A thermoelectricity collaborative control method for a photovoltaic grid hybrid power supply inverter

Abstract

The application provides a thermoelectricity collaborative control method of a photovoltaic grid hybrid power supply inverter, belongs to the technical field of new energy power generation and power electronics, and can at least partially solve the problem that power scheduling and thermal management independent operation cannot consider bus voltage stability and power device thermal safety in the prior art. The application comprises the following steps: synchronously sampling photovoltaic output power and load power at a first frequency, calculating a power difference value, and executing power distribution decision; adjusting the PWM duty cycle of a switching power supply by using an incremental PID algorithm to stabilize the DC bus voltage; sampling the junction temperature of a power device and the wall temperature of a phase change heat pipe at a second frequency, and calculating a temperature difference value; dynamically adjusting the fan speed by using a PI algorithm; and executing over-temperature protection and fault early warning. The application can realize photovoltaic and commercial power complementary power supply without a storage battery, the bus voltage fluctuation does not exceed the set ripple threshold, the junction temperature overshoot of the power device under step thermal load is controllable, and high dynamic power output and thermal safety are considered.

Description

Technical Field

[0001] This invention belongs to the field of new energy power generation and power electronics technology, and specifically relates to a thermoelectric synergistic control method for a photovoltaic grid hybrid power supply inverter. Background Technology

[0002] Photovoltaic inverters inevitably experience transient thermal shocks and power jumps during high-frequency switching and complementary switching between photovoltaic and mains power. When power devices such as IGBTs experience initial aging, localized thinning of the gate oxide, slight saturation of the filter inductor, or a sudden increase in mains power, the heat flux density on the chip surface can jump from a low value to a high value within seconds, causing a significant instantaneous rise in junction temperature. These early thermal fault characteristics have small amplitudes and are severely masked by ambient temperature, switching pulse losses, and environmental noise. If they are not detected and suppressed in time, they will lead to secondary failures such as insulation breakdown, solder fatigue, and wire stripping, resulting in downtime losses and maintenance costs.

[0003] Existing research has the following shortcomings: First, current engineering practices commonly employ aluminum extruded heat sinks combined with forced air cooling or water cooling plates for thermal management. Forced air cooling has limited ability to suppress transient thermal shocks under high ambient temperatures, and when the thermal signal-to-noise ratio is low, the junction temperature prediction error is large, making it difficult to meet early thermal warning requirements. Water cooling plates, on the other hand, rely on pump operation, which presents problems such as freezing in winter and condensation in summer, making them unsuitable for embedded online operation in residential scenarios.

[0004] Second, existing heat pipe cooling solutions are mostly concentrated in centralized inverters, where the evaporation section and power devices are still connected by thermal grease and bolts, resulting in high interface thermal resistance. Furthermore, they do not consider the impact of rapid step heat loads brought about by complementary power supply from photovoltaic and grid power in residential scenarios on the start-up and drying limits of heat pipes.

[0005] Third, while the hybrid photovoltaic and grid power supply topology without batteries eliminates the energy storage stage to reduce costs, existing solutions only focus on electrical energy dispatch and do not address the problem of transient heat accumulation in power devices. This results in inverters in small spaces such as home balconies frequently triggering thermal protection due to poor heat dissipation, leading to a poor user experience.

[0006] Fourth, existing control algorithms generally operate power scheduling and thermal management as independent loops, lacking a power-temperature coordinated control mechanism, and are unable to simultaneously ensure bus voltage stability and power device thermal safety under power step conditions.

[0007] Therefore, designing a thermoelectric synergistic control method that can balance bus voltage stability and power device thermal safety under power step conditions and is applicable to batteryless photovoltaic grid hybrid power supply inverters is a technical problem that urgently needs to be solved in the field of new energy power generation. Summary of the Invention

[0008] The present invention aims to solve at least one of the technical problems existing in the prior art, and provides a thermoelectric coordinated control method for a photovoltaic grid hybrid power supply inverter.

[0009] To achieve the above objectives, the present invention provides a thermoelectric coordinated control method for a photovoltaic grid hybrid power supply inverter, comprising: The photovoltaic output power and the load power are sampled synchronously at a first frequency, and the power difference between the photovoltaic output power and the load power is calculated. Power allocation decisions are made based on the power difference. When the power difference is greater than or equal to zero, the mains-side switching power supply is turned off and the photovoltaic system supplies power separately. When the power difference is less than zero, an incremental PID algorithm is used to adjust the PWM duty cycle of the mains-side switching power supply to keep the DC bus voltage at a set value. The incremental PID algorithm is calculated based on the voltage deviation between the DC bus voltage and the set value. The junction temperature of the power device and the wall temperature of the phase change heat pipe are sampled at a second frequency, and the temperature difference between the junction temperature of the power device and the wall temperature of the phase change heat pipe is calculated. A PI algorithm is used to dynamically adjust the fan speed based on the temperature difference deviation between the stated temperature difference and the target temperature difference setpoint. When the temperature difference exceeds a first temperature difference threshold, the fan speed is linearly increased until the temperature difference drops below the target temperature difference range. When the temperature difference is below a second temperature difference threshold, the fan speed is reduced to a silent mode. Over-temperature protection is implemented. When the junction temperature of the power device exceeds the preset over-temperature threshold and continues for a set time, the inverter output power is reduced to a preset ratio of the rated power, and the junction temperature of the power device, the wall temperature of the phase change heat pipe, and the power data are reported to the cloud through the communication module.

[0010] Furthermore, the photovoltaic output power is calculated as follows: The DC voltage on the photovoltaic side is obtained using voltage and current sensors, respectively. With DC current The formula for calculating the photovoltaic output power is: ; The load power is calculated by obtaining the AC side voltage through a voltage sensor and a current sensor, respectively. With alternating current The formula for calculating the load power is: ; in, Power factor; The formula for calculating the power difference is: ; The first frequency ranges from 0.5 to 2 kHz, and the ADC resolution is no less than 12 bits.

[0011] Furthermore, the incremental PID algorithm is calculated as follows: ; ; in, , , These are the proportional coefficient, integral coefficient, and differential coefficient, respectively. For the first The voltage deviation between the DC bus voltage and the set value at each sampling time. For the first PWM duty cycle at each sampling time; The incremental PID algorithm sets the integral separation threshold to a preset percentage range of the rated power, sets the anti-integral saturation limiting range, and sets the PWM carrier frequency to 15-25kHz.

