Off-grid mode-to-grid-connected mode switching control method for power device and power device

Abstract

An off-grid mode-to-grid-connected mode switching control method for a power device, comprising: when a power grid is on, directly calculating, on the basis of an output phase of a power device in an off-grid mode and a preset angular frequency, a given angular frequency difference required by a voltage-controlled oscillator when the phase of an off-grid output voltage is corrected to the phase of a power grid voltage; carrying out initial assignment for an integral result of a PI controller of a phase-locked loop on the basis of the given angular frequency difference, and then controlling the phase-locked loop to start working; configuring the oscillation angular frequency of the voltage-controlled oscillator on the basis of an output of the PI controller and the preset power grid frequency; and controlling the power device to be grid-connected.

Description

Control method for off-grid and grid-connected power equipment and power equipment

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application filed with the China Patent Office on September 13, 2023, with application number 202311181407.4 and invention name “Control method and power equipment for off-grid conversion of power equipment to grid”, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present application belongs to the field of power electronics technology, and in particular relates to a control method for off-grid and grid-connected power equipment, power equipment, and a computer-readable storage medium. Background Art

[0004] The statements herein merely provide background information related to the present application and do not necessarily constitute exemplary techniques.

[0005] With the increasing installation of distributed renewable energy and energy storage devices, structural changes have been brought to modern power distribution systems. Microgrids based on energy storage systems can continue to supply power to regional loads without disconnecting from the transmission system when the power grid fails, maintaining off-grid operation. When the power grid returns to normal, the microgrid system exits the off-grid operation mode and switches to the grid-connected operation mode. Energy storage devices such as energy storage converters (Power Conversion System, PCS) can be used for off-grid load operation and grid-connected rectification and inversion, that is, charging and discharging operation. After off-grid load operation, the power grid returns to normal, and the off-grid to grid-connected control strategy can be started. After switching to grid-connected operation, the energy storage device can control the working status of battery charging and discharging. However, in the related art, the process of switching from off-grid to grid-connected is relatively cumbersome, consumes a lot of computing resources and is prone to errors.

[0006] Summary of the Invention

[0007] According to various embodiments of the present application, a control method for switching an off-grid power device to a grid-connected power device, an electric power device, and a computer-readable storage medium are provided.

[0008] In a first aspect, an embodiment of the present application provides a control method for grid-connecting an electric power device, wherein the electric power device includes a phase-locked loop, and the control method includes:

[0009] When the grid receives power, obtain the real-time grid angular frequency value and real-time grid voltage;

[0010] In an off-grid operation mode, the oscillation angular frequency of the voltage-controlled oscillator of the phase-locked loop is set to the real-time angular frequency value of the power grid, and the voltage-controlled oscillator is controlled to operate according to the oscillation angular frequency to obtain the output phase of the power device;

[0011] When there is a deviation between the output phase and the real-time phase of the real-time grid voltage, adjusting the oscillation angular frequency so that the output phase tracks the real-time phase;

[0012] When the output phase tracks the real-time phase, obtaining a given angular frequency value of the oscillation angular frequency;

[0013] Calculating according to the real-time angular frequency value of the power grid and the given angular frequency value to obtain a given angular frequency difference, and performing an initial assignment on an integral result of a PI controller of the phase-locked loop using the given angular frequency difference;

[0014] Controlling the PI controller to start working, and configuring the oscillation angular frequency of the voltage-controlled oscillator based on the output angular frequency value of the PI controller and a preset grid angular frequency value;

[0015] Controlling the power equipment to be connected to the grid.

[0016] In the second aspect, an embodiment of the present application also provides an electric power device, which includes a phase-locked loop, a memory, a processor, and a computer program stored in the memory and runnable on the processor. The phase-locked loop is connected to the processor, and when the processor executes the computer program, it implements the steps of the control method for off-grid and grid-connected electric power equipment as described above.

[0017] In a third aspect, an embodiment of the present application further provides a computer-readable storage medium storing a computer program, which, when executed by a controller, can implement the steps of the control method for switching power equipment from off-grid to on-grid as described above.

[0018] The details of one or more embodiments of the present application are set forth in the following drawings and description. Other features, objects, and advantages of the present application will become apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments or exemplary technologies of the present application, the following briefly introduces the drawings required for use in the description of the embodiments or exemplary technologies. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, without paying any creative work, they can also obtain drawings of other embodiments based on these drawings.

[0020] FIG1 is a module diagram of a phase-locked loop provided in an embodiment of the present application.

[0021] FIG2 is a schematic diagram of the grid voltage provided in an embodiment of the present application after Clark and Park transformation.

[0022] FIG3 is a flow chart of a control method for switching an off-grid power device to a grid-connected power device according to an embodiment of the present application.

[0023] FIG4 is a flow chart of a control method for switching an off-grid power device to a grid-connected power device according to an embodiment of the present application.

[0024] FIG5 is a flow chart of a control method for switching off-grid and on-grid power equipment provided in one embodiment of the present application.

[0025] FIG6 is a flow chart of a control method for switching an off-grid power device to a grid-connected state according to an embodiment of the present application.

[0026] FIG7 is a phase tracking waveform diagram of a control method for off-grid and grid-connected power equipment according to a related art provided in an embodiment of the present application.

[0027] FIG8 is a module diagram of a control device for off-grid and grid-connected power equipment provided in one embodiment of the present application.

