Harmonic suppression method and system for grid-type converter

Abstract

The present invention relates to the technical field of converters, and discloses a harmonic suppression method and system for a grid-type converter. The method comprises: collecting voltage signals and current signals output by the grid-type converter; calculating the command voltage value of each bridge arm of the grid-type converter after harmonic suppression based on the voltage signal and the current signal; calculating the switch control angle required for harmonic suppression of each bridge arm based on the command voltage value of each bridge arm and the actual voltage value of each bridge arm; and controlling the switching action of the power switch tube on the corresponding bridge arm based on the switch control angle required for harmonic suppression of each bridge arm. The present invention achieves effective suppression of the harmonics of the grid-type converter itself, which not only improves the power quality and enhances the system stability, but also prolongs the life of the grid equipment.

Description

Technical Field

[0001] The present invention relates to the technical field of converters, and in particular to a harmonic suppression method and system for a grid-type converter. Background Art

[0002] Currently, traditional power systems are relatively stable in terms of energy production, transmission, and consumption. As these systems mature, they are no longer able to meet evolving societal demands. Consequently, the concept of the smart grid has emerged, providing a means of optimizing the control of energy conversion devices, effectively utilizing energy, and improving energy management efficiency. The development of power grids has enabled power electronics to play a greater role in these systems, leveraging the fast controllable characteristics of semiconductor devices to implement power factor correction, active power factor filtering, and static VAR compensation. However, the widespread use of these power electronics technologies has led to the injection of a large amount of harmonic energy into the grid. In practical engineering applications, the integration of power electronics into traditional grids or systems can significantly distort the grid voltage waveform. Furthermore, harmonic currents can adversely affect various devices within the grid, reducing system efficiency, increasing equipment losses, and severely impacting power quality. Summary of the Invention

[0003] The main purpose of the present invention is to provide a harmonic suppression method and system for a grid-type converter, aiming to solve the technical problem that harmonics in existing grid-type converters reduce the efficiency of the power grid system.

[0004] A first aspect of the present invention provides a harmonic suppression method for a grid-type converter, wherein the grid-type converter includes multiple bridge arms, each bridge arm includes multiple power switch tube units connected in series, all power switch tube units have the same structure, and each power switch tube unit includes the same number of multiple power switch tubes. The harmonic suppression method for the grid-type converter includes:

[0005] collecting voltage signals and current signals of the grid-type converter;

[0006] Calculating, according to the voltage signal and the current signal, a command voltage value of each bridge arm of the grid-type converter after harmonic suppression;

[0007] Calculate the switching control angle required for harmonic suppression of each bridge arm based on the command voltage value of each bridge arm and the actual voltage value of each bridge arm;

[0008] Based on the switching control angle required for harmonic suppression of each bridge arm, the switching action of the power switch tube on the corresponding bridge arm is controlled.

[0009] Optionally, in a first implementation of the first aspect of the present invention, calculating, based on the voltage signal and the current signal, the command voltage value of each bridge arm of the grid-type converter after harmonic suppression includes:

[0010] Using Fourier transform to extract the first fundamental wave component of the voltage signal and the second fundamental wave component of the current signal respectively;

[0011] Calculating active power and reactive power based on the extracted first fundamental wave component and the second fundamental wave component;

[0012] Comparing the calculated active power and reactive power with the power demand of the grid-connected converter to determine whether power adjustment is required;

[0013] If power adjustment is required, the active power adjustment amount and reactive power adjustment amount that need to be adjusted are calculated based on the currently calculated active power, reactive power and the set target power factor;

[0014] Generate a first current instruction according to the active power adjustment amount and the reactive power adjustment amount, wherein the first current instruction includes an active current instruction and a reactive current instruction;

[0015] Detecting harmonic currents in the power grid after power adjustment, generating a second current instruction for suppressing harmonics, and synthesizing the second current instruction with the first current instruction to obtain a final third current instruction;

[0016] The command voltage value of each bridge arm is calculated according to the third current command.

[0017] Optionally, in a second implementation of the first aspect of the present invention, calculating the switching control angle required for harmonic suppression of each bridge arm according to the command voltage value of each bridge arm and the actual voltage value of each bridge arm includes:

[0018] Based on the voltage difference between the command voltage value of each bridge arm and the actual voltage value of each bridge arm, the switching control angle required for harmonic suppression of each bridge arm is accumulated so that the switching control angle continuously approaches zero over time;

[0019] When the change in the switch control angle over time is less than a preset change threshold, the current switch control angle is used as the switch control angle required for harmonic suppression of each bridge arm;

[0020] The expression corresponding to the switch control angle based on the voltage change is as follows:

[0021]

[0022] Among them, α(t) is the switch control angle based on the change of time t, U1(t) is the parameter command voltage value of the bridge arm based on the change of time t, U2(t) is the actual voltage value of the bridge arm based on the change of time t, and C is the damping coefficient of the bridge arm filter capacitor.

[0023] Optionally, in a third implementation of the first aspect of the present invention, the bridge arm includes a plurality of diodes connected in parallel vertically, each diode being connected in series with a power switch tube, each power switch tube and the corresponding diode forming a power switch device group, and controlling the switching action of the power switch tube on the corresponding bridge arm based on the switching control angle required for harmonic suppression in each bridge arm includes:

[0024] Determine the voltage state of each diode in the corresponding bridge arm based on the switching control angle required for harmonic suppression in each bridge arm;

[0025] Based on the voltage state of each diode corresponding to each bridge arm, a switch control signal is generated for synchronously controlling each power switch tube in all power switch device groups;

[0026] Based on the switch control signal, the switching action of the power switch tube on the corresponding bridge arm is controlled.

[0027] Optionally, in a fourth implementation of the first aspect of the present invention, determining the voltage state of each diode in the corresponding bridge arm based on the switch control angle required for harmonic suppression in each bridge arm includes:

[0028] Configure the switch control angle range and switch control angle accuracy value for the switch control angle corresponding to each power switch tube in each bridge arm;

[0029] Calculate the bridge arm control angle of the corresponding bridge arm according to the configured switch control angle range and switch control angle accuracy value;

[0030] The bridge arm voltage of each power switch tube in different states is detected, and the voltage state of each diode in each bridge arm is determined according to the detected bridge arm voltage and the calculated bridge arm control angle, wherein the voltage state includes a reverse recovery state and a non-reverse recovery state.

