A synchronous control method for on-grid and off-grid switching based on a dual rotating coordinate system

Abstract

The present invention discloses a method for synchronous control of grid-on and off-grid switching based on a dual rotating coordinate system. The method is used to synchronize grid voltage and phase during grid connection and off-grid operation. The method collects the three-phase grid voltage and performs a Clark transform to calculate the phase angle of the grid voltage signal; calculates the phase angle increment, the angular frequency of the grid fundamental wave, and the output frequency; calculates the phase angle step size in the internal rotating coordinate system and the phase angle step size in grid-on mode; and calculates the grid-on phase angle #imgabs0# in a dual coordinate system formed by the grid phase rotating coordinate system and the internal rotating coordinate system. By performing a Clark transform on the three-phase grid voltage and applying a second-order generalized integral, the voltages #imgabs1# and #imgabs2# in the stationary coordinate system are phase-shifted by 90 degrees. The positive and negative sequence voltages are then separated, eliminating interference from the negative sequence component on phase estimation and improving phase-locking accuracy. The phase angle #imgabs3# in both the grid phase rotating coordinate system and the internal rotating coordinate system is calculated, achieving a faster, less-hysteresis phase-locking method and ensuring consistency in switching phase and frequency during grid connection and off-grid operation.

Description

Technical Field

[0001] The present invention relates to the field of microgrid control technology, and in particular to a method for synchronous control of on-grid and off-grid switching based on a dual rotating coordinate system. Background Art

[0002] As the proportion of renewable energy generation continues to grow year by year, the requirements for grid-connected energy storage systems are becoming increasingly stringent. For grid-following energy storage systems, efficient grid connection relies on precise tracking of grid frequency and phase. Traditional technical solutions employ a three-phase phase-locked loop (SRF-PLL) based on a synchronously rotating d and q coordinate system. This employs a PI controller to maintain the q-axis output voltage at zero, aligning the output phase with the grid. However, the introduction of the PI controller introduces phase lag, resulting in significant current surges during grid connection.

[0003] In addition, when switching from the grid-connected state to the off-grid state, the system converts from the current source mode to the voltage source mode. How to ensure the consistency of the switching phase and frequency between the two states is also one of the key technologies for on-grid and off-grid switching. Summary of the Invention

[0004] In view of this, it is necessary to provide a synchronous control method for on-grid and off-grid switching based on a dual rotating coordinate system that can ensure that the phase and frequency remain consistent.

[0005] A method for synchronous control of grid-on and off-grid switching based on a dual rotating coordinate system is provided for synchronizing grid voltage and phase when connected to and off-grid. The specific steps include:

[0006] Step 1: Collect the three-phase grid voltage and perform Clark transformation to calculate the phase angle of the grid voltage signal;

[0007] Step 2: Calculate the phase angle increment, the angular frequency of the grid fundamental wave and the output frequency;

[0008] Step 3: Calculate the phase angle step of the output voltage of the converter module in the off-grid mode;

[0009] Step 4: Calculate the estimated grid phase angle in the dual coordinate system formed by the grid phase rotation coordinate system and the internal rotation coordinate system. .

[0010] Preferably, the specific steps of collecting the three-phase grid voltage and performing Clark transformation to calculate the phase angle of the grid voltage in step 1 include:

[0011] Step 1.1: The digital signal processing module of the converter samples the voltage signal of the three-phase grid to obtain the current grid voltage value. The sampling period is the carrier period. ;

[0012] Step 1.2: Perform Clark transform on the three-phase grid voltage signal to obtain mutually orthogonal signals in the stationary coordinate system. 、 , the conversion formula is shown in formula (1):

[0013] (1);

[0014] Among them, U a 、U b 、U c is the three-phase grid voltage;

[0015] Step 1.3, use the biquad generalized integral to obtain two sets of mutually orthogonal signals and 、 and ;

[0016] Step 1.4: Separate the positive sequence voltage of the three-phase voltage in the stationary coordinate system by extracting the positive and negative sequence. and , as shown in formula (2):

[0017] (2);

[0018] in, , Indicates a 90-degree phase angle difference in the time domain;

[0019] Step 1.5, use the four-quadrant inverse tangent function atan2(y, x) to calculate the current instantaneous phase angle of the power grid , as shown in formula (3):

[0020] (3).

