Harmonic suppression method and system for network-forming converter

Abstract

The invention relates to the technical field of converters, and discloses a harmonic suppression method and system for a network-forming converter. The method comprises the following steps: acquiring a voltage signal and a current signal output by the network-forming converter; according to the voltage signal and the current signal, calculating an instruction voltage value of each bridge arm after harmonic suppression of the grid-forming converter; according to the instruction voltage value of each bridge arm and the actual voltage value of each bridge arm, calculating a switch 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 based on the switching control angle required for harmonic suppression of each bridge arm. According to the method, the harmonic waves of the grid-forming converter are effectively suppressed, the electric energy quality is improved, the system stability is enhanced, and meanwhile the service life of power grid equipment is prolonged.

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-connected converter. Background Art

[0002] At present, the traditional power system is relatively stable in the production, transmission and consumption of electric energy. The traditional power system has become mature. With the changes in social needs, the traditional power system can no longer meet the needs. As a result, the concept of smart grid has been proposed, which provides humans with a way to optimize the control of energy conversion devices, effectively utilize energy and improve energy management efficiency. The development of the power grid has enabled power electronics technology to play a greater role in the power grid, using the fast controllable characteristics of semiconductor devices to achieve power factor correction, active power factor filtering and static reactive power compensation. However, the extensive use of these power electronics technologies has led to a large amount of harmonic energy being injected into the power grid. In actual engineering applications, power electronic equipment is connected to the traditional power grid or system, which makes the grid voltage waveform distorted. At the same time, harmonic currents also have an adverse effect on various devices in the power grid, reducing system efficiency and increasing equipment losses, which seriously affects the quality of power. 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 exist in existing grid-type converters and 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 a plurality of bridge arms, each bridge arm includes a plurality of power switch tube units connected in series, all the power switch tube units have the same structure, and each power switch tube unit includes a plurality of power switch tubes of the same number. The harmonic suppression method for the grid-type converter includes: Collecting voltage signals and current signals of the grid-connected converter; Calculating 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; According to the command voltage value of each bridge arm and the actual voltage value of each bridge arm, the switch control angle required for each bridge arm to suppress harmonics is calculated; Based on the switch 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.

[0005] Optionally, in a first implementation of the first aspect of the present invention, calculating 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 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 according to 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 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; According to the third current command, the command voltage value of each bridge arm is calculated.

[0006] Optionally, in a second implementation of the first aspect of the present invention, calculating the switch 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 switch control angle required for harmonic suppression of each bridge arm is accumulated, so that the switch control angle approaches zero continuously over time; When the change of the switch control angle over time is less than the 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:

[0007] Among them, α(t) is the switch control angle based on the change of time t, U1(t) is the reference 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.

[0008] Optionally, in a third implementation of the first aspect of the present invention, 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, each power switch tube and the corresponding diode form a power switch device group, and the switching control angle required for harmonic suppression of each bridge arm to control the switching action of the power switch tube on the corresponding bridge arm includes: Based on the switch control angle required for harmonic suppression of each bridge arm, determine the voltage state of each diode in the corresponding bridge arm; Based on the voltage state of each diode corresponding to each bridge arm, a switch control signal for synchronously controlling each power switch tube in all power switch device groups is generated; Based on the switch control signal, the switching action of the power switch tube on the corresponding bridge arm is controlled.

[0009] 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 of each bridge arm includes: The switch control angle interval and the switch control angle accuracy value are configured 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 interval 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.

[0010] 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: Obtaining the voltage state 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, wherein 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 diodes corresponding to the current bridge arm are in a non-reverse recovery state, a second control signal is generated, and the second control signal is used to enable all power switch tubes in the corresponding bridge arm to perform switching actions in the current switching cycle.

[0011] 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: 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, 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 used to generate a switch trigger signal and a switch shielding signal on the corresponding bridge arm in the form of pulse width modulation, 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 changed 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 a switching action according to the bridge arm trigger signal.