[0031] Optionally, in a fifth implementation of the first aspect of the present invention, generating a switch control signal for synchronously controlling each power switch tube in all power switch device groups based on the voltage state of each diode corresponding to each bridge arm includes:

[0032] Obtain the voltage status of each diode corresponding to each bridge arm;

[0033] If the voltage state of any diode in the diodes corresponding to the current bridge arm is in a reverse recovery state, a first control signal is generated, where the first control signal is used to prevent all power switch tubes in the corresponding bridge arm from performing a switching action in the current switching cycle;

[0034] If the voltage states of all diodes in the current bridge arm corresponding to the diodes are in the non-reverse recovery state, a second control signal is generated, and the second control signal is used to make all power switch tubes in the corresponding bridge arm perform switching actions in the current switching cycle.

[0035] Optionally, in a sixth implementation of the first aspect of the present invention, controlling the switching action of the power switch tube on the corresponding bridge arm based on the switch control signal includes:

[0036] Based on the switch control signal, a bridge arm switch control signal is generated, wherein each bridge arm switch control signal corresponds to one bridge arm, and each bridge arm includes an upper bridge arm and a lower bridge arm, and the bridge arm switch control signal controls the power switch tube on the corresponding bridge arm to perform a switching action;

[0037] The bridge arm switch control signal is pulse-width modulated to generate a switch trigger signal and a switch shielding signal on the corresponding bridge arm, wherein the switch trigger signal is used to control the switching of the power switch tube on the corresponding bridge arm, and the switch shielding signal is used to shield the signal when the power switch tube on the bridge arm is switched;

[0038] Detect whether the switch trigger signal has a rising edge change. If the switch trigger signal has a rising edge change, determine whether the switch shielding signal is a high level. If the switch shielding signal is a high level, continue to monitor whether the switch trigger signal has a rising edge change;

[0039] If the switch shielding signal is at a low level, the counter of the bridge arm switch control signal corresponding to the switch state change is incremented by 1, and the counter of the bridge arm switch control signal corresponding to the switch state not changing is decremented by 1;

[0040] The size of the counter value is judged. If the counter value is greater than the preset value, a corresponding bridge arm trigger signal is generated according to the switch trigger signal, and the power switch tube on the bridge arm is controlled to perform the switching action according to the bridge arm trigger signal.

[0041] Optionally, in a seventh implementation of the first aspect of the present invention, the harmonic suppression method of the grid-type converter further includes:

[0042] Sampling the grid-side voltage signal of the AC-side grid of the grid-type converter and performing Fourier series expansion to obtain an AC voltage fundamental component and different order AC voltage harmonic components;

[0043] Inverting the AC voltage fundamental component and different order AC voltage harmonic components to obtain an inverted DC voltage component;

[0044] Converting the DC voltage component into an AC voltage component and superimposing it on the AC voltage fundamental component to obtain a compensated AC voltage fundamental component;

[0045] The compensated AC voltage fundamental component is added to the inverted DC voltage component to obtain a compensated voltage signal and distribute it to the AC side power grid of the grid-forming converter.

[0046] Optionally, in an eighth implementation of the first aspect of the present invention, the DC voltage component is converted into an AC voltage component using the following formula:

[0047]

[0048] in, is the AC voltage component, is the DC voltage component, is the fundamental frequency, is the sampling frequency, is the sampling point time, is a constant related to the sampling frequency, is the sampling period, is the maximum number of sampling points, is the initial phase angle of the DC voltage component.

[0049] A second aspect of the present invention provides a harmonic suppression system for a grid-type converter, wherein the grid-type converter includes multiple bridge arms, each bridge arm includes multiple power switch tube units connected in series, all power switch tube units have the same structure, and each power switch tube unit includes the same number of multiple power switch tubes. The harmonic suppression system for the grid-type converter includes:

[0050] An acquisition module, used for acquiring the voltage signal and current signal output by the grid-type converter;

[0051] A first calculation module is used to calculate the command voltage value of each bridge arm of the grid-type converter after harmonic suppression according to the voltage signal and the current signal;

[0052] A second calculation module is used to calculate the switching control angle required for harmonic suppression of each bridge arm according to the command voltage value of each bridge arm and the actual voltage value of each bridge arm;

[0053] The control module is used to control the switching action of the power switch tube on the corresponding bridge arm based on the switching control angle required for harmonic suppression of each bridge arm.

[0054] The harmonic suppression method for a grid-type converter provided by an embodiment of the present invention first collects the voltage and current signals output by the grid-type converter. The voltage and current signals reflect the actual operating status of the converter's voltage and current, including fundamental and harmonic components. Based on the voltage and current signals and in conjunction with a harmonic suppression algorithm, the command voltage value for each bridge arm of the grid-type converter after harmonic suppression is calculated. The command voltage value for each bridge arm represents the ideal bridge arm voltage waveform, designed to eliminate or minimize harmonic components. By comparing the command voltage value with the actual voltage value for each bridge arm, the switching control angle required for harmonic suppression in each bridge arm is calculated. The switching control angle determines the turn-on and turn-off timing of the power switch tube, thereby achieving precise control of the bridge arm voltage. Based on the calculated switching control angle, the switching operation of the power switch tube in the corresponding bridge arm is controlled. By precisely controlling the operation of the switch tube, the actual waveform of the bridge arm voltage is brought close to the reference value, thereby achieving harmonic suppression. The present invention effectively suppresses harmonics in the grid-type converter, improving power quality, enhancing system stability, and extending the life of power grid equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 FIG. 1 is a schematic diagram of an embodiment of a method for suppressing harmonics in a grid-type converter according to an embodiment of the present invention. DETAILED DESCRIPTION

[0056] The terms "first," "second," "third," "fourth," and so on (if any) in the description and claims of the present invention and in the accompanying drawings are used to distinguish similar objects and are not necessarily used to describe a particular order or precedence. It should be understood that the terms used in this manner are interchangeable where appropriate, so that the embodiments described herein can be implemented in an order other than that shown or described herein. In addition, the terms "including" or "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product, or apparatus that includes a series of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, product, or apparatus.

[0057] For ease of understanding, the specific process of the embodiment of the present invention is described below. Figure 1 , an embodiment of a method for suppressing harmonics of a grid-type converter according to an embodiment of the present invention includes:

[0058] 101. Collecting voltage and current signals output by the grid-type converter;

[0059] A grid-type converter consists of multiple bridge arms, each containing multiple power switching units connected in series. These units have identical structures, each containing the same number of power switching transistors (semiconductor devices such as IGBTs and MOSFETs). Power switching transistors are the core components of the converter, responsible for converting DC power to AC power (inversion) and AC power to DC power (rectification). By controlling the on and off of the power switching transistors, precise control of the output voltage and current can be achieved.

[0060] To collect the voltage and current signals output by the grid-type converter, this embodiment uses a voltage transformer and a current transformer to convert the high voltage and high current signals into low voltage and low current signals suitable for subsequent circuit processing.