[0021] Preferably, the specific steps of step 2, calculating the phase angle increment, the angular frequency of the grid fundamental wave and the output frequency, include:

[0022] Step 2.1: Calculate the increment of the phase angle of the grid fundamental wave in adjacent sampling periods. , as shown in formula (4):

[0023] (4);

[0024] in, is the current phase angle of the grid fundamental wave, is the phase angle of the previous control cycle of the grid fundamental wave;

[0025] Step 2.2, calculate the angular frequency of the grid fundamental wave , as shown in formula (5):

[0026] (5);

[0027] in, , is the carrier frequency of DSP;

[0028] Step 2.3, calculate the output frequency of the grid fundamental wave , as shown in formula (6):

[0029] (6).

[0030] Preferably, the specific steps of step three, calculating the phase angle step of the output voltage of the converter module in the off-grid mode, include:

[0031] In off-grid mode, the converter module is converted from a current source module to a voltage source module, and the phase step of the output voltage is Depends on fundamental frequency and DSP carrier frequency , as shown in formula (7):

[0032] (7).

[0033] Preferably, in step 4, the grid phase angle is calculated in a dual coordinate system formed by the grid phase rotation coordinate system and the internal rotation coordinate system. The specific steps include:

[0034] Step 4.1: Calculate the phase angle in the grid phase rotation coordinate system ;

[0035] Step 4.2, calculate the phase angle in the internal rotating coordinate system ;

[0036] Step 4.3: Rotate the grid phase by the phase angle in the coordinate system Phase angle with the internal rotating coordinate system Synchronize and get the estimated grid phase angle .

[0037] Preferably, step 4.1, calculate the phase angle in the grid phase rotation coordinate system The specific steps include:

[0038] Step 4.1.1, estimate the grid phase angle ;

[0039] Step 4.1.2, calculate the phase angle of the fundamental period and the estimated grid phase angle The difference is used as the input value of the PI controller;

[0040] Step 4.1.3, the increment of the phase angle of the grid fundamental wave in adjacent sampling periods As the phase angle step in the grid-connected mode, the phase angle step signal in the grid-connected mode is limited by a low-pass filter;

[0041] Step 4.1.4, in off-grid mode, the phase step of the output voltage As the phase angle step signal in off-grid mode;

[0042] Step 4.1.5: Calculate the output value of the PI controller and the phase angle step signal value after limiting in grid-connected mode or the phase step of the output voltage in off-grid mode. The phase angle in the grid phase rotation coordinate system is obtained by limiting the sum of ;

[0043] Step 4.1.6: Substitute the phase angle calculated in step 4.1.5 Feedback to the subtractor in step 4.1.2 and the adder in step 4.1.5 to correct the phase angle in the grid phase rotation coordinate system .

[0044] Preferably, the PI controller is used to compensate for the phase difference caused by phase accumulation, and the output value of the PI controller is limited to [-30, +30] degrees.

[0045] Preferably, step 4.2, calculate the phase angle in the internal rotating coordinate system The specific steps include:

[0046] Step 4.2.1, establish the internal rotating coordinate system. When the power grid is powered normally, the internal rotating coordinate system uses the phase angle step With coefficient The product of dynamically adjusts the phase step size, and the phase angle in the internal rotating coordinate system is obtained after limiting. , and the phase angle in the grid phase rotation coordinate system When crossing the power frequency cycle, the phase angle in the internal rotating coordinate system is Phase angle in the coordinate system rotated with the grid phase synchronous;

[0047] Step 4.2.2: In off-grid mode, the phase angle adjustment coefficient is 1 and the phase angle step size is used. The product of the coefficient 1 dynamically adjusts the phase step size.

[0048] Preferably, the phase angle of the grid phase rotation coordinate system in step 4.2.1 is The judgment method for crossing the power frequency cycle is: the phase angle of the power grid phase rotation coordinate system obtained in the current calculation cycle , and the phase angle of the grid phase rotation coordinate system in the previous calculation cycle is When , it is considered that the phase angle crosses the power frequency synchronization.