[0012] Optionally, in a seventh implementation of the first aspect of the present invention, the harmonic suppression method of the grid-connected converter further includes: Sampling the grid-side voltage signal of the AC-side power 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.

[0013] 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:

[0014] 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.

[0015] A second aspect of the present invention provides a harmonic suppression system for a grid-type converter, wherein the grid-type converter includes a plurality of bridge arms, each bridge arm includes a plurality of power switch tube units connected in series, all the power switch tube units have the same structure, and each power switch tube unit includes a plurality of power switch tubes of the same number. The harmonic suppression system for the grid-type converter includes: A collection module, used for collecting voltage signals and current signals output by the grid-forming converter; A first calculation module, used for calculating 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 switch 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; The control module is used to control 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.

[0016] The harmonic suppression method of the grid-type converter provided by the embodiment of the present invention first collects the voltage signal and current signal output by the grid-type converter, and the voltage signal and current signal reflect the actual operating state of the converter voltage and current, including the fundamental component and the harmonic component. According to the voltage signal and the current signal, combined with the harmonic suppression algorithm, the command voltage value of each bridge arm after the harmonic suppression of the grid-type converter is calculated. The command voltage value of the bridge arm represents the ideal bridge arm voltage waveform, which is intended to eliminate or minimize the harmonic component. By comparing the command voltage value and the actual voltage value of each bridge arm, the switch control angle required for harmonic suppression of each bridge arm is calculated. The switch control angle determines the opening and closing time of the power switch tube to achieve accurate control of the bridge arm voltage. Based on the calculated switch control angle, the switch action of the power switch tube on the corresponding bridge arm is controlled. By accurately controlling the action of the switch tube, the actual waveform of the bridge arm voltage is close to the reference value, thereby achieving the purpose of suppressing harmonics. The present invention realizes the effective suppression of the harmonics of the grid-type converter, which not only improves the power quality, enhances the system stability, but also prolongs the life of the power grid equipment. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of an embodiment of a harmonic suppression method for a grid-connected converter in an embodiment of the present invention. DETAILED DESCRIPTION

[0018] The terms "first", "second", "third", "fourth", etc. (if any) in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchanged where appropriate, so that the embodiments described herein can be implemented in an order other than that illustrated 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 device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0019] For ease of understanding, the specific process of the embodiment of the present invention is described below. Figure 1 , an embodiment of a harmonic suppression method for a grid-connected converter in an embodiment of the present invention includes: 101. Collecting voltage signals and current signals output by the grid-forming converter; The grid-type converter is composed of multiple bridge arms, each of which contains multiple power switch tube units connected in series. These power switch tube units have the same structure, and each unit contains the same number of power switch tubes (such as IGBT, MOSFET and other semiconductor devices). The power switch tube is the core component of the converter, responsible for converting DC power into AC power (inversion process), or converting AC power into DC power (rectification process). By controlling the opening and closing of the power switch tube, the output voltage and current can be accurately controlled.

[0020] In order to collect the voltage signal and current signal output by the grid-type converter, this embodiment uses a voltage transformer and a current transformer to convert the high voltage and large current signals into low voltage and small current signals suitable for subsequent circuit processing.

[0021] This embodiment uses a special trigger circuit or signal generator to generate a synchronous trigger signal to simultaneously trigger the sampling process of the voltage and current transformers. When the preset sampling time point is reached, the voltage and current sampling procedures are started simultaneously. Regardless of which trigger mechanism is used, it is necessary to ensure that the sampling frequency is high enough to capture the high-frequency harmonic components in the converter output voltage and circuit signal.

