General Assist Technical Reference
Intelligent Power Module (IPM or TR PCB)
What the inverter power module does and how it controls compressor speed
Technical explanation for inverter air-conditioning outdoor units
The Intelligent Power Module (IPM) is the power electronics section used to drive the inverter compressor. It may also be referred to as the Transistor PCB, TR PCB, inverter board or simply the IPM.
1. Common terminology
| Name | Meaning |
|---|---|
| IPM | Intelligent Power Module |
| TR PCB | Transistor PCB |
| Inverter board | Another common service description for the same power-control section. |
2. What the IPM does
The IPM supplies pulsating DC voltage to the compressor windings. By changing the frequency and voltage of the IPM output, the outdoor unit can control compressor RPM.
| 1 | DC supply enters the IPM. The DC bus is connected to the power module through the P and N terminals. |
| 2 | The IPM switches the DC supply. The power electronics create controlled, pulsating output waveforms for the compressor. |
| 3 | Three outputs feed the compressor. The switched outputs are identified as U, V and W. |
| 4 | Compressor speed is varied electronically. Changing output frequency and voltage changes compressor RPM. |
3. P, N, U, V and W terminals
| Terminal | Function |
|---|---|
| P | Positive side of the DC bus supplying the IPM. |
| N | Negative side of the DC bus supplying the IPM. |
| U | Compressor output phase. |
| V | Compressor output phase. |
| W | Compressor output phase. |
Important: P and N are the DC bus connections. U, V and W are the controlled compressor outputs. The board locations and physical terminal arrangement can vary between outdoor-unit PCB designs.
4. Key measurements
Compressor speed
Compressor speed frequency is measured in Hz (hertz).
Compressor speed frequency is measured in Hz (hertz).
Compressor current
Compressor current is measured in AC amperes (A).
Compressor current is measured in AC amperes (A).
5. Service interpretation
When diagnosing an inverter compressor circuit, understanding the role of the IPM helps separate the DC supply side from the controlled compressor-output side:
- P / N: DC bus supply to the inverter power module.
- U / V / W: controlled output from the IPM to the compressor windings.
- Frequency: relates to commanded compressor speed.
- Current: reflects the AC current being supplied to the compressor.
Electrical safety: Inverter outdoor units can retain hazardous DC voltage after the mains supply is isolated. Follow the applicable service manual, isolation procedure and discharge-time requirements before testing or handling the IPM/TR PCB.
General Assist Technical Reference