure 16, the method includes the following steps S101 to S102.

[0118] Step S101 : In response to the frequency of the AC power grid being a first frequency, controlling the output power of the grid-connected power converter to be adjusted from a preset reference power to a first power.

[0119] The preset reference power is the output power of the grid-connected power converter when the AC power grid is stable, the first power is the sum of the preset reference power and the first inertia power, and the first inertia power is the power obtained by the grid-connected power converter simulating the inertia characteristics of the synchronous generator.

[0120] Step S102 : In response to the frequency of the AC power grid being a second frequency, controlling the output power of the grid-connected power converter to be adjusted from a first power to a second power.

[0121] The second power is the sum of the first power and the first frequency-modulated power, and the absolute value of the difference between the second frequency and the AC power grid frequency is greater than the absolute value of the difference between the first frequency and the AC power grid frequency. The first frequency and the second frequency can be fixed values ​​or frequency ranges. Optionally, the AC power grid frequency is the frequency corresponding to the normal operation of the AC power grid.

[0122] In a specific implementation, the specific implementation of the power control method for the grid-connected power converter provided in the embodiment of the present application can be referred to the embodiment described in Figures 1 to 15 above, and will not be repeated here. In addition, the output power, maximum output power, and minimum output power of the grid-connected power converter in this method correspond to the output power, maximum output power, and minimum output power of the power conversion circuit in the embodiment described in Figures 1 to 15, respectively.

[0123] In an embodiment of the present application, when the frequency of the AC power grid deviates from the AC power grid operating frequency, the AC power grid can obtain rapid frequency support by preferentially superimposing the first inertia power on the basis of the preset reference power. When the frequency of the AC power grid further deviates from the AC power grid operating frequency, the AC power grid can obtain more stable and accurate frequency support by continuing to superimpose the first frequency modulation power on the basis of the preset reference power and the first inertia power.

[0124] It should be noted that the above terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance.

[0125] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection of the claims.

Claims

1. A grid-connected power converter, characterized in that: The grid-connected power converter comprises a power conversion circuit and a controller, wherein a first end of the power conversion circuit is used to connect to a DC source via a DC bus, and a second end of the power conversion circuit is used to connect to an AC grid via an AC bus; The controller is used for, in response to the frequency of the AC power grid being a first frequency, controlling the output power of the power conversion circuit to be adjusted from a preset reference power to a first power; wherein the preset reference power is the output power of the power conversion circuit when the AC power grid is stable, the first power is the sum of the preset reference power and a first inertia power, and the first inertia power is the power obtained by the power conversion circuit simulating the inertia characteristics of a synchronous generator; The controller is used to control the output power of the power conversion circuit to be adjusted from the first power to the second power in response to the frequency of the AC power grid being a second frequency; wherein the second power is the sum of the first power and the first frequency-modulated power; and the absolute value of the difference between the second frequency and the AC power grid operating frequency is greater than the absolute value of the difference between the first frequency and the AC power grid operating frequency.

2. The grid-connected power converter according to claim 1, characterized in that: When the second frequency is lower than the power frequency of the AC power grid and the absolute value of the difference between the second frequency and the power frequency of the AC power grid increases, the first frequency modulation power increases; When the second frequency is greater than the AC power grid power frequency and the absolute value of the difference between the second frequency and the AC power grid power frequency increases, the first frequency modulation power decreases.

3. The grid-connected power converter according to claim 2, characterized in that: When the second frequency is less than the power frequency of the AC power grid, the second power is less than or equal to the maximum output power of the power conversion circuit; When the second frequency is greater than the AC power grid operating frequency, the second power is greater than or equal to the minimum output power of the power conversion circuit.

4. The grid-connected power converter according to any one of claims 1 to 3, characterized in that: The controller is used for controlling the output power of the power conversion circuit to be adjusted from the second power to the third power in response to the frequency of the AC power grid being the third frequency; The third power is the difference between the second power and the first inertia power, and the absolute value of the difference between the third frequency and the AC power grid power frequency is greater than the absolute value of the difference between the second frequency and the AC power grid power frequency.

5. The grid-connected power converter according to claim 4, characterized in that: The controller is used for controlling the output power of the power conversion circuit to be adjusted from the third power to the fourth power in response to the frequency of the AC power grid changing from the third frequency to the fourth frequency; The fourth power is the sum of the third power, the second inertia power and the second frequency modulation power, and the absolute value of the difference between the fourth frequency and the AC power grid power frequency is smaller than the absolute value of the difference between the third frequency and the AC power grid power frequency.

6. The grid-connected power converter according to claim 5, characterized in that: When the fourth frequency is lower than the AC power grid power frequency and the absolute value of the difference between the fourth frequency and the AC power grid power frequency decreases, the second frequency modulation power decreases; When the fourth frequency is greater than the AC power grid power frequency and the absolute value of the difference between the fourth frequency and the AC power grid power frequency decreases, the second frequency modulation power increases.