[0022] 102. Calculate the command voltage value of each bridge arm of the grid-connected converter after harmonic suppression according to the voltage signal and the current signal; In this embodiment, after collecting the voltage and current signals, it is necessary to perform harmonic analysis on these signals, which specifically includes: using the fast Fourier transform (FFT) algorithm to convert the time domain signal into a frequency domain signal to obtain the amplitude and phase information of each harmonic. According to the FFT results, the harmonic components existing in the power grid are identified, and their amplitudes and phases are determined. The degree of influence of each harmonic on the power grid and the converter is evaluated to determine the number and amplitude of the harmonics that need to be suppressed. According to the results of the harmonic analysis, a harmonic suppression strategy is formulated. This usually involves steps such as selecting a suitable filter type, designing filter parameters, and determining the voltage reference value after harmonic suppression.

[0023] According to the harmonic order and amplitude, select the appropriate filter type, such as passive filter, active filter or hybrid filter. According to the type and requirements of the filter, design the filter's inductance, capacitance and other parameters to ensure that the filter can effectively filter out the target harmonics.

[0024] According to the output of the filter and the voltage requirements of the power grid, the voltage reference values ​​of each bridge arm after harmonic suppression are calculated. This usually involves inverse transformation of the filter output (such as inverse FFT) to obtain the voltage waveform in the time domain and extract the voltage reference value of each bridge arm.

[0025] In the process of calculating the voltage reference value, it is necessary to consider the real-time and robustness requirements. Real-time requires that the calculation process can quickly respond to changes in the power grid to ensure the timeliness of harmonic suppression; robustness requires that the calculation process can resist the influence of factors such as power grid fluctuations and noise interference to ensure the accuracy and stability of harmonic suppression.

[0026] In one embodiment, the above step 102 uses the following method to calculate the command voltage value of each bridge arm of the grid-connected converter after harmonic suppression, including: 1021. Use Fourier transform to extract the first fundamental wave component of the voltage signal and the second fundamental wave component of the current signal respectively; 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 highest frequency of the signal. The number of sampling points should be determined based on the period of the signal and the required frequency resolution.

[0027] Apply the Fast Fourier Transform (FFT) algorithm to the sampled discrete signal to extract specific frequency components. In the frequency domain representation, the fundamental component corresponds to the lowest non-zero frequency component. By looking up the corresponding frequency component in the FFT result, the amplitude and phase information of the fundamental component can be extracted. Use the Inverse Fourier Transform (IFFT) or reconstruct the time domain signal using only the extracted fundamental component information to obtain the fundamental voltage and current signals.

[0028] 1022. Calculate active power and reactive power based on the extracted first fundamental wave component and the second fundamental wave component; Active power (P) is the average value of the product of the in-phase components of voltage and current. Using instantaneous power theory, active power can be obtained by calculating the product of 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:

[0029] 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:

[0030] 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.

[0031] 1023. Compare the calculated active power and reactive power with the power demand of the grid-connected converter to determine whether power adjustment is required; Compare the actual calculated power with the set power demand to determine whether the power output needs to be adjusted. Set the target values ​​for active power and reactive power according to system requirements or control strategies. Compare the calculated active power and reactive power with the set target values. If the deviation exceeds the preset threshold, it is determined that power adjustment is required. Depending on the size and direction of the deviation, decide whether to increase or decrease the output of active power or reactive power.

[0032] 1024. If power adjustment is required, the active power adjustment amount and reactive power adjustment amount that need to be adjusted are calculated according to the currently calculated active power, reactive power and the set target power factor; When power adjustment is required, the required reactive power adjustment is calculated based on the target power factor. According to system requirements or operation strategies, the target power factor is set (usually close to 1, indicating a high power factor), and the active power adjustment and reactive power adjustment are calculated using the following formulas:

[0033] 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, It is the phase angle corresponding to the current power factor.

[0034] 1025. 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; Based on the adjustment amount of active power and reactive power, the corresponding current command is generated to control the output of the converter.

[0035] Active current command , reactive current command It can be calculated by the following formula: , where V represents the grid voltage.

[0036] The active current command and the reactive current command are combined into the total first current command:

[0037] 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; After power adjustment, the harmonic current in the power grid is detected and the corresponding harmonic suppression current command is generated and integrated with the basic current command to improve the power quality.