[0012] Furthermore, the junction temperature of the power device is obtained through an NTC thermistor mounted inside the power device module. The relationship between the resistance of the NTC thermistor and temperature is as follows: ; in, The nominal resistance is at 25℃. For material constants, The current temperature; The phase change heat pipe wall temperature is obtained by attaching a platinum resistance thermometer or a thermocouple to the outer wall of the evaporation section. The formula for calculating the temperature difference is: ; in, The junction temperature of the power device. The phase change heat pipe wall temperature; The second frequency ranges from 0.2 to 1 kHz, and the ADC resolution is no less than 10 bits.

[0013] Furthermore, the PI algorithm is calculated as follows: ; ; in, , These are the proportional coefficient and the integral coefficient, respectively. For the first Temperature difference deviation at each sampling time, For the first Fan speed at each sampling time; The proportional gain of the PI algorithm ranges from 10 to 30, the integral gain ranges from 0.2 to 1.0, the anti-integral saturation limiting range is ±5% to ±15%, and the PWM carrier frequency is 20-30kHz.

[0014] Furthermore, the fan speed adjustment adopts a piecewise linear strategy: When the temperature difference is greater than the first temperature difference threshold, the fan speed is linearly increased at a preset speed slope until the temperature difference drops to the target temperature difference range. When the temperature difference is between the second temperature difference threshold and the first temperature difference threshold, the fan speed is maintained at the current value. When the temperature difference is less than or equal to the second temperature difference threshold, the fan speed is reduced to the silent mode speed, which is in the range of 800-1500 rpm.

[0015] Furthermore, it also includes thermoelectric coordinated control steps: When the power difference is greater than zero and the temperature difference exceeds the first temperature difference threshold, the fan speed is first linearly increased to the rated speed, and then the mains power supplement power is increased with a preset power slope. The preset power slope ranges from 20 to 50 W / s to avoid the phase change heat pipe evaporation section from drying out. When the power difference is less than zero and the junction temperature of the power device is lower than the preset low temperature threshold, the fan speed is reduced to the silent mode speed to reduce energy consumption and noise.

[0016] Furthermore, it also includes a low-temperature start-up procedure: When the ambient temperature is lower than the preset low temperature start-up threshold, after power-on, the fan is driven to run at the preheating speed for a preset preheating time. The value of the preheating speed is in the range of 1000-3000 rpm, and the value of the preset preheating time is in the range of 10-60s. Once the phase change heat pipe wall temperature exceeds the preset wall temperature start-up threshold, it switches to normal PI control mode.

[0017] Furthermore, the over-temperature protection adopts a dual redundancy design in both hardware and software: The hardware layer implements hardware cutoff protection when the junction temperature of the power device exceeds the preset hardware cutoff temperature through a comparator, with a response time of less than 20μs. The software layer implements software-limited power operation when the junction temperature of the power device exceeds the preset software power limit temperature and continues for the set time. Fault reports are transmitted to the cloud via an encrypted channel. The cloud establishes a digital twin model based on thermal-fluid-structure interaction simulation to predict the lifespan degradation trend of power devices.

[0018] Furthermore, the communication module uploads the junction temperature of the power device, the wall temperature of the phase change heat pipe, the photovoltaic output power, the mains power supplement power, and the fan speed to the cloud at a preset message period, the preset message period being 0.5-2s. The communication module supports remote OTA upgrades. The upgrade package is written to the controller after being signed and verified. During the upgrade process, the DC bus maintains uninterrupted power supply.

[0019] The beneficial effects of this invention are as follows: This invention achieves stable DC bus voltage output without the need for batteries by using coordinated control of power distribution closed loop and thermal management closed loop. When photovoltaic power is sufficient, it can supply power solely from photovoltaic power and when photovoltaic power is insufficient, it can supplement power from the mains in real time. This reduces system cost.

[0020] This invention uses an incremental PID algorithm to adjust the PWM duty cycle of the mains-side switching power supply, which can achieve rapid recovery of DC bus voltage under load step conditions and control bus voltage fluctuation within the set ripple threshold, thus meeting the requirements of grid connection test for power output stability.

[0021] This invention uses a PI algorithm to dynamically adjust the fan speed, combined with a piecewise linear control strategy, which can effectively suppress junction temperature overshoot under power device thermal load step conditions, and automatically reduce the fan speed under low thermal load conditions to reduce energy consumption and noise.

[0022] This invention introduces a thermoelectric synergistic control mechanism. Under the condition of simultaneous power step and temperature change, it prioritizes improving heat dissipation capacity and then gradually increases the mains power supplement, avoiding the drying out of the evaporation section of the phase change heat pipe and ensuring the long-term reliable operation of the system.

[0023] This invention significantly improves the operational safety and maintainability of inverters through a dual-redundancy over-temperature protection design in both hardware and software, as well as the life prediction function of a cloud-based digital twin model. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the overall structure of the photovoltaic grid hybrid power supply inverter system according to an embodiment of the present invention; Figure 2 This is a schematic diagram of the power stage circuit according to an embodiment of the present invention; Figure 3 This is a flowchart of the thermoelectric synergistic control method according to an embodiment of the present invention; Figure 4 This is a flowchart illustrating the remote OTA differential upgrade process according to an embodiment of the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and beneficial effects of this application clearer, the following detailed description, in conjunction with the accompanying drawings and specific embodiments, further illustrates this application. It should be understood that the specific embodiments described in this specification are merely for explaining this application and are not intended to limit it.

[0026] The thermoelectric coordinated control method of the photovoltaic grid hybrid power supply inverter of the present invention is implemented based on the photovoltaic grid hybrid power supply inverter system. The inverter system integrates four functional layers—electrical power stage, thermal management stage, thermoelectric coordinated controller, and communication stage—within the same chassis.

[0027] See Figure 1 The electrical power stage features a photovoltaic input port, a mains input port, and an AC output port, and includes dual boost circuits and an inverter full-bridge. The first boost circuit performs maximum power point tracking on the photovoltaic DC voltage, while the second boost circuit draws power from the mains via a controllable switching power supply. The two outputs are connected in parallel to form a low-ripple DC bus. The inverter full-bridge inverts the DC bus to AC output to drive the load.

