A method and device for active modulation of switching frequency of network-forming converter under overload conditions

Abstract

The present disclosure provides a network configuration type converter overload operating condition switch frequency active modulation method and device. The method comprises: when any parameter value of the output current and the device junction temperature of the network configuration type converter is greater than the corresponding preset limit value, it is determined that the network configuration type converter is in the corresponding overload operating condition; under the condition that the network configuration type converter is in the overload operating condition and the three-phase modulation wave voltage instruction remains unchanged, the overload characteristic component of the network configuration type converter is extracted, and the corresponding switch frequency decreasing instruction is generated through the active frequency reduction module of the network configuration type converter; wherein, the three-phase modulation wave voltage instruction is used to maintain the normal network configuration closed-loop control of the network configuration type converter; according to the switch frequency decreasing instruction, the carrier frequency of the space vector pulse width modulator in the network configuration type converter is actively modulated to dynamically reduce the switch frequency of the network configuration type converter. The present disclosure improves the operation stability of the power grid by actively reducing the frequency under the premise of maintaining the normal network configuration closed-loop control.

Description

Technical Field

[0001] This disclosure relates to the field of power electronics and grid-connected control technology for new energy power generation, specifically to a method and device for active modulation of the switching frequency under overload conditions of a grid-connected converter. Background Technology

[0002] With the increasing penetration of new energy sources in the power system, grid-connected converters are playing an increasingly important role in enhancing system inertia and providing voltage support. However, in actual operating conditions, sudden changes in grid load, short-circuit disturbances, and grid connection impacts can easily cause the output current of grid-connected converters to exceed the limit, resulting in current overload; at the same time, the accumulation of power device conduction losses and switching losses can cause abnormal increases in device junction temperature, resulting in thermal overload.

[0003] Existing technologies for overload conditions of grid-connected converters mostly employ direct blocking of drive pulses or disconnection of grid-connected converter protection methods. However, this method alters the three-phase modulation voltage command of the grid-connected converter, disrupts the original grid closed-loop control characteristics, causes grid voltage drops, reduces grid support capacity, and affects the operational stability of the grid. Summary of the Invention

[0004] This disclosure addresses the problems existing in the prior art by providing a method and apparatus for active modulation of the switching frequency of a grid-type converter under overload conditions. This method can solve the problems of grid voltage drop and reduced grid support capability caused by directly blocking the drive pulse or cutting off the grid-type converter in the prior art, thereby improving the operational stability of the power grid.

[0005] To achieve the above objectives, the technical solution adopted in this disclosure is as follows: A first aspect of this disclosure provides a method for active modulation of the switching frequency of a grid-connected converter under overload conditions, comprising: determining that the grid-connected converter is in a corresponding overload condition when either the output current or the junction temperature of the device in the grid-connected converter is detected to be greater than a corresponding preset limit; the preset limit includes a preset current limit and a preset junction temperature limit; when the grid-connected converter is in an overload condition and the three-phase modulation wave voltage command remains unchanged, extracting the overload characteristic components of the grid-connected converter, and generating a corresponding switching frequency reduction command through the active frequency reduction module of the grid-connected converter; wherein, the three-phase modulation wave voltage command is used to maintain the normal grid-connected closed-loop control of the grid-connected converter; the overload characteristic components include at least one of an overload current component and an overload junction temperature component; and, according to the switching frequency reduction command, causing the space vector pulse width modulator in the grid-connected converter to actively modulate its own carrier frequency to dynamically reduce the switching frequency of the grid-connected converter.

[0006] In one possible implementation, the overload conditions include current overload conditions, junction temperature overload conditions, and superimposed overload conditions. When either the output current or the junction temperature of the grid-connected converter is detected to be greater than the corresponding preset limit, the grid-connected converter is determined to be in the corresponding overload condition, including: when the output current is detected to be greater than the preset current limit and the junction temperature is not greater than the preset junction temperature limit, the grid-connected converter is determined to be in current overload conditions; when the junction temperature is detected to be greater than the preset junction temperature limit and the output current is not greater than the preset current limit, the grid-connected converter is determined to be in junction temperature overload conditions; when the output current is detected to be greater than the preset current limit and the junction temperature is greater than the preset junction temperature limit, the grid-connected converter is determined to be in superimposed overload conditions.

[0007] In one possible implementation, the switching frequency reduction command includes a first switching frequency reduction command; when the grid-type converter is under overload conditions and the three-phase modulation wave voltage command remains unchanged, the overload characteristic component of the grid-type converter is extracted, and a corresponding switching frequency reduction command is generated through the active frequency reduction module of the grid-type converter, including: when the grid-type converter is under current overload conditions and the three-phase modulation wave voltage command remains unchanged, the overload current component is extracted, and a first switching frequency reduction command is generated through the active frequency reduction module; wherein, the reduction rate corresponding to the first switching frequency reduction command is positively correlated with the overload current component.