[0038] 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.

[0039] According to the detected harmonic current components, a reverse harmonic suppression current command is generated to offset the harmonic current. The command generation can be based on a proportional integral (PI) controller or a more complex control strategy such as a repetitive controller or predictive control. The harmonic suppression current command is combined with the basic current command (active current command and reactive current command) to obtain the final current command.

[0040] 1027. Calculate a command voltage value of each bridge arm according to the third current command.

[0041] 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.

[0042] (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). Apply the SVPWM algorithm to calculate the switching state or duty cycle of each bridge arm of the converter based on the current command and the grid voltage.

[0043] (2) Using the voltage reference value SVPWM algorithm, 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.

[0044] 103. Calculate the switch 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; The switch control angle refers to the angle of the moment when the power switch is turned on or off relative to a certain reference point. The specific calculation method of the switch control angle may vary depending on the modulation strategy and harmonic suppression strategy.

[0045] In one embodiment, the above step 103 further includes: 1031. Based on the voltage difference between the command voltage value of each bridge arm and the actual voltage value of each bridge arm, the switch control angle required for harmonic suppression of each bridge arm is accumulated, so that the switch control angle approaches zero continuously over time; The command voltage value of 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 end of the converter through 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.

[0046] Based on the voltage difference, a control algorithm (e.g., a proportional-integral-derivative controller, PID controller) is used to calculate the switch control angle that needs to be adjusted. This adjustment is intended to reduce the voltage difference so that the actual voltage is closer to the reference value. The calculated adjustment is accumulated to the current switch control angle to form a new switch control angle. This accumulation process may involve multiple iterations, with each iteration making fine adjustments based on the current voltage difference.

[0047] The updated switch control angle is applied to the converter control system to adjust the switch on and off time, thereby changing the output voltage. The above steps are repeated until the voltage difference is reduced to an acceptable range or a predetermined number of iterations is reached.

[0048] 1032. When the change of 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:

[0049] 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.

[0050] After each iteration, the change between the current switch control angle and the switch control angle after the previous iteration is calculated. The calculated change is compared with a preset change threshold. This threshold is usually set according to system performance and stability requirements. If the change is less than the preset change threshold, it is considered that the current switch control angle is close enough to the ideal value and can be determined as the final switch control angle. If the change is still greater than the threshold, the iterative process in step 1031 is continued until the condition is met. The determined final switch control angle is applied to the control system of the converter to achieve stable output voltage and harmonic suppression.

[0051] 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.

[0052] 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.

[0053] Based on the calculated switch control angle, a suitable switch action control strategy needs to be formulated to control the on and off of the power switch tube. For example, a corresponding PWM signal can be generated according to the switch control angle and the modulation period. The duty cycle and phase of the PWM signal should match the switch control angle, and then the PWM signal is input to the drive circuit to control the on and off of the power switch tube.

[0054] 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.

[0055] The power switch tube is usually an IGBT (insulated gate bipolar transistor), MOSFET (metal oxide semiconductor field effect transistor) or other types of semiconductor switching devices. It is responsible for controlling the opening and closing of the circuit, thereby regulating the output voltage and current.

[0056] In the bridge arm, the diode is usually used as a freewheeling diode or a reverse blocking diode. The freewheeling diode provides a current path when the power switch is turned off to prevent voltage spikes caused by a sudden interruption of current. The reverse blocking diode is used to prevent reverse current from flowing through the bridge arm.

[0057] 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 switch device group. This configuration ensures that sufficient current handling capability is provided when needed while maintaining effective control of voltage and current.

[0058] 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: 1041. Determine the voltage state of each diode in the corresponding bridge arm based on the switch control angle required for harmonic suppression of each bridge arm; In this embodiment, the switch control angle required for each bridge arm is obtained from the harmonic suppression algorithm or controller. These angles are usually calculated based on the output voltage waveform of the converter and the harmonic suppression target. According to the switch control angle and the circuit topology of the converter (such as H-bridge, three-phase bridge, etc.), the voltage distribution of each bridge arm under different switching states is analyzed.