[0028] The thermal management stage includes a phase change loop heat pipe cooling module. Its evaporation section is directly bonded to the back of the copper substrate of the power device module via vacuum brazing. The internal working fluid is a deionized water-ethanol mixture, and the capillary wick uses a copper mesh structure. The condensation section is located in the top cover air duct, with corrugated aluminum fins on the outside and a brushless DC fan for forced convection cooling.

[0029] The thermal-electric co-controller adopts a dual MCU architecture. The first MCU is responsible for maximum power point tracking, bus voltage regulation, inverter SPWM generation and protection logic, while the second MCU is responsible for thermal management PI control, fan PWM drive, life prediction and communication packet assembly.

[0030] The communication module uploads operating parameters to the cloud in real time, supporting remote monitoring and OTA upgrades.

[0031] Example 1 This embodiment uses a residential photovoltaic grid hybrid power inverter with a rated power of 5kW and a peak power of 6kW as the application scenario. The entire unit is installed in a 1U standard rack-mount aluminum alloy housing, which is divided into a power layer, a thermal management layer, and a control layer from top to bottom. The power layer is equipped with a photovoltaic input socket, a mains input socket, and an AC output socket. The side wall of the housing is equipped with ventilation louvers that are connected to the air duct of the thermal management layer, and the protection level reaches IP54.

[0032] See Figure 2The power stage hardware configuration is as follows. The first Boost circuit consists of a MOSFET switch Q1, a fast recovery diode D1, an iron-silicon-aluminum core inductor L1, and a film capacitor C1. Inductor L1 has an inductance of 100μH and a tolerance of ±10%. Film capacitor C1 has a capacitance of 10μF and a voltage rating of 100V. The switching frequency of the first Boost circuit is set to 45-55kHz, responsible for maximum power point tracking. The second Boost circuit uses a flyback topology and includes a switch Q2, a high-frequency transformer T1, an output diode D2, a filter inductor L2, and a bus capacitor Cbus. The high-frequency transformer T1 has a turns ratio of 6:1 and a leakage inductance of less than 2μH. The filter inductor L2 has an inductance of 50μH. The bus capacitor Cbus is a low-ESR polymer aluminum electrolytic capacitor with a capacitance of 4700-6800μF. The switching frequency of the second Boost circuit is set to 65-85kHz, responsible for drawing power from the AC mains. The two Boost circuit outputs are connected in parallel to form a 36V DC bus. The rated ripple of the bus does not exceed ±0.5V. When the voltage drops by ±50A under full load, the voltage sag is less than 0.4V and the recovery time is 15-20ms.

[0033] The inverter full-bridge uses 650V, 40A IGBT modules, driven by a 45-65Hz adjustable SPWM signal generated by the first MCU GD32F407. The modulation method employs third harmonic injection SPWM, improving DC voltage utilization by approximately 15%. The output filter uses an LCL structure, with an inductance of 1mH (tolerance ±5%), a capacitance of 10μF (tolerance ±5%), and a damping resistor of 2Ω. The measured total harmonic distortion (THD) of the output does not exceed 1.5%.

[0034] The sensing layer is configured as follows: DC voltage uses a CHV-25P Hall sensor with a range of 0-100V, accuracy of ±0.5%, and bandwidth of 20kHz. It outputs a 0-4V differential signal through a 200Ω load resistor. DC current uses a CHI-50A Hall sensor with a range of 0-50A, accuracy of ±0.5%, bandwidth of 20kHz, turns ratio of 1:1000, and output of 0-4V. AC voltage uses a ZMPT107 current transformer with a range of 0-300V, accuracy of ±0.5%, and bandwidth of 10kHz. A 200kΩ and 100nF low-pass filter in parallel at the downstream end suppresses switching noise. AC current uses a ZMCT103C current transformer with a range of 0-30A, accuracy of ±0.5%, bandwidth of 10kHz, and a sampling resistor of 100Ω. In terms of temperature sensing, the IGBT junction temperature uses a module-built-in NTC thermistor, and the heat pipe wall temperature uses a PT100 platinum resistance thermometer with a range of 0-200℃ and an accuracy of ±0.1℃. A three-wire connection method is used to eliminate lead resistance.

[0035] The first MCU GD32F407 and the second MCU GD32F303 hard-trigger the internal 12-bit ADC via timers TIM2-TIM3 in master-slave mode. The power loop sampling rate is 1kHz, the hot loop sampling rate is 500Hz, and the phase error between channels is less than 0.05 degrees, meeting the synchronization accuracy requirements.

[0036] The control board measures 120mm x 80mm and employs a four-layer PCB design, vertically integrated onto the power board. Power, signal, and fan interfaces are provided via a dual-row header. The first MCU, GD32F407, handles maximum power point tracking, bus voltage regulation, inverter SPWM generation, and protection logic. The second MCU, GD32F303, handles thermal management PI control, fan PWM drive, lifespan prediction, and MQTT communication packet assembly. Onboard FRAM non-volatile memory stores cumulative operating hours, IGBT switching counts, and maximum junction temperature records, supporting real-time storage upon power failure. The wireless communication module, ESP32, connects to the second MCU via a UART serial port, using the MQTT-TLS 1.3 encryption protocol to report junction temperature, wall temperature, total harmonic distortion, bus ripple, and fan speed data at 1-second intervals, with a reconnection time of less than 5 seconds. The communication module has built-in 4MByte storage to cache 24 hours of critical data, regularly transmitting complete records to the cloud daily. It supports remote OTA upgrades, with upgrade packages verified by AES-256 signatures.

