H4 bridge DC-AC modulation method and device suitable for micro-inverse

Abstract

The invention discloses an H4 bridge DC-AC modulation method and device suitable for micro inverters, relates to the technical field of grid connection of micro inverters, and solves the problems that in the prior art, a current loop controlled by PI in grid connection based on a PI controller is common in dynamic performance and anti-interference capability, and harmonic waves carried by a power grid cannot be accurately and effectively reduced. The method comprises the following steps: firstly connecting an output to a pure resistor, supplying power by using an auxiliary power supply to carry out open-loop debugging, then carrying out off-grid current loop debugging, carrying out fundamental wave regulation control by using a PR controller, carrying out off-grid current loop control by using a load, then carrying out low-voltage grid-connected debugging, and preferably carrying out high-voltage grid-connected debugging. Compared with other traditional PI control, the PR controller has the advantages that the board explosion risk can be effectively reduced, the correctness of each step is ensured, troubleshooting is facilitated, and compared with other traditional PI control, the PR controller can more accurately and effectively reduce harmonic waves with corresponding frequencies in a power grid, so that the total harmonic distortion of the current is reduced.

Description

Technical Field

[0001] This application relates to the field of grid connection technology for microinverters, and in particular to an H4 bridge DC-AC modulation method and apparatus suitable for microinverters. Background Technology

[0002] The H4 bridge, also known as a full-bridge inverter, is the most mainstream and mature DC-AC topology in microinverters. It consists of four power switches (typically MOSFETs or IGBTs), and its core objective is to convert the direct current (DC) generated by the photovoltaic panels into alternating current (AC) that is in phase and frequency with the power grid, and then inject it into the grid. The modulation technology of the H4 bridge DC-AC system controls how these four switches are turned on and off to precisely achieve this core objective.

[0003] In the grid-connected commissioning scheme of microinverters, the existing commissioning scheme involves many steps and stages from simulation to actual commissioning. During the commissioning process, there will be deviations between the actual and simulation results, which may lead to the risk of equipment damage.

[0004] Most existing micro-inverter DC-AC inverter terminals are connected to the grid using PI controller regulation or open-loop control. The dynamic performance and anti-interference capability of the current loop of PI control are generally poor, and it also has shortcomings in harmonic optimization capabilities, making it unable to accurately and effectively reduce the harmonics inherent in the power grid. Summary of the Invention

[0005] The purpose of this application is to overcome the problems of the general dynamic performance and anti-interference ability of the current loop of PI control in grid-connected systems based on PI controllers, and the inability to accurately and effectively reduce the harmonics of the grid itself, and to provide an H4 bridge DC-AC modulation method and device suitable for micro-inverters.

[0006] Firstly, an H4 bridge DC-AC modulation method suitable for micro-inverters is provided, including:

[0007] Connect the output to a pure resistor and use an auxiliary power supply for open-loop debugging.

[0008] Perform off-grid current loop commissioning, use a PR controller for fundamental frequency regulation and control, and use a load for off-grid current loop control;

[0009] Disconnect the load, connect to an AC source for low-voltage grid-connected commissioning, add voltage feedforward loop control, use a PR controller for harmonic modulation in the voltage feedforward loop control, and lower the protection threshold.

[0010] High-voltage grid connection commissioning is being carried out.

[0011] In some possible implementations, during open-loop debugging, an open-loop fixed proportional coefficient unipolar wave is generated, powered separately by an auxiliary power supply. After verifying that the drive is correct, the output voltage and current are observed on the bus by adjusting the power supply.

[0012] In some possible implementations, during open-loop debugging, in the H4 bridge, switches S1 and S3 are complementary, and switches S2 and S4 are complementary. The duty cycle of switch S1 is calculated using the following formula:

[0013] D=

[0014] Where D is the duty cycle of switch S1, and K p It is a proportionality coefficient. Angular frequency;

[0015] The period of the switching transistor S2 is consistent with the AC voltage. Observe whether the driving waveform and the output current waveform are normal.