[0049] Preferably, in step 4.3, the phase angle of the grid phase rotation coordinate system is Phase angle with the internal rotating coordinate system Synchronize and get the estimated grid phase angle The specific steps include:

[0050] Step 4.3.1: When the grid is detected, measures 1 and 2 are used to rotate the grid phase to the phase angle in the coordinate system. Phase angle with the internal rotating coordinate system Synchronization, as estimated grid phase angle ;

[0051] Among them, measure 1, the phase angle in the grid phase rotation coordinate system Phase angle in the internal rotating coordinate system when crossing the power frequency cycle Phase angle in the coordinate system rotated with the grid phase Synchronization; Measure 2, phase angle step in internal rotating coordinate system Pass coefficient Associated with the grid output frequency to dynamically adjust the phase step size;

[0052] Step 4.3.2: When the power grid is lost, the input phase angle step of the grid phase rotation coordinate system and the internal rotation coordinate system are both , the phase angle in the internal rotating coordinate system Phase angle in the coordinate system rotated with the grid phase After synchronization, the estimated grid phase angle .

[0053] In the above-mentioned on-grid and off-grid switching synchronization control method based on the dual rotating coordinate system, the voltage in the stationary coordinate is converted by Clark transformation of the three-phase grid voltage and the second-order generalized integral. and The phase is shifted by 90 degrees and the positive and negative sequences of the voltage are separated, which avoids the interference of the negative sequence component on the phase estimation and improves the accuracy of the phase lock. Calculate the phase angle in the grid phase rotation coordinate system and the internal rotation coordinate system , achieving a faster and less delayed phase-locking method, ensuring the consistency of switching phase and frequency when the grid is connected to or off the grid. The algorithm of the present invention is simple, easy to implement, low-cost, and easy to promote. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Figure 1 This is a flow chart of a method for synchronous control of on-grid and off-grid switching based on a dual rotating coordinate system according to an embodiment of the present invention.

[0055] Figure 2 This is a signal processing structure block diagram of step 1 in the on-grid and off-grid switching synchronization control method based on a dual rotating coordinate system according to an embodiment of the present invention.

[0056] Figure 3 This is a structural block diagram of the SOGI module in step 1 of the on-grid and off-grid switching synchronization control method based on a dual rotating coordinate system according to an embodiment of the present invention.

[0057] Figure 4 This is a structural block diagram of a grid phase angle estimation structure in a grid phase rotating coordinate system in a method for synchronous control of on-grid and off-grid switching in a dual rotating coordinate system according to an embodiment of the present invention.

[0058] Figure 5 This is a structural block diagram of the grid phase angle estimation structure in the internal synchronous rotating coordinate system in the on-grid and off-grid switching synchronous control method based on the dual rotating coordinate system in an embodiment of the present invention.

[0059] Figure 6 It is an application structure block diagram of an embodiment of the present invention.

[0060] Figure 7 This is the oscilloscope display graph 1 when the grid is connected or disconnected according to the embodiment of the present invention.

[0061] Figure 8 This is the second oscilloscope display graph when the embodiment of the present invention is connected to the grid and disconnected from the grid.

[0062] Figure 9 This is the third oscilloscope display graph when the embodiment of the present invention is connected to the grid and disconnected from the grid. DETAILED DESCRIPTION

[0063] This embodiment takes the on-grid and off-grid switching synchronization control method based on a dual rotating coordinate system as an example, and the present invention will be described in detail below with reference to specific embodiments and drawings.

[0064] See also Figure 1 , showing a method for synchronous control of on-grid and off-grid switching based on a dual rotating coordinate system provided by an embodiment of the present invention, the specific steps are as follows:

[0065] Step 1: The DSP of the converter module samples the three-phase grid voltage to obtain the current grid voltage value. The sampling period is the carrier period. .

[0066] Step 2: Use Clark transform to transform the three-phase voltage signals into mutually orthogonal signals in a stationary coordinate system. 、 , the conversion formula is:

[0067] (1);

[0068] Among them, U a 、U b 、U c is the three-phase voltage. The specific operation is as follows Figure 2 Follow step 2 in the .

[0069] Step 3: Use the biquad generalized integral to obtain two sets of mutually orthogonal signals and 、 and The structure of the SOGI module is as follows: Figure 2 The whole operation is as shown. Figure 2 Step 3 in .

[0070] Specifically, the dual second-order generalized integrator (DSOGI) generates orthogonal signals (α-β coordinate system) through two parallel second-order generalized integrators (SOGI), achieving a 90° phase shift of the fundamental component and harmonic suppression. Its transfer function exhibits a bandpass filter characteristic with the center frequency being the grid fundamental frequency, which can effectively filter out non-fundamental components. The structure diagram of the SOGI module is shown in Figure 1. Figure 3 shown.