[0037] The heat pipe cooling module is configured as follows: The evaporation section uses oxygen-free copper C1100 material, with dimensions of 40mm x 30mm x 2mm. Two layers of 120-mesh copper mesh are sintered on the inner wall as a capillary core, with a porosity of 60%-70% and an equivalent thermal conductivity of not less than 5000W / (m·K). The working fluid is a deionized water-ethanol mixture with a volumetric fill rate of 30%-40%, remaining liquid even at -25℃. The condensation section is fitted with 0.2mm thick corrugated aluminum fins with a fin spacing of 1.0-1.5mm. The surface is treated with black anodizing, and the emissivity is not less than 0.85. The fan is a 24V brushless DC fan with a rated speed of 6000rpm, an airflow of 5-10CFM, and a full-speed noise level not exceeding 45dB(A). PM2.5 filter cotton is embedded in the air duct inlet, with a filtration efficiency of not less than 95% and a wind resistance not exceeding 22Pa at an airflow of 8CFM. The evaporation section is connected to the IGBT copper substrate by vacuum brazing. The solder is Ag-Cu solder sheet with a melting point of 780℃. The welding void rate is less than 2%, and the interface thermal resistance does not exceed 0.01K / W. Anti-gravity start-up can be achieved within the tilt angle range of 0 degrees to 90 degrees.

[0038] See Figure 3 The thermoelectric coordinated control method in this embodiment includes the following steps: Step S1: Power sampling and power difference calculation.

[0039] At the first frequency Synchronous sampling of photovoltaic output power With load power Calculate the power difference .

[0040] The DC voltage is obtained on the photovoltaic side using a CHV-25P Hall voltage sensor. DC current is obtained through a CHI-50A Hall current sensor. The formula for calculating photovoltaic output power is: ; The load side obtains AC voltage through a ZMPT107 current transformer. AC current is obtained through ZMCT103C current transformer. The formula for calculating load power is: ; in, The power factor.

[0041] The formula for calculating the power difference is: ; In this embodiment, the first frequency Set to 1kHz, ADC resolution is 12 bits. When this time is reached, it indicates that the photovoltaic power is sufficient and no supplemental power from the mains is needed. When the voltage is low, it indicates that the photovoltaic power is insufficient and the mains power needs to be supplemented to maintain the stability of the bus voltage.

[0042] Step S2: Power distribution and bus voltage stabilization control.

[0043] when When the second Boost circuit is switched off, the photovoltaic power supply is used for power supply.

[0044] when At that time, an incremental PID algorithm is used to adjust the PWM duty cycle of the second Boost circuit switching power supply. This makes the DC bus voltage Maintain the set value In this embodiment, the set value It is 36V.

[0045] The formula for calculating the incremental PID algorithm is: ; ; in, , , These are the proportional coefficient, integral coefficient, and differential coefficient, respectively. For the first The voltage deviation between the DC bus voltage and the set value at each sampling time.

[0046] In this embodiment, the PID parameter is set to , , The integral separation threshold is set to ±5% of the rated power, meaning that integral separation is activated when the power deviation exceeds ±250W to avoid integral saturation. The anti-integral saturation limit is set to ±10%. The PWM carrier frequency is set to 20kHz, and the duty cycle resolution is 0.1%.

[0047] In the test where the load jumps from 10% to 90% of the rated power, the recovery time of the DC bus voltage is 18ms, the overshoot is less than 1%, and the bus voltage ripple remains within ±0.5V.

[0048] Step S3: Temperature sampling and temperature difference calculation.

[0049] At the second frequency Sampling IGBT junction temperature With phase change heat pipe wall temperature Calculate the temperature difference .

[0050] IGBT junction temperature The resistance is obtained through an NTC thermistor mounted inside the IGBT module. The relationship between the resistance of the NTC thermistor and temperature is as follows: ; in, The nominal resistance is at 25℃. This is a material constant. In this embodiment, Take 10kΩ, Take 3950K.

[0051] Phase change heat pipe wall temperature The resistance was obtained by using a PT100 platinum resistance thermometer attached to the outer wall of the evaporation section, and a three-wire connection method was used to eliminate the influence of lead resistance.

[0052] The formula for calculating temperature difference is: ; In this embodiment, the second frequency Set to 500Hz, ADC resolution is 12 bits.

[0053] Step S4: Thermal management PI control and fan speed regulation.

[0054] The fan speed is dynamically adjusted using a PI algorithm. This causes temperature difference With junction temperature The control requirements are met. The calculation formula for the PI algorithm is: ; ; in, , These are the proportional coefficient and the integral coefficient, respectively. For the first Temperature difference deviation at each sampling time.

[0055] In this embodiment, the PI parameter is set to , The anti-integral saturation limit is set to ±10%. The PWM carrier frequency is set to 25kHz, and the speed resolution is 30rpm.

[0056] The fan speed regulation adopts a piecewise linear strategy. When the temperature difference... When the temperature difference exceeds the first temperature threshold of 15℃, the fan speed is linearly increased at a rate of 100 rpm / ℃ until the temperature difference drops below 10℃. When the temperature difference is between the second temperature difference threshold of 5℃ and the first temperature difference threshold of 15℃, the fan speed is maintained at the current value. When the temperature difference... When the temperature difference is less than or equal to the second temperature threshold of 5°C, reduce the fan speed to the silent mode of 1000 rpm. During silent mode operation, the sound power level does not exceed 25 dB(A), saving approximately 3W of power consumption.

[0057] Step S5: Thermoelectric Co-control.

[0058] This step enables coordinated scheduling between the power allocation closed loop and the thermal management closed loop.

[0059] When the power difference And temperature difference At ℃, the fan speed is first linearly increased to the rated speed of 6000 rpm. After the heat dissipation capacity is improved, the mains power supplement is gradually increased at a power slope of 20-50 W / s. This strategy avoids the working fluid drying out in the evaporation section of the phase change heat pipe due to a sudden increase in heat load by first improving the heat dissipation capacity and then increasing the heat load.

[0060] When the power difference And the junction temperature At ℃, the fan runs at a silent speed of 1000rpm, reducing system energy consumption and noise, and improving user experience.

[0061] Step S6: Over-temperature protection and fault warning.

[0062] The over-temperature protection adopts a dual redundancy design of hardware and software.

[0063] The hardware layer implements hardware cutoff protection when the junction temperature exceeds 90°C through an analog comparator, with a response time of less than 20μs, directly cutting off the IGBT drive signal to prevent device damage.

[0064] The software layer implements power-limiting operation after the junction temperature exceeds 85℃ for 200ms. During power-limiting operation, the inverter output power is reduced to 90% of the rated power, i.e., 4.5kW. At the same time, alarm information is reported to the cloud via the ESP32 communication module, and a local red LED flashes at a frequency of 1Hz to remind the user to reduce the load.