[0061] This embodiment utilizes a dedicated trigger circuit or signal generator to generate a synchronous trigger signal, simultaneously triggering the sampling process of the voltage and current transformers. When the preset sampling time is reached, both voltage and current sampling processes are initiated. Regardless of the trigger mechanism used, the sampling frequency must be high enough to capture the high-frequency harmonic components in the converter output voltage and circuit signals.

[0062] 102. Calculate, based on the voltage signal and the current signal, a command voltage value of each bridge arm of the grid-type converter after harmonic suppression;

[0063] In this embodiment, after collecting the voltage and current signals, harmonic analysis is performed on these signals. Specifically, this involves using a fast Fourier transform (FFT) algorithm to convert the time-domain signals into frequency-domain signals to obtain the amplitude and phase information of each harmonic. Based on the FFT results, the harmonic components present in the power grid are identified, and their amplitudes and phases are determined. The impact of each harmonic on the power grid and converter is evaluated to determine the harmonic order and amplitude that need to be suppressed. Based on the harmonic analysis results, a harmonic suppression strategy is formulated. This typically involves steps such as selecting an appropriate filter type, designing filter parameters, and determining the voltage reference value after harmonic suppression.

[0064] Based on the harmonic order and amplitude, select the appropriate filter type, such as passive filter, active filter, or hybrid filter. Based on the filter type and requirements, design the filter parameters such as inductance and capacitance to ensure that the filter can effectively filter out the target harmonics.

[0065] Based on the filter output and the grid voltage requirements, the voltage reference values ​​for each bridge arm after harmonic suppression are calculated. This typically involves performing an inverse transform (such as an inverse FFT) on the filter output to obtain the voltage waveform in the time domain and extract the voltage reference values ​​for each bridge arm.

[0066] When calculating the voltage reference value, both real-time and robustness requirements must be considered. Real-time requires that the calculation process can quickly respond to grid changes to ensure timely harmonic suppression. Robustness requires that the calculation process can withstand the influence of factors such as grid fluctuations and noise interference to ensure the accuracy and stability of harmonic suppression.

[0067] In one embodiment, the above step 102 calculates the command voltage value of each bridge arm of the grid-type converter after harmonic suppression in the following manner, including:

[0068] 1021. Use Fourier transform to extract the first fundamental component of the voltage signal and the second fundamental component of the current signal respectively;

[0069] Use a high-precision analog-to-digital converter (ADC) to synchronously sample the voltage and current, ensuring that the sampling frequency is at least twice the maximum frequency of the signal. The number of sampling points should be determined based on the signal period and the required frequency resolution.

[0070] Applying the Fast Fourier Transform (FFT) algorithm to the sampled discrete signal allows the extraction of specific frequency components. In the frequency domain, the fundamental component corresponds to the lowest non-zero frequency component. By finding the corresponding frequency component in the FFT result, the amplitude and phase information of the fundamental component can be extracted. The time domain signal can be reconstructed using an Inverse Fourier Transform (IFFT) or using only the extracted fundamental component information to obtain the fundamental voltage and current signals.

[0071] 1022. Calculate active power and reactive power based on the extracted first fundamental wave component and the second fundamental wave component;

[0072] Active power (P) is the average of the product of the in-phase components of the voltage and current. Using instantaneous power theory, active power can be calculated by multiplying the voltage and current signals and integrating (or averaging) the product over one cycle. Alternatively, it can be calculated directly using the amplitude and phase difference of the fundamental voltage and current using the following formula:

[0073]

[0074] Reactive power (Q) is the average value of the product of the quadrature components of voltage and current. It is also calculated using instantaneous power theory or by the following formula:

[0075]

[0076] in, is the effective value of the voltage, is the effective value of the current, It is the phase difference between the effective value of voltage and the effective value of current.

[0077] 1023. Compare the calculated active power and reactive power with the power requirement of the grid-connected converter to determine whether power adjustment is required;

[0078] The actual calculated power is compared with the set power demand to determine whether power output needs to be adjusted. Target values ​​for active and reactive power are set based on system requirements or control strategies. The calculated active and reactive power are compared with the set target values. If the deviation exceeds a preset threshold, power adjustment is determined. Based on the magnitude and direction of the deviation, the system determines whether to increase or decrease the active or reactive power output.

[0079] 1024. If power adjustment is required, the active power adjustment amount and reactive power adjustment amount required to be adjusted are calculated based on the currently calculated active power, reactive power and the set target power factor;

[0080] When power adjustment is required, the required reactive power adjustment is calculated based on the target power factor. Based on system requirements or operating strategies, set the target power factor (usually close to 1, indicating a high power factor). The following formulas are used to calculate the active and reactive power adjustment amounts:

[0081]

[0082] in, is the active power regulation quantity, is the reactive power regulation, P is the calculated active power, Q is the calculated reactive power, is the phase angle corresponding to the target power factor, is the phase angle corresponding to the current power factor.

[0083] 1025. Generate a first current instruction according to the active power adjustment amount and the reactive power adjustment amount, where the first current instruction includes an active current instruction and a reactive current instruction;

[0084] Based on the adjustment amount of active power and reactive power, the corresponding current command is generated to control the output of the converter.

[0085] Active current command , reactive current command It can be calculated by the following formula:

[0086] , where V represents the grid voltage.

[0087] The active current command and the reactive current command are combined into the total first current command:

[0088]

[0089] 1026. Detect harmonic currents in the power grid after power adjustment, generate a second current instruction for suppressing harmonics, and combine the second current instruction with the first current instruction to obtain a final third current instruction;

[0090] After power adjustment, the harmonic current in the power grid is detected and the corresponding harmonic suppression current instructions are generated and integrated with the basic current instructions to improve the power quality.

[0091] Use harmonic detection algorithms (such as the pq method and ip-iq method based on instantaneous reactive power theory) to detect harmonic currents in the power grid in real time. Alternatively, identify and extract harmonic components by performing FFT analysis on the power grid current signal.

[0092] Based on the detected harmonic current components, an inverse harmonic suppression current command is generated to offset the harmonic current. This command can be based on a proportional-integral (PI) controller or more complex control strategies such as a repetitive controller or predictive control. The harmonic suppression current command is combined with the basic current commands (active current command and reactive current command) to generate the final current command.

[0093] 1027. Calculate a command voltage value of each bridge arm according to the third current command.

[0094] According to the final current command, the command voltage value of each bridge arm of the converter is calculated to control the switching action of the converter.

[0095] (1) Use the space vector pulse width modulation (SVPWM) algorithm to convert the current command into components in the α-β coordinate system (if a two-phase stationary coordinate system is used). Applying the SVPWM algorithm, the switching state or duty cycle of each bridge arm of the converter is calculated based on the current command and the grid voltage.