[0008] In one possible implementation, the switching frequency reduction command includes a second switching frequency reduction command. When the grid-type converter is under overload conditions and the three-phase modulation voltage command remains unchanged, the overload characteristic component of the grid-type converter is extracted, and a corresponding switching frequency reduction command is generated through the active frequency reduction module of the grid-type converter. This includes: when the grid-type converter is under junction temperature overload conditions and the three-phase modulation voltage command remains unchanged, the overload junction temperature component is extracted, and a second switching frequency reduction command is generated through the active frequency reduction module; wherein the reduction rate corresponding to the second switching frequency reduction command is positively correlated with the overload junction temperature component.

[0009] In one possible implementation, the switching frequency reduction command includes a third switching frequency reduction command. When the grid-type converter is under overload conditions and the three-phase modulation voltage command remains unchanged, the overload characteristic components of the grid-type converter are extracted, and a corresponding switching frequency reduction command is generated through the active frequency reduction module of the grid-type converter. This includes: when the grid-type converter is under superimposed overload conditions and the three-phase modulation voltage command remains unchanged, extracting the overload current component and the overload junction temperature component, and generating a third switching frequency reduction command through the active frequency reduction module; wherein the reduction rate corresponding to the third switching frequency reduction command is positively correlated with the sum of the overload current component and the overload junction temperature component.

[0010] In one possible implementation, the overload characteristic components of the grid-type converter are extracted, and a corresponding switching frequency reduction command is generated through the active frequency reduction module of the grid-type converter. This includes: determining the target switching frequency based on the overload characteristic components using the active frequency reduction module; the target switching frequency is greater than a preset lower limit value for the switching frequency; the preset lower limit value for the switching frequency is the critical minimum switching frequency that ensures the output current waveform quality of the grid-type converter and the stable operation of the equipment; determining the corresponding deceleration rate based on the overload characteristic components using the active frequency reduction module, and calculating the corresponding deceleration duration by combining the current switching frequency and the target switching frequency of the grid-type converter; and generating a switching frequency reduction command based on the deceleration rate, the deceleration duration, and the target switching frequency using the active frequency reduction module.

[0011] In one possible implementation, the overload current component is the difference or ratio between the output current and the preset current limit; the overload junction temperature component is the difference or ratio between the device junction temperature and the preset junction temperature limit.

[0012] In one possible implementation, the preset current limit is 1.2 to 1.6 times the rated current of the grid-type converter; the preset junction temperature limit is 115°C to 128°C.

[0013] In one possible implementation, the method further includes: when the overload condition is detected to be lifted and the output current and device junction temperature are both less than or equal to the corresponding preset limits, determining that the grid converter has returned to normal operation; under normal operation, setting the switching frequency decrement command to zero and resetting the carrier frequency of the space vector pulse width modulator to the rated value, so that the switching frequency of the grid converter is maintained at the rated switching frequency.

[0014] A second aspect of this disclosure provides an active modulation device for the switching frequency of a grid-type converter under overload conditions, comprising: a condition determination module for detecting the output current and junction temperature of the grid-type converter; determining that the grid-type converter is under overload conditions when either the output current or the junction temperature exceeds a corresponding preset limit; the preset limit includes a preset current limit and a preset junction temperature limit; a switching frequency reduction command generation module for extracting the overload characteristic components of the grid-type converter and generating a corresponding switching frequency reduction command when the grid-type converter is under overload conditions and the three-phase modulation wave voltage command remains unchanged; wherein the three-phase modulation wave voltage command is used to maintain the normal grid-type closed-loop control of the grid-type converter; the overload characteristic components include at least one of an overload current component and an overload junction temperature component; and a switching frequency modulation module for causing the space vector pulse width modulator in the grid-type converter to actively modulate its own carrier frequency according to the switching frequency reduction command, so as to dynamically reduce the switching frequency of the grid-type converter.

[0015] This disclosure also provides an electronic device, comprising: a memory for storing at least one instruction; and a processor for calling the instruction stored in the memory to execute the active modulation method for switching frequency under overload conditions of a grid-type converter according to the first aspect and any embodiment of the first aspect.

[0016] This disclosure also provides a computer-readable storage medium storing at least one executable instruction, which is loaded and executed by a processor to implement the active modulation method for switching frequency under overload conditions of a grid-type converter in the first aspect and any embodiment of the first aspect.

[0017] This disclosure also provides a computer program product, which includes: computer program code, which, when executed by a computer, causes the computer to perform the active modulation method for switching frequency under overload conditions of a grid-type converter as described in the first aspect and any embodiment of the first aspect.

[0018] Compared with the prior art, this disclosure has the following beneficial effects: The overload frequency modulation method for grid-connected converters provided in this disclosure maintains the three-phase modulation wave voltage command unchanged throughout the entire process without altering the original grid-connected closed-loop control logic. It achieves thermal safety protection for power devices by dynamically adjusting the switching frequency based solely on overload conditions. This completely avoids interference with the grid-connected function caused by traditional protection methods, ensuring that the grid-connected converter continues to play its role in grid support. It effectively prevents problems such as grid voltage drops and reduced grid support capabilities. While achieving overload protection, it also ensures the stability of grid operation and makes up for the shortcomings of existing protection methods that are unreasonable and easily affect the safe operation of the grid. Attached Figure Description

[0019] Figure 1 This is a topology diagram of a grid-type converter provided in an embodiment of this disclosure; Figure 2 This is a control architecture diagram of a grid-type converter provided in an embodiment of this disclosure; Figure 3 This is a flowchart illustrating an active modulation method for the switching frequency under overload conditions of a grid-type converter, provided in an embodiment of this disclosure. Figure 4 This is a rendering of an active modulation method for the switching frequency under overload conditions of a grid-type converter provided in this embodiment of the present disclosure; Figure 5 This is a structural block diagram of an active modulation device for switching frequency under overload conditions of a grid-type converter, provided in an embodiment of this disclosure. Detailed Implementation

[0020] The present disclosure will now be further described with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solutions of the present disclosure and should not be construed as limiting the scope of protection of the present disclosure. It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of this application.

