Mitsubishi Electronics MS-AWA Outline of main power supply circuit, Power factor improvement

Function of main parts

SYMBOL	NAME	FUNCTION
IPM	INTELLIGENT POWER MODULE	It supplies three-phase AC power to compressor.
CB1~3	SMOOTHING CAPACITOR	It stabilizes the DC voltage.
CT1~2	CURRENT TRANSFORMER	It measures the current of the compressor motor.
CT61	CURRENT TRANSFORMER	It measures the current of the main power supply circuit.
L	REACTOR	It rectifies AC, controls its voltage and improves the power factor of
PFC	POWER FACTOR CONTROLLER	power supply.
R64A, R64B	CURRENT-LIMITING RESISTOR	It restricts rush current with the resistance.
X64	RELAY	It short-circuits the resistance which restricts rush current during the
		compressor operates.

2-7-2-2. Outline of main power supply circuit

1.At the start of operation

Main power supply circuit is formed when X64 (Relay) is turned ON at compressor startup.

To prevent rush current from running into the circuit when power supply is turned ON, R64A and R64B (Current-limiting resistor) are placed in sub circuit.

2.At normal operation

1 When AC runs into noise filter P.C. board, its external noise is eliminated in the noise filter circuit.

2 After noise being eliminated from AC, it is rectified to DC by L (Reactor) and PFC (Power factor controller). If the operating frequency becomes 25Hz or more, DC voltage rises to 370V.

3 DC voltage, to which has AC been rectified by process 2, is stabilized by CB1~3 (Smoothing capacitor) and supplied to IPM (Intelligent power module).

4 The DC (Bus voltage), which has been stabilized in process 3, is converted to three-phase AC by IPM and supplied to compressor.

5 CT1 and CT2 (Current Transformer), which are placed in the power supply circuit to compressor, are used to measure the value of phase current and locate the polar direction of rotor with algorithm. PWM (Pulse width modulation) controls impre- ssed voltage and frequency with those information.

3.Power factor improvement

Booster coil L (Reactor) and PFC rectify AC to DC and control its voltage.

In the motor drive system of sine wave control, power factor can be improved by reducing harmonics PFC and L (Reactor) stabilize the voltage of DC supplied to inverter circuit and make its waveform smooth.

4.Power transistor module

IPM consists of the following components.

·Power Transistors (x6): Converts DC waveform to three-phase AC waveform and outputs it.

· Drive Circuit	: Drives transistors.
· Protection circuit	: Protects transistors from over current.

Since the above components are all integrated in IPM, IPM has a merit that can get the control circuit simplified and mini- aturized.

5. Smoothing capacitor

CB1, CB2 and CB3 stabilize the DC voltage and supply it to IPM.

6. Elimination of electrical noise

Noise filter circuit, which is formed by *CMC COILS and capacitors placed on the noise filter P.C. board, eliminates electrical noise of AC power that is supplied to main power supply circuit. In short, common mode noise is absorbed in this circuit. Moreover, normal mode noise is absorbed in another noise filter circuit which is formed by *NMC COILS and capacitors. Both noise filter circuit exists for preventing the electrical noise generated in the inverter circuit from leaking out.

*CMC COILS; Common mode choke coils *NMC COILS; Normal mode choke coils

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