Tag: SC FAULT

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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.

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Handling Method for SC Jumping Fault of GS Series INVT VSD

SC: Refers to a short circuit in the output load of the frequency converter. In the state of power outage, there is no short circuit between U, V, W and between U, V, W and DC P, N. To distinguish whether it is a current detection circuit fault on the CPU motherboard or a signal returned by the driving IC, short circuit the signal to the diode side of the optocoupler device with a wire, and operate the RUN key after power on. The output frequency displayed on the panel is normal. The SC signal is returned by the driving IC, and there are two reasons for the malfunction: first, the inverter module is damaged, and second, the driving IC itself is faulty.

After cutting off the power supply to the inverter module, the six pulse signals of the drive IC were checked again. It was found that the U-upper arm drive IC had input pulses but no output pulses (static negative pressure normal). After replacing the drive IC, the output was normal. The static negative pressure of the U lower arm drive IC is only a few tenths of a volt. After replacement, the fault still persists. After welding the 100 ohm resistor connected to the trigger end of the inverter module, the static negative pressure rises to the normal value. The forward resistance of the lower arm terminal of the module U is consistent with the resistance of other trigger terminals, but its reverse resistance is slightly smaller than that of other trigger terminals, indicating that the circuit inside the U-phase trigger terminal of the module is damaged!
This is a key point in checking module faults: the resistance of the main terminal cannot be roughly measured to be normal, which means that the module is good. It is not uncommon for the circuit inside the triggering terminal to be damaged, but it is more concealed! When the frequency converter reports an SC or OC fault and the main terminal of the detection module is normal, the inspection of the forward and reverse resistance of the triggering terminal should not be missed!
The damage of modules and the damage of driving ICs are usually related: when the U-phase main circuit is damaged, the upper and lower arm driving ICs of the U-phase are often also damaged by strong voltage shocks; When the driver IC of the phase is found to be damaged, it often hides the internal circuit damage of the triggering terminal of the phase. So one of the two is that a comprehensive inspection must be conducted. Of course, there are also cases where modules and driver ICs are damaged separately, but it is extremely rare.

During maintenance, another phenomenon of drive IC failure was also discovered in the low-power model of the Envision GS: when the frequency converter is powered on and there is an SC fault signal output, the CPU performs self check, reset, and reset, and after clearing, the panel only displays H:00, and all panel buttons fail to operate. When the corresponding optocoupler circuit is short circuited to eliminate the SC signal, all panel operations are normal. If the model detects an SC fault signal output when powered on, it may perform a “program lock” and refuse to operate! When this phenomenon occurs, the fault signal output circuit should be checked and corresponding measures should be taken to temporarily eliminate the fault signal, in order to facilitate operation and judgment, and thus solve the fault.