[0021] The acquisition, transmission, storage, use, and processing of data in this disclosed technical solution comply with relevant national laws and regulations. In the embodiments of this disclosure, certain existing industry solutions such as software, components, and models may be mentioned. These should be considered exemplary, intended only to illustrate the feasibility of implementing the technical solution of this disclosure, and do not imply that the applicant has already used or necessarily used such solutions.

[0022] All terms used in this disclosure have the same meaning as understood by one of ordinary skill in the art to which this disclosure pertains, unless otherwise specifically defined. It should also be understood that terms defined in general dictionaries should be interpreted as having meanings consistent with their meanings in the context of the relevant art, and not as idealized or highly formalized, unless expressly defined herein.

[0023] It should be noted that, in the embodiments of this disclosure, the active modulation method of the switching frequency under overload conditions of the grid-connected converter is applied to a grid-connected converter based on virtual synchronous machine control. The upper-level grid-connected closed-loop control unit continuously outputs three-phase modulation wave voltage commands to maintain the system voltage amplitude, phase, and frequency support characteristics. This modulation method keeps the amplitude and phase of the three-phase modulation wave voltage commands constant throughout the process, and only independently controls the carrier frequency of the space vector pulse width modulator. The carrier frequency of the space vector pulse width modulator is equivalent to the switching frequency of the power devices in the grid-connected converter.

[0024] like Figure 1 As shown, the grid-type converter disclosed herein adopts a two-level three-phase full-bridge topology. The overall power conversion link consists of a DC-side power supply, a two-level converter, an LCL filter, and an AC network. The two-level converter comprises three sets of three-phase bridge arms, each containing two power semiconductor switching devices. The DC-side power supply provides a stable DC bus voltage to the two-level converter. The power devices in each bridge arm perform DC-to-AC inversion using a Space Vector Pulse Width Modulation (SVPWM) device, with the switching frequency of the power devices corresponding to the carrier frequency of the SVPWM. The three-phase AC output terminals of the two-level converter are connected to an LCL filter, and after filtering, the signal is connected to the AC network to achieve voltage and frequency support for the AC grid and grid-connected power transmission.

[0025] The overload condition modulation method provided in this disclosure operates on the switching frequency regulation link of the power devices inside the two-level converter throughout the entire process. Under the premise of keeping the three-phase modulation wave voltage command generated by the upper-level grid control constant, the switching frequency of the power devices is changed synchronously by adjusting the carrier frequency of the space vector pulse width modulator, thereby realizing the regulation of device switching losses and thermal safety protection, without changing the overall topology power conversion link and grid-connected operation characteristics throughout the entire process.

[0026] like Figure 2 The diagram shown is the control architecture of the grid-connected converter disclosed herein. The grid-connected converter of this disclosure is based on a Virtual Synchronous Generator (VSG) control architecture for network operation. The overall control link is divided into three levels from top to bottom: an upper-level grid control layer, a lower-level current closed-loop limiting layer, and a lower-level modulation drive layer. The signal flow and control logic of each level are as follows: Active power reference commands and reactive power reference commands are input to the virtual synchronous generator control module. This module simulates the external characteristics of a synchronous generator, generates a fundamental voltage waveform, and outputs a three-phase modulated voltage command (i.e., the voltage reference command in the diagram), providing grid voltage and frequency support capabilities for the system. The current control loop is the core control unit for overload protection in this disclosure, acquiring the output current I of the grid-connected converter. out Device junction temperature T j The system connects to a current limiting loop, a junction temperature limiting loop, and a proportional-integral (PI) control loop for closed-loop regulation before outputting an overload signal. This current control loop provides dual-parameter safety constraints on the output current and device junction temperature throughout the entire process, corresponding to the criteria for determining the three operating conditions of current overload, junction temperature overload, and superimposed overload disclosed in this invention. The three-phase modulated voltage command output by the virtual synchronous machine control module and the overload signal output by the current control loop are jointly input to the SVPWM module. While maintaining the three-phase modulated voltage command generated by the upper-level network control constant, the SVPWM module performs adaptive frequency reduction modulation based on the overload signal to generate the gate drive signal for the Insulated Gate Bipolar Transistor (IGBT) power device, completing the DC-to-AC inverter power conversion.

[0027] Based on the control architecture diagram of the above-mentioned grid-type converter, this disclosure provides a corresponding active modulation method for the switching frequency of the grid-type converter under overload conditions, which is used to achieve overload protection without changing the three-phase modulation wave voltage command.

