Temperature-limited frequency modulation and exiting method of network-configuration type converter based on temperature-limited control loop

Abstract

The application relates to a temperature-limiting frequency-regulation and exiting method of a network-constructing type converter based on a temperature-limiting control loop, which comprises the following steps: collecting power device shell temperature data, power device operation parameters, environmental temperature and power grid data; based on the shell temperature data and the power device operation parameters, equivalent junction temperature is calculated; a thermal weight calculation model is constructed, the input is the equivalent junction temperature, the output is a normalized processed equivalent junction temperature dimensionless parameter, the active output and the damping reference angular frequency are regulated and controlled through a thermal safety weight coefficient, and the temperature-limiting and frequency-regulation collaborative control is carried out; based on the power device operation parameters, the environmental temperature, the power grid data, the equivalent junction temperature and the thermal weight calculation model, the determination and switching of three modes of pure network support, stress release smooth transition and network following self-protection are realized. The application realizes the dynamic balance of the converter self-safety and power grid frequency-regulation support, solves the problem that the frequency-regulation and temperature-limiting of the prior art are disjointed, strengthens the system stability and anti-disturbance capacity, and is suitable for multi-module industrial scenes.

Description

Technical Field

[0001] This application relates to the field of energy storage system technology, specifically to a method for temperature-limited frequency regulation and shutdown of a grid-type converter based on a temperature-limited control loop. Background Technology

[0002] With the advancement of new power system construction, the proportion of traditional synchronous generators is gradually decreasing, leading to a significant weakening of the power grid's rotational inertia and frequency support capabilities. When faced with large disturbances, the power grid is highly susceptible to severe frequency change rate problems, such as a frequency drop at a high slope of 2Hz / s, seriously threatening the safe and stable operation of the power grid.

[0003] High-power grid-connected converters (GFMs) with overload capacity can autonomously establish grid connection point voltage and frequency, making them a key supporting technology for solving the frequency stability problem of new power grids. For example, high-power converters with a scale of GW have the enormous potential to provide sufficient active power to participate in the system frequency regulation process in a short period of time.

[0004] However, existing grid-connected converter protection and control strategies have significant drawbacks: 1. Conservative control paradigm: Existing high-power converters generally adopt a "current-limiting control loop." Due to the extremely small thermal capacitance of power electronic devices, to prevent overcurrent damage under large disturbances, current is often forcibly limited or switched to grid-connected control when the current reaches a fixed threshold. 2. Incomplete frequency regulation potential: The current-limiting control loop does not address the physical essence of device damage—thermal stress. When dealing with ROCOF drops such as 2Hz / s, the converter could utilize the transient thermal capacity accumulation effect of the devices to provide more and longer active power support, but due to rigid current thresholds, it often exits the frequency regulation stage prematurely, resulting in a significant waste of the hardware potential of GW-level converters. 3. Rigid exit mechanism: Traditional mode switching based on electrical quantity thresholds is often a hard switch, suddenly exiting when the converter is fully loaded and participating in frequency regulation, which can easily cause secondary power surges and low-frequency oscillations in the grid.

[0005] Therefore, this invention proposes a method for temperature-limited frequency regulation and shutdown of a grid-type converter based on a temperature-limited control loop. Summary of the Invention

[0006] To overcome the shortcomings of the prior art, this application provides a method for temperature-limited frequency regulation and shutdown of a grid-type converter based on a temperature-limited control loop, specifically adopting the following technical solution.

[0007] A method for temperature-limited frequency regulation and shutdown of a grid-type converter based on a temperature-limited control loop includes the following steps.

[0008] Step S1, System Initialization and Parameter Preset: After the system starts, it performs hardware self-checks on core modules such as power devices, temperature acquisition, and phase-locked loop to prevent faulty startup; it presets core parameters such as device safety, thermal weighting, and frequency, as well as the basis for their values, and combines the grid frequency change rate ROCOF to preset three levels of disturbance thresholds, matches the corresponding thermal weighting filter coefficients and frequency difference enhancement factors, and simultaneously presets environmental compensation, low temperature adaptation, grid emergency priority, and self-learning parameters to provide a precise benchmark for subsequent control.

[0009] Step S2, Temperature Acquisition, Equivalent Junction Temperature Estimation and Thermal Stress Prediction: Acquire power device case temperature, ambient temperature, and power grid harmonic data. After anomaly removal and filtering calibration, ensure data reliability. Introduce a dual compensation mechanism for ambient temperature and harmonic loss to correct the total loss of power devices. Combine the junction-to-case thermal resistance to estimate the equivalent junction temperature, detect thermal resistance drift in real time, and automatically update parameters. Through junction temperature change rate and linear regression algorithm, predict thermal stress changes within 5~10ms, trigger thermal weight adjustment preparatory actions in advance, and avoid the risk of junction temperature exceeding the standard.

[0010] Step S3: Multi-mode frequency regulation control based on temperature-limited control loop: Combining equivalent junction temperature, thermal stress prediction, and grid disturbance intensity, three modes are determined: pure grid support, stress release, and grid self-protection. An anti-jitter mechanism is adopted to avoid erroneous switching. In the pure grid support mode, frequency regulation support is provided at full load. In the stress release mode, dynamic thermal weight is calculated through the temperature-limited control loop, the damping reference angular frequency is reconstructed, and the active power output is dynamically adjusted. In the grid self-protection mode, the grid angular frequency is locked and the active power output is reduced to prioritize the safety of the devices. Thermal stress balance control is achieved in multi-module scenarios to avoid overload of a single module.

[0011] Step S4, Smooth Exit and Mode Recovery: Under grid self-protection status, gradient voltage reduction and current limiting strategies are adopted to achieve shock-free exit; a minimum holding time for mode switching is set to prevent jitter near the threshold; when the junction temperature continues to rise abnormally, linkage alarms and emergency disconnection are triggered to reduce fault losses; during mode recovery, the grid and device status are verified from multiple dimensions, and the grid support capability is quickly rebuilt through smooth transition of frequency and active power output; a self-learning function is introduced to correct control parameters based on fault data and optimize subsequent processes.

[0012] Step S5, Real-time Monitoring and Anomaly Handling: Full coverage of common anomaly scenarios such as temperature acquisition, phase-locked loop, and output, quickly triggering alarms and protection; realizing dynamic compensation for thermal resistance drift, regularly updating thermal resistance parameters, and solving the problem of decreased control accuracy during long-term operation; for extreme conditions such as strong disturbances and harmonic overloads, initiating emergency control to prioritize device safety; in the event of harmonic overload, synchronously adjusting the converter output and alarming the power grid monitoring platform, achieving device protection and power grid collaborative optimization.

[0013] The technical solution of this application has achieved the following beneficial effects.

[0014] This invention achieves a dynamic balance between the converter's own safety and grid frequency regulation support, solving the problem of disconnect between frequency regulation and temperature limiting in existing technologies; it enhances system stability and anti-disturbance capabilities, adapting to multi-module industrial scenarios; and it reduces operation and maintenance costs through functions such as self-learning and thermal resistance drift compensation. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the temperature-limited frequency regulation and exit method of a grid-type converter based on a temperature-limited control loop in the embodiments of this application. Detailed Implementation

[0016] The present application 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 application and should not be construed as limiting the scope of protection of the present application. It should be noted that the following detailed descriptions are exemplary and intended to provide further explanation of the present application.

[0017] This invention discloses a temperature-limited frequency regulation and shutdown system for a grid-type converter based on a temperature-limited control loop, comprising: a main circuit, a control circuit, and a detection feedback circuit.

[0018] The main circuit is the core of power transmission in the grid-connected converter. It is responsible for converting DC power into AC power and feeding it into the grid. At the same time, it responds to the commands of the control circuit, adjusts the output power and frequency, and realizes frequency modulation control and smooth shutdown. It includes a rectifier unit, an inverter unit, a filter unit and a grid-connected unit. The structure, component selection and function of each unit are as follows.

[0019] The rectifier unit rectifies the input AC power into stable DC power. The AC power source can be grid AC or AC power from renewable energy sources, providing a qualified DC input for the inverter unit. Simultaneously, it suppresses input harmonics, ensuring stable DC voltage and laying the foundation for subsequent frequency regulation control. A three-phase bridge uncontrolled rectifier circuit is used, consisting of six rectifier diodes in a full-bridge topology. A surge absorber is connected in parallel on the input side, and a filter capacitor bank is connected in parallel on the output side to achieve smooth DC voltage filtering. The entire circuit is directly connected to the DC side of the main circuit and the inverter unit input terminal, ensuring continuous power transmission. The selected components and parameters are as follows: The rectifier diode is the SKM100GB12T4 matching diode, model: DSEP100-12A, rated voltage 1200V, rated current 100A, reverse recovery time ≤500ns, meeting the power transmission requirements of the high-power converter; the surge absorber is a varistor, model: MOV-1200V / 20kA, maximum clamping voltage ≤1500V, response time ≤10ns, used to suppress input-side surge voltage and protect the rectifier components; the filter capacitor bank uses electrolytic capacitors with a rated voltage ≥1000V, suitable for 600~800V DC side voltage; recommended model: CD294G-1000V / 2200μF, 3 star connections per group, temperature range -40℃~85℃, ensuring that the rated voltage of the capacitor is ≥1.2 times the actual operating voltage to avoid the risk of breakdown. The working principle is as follows: The input three-phase AC power of 380V / 50Hz is rectified by the rectifier diodes and outputs a pulsating DC voltage with a fluctuation range of 600~800V. After being filtered by the filter capacitor bank, a stable DC voltage is output. The preset DC side voltage is 750V, which provides a stable input for the inverter unit. The surge absorber monitors the input voltage in real time. When a surge voltage occurs, it quickly conducts to discharge the voltage, clamping the voltage within a safe range and protecting the rectifier unit components from damage.