[0028] FIG9 is a schematic structural diagram of an electric power device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0029] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, this application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0030] In power systems and power electronics applications, phase-locked loops (PLLs) are primarily used to lock and track the phase angle of the grid voltage. A three-phase phase-locked loop (SRF-PLL) based on dq synchronous rotating coordinate transformation, also known as a single synchronous rotating coordinate system phase-locked loop (SSRF-PLL), requires no additional hardware and is implemented entirely by software algorithms. Under ideal three-phase voltage sources, it can quickly and accurately synchronize with the grid voltage, making it a highly effective and widely used grid synchronization technology.

[0031] The block diagram of the SRF-PLL is shown in Figure 1, corresponding to the three modules defined in the phase-locked loop. The Clark converter 111 and Park converter 112 act as phase detectors, equivalent to the phase detector (PD) 11 of the phase-locked loop, obtaining the q-axis component Vq of the three-phase voltage to obtain phase information. The PI controller serves as the loop filter (LF) 12 of the phase-locked loop. The output ωn of the PI controller is added to the given angular frequency ω' to obtain the angular frequency of the voltage. The integrator (1 / S) serves as the voltage-controlled oscillator (VCO) 13 in the phase-locked loop. After passing through the integrator (1 / S), the angular frequency outputs the phase-locked voltage phase and is fed back as the angle θ used for the rotational coordinate transformation.

[0032] The basic principle of SRF-PLL is based on the dq synchronous rotating coordinate system. First, the three-phase voltages u, v, and w are converted to the stationary coordinate system by the Clark transformer 111, and then converted to the rotating coordinate system by the Park transformer 112. Please refer to Figure 2, which shows a schematic diagram of the three-phase voltage after Clark and Park transformation. Among them, the voltage vector is the spatial composite voltage vector of the three-phase voltages u, v, and w. Vq is the voltage vector The q-axis component in the rotating coordinate system, Vd is the voltage vector The d-axis component in the rotated coordinate system.

[0033] Voltage Vector The component Vq on the q axis contains the phase information and frequency information of the grid voltage. Vq reflects the phase relationship between the grid voltage and the d axis. When Vq>0, the voltage vector If you want to achieve synchronous phase lock, you need to increase the frequency (that is, speed up the rotation speed of the rotating coordinate system). When Vq < 0, the voltage vector If you want to achieve synchronous phase lock, you need to reduce the frequency (i.e. slow down the rotation speed of the rotating coordinate system). In phase with the d-axis. Therefore, phase locking can be achieved by taking Vq = 0 as the control target, even if θ = ωt.

[0034] In related technologies, when power electronic equipment is off-grid and loaded, switching to grid connection requires two phase-locked loops. One is used to self-oscillate and maintain stable output of the power electronic equipment when off-grid, and the other is used to lock the grid phase when connected to the grid. This makes switching from off-grid to grid connection more complicated, requires mutual assignment, is prone to errors, and wastes chip algorithm resources.

[0035] On the other hand, if only a phase-locked loop (PLL) is used, a long switching time may be required, making it impossible to achieve a smooth transition from off-grid to grid-connected operation. Specifically, during off-grid operation, since the PLL needs to provide a self-oscillating phase, the PI controller output is typically assigned to 0, and the given angular frequency ω' is assigned to the AC angular frequency, for example, 50 Hz*2π. This allows the voltage-controlled oscillator 13 to continuously self-oscillate at a frequency of 50 Hz and trigger a phase, so that the output voltage of the power device remains at that phase. When grid-connected operation is to be performed, the transformed q-axis component Vq equals zero, indicating that the PLL has locked the grid phase. The PI controller outputs ωn, and ωn + ω' together generate the grid angular velocity. After integration by the voltage-controlled oscillator 13, the grid phase is obtained, indicating successful phase lock. However, since the PLL is already occupied during off-grid operation (ωn is always assigned to zero), it is impossible to track the grid voltage in real time for phase lock during off-grid operation. When switching from off-grid to grid-connected operation, if the PLL is used directly for phase lock, the lock time will be long, failing to meet the time requirements for switching from off-grid to grid-connected operation.

[0036] To address the above issues, an embodiment of the present application provides a control method for connecting a power device to the grid based on a phase-locked loop, that is, the power device includes a phase-locked loop. Referring to FIG3 in conjunction with FIG1-FIG2, the control method for connecting a power device to the grid includes the following steps:

[0037] Step S110 , when power is supplied from the grid, obtaining the real-time grid angular frequency value and the real-time grid voltage.

[0038] The real-time grid voltage can be detected by a corresponding detection circuit. Furthermore, the real-time grid frequency f_grid can be calculated based on the obtained grid voltage and the zero-crossing frequency. The real-time grid angular frequency 2πf_grid can then be calculated based on the real-time grid frequency f_grid. The detection circuit can be composed of one or more of a voltage divider circuit, a mutual inductor, a filter circuit, an analog-to-digital conversion circuit, and an amplifier circuit.

[0039] Step S120: in the off-grid operation mode, the oscillation angular frequency of the voltage controlled oscillator of the phase-locked loop is set to the real-time angular frequency value of the grid, and the voltage controlled oscillator is controlled to operate according to the oscillation angular frequency to obtain the output phase of the power equipment.

[0040] Setting the oscillation angular frequency ωn+ω' of the phase-locked loop's voltage-controlled oscillator 13 to the real-time grid angular frequency value 2πf_grid is equivalent to setting the PI controller's output ωn to 0 and the given angular frequency value ω' to the real-time grid angular frequency value. That is, the initial value of the given angular frequency value ω' is ω0 = 2πf_grid. The power equipment operates at this oscillation angular frequency ωn+ω' and outputs AC power, resulting in an AC output (voltage) phase, namely the self-oscillation phase θ of the voltage-controlled oscillator 13.