[0096] (2) The voltage reference SVPWM algorithm is used, and its output is usually the switching state or duty cycle of each bridge arm, which can be directly used to control the switching action of the converter.

[0097] 103. Calculate the switching control angle required for harmonic suppression of each bridge arm based on the command voltage value of each bridge arm and the actual voltage value of each bridge arm;

[0098] The switching control angle is the angle at which the power switch turns on or off relative to a reference point. The specific calculation method for the switching control angle may vary depending on the modulation strategy and harmonic suppression strategy.

[0099] In one embodiment, the step 103 further includes:

[0100] 1031. Based on the voltage difference between the command voltage value of each bridge arm and the actual voltage value of each bridge arm, a switching control angle required for harmonic suppression of each bridge arm is accumulated, so that the switching control angle continuously approaches zero over time;

[0101] The command voltage value for each bridge arm is obtained in real time, and the actual voltage value of each bridge arm is measured in real time (which can be obtained from the output of the converter via a sensor). For each bridge arm, the difference between its voltage reference value and the actual value is calculated. This difference reflects the deviation between the current output voltage and the expected output voltage.

[0102] Based on the voltage difference, a control algorithm (such as a proportional-integral-derivative (PID) controller) is used to calculate the required adjustment to the switching control angle. This adjustment is intended to reduce the voltage difference, thereby bringing the actual voltage closer to the reference value. The calculated adjustment is then accumulated with the current switching control angle to form a new switching control angle. This accumulation process may involve multiple iterations, with each iteration making fine adjustments based on the current voltage difference.

[0103] The updated switching control angle is applied to the converter's control system to adjust the switch's on and off times, thereby changing the output voltage. This process is repeated until the voltage difference decreases to an acceptable level or a predetermined number of iterations is reached.

[0104] 1032. When the change in the switch control angle over time is less than a preset change threshold, the current switch control angle is used as the switch control angle required for harmonic suppression of each bridge arm;

[0105] The expression corresponding to the switch control angle based on the voltage change is as follows:

[0106]

[0107] Among them, α(t) is the switch control angle based on the change of time t, U1(t) is the command voltage value of the bridge arm based on the change of time t, U2(t) is the actual voltage value of the bridge arm based on the change of time t, and C is the damping coefficient of the bridge arm filter capacitor.

[0108] After each iteration, the change between the current switching control angle and the switching control angle after the previous iteration is calculated. The calculated change is compared with a preset change threshold. This threshold is typically set based on system performance and stability requirements. If the change is less than the preset change threshold, the current switching control angle is considered close enough to the ideal value and can be determined as the final switching control angle. If the change is still greater than the threshold, the iterative process in step 1031 is continued until the conditions are met. The determined final switching control angle is applied to the converter control system to achieve stable output voltage and harmonic suppression.

[0109] Through the above steps, it can be ensured that the output voltage of the power electronic converter can stably approach the expected value while effectively suppressing the harmonic components.

[0110] 104. Based on the switch control angle required for harmonic suppression of each bridge arm, control the switching action of the power switch tube on the corresponding bridge arm.

[0111] Based on the calculated switching control angle, an appropriate switching control strategy must be developed to control the on and off of the power switch. For example, a PWM signal can be generated based on the switching control angle and modulation period. The duty cycle and phase of the PWM signal should match the switching control angle. The PWM signal is then input into the driver circuit to control the on and off of the power switch.

[0112] In one embodiment, the bridge arm includes a plurality of diodes connected in parallel up and down, each diode is connected in series to a power switch tube, and each power switch tube and the corresponding diode form a power switch device group.

[0113] Power switches are typically IGBTs (insulated gate bipolar transistors), MOSFETs (metal oxide semiconductor field effect transistors), or other types of semiconductor switching devices. They are responsible for controlling the on and off of circuits, thereby regulating output voltage and current.

[0114] In a bridge arm, diodes typically function as freewheeling diodes or reverse-blocking diodes. A freewheeling diode provides a current path when the power switch turns off, preventing voltage spikes caused by a sudden current interruption. A reverse-blocking diode prevents reverse current from flowing through the bridge arm.

[0115] In a bridge arm, multiple diodes may be connected in parallel to increase current capacity, while each diode is connected in series with a corresponding power switch to form a power switching device group. This configuration ensures sufficient current handling capability when needed while maintaining effective control of voltage and current.

[0116] In one embodiment, the above step 104 controls the switching action of the power switch tube on the bridge arm in the following manner, including:

[0117] 1041. Determine the voltage state of each diode in the corresponding bridge arm based on the switch control angle required for harmonic suppression in each bridge arm;

[0118] In this embodiment, the required switching control angles for each bridge arm are obtained from a harmonic suppression algorithm or controller. These angles are typically calculated based on the converter's output voltage waveform and harmonic suppression targets. Based on the switching control angles and the converter's circuit topology (e.g., H-bridge, three-phase bridge, etc.), the voltage distribution of each bridge arm under different switching states is analyzed.

[0119] Determine the on (forward voltage) and off (reverse voltage or zero voltage) states of each diode during the switching cycle. This typically requires a deep understanding of converter operation and accurate modeling of the relationship between switching angles and circuit response. Record the voltage state of each diode in a state table that associates the diode leg with the different points in time during the switching cycle.

[0120] Optionally, in one embodiment, step 1041 further includes:

[0121] Step S101: configuring a switching control angle interval and a switching control angle accuracy value for the switching control angle corresponding to each power switch tube in each bridge arm;

[0122] Based on the converter's design requirements and operating conditions, determine a reasonable switching control angle range for each power switch in each bridge arm. This range should cover the full range of possible operating angles for the switch while leaving sufficient margin to account for parameter variations and disturbances. Within this range, set a switching control angle precision. This precision determines the resolution of the control signal—the minimum difference between two adjacent control angles. The choice of precision should balance control performance and computational complexity.

[0123] Step S102: Calculate the bridge arm control angle of the corresponding bridge arm according to the configured switch control angle interval and switch control angle accuracy value;

[0124] The control angle range and accuracy configured in step S101 are read. Based on the converter's current operating state and output requirements, an appropriate algorithm (such as PWM modulation or space vector modulation) is used to calculate the control angle for each bridge arm. This angle typically indicates the time at which the power switch should be turned on or off. The calculated control angle is output to the execution portion of the control system for use in turning the power switch on and off.

[0125] Step S103: Detect the bridge arm voltage of each power switch tube in different states, and determine the voltage state of each diode in each bridge arm according to the detected bridge arm voltage and the calculated bridge arm control angle, wherein the voltage state includes a reverse recovery state and a non-reverse recovery state.

