Repair process of INVT frequency converter G9 series “crash” fault

User feedback: This frequency converter was not turned on at the time, but other machines on the three-phase power supply side had abnormalities, resulting in a short circuit and tripping. The power switch of this machine also tripped, but after reclosing, it was found that the operation panel was no longer displayed, so it was sent for repair.

Detection: There is an open circuit between R, S, T and the main DC circuit P and N. Upon disassembly and observation, the copper foil strip introduced into the module has been burned by an arc. The three-phase power supply terminal of the module is being tested for a short circuit.
Cause of malfunction: The disturbance caused by instantaneous short circuit and tripping of other load branches in the power supply caused abnormal voltage spikes in the three-phase power supply. This dangerous voltage caused breakdown and short circuit of the rectifier circuit in the frequency converter module. The strong arc generated by the short circuit burned the copper foil strip introduced by the three-phase power supply, and also caused the protection of the power switch to trip.
The inverter part of the testing module is still normal, and there is no bulging or deformation observed in the module. Therefore, the module rectification part is cut off, and an additional three-phase rectification bridge is installed. The low-cost repair plan of the original three-phase inverter circuit in the module is still used for repair testing.
Inspection: To prevent abnormal phenomena from occurring, first cut off the power supply to the inverter section of the module; Add a 500V DC voltage from the external repair power supply, power on, and the operation panel displays H.00. All operations are invalid. Based on experience, when the module of this model of frequency converter is damaged, its power on module short circuit detection function takes effect, and the CPU refuses all operations. Therefore, the OC signal returned by the inverter is released, and the phenomenon of power on still persists. The overcurrent signals of 4 and 6 in the fault signal collection and processing circuit U7-HC4044 are all negative voltage, while under normal conditions, the static voltage should be 6V positive. Looking forward with the current detection circuit, the voltage at pins 8 and 14 of the current signal input amplifier U12D is 0V, which is normal; The 14 pin of U13D is negative 8V, and there is an incorrect overcurrent signal output. Solder R151 off and disconnected the overcurrent fault signal. All parameter settings on the operation panel were normal, but there was no response to the start/stop operation.
Is there any other fault signal that has not been eliminated, and the frequency converter is still in the protection state, so the start/stop operation is refused? The measured voltage of the module’s thermal alarm terminal is 3V. From the circuit analysis, when this voltage is normal, it should be around 5V. Does the three-phase rectifier circuit inside the module output a thermal alarm signal when it is damaged? Or is it the damage to the rectification circuit that causes the circuit to be damaged simultaneously and mistakenly outputs a thermal alarm signal? After cutting off the copper foil strip outputted by the thermal alarm, the start/stop operation of the operation panel has taken effect!
The protection sequence of the Envision G9/P9 frequency converter is roughly as follows: when there is a fault in the power inverter output section during power on detection, even if no start/stop signal is received, the SC – output short circuit fault code will still jump, and all operations will be rejected; When an overcurrent signal is detected from the current detection circuit when powered on, H.00 is displayed, and all operations are still rejected; When there is a thermal alarm signal detected during power on, most other operations can be carried out, but the startup operation is rejected. Perhaps the CPU thinks that the output module is still in a high temperature rise state and waits for it to return to room temperature before allowing it to start running. For module short circuit faults and overcurrent faults, in order to ensure safe operation, all operations are simply rejected! However, this protective measure is often mistaken by people for entering a dead cycle in the program, or for a malfunction in the CPU peripheral circuit, such as a reset circuit or abnormal crystal oscillator circuit.

Repair: Cut off the copper foil strip lead of the three-phase power supply, and clean and insulate it properly. Connect an external three-phase rectifier circuit and introduce its DC output to the P and N terminals; Equipped with a thermal protection circuit: There is a 60 ℃ normally closed thermal relay on hand, which is connected in series with the NPN type transistor base to the 5V ground circuit. A 10k resistor is used to connect the+5V and base, connect the transistor emitter to the 5V ground, and connect the collector to the thermal alarm circuit signal output terminal. When the module temperature rises normally, the transistor is cut off without driving voltage and does not transmit a thermal alarm signal. When the temperature rise of the module is abnormal, the normally closed point of the thermal relay is disconnected, and the transistor receives the driving current and fully outputs, causing the voltage of the output terminal of the thermal alarm signal to drop below 3V, sending a thermal alarm shutdown protection signal to prevent the module from overheating and burning.