[0065] Fault reports are transmitted to the cloud via an MQTT-TLS 1.3 encrypted channel. The cloud uses a digital twin model based on the Coffin-Manson model to predict IGBT lifespan degradation trends. The calculation formula for the Coffin-Manson lifespan prediction model is as follows: ; in, For cycle life, For material constants, This represents the junction temperature fluctuation amplitude. This represents the fatigue index. In this embodiment, Pick , Take 2.5. Measured junction temperature fluctuation amplitude. The temperature is 6℃, and the predicted cycle life is... The equivalent service life is 25 years. The prediction error is less than 5%, and the prediction time range is 48-96 hours.

[0066] Step S7: Low temperature start-up protection.

[0067] When the ambient temperature is below -10℃, after powering on, the fan will run at a preheating speed of 2000rpm for 30 seconds to allow the phase change heat pipe wall temperature to reach a suitable level. Once the temperature exceeds 5°C, the system switches to normal PI control mode. This strategy prevents the deionized water-ethanol mixture from solidifying at low temperatures, thus avoiding dry burning of the evaporation section due to the inability of the phase change heat pipe to circulate properly.

[0068] Step S8: Remote OTA upgrade.

[0069] See Figure 4The remote OTA upgrade process is as follows: A differential upgrade package is pushed to the cloud and signed with AES-256. The ESP32 communication module receives the upgrade package and verifies the signature. Upon successful verification, the upgrade segment is written to the MCU's backup partition. The MCU performs a local hot boot, and the DC bus maintains uninterrupted power supply throughout the upgrade process. After the upgrade is complete, the MCU sends the new version number back to the cloud, and the cloud confirms the upgrade success. The upgrade package size does not exceed 256kByte, the transmission time does not exceed 30 seconds, and the user is unaware of the upgrade.

[0070] Grid connection testing and performance verification. Grid connection testing was completed in a third-party laboratory according to national standards. Under voltage drop to 0% of rated voltage, the bus voltage fluctuation was ±0.3V, and the recovery time was 17ms. Under a frequency step of +5Hz, the output frequency tracking error was 0.03Hz. Under a harmonic injection of 5% THD, the output THD increment was 0.28%. High and low temperature storage: continuous operation for 48 hours at -30℃ to +70℃ without condensation or refrigerant leakage. In the 0% to 100% rated power step heat load test, the IGBT junction temperature overshoot was less than 5℃, the phase change heat pipe start-up time did not exceed 30s, the overall efficiency was not less than 94%, and the cost was reduced by approximately 30% compared to a battery-based solution of the same power.

[0071] Example 2 This embodiment uses a small-scale residential balcony photovoltaic grid hybrid power supply inverter with a rated power of 3kW as the application scenario. The entire unit is installed in a compact aluminum alloy casing, which is about 40% smaller than the casing size in Embodiment 1, making it suitable for balcony railing or wall mounting.

[0072] The power stage hardware configuration is as follows. The inductance of L1 in the first Boost circuit is adjusted to 150μH, the capacitance of film capacitor C1 remains unchanged at 10μF, and the switching frequency is set to 50kHz. The turns ratio of the high-frequency transformer T1 in the second Boost circuit is adjusted to 8:1, and the bus capacitor Cbus capacitance is adjusted to 3300μF. The outputs of the two Boost circuits are connected in parallel to form a 36V DC bus, with a rated ripple not exceeding ±0.5V. The inverter full-bridge uses 600V, 30A IGBT modules, driven by a 50Hz SPWM signal generated by a GD32F407. The output filter still uses an LCL structure.

[0073] The sensing layer configuration is the same as in Example 1, using Hall effect sensors and current transformers to collect voltage and current parameters, and NTC thermistors and PT100 platinum resistance thermometers to collect temperature parameters. The power loop sampling rate of the first MCU GD32F407 and the second MCU GD32F303 is 1kHz, and the thermal loop sampling rate is 500Hz.

[0074] The heat pipe cooling module is configured as follows: The evaporation section uses oxygen-free copper C1100 material, with dimensions adjusted to 35mm x 25mm x 2mm. Two layers of 120-mesh copper mesh are sintered on the inner wall as a capillary core, with a porosity of 60%-70% and an equivalent thermal conductivity of not less than 5000 W / (m·K). The working fluid is a deionized water-ethanol mixture with a volumetric charge rate of 35%. The condensation section is fitted with 0.2mm thick corrugated aluminum fins with a fin spacing of 1.2mm. The surface is treated with black anodizing, and the emissivity is not less than 0.85. The fan uses a 24V brushless DC fan with a rated speed of 5000rpm, an airflow of 4-8 CFM, and a full-speed noise level not exceeding 40dB(A).

[0075] The thermoelectric coordinated control method in this embodiment includes the following steps: Step S1: Power sampling and power difference calculation.

[0076] At the first frequency Synchronous sampling of photovoltaic output power With load power Calculate the power difference The formula for calculating photovoltaic output power is: The formula for calculating load power is: The formula for calculating the power difference is: In this embodiment, the first frequency Set to 1kHz, ADC resolution is 12 bits.

[0077] Step S2: Power distribution and bus voltage stabilization control.

[0078] when When this occurs, the switching power supply of the second Boost circuit is turned off, and the photovoltaic system supplies power alone. At that time, an incremental PID algorithm is used to adjust the PWM duty cycle of the switching power supply. This keeps the DC bus voltage at the set value of 36V.

[0079] The formula for calculating the incremental PID algorithm is: ; ; In this embodiment, the PID parameter is set to , , The integral separation threshold is set to ±4% of the rated power, meaning integral separation is activated when the power deviation exceeds ±120W. The anti-integral saturation limit is set to ±8%. The PWM carrier frequency is set to 18kHz, and the duty cycle resolution is 0.1%.

[0080] In the test where the load jumps from 10% to 90% of the rated power, the recovery time of the DC bus voltage is 20ms, the overshoot is less than 1.2%, and the bus voltage ripple remains within ±0.5V.

[0081] Step S3: Temperature sampling and temperature difference calculation.