[0020] The inverter unit is the core execution unit. It receives the PWM control signal from the pulse width modulation circuit in the control circuit and inverts the DC power output from the rectifier unit into AC power that is in phase and frequency with the power grid. Simultaneously, based on the frequency modulation command from the main controller circuit, it dynamically adjusts the output voltage, frequency, and power to support power grid frequency regulation. During smooth shutdown, it gradually reduces the output power in response to control commands, achieving a shock-free shutdown and avoiding disturbance to the power grid. The inverter unit adopts a three-phase bridge inverter topology, consisting of six IGBT power device modules. Each IGBT module is connected in parallel with a freewheeling diode, and a buffer inductor is connected in series on the output side. These modules are directly connected to the DC side of the rectifier unit and the input of the filter unit to suppress IGBT switching losses and current surges, ensuring the stability of power conversion. The selected components and parameters are as follows: The IGBT module is SKM100GB12T4, with a rated voltage of 1200V, a rated current of 100A, a switching frequency of 10kHz, and a forward voltage drop of ≤1.8V, suitable for the high-power transmission and high-frequency switching requirements of the converter; the freewheeling diode is a fast recovery diode matched with the IGBT module, with a reverse recovery time of ≤300ns, a rated current of 100A, a rated voltage of 1200V, and a forward voltage drop of ≤0.8V; the buffer inductor is a manganese-zinc ferrite inductor, with the following adjustment parameters: inductance value 0.1~0.2mH, rated current 150A, DC resistance ≤0.005Ω, temperature coefficient ≤30ppm / ℃, suitable for a 10kHz switching frequency, reducing high-frequency losses and improving current spike suppression. The working principle is as follows: The PWM signal output by the pulse width modulation circuit in the control circuit is transmitted to the control terminals of the six IGBT modules through the isolation drive unit to control their conduction and turn-off; by adjusting the duty cycle of the PWM signal, the amplitude and frequency of the AC voltage output by the inverter unit are changed, so as to achieve grid connection with the grid at the same frequency and in phase; when the frequency modulation command of the main controller circuit is received, the duty cycle of the PWM signal is dynamically adjusted to adjust the output power, the adjustment range is 0~120% of the rated power, and the response is made to grid frequency fluctuations; when the smooth exit command is received, the duty cycle of the PWM signal is gradually reduced, so that the output power drops linearly to 0, avoiding the impact of power sudden change on the grid.

[0021] The filtering unit filters out harmonic components in the AC output power of the inverter unit, mainly high-frequency harmonics generated by IGBT switching, ensuring that the total harmonic distortion (THD) of the output power is ≤5%, meeting the GB / T 19964-2012 grid connection standard. It also suppresses harmonic interference to the grid and the converter's own components, guaranteeing power quality. The filtering unit adopts an LCL filter topology, consisting of an inverter-side inductor, a filter capacitor, and a grid-side inductor. The filter capacitor is connected in parallel between the inverter-side and grid-side inductors, along with a damping resistor connected in parallel. This capacitor is directly connected to the inverter unit output and the grid-connected unit input to suppress resonance in the filter circuit and ensure stable operation of the filtering unit. The selected components and parameters are as follows: The filter capacitor is a film capacitor, model: CBB61-1000V / 10μF, rated voltage 1000V, capacitance 10μF, temperature range -40℃~85℃, non-polar, loss tangent ≤0.001, suitable for high-frequency filtering scenarios; the mains-side inductor is a silicon steel sheet inductor, inductance value 2mH, rated current 150A, DC resistance ≤0.02Ω, excitation current ≤5% of rated current; the damping resistor is a metal film resistor, model: RX21-100W / 10Ω, rated power 100W, resistance value 10Ω, tolerance ±1%, temperature coefficient ≤100ppm / ℃, used to suppress the resonance phenomenon of the LCL topology and avoid harmonic amplification. The AC power output from the inverter unit, containing high-frequency harmonics, is filtered by the LCL filter topology. The high-frequency harmonics are absorbed by the filter capacitor, and the grid-side inductor further suppresses the remaining harmonic components. The final output is a sinusoidal AC power with a THD of ≤5% that meets the grid standard. The damping resistor is connected in parallel across the filter capacitor. When resonance occurs in the filter circuit, the resonant frequency is about 500Hz. By consuming the resonant energy, the resonant amplitude is suppressed. The resonant amplitude is ≤10% of the rated voltage, ensuring the stable operation of the filter unit and avoiding damage to the components due to resonance.

[0022] Grid connection unit: realizes reliable connection and disconnection between the converter and the power grid. Under normal operating conditions, it connects the filtered AC power to the power grid and transmits frequency regulation power. During smooth disconnection, it smoothly disconnects from the power grid to ensure that there is no current surge or voltage fluctuation during the converter disconnection process. The surge current is ≤5% of the rated current and the voltage fluctuation is ≤±3% of the rated voltage, protecting the safety of the power grid and the converter.

[0023] The grid-connected unit consists of a grid-connected contactor, a disconnecting switch, a voltage transformer (VT), and a current transformer (CT). The grid-connected contactor and the disconnecting switch are connected in series between the output of the filter unit and the power grid. The voltage transformer is connected in parallel in the grid-connected circuit, and the current transformer is connected in series in the grid-connected circuit. These are used to collect grid-connected voltage and current parameters, respectively. At the same time, it is directly connected to the power grid parameter acquisition unit of the detection feedback circuit to realize real-time parameter transmission. The selected components and parameters are as follows: The grid-connected contactor is an AC contactor, model CJX2-2501, rated voltage 380V, rated current 250A, coil voltage 220V, pull-in time ≤50ms, release time ≤30ms, with arc-extinguishing function to ensure no arcing during disconnection; the disconnecting switch is a knife-fuse switch, model HR6-250 / 3, rated current 250A, fuse rated current 200A, used to isolate the power supply during maintenance to ensure maintenance safety; the voltage transformer is a PSET6000-AIS, used to collect grid-connected voltage parameters and transmit them to the detection feedback circuit; the current transformer is an LZZBJ-10, used to collect grid-connected current parameters and transmit them to the detection feedback circuit. During normal grid connection, the main controller circuit outputs a control signal to close the grid-connected contactor and keep the disconnecting switch closed. The filtered AC power is then fed into the grid through the grid-connected circuit. Voltage and current transformers collect grid-connected voltage and current parameters in real time and transmit them to the grid parameter acquisition unit in the detection feedback circuit, providing data support for phase-locked loop synchronization, mode determination, and frequency regulation control. During smooth disconnection, the main controller circuit first controls the converter output power to drop to 0, then controls the grid-connected contactor to open, and finally opens the disconnecting switch, achieving a shock-free disconnection between the converter and the grid, completing the smooth disconnection. During maintenance, the disconnecting switch is opened to isolate the power supply and ensure the safety of maintenance personnel. After the power drops to 0, it maintains 0 power operation for 50-100ms until the residual current in the grid-connected circuit drops below 0.5% of the rated current, then controls the grid-connected contactor to open, and finally opens the disconnecting switch, ensuring a shock-free connection.

[0024] Control circuit: including main converter circuit, external temperature acquisition circuit, phase-locked loop circuit, main controller circuit, virtual synchronous generator control circuit, thermal limiter circuit, and pulse width modulation circuit.

[0025] Main controller circuit: This is the core of the system's calculations and control. It receives real-time case temperature signals from the external temperature acquisition circuit, grid frequency signals from the phase-locked loop circuit, and feedback signals from the thermal limiter circuit. Simultaneously, it receives grid parameters and operating parameters transmitted by the detection feedback circuit. It coordinates the thermal limiter circuit, virtual synchronous generator control circuit, and pulse width modulation circuit to work together, executing the core logic of the temperature-limited control loop, handling abnormal temperature and operating condition signals, and outputting control commands such as mode switching and frequency adjustment. It includes a built-in critical limit judgment unit and a safety starting threshold judgment unit, primarily responsible for determining the equivalent junction temperature threshold, clarifying the IGBT module's temperature status (not exceeding the safe range, approaching the safe limit, or exceeding the safe limit). Simultaneously, it works with the thermal limiter circuit to set temperature judgment thresholds, triggering switching between three control modes: pure grid support, stress release, and grid self-protection, ensuring the coordinated stability of the main controller circuit and all related circuits. The main controller circuit uses an industrial-grade microcontroller, model STM32H743VIT6, with a main frequency of 480MHz. It can synchronously process multi-channel signals, including temperature signals, mode switching signals, frequency signals, and power signals. It has built-in critical limit judgment unit and safety start threshold judgment unit. It can achieve bidirectional signal interaction with external temperature acquisition circuit, thermal limiter circuit, virtual synchronous generator control circuit, and pulse width modulation circuit through CAN bus, with a communication rate of ≥1Mbps, to ensure the accuracy and real-time performance of temperature threshold judgment and mode switching command output. It is compatible with the multi-mode switching logic of temperature-limited control loop.

[0026] Phase-locked loop (PLL) circuit: As an independent core circuit of the system, it communicates bidirectionally with the main converter circuit, main controller circuit, and thermal limiter circuit. It collects voltage and current signals from the output of the grid-connected unit of the main converter circuit. Through the collaborative work of internal core units, it extracts the real-time angular frequency of the power grid and achieves synchronization locking with the power grid frequency. It transmits the real-time angular frequency signal to the thermal limiter circuit to provide basic data for the reconstruction of the dynamic damping reference frequency. At the same time, it outputs the real-time frequency signal of the power grid and transmits it to the main controller circuit and the thermal limiter circuit for mode determination of the thermal limiter circuit and operating condition determination of the main controller.