[0041] Step S130 : When there is a deviation between the output phase and the real-time phase of the real-time grid voltage, the oscillation angular frequency is adjusted to make the output phase track the real-time phase.

[0042] As mentioned above, whether the output phase θ deviates from the real-time phase can be determined by the voltage vector The component Vq of the q axis is confirmed. When Vq is not zero (or the absolute value is greater than the preset voltage value), it means that there is a deviation between the output phase and the real-time phase, for example, leading or lagging. It can be understood that the implementation of this step is to directly adjust the oscillation angular frequency ωn+ω' before the power equipment is connected to the grid, so that the output phase θ of the power equipment changes, thereby tracking the real-time phase. The goal is to make the output phase θ consistent with the real-time phase, or the deviation between the two is within the allowable range, so as to wait for further fine-tuning, thereby saving tracking time. For example, the oscillation angular frequency ωn+ω' of the voltage-controlled oscillator 13 is adjusted with a fixed or preset angular frequency with a certain change rate set based on the real-time frequency f_grid of the grid, thereby changing the output phase θ to track the real-time phase. The size of the preset angular frequency depends on the size of the above-mentioned deviation. For example, the larger the deviation, the larger the preset angular frequency or the larger its change rate.

[0043] Step S140 : When the output phase tracks the real-time phase, a given angular frequency value of the oscillation angular frequency is obtained.

[0044] When the output phase θ matches the real-time phase, or the deviation between the two is within the allowable range, it can be considered that the output phase θ tracks the real-time phase. Since the PI controller's output ωn is assigned a value of 0, the given angular frequency ω' is the oscillation angular frequency ωn + ω'. Assuming the oscillation angular frequency is ω1, when the output phase θ tracks the real-time phase, the given angular frequency ω' = ω1.

[0045] It can be understood that in order to ensure that the output phase θ remains consistent with the real-time phase or the deviation continues to remain within the allowable range, the oscillation angular frequency ωn+ω' should be maintained near ω1.

[0046] Step S150 , calculating based on the real-time angular frequency value of the power grid and the given angular frequency value to obtain a given angular frequency difference, and performing initial assignment on the integral result of the PI controller of the phase-locked loop using the given angular frequency difference.

[0047] By assigning an initial value to the integral result of the phase-locked loop's PI controller (i.e., the output of the PI controller), ωn, using a given angular frequency difference, the PI controller's output angular frequency value, ωn, does not start from zero, but rather has a certain initial value. The sum of this initial value and the grid's real-time angular frequency value is essentially consistent with the oscillation angular frequency, i.e., ωn + ω' = ω1. At this point, the PI controller's output angular frequency value, ωn, ensures that the oscillation frequency of the voltage-controlled oscillator 13 remains at the oscillation angular frequency value, ω1, when the output phase θ tracks the real-time phase. This reduces the tracking time of the PI controller after grid connection, speeds up the tracking process, and enables control of grid connection of power equipment.

[0048] Step S160 : Control the PI controller to start working, and configure the oscillation angular frequency of the voltage controlled oscillator based on the output angular frequency value of the PI controller and the preset grid angular frequency value.

[0049] Specifically, the system switches to a phase-locked loop (PLL) to continue tracking the real-time phase. At this point, the PI controller in the PLL is controlled to start operating, and the oscillation angular frequency ωn+ω' of the voltage-controlled oscillator 13 is configured based on the output angular frequency value ωn of the PI controller and the preset grid angular frequency value (i.e., the given angular frequency value ω' is fixed to the preset grid angular frequency value at this time). The system controls the voltage-controlled oscillator 13 to operate according to the configured oscillation angular frequency ωn+ω', and continues to fine-tune the output phase θ of the power equipment, so that the output phase θ is ultimately consistent with the real-time phase. The preset grid angular frequency value ω' can be a fixed value, such as 50*2π=100π; or it can be the real-time AC angular frequency.

[0050] Step S170: Control the power equipment to be connected to the grid.

[0051] Because the output phase θ of the off-grid power equipment has been corrected to the real-time phase before grid connection, or the deviation between the two is within the allowable range, and the output angular frequency ωn of the PI controller has been initially assigned, the switching to grid connection can be smooth. In this way, a phase-locked loop is used to achieve smooth off-grid to grid connection switching, saving chip computing resources.

[0052] Referring to FIG. 1 , FIG. 2 and FIG. 4 , in one embodiment, step S130 adjusts the oscillation angular frequency when there is a deviation between the output phase θ and the real-time phase of the real-time grid voltage, including:

[0053] Step S131 : transforming the real-time grid voltage by the output phase to obtain a d-axis voltage component and a q-axis voltage component in a rotating coordinate system.

[0054] Specifically, the three-phase voltages u, v, and w are first converted to a stationary coordinate system based on the output phase θ using the Clark converter 111 in the phase-locked loop, and then converted to a rotating coordinate system using the Park converter 112 to obtain the d-axis voltage component Vd and the q-axis voltage component Vq in the rotating coordinate system.

[0055] Step S132: When the difference between the d-axis voltage component and the grid voltage amplitude is greater than the first preset voltage value or the absolute value of the q-axis voltage component is greater than the second preset voltage value, the oscillation angular frequency of the voltage-controlled oscillator is adjusted based on the preset angular frequency adjustment value, and the step of controlling the voltage-controlled oscillator according to the oscillation angular frequency to obtain the output phase of the power equipment is returned to step S120.