[0016] In some possible implementations, off-grid current loop commissioning includes:

[0017] Sample the alternating current and bus voltage;

[0018] Self-defined target current;

[0019] Calculate the difference between the target current and the alternating current;

[0020] Calculate the output current based on the transfer function of the PR controller;

[0021] The high-level time within one cycle is calculated based on the output current.

[0022] In some possible implementations, the formula for calculating the high-level time within one cycle is:

[0023] T on =(I out_d / V bus )*T prd

[0024] Among them, T on For the high-level time within one cycle, I out_d V represents the current output by the PR controller. bus T is the bus voltage. prd This represents the total time of the switching cycle.

[0025] In some possible implementations, during low-voltage grid-connected commissioning, the high-level time within one cycle is calculated to improve the output waveform and reduce harmonics.

[0026] Ton=((Iout_d +V ac ) / V bus )*T prd

[0027] Among them, T on For the high-level time within one cycle, I out_d V represents the current output by the PR controller. ac For alternating current voltage, V bus T is the bus voltage. prd This represents the total time of the switching cycle.

[0028] In some possible implementations, during high-voltage grid-connected commissioning, the protection threshold is increased, voltage harmonics are added for system verification, the inherent harmonics in the voltage are analyzed using FFT, several high harmonic components are identified, active compensation is performed on the identified high harmonic components, the output variables are summed, and the proportional coefficient, cutoff frequency and resonance coefficient are adjusted to reduce harmonics.

[0029] Secondly, an H4 bridge DC-AC modulation device suitable for micro-inverters is provided, comprising:

[0030] The open-loop debugging module is used to connect the output to a pure resistor and perform open-loop debugging using an auxiliary power supply.

[0031] The off-grid current loop debugging module is used for off-grid current loop debugging. It uses a PR controller for fundamental frequency regulation and a load for off-grid current loop control.

[0032] Low-voltage grid connection commissioning is used to disconnect the load and connect to an AC source for low-voltage grid connection commissioning. It adds voltage feedforward loop control, uses a PR controller for harmonic modulation in the voltage feedforward loop control, and lowers the protection threshold.

[0033] High-voltage grid connection commissioning is used for high-voltage grid connection commissioning.

[0034] Thirdly, a computer-readable storage medium is provided for program code executable by a device, the program code including steps for performing a method as described in any of the implementations of the first aspect above.

[0035] Fourthly, an electronic device is provided, the electronic device including a processor, a memory, and a program or instructions stored in the memory and executable on the processor, wherein the program or instructions, when executed by the processor, implement the method as described in any of the implementations of the first aspect above.

[0036] This application has the following beneficial effects:

[0037] 1. This application involves off-grid open-loop commissioning, current loop closed-loop commissioning, low-voltage grid-connected commissioning, and finally high-voltage grid-connected commissioning. This commissioning process effectively reduces the risk of board failure and ensures the correctness of each step, facilitating troubleshooting.

[0038] 2. This application first uses an open-loop, fixed-proportional-coefficient unipolar waveform generator, powered separately by an auxiliary power supply, to verify the correctness of the drive. Then, the output voltage and current are observed on the bus by adjusting the power supply. This method avoids the risk of the transistor exploding due to driver chip issues during grid connection. A PR controller (proportional resonant controller) is then used for fundamental frequency regulation control, and a load is used for off-grid current loop control. This method verifies the accuracy of loop parameters in off-grid mode, avoiding unnecessary breakdowns during debugging. For low-voltage grid connection debugging, a voltage feedforward loop control is added to enhance the loop control response speed, while simultaneously verifying the actual grid connection loop parameters and lowering the protection value to prevent breakdowns caused by problems during actual grid connection debugging. Finally, high-voltage grid connection debugging is performed.