[0027] The phase-locked loop circuit is independently integrated into the control circuit and works in conjunction with the main controller circuit. It includes three core units: a phase detector, a loop filter, and a voltage-controlled oscillator. It uses an industrial-grade integrated phase-locked loop chip, model CD4046, and is matched with a signal amplification unit, which uses an LM324 operational amplifier to ensure the stability of signal acquisition and output, avoid electromagnetic interference, and its anti-interference capability meets the GB / T 14714-2008 standard.

[0028] Phase detector: It realizes phase comparison. Its input terminal is connected to the voltage signal output terminal of the grid-connected unit of the main converter circuit and the feedback signal output by the voltage-controlled oscillator. By comparing the phase difference of the two signals, it outputs an error voltage signal that is proportional to the phase difference.

[0029] Loop filter: Connected in series between the phase detector and the voltage-controlled oscillator (VCO), its function is to filter out high-frequency noise and ripple in the phase detector's output error voltage, outputting a stable control voltage signal and avoiding high-frequency interference that causes fluctuations in the VCO's output frequency. It adopts an active low-pass filter topology, consisting of an LM324 operational amplifier, resistors, and capacitors. The cutoff frequency is set to 10Hz, the filtering accuracy is ≤0.01V, and the output control voltage range is 0~5V, ensuring the stability of the output control voltage and guaranteeing the synchronization accuracy of the phase-locked loop circuit.

[0030] Voltage-controlled oscillator (VCO): Receives a stable control voltage signal from the loop filter and outputs an oscillation frequency signal proportional to the control voltage, ultimately achieving synchronization locking with the grid frequency. A voltage-controlled crystal oscillator (VCXO-10MHz) is selected, with an oscillation frequency range of 9.999~10.001MHz, frequency stability ≤1ppm, and a control voltage range of 0~5V. After frequency division processing, the output signal is transmitted to the thermal limiter circuit, providing real-time grid angular frequency data for the reconstruction of the dynamic damping reference frequency. Simultaneously, it is fed back to the phase detector, forming a phase-locked loop closed-loop control to ensure synchronization stability.

[0031] Thermal limiter circuit: It communicates bidirectionally with the main controller circuit, phase-locked loop circuit, and virtual synchronous generator control circuit. It receives mode switching control signals from the main controller circuit, real-time angular frequency signals from the phase-locked loop circuit, and real-time shell temperature signals from the external temperature acquisition circuit. Based on the control signal status and temperature threshold, it selectively outputs a fixed rated angular frequency or a dynamically reconstructed damping reference frequency to achieve smooth switching between three modes of converter: pure grid support, stress release, and grid self-protection. The core components are the thermal weight calculation module and the mode determination module, which are adapted to the core functions of the thermal limiter in the application scheme. The thermal limiter circuit is independently integrated into the control circuit and is directly connected to the main controller circuit, phase-locked loop circuit, and virtual synchronous generator control circuit. It has a built-in thermal weight calculation module and mode determination module, uses an LM324 industrial-grade operational amplifier, and is equipped with a signal isolation unit. It uses an industrial-grade high-isolation voltage optocoupler, model: TLP2355, which adopts optocoupler isolation with an isolation voltage ≥2500V to ensure interference-free signal transmission. It can directly receive the case temperature signal of the NTC thermistor, the real-time angular frequency signal of the phase-locked loop, and the mode switching control signal of the main controller, and output the corresponding angular frequency signal to the virtual synchronous generator control circuit. At the same time, it feeds back the working status signal (normal / abnormal) to the main controller circuit. The thermal weight calculation module uses an industrial-grade dedicated weight calculation chip, model AD8421, which is a mature mass-produced product of Texas Instruments (TI). It supports temperature signal input from 0 to 120°C, with a weight calculation accuracy of ≤0.001 and an operation frequency of ≥100MHz. It can be directly integrated into the thermal limiter circuit and is fully compatible with the STM32H743VIT6 microcontroller and NTC temperature acquisition circuit, requiring no additional development of operation logic. The mode determination module uses an industrial-grade dedicated mode determination chip, model ADG719.

[0032] The virtual synchronous generator control circuit is directly connected to the main controller circuit, thermal limiter circuit, and pulse width modulation circuit. It integrates a virtual synchronous generator control algorithm, including active power-frequency droop control and reactive power-voltage droop control logic, enabling dynamic adjustment of active and reactive power. It receives the dynamic damping reference frequency or fixed rated angular frequency output from the thermal limiter circuit, and combines it with the real-time grid angular frequency output from the phase-locked loop circuit to dynamically adjust the output power to respond to grid frequency regulation requirements. Simultaneously, it receives mode switching commands from the main controller, achieving smooth switching between three modes: pure grid support, stress relief, and grid self-protection, ensuring a shock-free and fluctuation-free frequency regulation process. The virtual synchronous generator control circuit uses an industrial-grade DSP chip, model TMS320F28335, with a main frequency of 150MHz. It incorporates a virtual synchronous generator control algorithm and communicates with the main controller circuit, thermal limiter circuit, and pulse width modulation circuit via a CAN bus, achieving a signal transmission rate ≥1Mbps. It possesses electromagnetic interference resistance, is adaptable to complex industrial conditions, and can quickly respond to control commands, adjusting the output phase signal to provide a precise phase reference for the pulse width modulation circuit.

[0033] Pulse Width Modulation (PWM) Circuit: The core unit of the system power drive, connected in series with the main controller circuit, virtual synchronous generator control circuit, and main converter circuit. It receives the phase signal from the virtual synchronous generator control circuit and converts it into a PWM drive signal that can drive the IGBT module of the main converter circuit to turn on / off. It controls the switching frequency of the IGBT, which is fixed at 10kHz with a frequency fluctuation of ≤±1%, ensuring a smooth frequency modulation process and avoiding frequency abrupt changes. At the same time, based on the feedback signal from the thermal limiter circuit, it dynamically adjusts the duty cycle of the PWM signal to match the thermal weight changes, achieving smooth adjustment of the output power and balancing frequency modulation support and thermal safety protection. It has overcurrent and overvoltage protection functions and can quickly cut off the drive signal to protect the IGBT module. The pulse width modulation circuit uses an industrial-grade PWM driver chip, model IR2110, with a matching isolated driver unit. It is optocoupler isolated with an isolation voltage ≥2500V. The input side is connected to the virtual synchronous generator control circuit to receive the phase reference signal. The output side is connected one-to-one to the IGBT module control terminals of the main converter circuit. It has overcurrent and overvoltage protection functions, which can effectively protect the IGBT modules and avoid device damage caused by abnormal drive signals. The drive signal delay is ≤100ns, and the rise / fall time is ≤50ns, ensuring the synchronization of the switching actions of the 6 IGBT modules and ensuring the stability of the converter output.

[0034] The detection and feedback circuit collects grid parameters, converter temperature, and operating parameters. After preprocessing, these parameters are transmitted to the core units of the control circuit, providing accurate raw data for control logic operations, mode determination, and frequency regulation control. Simultaneously, it collects the execution results of each circuit in real time and feeds them back to the main controller circuit, realizing a detection-control-feedback closed loop to ensure control accuracy and system stability. The data acquisition period is ≤1ms, and the acquisition accuracy is ≤0.5%. It includes an external temperature acquisition circuit, a grid parameter acquisition unit, and an operating parameter acquisition unit.

[0035] External temperature acquisition circuit: This circuit acquires the case temperature data of the IGBT module in the main converter circuit in real time and transmits it to the main controller circuit and thermal limiter circuit without delay. It provides raw data for temperature anomaly detection, thermal weight calculation, and equivalent junction temperature estimation, acting as the "temperature sensing terminal" of the temperature-limited control loop. Simultaneously, it monitors the operating status of the acquisition circuit itself and promptly sends an alarm signal to the main controller circuit when an anomaly occurs. The external temperature acquisition circuit uses a surface-mount NTC thermistor, directly attached to the surface of the IGBT module in the main converter circuit, inside the power module, in close contact with the IGBT chip. No additional wiring is required; it is directly integrated into the power module of the main converter circuit, reducing line interference and ensuring the accuracy of temperature acquisition. It is equipped with a signal conditioning unit and a filtering unit, which are directly connected to the main controller circuit and thermal limiter circuit to realize signal conversion and transmission. The selected components and parameters are as follows: A fast-response NTC thermistor is chosen, with the following parameters: temperature range -20℃ to 120℃, accuracy ±0.5℃, response time ≤10ms, and nominal resistance of 10kΩ at 25℃. This ensures the response time is ≤10 times the acquisition cycle, guaranteeing real-time temperature acquisition. The accompanying signal conditioning unit uses an LM324 operational amplifier to convert the resistance signal to a voltage signal with a conversion accuracy ≤0.1%. The filtering unit uses a first-order low-pass filter with a cutoff frequency of 10Hz to filter out high-frequency noise during temperature acquisition, ensuring signal stability. Shielded cables are used for transmission to reduce electromagnetic interference. The case temperature data acquired by the external temperature acquisition circuit needs to be transmitted to the thermal limiter circuit for estimating the equivalent junction temperature.