[0056] On the one hand, when there is a deviation between the output phase θ and the real-time phase, there is a difference between the d-axis voltage component Vd converted by the phase detector 11 and the grid voltage amplitude. The magnitude of the difference can be used to determine whether the tracking is complete. The grid voltage amplitude is usually known, for example, the 220V grid amplitude is On the other hand, when the q-axis voltage component Vq is greater than zero, it indicates that the output phase θ is leading. Similarly, when the q-axis voltage component Vq is less than zero, it indicates that the output phase θ is lagging. Thus, the absolute value of the q-axis voltage component Vq can be used to determine whether tracking is complete.

[0057] Therefore, if the difference between the d-axis voltage component Vd and the grid voltage amplitude is greater than the first preset voltage value, the oscillation angular frequency ωn+ω' of the voltage-controlled oscillator 13 is adjusted based on the preset angular frequency adjustment value, and the process returns to step S120. The voltage-controlled oscillator 13 is controlled to operate according to the oscillation angular frequency ωn+ω' to obtain a new output phase θ of the power device. This cycle is repeated until the difference between the d-axis voltage component Vd and the grid voltage amplitude is less than or equal to the first preset voltage value. Alternatively, when the absolute value of the q-axis voltage component Vq is greater than the second preset voltage value, the oscillation angular frequency ωn+ω' of the voltage-controlled oscillator 13 is adjusted based on the preset angular frequency adjustment value, and the process returns to step S120. The voltage-controlled oscillator 13 is controlled to operate according to the oscillation angular frequency ωn+ω' to obtain a new output phase θ of the power device. This cycle is repeated until the absolute value of the q-axis voltage component Vq is less than or equal to the second preset voltage value.

[0058] Among them, as long as one of the two aforementioned methods of determining whether there is a deviation between the output phase θ and the real-time phase is met, the oscillation angular frequency ωn+ω' of the voltage-controlled oscillator 13 is adjusted based on the preset angular frequency adjustment value, so as to return to the step of controlling the voltage-controlled oscillator 13 according to the oscillation angular frequency ωn+ω' to obtain the output phase θ of the power equipment.

[0059] It can be understood that since the output ωn of the PI controller before grid connection is kept at 0, the oscillation angular frequency ωn+ω' of the voltage controlled oscillator 13 is adjusted based on the preset angular frequency adjustment value, and in fact only ω' needs to be adjusted.

[0060] The first preset voltage value can be set to 5V, 10V, 15V, or 20V, and the second preset voltage value can be set to 5V, 10, 15, or 20. The preset angular frequency adjustment value can be set based on the deviation between the output phase θ and the real-time phase of the real-time grid voltage. For example, the preset angular frequency adjustment value is proportional to the difference between the d-axis voltage component Vd and the grid voltage amplitude, or the preset angular frequency adjustment value is proportional to the absolute value of the q-axis voltage component Vq, thereby improving tracking speed.

[0061] Please refer to FIG. 4 and FIG. 5 . In one embodiment, after step S131 , the process further includes:

[0062] Step S133 : when the difference between the d-axis voltage component and the grid voltage amplitude is less than the first preset voltage value and the absolute value of the q-axis voltage component is less than the second preset voltage value, the current value of the oscillation angular frequency is determined as the given angular frequency value.

[0063] It can be understood that when the difference between the d-axis voltage component and the grid voltage amplitude is less than a first preset voltage value, and the absolute value of the q-axis voltage component is less than a second preset voltage value, this indicates that the deviation between the output phase θ and the real-time phase is within the allowable range for grid connection. At this time, because the PI controller output ωn is 0, the oscillation angular frequency ωn + ω' = ω', and the current value of the oscillation angular frequency ω1 is the current given angular frequency value.

[0064] In one embodiment, adjusting the oscillation angular frequency of the voltage controlled oscillator based on the preset angular frequency adjustment value in step S132 includes:

[0065] Step 1: sum the real-time angular frequency value of the power grid and the preset angular frequency adjustment value to obtain the tracking angular frequency value.

[0066] The real-time grid angular frequency value 2πf_grid is, for example, 50*2π=100π. The preset angular frequency adjustment value can be 2πΔf, which can be set based on the difference between the first calculated d-axis voltage component Vd and the grid voltage amplitude. For example, if the difference between the d-axis voltage component Vd and the grid voltage amplitude is significant, the preset angular frequency adjustment value 2πΔf can be set larger, such as 0.5 (Hz) or 1 (Hz); otherwise, it can be set smaller, such as 0.1 (Hz). The positive or negative value of the preset angular frequency 2πΔf depends on whether the output phase θ is leading or lagging. When the q-axis voltage component Vq is greater than zero, the output phase is leading, and the tracking angular frequency value is 2π(f_grid-Δf). When the q-axis voltage component Vq is less than zero, the output phase is lagging. The tracking angular frequency value is 2π(f_grid+Δf). It will be understood that in this embodiment, the preset angular frequency adjustment value can be a fixed value, in which case the tracking angular frequency value is also a fixed value.

[0067] Step 2: Configure the oscillation angular frequency to track the angular frequency value.

[0068] That is, in step S132, each time the step of controlling the voltage-controlled oscillator 13 according to the oscillation angular frequency ωn + ω' to obtain the output phase θ of the power device is returned to, the voltage-controlled oscillator 13 is controlled according to a fixed oscillation angular frequency ωn + ω'. For example, assuming that the output phase θ lags the real-time phase of the grid voltage and the tracking angular frequency value is 2π(f_grid + Δf), the oscillation angular frequency can be maintained at the tracking angular frequency value throughout the tracking process, that is, ωn + ω' = 2π(f_grid + Δf).