[0082] At the second frequency Sampling IGBT junction temperature With phase change heat pipe wall temperature Calculate the temperature difference The relationship between the resistance of an NTC thermistor and temperature is as follows: ; In this embodiment, Take 10kΩ, Take 3950K. The formula for calculating the temperature difference is: Second frequency Set to 500Hz.

[0083] Step S4: Thermal management PI control and fan speed regulation.

[0084] The formula for the PI algorithm is: ; ; In this embodiment, the PI parameter is set to , The anti-integral saturation limit is set to ±8%. The PWM carrier frequency is set to 22kHz, and the speed resolution is 30rpm.

[0085] The fan speed regulation adopts a piecewise linear strategy. When the temperature difference... When the temperature difference exceeds the first temperature threshold of 12℃, the fan speed is linearly increased at a rate of 80 rpm / ℃ until the temperature difference drops below 8℃. When the temperature difference is between the second temperature difference threshold of 4℃ and the first temperature difference threshold of 12℃, the fan speed is maintained at the current value. When the temperature difference... When the temperature difference is less than or equal to the second temperature difference threshold of 4°C, reduce the fan speed to the silent setting of 800 rpm.

[0086] Step S5: Thermoelectric Co-control.

[0087] When the power difference And temperature difference At ℃, the fan speed should be linearly increased to the rated speed of 5000rpm first. After the heat dissipation capacity is improved, the mains power supplement power should be gradually increased at a power slope of 25W / s to avoid the phase change heat pipe evaporation section drying out.

[0088] When the power difference And the junction temperature At ℃, the fan runs at a silent speed of 800 rpm.

[0089] Step S6: Over-temperature protection and fault warning.

[0090] The hardware layer implements hardware-based shutdown protection when the junction temperature exceeds 88°C using an analog comparator, with a response time of less than 20μs. The software layer implements software-based power limiting operation after the junction temperature exceeds 82°C for 300ms, reducing the inverter output power to 85% of the rated power. Fault information is reported to the cloud via the ESP32 communication module through an MQTT-TLS 1.3 encrypted channel. The cloud-based digital twin model predicts IGBT lifetime based on the Coffin-Manson model, with the prediction formula being... The parameters are the same as in Example 1.

[0091] Step S7: Low temperature start-up protection.

[0092] When the ambient temperature is below -15℃, after powering on, the fan will run at a preheating speed of 1500rpm for 45 seconds to allow the phase change heat pipe wall temperature to reach a suitable level. Switch to normal PI control mode only after the temperature exceeds 3°C.

[0093] Step S8: Remote OTA upgrade.

[0094] The remote OTA upgrade process is the same as in Example 1. After the differential upgrade package is pushed from the cloud and verified by AES-256 signature, it is written to the MCU backup partition. The MCU performs a local hot start, and the DC bus maintains uninterrupted power supply during the upgrade process.

[0095] The results of the grid connection test show that in the step heat load test from 0% to 100% of the rated power, the IGBT junction temperature overshoot is less than 4°C, the phase change heat pipe start-up time is no more than 25 seconds, and the overall efficiency is no less than 93%.

[0096] Example 3 This embodiment uses a small-scale industrial and commercial photovoltaic grid hybrid power supply inverter with a rated power of 10kW as the application scenario. The entire unit is installed in a 2U standard rack-mount aluminum alloy housing, suitable for installation on industrial and commercial rooftops or in power distribution rooms.

[0097] The power stage hardware configuration is as follows. In the first Boost circuit, the inductance of L1 is adjusted to 68μH, the capacitance of film capacitor C1 is adjusted to 22μF, the withstand voltage is 100V, and the switching frequency is set to 50kHz. In the second Boost circuit, the high-frequency transformer T1 has a turns ratio of 5:1, the bus capacitor Cbus has a capacitance of 9400μF, and two sets of 4700μF low-ESR polymer aluminum electrolytic capacitors are connected in parallel. The parallel outputs of the two Boost circuits form a 36V DC bus with a rated ripple not exceeding ±0.5V. Under a full-load step of ±100A, the voltage sag is less than 0.6V, and the recovery time is 18-22ms. The inverter full-bridge uses two sets of 650V, 40A IGBT modules connected in parallel, driven by a 45-65Hz adjustable SPWM signal generated by a GD32F407. The output filter adopts an LCL structure with an inductance of 0.5mH, a capacitance of 22μF, a damping resistor of 1Ω, and an output THD of no more than 2%.

[0098] The sensing layer is configured as follows: DC voltage uses a CHV-50P Hall sensor with a range of 0-100V, an accuracy of ±0.3%, and a bandwidth of 30kHz. DC current uses a CHI-100A Hall sensor with a range of 0-100A, an accuracy of ±0.3%, and a bandwidth of 30kHz. The AC voltage and AC current sensors are configured the same as in Example 1. For temperature sensing, each IGBT module is equipped with an NTC thermistor, and the higher of the two junction temperatures is used as the control input. The heat pipe wall temperature is measured using a PT100 platinum resistance thermometer with a three-wire connection. The power loop sampling rate is 1kHz, and the heat loop sampling rate is 500Hz.

[0099] The heat pipe cooling module is configured as follows. Due to the increased rated power, this embodiment adopts a dual-evaporation-section parallel structure. Each evaporation section uses oxygen-free copper C1100 material, with dimensions of 40mm x 30mm x 2mm, and is connected to two IGBT modules via vacuum brazing. The capillary core uses two layers of 120-mesh copper mesh with a porosity of 65% and an equivalent thermal conductivity of not less than 5000W / (m·K). The condensation sections of the two evaporation sections merge into the same heat dissipation duct. The condensation section is covered with 0.2mm thick corrugated aluminum fins with a fin spacing of 1.0mm and a black anodized surface. The fan configuration includes two 24V brushless DC fans, each with a rated speed of 6000rpm and an airflow of 5-10CFM. The total airflow of the two fans in parallel is 10-20CFM, and the noise level at full speed does not exceed 50dB(A). PM2.5 filter cotton is embedded at the air duct inlet, with a filtration efficiency of not less than 95%.

[0100] The thermoelectric coordinated control method in this embodiment includes the following steps: Step S1: Power sampling and power difference calculation.