[0036] The power grid parameter acquisition unit collects power grid parameters such as voltage, current, frequency, and total harmonic distortion (THD) of the grid-connected circuit, and transmits them to the phase-locked loop (PLL) circuit and the main controller circuit, providing data support for PLL synchronization, mode determination, and frequency regulation control. It also monitors the rate of change of grid frequency (ROCOF) for disturbance intensity classification. The acquisition period is ≤1ms, and the acquisition accuracy is ≤0.5%, ensuring real-time and accurate data. This unit includes voltage transformers, current transformers, and a harmonic detection module, directly connected to the grid-connected unit, PLL circuit, and main controller circuit. The voltage and current transformers respectively acquire grid voltage and current signals, transmitting them to the harmonic detection module and the PLL circuit. The harmonic detection module uses a Fast Fourier Transform (FFT) algorithm with 1024 FFT points and a calculation error ≤1%, accurately detecting the total harmonic distortion (THD) of the power grid, and also detecting the distortion rate of each harmonic, providing data support for harmonic overload determination. The module has built-in signal amplification and filtering units to ensure the stability of the acquired signals. The voltage transformer is selected from the PSET6000 series of Guodian Nanzhi, model PSET6000-AIS; the current transformer is selected from the dry-type cast type of Hebei Beihu, model: LZZBJ-10; the core chip of the harmonic detection module is BP1048B2; the phase-locked loop circuit collects the instantaneous value of the grid voltage, the main controller circuit performs FFT operation on the voltage signal, calculates the total harmonic distortion (THD) of the grid, and transmits the THD to the thermal limiter circuit.

[0037] Operating Parameter Acquisition Unit: This unit acquires operating parameters of each circuit in the converter, including DC-side voltage, inverter unit output current, PWM drive signal status, and the operating status of each module. These parameters are transmitted to the main controller circuit for abnormal operating condition detection and fault tracing, ensuring safe and stable system operation. Simultaneously, it acquires ambient temperature for ambient temperature compensation and low-temperature condition detection. The acquisition period is ≤1ms, and data is transmitted after CRC-16 verification to avoid data errors. Specifically, it includes: a core acquisition module using an industrial-grade data acquisition module with a CAN bus interface (Advantech USB-4711); a DC-side voltage acquisition sensor using a Chipsen CMV-3000 high-voltage sensor; an inverter unit output current acquisition sensor using a Chipsen CM5A2000 H20 high-precision closed-loop current sensor; and an ambient temperature acquisition module using a PT100 temperature acquisition module (TS-600).

[0038] like Figure 1 As shown, this invention discloses a method for temperature-limited frequency regulation and shutdown of a grid-type converter based on a temperature-limited control loop, including the following steps.

[0039] Step S1: System initialization and parameter preset.

[0040] Step S2: Temperature acquisition, equivalent junction temperature estimation, and thermal stress prediction.

[0041] Step S3: Multi-mode frequency modulation control based on temperature-limited control loop.

[0042] Step S4: Smooth Exit and Mode Resumption.

[0043] Step S5: Real-time monitoring and anomaly handling.

[0044] Example 1.

[0045] This embodiment 1 discloses a method for temperature-limited frequency regulation and exit of a grid-type converter based on a temperature-limited control loop, wherein step S1 includes the following steps.

[0046] S11. System Startup and Hardware Self-Test: Upon starting the grid-connected converter control system, the main controller circuit first executes a self-test program. The self-test process is as follows: 1) Detecting the on / off status of the three-phase bridge arm power devices in the main converter circuit, and determining no short-circuit or open-circuit faults by collecting IGBT drive signal feedback; 2) Detecting the communication status between the external temperature acquisition circuit and the ambient temperature acquisition module, collecting 10 sets of initial temperature data, determining no acquisition abnormalities, and data fluctuation ≤ ±0.5℃; 3) Detecting the input signal of the phase-locked loop circuit, determining that the signal amplitude and frequency are within the normal range, voltage amplitude fluctuation ≤ ±5% of the rated value, and frequency 49.5Hz~50.5Hz; 4) Detecting the linkage status of the virtual synchronous generator control circuit, thermal limiter circuit, and pulse width modulation circuit, sending test control commands, and determining that each module responds normally; 5) Detecting the read / write status of the local storage module, determining that data can be stored normally; After all modules pass the self-test, the system enters the parameter preset stage. If the self-test fails, an alarm signal is triggered, prohibiting the converter from starting. The external temperature acquisition circuit includes an NTC thermistor.

[0047] S12. Preset Core Basic Parameters: The main controller circuit has preset core parameters with clearly defined value ranges to ensure feasibility. Specifically: 1) Device Parameters: Maximum junction temperature of the device... Based on the IGBT model setting, the SKM100GB12T4 model is set to 150℃; safety margin. The value range is 5℃~15℃, with 10℃ being the preferred value; safety starting threshold. The value range is 100℃~120℃; critical limit. ,follow 1) Value range: 135℃~145℃; 2) Thermal weight related parameters: thermal weight filtering time constant The value ranges from 0.1s to 1s, corresponding to discrete filter coefficients in discrete scenarios. The value ranges from 0.6 to 0.9, satisfying... ,in 1ms is used as the control period; 3) Frequency-related parameters: rated angular frequency ,Pick The upper limit of the frequency change rate corresponding to 50Hz in the power grid. The maximum frequency change of the step The value range is 0.01 rad / s to 0.1 rad / s, and the frequency difference normalization limit is... ; Value range: 0.05 rad / s ~ 0.2 rad / s; 4) Mode switching parameters: Minimum hold time for mode switching The value range is 0.5s to 2s, with 1s being the preferred value. The threshold for entering and exiting the transition zone is: , ,satisfy Critical zone entry and exit limits: , A hysteresis threshold is introduced to avoid jitter near the threshold, with jitter amplitude ≤ ±1℃.

[0048] S13. Disturbance Intensity Classification Parameter Preset: Based on the grid frequency change rate ROCOF, three levels of disturbance intensity thresholds are preset, the classification criteria are clearly defined, and different thermal weighting filter coefficients are set accordingly. Sum of frequency difference enhancement factor The baseline value enables dynamic adaptation between disturbance intensity and control parameters, with specific classifications as follows: 1) Weak disturbance: ROCOF < 0.5 Hz / s, corresponding to... =0.8~0.9, Reference value = 0.5~0.6; 2) Medium disturbance: 0.5Hz / s ≤ ROCOF < 1.5Hz / s, corresponding to =0.7~0.8, Reference value = 0.7~0.8; 3) Strong disturbance: ROCOF ≥ 1.5Hz / s, corresponding to =0.6~0.7, The baseline value is 0.9~1.0; at the same time, the ROCOF detection cycle is preset to 10ms. If the corresponding classification standard is met for 3 consecutive detection cycles, it is determined to be the disturbance level, so as to avoid misjudgment caused by instantaneous fluctuations.

[0049] S14, Environmental and Harmonic Adaptation Parameter Preset.

[0050] 1) Ambient temperature compensation coefficient: It is set in segments according to the range of -40℃ to 60℃, with each segment being 10℃. The specific values ​​are: 1.3 for -40℃ to -30℃, 1.25 for -30℃ to -20℃, 1.2 for -20℃ to -10℃, 1.1 for -10℃ to 0℃, 1.05 for 0℃ to 10℃, and 1.0 for 10℃ to 60℃.

[0051] 2) Harmonic loss correction coefficient: set according to the total harmonic distortion (THD) classification of the power grid, with specific values ​​as follows: 1.0 when THD≤5%, 1.1 when 5%<THD≤10%, 1.2 when 10%<THD≤15%, and 1.3 when THD>15%.

[0052] 3) Low-temperature operating condition judgment threshold: -20℃. When the ambient temperature Ta≤-20℃, it is judged as a low-temperature operating condition, and the thermal weighting filter coefficient is adjusted accordingly. At the corresponding disturbance level Increase the initial safety threshold by 0.2~0.3 based on the existing value. Lower by 5-8℃.

[0053] 4) Harmonic overload judgment threshold: If THD > 15% and the duration is ≥ 50ms, it is judged as a harmonic overload condition.

[0054] S15, Priority and Self-Learning Parameter Presets.

[0055] 1) Power grid emergency priority threshold: When the power grid frequency is ≤49.0Hz, the power grid emergency priority is higher than the converter's own safety; when the power grid frequency is >49.0Hz, the converter's own safety priority is higher; at the same time, the power grid frequency detection period is preset to 5ms. If the frequency threshold is met for 5 consecutive detection periods, the priority switching is triggered.

[0056] 2) Self-learning parameters: self-learning cycle is 24 hours, fault data storage threshold, self-learning correction magnitude, and correction parameter range. Even after correction, it remains between 0.6 and 0.9. The corrected temperature is still between 100℃ and 120℃.

[0057] S16, Module startup and initial data acquisition.

[0058] 1) The external temperature acquisition circuit is started, with a sampling frequency of 100Hz, to collect the power module case temperature in real time. Every 10 sets of data are subjected to a moving average filter to initially suppress noise.

[0059] 2) The phase-locked loop (SPLL) circuit starts up with a sampling frequency of 1kHz, acquiring the voltage and current signals at the grid connection point in real time, and extracting the real-time angular frequency of the power grid through synchronous coordinate transformation. Total Harmonic Distortion (THD) of the power grid was calculated using Fast Fourier Transform (FFT) with 1024 FFT points and a calculation error of ≤1%.

[0060] 3) The ambient temperature acquisition module is started, with a sampling frequency of 10Hz, and the ambient temperature Ta is acquired in real time.

[0061] 4) The multi-module converter presets the thermal stress equalization threshold for each module, with the difference between modules ≤5℃. It initializes the module collaborative control parameters, and the initial allocation ratio of active power output of each module is 1:1, with a deviation ≤±5%; ⑤ All collected data are synchronously transmitted to the main controller circuit. The main controller circuit performs preliminary verification on the data and removes data that exceeds the reasonable range, such as case temperature >150℃ or <-40℃, which is judged as abnormal acquisition. After verification, the data is stored in the local cache.

