Temperature self-adaptation is an electro-thermal closed-loop intelligent control system of inverter. The core logic is: multi-node temperature measurement → junction temperature model estimation → multi-level adaptive adjustment (heat dissipation/power/switching parameters/drive compensation) → hysteresis protection, which maximizes power generation, reduces heat dissipation power consumption and prolongs the life of the whole machine on the premise of ensuring device safety.
1. Hardware sensing layer: global temperature acquisition (adaptive input basis)
1. Multi-point sensor layout (NTC thermistor/digital temperature chip)
The key temperature measuring points are fully covered, and the shell temperature (directly measurable) and IGBT junction temperature (indirectly modeled and estimated) are distinguished:
Ambient temperature: air inlet, judging external foundation heat load;
Power module shell temperature TC: bottom radiator of IGBT/SiC module (the core temperature measuring point);
DC bus capacitance: electrolytic/thin film capacitance (easy to bulge at high temperature);
Transformer/inductance winding: the magnetic element is saturated at high temperature and the loss is soaring;
Air duct/cold plate temperature: temperature of air-cooled/liquid-cooled cooling medium.
2. Signal preprocessing (eliminating interference and ensuring adaptive accuracy)
ADC sampling+extreme moving average filtering to filter out electromagnetic interference and instantaneous temperature jump;
Multi-sensor cross-check, automatic compensation and fault alarm when single sensor drifts;
The sampling period is 50~100ms, and the temperature control response delay is less than 100ms.
3. Estimation of IGBT true junction temperature Tj (adaptive control core input)
The temperature can't be measured directly inside the chip, so the Foster/Cauer RC thermal network model is used for real-time calculation:
Real-time acquisition of DC voltage, grid-connected current and PWM switching frequency;
Look-up table to calculate IGBT conduction loss+switching loss (loss varies with temperature and current);
The loss is input into the RC thermal circuit as a heat source, and the junction temperature TJ of the chip is calculated by combining the measured shell temperature Tc.
On-line calibration of saturated pressure drop Vce superimposed on high-end models improves the estimation accuracy of high-temperature section.
Two or four layers of adaptive regulation execution logic (from passive heat dissipation to active power regulation)
The first floor: self-adaptation of cooling system (fan/liquid cooling flow speed regulation, priority regulation, minimum power generation loss)
Fuzzy PID closed-loop speed regulation is adopted, and the heat dissipation capacity is dynamically matched according to the environment, shell temperature, junction temperature and load rate, and the zones are adaptive:
Low temperature range (TC < 35℃)
Fan shutdown/minimum speed, only natural heat dissipation; The low temperature environment automatically raises the fan start threshold, reducing the power consumption and wear of the fan.
Medium temperature range (35℃ ≤ TC < 65℃)
The temperature linearly corresponds to the speed of PWM fan, and the heat dissipation is predicted in advance when the load is more than 70%, so as to avoid the sudden temperature rise; Multi-fan unit zone speed regulation.
High temperature range (Tc≥65℃)
Fan at full speed; Liquid-cooled models increase pump flow and open standby cooling channels; Automatically identify and give an alarm when the cooling efficiency decreases due to air duct blockage.
Low temperature compensation logic
Reduce the heat dissipation intensity when the environment is less than 10℃; When the outdoor natural wind speed is high, the fan speed is lowered, and 10%~15% of energy is saved by convection.
Hysteresis and shock prevention: the threshold of starting the fan is 35℃, and the threshold of stopping is 30℃; Back difference is also set for derating and shutdown to avoid frequent start/stop/power jump.
Layer 2: switch parameter adaptation (reducing device heating and delaying power derating)
Before the heat dissipation reaches the upper limit, modify the PWM control parameters to reduce the loss and delay the power derating stage;
Switching frequency adaptation
When the junction temperature Tj approaches the early warning threshold, the switching frequency of IGBT is reduced and the switching loss is greatly reduced. When the temperature drops, the rated switching frequency will be restored, giving consideration to waveform harmonics and heating.