[0039] 3. This application uses a PR controller for harmonic modulation in the loop control. Since the PR controller has high gain at a specific frequency, multiple resonant units are connected in parallel. For each harmonic order that needs to be suppressed (e.g., 3rd, 5th, 7th, etc.), each harmonic corresponds to a resonator. Compared with other traditional PI control, it can more accurately and effectively reduce the harmonics of the corresponding frequency in the power grid, thereby reducing the total harmonic distortion (THDI) of the current, meeting the grid connection standard, and thus reducing the impact on the power grid. Furthermore, AC voltage feedforward is added to the current loop to directly compensate for grid voltage disturbances in advance, significantly improving the dynamic performance and anti-interference capability of the current loop, and reducing the coupling effect of voltage on the current loop. Attached Figure Description

[0040] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application.

[0041] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0042] Figure 1 This is a flowchart of the H4 bridge DC-AC modulation method applicable to micro-inversion in Embodiment 1 of this application;

[0043] Figure 2This is a block diagram of the system in the H4 bridge DC-AC modulation method applicable to micro-inversion in Embodiment 1 of this application;

[0044] Figure 3 This is a circuit diagram of the H4 bridge during open-loop debugging in the H4 bridge DC-AC modulation method applicable to micro-inverters according to Embodiment 1 of this application;

[0045] Figure 4 This is a flowchart illustrating the calculation of the conduction time in the H4 bridge DC-AC modulation method applicable to micro-inverters according to Embodiment 1 of this application;

[0046] Figure 5 This is a control system framework diagram of the low-voltage grid connection loop with voltage feedforward in the H4 bridge DC-AC modulation method applicable to micro-inverters in Embodiment 1 of this application;

[0047] Figure 6 This is a waveform diagram of the AC voltage in the H4 bridge DC-AC modulation method applicable to micro-inverters according to Embodiment 1 of this application;

[0048] Figure 7 This is the final current waveform diagram in the H4 bridge DC-AC modulation method applicable to micro-inverters in Embodiment 1 of this application;

[0049] Figure 8 This is a structural block diagram of the H4 bridge DC-AC modulation device suitable for micro-inverters according to Embodiment 2 of this application;

[0050] Figure 9 This is a schematic diagram of the internal structure of the electronic device according to Embodiment 4 of this application.

[0051] Figure label:

[0052] 100. Open-loop commissioning module; 200. Off-grid current loop commissioning module; 300. Low-voltage grid-connected commissioning; 400. High-voltage grid-connected commissioning. Detailed Implementation

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] Example 1

[0055] like Figure 1 As shown, Embodiment 1 of this application relates to an H4 bridge DC-AC modulation method suitable for micro-inverters, comprising:

[0056] S100. Connect the output to a pure resistor and use the auxiliary power supply for open-loop debugging.

[0057] like Figure 2 The diagram shown is a basic block diagram of the system. When performing off-grid testing, only the load needs to be connected for control, and the auxiliary power supply is used for separate power supply to ensure that the system's power supply is normal.

[0058] like Figure 3 As shown, in the H4 bridge, switches S1 and S3 are complementary, and switches S2 and S4 are complementary. During open-loop debugging, the output is connected to a resistor. The duty cycle of switch S1 is calculated as follows, where K... p This is the proportional gain, which determines the ratio of the output voltage to the input voltage. The current angle is user-defined, and a switching frequency of 20kHz is sufficient. The period of the switching transistor S2 is consistent with the AC voltage and can be set to 0.02ms. It is related to the user-defined angle and flips at the zero-crossing level.

[0059] The formula for calculating the high-level time within one cycle is as follows:

[0060] T on =(I out_d / V bus )*T prd

[0061] Among them, T on For the high-level time within one cycle, I out_d V represents the current output by the PR controller. bus T is the bus voltage. prd Total time of the switching cycle

[0062] Observe whether the drive waveform and output current waveform are normal.

[0063]

[0064] Among them, T on K is the high-level time within one cycle, i.e., the conduction time. p It is the proportionality coefficient, which determines the ratio of the output voltage to the input voltage. Where ω is the angular frequency and T is the sampling period. Represents an angular frequency of The standard sine wave.

[0065] S200: Perform off-grid current loop debugging, use the PR controller for fundamental frequency regulation and control, and use the load for off-grid current loop control.