[0071] Step 4: Use the positive sequence extraction module to separate the positive sequence voltage of the three-phase voltage in the stationary coordinate system. and ,like Figure 2 Follow step 4 in the .

[0072] (2);

[0073] in, , Indicates a 90-degree phase angle difference in the time domain.

[0074] Step 5: Use the four-quadrant inverse tangent function Calculate the current phase angle of the power grid ,like Figure 2 Follow step 5 in the previous step.

[0075] Specifically, when (x, y) falls in the first quadrant, the range of atan2(y, x) output is ; When (x, y) falls in the second quadrant, the range of atan2(y, x) output is ; When (x, y) falls in the third quadrant, the range of atan2(y, x) output is ; When (x, y) falls in the fourth quadrant, the range of atan2(y, x) output is .

[0076] Right now,

[0077] (3).

[0078] Step 6, calculate the angular frequency. The phase angle obtained in step 5 , according to the phase angle difference between the two times and the sampling time interval, the angular frequency can be calculated .

[0079] (4);

[0080] (5);

[0081] (6);

[0082] in, is the carrier frequency.

[0083] Step 7: Calculate the output frequency of the grid fundamental wave .

[0084] (7).

[0085] Step 8: Calculate the step size of the internal rotation coordinate system .

[0086] Since the module no longer follows the grid frequency in off-grid mode, the output frequency is fixed in off-grid mode and does not need to follow the dynamic changes of the large grid. In off-grid mode, the converter module is converted from current source mode to voltage source mode. Therefore, the phase angle step of the output voltage is The fundamental frequency and DSP carrier frequency The phase angle step size in off-grid mode is determined as follows:

[0087] (8);

[0088] In grid-connected mode, the phase angle step size is :

[0089] (9).

[0090] Steps 1 to 8 obtain the basic values required for all calculations in the dual coordinate system. Based on these calculation results, the phase locking of the present invention is divided into two parts. One part is the grid phase rotation coordinate system, the structure of which is as follows: Figure 4 As shown, one part is the internal rotating coordinate system, the structure is as follows Figure 5 shown.

[0091] is the estimated value of the grid phase, and the reference phase angle The difference is made and the deviation is input to the PI controller. The output of the PI controller is then limited to obtain the phase angle adjustment result, which is then compared with the increment of the reference phase angle. Add, estimate the phase angle and limit it to In the range of .

[0092] The PI controller is a proportional-integral controller. The control of the PI loop in the block diagram is to compensate for the phase difference caused by phase accumulation, and its output is limited between [-30, 30] degrees.

[0093] In the grid-connected state, the internal total rotating coordinate system detects the output (grid) frequency in real time , and divided by the given frequency, the ratio of the two is used as the adjustment coefficient of the internal phase angle; in off-grid mode, this coefficient is 1.

[0094] is the internal phase angle, whose size is limited to Within the range, It is the fundamental frequency of the power grid, such as 50Hz.

[0095] As mentioned above, the dual coordinate system phase angle synchronization mechanism is: The internal rotating coordinate system phase angle is detected when the grid phase When crossing the power frequency cycle, and Synchronization ensures that when there is no grid, the phase when switching to off-grid mode is consistent with the phase when the grid is present.

[0096] The method for judging the cross-frequency cycle is to use the estimated phase angle obtained in the current calculation cycle , and the phase angle estimated in the previous calculation cycle When , it is considered that the phase angle crosses the power frequency synchronization.

[0097] The grid disconnect signal is a dry-node signal provided by the static transfer switch (STS). When the STS detects grid loss, it disconnects the three-phase AC input and simultaneously sends a grid disconnect dry-node signal. Upon receiving this signal, the DSP estimates the phases and switches to off-grid mode.

[0098] When the STS detects that the grid has recovered, it sends the grid phase and grid voltage amplitude to the PCS module. The PCS pre-starts grid connection control so that the phase and amplitude of the PCS meet the following two conditions:

[0099] (1) Adjust the phase angle step size , when estimating the phase angle The phase angle difference with that detected by STS is between -0.02777 and 0.02777 rad;

[0100] (2) Adjust the amplitude of the inverter voltage so that the amplitude of the three-phase inverter voltage is less than 50V compared with the grid voltage amplitude;

[0101] After conditions (1) and (2) are met, the PCS module can send a grid-connected instruction to the STS module, and the PCS module can switch to the grid-connected mode.