[0126] Use a voltage sensor to detect the voltage of each bridge arm in different states in real time. These states include the on state, off state and possible transition state of the power switch tube. Read the bridge arm control angle calculated in step S102. Based on the detected bridge arm voltage and control angle, analyze the voltage state of the diode in each bridge arm. This usually involves precise measurement and comparison of voltage waveforms and time points. Based on the analysis results, determine whether each diode is in a reverse recovery state or a non-reverse recovery state. The reverse recovery state refers to the brief rise in reverse current and voltage caused by the charge storage effect during the transition process of the diode from forward conduction to reverse blocking. The non-reverse recovery state refers to the diode being in a stable forward conduction or reverse blocking state.

[0127] 1042. Generate a switch control signal for synchronously controlling each power switch tube in all power switch device groups based on the voltage state of each diode corresponding to each bridge arm;

[0128] Based on the diode voltage state, the power switch should be inferred to be in the on or off state, ensuring proper converter operation and harmonic suppression. A logic controller (such as an FPGA, PLC, or microcontroller) generates switch control signals based on the diode voltage state table. These signals are synchronized to ensure that the power switches in all bridge legs are turned on or off at the correct time.

[0129] When generating the switching control signal, consider adding dead time between the turn-on and turn-off of the power switch tube to prevent short circuits caused by switching delays or device characteristics. The generated switching control signal is output to the gate (for MOSFET) or base (for IGBT) of each power switch tube through the driver circuit to control its turn-on and turn-off.

[0130] In an optional embodiment, the above step 1042 further includes:

[0131] Step S201: obtaining the voltage state of each diode corresponding to each bridge arm;

[0132] Step S202: If the voltage state of any diode in the diodes corresponding to the current bridge arm is in a reverse recovery state, a first control signal is generated, where the first control signal is used to prevent all power switches in the corresponding bridge arm from performing a switching action in the current switching cycle.

[0133] The state variables of all diodes in the current bridge arm are traversed to check whether there is at least one diode marked as "reverse recovery state". If a diode is found to be in the reverse recovery state, a specific control signal (first control signal) is output through the I / O port of the microcontroller or DSP. This signal can be a high or low level signal, which is used to instruct all power switches (such as IGBTs, MOSFETs, etc.) in the corresponding bridge arm not to switch during the current switching cycle.

[0134] Step S203: If the voltage states of all diodes in the current bridge arm corresponding to the diodes are in the non-reverse recovery state, a second control signal is generated, and the second control signal is used to make all power switches in the corresponding bridge arm perform switching actions in the current switching cycle.

[0135] Similarly, the state variables of all diodes in the current bridge arm are traversed to confirm that all diodes are marked as "non-reverse recovery state." If all diodes are in the non-reverse recovery state, another specific control signal (second control signal) is output through the I / O port of the microcontroller or DSP. This signal is used to instruct all power switches in the corresponding bridge arm to perform normal switching operations during the current switching cycle. Based on the second control signal, the corresponding switching action instructions are generated through PWM (pulse width modulation) or other modulation techniques and sent to the driver circuit of the power switch.

[0136] 1043. Based on the switch control signal, control the switching action of the power switch tube on the corresponding bridge arm.

[0137] The driver circuit for each power switch receives a switching control signal from the logic controller. Based on the control signal, the driver circuit switches the power switch on or off. This typically involves applying an appropriate voltage or current to the gate or base of the switch. Feedback sensors (such as current or voltage sensors) can be used to monitor the switching state of the power switches to ensure they are responding correctly to the control signal.

[0138] In an optional embodiment, the step 1043 further includes:

[0139] Step 301: Generate a bridge arm switch control signal based on the switch control signal, wherein each bridge arm switch control signal corresponds to one bridge arm, and each bridge arm includes an upper bridge arm and a lower bridge arm, and the bridge arm switch control signal controls the power switch tube on the corresponding bridge arm to perform a switching action;

[0140] Obtain the switching control signals for each power switch. Decode the switching control signals to determine the desired switching state for each bridge arm (including the upper and lower arms). Based on this decoded information, generate corresponding switching control signals for each bridge arm. These signals are typically in binary form, indicating whether the power switch in that bridge arm should be turned on or off. Finally, the generated bridge arm switching control signals are distributed to the corresponding bridge arm control module for further processing.

[0141] Step 302: Generate a switch trigger signal and a switch shielding signal on the corresponding bridge arm in the form of pulse width modulation of the bridge arm switch control signal, wherein the switch trigger signal is used to control the switching of the power switch tube on the corresponding bridge arm, and the switch shielding signal is used to shield the signal when the power switch tube on the bridge arm is switched;

[0142] A pulse width modulation (PWM) generator converts the bridge arm switching control signals into PWM-based switch trigger signals. Simultaneously, a switch blocking signal is generated based on system protection logic or specific conditions (such as overheating or overcurrent). When these conditions are met, the blocking signal is set high to prevent the switch trigger signal from executing. The generated switch trigger signal and switch blocking signal are then output to the corresponding bridge arm driver circuits to control the switching operation of the power switches.

[0143] Step 303: Detect whether the switch trigger signal has a rising edge change. If the switch trigger signal has a rising edge change, determine whether the switch shielding signal is at a high level. If the switch shielding signal is at a high level, continue to monitor whether the switch trigger signal has a rising edge change.

[0144] This embodiment uses an edge detection circuit or software algorithm to monitor the rising edge of the switch trigger signal, indicating the start of a switching operation. Upon detecting the rising edge, the switch shield signal is immediately checked. If the shield signal is high, the switching operation is not permitted. If the shield signal is high, the switch trigger signal is continuously monitored until the shield signal becomes low.

[0145] Step 304: If the switch shielding signal is at a low level, the counter of the bridge arm switch control signal corresponding to the switch state change is incremented by 1, and the counter of the bridge arm switch control signal corresponding to the switch state not changed is decremented by 1;

[0146] First, initialize the counters. Each bridge arm's switch control signal is assigned a counter and initialized to its value (usually 0). When a rising edge of the switch trigger signal is detected and the switch shield signal is low, the counter corresponding to the bridge arm whose switch state changed is incremented by 1. If the switch state does not change (that is, the switch trigger signal does not cause actual switching), the corresponding counter is decremented by 1 (or remains unchanged, depending on the design). Ensure that the counter value is within a reasonable range to avoid overflow or negative values.

[0147] Step 305: Determine the size of the counter value. If the counter value is greater than the preset value, generate a corresponding bridge arm trigger signal according to the switch trigger signal, and control the power switch tube on the bridge arm to perform the switching action according to the bridge arm trigger signal.

[0148] The counter value is compared with a preset threshold. This threshold is typically set based on system requirements (such as stability and efficiency). If the counter value exceeds the threshold, a corresponding bridge arm trigger signal is generated based on the current switch trigger signal (which may have been filtered or processed). This signal is used to directly control the power switch in the bridge arm to switch. The generated bridge arm trigger signal is sent to the bridge arm driver circuit to drive the power switch to switch. At the same time, the system may need to update relevant status information or perform other subsequent processing.