[0062] Example 2.

[0063] This embodiment 2 discloses a method for temperature-limited frequency regulation and exit of a grid-type converter based on a temperature-limited control loop, wherein step S2 includes the following steps.

[0064] S21. Temperature pretreatment.

[0065] 1) The external temperature acquisition circuit transmits the real-time raw shell temperature value to the thermal limiter circuit.

[0066] The thermal limiter circuit integrates the following three core sub-units, which interact with each other through a preset communication interface.

[0067] Temperature preprocessing subunit: Responsible for receiving raw case temperature data transmitted from the external temperature acquisition circuit. It performs outlier data removal and second-order low-pass filtering, and performs temperature calibration based on the temperature-resistance characteristic curve of the NTC thermistor, outputting stable case temperature data. .

[0068] Heat loss and junction temperature calculation subunit: Receives the total power device loss transmitted from the power loss calculation module. and ambient temperature compensation coefficient Through the formula The equivalent junction temperature is estimated, and an estimation error compensation term is introduced for calibration to output the real-time equivalent junction temperature. .

[0069] Thermal weighting and dynamic frequency generation subunit: receiving equivalent junction temperature Grid ROCOF value and THD data. Based on preset safety thresholds. Thermal limit threshold Once the execution mode is determined, the corresponding hot weighted filter coefficients are generated. With frequency difference enhancement factor Based on thermal weight w for rated angular frequency With real-time angular frequency Weighted synthesis is performed to generate a dynamically damped reference angular frequency. The output is sent to the virtual synchronous generator control circuit.

[0070] The temperature preprocessing subunit of the thermal limiter circuit first performs abnormal data removal: removing data that exceeds the range of -40℃ to 150℃, as well as data that deviates from the adjacent 3 sets of data by more than 2℃, and replacing them with the average value of the adjacent 3 sets of data.

[0071] 2) Perform second-order low-pass filtering with a cutoff frequency of 10Hz. The filtering formula is as follows: ,in To stabilize the shell temperature at the current moment, This is the original shell temperature value at the current moment. This is the original shell temperature value from the previous moment. To stabilize the shell temperature at the previous moment.

[0072] 3) Perform temperature calibration: Based on the temperature-resistance characteristic curve of the NTC thermistor, calibrate the filtered case temperature data. The calibration formula is: ,in To stabilize the shell temperature after calibration, To obtain the filtered case temperature, the nonlinear error of the thermistor is compensated, ultimately resulting in a stable case temperature. .

[0073] 4) The ambient temperature acquisition module transmits the real-time ambient temperature Ta to the main controller circuit, and the phase-locked loop circuit transmits the total harmonic distortion (THD) of the power grid to the thermal limiter circuit. Both of these processes perform the above-mentioned abnormal data removal and filtering to ensure data accuracy.

[0074] S22, Power Loss Calculation and Dual Compensation.

[0075] 1) Total losses of power devices Using conduction loss With switching losses The accurate model calculation of the sum is as follows: Conduction Loss ,in , , The conduction loss coefficient is obtained from actual measurements based on the IGBT model, for example, for the SKM100GB12T4 model. , , I represents the converter output current; switching losses ,in , The switching loss factor (for SKM100GB12T4 model) is taken as... , ), DC side voltage The switching frequency is a fixed value, determined by the set parameters. It is the conduction loss coefficient related to the square of the converter output current; It is the conduction loss coefficient related to the converter output current; It is a fixed coefficient of conduction loss and is independent of current. It is the switching loss coefficient related to DC-side voltage, converter output current, and switching frequency; It is the switching loss coefficient related to the DC side voltage and the converter output current.

[0076] 2) Ambient temperature compensation: Based on the real-time ambient temperature Ta, a corresponding ambient temperature compensation coefficient is matched. The compensation formula is: ,in This is to compensate for losses after adjusting for ambient temperature.

[0077] 3) Harmonic loss correction: Based on the total harmonic distortion (THD) of the power grid, a corresponding harmonic loss correction coefficient is matched. The corrected formula is: ,in To ensure the accuracy of loss estimation and avoid junction temperature estimation deviations caused by ambient temperature and power grid harmonics, the final correction is made for the total loss of power devices.

[0078] S23, Equivalent junction temperature estimation.

[0079] 1) Equivalent junction temperature estimation sub-unit for thermal limiter circuit, based on stable case temperature The thermal resistance from junction to shell and the total loss of the corrected power devices Through formula Estimating equivalent junction temperature ,in This is the thermal resistance from the junction to the shell.

[0080] 2) Error Correction: A junction temperature estimation error compensation term is introduced to correct the junction temperature error caused by thermal resistance drift and loss estimation deviation, ultimately obtaining the calibrated equivalent junction temperature. The junction temperature estimation error compensation is as follows: .

[0081] 3) Real-time monitoring of junction-to-shell thermal resistance The drift is calculated every hour. The actual value, through , , Reverse reasoning: , It is the measured value of the junction-to-shell thermal resistance; if If the deviation from the preset value is greater than 5%, it will be automatically updated. Parameters are used to avoid errors in junction temperature estimation caused by long-term operation.

[0082] S24, adapted for low-temperature operating conditions.

[0083] 1) The main controller circuit compares the ambient temperature Ta with the low-temperature condition judgment threshold of -20℃ in real time. If Ta ≤ -20℃, it is judged as a low-temperature condition, and the following adaptation adjustments are immediately performed: a. Adjust the thermal weighting filter coefficient. At the current disturbance level Increase by 0.2~0.3 on the basis, such as under strong disturbances. a. Adjusted from 0.6~0.7 to 0.8~1.0 to slow down the rate of change of thermal weight and adapt to the characteristic of increased heat capacity of devices at low temperatures; b. Adjusted the safety starting threshold. Lower the temperature by 5-8°C to initiate stress release earlier and prevent excessive thermal stress accumulation in the device at low temperatures; c. Adjust the switching frequency. This reduces losses by 20% to 30%, decreases switching losses, and lowers thermal stress.

[0084] 2) If Ta > -20℃, restore all parameters to the initial preset values ​​to ensure control performance under normal temperature conditions; after adjusting for low temperature conditions, monitor Ta every 100ms and dynamically switch the adaptation state to avoid frequent parameter adjustments caused by temperature fluctuations.

[0085] S25, thermal stress prediction.

[0086] 1) The main controller circuit is based on the equivalent junction temperature. Real-time rate of change ( Make a prediction. Calculation using the finite difference method: ,in The current temperature is the set temperature. The sampled temperature is set to the junction temperature 10ms prior, with a sampling period of 1ms, to avoid misjudgment of the rate of change caused by instantaneous fluctuations.

[0087] 2) A linear regression algorithm is used to predict the junction temperature change trend within the next 5-10 ms. The regression equation is: Where t is the prediction time, t = 5ms~10ms, and we take 8ms. The value is the predicted value of thermal stress at time t.

[0088] 3) Setting the warning threshold: ,like If the sampling continues for two consecutive sampling cycles, the preparatory action for thermal weight adjustment will be triggered in advance: the adjustment rate of thermal weight w will be increased by 10% to 20%, and the active power output command of the virtual synchronous generator control circuit will be reduced by 10% to avoid the junction temperature from rising sharply beyond the critical limit.

[0089] 4) If If the preparatory action is not performed, the normal control rhythm is restored to ensure the accuracy of the prediction and avoid false warnings.

[0090] S26. Data synchronization and transmission.

[0091] 1) The thermal limiter circuit will stabilize the case temperature. Equivalent junction temperature Corrected losses thermal stress prediction value The data is synchronously transmitted to the main controller circuit at a rate of 1kHz, using CRC check with a check polynomial of CRC-16 to ensure data transmission without loss or error.

[0092] 2) The phase-locked loop circuit will record the real-time angular frequency. The total harmonic distortion (THD) of the power grid is synchronously transmitted to the thermal limiter circuit and the main controller circuit, and CRC verification is also used.

[0093] 3) In a multi-module converter, each module synchronously collects its own data. , , The data is transmitted to the collaborative control unit of the main controller circuit. The main controller circuit performs consistency verification on the data of each module. The deviation of the data of each module is ≤±2℃. After the verification is passed, it is used for subsequent multi-module collaborative control. If the verification fails, the alarm of the module is triggered and it is switched to standby state.

[0094] This technical solution significantly improves the accuracy of temperature acquisition and junction temperature estimation through temperature preprocessing, dual compensation mechanisms, and junction temperature estimation correction; it adapts to low-temperature conditions and expands the system's operating temperature range; it avoids the risk of device overheating in advance by predicting thermal stress, thus extending the device's service life; and it standardizes data synchronization and verification to ensure reliable core data transmission and provide precise support for subsequent control.

[0095] Example 3.

[0096] This embodiment 3 discloses a method for temperature-limited frequency regulation and exit of a grid-type converter based on a temperature-limited control loop, wherein step S3 includes the following steps.

[0097] S31, Mode Determination Logic: The main controller circuit determines the mode based on the equivalent junction temperature. thermal stress prediction value The system considers the grid disturbance intensity, ambient temperature Ta, and total harmonic distortion (THD) of the grid, combined with preset thresholds, to perform multi-mode judgment with a judgment period of 1ms. It also introduces an anti-jitter mechanism, and only performs mode switching if the same mode condition is met for three consecutive judgment periods. The specific judgment conditions are as follows.

[0098] 1) Pure network support mode: ,and Furthermore, Ta > -20℃, THD ≤ 15%, and ROCOF < 0.5Hz / s weak disturbance.