[0101] At the first frequency Synchronous sampling of photovoltaic output power With load power Calculate the power difference The formula for calculating photovoltaic output power is: The formula for calculating load power is: The formula for calculating the power difference is: In this embodiment, the first frequency Set to 1kHz, ADC resolution is 12 bits.

[0102] Step S2: Power distribution and bus voltage stabilization control.

[0103] when When this occurs, the switching power supply of the second Boost circuit is turned off. At that time, an incremental PID algorithm is used to adjust the PWM duty cycle of the switching power supply to keep the DC bus voltage at the set value of 36V.

[0104] The formula for calculating the incremental PID algorithm is: ; ; In this embodiment, the PID parameter is set to , , The integral separation threshold is set to ±6% of the rated power, meaning integral separation is activated when the power deviation exceeds ±600W. The anti-integral saturation limit is set to ±12%. The PWM carrier frequency is set to 22kHz, and the duty cycle resolution is 0.1%.

[0105] In the test where the load jumps from 10% to 90% of the rated power, the recovery time of the DC bus voltage is 22ms, the overshoot is less than 1.5%, and the bus voltage ripple remains within ±0.5V.

[0106] Step S3: Temperature sampling and temperature difference calculation.

[0107] At the second frequency The junction temperatures of the two IGBT modules were sampled, and the higher value was taken as the base value. Sampling phase change heat pipe wall temperature Calculate the temperature difference The relationship between the resistance of an NTC thermistor and temperature is as follows: ; In this embodiment, Take 10kΩ, Take 3950K. The formula for calculating the temperature difference is: Second frequency Set to 500Hz.

[0108] Step S4: Thermal management PI control and fan speed regulation.

[0109] The formula for the PI algorithm is: ; ; In this embodiment, the PI parameter is set to , The anti-integral saturation limit is set to ±12%. The PWM carrier frequency is set to 25kHz, and the speed resolution is 30rpm. The dual fans adopt a synchronous control strategy, with both fans receiving the same speed command.

[0110] The fan speed regulation adopts a piecewise linear strategy. When the temperature difference... When the temperature difference exceeds the first temperature threshold of 18°C, the fan speed is linearly increased at a rate of 120 rpm / °C until the temperature difference drops below 12°C. When the temperature difference is between the second temperature difference threshold of 6℃ and the first temperature difference threshold of 18℃, the fan speed is maintained at the current value. When the temperature difference... When the temperature difference is less than or equal to the second temperature difference threshold of 6°C, reduce the fan speed to the silent setting of 1200 rpm.

[0111] Step S5: Thermoelectric Co-control.

[0112] When the power difference And temperature difference At ℃, the speed of the two fans is first synchronously and linearly increased to the rated speed of 6000rpm. After the heat dissipation capacity is improved, the mains power supplement is gradually increased at a power slope of 40W / s to avoid either of the two evaporation sections from drying out.

[0113] When the power difference And the junction temperature At ℃, the dual fans operate at a silent speed of 1200rpm.

[0114] Step S6: Over-temperature protection and fault warning.

[0115] The hardware layer implements hardware shutdown protection when the junction temperature of any IGBT module exceeds 92℃ via an analog comparator, with a response time of less than 20μs. The software layer implements software power limiting operation after the junction temperature of any IGBT module exceeds 87℃ for 150ms, reducing the inverter output power to 90% of the rated power. Fault information is reported to the cloud via the ESP32 communication module through an MQTT-TLS1.3 encrypted channel. The cloud-based digital twin model predicts IGBT lifetime based on the Coffin-Manson model, with the prediction formula being... ,in Pick , Take 2.5.

[0116] Step S7: Low temperature start-up protection.

[0117] When the ambient temperature is below -10℃, after powering on, the dual fans will be driven to run at a preheating speed of 2500rpm for 40s. After the heat pipe wall temperature corresponding to the two evaporation sections exceeds 5℃, the system will switch to normal PI control mode.

[0118] Step S8: Remote OTA upgrade.

[0119] The remote OTA upgrade process is the same as in Example 1. After the differential upgrade package is pushed from the cloud and verified by AES-256 signature, it is written to the MCU backup partition. The MCU performs a local hot start, and the DC bus maintains uninterrupted power supply during the upgrade process.

[0120] The results of the grid-connected test show that in the step heat load test from 0% to 100% of the rated power, the IGBT junction temperature overshoot is less than 6°C, the phase change heat pipe start-up time is no more than 35 seconds, the overall efficiency is no less than 94%, and the cost is reduced by about 25% compared with the same power solution including the battery.

[0121] In summary, the embodiments of the present invention have at least the following technical effects: This invention achieves stable DC bus voltage output by using coordinated control of power distribution closed loop and thermal management closed loop. When the photovoltaic power is sufficient, the photovoltaic system provides power independently; when the photovoltaic power is insufficient, the mains power provides real-time supplementary power. This eliminates the need for batteries.

[0122] This invention uses an incremental PID algorithm to adjust the PWM duty cycle of the mains-side switching power supply, which enables rapid recovery of the DC bus voltage under load step conditions.

[0123] This invention uses a PI algorithm to dynamically adjust the fan speed, combined with a piecewise linear control strategy, which can effectively suppress junction temperature overshoot under power device thermal load step conditions.

[0124] This invention introduces a thermoelectric synergistic control mechanism, which prioritizes improving heat dissipation capacity and then gradually increases the mains power supplementation, thus preventing the evaporation section of the phase change heat pipe from drying out.

[0125] This invention significantly improves the operational safety and maintainability of inverters through a dual-redundancy over-temperature protection design in both hardware and software, as well as a cloud-based digital twin model.