[0028] Figure 3 This is a flowchart illustrating an active modulation method for the switching frequency under overload conditions of a grid-type converter, as provided in an embodiment of this disclosure. Figure 3As shown, the modulation method includes the following steps S11 to S14.

[0029] Step S11: When the output current or junction temperature of the grid converter is detected to be greater than the corresponding preset limit, it is determined that the grid converter is in the corresponding overload condition.

[0030] It should be noted that in this embodiment, the output current refers to the current output by the grid-connected converter to the AC grid, including active current and reactive current, which is a core parameter reflecting the converter's operating load; the junction temperature refers to the actual temperature of the power devices (such as insulated-gate bipolar transistors) inside the grid-connected converter during operation, which is a key indicator for determining whether the power devices will overheat and be damaged; the preset limit refers to the parameter thresholds that are pre-set to ensure the safe and stable operation of the grid-connected converter, including the preset current limit and the preset junction temperature limit. The preset current limit is set according to the rated power of the grid-connected converter and the grid's withstand capability, while the preset junction temperature limit is set according to the withstand characteristics of the power devices, in order to prevent the power devices from being damaged due to overheating.

[0031] In one possible implementation, the preset current limit is 1.2 to 1.6 times the rated current of the grid-type converter; the preset junction temperature limit is 115°C to 128°C. The preset limits can be adjusted according to the application scenario of the grid-type converter. For example, in industrial applications, the preset current limit is set to 1.5 times the rated current of the grid-type converter, and the preset junction temperature limit is set to 125°C.

[0032] In one possible implementation, when determining an overload condition, a time delay determination mechanism can be introduced. That is, an overload condition is determined only when the output current or device junction temperature is continuously greater than the corresponding preset limit for a preset duration (e.g., 50ms). This avoids misjudgment caused by instantaneous fluctuations and ensures the accuracy of the determination result.

[0033] In one possible implementation, the overload conditions include current overload conditions, junction temperature overload conditions, and superimposed overload conditions. When the output current or junction temperature of the grid converter is detected to be greater than the corresponding preset limit, the grid converter is determined to be in the corresponding overload condition, including the following three situations.

[0034] The first scenario: When the output current is detected to be greater than the preset current limit and the junction temperature of the device is not greater than the preset junction temperature limit, the grid-type converter is determined to be in a current overload condition.

[0035] The second scenario: When the junction temperature of the device is detected to be greater than the preset junction temperature limit and the output current is not greater than the preset current limit, the grid-type converter is determined to be in junction temperature overload condition.

[0036] The third scenario: When the output current is detected to be greater than the preset current limit and the junction temperature of the device is greater than the preset junction temperature limit, the grid-type converter is determined to be in a superimposed overload condition.

[0037] The core purpose of this step is to monitor the operating status of the grid-type converter in real time. By judging the threshold values ​​of two key parameters, output current and device junction temperature, overload conditions can be accurately identified, providing a prerequisite for subsequent active modulation of the switching frequency.

[0038] Step S12: When the grid converter is under overload condition and the three-phase modulation wave voltage command remains unchanged, extract the overload characteristic component of the grid converter, and generate the corresponding switching frequency reduction command through the active frequency reduction module of the grid converter.

[0039] It should be noted that, in this embodiment, the three-phase modulated voltage command refers to the voltage control command used by the grid-connected converter to achieve the grid-connection function. It includes the voltage amplitude and phase information required for grid connection, used to maintain the synchronous operation of the grid-connected converter and the AC grid. Keeping this command unchanged is to avoid interference with the grid-connection function, ensuring that the grid-connected converter can continuously provide voltage support to the grid and guarantee the stable operation of the grid. The overload characteristic component refers to a quantitative parameter that reflects the degree of overload, including the overload current component and the overload junction temperature component. In one possible implementation, the overload current component is the output current and... The difference or ratio of the preset current limit; the overload junction temperature component is the difference or ratio between the device junction temperature and the preset junction temperature limit, which is the core basis for generating subsequent switching frequency reduction commands; the active frequency reduction module refers to the control module inside the grid-type converter specifically used to generate switching frequency adjustment commands. Its core function is to generate corresponding switching frequency reduction commands based on the magnitude of the overload characteristic component; the switching frequency reduction command refers to the control command used to control the reduction of the switching frequency of the power devices in the grid-type converter. It includes key parameters such as reduction rate, reduction duration, and target switching frequency to guide subsequent frequency adjustment operations.

[0040] In one possible implementation, the overload characteristic component can be extracted using real-time sampling. That is, the system collects output current and device junction temperature data every preset time interval (e.g., 10ms) and calculates the corresponding overload characteristic component to ensure the real-time nature of the component data. When the active frequency reduction module generates the switching frequency reduction command, it will combine the magnitude of the overload characteristic component to determine the reduction rate. The more severe the overload, the faster the reduction rate, ensuring rapid reduction of power device losses.

[0041] In one possible implementation, the switching frequency reduction instruction includes a first switching frequency reduction instruction, a second switching frequency reduction instruction, and a third switching frequency reduction instruction; furthermore, different overload characteristic components are extracted according to different overload conditions to generate different switching frequency reduction instructions. Specifically, as follows.