[0099] 2) Stress relief smooth transition mode: satisfies any of the following conditions: a. b. c. Disturbances in the range of 0.5Hz / s ≤ ROCOF < 1.5Hz / s and d. THD > 10% and .

[0100] 3) Network self-protection mode: meets any of the following conditions: a. b. c. THD > 15% and d. Unexpected strong disturbance ROCOF ≥ 2.5 Hz / s and After mode determination, the main controller circuit sends a mode switching control signal to the thermal limiter circuit. The invalid low level is 0V, the valid high level is 5V, and the signal delay is ≤1ms.

[0101] S32, pure mesh support.

[0102] 1) The main controller circuit sends an invalid low-level mode switching control signal (0V) to the thermal limiter circuit. The thermal limiter circuit does not activate the thermal weight calculation module and sends a fixed rated angular frequency to the virtual synchronous generator control circuit. The transmission period is 1ms, and the frequency fluctuation is ≤±0.01rad / s.

[0103] 2) The main controller circuit sends a valid high-level active power output command of 5V to the virtual synchronous generator control circuit. The amplitude of the active power output command is linked to the grid frequency regulation requirement. Specifically, when the grid frequency... At that time, the amplitude of the active power output command varies with the frequency difference. Increased accordingly, the maximum output active power is 1.2 times the rated power of the converter, with short-time overload capacity, duration ≤10s; when the grid frequency... At this time, the active power output command amplitude is 0.8 to 1.0 times the rated power of the converter to maintain grid frequency stability.

[0104] 3) The virtual synchronous generator control circuit is based on With the active power output command, the output phase signal is adjusted, and the control law is as follows: ,in To output the phase reference value, To control the cycle, This is a proportionality coefficient, with a value ranging from 1 to 5. This is the integral coefficient, with a value ranging from 0.1 to 1. This is the output power of the converter.

[0105] 4) In the multi-module converter, each module is under full-load frequency regulation, and the main controller circuit monitors each module in real time. If a certain module If the temperature difference with other modules is greater than 3℃, then the active power output of this module is finely adjusted by ±5% to maintain thermal stress balance.

[0106] 5) Monitor the power grid frequency and ambient temperature in real time. If there are changes in operating conditions, such as an increase in ROCOF or Ta≤-20℃, immediately re-execute the mode determination to avoid incorrect mode maintenance.

[0107] S33, Smooth transition of stress relief.

[0108] 1) The main controller circuit sends a valid high-level mode switching control signal (5V) to the thermal limiter circuit. The thermal limiter circuit activates the thermal weight calculation module and, based on the ROCOF value extracted by the phase-locked loop, matches the control parameters corresponding to the disturbance strength. , The baseline value is used, and the values ​​are dynamically adjusted in conjunction with the ambient temperature (Ta) and THD.

[0109] 2) Temperature normalization: Construct a thermal weighting calculation model to normalize the equivalent junction temperature. The mapping is to a dimensionless normalized variable z, and the heat weight calculation model is as follows: Where sat(x,0,1) is the amplitude limiting function, and the specific implementation logic is as follows: when x < 0, z = 0; when 0 ≤ x ≤ 1, z = x; when x > 1, z = 1; at the same time, normalization smoothing is introduced. To avoid sudden changes in z-value.

[0110] 3) Ideal heat weight generation: Based on the normalized variable z, the ideal heat weight is calculated using an S-shaped smoothing function. The specific formula is as follows: The derivative of this function is zero at z=0 and z=1, which reduces the transient impact during switching.

[0111] 4) Hot weight smoothing filter: for ideal hot weights Applying a first-order low-pass filter, the filtering formula for continuous scenes is: The filtering formula for discrete scenarios is: ,in The value is dynamically adjusted based on the disturbance intensity and ambient temperature, increasing by 0.2 to 0.3 under low-temperature conditions; at the same time, a slope limit is applied, with the rate of change of w ≤ 0.1 / s, to avoid frequency fluctuations caused by weight transients.

[0112] 5) Frequency Difference Enhancement Optimization: Targeting power grid frequency sag scenarios, Introducing frequency difference enhancement factor Accelerated protection, specific calculations: ,in For frequency difference, Frequency deviation normalization limit; comprehensive weight calculate: When the power grid frequency is significantly lower than the rated value and the temperature rise is close to the limit hour, As the value approaches 1, w increases, and the converter reduces its support to the power grid more quickly.

[0113] 6) Dynamic Priority Adaptation: Real-time monitoring of power grid frequency; if the power grid frequency is ≤ 49.0Hz and meets the emergency threshold for 5 consecutive detection cycles, even if... near This will also slow down the adjustment rate of w by 20% to 30%, prioritizing grid frequency regulation support, and allowing Brief approach But no more than If the grid frequency is greater than 49.0 Hz, the adjustment rate of W will be increased to 0.12~0.15 / s to prioritize the safety of the converter itself.

[0114] 7) Damped reference frequency reconstruction: The thermal limiter circuit reconstructs the rated angular frequency according to the comprehensive weight w. With real-time angular frequency Weighting is performed to generate a dynamically reconstructed damped reference angular frequency. The calculation formula is: Simultaneously apply a frequency change rate constraint in continuous scenarios. In discrete scenarios.

[0115] .

[0116] .

[0117] in, For the maximum frequency change of the discrete step, ensure Smooth changes, avoiding sudden frequency shifts. It is the damping reference angular frequency dynamically reconstructed at the current time k, which is used to transmit to the virtual synchronous generator control circuit as the core reference quantity for frequency regulation control, ensuring smooth frequency changes. It is the damping reference angular frequency at time k-1, i.e., the frequency of the previous control cycle. The value is used to achieve a smooth transition of frequency at the current moment. It's a limiting function; its purpose is to limit the difference within the parentheses to a certain value. to Between, avoid Sudden changes ensure frequency modulation stability; It is the mixed angular frequency at the current time k, which is the weighted composite value of the rated angular frequency and the real-time angular frequency of the power grid. It is the comprehensive thermal weight at the current time k, dimensionless, with a value range of 0 to 1. It is dynamically calculated by the thermal limiter circuit based on parameters such as equivalent junction temperature and disturbance intensity, and is mainly used to balance the safety of the converter itself and the frequency regulation support of the power grid. It is the rated angular frequency, which is a fixed preset parameter. It is the real-time angular frequency of the power grid at the current time k, which is collected and extracted in real time by the phase-locked loop circuit SPLL, reflecting the current frequency status of the power grid. It is the maximum frequency change of the distance step.

[0118] 8) Multi-module collaborative control: The collaborative control unit of the main controller circuit compares the data of each module in real time. Calculate each module With average junction temperature The difference, ,like If the junction temperature of a certain module is too high, adjust the thermal weight w of that module by increasing it by 0.1~0.2, while simultaneously reducing its active power output ratio by 5%~10%; if If the junction temperature of a certain module is too low, adjust the thermal weight w of that module by reducing it by 0.1~0.2, while increasing its active power output ratio by 5%~10%. After the adjustment, the deviation of the active power output ratio of each module is ≤±5%, ensuring that the overall frequency regulation capability does not decrease, while achieving thermal stress balance of each module and avoiding overload of a single module.

[0119] 9) Frequency modulation support adjustment: The thermal limiter circuit will dynamically reconfigure... The data is transmitted to the virtual synchronous generator control circuit with a transmission period of 1ms and CRC checksum. The virtual synchronous generator control circuit... Adjust the active power output according to the following rules: ,in This is the reference value for active power output. The rated active power of the converter is w. The larger the w value, the smaller the active power output, which actively reduces the support for the power grid, reduces the thermal stress of the device, and achieves the synergy of temperature limiting and frequency regulation.

[0120] 10) Harmonic overload adaptation: If a harmonic overload condition with THD > 15% is detected, the active power output reference value will be reduced by an additional 10% to 15%, and a harmonic alarm signal will be sent to the power grid monitoring platform to prompt the power grid to manage harmonics.

[0121] S34, follow the network to protect yourself.

[0122] 1) The main controller circuit maintains the mode switching control signal at a valid high level of 5V, forces the thermal limiter circuit to set the thermal weight w=1 and locks it unchanged, and sets the damping reference angular frequency. The real-time angular frequency is fully locked to the output of the phase-locked loop circuit. Locking accuracy ≤ 0.01 rad / s, avoiding fluctuation.

[0123] 2) The internal frequency of the virtual synchronous generator control circuit is forcibly synchronized with... The synchronization logic is as follows: Stop outputting additional active power to resist frequency drops; active power output reference value. It only sustains its own losses and does not provide support to the power grid.

[0124] 3) The converter enters the grid self-protection state, and the output voltage and current of the main converter circuit are synchronized with the grid frequency to avoid overload and burnout of the main converter circuit, and start the smooth exit process.

[0125] 4) Multi-module converters synchronously switch to grid self-protection mode, stop coordinated frequency regulation, and each module independently protects itself. The main controller circuit monitors each module in real time. If a certain module If the power supply continues to rise, immediately disconnect the power to this module to avoid affecting other modules.

[0126] 5) Fault Source Tracing Record: After the converter enters the grid self-protection mode, the main controller circuit automatically starts the fault source tracing recording program. The recorded data includes: equivalent junction temperature. Ambient temperature Ta, grid ROCOF, total harmonic distortion (THD), thermal weighting (w) adjustment process, mode switching time, and power output change curve are all stored on the local storage module SD card for easy subsequent reading and analysis.

[0127] 6) Monitor the status of devices in real time during self-protection mode. If any issues arise... If the temperature continues to drop and the conditions for mode recovery are met, the mode recovery judgment can be triggered in advance, shortening the self-protection time and improving the grid support efficiency.

