Tag: alpha vsd

A. One Dongyuan 7300PA3.7kW frequency converter was sent for repair. The power was connected and it was detected that there was output in the U, V, and W phases, but there was severe phase deviation. It was determined that the drive circuit was abnormal or the module was damaged. Measure the open circuit of the upper arm diode inside the U-phase power stage of the inverter circuit. In general, the IGBT transistor connected in parallel with this diode is also often damaged. In fact, the IGBT tubes were first burnt out by short-circuit current, and the parallel diodes were also damaged by the impact.

After removing the inverter module SPIi12E, all the pins of the inverter module are empty, and the six drive circuits are ready to be tested when powered on. Once powered on, the frequency converter experiences an overheating fault, and the CPU locks the output of the drive pulse in the fault state. Due to the absence of trigger pulse output, it is impossible to detect the quality of the driving circuit. The locking state of the overheating fault must be temporarily released before checking the quality of the drive circuit.
Observe that the inverter module on the circuit board has two terminals labeled T1 and T2, which may be the internal overheat alarm output terminals of the module. One end is led into a 5V power supply through a resistor, and the other end is grounded. When this terminal is suspended, T1 terminal outputs a high-level module overheating signal through an pull-up resistor to protect the shutdown. After short circuiting the T1 and T2 terminals, there will be no protective shutdown when power is supplied.
Check that there is no trigger pulse output in the IGBT drive circuit of the U-phase upper arm. After replacing the drive circuit IC/PC923, the six pulse outputs are normal.
After replacing the IGTB inverter module with a new one, remove the short circuit of the T1 and T2 terminals, and conduct a power test to ensure normal operation. Experience has shown that when an IGBT tube is damaged, the corresponding drive IC will also be damaged due to impact. It is also necessary to inspect the drive IC of the same branch of the damaged module and not hastily replace it with a new module to avoid causing damage to the new module again due to abnormal drive circuit!
B. An Alpha 18.5kW frequency converter with six single tube IGBT tubes (modules) forming a three-phase output circuit, one of which is damaged. CPU motherboard jumps 2501, panel operation fails. The cause of the malfunction of the machine was damage caused by lightning strikes.

The operation panel shows 2501 when powered on, and all operations are malfunctioning. CPU motherboard malfunction, caused by damage to the CPU and peripheral communication circuits. Let’s not worry about it for now. First, fix the driver board before proceeding.
Check the driving circuit, a total of six A316J chips are responsible for six driving pulse output tasks. Three drive circuits that output upper arm pulses are damaged, but there are no integrated circuits of the same model available for replacement. Based on the experience of repairing other brands of frequency converters, using only three A316J chips (used for three-phase lower arm drive) as the three-phase OC signal alarm output can meet the protection requirements. Therefore, the other three pieces were replaced with 3120 (same as PL250V) to drive the optocoupler IC. The original IC was packaged in a 16 pin dual row SMT package, and the replaced IC was packaged in an 8-pin dual row inline package. But the connection is also relatively convenient. Only weld the 8 pins of the new IC to the original 12/13 pins, weld the 5 pins of the new IC to the original 9/10 pins, and connect the 6/7 pins of the new IC to the original 11 pins; Due to the original IC input method being an operational amplifier input and the new IC being a photoelectric tube input, a larger input current is required. Remove the 202 grounding resistor from the original input side and replace it with a 5.1k resistor. Connect the 3 pins of the new IC to ground, and connect the original 1 pin in series with a 300 ohm resistor to the 2 pins of the new IC. Power on and test, and the static voltage is normal.
At this point, after replacing the CPU motherboard with a new one, the static output negative pressure and dynamic pulse output of the six drive circuits were tested to be normal upon power on. After replacing the damaged IGBT module, the machine was tested normally.

C. A 7.5kW frequency converter has been reported by the user as having no major issues, but it has output but cannot operate due to phase deviation. Check if there is an abnormality in one of the six driving circuits. The driving IC model is PC929 (or A4503?). Measure that there are no pulse outputs on the input and output sides of the driving IC. The input side of the IC is directly connected to the pulse output terminal of the CPU. Suspecting a faulty internal pin circuit of the CPU, the PC929 input terminal was disconnected. The voltage at the CPU pulse output terminal increased, but as soon as the driver IC was connected, it dropped to nearly 0V.
Analysis: Due to the direct output of the CPU driving the photoelectric tube, it needs to output a large current. Long term operation may cause aging and failure of the output stage or other faults, resulting in an increase in output internal resistance. When unloaded, there is a certain amplitude of voltage signal, but once connected to the load, even if the signal voltage drops significantly. Replacing the CPU motherboard for this malfunction is a quick solution. One reason is that the maintenance cost is high, and the other reason is that it still needs to be purchased externally, and the repair time required by the user is very tight. Isn’t there a better way? Based on the above analysis, although the pulse output pin of the CPU has aging and failure phenomena, which greatly reduces its load capacity, assuming that its signal current is not used and only its output voltage signal is used, this defect can still be remedied to achieve the purpose of repair. By passing the CPU pin through an external amplifier stage, the signal voltage should meet the requirements for driving the photodiode (PC929 input side photodiode).
Measure that both pins on the input side are 5V high level, and the pin connected to the CPU is a negative pulse input. If you have a PNP transistor on hand, connecting one transistor and a 5k resistor should be able to complete the task. But I only have NPN type transistors on hand, which can only be achieved by using two inverters. Disconnect one pin of the driver IC from the CPU output, connect the copper foil strip to a 50k resistor, and then connect the base of the transistor. Connect the collector in series to the base of the next transistor, and then connect it to+15V through a 10k resistor. Ground the two emitters and connect the lower collector to the disconnect pin of the driver IC. Power on test machine, six pulse outputs are normal. Restore the power supply to the inverter module, and the three-phase voltage output is normal.
The CPU of this machine is damaged and faulty. After using two resistors and two transistors, the problem was resolved and successfully repaired.