[0042] For current overload conditions: When the grid-connected converter is under current overload conditions and the three-phase modulation waveform voltage command remains unchanged, the overload current component is extracted, and a first switching frequency reduction command is generated through the active frequency reduction module. The reduction rate corresponding to the first switching frequency reduction command is positively correlated with the overload current component. That is, the larger the overload current component, the faster the reduction rate corresponding to the first switching frequency reduction command.

[0043] For junction temperature overload conditions: When the grid-type converter is under junction temperature overload conditions and the three-phase modulation waveform voltage command remains unchanged, the overload junction temperature component is extracted, and a second switching frequency reduction command is generated through the active frequency reduction module. The reduction rate corresponding to the second switching frequency reduction command is positively correlated with the overload junction temperature component. That is, the larger the overload junction temperature component, the faster the reduction rate corresponding to the second switching frequency reduction command.

[0044] For superimposed overload conditions: When the grid-type converter is under superimposed overload conditions and the three-phase modulation voltage command remains unchanged, the overload current component and the overload junction temperature component are extracted, and a third switching frequency reduction command is generated through the active frequency reduction module. The reduction rate corresponding to the third switching frequency reduction command is positively correlated with the sum of the overload current component and the overload junction temperature component. That is, the larger the sum of the overload current component and the overload junction temperature component, the faster the reduction rate corresponding to the third switching frequency reduction command.

[0045] In one possible implementation, the overload characteristic components of the grid-type converter are extracted, and the corresponding switching frequency reduction command is generated through the active frequency reduction module of the grid-type converter, including the following steps S121 to S123.

[0046] Step S121: Determine the corresponding target switching frequency based on the overload characteristic components using the active frequency reduction module.

[0047] The target switching frequency is greater than the preset lower limit of the switching frequency; the preset lower limit of the switching frequency is the critical minimum switching frequency that ensures the output current waveform quality of the grid-type converter and the stable operation of the equipment.

[0048] In one possible implementation, the active down-frequency module internally stores multiple sets of mapping relationship curves between overload characteristic components and target frequencies. The system can directly look up the table to match and obtain the target switching frequency, thereby improving the computational response speed.

[0049] Step S122: The active frequency reduction module determines the corresponding deceleration rate based on the overload characteristic components, and calculates the corresponding deceleration duration by combining the current switching frequency and the target switching frequency of the grid-type converter.

[0050] In another possible implementation, the space vector pulse width modulator can dynamically adjust the deceleration rate according to the changes in the overload characteristic components. For example, when the overload intensifies, the adjustment speed of the carrier frequency is accelerated; when the overload is relieved, the adjustment speed is slowed down.

[0051] Step S123: The active frequency reduction module generates a switching frequency reduction command based on the reduction rate, reduction duration and target switching frequency.

[0052] In one possible implementation, the active frequency reduction module can verify the matching of the deceleration rate, deceleration duration and target switching frequency in real time. If the parameters exceed the safe range, the instruction will be automatically corrected to avoid abnormal adjustment.

[0053] The core purpose of the above steps is to provide a basis for subsequent switching frequency adjustment by extracting overload characteristic components and generating decreasing commands, without affecting the grid-connected function of the grid-connected converter.

[0054] Step S13: According to the switching frequency reduction command, the space vector pulse width modulator in the grid converter actively modulates its own carrier frequency to dynamically reduce the switching frequency of the grid converter.

[0055] It should be noted that in this embodiment, the carrier frequency refers to the reference frequency used to generate the drive signal inside the space vector pulse width modulator, which corresponds one-to-one with the switching frequency of the grid converter. Changes in the carrier frequency will synchronously drive changes in the switching frequency. The switching frequency refers to the on / off frequency of the power devices (such as insulated gate bipolar transistors) inside the grid converter, and its magnitude directly affects the power device losses and operating temperature.

[0056] The core objective of this step is to adjust the carrier frequency of the space vector pulse width modulator to synchronously reduce the switching frequency of the grid-type converter, thereby reducing the switching losses of power devices and lowering the operating temperature of the devices. At the same time, since the three-phase modulation wave voltage command remains unchanged, the grid-type converter's grid-building function is not affected, ensuring that the voltage support capability of the power grid is not weakened.

[0057] In one possible implementation, steps S14 and S15 are also included.

[0058] Step S14: When the overload condition is detected to be relieved and the output current and device junction temperature are both less than or equal to the corresponding preset limits, it is determined that the grid-type converter has returned to normal operating conditions.

[0059] It should be noted that in the embodiments of this disclosure, normal operating condition refers to the working state in which the output current and junction temperature of the grid-connected converter are within the preset safety range, and the grid-connected converter can normally realize the grid-connected function and operate stably in grid connection. At this time, the switching frequency of the grid-connected converter can be restored to the rated value to ensure the output waveform quality and grid-connected performance.

[0060] In one possible implementation, the system continuously collects output current and device junction temperature data in real time, and performs a threshold comparison every preset time interval (e.g., 5ms). Only when the output current and device junction temperature are detected to be less than or equal to the corresponding preset limit multiple times (e.g., 3 times) is the grid-type converter determined to have returned to normal operating conditions, thus avoiding misjudgment caused by instantaneous parameter fluctuations.