Dynamic compensation of gate voltage of SiC devices
The threshold voltage of SiC MOSFET drifts at high temperature, and the controller can fine-tune the driving gate voltage according to the junction temperature in real time, so as to stabilize the switching characteristics and suppress extra heating.
Adaptive constraint of reactive power output
Reactive power of inverter will increase IGBT heating; Automatically limit reactive power output at high temperature and give priority to active photovoltaic power generation.
Layer 3: adaptive derating of output power (core thermal protection mechanism, linear smooth adjustment)
When the heat dissipation and switch parameter adjustment still can't restrain the junction temperature rise, start the temperature-power linear derating curve instead of directly shutting down:
Grading threshold standard (common in the industry)
Early warning point: Tc=60℃, full-speed heat dissipation+alarm upload;
Starting point of derating: Tc=65℃, and the output power decreases linearly from 100%;
Maximum derating point: Tc=90℃, and the output is locked at 50% of the rated power (the lower limit is clamped to ensure the basic grid connection);
Emergency shutdown: Tc≥95℃, cut off power output to prevent device burning.
Time lag protection
Short-term instantaneous high temperature (such as sudden rise of irradiation after cloud cover) allows short-term full load; If the high temperature continues to exceed the set time, the rating will be gradually reduced to avoid the loss of power generation due to small temperature fluctuation.
Multi-device joint constraint
If any component of capacitor or inductor overtemperature, start slight derating synchronously, not only depending on IGBT temperature.
Layer 4: Coordinated temperature adaptation between MPPT and grid connection.
At high temperature, the working voltage of MPPT is slightly raised, the input current of DC side is reduced, and the conduction loss of power module is reduced;
In the scene of high-temperature weak current network, the grid-connected filtering impedance is adjusted adaptively, and the harmonic THD is controlled to avoid the disturbance of high-temperature superimposed power network.
Third, the complete closed-loop control process (sequential logic)
Real-time acquisition: multi-channel temperature, voltage, current and fan speed are sent to DSP/MCU；;
Data fusion: filter+RC thermal model to calculate IGBT junction temperature TJ;
Hierarchical judgment (from low priority to high priority)
① Only adjust the fan speed;
② Adjust PWM switching frequency and reactive power limit;
③ Linear power derating;
(4) overtemperature emergency stop;
Issue control instructions: fan PWM, PWM carrier frequency, active power limiting, MPPT voltage correction;
State mining correction: read the adjusted temperature, modify PID parameters in closed loop, and dynamically adapt aging devices (fan attenuation, compensation for automatically increasing cooling speed after dust accumulation in radiator);
Data upload: upload temperature curves and derating records to the photovoltaic monitoring platform to predict the life of fans and capacitors.
Fourth, the exclusive adaptive strategy of high and low temperature extreme scenes
1. High temperature environment (desert, summer noon, environment 50~60℃)
Start heat dissipation in advance and lower the threshold of fan start;
Give priority to reducing switching frequency, limiting reactive power and delaying power derating;
The MPC is enabled to predict the temperature rise according to the rising trend of irradiation and dissipate heat in advance.
2. Low temperature environment (below-20℃ in winter)
The fan is shut down for a long time to avoid solidification damage of low-temperature lubricating oil;
At low temperature, the current carrying capacity of the device is improved, and the rated power is allowed to exceed slightly for a short time;
The low-temperature capacity of bus capacitor decays, which slightly limits the impact current.
V. Comparison of traditional fixed threshold vs. temperature adaptation
form
VI. Core values
Maximize power generation: avoid limiting power greatly as soon as the temperature rises, and reduce power generation loss by multi-stage buffering;
Heat dissipation and energy saving: the fan adjusts speed as needed, stops at low temperature under light load, and reduces its own power consumption;
Reliability improvement: the fluctuation range of IGBT junction temperature is reduced, following the "10℃ rule" (life at 10℃ per liter is halved) to delay aging;
Wide environment adaptation: stable operation at -25℃~60℃, suitable for household, industrial and commercial, desert power stations.