[0066] like Figure 4 The diagram shown is the off-grid current closed-loop flowchart. After open-loop verification is completed, the current loop closed-loop debugging is prepared, and the current angle is still custom-built. It is controlled by a PR controller, as shown below (G).PR (S) is the transfer function of the PR controller. After discretization and simplification, the output y = A(x(n)-x(n-2))-B1*y(n-1)-B2*y(n-2) is obtained, where A, B1, and B2 are defined coefficients; X(n) represents the current input parameter; X(n-1) represents the previous input parameter; X(n-2) represents the input parameter from the previous time; Y(n) represents the current output parameter; Y(n-1) represents the previous output parameter; and Y(n-2) represents the output parameter from the previous time. The coefficients of A and B1 and B2 are shown in the following formula. Where K r It is the resonance coefficient. It's bandwidth. T is the fundamental bandwidth, and T is the sampling period. Finally, calculate T. on =(I out_d / V bus )*T prd Where Ton is the conduction time, I out_d V represents the current output by the PR controller. bus T is the bus voltage. prd I is the total time of the switching cycle. out_d =I out +I err *K p , among which, I out For the output current, K p It is the proportionality coefficient, which determines the ratio of the output voltage to the input voltage. err =I ref -I ac , among which, I ref To establish a target current, I ac Alternating current:

[0067]

[0068]

[0069]

[0070]

[0071] S300: Disconnect the load and connect an AC source for low-voltage grid-connected commissioning. Add voltage feedforward loop control, use a PR controller for harmonic modulation in the voltage feedforward loop control, and lower the protection threshold.

[0072] Specifically, after the off-grid current loop is debugged and the parameters are adjusted, low-voltage grid connection is implemented. After removing the load, an AC power source is connected. Voltage feedforward is added to the loop, and the control system framework is as follows: Figure 5 As shown, calculate Ton =((I out_d +V ac ) / V bus )*T prd , among which, T on For the conduction time, I out_d V represents the current output by the PR controller. ac For alternating current voltage, V bus T is the bus voltage. prd This is the total time of the switching cycle, thereby improving the output current waveform and reducing harmonics.

[0073] In the above embodiments, an open-loop, fixed-proportional-coefficient unipolar waveform is first generated, powered separately by an auxiliary power supply. After verifying the correctness of the drive, the output voltage and current are observed on the bus by adjusting the power supply. This method avoids the risk of the transistor exploding due to problems with the driver chip. A PR controller (proportional resonant controller) is then used for fundamental frequency regulation control, and a load is used for off-grid current loop control. This method can verify the accuracy of loop parameters in off-grid mode, avoiding unnecessary breakdowns during debugging. For low-voltage grid-connected debugging, a voltage feedforward loop control is added to enhance the loop control response speed, while simultaneously verifying the actual grid-connected loop parameters and lowering the protection value to prevent breakdowns caused by problems during actual grid-connected debugging.

[0074] Furthermore, harmonic modulation is achieved using a PR controller in the loop control. Since the PR controller has high gain at specific frequencies, multiple resonant units are connected in parallel. For each harmonic order to be suppressed (e.g., 3rd, 5th, 7th, etc.), one resonator corresponds to each harmonic. Compared to other traditional PI control methods, this can more accurately and effectively reduce harmonics of the corresponding frequencies inherent in the power grid, thereby reducing THDI (Total Harmonic Distortion for Current), meeting grid connection standards, and thus reducing the impact on the power grid. Additionally, adding AC voltage feedforward to the current loop directly compensates for grid voltage disturbances in advance, significantly improving the dynamic performance and anti-interference capability of the current loop, and reducing the coupling effect of voltage on the current loop.

[0075] S400, conduct high-voltage grid connection commissioning.

[0076] Specifically, the final step is high-voltage grid connection. The protection threshold is raised, the bus voltage is set to 370V, and the AC voltage to 220V, for testing. Voltage harmonics are then introduced for system verification. For example... Figure 6The image shows the waveform of the AC voltage. FFT analysis is performed on the inherent harmonics in the voltage to identify high-order harmonic components, such as the 3rd and 5th harmonics. Active compensation is then applied to these high-order harmonic components. As in step 2 above, compensation is applied to high frequencies such as 150Hz and 250Hz. The output variables are summed, and the proportional coefficient Kp, cutoff frequency, and resonance coefficient Kr are adjusted to reduce harmonics. The final current waveform is shown below. Figure 7 The image shown is a standard sine wave.