[0069] In one embodiment, adjusting the oscillation angular frequency of the voltage controlled oscillator based on the preset angular frequency adjustment value in step S132 includes:

[0070] Step A: sum the current value of the oscillation angular frequency and the preset angular frequency adjustment value to obtain a tracking angular frequency value.

[0071] The current value of the oscillation angular frequency ωn+ω' is the real-time value. The preset angular frequency adjustment value can be set as needed. For example, if there is a significant difference between the d-axis voltage component Vd and the grid voltage amplitude, the preset angular frequency adjustment value 2πΔf can be set to a larger value, such as 0.5 (Hz) or 1 (Hz); otherwise, it can be set to a smaller value, such as 0.1 (Hz). The positive or negative value of the preset angular frequency adjustment value 2πΔf depends on whether the output phase θ is leading or lagging. When the q-axis voltage component Vq is greater than zero, the tracking angular frequency value is 2π(f_grid-nΔf). When the q-axis voltage component Vq is less than zero, the tracking angular frequency value is 2π(f_grid+nΔf), where n is the number of steps to return to the step of controlling the voltage-controlled oscillator 13 according to the oscillation angular frequency ωn+ω' to obtain the output phase θ of the power device. It will be understood that in this embodiment, the preset angular frequency adjustment value can be a variable value. In this case, the tracking angular frequency value is a value with a certain rate of change.

[0072] Step B: configuring the oscillation angular frequency to track the angular frequency value.

[0073] That is, in step S132, each time the step of controlling the voltage-controlled oscillator 13 to operate according to the oscillation angular frequency ωn+ω' to obtain the output phase θ of the power equipment is returned, the value of the oscillation angular frequency ωn+ω' has a certain rate of change. For example, assuming that the output phase θ lags behind the real-time phase of the grid voltage, and the tracking angular frequency value is 2π(f_grid+nΔf), then during the entire tracking process, when the grid is powered, the oscillation angular frequency of the oscillator is first configured to 2πf_grid. When it is first confirmed that there is a deviation between the output phase θ and the real-time phase, the oscillation angular frequency is configured to the tracking angular frequency value, that is, ωn+ω'=2π(f_grid+nΔf). grid +Δf), and get the output phase θ of the next control cycle. If the output phase θ still deviates from the real-time phase, the oscillation angular frequency is configured as ωn+ω'=2π(f grid +2×Δf), and so on.

[0074] In one embodiment, in step 150 , calculating based on the real-time grid angular frequency value and the given angular frequency value to obtain the given angular frequency difference includes: subtracting the real-time grid angular frequency value from the given angular frequency value to obtain the given angular frequency difference.

[0075] Because the power equipment is operating off-grid and the voltage-controlled oscillator 13 is constantly self-oscillating, the phase-locked loop's PI controller is not yet operational. Direct grid connection at this point will result in voltage output distortion. The given angular frequency difference ωn is inferred from the fixed angular frequency value ω' and assigned to the integral result of the PI controller in the phase-locked loop. This allows the phase-locked loop to smoothly and quickly track the grid in the next cycle, ensuring that the self-oscillation phase is determined by the grid phase.

[0076] Taking the preset angular frequency adjustment value as a fixed value 2πΔf and the preset grid angular frequency as the real-time grid angular frequency 2πf_grid as an example, it can be seen from the above description that when the output phase θ tracks the real-time phase of the grid voltage, the current value of the oscillation angular frequency ωn+ω'=ω1=2π(f grid ±Δf), given angular frequency difference Δω'=ω1-ω0=2π(f grid ±Δf)-2π(f grid =±2πΔf.

[0077] At this time, the PI controller is switched to work, and the oscillation angular frequency is ωn+ω'=pi out +ω', the given angular frequency ω' is fixed to the preset grid angular frequency, so ω'=2πf grid To maintain smooth switching, the oscillation angular frequency remains unchanged, so ωn+ω'=pi out +ω'=ω1, so there exists:

[0078] pi out =ω1-ω'=2π(f grid ±Δf)-2πf grid = ±2πΔf = Δω'

[0079] The PI controller output is kp*error+ki_out, where kp*error is the proportional calculation result and ki_out is the integral calculation result. After parameter configuration, the PI controller's proportional adjustment step size, kp*error, is known. Based on Δω', the integral result, ki_out, can be inferred. After an initial value is assigned to the integral result, ki_out, the PI controller's integral calculation results are accumulated, and the phase-locked loop (PLL) is used to continue real-time phase tracking.

[0080] In one embodiment, before adjusting the oscillation angular frequency of the voltage-controlled oscillator based on the preset angular frequency adjustment value in step S132, the method further includes:

[0081] Configuring a preset angular frequency adjustment value based on the q-axis voltage component;

[0082] When the q-axis voltage component is positive, the preset angular frequency adjustment value is configured as a negative value; when the q-axis voltage component is negative, the preset angular frequency adjustment value is configured as a positive value. The absolute value of the preset angular frequency adjustment value is positively correlated with the absolute value of the q-axis voltage component.

[0083] It can be understood that when the q-axis voltage component Vq is greater than zero, the output phase θ leads the real-time phase, requiring speed tracking that is less than the real-time grid angular frequency value 2πf_grid. Therefore, the preset angular frequency adjustment value 2πΔf is configured as a negative value to cause the output phase θ to track the real-time phase. When the q-axis voltage component Vq is less than zero, the output phase θ lags the real-time phase, requiring speed tracking that is greater than the real-time grid angular frequency value 2πf_grid. Therefore, the preset angular frequency adjustment value 2πΔf is configured as a positive value to cause the output phase θ to track the real-time phase. The larger the absolute value of the preset angular frequency adjustment value 2πΔf and the absolute value of the q-axis voltage component Vq, the more serious the advance or lag of the output phase θ. Therefore, the corresponding preset angular frequency adjustment value 2πΔf is configured as a larger value; conversely, the corresponding preset angular frequency adjustment value 2πΔf is configured as a smaller value, resulting in a positive correlation between the two.