[0059] Determine the on (forward voltage) and off (reverse voltage or zero voltage) states of each diode during the switching cycle. This typically involves a deep understanding of the converter's operation and accurate modeling of the relationship between the switching angle and the circuit's response. The voltage state of each diode is recorded in a state table that is associated with the bridge leg and different points in time during the switching cycle.

[0060] Optionally, in one embodiment, the step 1041 further includes: Step S101, configuring a switch control angle interval and a switch control angle accuracy value for a switch control angle corresponding to each power switch tube in each bridge arm; According to the design requirements and working conditions of the converter, a reasonable switch control angle range is determined for each power switch tube in each bridge arm. This range should cover all possible angle ranges of the switch tube, while leaving enough margin to cope with parameter changes and disturbances. Within the determined control angle range, set a switch control angle accuracy value. This accuracy value determines the resolution of the control signal, that is, the minimum difference between two adjacent control angles. The choice of accuracy value should balance control performance and computational complexity.

[0061] Step S102, calculating the bridge arm control angle of the corresponding bridge arm according to the configured switch control angle interval and switch control angle accuracy value; Read the control angle interval and accuracy value configured in step S101. According to the current working state and output requirements of the converter, use an appropriate algorithm (such as PWM modulation algorithm, space vector modulation algorithm, etc.) to calculate the bridge arm control angle of each bridge arm. This angle usually indicates the time point when the power switch tube should be turned on or off. The calculated bridge arm control angle is output to the execution part of the control system so as to be used to control the opening and closing of the power switch tube.

[0062] Step S103, detecting the bridge arm voltage of each power switch tube in different states, and determining 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.

[0063] 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. According to the detected bridge arm voltage and control angle, analyze the voltage state of the diode in each bridge arm. This usually involves accurate measurement and comparison of voltage waveforms and time points. According to 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 short-term rise in reverse current and voltage caused by the charge storage effect during the transition process from forward conduction to reverse blocking of the diode. The non-reverse recovery state refers to the diode being in a stable forward conduction or reverse blocking state.

[0064] 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; Based on the voltage state of the diode, it is inferred that the power switch tube should be in the on or off state to ensure the correct operation of the converter and harmonic suppression. A logic controller (such as FPGA, PLC or microcontroller) is used to generate switch control signals based on the diode voltage state table. These signals are synchronized to ensure that the power switch tubes on all bridge arms are turned on or off at the correct time.

[0065] When generating the switch control signal, consider adding dead time between the turn-on and turn-off of the power switch tube to prevent short circuits caused by switch delays or device characteristics. The generated switch control signal is output to the gate (for MOSFET) or base (for IGBT) of each power switch tube through the drive circuit to control its turn-on and turn-off.

[0066] In an optional embodiment, the above step 1042 further includes: Step S201, obtaining the voltage state of each diode corresponding to each bridge arm; 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, wherein 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; Traverse the state variables of all diodes in the current bridge arm to check whether there is at least one diode marked as "reverse recovery state". If a diode is found to be in 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 level or low level signal, which is used to instruct all power switch tubes (such as IGBT, MOSFET, etc.) in the corresponding bridge arm not to perform switching action in the current switching cycle.

[0067] Step S203: If the voltage states of all diodes in the diodes corresponding to the current bridge arm are in a non-reverse recovery state, a second control signal is generated, and the second control signal is used to enable all power switch tubes in the corresponding bridge arm to perform switching actions in the current switching cycle.

[0068] 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 indicate that all power switch tubes in the corresponding bridge arm can perform normal switching actions in the current switching cycle. According to the second control signal, the corresponding switching action instructions are generated through PWM (pulse width modulation) or other modulation techniques and sent to the drive circuit of the power switch tube.

[0069] 1043. Based on the switch control signal, control the switching action of the power switch tube on the corresponding bridge arm.