[0077] In this embodiment, the debugging process involves off-grid open-loop debugging, current loop closed-loop debugging, low-voltage grid-connected debugging, and finally high-voltage grid-connected debugging. This process effectively reduces the risk of board failure and ensures the correctness of each step, facilitating troubleshooting.

[0078] Example 2

[0079] like Figure 8 As shown, Embodiment 2 of this application relates to an H4 bridge DC-AC modulation device suitable for micro-inverters, comprising:

[0080] The open-loop debugging module 100 is used to connect the output to a pure resistor and perform open-loop debugging using an auxiliary power supply.

[0081] The off-grid current loop debugging module 200 is used for off-grid current loop debugging. It uses a PR controller for fundamental frequency regulation and a load for off-grid current loop control.

[0082] The 300 low-voltage grid-connected commissioning unit is used to disconnect the load and connect to an AC source for low-voltage grid-connected commissioning. It adds voltage feedforward loop control, uses a PR controller for harmonic modulation in the voltage feedforward loop control, and lowers the protection threshold.

[0083] High-voltage grid connection commissioning 400 is used for high-voltage grid connection commissioning.

[0084] It should be noted that other specific implementations of the H4 bridge DC-AC modulation device applicable to micro-inversion in this embodiment can be found in the specific implementations of the H4 bridge DC-AC modulation method applicable to micro-inversion described above. To avoid redundancy, they will not be repeated here.

[0085] Example 3

[0086] This application relates to a computer-readable storage medium in Embodiment 3, which is used for program code executed by a device, the program code including steps for performing a method as described in any implementation of Embodiment 1 of this application;

[0087] The computer-readable storage medium may be a read-only memory (ROM), a static storage device, a dynamic storage device, or a random access memory (RAM); the computer-readable storage medium may store program code, and when the program stored in the computer-readable storage medium is executed by a processor, the processor is used to perform the steps of the method in any of the implementations of Embodiment 1 of this application.

[0088] Example 4

[0089] like Figure 9 As shown, an electronic device according to Embodiment 4 of this application includes a processor, a memory, and a program or instructions stored in the memory and executable on the processor. When the program or instructions are executed by the processor, they implement the method in any of the implementations in Embodiment 1 of this application.

[0090] The processor can be a general-purpose central processing unit (CPU), microprocessor, application-specific integrated circuit (ASIC), graphics processing unit (GPU), or one or more integrated circuits, used to execute related programs to implement the method in any of the implementations of Embodiment 1 of this application.

[0091] The processor can also be an integrated circuit electronic device with signal processing capabilities. In implementation, each step of the method in any of the implementations of Embodiment 1 of this application can be completed by the integrated logic circuitry in the processor's hardware or by software instructions.

[0092] The aforementioned processor can also be a general-purpose processor, digital signal processor, application-specific integrated circuit (ASIC), field-programmable gate array (FPGA), or other programmable logic device, discrete gate or transistor logic device, or discrete hardware component. It can implement or execute the methods, steps, and logic block diagrams disclosed in the embodiments of this application. The general-purpose processor can be a microprocessor or any conventional processor. The steps of the methods disclosed in the embodiments of this application can be directly embodied in the execution of a hardware decoding processor, or executed by a combination of hardware and software modules in the decoding processor. The software modules can be located in random access memory, flash memory, read-only memory, programmable read-only memory, electrically erasable programmable memory, registers, or other mature storage media in the art. The storage medium is located in memory; the processor reads information from the memory and, in conjunction with its hardware, completes the functions required by the units included in the data processing apparatus of the embodiments of this application, or executes the methods in any implementation of Embodiment 1 of this application.

[0093] The above are merely preferred embodiments of this application; however, the scope of protection of this application is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in this application, based on the technical solution and its improved concept, should be covered within the scope of protection of this application.