[0084] Referring to FIG. 1 , FIG. 2 , FIG. 6 and FIG. 7 , in one embodiment, after step S170 of controlling the power equipment to be connected to the grid, the method further includes:

[0085] Step S180 : transforming the real-time grid voltage using the output phase of the phase-locked loop to obtain a d-axis voltage component and a q-axis voltage component in a rotating coordinate system.

[0086] Specifically, the three-phase voltages u, v, and w are first converted to a stationary coordinate system based on the output phase θ using the Clark converter 111 in the phase-locked loop. The three-phase voltages are then converted to a rotating coordinate system using the Park converter 112, yielding the d-axis voltage component Vd and the q-axis voltage component Vq in the rotating coordinate system. This allows the PI controller to calculate the deviation between the d-axis voltage component Vd and the grid voltage amplitude, and to determine whether the output phase θ is leading or lagging based on the q-axis voltage component Vq.

[0087] Step S190: Utilize a PI controller to calculate based on the q-axis voltage component to obtain a real-time given angular frequency difference.

[0088] After the power equipment is connected to the grid (time t1 shown in Figure 7), the phase-locked loop is switched to continue tracking the real-time phase of the grid. The subsequent real-time given angular frequency difference (i.e., ωn) will no longer be directly assigned, but will be calculated by the PI controller based on the q-axis voltage component Vq and Vq_ref (usually configured as 0).

[0089] Step S200 : setting the oscillation angular frequency of the voltage-controlled oscillator to the sum of the real-time given angular frequency difference and the preset grid angular frequency value.

[0090] The real-time given angular frequency difference ωn, i.e., the real-time output value of the PI controller, controls the voltage-controlled oscillator 13 according to the oscillation angular frequency ωn + ω' to obtain the output phase θ of the power device. The preset grid angular frequency value ω' can be a fixed value, such as 50*2π, or it can be the real-time AC angular frequency.

[0091] As shown in Figure 7, curve L1 is a phase change curve corresponding to the control method for off-grid and grid-connected power equipment provided in an embodiment of the present application. After the grid power is received (time 0), the PI controller is assigned an initial integral value according to the method of the embodiment of the present application. At t1, the phase-locked loop starts to work and can immediately lock the actual phase of the grid. Curve L2 is a phase change curve corresponding to off-grid and grid-connected power equipment in the related art. The initial value of the PI controller starts from zero and locks the grid phase until time t2. Compared with the two, the control method for off-grid and grid-connected power equipment provided in an embodiment of the present application requires much less time to control off-grid and grid-connected power equipment.

[0092] In one embodiment, before power is supplied from the grid, the control method for switching power equipment from off-grid to on-grid further includes: in an off-grid operation mode, setting the oscillation angular frequency of a voltage-controlled oscillator of a phase-locked loop to a preset grid angular frequency value.

[0093] Generally, the preset grid angular frequency value is set to a conventional grid angular frequency value so that the power equipment can quickly track the grid phase when switching from an off-grid to a grid-connected device. This grid angular frequency value can be a preconfigured grid angular frequency value based on the local grid, or it can be a real-time grid angular frequency detected in real time, and this application does not impose any restrictions on this.

[0094] Referring to FIG8 , an embodiment of the present application further provides a control device for grid-connecting power equipment. Referring to FIG1 , the power equipment includes a phase-locked loop, and the control device includes:

[0095] The acquisition module 801 is configured to acquire the real-time grid angular frequency value and the real-time grid voltage when power is supplied to the grid.

[0096] The configuration module 802 is configured to set the oscillation angular frequency of the voltage-controlled oscillator 13 of the phase-locked loop to the real-time angular frequency value of the power grid in the off-grid operation mode, and control the voltage-controlled oscillator 13 to operate according to the oscillation angular frequency to obtain the output phase of the power equipment.

[0097] The adjustment module 803 is configured to adjust the oscillation angular frequency when there is a deviation between the output phase and the real-time phase of the real-time grid voltage, so that the output phase tracks the real-time phase.

[0098] The acquisition module 801 is further configured to acquire a given angular frequency value of the oscillation angular frequency when the output phase tracks the real-time phase.

[0099] The calculation module 804 is configured to calculate according to the real-time angular frequency value of the power grid and the given angular frequency value to obtain a given angular frequency difference, and to perform an initial assignment on the integral result of the PI controller of the phase-locked loop with the given angular frequency difference.

[0100] The configuration module 802 is further configured to control the PI controller to start working, and configure the oscillation angular frequency of the voltage controlled oscillator based on the output angular frequency value of the PI controller and a preset grid angular frequency value.

[0101] The control module 805 is configured to control the power equipment to be connected to the grid.

[0102] In one embodiment, the adjustment module 803 includes:

[0103] The conversion and acquisition unit is configured to acquire a d-axis voltage component and a q-axis voltage component in a rotating coordinate system obtained by transforming the real-time grid voltage with the output phase.

[0104] The adjustment execution unit is configured to adjust the oscillation angular frequency of the voltage-controlled oscillator based on a preset angular frequency adjustment value when the difference between the d-axis voltage component and the grid voltage amplitude is greater than a first preset voltage value or the absolute value of the q-axis voltage component is greater than a second preset voltage value, and return to execute the step of controlling the voltage-controlled oscillator according to the oscillation angular frequency to obtain the output phase of the power equipment.