[0149] In one embodiment, after step 104, the method further includes:

[0150] 105. Sampling the grid-side voltage signal of the AC-side grid of the grid-type converter and performing Fourier series expansion to obtain an AC voltage fundamental component and different-order AC voltage harmonic components;

[0151] High-precision, high-speed sampling equipment (such as an analog-to-digital converter (ADC)) is used to sample the grid-side voltage signal of the AC power grid of the grid-connected converter in real time. The sampling frequency must be high enough to capture all important characteristics of the voltage signal, including the fundamental wave and its harmonics.

[0152] The sampled discrete voltage signal is subjected to a Fourier series expansion (also known as a Fourier transform). This step decomposes the complex voltage signal into a series of sinusoidal components of different frequencies: the fundamental wave (usually the same as the grid frequency) and its harmonics (with frequencies that are integer multiples of the fundamental wave). The Fourier series expansion provides a detailed analysis of the voltage signal's frequency components and forms the basis for subsequent processing.

[0153] 106. Inverting the AC voltage fundamental component and different order AC voltage harmonic components to obtain an inverted DC voltage component;

[0154] In this embodiment, AC voltage components of different frequencies (including the fundamental wave and its harmonics) are converted into corresponding DC voltage components. This can be achieved, for example, using a rectifier circuit (such as a diode bridge rectifier or a thyristor rectifier circuit). The inverted DC voltage components may require further processing, such as filtering and voltage level adjustment, to meet the requirements of subsequent steps.

[0155] 107. Convert the DC voltage component into an AC voltage component and superimpose the component onto the AC voltage fundamental component to obtain a compensated AC voltage fundamental component;

[0156] This embodiment requires reconverting the inverted DC voltage component into an AC voltage component. For example, this can be achieved using an inverter (such as a PWM inverter), which generates the required AC voltage waveform by controlling the on / off switching of switching devices (such as IGBTs and MOSFETs). The converted AC voltage component (which may include a fundamental and harmonic compensation component) is then superimposed with the original AC voltage fundamental component to compensate for the original voltage signal. This eliminates or reduces the impact of harmonic components on the power grid, thereby improving power quality.

[0157] After the above processing, the compensated AC voltage fundamental component will have fewer harmonic components and be closer to the ideal sine waveform, which will help improve the stability of the power grid, reduce equipment losses, and improve the operating efficiency of power equipment.

[0158] In one embodiment, the DC voltage component is converted into an AC voltage component using the following formula:

[0159]

[0160] in, is the AC voltage component, is the DC voltage component, is the fundamental frequency, is the sampling frequency, is the sampling point time, is a constant related to the sampling frequency, is the sampling period, is the maximum number of sampling points, is the initial phase angle of the DC voltage component.

[0161] 108. Add the compensated AC voltage fundamental component and the inverted DC voltage component to obtain a compensated voltage signal and distribute it to the AC side grid of the grid-forming converter.

[0162] In this embodiment, the compensated AC voltage fundamental component is further added to the inverted DC voltage component to obtain a compensated voltage signal which is distributed to the AC side grid through the output terminal of the grid-type converter to improve the power quality of the grid.

[0163] The above describes the harmonic suppression method of the meshed converter in the embodiment of the present invention. The following describes the harmonic suppression system of the meshed converter in the embodiment of the present invention. An embodiment of the harmonic suppression system of the meshed converter in the embodiment of the present invention includes:

[0164] An acquisition module, used for acquiring the voltage signal and current signal output by the grid-type converter;

[0165] A first calculation module is used to calculate the command voltage value of each bridge arm of the grid-type converter after harmonic suppression according to the voltage signal and the current signal;

[0166] A second calculation module is used to calculate the switching control angle required for harmonic suppression of each bridge arm according to the command voltage value of each bridge arm and the actual voltage value of each bridge arm;

[0167] The control module is used to control the switching action of the power switch tube on the corresponding bridge arm based on the switching control angle required for harmonic suppression of each bridge arm.

[0168] Optionally, in one embodiment, the first calculation module is specifically configured to:

[0169] Using Fourier transform to extract the first fundamental wave component of the voltage signal and the second fundamental wave component of the current signal respectively;

[0170] Calculating active power and reactive power based on the extracted first fundamental wave component and the second fundamental wave component;

[0171] Comparing the calculated active power and reactive power with the power demand of the grid-connected converter to determine whether power adjustment is required;

[0172] If power adjustment is required, the active power adjustment amount and reactive power adjustment amount that need to be adjusted are calculated based on the currently calculated active power, reactive power and the set target power factor;

[0173] Generate a first current instruction according to the active power adjustment amount and the reactive power adjustment amount, wherein the first current instruction includes an active current instruction and a reactive current instruction;

[0174] Detecting harmonic currents in the power grid after power adjustment, generating a second current instruction for suppressing harmonics, and synthesizing the second current instruction with the first current instruction to obtain a final third current instruction;

[0175] The command voltage value of each bridge arm is calculated according to the third current command.

[0176] Optionally, in one embodiment, the second calculation module is specifically configured to:

[0177] Based on the voltage difference between the command voltage value of each bridge arm and the actual voltage value of each bridge arm, the switching control angle required for harmonic suppression of each bridge arm is accumulated so that the switching control angle continuously approaches zero over time;

[0178] When the change in the switch control angle over time is less than a preset change threshold, the current switch control angle is used as the switch control angle required for harmonic suppression of each bridge arm;

[0179] The expression corresponding to the switch control angle based on the voltage change is as follows:

[0180]

[0181] Among them, α(t) is the switch control angle based on the change of time t, U1(t) is the command voltage value of the bridge arm based on the change of time t, U2(t) is the actual voltage value of the bridge arm based on the change of time t, and C is the damping coefficient of the bridge arm filter capacitor.

[0182] Optionally, in one embodiment, the bridge arm includes a plurality of diodes connected in parallel up and down, each diode is connected in series with a power switch tube, and each power switch tube and the corresponding diode form a power switch device group, and the control module is specifically configured to:

[0183] Determine the voltage state of each diode in the corresponding bridge arm based on the switching control angle required for harmonic suppression in each bridge arm;

[0184] Based on the voltage state of each diode corresponding to each bridge arm, a switch control signal is generated for synchronously controlling each power switch tube in all power switch device groups;

[0185] Based on the switch control signal, the switching action of the power switch tube on the corresponding bridge arm is controlled.