[0102] like Figure 6 In the energy storage system shown, the output of the photovoltaic system is connected to the maximum power point tracking module (MPPT). The output of the MPPT forms a DC coupling with the battery to provide DC voltage input for the PCS module. The PCS system consists of an AC / DC bidirectional converter, an AC contactor, and a static transfer switch (STS). The output of the PCS is connected to the load, and the STS is connected to the grid.

[0103] The waveform diagram when the grid is connected and disconnected is as follows: Figure 7 、 Figure 8 and Figure 9 As shown, Figure 7 The diagram shows the various operating stages of the module, including shutdown (section A), grid-connected startup (section B), grid-connected stable operation (section C), grid-connected to off-grid switching (section D), and finally off-grid stable operation (section E). Figure 8 and Figure 9 This is an enlarged view of segment D. Figure 8 China grid voltage (U a 、U b 、U c ) is not connected to the inverter voltage (U inva 、U invb 、U invc ) overlap together, Figure 9 In the example, the grid voltage and the inverter voltage are moved to the same level. Figure 8 It can be seen that the time from grid connection to off-grid connection to voltage stabilization is about 4ms. Figure 9 It can be seen that the amplitude of the three-phase voltage does not change after the grid-connected mode is switched to the off-grid mode.

[0104] In the above-mentioned on-grid and off-grid switching synchronization control method based on the dual rotating coordinate system, the voltage in the stationary coordinate is converted by Clark transformation of the three-phase grid voltage and the second-order generalized integral. and The phase is shifted by 90 degrees and the positive and negative sequences of the voltage are separated, which avoids the interference of the negative sequence component on the phase estimation and improves the accuracy of the phase lock. Calculate the phase angle in the grid phase rotation coordinate system and the internal rotation coordinate system , achieving a faster and less delayed phase-locking method, ensuring the consistency of switching phase and frequency when the grid is connected to or off the grid. The algorithm of the present invention is simple, easy to implement, low-cost, and easy to promote.

[0105] It should be noted that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for synchronous control of grid connection and off-grid switching based on a dual rotating coordinate system, which is used for grid voltage and phase synchronization during grid connection and off-grid operation, characterized in that: The specific steps include: Step 1: Collect the three-phase grid voltage and perform Clark transformation to calculate the phase angle of the grid voltage signal; Step 2: Calculate the phase angle increment, the angular frequency of the grid fundamental wave and the output frequency; Step 3: Calculate the phase angle step size of the internal rotating coordinate system and the phase angle step size in the grid-connected mode; Step 4: Calculate the grid phase angle in the dual coordinate system formed by the grid phase rotation coordinate system and the internal rotation coordinate system. ; In the fourth step, the grid phase angle is calculated in the dual coordinate system formed by the grid phase rotation coordinate system and the internal rotation coordinate system. The specific steps include: Step 4.1: Calculate the phase angle in the grid phase rotation coordinate system ; Specifically include: Step 4.1.1, estimate the grid phase angle ; Step 4.1.2, calculate the phase angle of the fundamental period and the estimated grid phase angle The difference is used as the input value of the PI controller; Step 4.1.3, the increment of the phase angle of the grid fundamental wave in adjacent sampling periods As the phase angle step in the grid-connected mode, the phase angle step signal in the grid-connected mode is limited by a low-pass filter; Step 4.1.4, in off-grid mode, the phase step of the output voltage As the phase angle step signal in off-grid mode; Step 4.1.5: Calculate the output value of the PI controller and the phase angle step signal value after limiting in grid-connected mode or the phase step of the output voltage in off-grid mode. The phase angle in the grid phase rotation coordinate system is obtained by limiting the sum of ; Step 4.1.6: Substitute the phase angle calculated in step 4.1.5 Feedback to the subtractor in step 4.1.2 and the adder in step 4.1.5 to correct the phase angle in the grid phase rotation coordinate system ; Step 4.2, calculate the phase angle in the internal rotating coordinate system ; Specifically include: Step 4.2.1, establish the internal rotating coordinate system. When the power grid is powered normally, the internal rotating coordinate system uses the phase angle step With coefficient The product of dynamically adjusts the phase step size, and the phase angle in the internal rotating coordinate system is obtained after limiting. , and the phase angle in the grid phase rotation coordinate system When crossing the power frequency cycle, the phase angle in the internal rotating coordinate system is Phase angle in the coordinate system rotated with the grid phase synchronous; Step 4.2.2: In off-grid mode, the phase angle adjustment coefficient is 1 and the phase angle step size is used. The product with the coefficient 1 dynamically adjusts the phase step size; Step 4.3: Rotate the grid phase by the phase angle in the coordinate system Phase angle with the internal rotating coordinate system Synchronize and get the estimated grid phase angle ; Specifically include: Step 4.3.1: When the grid is detected, measures 1 and 2 are used to rotate the grid phase to the phase angle in the coordinate system. Phase angle with the internal rotating coordinate system Synchronization, as estimated grid phase angle ; Among them, measure 1, the phase angle in the grid phase rotation coordinate system Phase angle in the internal rotating coordinate system when crossing the power frequency cycle Phase angle in the coordinate system rotated with the grid phase Synchronization; Measure 2, phase angle step in internal rotating coordinate system Pass coefficient Associated with the grid output frequency to dynamically adjust the phase step size; Step 4.3.2: When the power grid is lost, the input phase angle step of the grid phase rotation coordinate system and the internal rotation coordinate system are both , the phase angle in the internal rotating coordinate system Phase angle in the coordinate system rotated with the grid phase After synchronization, the estimated grid phase angle .