[0105] In one embodiment, the adjustment module 803 further includes:

[0106] The determination unit is configured to determine the current value of the oscillation angular frequency as the given angular frequency value when the difference between the d-axis voltage component and the grid voltage amplitude is less than a first preset voltage value and the absolute value of the q-axis voltage component is less than the second preset voltage value.

[0107] In one embodiment, the adjustment execution unit includes:

[0108] The summing subunit is configured to sum the real-time angular frequency value of the power grid and the preset angular frequency adjustment value to obtain a tracking angular frequency value.

[0109] The configuration subunit is configured to configure the oscillation angular frequency to the tracking angular frequency value.

[0110] In one embodiment:

[0111] The summing subunit is further configured to sum the current value of the oscillation angular frequency and the preset angular frequency adjustment value to obtain a tracking angular frequency value.

[0112] The configuration subunit is further configured to configure the oscillation angular frequency to the tracking angular frequency value.

[0113] In one embodiment, the calculation module 804 is configured to: subtract the real-time angular frequency value of the power grid from the given angular frequency value to obtain the given angular frequency difference.

[0114] In one embodiment, the configuration subunit is further configured to configure the preset angular frequency adjustment value based on the q-axis voltage component. When the q-axis voltage component is positive, the preset angular frequency adjustment value is configured to be negative; and when the q-axis voltage component is negative, the preset angular frequency adjustment value is configured to be positive. The absolute value of the preset angular frequency adjustment value is positively correlated with the absolute value of the q-axis voltage component.

[0115] In one embodiment, after controlling the power equipment to be connected to the grid:

[0116] The phase detector 11 of the phase-locked loop transforms the real-time grid voltage with the output phase of the phase-locked loop to obtain the d-axis voltage component and the q-axis voltage component in the rotating coordinate system.

[0117] The phase-locked loop uses a PI controller to calculate the real-time given angular frequency difference based on the q-axis voltage component

[0118] The loop filter 12 of the phase-locked loop sets the oscillation angular frequency of the voltage-controlled oscillator 13 to the sum of the real-time given angular frequency difference and the preset grid angular frequency value.

[0119] Please refer to Figure 9. An embodiment of the present application also provides an electric power device 90, which includes a phase-locked loop, a memory 92, a processor 93, and a computer program 921 stored in the memory 92 and executable on the processor 93. The phase-locked loop is connected to the processor 93. When the processor 93 executes the computer program 921, the steps of the control method for switching the electric power device from off-grid to on-grid are implemented as described above.

[0120] Optionally, a power converter 91 is also included, wherein the first end of the power converter 91 is used to connect to the energy storage module 901, the second end of the power converter 91 is used to connect to the power grid and / or load, and the third end of the power converter 91 is used to connect to the power generation equipment.

[0121] It is understandable that the power device 90 is, for example, an independent device for connecting to the energy storage module 901 and drawing power from or charging the energy storage module 901.

[0122] Of course, the power equipment 90 can also be integrated into the energy storage module 901. Therefore, an embodiment of the present application also provides an energy storage device, including a phase-locked loop, an energy storage module 901, a power converter 91, a memory 92, a processor 93, and a computer program 921 stored in the memory 92 and runnable on the processor 93. The power converter 91 is connected to the energy storage module 901 and the processor 93. When the processor 93 executes the computer program 921, the steps of the control method for off-grid and grid-connected power equipment as described above are implemented.

[0123] It is understandable that the number of batteries (ie, energy storage modules) 901 and power equipment 90 in the energy storage device corresponds one to one, and can be one or more, and this application does not impose any limitation on this.

[0124] Those skilled in the art will understand that Figure 9 is merely an example of the power equipment 90 and the energy storage device, and does not constitute a limitation on the power equipment 90 and the energy storage device. It may include more or fewer components than shown in the figure, or a combination of certain components, or different components, such as input and output devices, network access devices, etc.

[0125] The processor 93 may be a central processing unit (CPU), or may be another general-purpose controller, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), an off-the-shelf programmable gate array (FPGA), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose controller may be a microcontroller or any conventional controller.

[0126] In some embodiments, the memory 92 may be an internal storage unit of the power device 90 or the energy storage module, such as a hard disk or memory of the power device 90 or the energy storage module. In other embodiments, the memory 92 may also be an external storage device of the power device 90 or the energy storage module, such as a plug-in hard disk, a smart media card (SMC), a secure digital (SD) card, a flash card, etc. equipped on the power device 90 or the energy storage module. Furthermore, the memory 92 may also include both an internal storage unit of the power device 90 or the energy storage module and an external storage device. The memory 92 is used to store an operating system, an application program, a boot loader, data, and other programs. The memory 92 may also be used to temporarily store data that has been output or is to be output.

[0127] The embodiment of the present application further provides a computer-readable storage medium, which stores a computer program 921. When the computer program 921 is executed by the processor 93, it can implement the steps in the above-mentioned various method embodiments.

[0128] An embodiment of the present application provides a computer program product, which, when executed on a computer, enables the computer to execute the steps in the above-mentioned various method embodiments.