[0186] Optionally, in one embodiment, the control module is further configured to:

[0187] Configure the switch control angle range and switch control angle accuracy value for the switch control angle corresponding to each power switch tube in each bridge arm;

[0188] Calculate the bridge arm control angle of the corresponding bridge arm according to the configured switch control angle range and switch control angle accuracy value;

[0189] The bridge arm voltage of each power switch tube in different states is detected, and the voltage state of each diode in each bridge arm is determined according to the detected bridge arm voltage and the calculated bridge arm control angle, wherein the voltage state includes a reverse recovery state and a non-reverse recovery state.

[0190] Optionally, in one embodiment, the control module is further configured to:

[0191] Obtain the voltage status of each diode corresponding to each bridge arm;

[0192] If the voltage state of any diode in the diodes corresponding to the current bridge arm is in a reverse recovery state, a first control signal is generated, where the first control signal is used to prevent all power switch tubes in the corresponding bridge arm from performing a switching action in the current switching cycle;

[0193] If the voltage states of all diodes in the current bridge arm corresponding to the diodes are in the non-reverse recovery state, a second control signal is generated, and the second control signal is used to make all power switch tubes in the corresponding bridge arm perform switching actions in the current switching cycle.

[0194] Optionally, in one embodiment, the control module is further configured to:

[0195] Based on the switch control signal, a bridge arm switch control signal is generated, wherein each bridge arm switch control signal corresponds to one bridge arm, and each bridge arm includes an upper bridge arm and a lower bridge arm, and the bridge arm switch control signal controls the power switch tube on the corresponding bridge arm to perform a switching action;

[0196] The bridge arm switch control signal is pulse-width modulated to generate a switch trigger signal and a switch shielding signal on the corresponding bridge arm, wherein the switch trigger signal is used to control the switching of the power switch tube on the corresponding bridge arm, and the switch shielding signal is used to shield the signal when the power switch tube on the bridge arm is switched;

[0197] Detect whether the switch trigger signal has a rising edge change. If the switch trigger signal has a rising edge change, determine whether the switch shielding signal is a high level. If the switch shielding signal is a high level, continue to monitor whether the switch trigger signal has a rising edge change;

[0198] If the switch shielding signal is at a low level, the counter of the bridge arm switch control signal corresponding to the switch state change is incremented by 1, and the counter of the bridge arm switch control signal corresponding to the switch state not changing is decremented by 1;

[0199] The size of the counter value is judged. If the counter value is greater than the preset value, a corresponding bridge arm trigger signal is generated according to the switch trigger signal, and the power switch tube on the bridge arm is controlled to perform the switching action according to the bridge arm trigger signal.

[0200] Optionally, in one embodiment, the harmonic suppression system of the grid-type converter further includes:

[0201] A sampling module is used to sample the grid-side voltage signal of the AC-side grid of the grid-type converter and perform Fourier series expansion to obtain the AC voltage fundamental component and different order AC voltage harmonic components;

[0202] The inverter module is used to invert the AC voltage fundamental component and the different order AC voltage harmonic components to obtain the inverted DC voltage component;

[0203] The compensation module is used to convert the DC voltage component into an AC voltage component and superimpose it on the AC voltage fundamental component to obtain a compensated AC voltage fundamental component; add the compensated AC voltage fundamental component to the inverted DC voltage component to obtain a compensated voltage signal and distribute it to the AC side power grid of the grid-type converter.

[0204] Optionally, in one embodiment, the DC voltage component is converted into an AC voltage component using the following formula:

[0205]

[0206] in, is the AC voltage component, is the DC voltage component, is the fundamental frequency, is the sampling frequency, is the sampling point time, is a constant related to the sampling frequency, is the sampling period, is the maximum number of sampling points, is the initial phase angle of the DC voltage component.

[0207] Since the embodiments of the device part correspond to the embodiments of the above-mentioned method, please refer to the above-mentioned method embodiments for the introduction of the harmonic suppression system of the grid-type converter provided by the present invention. The present invention will not be repeated here, and it has the same beneficial effects as the harmonic suppression method of the above-mentioned grid-type converter.

[0208] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features thereof can be replaced by equivalents. However, 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 embodiments of the present invention.

Claims

1. A method for suppressing harmonics in a grid-type converter, characterized in that: The grid-type converter includes multiple bridge arms, each bridge arm includes multiple power switch tube units connected in series, all power switch tube units have the same structure, and each power switch tube unit includes the same number of multiple power switch tubes. The harmonic suppression method of the grid-type converter includes: collecting voltage signals and current signals output by the grid-type converter; Calculating, according to the voltage signal and the current signal, a command voltage value of each bridge arm of the grid-type converter after harmonic suppression; Calculate the switching control angle required for harmonic suppression of each bridge arm based on the command voltage value of each bridge arm and the actual voltage value of each bridge arm; Based on the switching control angle required for harmonic suppression in each bridge arm, the switching action of the power switch tube on the corresponding bridge arm is controlled; The step of calculating the switching control angle required for harmonic suppression of each bridge arm according to the command voltage value of each bridge arm and the actual voltage value of each bridge arm includes: Based on the voltage difference between the command voltage value of each bridge arm and the actual voltage value of each bridge arm, the switching control angle required for harmonic suppression of each bridge arm is accumulated so that the switching control angle continuously approaches zero over time; When the change in the switch control angle over time is less than a preset change threshold, the current switch control angle is used as the switch control angle required for harmonic suppression of each bridge arm; The expression corresponding to the switch control angle based on the voltage change is as follows: Wherein, α(t) is the switch control angle based on the time t change, U1(t) is the command voltage value of the bridge arm based on the time t change, U2(t) is the actual voltage value of the bridge arm based on the time t change, and C is the damping coefficient of the bridge arm filter capacitor; The bridge arm includes a plurality of diodes connected in parallel up and down, each diode is connected in series to a power switch tube, and each power switch tube and the corresponding diode form a power switch device group. The switching control angle required for harmonic suppression of each bridge arm and controlling the switching action of the power switch tube on the corresponding bridge arm include: Determine the voltage state of each diode in the corresponding bridge arm based on the switching control angle required for harmonic suppression in each bridge arm; Based on the voltage state of each diode corresponding to each bridge arm, a switch control signal is generated for synchronously controlling each power switch tube in all power switch device groups; Based on the switch control signal, the switching action of the power switch tube on the corresponding bridge arm is controlled.