7. The grid-connected power converter according to claim 6, characterized in that: When the fourth frequency is lower than the power frequency of the AC power grid, the fourth power is greater than or equal to the minimum output power of the power conversion circuit; When the fourth frequency is greater than the AC power grid operating frequency, the fourth power is less than or equal to the maximum output power of the power conversion circuit.

8. The grid-connected power converter according to any one of claims 5 to 7, characterized in that: The controller is used for controlling the output power of the power conversion circuit to be adjusted from the fourth power to the preset reference power in response to the frequency of the AC power grid changing from the fourth frequency to the AC power grid working frequency.

9. The grid-connected power converter according to any one of claims 1 to 8, characterized in that: The first frequency modulation power is determined by the controller based on a preset power and frequency droop curve, the preset reference power, the output power of the power conversion circuit, the frequency of the AC power grid and a preset lower limit frequency, wherein the preset lower limit frequency is the minimum value of the first frequency.

10. An energy storage system, characterized in that: The energy storage system comprises an energy storage battery and a grid-connected power converter according to any one of claims 1 to 9, wherein the energy storage battery is connected to a first end of the power conversion circuit via a DC bus; The power conversion circuit is used to output alternating current based on the direct current provided by the energy storage battery; or, the power conversion circuit is used to output direct current to the energy storage battery.

11. A power control method for a grid-connected power converter, characterized in that: The method comprises: In response to the frequency of the AC power grid being a first frequency, controlling the output power of the grid-connected power converter to be adjusted from a preset reference power to a first power; wherein the preset reference power is the output power of the grid-connected power converter when the AC power grid is stable, the first power is the sum of the preset reference power and a first inertia power, and the first inertia power is the power obtained by the grid-connected power converter simulating the inertia characteristics of a synchronous generator; In response to the frequency of the AC power grid being a second frequency, the output power of the grid-connected power converter is controlled to be adjusted from the first power to a second power; wherein the second power is the sum of the first power and the first frequency-modulated power; and the absolute value of the difference between the second frequency and the AC power grid operating frequency is greater than the absolute value of the difference between the first frequency and the AC power grid operating frequency.

12. The method according to claim 11, characterized in that In response to the second frequency being less than the AC power grid power frequency and the absolute value of the difference between the second frequency and the AC power grid power frequency increasing, increasing the first frequency modulation power; In response to the second frequency being greater than the AC power grid power frequency and the absolute value of the difference between the second frequency and the AC power grid power frequency increasing, the first frequency modulation power is reduced.

13. The method according to claim 12, characterized in that In response to the second frequency being less than the AC power grid power frequency, controlling the second power to be less than or equal to the maximum output power of the grid-connected power converter; In response to the second frequency being greater than the AC power grid operating frequency, the second power is controlled to be greater than or equal to a minimum output power of the grid-connected power converter.

14. The method according to any one of claims 11 to 13, characterized in that: The method further comprises: In response to the frequency of the AC power grid being a third frequency, controlling the output power of the grid-connected power converter to be adjusted from the second power to a third power; The third power is the difference between the second power and the first inertia power, and the absolute value of the difference between the third frequency and the AC power grid power frequency is greater than the absolute value of the difference between the second frequency and the AC power grid power frequency.

15. The method according to claim 14, characterized in that The method further comprises: In response to the frequency of the AC power grid changing from the third frequency to a fourth frequency, controlling the output power of the grid-connected power converter to be adjusted from the third power to a fourth power; The fourth power is the sum of the third power, the second inertia power and the second frequency modulation power, and the absolute value of the difference between the fourth frequency and the AC power grid power frequency is smaller than the absolute value of the difference between the third frequency and the AC power grid power frequency.

16. The method according to claim 15, characterized in that In response to the fourth frequency being less than the AC power grid power frequency and the absolute value of the difference between the fourth frequency and the AC power grid power frequency decreasing, reducing the second frequency modulation power; In response to the fourth frequency being greater than the AC power grid power frequency and the absolute value of the difference between the fourth frequency and the AC power grid power frequency decreasing, the second frequency modulation power is increased.

17. The method according to claim 16, characterized in that In response to the fourth frequency being less than the AC power grid power frequency, controlling the fourth power to be greater than or equal to the minimum output power of the grid-connected power converter; In response to the fourth frequency being greater than the AC power grid operating frequency, the fourth power is controlled to be less than or equal to the maximum output power of the grid-connected power converter.

18. The method according to any one of claims 15 to 17, characterized in that: The method further comprises: In response to the frequency of the AC power grid changing from the fourth frequency to the AC power grid operating frequency, the output power of the grid-connected power converter is controlled to be adjusted from the fourth power to the preset reference power.

19. The method according to any one of claims 11 to 18, characterized in that: The first frequency modulation power is based on a preset power and frequency droop curve, and is determined by the preset reference power, the output power of the grid-connected power converter, the frequency of the AC power grid and a preset lower limit frequency, wherein the preset lower limit frequency is the minimum value of the first frequency.

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