[0129] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the present application can implement all or part of the processes in the above-mentioned method embodiments by using a computer program 921 to instruct the relevant hardware. The computer program 921 can be stored in a computer-readable storage medium. When executed by the processor 93, the computer program 921 can implement the steps of each of the above-mentioned method embodiments. The computer program 921 includes computer program 921 code, which can be in source code form, object code form, executable file, or some intermediate form. The computer-readable medium can at least include: any entity or device capable of carrying the computer program 921 code to the camera / terminal device, a recording medium, computer memory 92, ROM (Read-Only Memory), RAM (Random Access Memory), CD-ROM (Compact Disc Read-Only Memory), magnetic tape, floppy disk, and optical data storage device. The computer-readable storage medium mentioned in this application may be a non-volatile storage medium, in other words, a non-transitory storage medium.

[0130] It should be understood that all or part of the steps for implementing the above embodiments can be implemented using software, hardware, firmware, or any combination thereof. When implemented using software, all or part of the steps can be implemented in the form of a computer program 921 product. The computer program 921 product includes one or more computer instructions. The computer instructions can be stored in the above-mentioned computer-readable storage medium.

[0131] In the above embodiments, the description of each embodiment has its own focus. For parts that are not described or recorded in detail in a certain embodiment, reference can be made to the relevant description of other embodiments.

[0132] The above-described embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A control method for connecting an electric power device to a grid, the electric power device comprising a phase-locked loop, the control method comprising: When the power grid receives power, obtain the real-time angular frequency value and real-time power grid voltage of the power grid; In an off-grid operation mode, the oscillation angular frequency of the voltage-controlled oscillator of the phase-locked loop is set to the real-time angular frequency value of the power grid, and the voltage-controlled oscillator is controlled to work according to the oscillation angular frequency to obtain the output phase of the power equipment; When there is a deviation between the output phase and the real-time phase of the real-time grid voltage, adjusting the oscillation angular frequency so that the output phase tracks the real-time phase; When the output phase tracks the real-time phase, obtaining a given angular frequency value of the oscillation angular frequency; Calculating according to the real-time angular frequency value of the power grid and the given angular frequency value to obtain a given angular frequency difference, and performing initial assignment on the integral result of the PI controller of the phase-locked loop with the given angular frequency difference; Controlling the PI controller to start working, and configuring the oscillation angular frequency of the voltage-controlled oscillator based on the output angular frequency value of the PI controller and a preset grid angular frequency value; Control the power equipment to connect to the grid.

2. The control method according to claim 1, wherein: When there is a deviation between the output phase and the real-time phase of the real-time grid voltage, adjusting the oscillation angular frequency comprises: The real-time grid voltage is transformed by the output phase to obtain a d-axis voltage component and a q-axis voltage component in a rotating coordinate system; When the difference between the d-axis voltage component and the grid voltage amplitude is greater than a first preset voltage value or the absolute value of the q-axis voltage component is greater than a second preset voltage value, the oscillation angular frequency of the voltage-controlled oscillator is adjusted based on a preset angular frequency adjustment value.

3. The control method according to claim 2, wherein: After transforming the real-time grid voltage by the output phase to obtain a d-axis voltage component and a q-axis voltage component in a rotating coordinate system, the method further includes: When the difference between the d-axis voltage component and the grid voltage amplitude is less than a first preset voltage value and the absolute value of the q-axis voltage component is less than the second preset voltage value, the current value of the oscillation angular frequency is determined as the given angular frequency value.

4. The control method according to claim 2, wherein: The step of adjusting the oscillation angular frequency of the voltage-controlled oscillator based on a preset angular frequency adjustment value comprises: The real-time angular frequency value of the power grid and the preset angular frequency adjustment value are summed to obtain a tracking angular frequency value; The oscillation angular frequency is configured to be the tracking angular frequency value.

5. The control method according to claim 2, wherein: The step of adjusting the oscillation angular frequency of the voltage-controlled oscillator based on a preset angular frequency adjustment value comprises: The current value of the oscillation angular frequency is summed with the preset angular frequency adjustment value to obtain a tracking angular frequency value; The oscillation angular frequency is configured to be the tracking angular frequency value.

6. The control method according to claim 2, wherein: The step of calculating according to the real-time angular frequency value of the power grid and the given angular frequency value to obtain a given angular frequency difference comprises: The given angular frequency value is subtracted from the real-time angular frequency value of the power grid to obtain the given angular frequency difference.

7. The control method according to claim 2, wherein: Before adjusting the oscillation angular frequency of the voltage-controlled oscillator based on the preset angular frequency adjustment value, the method further includes: configuring the preset angular frequency adjustment value based on the q-axis voltage component; Wherein, when the q-axis voltage component is a positive value, the preset angular frequency adjustment value is configured to be a negative value; when the q-axis voltage component is a negative value, the preset angular frequency adjustment value is configured to be a positive value; wherein the absolute value of the preset angular frequency adjustment value is positively correlated with the absolute value of the q-axis voltage component.

8. The control method according to any one of claims 1 to 7, wherein: After controlling the power equipment to be connected to the grid, the method further includes: The real-time grid voltage is transformed by the output phase of the phase-locked loop to obtain a d-axis voltage component and a q-axis voltage component in a rotating coordinate system; Using a PI controller to calculate based on the q-axis voltage component to obtain a real-time given angular frequency difference; The oscillation angular frequency of the voltage-controlled oscillator is set to the sum of the real-time given angular frequency difference and the preset grid angular frequency value.

9. The control method according to any one of claims 1 to 7, wherein: Before the power grid is powered, the method further includes: In the off-grid operation mode, the oscillation angular frequency of the voltage-controlled oscillator of the phase-locked loop is set to a preset grid angular frequency value.

10. An electric power device, comprising a phase-locked loop, a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the phase-locked loop is connected to the processor, and when the processor executes the computer program, the steps of the control method for off-grid and grid-connected power equipment as claimed in any one of claims 1 to 9 are implemented.

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