[0128] This technical solution enables precise and smooth switching between three modes: pure grid support, stress release, and grid self-protection, avoiding erroneous mode switching; it optimizes the frequency regulation control logic, balances converter safety and grid support requirements, and solves the problem of incoordination between frequency regulation and temperature limiting; it achieves thermal stress balancing of multiple modules, adapts to complex grid conditions, and improves system adaptability and operational stability.

[0129] Example 4.

[0130] This embodiment 4 discloses a method for temperature-limited frequency regulation and exit of a grid-type converter based on a temperature-limited control loop, wherein step S4 includes the following steps.

[0131] S41, Smooth Exit Maintenance.

[0132] 1) When the converter is in grid self-protection mode, the main controller circuit continuously monitors the equivalent junction temperature. and thermal stress prediction value Minimum hold time for mode switching ,exist Even if the mode recovery conditions are met, mode switching will not be performed to avoid jitter near the threshold.

[0133] 2) The pulse width modulation circuit smoothly adjusts the output voltage and current according to the output signal of the virtual synchronous generator control circuit, and adopts a gradient voltage reduction strategy: the voltage drop rate is ≤0.5V / ms. Specifically, the output voltage is reduced by 0.5V every 1ms until the voltage drops to 30% of the rated voltage, so as to avoid power surges caused by voltage changes.

[0134] 3) Current Limitation: Under grid self-protection mode, the output current is ≤ 0.3 times the rated current of the converter. If the current exceeds the limit, the current limiting will be triggered immediately to reduce the output voltage and ensure current stability.

[0135] 4) Monitor the grid frequency and converter output parameters in real time. If the grid frequency recovers to 49.5Hz-50.5Hz, and If the voltage continues to decrease, the step-down rate can be appropriately increased to ≤0.8V / ms to shorten the exit time.

[0136] S42, Exit fault linkage.

[0137] 1) Under self-protection mode, the main controller circuit monitors the equivalent junction temperature in real time. rate of change ,like If the temperature continues to rise for two consecutive sampling cycles, it is determined that the junction temperature is continuously rising, and a fault alarm is immediately triggered, including local alarms and remote alarms. The local alarm is indicated by a flashing indicator light at a frequency of 1Hz and a red indicator light. The remote alarm is transmitted to the power grid monitoring platform via RS485 communication.

[0138] 2) After the alarm is triggered, there is a 50ms delay to avoid false triggering due to instantaneous fluctuations. If the condition is still met, immediately disconnect the converter from the power grid and open the grid-connected switch of the main converter circuit. The disconnection time should be ≤10ms to avoid device burnout.

[0139] 3) After disconnecting from the power grid, the converter enters standby mode and continues to monitor. until Falling back to Only after these steps can the system be restarted; simultaneously, the fault information will be uploaded to the power grid monitoring platform to facilitate troubleshooting by maintenance personnel. Fault information includes junction temperature data, disturbance intensity, and outage time.

[0140] S43, Mode recovery determination.

[0141] 1) When the short-term overload condition disappears, the main controller circuit executes the mode recovery determination. The determination conditions are as follows, and must be met simultaneously: a. Equivalent junction temperature Falling back to Below, and duration ≥ b. Predicted thermal stress value c. Power grid frequency d. The total harmonic distortion (THD) of the power grid is ≤10%; e. The ambient temperature Ta is >-20℃. If it is a low-temperature operating condition, Ta must be >-20℃ and the duration must be ≥1s.

[0142] 2) The judgment period is 1ms. Only when all the above conditions are met for 3 consecutive judgment periods is it determined to be a recoverable pure network support mode, so as to avoid mode erroneous recovery caused by instantaneous changes in operating conditions.

[0143] 3) If a certain condition is not met, continue to maintain the self-protection state with the network, and re-execute the judgment every 100ms until all conditions are met.

[0144] S44, the mode recovery process is as follows.

[0145] 1) The main controller circuit will change the mode switching control signal sent to the thermal limiter circuit from an effective high level of 5V to an ineffective low level of 0V, controlling the thermal limiter circuit to stop following the real-time angular frequency. Resume sending a fixed rated angular frequency to the virtual synchronous generator control circuit. The sending process uses a smooth transition: From the present Gradually transition to The transition time is 0.5s~1s, and the transition rate is ≤0.2π rad / s to avoid power grid impact caused by frequency abrupt changes.

[0146] 2) The virtual synchronous generator control circuit restarts the active power output command, and the active power output reference value is... The power output is gradually increased from 0.2 to 0.3 times the rated power to 0.8 to 1.0 times the rated power, with an increase rate of ≤0.1 times the rated power / s, to ensure a smooth transition of active power output and avoid power surges.

[0147] 3) The multi-module converter synchronously restores the coordinated frequency regulation mode, redistributes the active power output ratio of each module to restore it to a 1:1 ratio, and monitors the thermal stress balance of each module to ensure that each module... The difference is ≤5℃.

[0148] 4) The thermal limiter circuit resets the thermal weight w to 0, restarts the thermal weight calculation module, and enters the normal control process.

[0149] 5) After mode recovery, continuously monitor the working status of each module, verify the data every 100ms to ensure stable operation of the converter, re-establish the grid voltage source characteristics, and complete the closed-loop control of frequency regulation-exit-recovery.

[0150] S45, Self-learning optimization.

[0151] 1) After mode recovery, the main controller circuit starts a self-learning program. The self-learning process is as follows: a. Read the fault tracing data stored in the local storage module, filter valid data, and remove abnormal data, such as data acquired by errors or lost during transmission; b. Analyze the adaptability of the current control parameters to the fault condition and calculate the parameter deviation: if Exceeding ,illustrate Setting too low or The setting is too low and needs adjustment; if the power surge is too large during mode switching, it indicates that the thermal weighting smoothing filter coefficient is too low. c. If the setting is too small, it needs to be increased; d. Based on the parameter deviation, automatically correct the core parameters for the next run, with a correction range of 5% to 10%, and the corrected parameters must be within the preset value range; e. Store the corrected parameters in the main controller's memory as the initial parameters for the next startup.

[0152] 2) The self-learning cycle is 24 hours. If no switch to network self-protection mode occurs within 24 hours, the self-learning program will still be executed to fine-tune parameters with a correction range of ≤3% to optimize control performance.

[0153] 3) During the self-learning process, if an abnormality is detected in the converter, the self-learning will be stopped immediately and the original parameters will be restored to avoid control failure caused by error correction.

[0154] 4) Self-learning data is synchronously stored in the local storage module, which makes it easier for operation and maintenance personnel to trace the parameter adjustment process and optimize the self-learning algorithm.

[0155] In this technical solution, strategies such as gradient voltage reduction and current limiting are used to achieve smooth converter shutdown and avoid power surges; the linkage protection against abnormal junction temperature is strengthened to reduce fault losses; the mode recovery conditions are accurately determined to achieve smooth recovery and quickly rebuild the grid support capability; and the control parameters are automatically optimized through the self-learning function to reduce manual operation and maintenance and improve the system's adaptability and long-term operational stability.

[0156] Example 5.

[0157] This embodiment discloses a method for temperature-limited frequency regulation and shutdown of a grid-type converter based on a temperature-limited control loop, wherein step S5 includes the following steps.

[0158] S51. Routine anomaly monitoring and handling.

[0159] 1) Temperature acquisition abnormality: If the data collected by the external temperature acquisition circuit or the ambient temperature acquisition module exceeds the reasonable range, or if there is no data transmission for 10 consecutive sampling cycles, it is determined to be a temperature acquisition abnormality, and a local + remote alarm is immediately triggered. It will also force a switch to the network self-protection state and stop the active power output to avoid device damage caused by incorrect junction temperature estimation.

[0160] 2) Phase-locked loop (PLL) fault: If the PLL circuit outputs... Beyond the 45Hz~55Hz range, or no signal for 10 consecutive sampling cycles. If the output is determined to be a phase-locked loop fault, an alarm is immediately triggered, and the system is forced to switch to grid self-protection mode, simultaneously disconnecting the converter from the grid to prevent frequency runaway.

[0161] 3) Abnormal converter output: If the converter output current is greater than 1.5 times the rated current, or the output voltage exceeds ±10% of the rated voltage for a duration of ≥10ms, it is judged as an abnormal output. The current / voltage limit is immediately triggered to reduce the active power output. If the abnormality persists after the limit is applied, the converter is forced to switch to the grid self-protection state and disconnect the grid connection.

[0162] S52, Thermal resistance drift compensation.

[0163] 1) During long-term operation, the main controller circuit executes the junction-to-case thermal resistance once every hour. Drift detection: via , , Back-calculation of actual thermal resistance .

[0164] 2) Calculate the deviation between the actual thermal resistance and the preset thermal resistance: ,like If determined to be thermal resistance drift, it will be automatically updated immediately. parameter, And store it in memory.

[0165] 3) After thermal resistance drift compensation, recalculate the equivalent junction temperature. Adjust the thermal weight w to ensure control accuracy and avoid protection malfunctions or delays caused by thermal resistance drift.

[0166] 4) If This indicates that the power device may be aging, triggering an alarm signal and prompting maintenance personnel to check the device status.

[0167] S53, Emergency handling under extreme working conditions.

[0168] 1) When the power grid experiences an unexpected strong disturbance, such as ROCOF ≥ 2.5 Hz / s, and this condition is met for three consecutive detection cycles, the emergency temperature limiting mode is immediately activated: a. The heat weight w is forcibly reduced to below 0.8, regardless of the current... a. Size; b. Active power output reference value drops to 0.5~0.6 times the rated power, prioritizing device safety; c. Upper limit of frequency change rate. Adjusted to 0.5 slow down d. Send extreme disturbance alarm signals to the power grid monitoring platform.