Claims

1. A DC-AC modulation method using an H4 bridge suitable for micro-inverters, characterized in that, include: Connect the output to a pure resistor and use an auxiliary power supply for open-loop debugging. Perform off-grid current loop commissioning, use a PR controller for fundamental frequency regulation and control, and use a load for off-grid current loop control; Disconnect the load, connect to an AC source for low-voltage grid-connected commissioning, add voltage feedforward loop control, use a PR controller for harmonic modulation in the voltage feedforward loop control, and lower the protection threshold. High-voltage grid connection commissioning is being carried out.

2. The H4 bridge DC-AC modulation method suitable for micro-inverters according to claim 1, characterized in that, During the open-loop commissioning process, the open-loop fixed proportional coefficient unipolar wave is generated and powered separately by an auxiliary power supply. After verifying that the drive is correct, the output voltage and current are observed by adjusting the power supply on the bus.

3. The H4 bridge DC-AC modulation method suitable for micro-inverters according to claim 2, characterized in that, During open-loop commissioning, in bridge H4, switches S1 and S3 are complementary, and switches S2 and S4 are complementary. The duty cycle of switch S1 is calculated using the following formula: D= Where D is the duty cycle of switch S1, and K p It is a proportionality coefficient. Angular frequency; The period of the switching transistor S2 is consistent with the AC voltage. Observe whether the driving waveform and the output current waveform are normal.

4. The H4 bridge DC-AC modulation method suitable for micro-inverters according to claim 1, characterized in that, Off-grid current loop commissioning includes: Sample the alternating current and bus voltage; Self-defined target current; Calculate the difference between the target current and the alternating current; Calculate the output current based on the transfer function of the PR controller; The high-level time within one cycle is calculated based on the output current.

5. The H4 bridge DC-AC modulation method suitable for micro-inverters according to claim 4, characterized in that, The formula for calculating the high-level time within one cycle is: T on =(I out_d / V bus )*T prd Among them, T on For the high-level time within one cycle, I out_d V represents the current output by the PR controller. bus T is the bus voltage. prd This represents the total time of the switching cycle.

6. The H4 bridge DC-AC modulation method suitable for micro-inverters according to claim 1, characterized in that, During low-voltage grid-connected commissioning, the high-level time within one cycle is calculated to improve the output waveform and reduce harmonics. Ton=((I out_d +V ac ) / V bus )*T prd Among them, T on For the high-level time within one cycle, I out_d V represents the current output by the PR controller. ac For AC voltage, V bus T is the bus voltage. prd This represents the total time of the switching cycle.

7. The H4 bridge DC-AC modulation method suitable for micro-inverters according to claim 1, characterized in that, During high-voltage grid connection commissioning, the protection threshold is increased, voltage harmonics are added for system verification, and the inherent harmonics in the voltage are analyzed by FFT. Several high harmonic components are identified, and active compensation is performed on the high harmonic components. The output variables are summed, and the proportional coefficient, cutoff frequency and resonance coefficient are adjusted to reduce harmonics.

8. An H4 bridge DC-AC modulation device suitable for micro-inverters, characterized in that, include: The open-loop debugging module is used to connect the output to a pure resistor and perform open-loop debugging using an auxiliary power supply. The off-grid current loop debugging module is used for off-grid current loop debugging. It uses a PR controller for fundamental frequency regulation and a load for off-grid current loop control. Low-voltage grid connection commissioning is used to disconnect the load and connect to an AC source for low-voltage grid connection commissioning. It adds voltage feedforward loop control, uses a PR controller for harmonic modulation in the voltage feedforward loop control, and lowers the protection threshold. High-voltage grid connection commissioning is used for high-voltage grid connection commissioning.

9. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores program code for execution by the device, the program code including steps for performing the method as described in any one of claims 1-7.

10. An electronic device, characterized in that, The electronic device includes a processor, a memory, and a program or instructions stored in the memory and executable on the processor, wherein the program or instructions, when executed by the processor, implement the method as described in any one of claims 1-7.

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