2. The harmonic suppression method of the grid-type converter according to claim 1, characterized in that: Calculating the command voltage value of each bridge arm of the grid-type converter after harmonic suppression based on the voltage signal and the current signal includes: Using Fourier transform to extract the first fundamental wave component of the voltage signal and the second fundamental wave component of the current signal respectively; Calculating active power and reactive power based on the extracted first fundamental wave component and the second fundamental wave component; Comparing the calculated active power and reactive power with the power demand of the grid-connected converter to determine whether power adjustment is required; If power adjustment is required, the active power adjustment amount and reactive power adjustment amount that need to be adjusted are calculated based on the currently calculated active power, reactive power and the set target power factor; Generate a first current instruction according to the active power adjustment amount and the reactive power adjustment amount, wherein the first current instruction includes an active current instruction and a reactive current instruction; detecting harmonic current after power adjustment, generating a second current instruction for suppressing harmonics, and synthesizing the second current instruction with the first current instruction to obtain a final third current instruction; The command voltage value of each bridge arm is calculated according to the third current command.

3. The harmonic suppression method of the grid-type converter according to claim 1, characterized in that: Determining the voltage state of each diode in the corresponding bridge arm based on the switch control angle required for harmonic suppression in each bridge arm includes: Configure the switch control angle range and switch control angle accuracy value for the switch control angle corresponding to each power switch tube in each bridge arm; Calculate the bridge arm control angle of the corresponding bridge arm according to the configured switch control angle range and switch control angle accuracy value; The bridge arm voltage of each power switch tube in different states is detected, and the voltage state of each diode in each bridge arm is determined according to the detected bridge arm voltage and the calculated bridge arm control angle, wherein the voltage state includes a reverse recovery state and a non-reverse recovery state.

4. The harmonic suppression method of the grid-type converter according to claim 1, characterized in that: The step of generating a switch control signal for synchronously controlling each power switch tube in all power switch device groups based on the voltage state of each diode corresponding to each bridge arm includes: Obtain the voltage status of each diode corresponding to each bridge arm; If the voltage state of any diode in the diodes corresponding to the current bridge arm is in a reverse recovery state, a first control signal is generated, where the first control signal is used to prevent all power switch tubes in the corresponding bridge arm from performing a switching action in the current switching cycle; If the voltage states of all diodes in the current bridge arm corresponding to the diodes are in the non-reverse recovery state, a second control signal is generated, and the second control signal is used to make all power switch tubes in the corresponding bridge arm perform switching actions in the current switching cycle.

5. The harmonic suppression method of a grid-type converter according to claim 1, characterized in that: The controlling the switching action of the power switch tube on the corresponding bridge arm based on the switch control signal includes: Based on the switch control signal, a bridge arm switch control signal is generated, wherein each bridge arm switch control signal corresponds to one bridge arm, and each bridge arm includes an upper bridge arm and a lower bridge arm, and the bridge arm switch control signal controls the power switch tube on the corresponding bridge arm to perform a switching action; The bridge arm switch control signal is pulse-width modulated to generate a switch trigger signal and a switch shielding signal on the corresponding bridge arm, wherein the switch trigger signal is used to control the switching of the power switch tube on the corresponding bridge arm, and the switch shielding signal is used to shield the signal when the power switch tube on the bridge arm is switched; Detect whether the switch trigger signal has a rising edge change. If the switch trigger signal has a rising edge change, determine whether the switch shielding signal is a high level. If the switch shielding signal is a high level, continue to monitor whether the switch trigger signal has a rising edge change; If the switch shielding signal is at a low level, the counter of the bridge arm switch control signal corresponding to the switch state change is incremented by 1, and the counter of the bridge arm switch control signal corresponding to the switch state not changing is decremented by 1; The size of the counter value is judged. If the counter value is greater than the preset value, a corresponding bridge arm trigger signal is generated according to the switch trigger signal, and the power switch tube on the bridge arm is controlled to perform the switching action according to the bridge arm trigger signal.

6. The harmonic suppression method of a grid-connected converter according to any one of claims 1 to 5, characterized in that: The harmonic suppression method of the grid-type converter further includes: Sampling the grid-side voltage signal of the AC-side grid of the grid-type converter and performing Fourier series expansion to obtain an AC voltage fundamental component and different order AC voltage harmonic components; Inverting the AC voltage fundamental component and different order AC voltage harmonic components to obtain an inverted DC voltage component; Converting the DC voltage component into an AC voltage component and superimposing it on the AC voltage fundamental component to obtain a compensated AC voltage fundamental component; The compensated AC voltage fundamental component is added to the inverted DC voltage component to obtain a compensated voltage signal and distribute it to the AC side power grid of the grid-forming converter.

7. The harmonic suppression method of a grid-type converter according to claim 6, characterized in that: Use the following formula to convert the DC voltage component into the AC voltage component: in, is the AC voltage component, is the DC voltage component, is the fundamental frequency, is the sampling frequency, is the sampling point time, is a constant related to the sampling frequency, is the sampling period, is the maximum number of sampling points, is the initial phase angle of the DC voltage component.

8. A harmonic suppression system for a grid-type converter, characterized in that: The grid-type converter includes multiple bridge arms, each bridge arm includes multiple power switch tube units connected in series, all power switch tube units have the same structure, and each power switch tube unit includes the same number of multiple power switch tubes. The harmonic suppression system of the grid-type converter includes: An acquisition module, used for acquiring the voltage signal and current signal output by the grid-type converter; A first calculation module is used to calculate the command voltage value of each bridge arm of the grid-type converter after harmonic suppression according to the voltage signal and the current signal; A second calculation module is used to calculate the switching control angle required for harmonic suppression of each bridge arm according to the command voltage value of each bridge arm and the actual voltage value of each bridge arm; A control module is used to control the switching action of the power switch tube on the corresponding bridge arm based on the switching control angle required for harmonic suppression of each bridge arm; The second calculation module is specifically configured to: Based on the voltage difference between the command voltage value of each bridge arm and the actual voltage value of each bridge arm, the switching control angle required for harmonic suppression of each bridge arm is accumulated so that the switching control angle continuously approaches zero over time; When the change in the switch control angle over time is less than a preset change threshold, the current switch control angle is used as the switch control angle required for harmonic suppression of each bridge arm; The expression corresponding to the switch control angle based on the voltage change is as follows: Wherein, α(t) is the switch control angle based on the time t change, U1(t) is the command voltage value of the bridge arm based on the time t change, U2(t) is the actual voltage value of the bridge arm based on the time t change, and C is the damping coefficient of the bridge arm filter capacitor; The bridge arm includes a plurality of diodes connected in parallel up and down, each diode is connected in series with a power switch tube, and each power switch tube and the corresponding diode form a power switch device group. The control module is specifically used to: Determine the voltage state of each diode in the corresponding bridge arm based on the switching control angle required for harmonic suppression in each bridge arm; Based on the voltage state of each diode corresponding to each bridge arm, a switch control signal is generated for synchronously controlling each power switch tube in all power switch device groups; Based on the switch control signal, the switching action of the power switch tube on the corresponding bridge arm is controlled.

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