[0061] In another possible implementation, after determining that the normal operating condition has been restored, a buffer period can be added. During the buffer period, the output current and device junction temperature are continuously monitored. If the parameters remain stable within the preset limits during the buffer period, the normal operating condition is then officially confirmed, further improving the accuracy of the determination.

[0062] The core purpose of this step is to monitor the mitigation of overload conditions in real time, accurately determine whether the grid-type converter has the conditions to resume normal operation, provide a basis for subsequent switching frequency reset, achieve a smooth switch between overload and normal conditions, and ensure the long-term stable operation of the grid-type converter.

[0063] Step S15: Under normal operating conditions, set the switching frequency decrement command to zero and reset the carrier frequency of the space vector pulse width modulator to the rated value so that the switching frequency of the grid converter is maintained at the rated switching frequency.

[0064] It should be noted that in the embodiments of this disclosure, the rated value is the rated carrier frequency. The rated carrier frequency refers to the reference carrier frequency used by the space vector pulse width modulator of the grid-type converter under normal operating conditions. Its value is set according to the output waveform quality requirements of the grid-type converter to ensure that the output current waveform is smooth and the harmonic content meets the grid standard. The rated switching frequency refers to the standard switching frequency of the power devices of the grid-type converter under normal operating conditions, which corresponds one-to-one with the rated carrier frequency to ensure the output waveform quality and grid performance of the grid-type converter.

[0065] In one possible implementation, after receiving the operating condition recovery command, the space vector pulse width modulator gradually restores the carrier frequency from the overload adjustment value to the rated value according to the preset reset rate, so as to avoid the output waveform distortion caused by the sudden change of carrier frequency, ensure the smooth transition of the grid-type converter output, and not affect the stable operation of the power grid.

[0066] In another possible implementation, if the grid-type converter detects that the output current or device junction temperature exceeds the preset limit again during the recovery process, the carrier frequency reset operation is immediately stopped, and the switching frequency modulation process under overload conditions is re-entered to ensure equipment safety.

[0067] The core objective of this step is to restore the operating state of the grid-connected converter to its initial normal state after the overload condition is removed, ensuring that the grid-connected function is not affected, while also guaranteeing the quality of the output power, thus achieving a closed loop in the entire control process.

[0068] Combining the aforementioned active modulation method for switching frequency under overload conditions of a grid-type converter provided in this disclosure embodiment, the overall timing performance of this method can be achieved by... Figure 4 The waveforms shown intuitively illustrate that: at time t1, a grid fault occurs, causing the effective value of the grid-side current of the grid-connected converter to rise and enter overload mode. The increased load on the power devices leads to a continuous rise in junction temperature. At this time, this method triggers adaptive frequency reduction control, and the switching frequency of the devices is smoothly reduced from the initial rated high switching frequency to the low switching frequency range, and is never lower than the minimum switching frequency required to meet the grid-connected harmonic content requirements. While effectively reducing switching losses, suppressing device temperature rise, and confining the device junction temperature within the maximum junction temperature limit to achieve thermal safety protection, the three-phase modulation wave voltage command is always kept constant, without damaging the original grid-connected control characteristics and grid support capability of the converter. Until time t2, the grid fault is cleared, the overload condition is relieved, the grid-side current falls back to the normal operating range, the device junction temperature gradually decreases, and the device switching frequency synchronously and smoothly rises back to the initial rated high switching frequency. The converter fully returns to the normal operating mode, fully verifying the excellent operating effect of this method in balancing overload protection, grid-connected power quality assurance, and grid-connected operating characteristics.

[0069] The overload frequency modulation method for grid-connected converters provided in this disclosure, compared to existing technologies that often employ direct blocking of drive pulses or disconnection of the grid-connected converter for overload conditions, effectively solves the problems of existing protection methods altering the three-phase modulation voltage command, disrupting the original grid-connected closed-loop control characteristics, causing grid voltage drops, reduced grid support capability, and affecting grid operation stability. By maintaining the three-phase modulation voltage command unchanged and without altering the original grid-connected closed-loop control logic, and only adjusting the switching frequency, it achieves thermal safety protection under overload conditions while avoiding interference with the original grid-connected function. This ensures that the grid-connected converter's grid support capability remains unaffected, guarantees grid voltage stability, and avoids grid voltage drops and reduced grid support capability. It overcomes the shortcomings of existing protection methods that are unreasonable and affect grid operation stability, while also considering the thermal safety protection of power devices. It achieves dual protection for overload protection and grid-connected function, improving the operational reliability and grid support capability of the grid-connected converter.

[0070] Figure 5 This is a structural block diagram of an active modulation device for switching frequency under overload conditions of a grid-type converter, as provided in this embodiment. Figure 5 As shown, the modulation device 100 includes a working condition determination module 110, a switching frequency decrease instruction generation module 120, and a switching frequency modulation module 130.