[0126] It is understood that the above embodiments are merely exemplary implementations used to illustrate the principles of the present invention, and the present invention is not limited thereto. For those skilled in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A thermoelectric synergistic control method for a photovoltaic grid hybrid power supply inverter, characterized in that, include: The photovoltaic output power and the load power are sampled synchronously at a first frequency, and the power difference between the photovoltaic output power and the load power is calculated. Power allocation decisions are made based on the power difference. When the power difference is greater than or equal to zero, the mains-side switching power supply is turned off and the photovoltaic system supplies power separately. When the power difference is less than zero, an incremental PID algorithm is used to adjust the PWM duty cycle of the mains-side switching power supply to keep the DC bus voltage at the voltage set value. The incremental PID algorithm is calculated based on the voltage deviation between the DC bus voltage and the voltage set value. The junction temperature of the power device and the wall temperature of the phase change heat pipe are sampled at a second frequency, and the temperature difference between the junction temperature of the power device and the wall temperature of the phase change heat pipe is calculated. The PI algorithm is used to dynamically adjust the fan speed according to the temperature difference deviation between the temperature difference and the target temperature difference set value. When the temperature difference exceeds the first temperature difference threshold, the fan speed is linearly increased until the temperature difference drops to the target temperature difference range. When the temperature difference is lower than the second temperature difference threshold, the fan speed is reduced to the silent mode speed. as well as Over-temperature protection is implemented. When the junction temperature of the power device exceeds the preset over-temperature threshold and continues for a set time, the inverter output power is reduced to a preset ratio of the rated power, and the junction temperature of the power device, the wall temperature of the phase change heat pipe, and the power data are reported to the cloud.

2. The thermoelectric synergistic control method for a photovoltaic grid hybrid power supply inverter according to claim 1, characterized in that, The photovoltaic output power is calculated as follows: The DC voltage on the photovoltaic side is obtained using voltage and current sensors, respectively. With DC current The formula for calculating the photovoltaic output power is: ； The load power is calculated by obtaining the AC side voltage through a voltage sensor and a current sensor, respectively. With alternating current The formula for calculating the load power is: ； in, Power factor; The formula for calculating the power difference is: ； The first frequency ranges from 0.5 to 2 kHz, and the ADC resolution is no less than 12 bits.

3. The thermoelectric synergistic control method for a photovoltaic grid hybrid power supply inverter according to claim 1, characterized in that, The incremental PID algorithm is calculated as follows: ； ； in, , , These are the proportional coefficient, integral coefficient, and differential coefficient, respectively. For the first The voltage deviation between the DC bus voltage and the set value at each sampling time. For the first PWM duty cycle at each sampling time; The incremental PID algorithm sets the integral separation threshold to a preset percentage range of the rated power, sets the anti-integral saturation limiting range, and sets the PWM carrier frequency to 15-25kHz.

4. The thermoelectric synergistic control method for a photovoltaic grid hybrid power supply inverter according to claim 1, characterized in that, The junction temperature of the power device is obtained by an NTC thermistor mounted inside the power device module. The relationship between the resistance of the NTC thermistor and temperature is as follows: ； in, The nominal resistance is at 25℃. For material constants, The current temperature; The phase change heat pipe wall temperature is obtained by attaching a platinum resistance thermometer or a thermocouple to the outer wall of the evaporation section. The formula for calculating the temperature difference is: ； in, The junction temperature of the power device. The phase change heat pipe wall temperature; The second frequency ranges from 0.2 to 1 kHz, and the ADC resolution is no less than 10 bits.

5. The thermoelectric synergistic control method for a photovoltaic grid hybrid power supply inverter according to claim 1, characterized in that, The calculation method of the PI algorithm is as follows: ； ； in, , These are the proportional coefficient and the integral coefficient, respectively. For the first Temperature difference deviation at each sampling time, For the first Fan speed at each sampling time; The proportional gain of the PI algorithm ranges from 10 to 30, the integral gain ranges from 0.2 to 1.0, the anti-integral saturation limiting range is ±5% to ±15%, and the PWM carrier frequency is 20-30kHz.

6. The thermoelectric synergistic control method for a photovoltaic grid hybrid power supply inverter according to claim 1, characterized in that, The fan speed adjustment adopts a piecewise linear strategy: When the temperature difference is greater than the first temperature difference threshold, the fan speed is linearly increased at a preset speed slope until the temperature difference drops to the target temperature difference range. When the temperature difference is between the second temperature difference threshold and the first temperature difference threshold, the fan speed is maintained at the current value. When the temperature difference is less than or equal to the second temperature difference threshold, the fan speed is reduced to the silent mode speed, which is in the range of 800-1500 rpm.

7. The thermoelectric synergistic control method for a photovoltaic grid hybrid power supply inverter according to claim 1, characterized in that, It also includes thermoelectric coordinated control steps: When the power difference is greater than zero and the temperature difference exceeds the first temperature difference threshold, the fan speed is first linearly increased to the rated speed, and then the mains power supplement power is increased with a preset power slope. The preset power slope ranges from 20 to 50 W / s to avoid the phase change heat pipe evaporation section from drying out. When the power difference is less than zero and the junction temperature of the power device is lower than the preset low temperature threshold, the fan speed is reduced to the silent mode speed to reduce energy consumption and noise.

8. The thermoelectric synergistic control method for a photovoltaic grid hybrid power supply inverter according to claim 1, characterized in that, It also includes a low-temperature start-up procedure: When the ambient temperature is lower than the preset low temperature start-up threshold, after power-on, the fan is driven to run at the preheating speed for a preset preheating time. The value of the preheating speed is in the range of 1000-3000 rpm, and the value of the preset preheating time is in the range of 10-60s. Once the phase change heat pipe wall temperature exceeds the preset wall temperature start-up threshold, it switches to normal PI control mode.

9. The thermoelectric synergistic control method for a photovoltaic grid hybrid power supply inverter according to claim 1, characterized in that, The over-temperature protection adopts a dual redundancy design in both hardware and software: The hardware layer implements hardware cutoff protection when the junction temperature of the power device exceeds the preset hardware cutoff temperature through a comparator, with a response time of less than 20μs. The software layer enables the power device to operate at its maximum power level after the junction temperature exceeds the preset software power limit temperature and continues for the set time. Fault reports are transmitted to the cloud via an encrypted channel. The cloud establishes a digital twin model based on thermal-fluid-structure interaction simulation to predict the lifespan degradation trend of power devices.

10. The thermoelectric synergistic control method for a photovoltaic grid hybrid power supply inverter according to any one of claims 1 to 9, characterized in that, The communication module uploads the junction temperature of the power device, the wall temperature of the phase change heat pipe, the photovoltaic output power, the mains power supplement power, and the fan speed to the cloud at a preset message period, the preset message period being 0.5-2s. The communication module supports remote OTA upgrades. The upgrade package is written to the controller after being signed and verified. During the upgrade process, the DC bus maintains uninterrupted power supply.

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