[0169] 2) Under emergency temperature limiting mode, continuously monitor ROCOF and If ROCOF < 2.5 Hz / s and duration ≥ 1 s, and Exit emergency temperature limiting mode and restore normal control; if Immediately switch to network self-protection mode.

[0170] 3) Emergency handling under extreme operating conditions has the highest priority, taking precedence over other control logic, to ensure the converter's survivability under unexpected disturbances.

[0171] S54, Harmonic overload protection.

[0172] 1) Monitor the total harmonic distortion (THD) of the power grid in real time. If THD > 15% and the duration is ≥ 50ms, it is determined to be a harmonic overload condition, and the following protective actions are immediately executed: a. Automatically reduce the thermal weight w, reduce the active power output reference value by 10%~15%, and avoid the surge in losses caused by harmonics that may lead to device overheating; b. Send a harmonic alarm signal to the power grid monitoring platform to prompt the power grid to manage harmonics; c. Monitor the THD change in real time. If THD ≤ 10% and the duration is ≥ 1s, restore the normal active power output and thermal weight settings.

[0173] 2) Under harmonic overload conditions, Immediately switch to network self-protection mode to avoid damage to the device.

[0174] 3) Harmonic overload protection and thermal stress protection work together to prioritize device safety while minimizing the impact on power grid support.

[0175] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A method for temperature-limited frequency regulation and shutdown of a grid-type converter based on a temperature-limited control loop, characterized in that, Includes the following steps: Collect power device case temperature data, power device operating parameters, ambient temperature and power grid data; calculate the equivalent junction temperature of the power device based on the case temperature data and power device operating parameters; A thermal weighting calculation model is constructed; the input of the thermal weighting calculation model is the equivalent junction temperature, and the output is a dimensionless parameter of the normalized equivalent junction temperature; a thermal safety weighting coefficient is dynamically generated based on the dimensionless parameter of the equivalent junction temperature; based on the thermal safety weighting coefficient, the real-time angular frequency of the power grid and the rated angular frequency are weighted and synthesized to construct a dynamic damping reference angular frequency; Based on the equivalent junction temperature, grid data, and thermal safety weighting coefficient, the three control modes of pure grid support, stress release smooth transition, and grid self-protection are judged, and the mode judgment results are obtained. Based on the mode determination result, the active power output of the power device is adjusted by the dynamic damping reference angular frequency to perform coordinated control of temperature limiting protection and grid frequency regulation support.

2. The method for temperature-limited frequency regulation and shutdown of a grid-type converter based on a temperature-limited control loop according to claim 1, characterized in that... The coordinated control of temperature limiting protection and power grid frequency regulation support includes the following steps: Extract the real-time angular frequency of the power grid based on the power grid data; Based on the equivalent junction temperature and ambient temperature, and combined with the preset thresholds of the equivalent junction temperature and ambient temperature and the anti-shake mechanism, multi-mode determination is performed, and a mode switching control signal is sent after determination. Pure network support: Sends fixed rated angular frequency and active power output commands, adjusts output phase signals, and maintains thermal stress balance; Smooth stress release transition: Reconstruct the damping reference angular frequency, adjust the active power output, and achieve coordinated temperature limiting and frequency modulation; Self-protection with grid connection: Locking the thermal weight and damping reference angular frequency, the converter enters self-protection mode.

3. The method for temperature-limited frequency regulation and shutdown of a grid-type converter based on a temperature-limited control loop according to claim 2, characterized in that... The stress relief smooth transition Includes the following steps: Send a valid high-level mode switching control signal and dynamically adjust the control parameters based on the grid disturbance intensity, ambient temperature, and grid harmonic conditions; The equivalent junction temperature is mapped to a dimensionless equivalent junction temperature dimensionless parameter, and an ideal thermal weight is generated based on the dimensionless equivalent junction temperature parameter. The ideal thermal weight is smoothed and filtered, and an enhancement factor is introduced in combination with the power grid frequency difference to obtain the thermal safety weight coefficient. The adjustment rate of the thermal safety weight coefficient is adapted to the real-time angular frequency of the power grid to balance the frequency regulation support of the power grid and the safety of the converter itself. According to the aforementioned thermal safety weighting coefficient, the rated angular frequency and the real-time angular frequency of the power grid are weighted, the damping reference frequency is reconstructed, and a rate of change constraint is applied. Adjusting the converter output phase and active power output achieves coordinated temperature limiting and frequency regulation; Real-time monitoring of the power grid and power device status, and dynamic adjustment of control parameters according to changes in operating conditions to ensure stable system operation.

4. The method for temperature-limited frequency regulation and shutdown of a grid-type converter based on a temperature-limited control loop according to claim 2, characterized in that... The aforementioned self-protection with the network includes the following steps: Maintain a valid high-level mode switching signal to lock the thermal safety weighting coefficient and damping reference angular frequency to ensure no fluctuations; The internal frequency of the control converter is synchronized with the real-time angular frequency of the power grid, and the output of additional active power is stopped. It only maintains the power output required for its own losses and no longer provides support to the power grid. Real-time monitoring of the equivalent junction temperature of power devices; timely disconnection of power devices with abnormal junction temperatures. The device status is monitored in real time, and a mode switch is triggered when the recovery conditions are met.

5. The method for temperature-limited frequency regulation and shutdown of a grid-type converter based on a temperature-limited control loop according to claim 1, characterized in that... The steps for acquiring the case temperature data of the power device include: The system collects raw case temperature data of the power device, performs abnormal data removal, second-order low-pass filtering and temperature calibration in sequence, and outputs stable case temperature data of the power device. The abnormal data removal process involves removing data that exceeds the preset temperature range or deviates too much from multiple adjacent data sets, and replacing it with the average value of the adjacent data sets. The temperature calibration is based on the temperature-resistance characteristic curve of the thermistor and is used to compensate for the nonlinear error of the thermistor.

6. The method for temperature-limited frequency regulation and shutdown of a grid-type converter based on a temperature-limited control loop according to claim 1, characterized in that... The heat weight calculation model is as follows: ， ； In the formula, It's shell temperature data. It is the equivalent junction temperature of the power device; It is the safety threshold of power devices. It is the thermal limit threshold of the power device; sat(x,0,1) is the limiting function; It is the equivalent junction temperature dimensionless parameter; This refers to the junction-to-case thermal resistance of power devices. This represents the total power device loss after correction.

7. The method for temperature-limited frequency regulation and shutdown of a grid-type converter based on a temperature-limited control loop according to claim 6, characterized in that... The process of obtaining the corrected total power device loss includes the following steps: The total basic loss of the power device is calculated based on the conduction loss and switching loss of the power device, where the conduction loss and switching loss are determined based on the power device model and the converter operating parameters. Real-time ambient temperature is collected and preprocessed. Based on the preprocessed ambient temperature, a corresponding ambient temperature compensation coefficient is matched. The ambient temperature compensation coefficient is used to compensate for the basic total loss of the power device to obtain the loss after ambient temperature compensation. The total harmonic distortion rate of the power grid is obtained and preprocessed. Based on the preprocessed total harmonic distortion rate of the power grid, the corresponding harmonic loss correction coefficient is matched. The loss after ambient temperature compensation is corrected using the harmonic loss correction coefficient to obtain the corrected total loss of the power device.

8. The method for temperature-limited frequency regulation and shutdown of a grid-type converter based on a temperature-limited control loop according to claim 7, characterized in that... The formula for calculating the total loss of the corrected power device is as follows: ； ； In the formula, It is the total loss of power devices; This is the total loss of the power devices after correction; , , I is the conduction loss coefficient; I is the converter output current; , This is the switching loss factor; DC side voltage The switching frequency; It represents the real-time ambient temperature. It is the harmonic loss correction factor. Loss after compensation for ambient temperature; It is the ambient temperature compensation coefficient.

9. The method for temperature-limited frequency regulation and shutdown of a grid-type converter based on a temperature-limited control loop according to claim 1, characterized in that... The process of calculating the equivalent junction temperature also includes real-time acquisition of the equivalent junction temperature data of the power device, recording the equivalent junction temperature values ​​of two adjacent cycles according to a fixed control cycle, calculating the difference between the equivalent junction temperatures of two adjacent cycles, and then dividing it by the time interval between the two cycles to obtain the real-time change rate of the equivalent junction temperature of the power device. Based on the real-time change rate of the equivalent junction temperature of the power device, the rate of change of the equivalent junction temperature is calculated using the difference method, and the trend of the equivalent junction temperature change within a preset time period is predicted by a linear regression algorithm to determine the temperature rise trend of the power device.

10. The method for temperature-limited frequency regulation and shutdown of a grid-type converter based on a temperature-limited control loop according to claim 1, characterized in that... It also includes a smooth exit and mode recovery step, specifically including the following steps: Under self-protection mode, continuously monitor the equivalent junction temperature and thermal stress prediction value, and maintain the minimum hold time for mode switching to prevent jitter; A gradient voltage reduction strategy is adopted and the output current is limited to achieve shockless shutdown; The equivalent junction temperature change rate is monitored in real time. If it is determined to be abnormal, a linkage alarm is triggered and the grid connection is cut off in an emergency. The converter enters standby mode until the equivalent junction temperature drops back to the safe threshold. Once the complex conditions are met and the anti-jitter determination is passed, a smooth transition of the damping reference angular frequency and active power output is performed to restore the pure grid support mode.

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