[0071] The operating condition determination module 110 is used to detect the output current and junction temperature of the grid-type converter. When the value of either the output current or the junction temperature is found to be greater than the corresponding preset limit, the grid-type converter is determined to be in the corresponding overload condition. The preset limit includes a preset current limit and a preset junction temperature limit. The switching frequency reduction instruction generation module 120 is used to extract the overload characteristic components of the grid-type converter and generate the corresponding switching frequency reduction instruction when the grid-type converter is under overload conditions and the three-phase modulation wave voltage instruction remains unchanged; wherein, the three-phase modulation wave voltage instruction is used to maintain the normal grid-type closed-loop control of the grid-type converter; the overload characteristic components include at least one of the overload current component and the overload junction temperature component; The switching frequency modulation module 130 is used to enable the space vector pulse width modulator in the grid converter to actively modulate its own carrier frequency according to the switching frequency reduction command, so as to dynamically reduce the switching frequency of the grid converter.

[0072] For specific details and benefits of the active modulation device for the switching frequency under overload conditions of the grid converter provided in the embodiments of this disclosure, please refer to the above description of the active modulation method for the switching frequency under overload conditions of the grid converter, which will not be repeated here.

[0073] This disclosure also provides an electronic device, comprising: a memory for storing at least one instruction; and a processor for calling the instruction stored in the memory to execute the active modulation method of switching frequency under overload conditions of a grid-type converter in any of the above embodiments.

[0074] This disclosure also provides a computer-readable storage medium storing at least one executable instruction, which is loaded and executed by a processor to implement the active modulation method for switching frequency under overload conditions of a grid-type converter in any of the above embodiments.

[0075] This disclosure also provides a computer program product, which includes computer program code. When the computer program code is run by a computer, it causes the computer to execute the active modulation method of switching frequency under overload conditions of the grid-type converter in any of the above embodiments.

[0076] Those skilled in the art will understand that embodiments of this disclosure can be provided as methods, systems, or computer program products. Therefore, this disclosure can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this disclosure can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0077] This disclosure is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this disclosure. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create a machine for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0078] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0079] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0080] In a typical configuration, a computing device includes one or more processors (CPU), input / output interfaces, network interfaces, and memory.

[0081] Memory may include non-persistent memory in computer-readable media, such as random access memory (RAM) and / or non-volatile memory, like read-only memory (ROM) or flash RAM. Memory is an example of computer-readable media.

[0082] Computer-readable media includes both permanent and non-permanent, removable and non-removable media that can store information using any method or technology. Information can be computer-readable instructions, data structures, modules of programs, or other data. Examples of computer storage media include, but are not limited to, phase-change memory (PRAM), static random access memory (SRAM), dynamic random access memory (DRAM), other types of random access memory (RAM), read-only memory (ROM), electrically erasable programmable read-only memory (EEPROM), flash memory or other memory technologies, CD-ROM, digital versatile optical disc (DVD) or other optical storage, magnetic tape, magnetic magnetic disk storage or other magnetic storage devices, or any other non-transferable medium that can be used to store information accessible by a computing device. As defined herein, computer-readable media does not include transient computer-readable media, such as modulated data signals and carrier waves.

[0083] It should be noted that the terms "first," "second," and similar terms used in this disclosure do not indicate any order, quantity, or importance, but are merely used to distinguish different parts. Terms such as "including" or "contains" mean that the element preceding the word covers the element listed after the word, and do not exclude the possibility of covering other elements as well.

[0084] Although operations are described in a specific order in the accompanying drawings in this disclosure, it should not be construed as requiring these operations to be performed in the specific order or serial order shown, or requiring all of the shown operations to obtain the desired result. In certain environments, multitasking and parallel processing may be advantageous.

[0085] Finally, it should be noted that the above content is only used to illustrate the technical solution of this disclosure, and is not intended to limit the scope of protection of this disclosure. Simple modifications or equivalent substitutions made by those skilled in the art to the technical solution of this disclosure do not depart from the substance and scope of the technical solution of this disclosure.

Claims

1. A method for active modulation of the switching frequency under overload conditions in a grid-type converter, characterized in that, include: When the output current or junction temperature of the grid converter is detected to be greater than the corresponding preset limit, the grid converter is determined to be in the corresponding overload condition; the preset limit includes a preset current limit and a preset junction temperature limit; When the grid-type converter is under overload conditions and the three-phase modulation voltage command remains unchanged, the overload characteristic components of the grid-type converter are extracted, and a corresponding switching frequency reduction command is generated through the active frequency reduction module of the grid-type converter; wherein, the three-phase modulation voltage command is used to maintain the normal grid-type closed-loop control of the grid-type converter; the overload characteristic components include at least one of overload current component and overload junction temperature component; According to the switching frequency reduction command, the space vector pulse width modulator in the grid converter actively modulates its own carrier frequency to dynamically reduce the switching frequency of the grid converter.

2. The active modulation method for switching frequency under overload conditions of a grid-type converter according to claim 1, characterized in that, The overload conditions include current overload conditions, junction temperature overload conditions, and superimposed overload conditions; the determination that the grid-type converter is in the corresponding overload condition when any parameter value among the output current and device junction temperature of the grid-type converter is detected to be greater than the corresponding preset limit includes: When the output current is detected to be greater than the preset current limit and the junction temperature of the device is not greater than the preset junction temperature limit, the grid-type converter is determined to be in the current overload condition. When the junction temperature of the device is detected to be greater than the preset junction temperature limit and the output current is not greater than the preset current limit, the grid-type converter is determined to be in the junction temperature overload condition. When the output current is detected to be greater than the preset current limit and the junction temperature of the device is greater than the preset junction temperature limit, the grid-type converter is determined to be in the superimposed overload condition.