[0070] The driver circuit of each power switch tube receives a switch control signal from the logic controller. Based on the control signal received, the driver circuit turns the power switch tube on or off. This usually involves providing an appropriate voltage or current to the gate or base of the switch tube. Feedback sensors (such as current sensors or voltage sensors) can be used to monitor the switching state of the power switches to ensure that they respond correctly to the control signal.

[0071] In an optional embodiment, the above step 1043 further includes: 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, 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; Obtain the switch control signal of each power switch tube. Decode the switch control signal to determine the required switch state of each bridge arm (including the upper bridge arm and the lower bridge arm). Based on the decoded information, generate corresponding switch control signals for each bridge arm. These signals are usually in binary form, indicating whether the power switch tube on the bridge arm should be turned on or off. Finally, the generated bridge arm switch control signal is assigned to the corresponding bridge arm control module for further processing.

[0072] Step 302: Generate a switch trigger signal and a switch shielding signal on the corresponding bridge arm in the form of pulse width modulation using 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; A pulse width modulation (PWM) generator is used to convert the bridge arm switch control signal into a switch trigger signal in the form of PWM. At the same time, a switch shielding signal is generated according to the system protection logic or specific conditions (such as overheating, overcurrent, etc.). When these conditions are met, the shielding signal will be set to a high level to prevent the execution of the switch trigger signal. The generated switch trigger signal and switch shielding signal are output to the corresponding bridge arm drive circuit to control the switching action of the power switch tube.

[0073] Step 303, detecting whether the switch trigger signal has a rising edge change, if the switch trigger signal has a rising edge change, determining whether the switch shielding signal is at a high level, if the switch shielding signal is at a high level, continuously monitoring whether the switch trigger signal has a rising edge change; This embodiment uses an edge detection circuit or software algorithm to monitor the rising edge change of the switch trigger signal, indicating the start of the switch action. After the rising edge change is detected, the state of the switch shielding signal is immediately checked. If the shielding signal is at a high level, it indicates that the switch action is not allowed at present. If the shielding signal is at a high level, the switch trigger signal will continue to be monitored until the shielding signal becomes a low level.

[0074] 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; First, initialize the counter, assign a counter to the switch control signal of each bridge arm, and initialize its value (usually 0). When the rising edge change of the switch trigger signal is detected and the switch shield signal is at a low level, add 1 to the counter corresponding to the bridge arm whose switch state has changed. If the switch state has not changed (that is, the switch trigger signal does not cause an actual switch action), subtract 1 from the corresponding counter (or keep it unchanged, depending on the design). Ensure that the counter value is within a reasonable range to avoid overflow or negative values.

[0075] 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 a switching action according to the bridge arm trigger signal.

[0076] Compare the counter value with the preset threshold. This threshold is usually set according to the system requirements (such as stability, efficiency, etc.). If the counter value exceeds the threshold, the corresponding bridge arm trigger signal is generated according to the current switch trigger signal (which may have been filtered or processed), which will be directly used to control the power switch tube on the bridge arm to perform the switching action. The generated bridge arm trigger signal is sent to the bridge arm drive circuit to drive the power switch tube to perform the switching action. At the same time, the system may also need to update related status information or perform other subsequent processing.

[0077] In one embodiment, after the above step 104, the method further includes: 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; Use high-precision, high-speed sampling equipment (such as analog-to-digital converter ADC) to sample the grid-side voltage signal of the AC-side grid of the grid-type converter in real time. The sampling frequency needs to be high enough to ensure that all important features of the voltage signal can be captured, including the fundamental wave and each harmonic.

[0078] The sampled discrete voltage signal is subjected to Fourier series expansion (or Fourier transform). The purpose of this step is to decompose the complex voltage signal into a series of sinusoidal components of different frequencies, namely the fundamental wave (usually the same as the grid frequency) and each harmonic (the frequency is an integer multiple of the fundamental wave frequency). The Fourier series expansion provides a detailed analysis of the frequency components of the voltage signal and is the basis for subsequent processing.