2. The method for synchronous control of on-grid and off-grid switching based on a dual rotating coordinate system according to claim 1, characterized in that: The specific steps of step 1, collecting the three-phase grid voltage and performing Clark transformation to calculate the phase angle of the grid voltage, include: Step 1.1: The digital signal processing module of the converter samples the voltage signal of the three-phase grid to obtain the current grid voltage value. The sampling period is the carrier period. ; Step 1.2: Perform Clark transform on the three-phase grid voltage signal to obtain mutually orthogonal signals in the stationary coordinate system. 、 , the conversion formula is shown in formula (1): （1）； Among them, U a 、U b 、U c is the three-phase grid voltage; Step 1.3, use the biquad generalized integral to obtain two sets of mutually orthogonal signals and 、 and ; Step 1.4: Separate the positive sequence voltage of the three-phase voltage in the stationary coordinate system by extracting the positive and negative sequence. and , as shown in formula (2): （2）； in, , Indicates a 90-degree phase angle difference in the time domain; Step 1.5, use the four-quadrant inverse tangent function atan2(y, x) to calculate the current instantaneous phase angle of the power grid , as shown in formula (3): （3）。 3. The method for synchronous control of on-grid and off-grid switching based on a dual rotating coordinate system according to claim 2, wherein: The specific steps of the step 2, calculating the phase angle increment, the angular frequency of the grid fundamental wave and the output frequency, include: Step 2.1: Calculate the increment of the phase angle of the grid fundamental wave in adjacent sampling periods. , as shown in formula (4): （4）； in, is the current phase angle of the grid fundamental wave, is the phase angle of the previous control cycle of the grid fundamental wave; Step 2.2, calculate the angular frequency of the grid fundamental wave , as shown in formula (5): （5）； in, , is the carrier frequency of DSP; Step 2.3, calculate the output frequency of the grid fundamental wave , as shown in formula (6): （6）。 4. The method for synchronous control of on-grid and off-grid switching based on a dual rotating coordinate system according to claim 3, wherein: The specific steps of step 3, calculating the phase angle step of the output voltage of the converter module in the off-grid mode, include: In off-grid mode, the converter module is converted from a current source module to a voltage source module, and the phase step of the output voltage is Depends on fundamental frequency and DSP carrier frequency , as shown in formula (7): （7）。 5. The method for synchronous control of on-grid and off-grid switching based on a dual rotating coordinate system according to claim 1, wherein: The PI controller is used to compensate for the phase difference caused by phase accumulation, and the output value of the PI controller is limited to [-30, +30] degrees.

6. The method for synchronous control of on-grid and off-grid switching based on a dual rotating coordinate system according to claim 1, wherein: The phase angle of the grid phase rotation coordinate system in step 4.2.1 The judgment method for crossing the power frequency cycle is: the phase angle of the power grid phase rotation coordinate system obtained in the current calculation cycle , and the phase angle of the grid phase rotation coordinate system in the previous calculation cycle is When , it is considered that the phase angle crosses the power frequency synchronization.

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