3. The active modulation method for switching frequency under overload conditions of a grid-type converter according to claim 2, characterized in that, The switching frequency reduction command includes a first switching frequency reduction command; the step of extracting the overload characteristic components of the grid-type converter when the grid-type converter is under overload conditions and the three-phase modulation wave voltage command remains unchanged, and generating a corresponding switching frequency reduction command through the active frequency reduction module of the grid-type converter, includes: When the grid-type converter is under the current overload condition and the three-phase modulation wave voltage command remains unchanged, the overload current component is extracted and the first switching frequency reduction command is generated through the active frequency reduction module. The deceleration rate corresponding to the first switching frequency reduction command is positively correlated with the overload current component.

4. The active modulation method for switching frequency under overload conditions of a grid-type converter according to claim 2, characterized in that, The switching frequency reduction command includes a second switching frequency reduction command; the step of extracting the overload characteristic components of the grid-type converter when the grid-type converter is under overload conditions and the three-phase modulation wave voltage command remains unchanged, and generating a corresponding switching frequency reduction command through the active frequency reduction module of the grid-type converter, includes: When the grid-type converter is under junction temperature overload condition and the three-phase modulation wave voltage command remains unchanged, the overload junction temperature component is extracted and the second switching frequency reduction command is generated through the active frequency reduction module. The deceleration rate corresponding to the second switching frequency deceleration command is positively correlated with the overload junction temperature component.

5. The active modulation method for switching frequency under overload conditions of a grid-type converter according to claim 2, characterized in that, The switching frequency reduction instruction includes a third switching frequency reduction instruction; the step of extracting the overload characteristic components of the grid-type converter when the grid-type converter is under overload condition and the three-phase modulation wave voltage instruction remains unchanged, and generating a corresponding switching frequency reduction instruction through the active frequency reduction module of the grid-type converter, includes: When the grid-type converter is under the superimposed overload condition and the three-phase modulation wave voltage command remains unchanged, the overload current component and the overload junction temperature component are extracted, and the third switching frequency reduction command is generated through the active frequency reduction module. The deceleration rate corresponding to the third switching frequency reduction command is positively correlated with the sum of the overload current component and the overload junction temperature component.

6. The active modulation method for switching frequency under overload conditions of a grid-type converter according to any one of claims 1-5, characterized in that, The step of extracting the overload characteristic components of the grid-type converter and generating a corresponding switching frequency reduction command through the active frequency reduction module of the grid-type converter includes: The active frequency reduction module determines the corresponding target switching frequency based on the overload characteristic components; the target switching frequency is greater than the preset lower limit of the switching frequency; the preset lower limit of the switching frequency is the critical minimum switching frequency to ensure the output current waveform quality of the grid converter and the stable operation of the equipment. The active frequency reduction module determines the corresponding deceleration rate based on the overload characteristic components, and calculates the corresponding deceleration duration by combining the current switching frequency of the grid converter and the target switching frequency. The active frequency reduction module generates the switching frequency reduction command based on the reduction rate, the reduction duration, and the target switching frequency.

7. The active modulation method for switching frequency under overload conditions of a grid-type converter according to any one of claims 1-5, characterized in that, The overload current component is the difference or ratio between the output current and the preset current limit; the overload junction temperature component is the difference or ratio between the device junction temperature and the preset junction temperature limit.

8. The active modulation method for switching frequency under overload conditions of a grid-type converter according to any one of claims 1-5, characterized in that, The preset current limit is 1.2 to 1.6 times the rated current of the grid-type converter; the preset junction temperature limit is 115℃ to 128℃.

9. The active modulation method for switching frequency under overload conditions of a grid-type converter according to any one of claims 1-5, characterized in that, Also includes: When the overload condition is detected to be relieved and the output current and the junction temperature of the device are both less than or equal to the corresponding preset limits, it is determined that the grid-type converter has returned to normal operating conditions. Under normal operating conditions, the switching frequency decrement command is set to zero, and the carrier frequency of the space vector pulse width modulator is reset to the rated value, so that the switching frequency of the grid converter is maintained at the rated switching frequency.

10. A switching frequency active modulation device for overload conditions of a grid-type converter, characterized in that, include: The operating condition determination module is used to detect the output current and junction temperature of the grid-type converter. When the value of either the output current or the junction temperature is found to be greater than the corresponding preset limit, the grid-type converter is determined to be in the corresponding overload condition. The preset limit includes a preset current limit and a preset junction temperature limit. The switching frequency reduction command generation module is used to extract the overload characteristic components of the grid-type converter and generate a corresponding switching frequency reduction command when the grid-type converter is under the overload condition and the three-phase modulation wave voltage command remains unchanged; wherein, the three-phase modulation wave voltage command is used to maintain the normal grid-type closed-loop control of the grid-type converter; the overload characteristic components include at least one of overload current component and overload junction temperature component; The switching frequency modulation module is used to cause the space vector pulse width modulator in the grid converter to actively modulate its own carrier frequency according to the switching frequency reduction command, so as to dynamically reduce the switching frequency of the grid converter.

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