[0079] 106. Inverting the AC voltage fundamental component and different order AC voltage harmonic components to obtain an inverted DC voltage component; In this embodiment, the AC voltage components of different frequencies (including the fundamental wave and each harmonic) are converted into corresponding DC voltage components. For example, this can be achieved using a rectifier circuit (such as a diode rectifier bridge or a thyristor rectifier circuit). The inverted DC voltage component may need to be further processed, such as filtering, adjusting the voltage level, etc., to meet the requirements of subsequent steps.

[0080] 107. 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; This embodiment needs to reconvert the DC voltage component obtained by inversion 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 and off of switching devices (such as IGBT, MOSFET, etc.). Then, the converted AC voltage component (which may include a fundamental compensation component and a harmonic compensation component) is superimposed with the original AC voltage fundamental component, and then the original voltage signal is compensated to eliminate or reduce the impact of the harmonic component on the power grid and improve the power quality.

[0081] After the above processing, the compensated AC voltage fundamental component will have fewer harmonic components and be closer to an ideal sinusoidal waveform, which will help improve the stability of the power grid, reduce equipment losses, and improve the operating efficiency of power equipment.

[0082] In one embodiment, the DC voltage component is converted into the AC voltage component using the following formula:

[0083] 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.

[0084] 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.

[0085] 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 end of the grid-forming converter to improve the power quality of the grid.

[0086] The above describes the harmonic suppression method of the grid-type converter in the embodiment of the present invention. The following describes the harmonic suppression system of the grid-type converter in the embodiment of the present invention. An embodiment of the harmonic suppression system of the grid-type converter in the embodiment of the present invention includes: A collection module, used for collecting voltage signals and current signals output by the grid-forming converter; A first calculation module, used for calculating 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 switch 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; The control module is used to control 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.

[0087] Optionally, in one embodiment, the first calculation module is specifically used for: 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 according to 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 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; According to the third current command, the command voltage value of each bridge arm is calculated.

[0088] Optionally, in one embodiment, the second calculation module is specifically used for: Based on the voltage difference between the command voltage value of each bridge arm and the actual voltage value of each bridge arm, the switch control angle required for harmonic suppression of each bridge arm is accumulated, so that the switch control angle approaches zero continuously over time; When the change of the switch control angle over time is less than the 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:

[0089] 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.

[0090] 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, each power switch tube and the corresponding diode form a power switch device group, and the control module is specifically used for: Based on the switch control angle required for harmonic suppression of each bridge arm, determine the voltage state of each diode in the corresponding bridge arm; Based on the voltage state of each diode corresponding to each bridge arm, a switch control signal for synchronously controlling each power switch tube in all power switch device groups is generated; Based on the switch control signal, the switching action of the power switch tube on the corresponding bridge arm is controlled.

[0091] Optionally, in one embodiment, the control module is further configured to: The switch control angle interval and the switch control angle accuracy value are configured 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 interval 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.

[0092] Optionally, in one embodiment, the control module is further configured to: Obtaining the voltage state 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, wherein 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 diodes corresponding to the current bridge arm are in a non-reverse recovery state, a second control signal is generated, and the second control signal is used to enable all power switch tubes in the corresponding bridge arm to perform switching actions in the current switching cycle.

[0093] Optionally, in one embodiment, the control module is further configured to: 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, 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 used to generate a switch trigger signal and a switch shielding signal on the corresponding bridge arm in the form of pulse width modulation, 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 changed 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 a switching action according to the bridge arm trigger signal.

[0094] Optionally, in one embodiment, the harmonic suppression system of the grid-connected converter further includes: 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 an AC voltage fundamental component and different-order AC voltage harmonic components; An inverter module is used to invert the AC voltage fundamental component and different order AC voltage harmonic components to obtain an inverted DC voltage component; 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-forming converter.

[0095] Optionally, in one embodiment, the DC voltage component is converted into the AC voltage component using the following formula:

[0096] 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.

[0097] 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.

[0098] 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 aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features thereof may 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 of a grid-connected converter, characterized in that: The grid-type converter comprises a plurality of bridge arms, each bridge arm comprises a plurality of power switch tube units connected in series, all the power switch tube units have the same structure, and each power switch tube unit comprises a plurality of power switch tubes of the same number. The harmonic suppression method of the grid-type converter comprises: Collecting voltage signals and current signals output by the grid-forming converter; Calculating 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; According to the command voltage value of each bridge arm and the actual voltage value of each bridge arm, the switch control angle required for each bridge arm to suppress harmonics is calculated; Based on the switch 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.

2. The harmonic suppression method of a grid-connected converter according to claim 1, characterized in that: The step of calculating 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 comprises: 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 according to 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 the harmonic current after power adjustment, generating a second current instruction for suppressing harmonics and synthesizing it with the first current instruction to obtain a final third current instruction; According to the third current command, the command voltage value of each bridge arm is calculated.

3. The harmonic suppression method of a grid-connected converter according to claim 1, characterized in that: The step of calculating the switch 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 comprises: Based on the voltage difference between the command voltage value of each bridge arm and the actual voltage value of each bridge arm, the switch control angle required for harmonic suppression of each bridge arm is accumulated, so that the switch control angle approaches zero continuously over time; When the change of the switch control angle over time is less than the 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: 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.

4. The harmonic suppression method of a grid-connected converter according to claim 1, characterized in that: 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, each power switch tube and the corresponding diode form a power switch device group, and the switching control angle required for harmonic suppression of each bridge arm to control the switching action of the power switch tube on the corresponding bridge arm includes: Based on the switch control angle required for harmonic suppression of each bridge arm, determine the voltage state of each diode in the corresponding bridge arm; Based on the voltage state of each diode corresponding to each bridge arm, a switch control signal for synchronously controlling each power switch tube in all power switch device groups is generated; Based on the switch control signal, the switching action of the power switch tube on the corresponding bridge arm is controlled.

5. The harmonic suppression method of a grid-connected converter according to claim 4, characterized in that: The step of determining the voltage state of each diode in the corresponding bridge arm based on the switch control angle required for harmonic suppression of each bridge arm includes: The switch control angle interval and the switch control angle accuracy value are configured 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 interval 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.

6. The harmonic suppression method of a grid-connected converter according to claim 4, characterized in that: The generating of the 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: Obtaining the voltage state 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, wherein 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 diodes corresponding to the current bridge arm are in a non-reverse recovery state, a second control signal is generated, and the second control signal is used to enable all power switch tubes in the corresponding bridge arm to perform switching actions in the current switching cycle.

7. The harmonic suppression method of a grid-connected converter according to claim 4, 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, 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 used to generate a switch trigger signal and a switch shielding signal on the corresponding bridge arm in the form of pulse width modulation, 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 changed 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 a switching action according to the bridge arm trigger signal.

8. The harmonic suppression method of a grid-connected converter according to any one of claims 1 to 7, characterized in that: The harmonic suppression method of the grid-connected converter also includes: Sampling the grid-side voltage signal of the AC-side power 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.

9. The harmonic suppression method of a grid-connected converter according to claim 8, characterized in that: The DC voltage component is converted to AC voltage component using the following formula: 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.

10. A harmonic suppression system for a grid-connected converter, characterized in that: The grid-type converter comprises a plurality of bridge arms, each bridge arm comprises a plurality of power switch tube units connected in series, all the power switch tube units have the same structure, and each power switch tube unit comprises a plurality of power switch tubes of the same number. The harmonic suppression system of the grid-type converter comprises: A collection module, used for collecting voltage signals and current signals output by the grid-forming converter; A first calculation module, used for calculating 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 switch 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; The control module is used to control 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.

Images