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The IMA system assists the engine with an electric motor using power from the Battery Module. It must also recharge the Battery Module by using power generated by the motor. It is the Motor Drive Module or MDM which makes this possible. It can bi-directionally send current from the motor to the battery and from the battery to the motor.
During assist mode, power from the Battery Module is supplied to the IMA Motor in the form of 3-phase Alternating Current. The current isn't true AC, but IGBT's (Insulated Gate Bi-polar Transistors) in the Motor Power Inverter Module (part of the MDM) are switched in such a way as to simulate AC current.
The Motor Control Module receives constant feedback from three commutation sensors in the IMA Motor, and therefore knows the position of the motor. Accurate position information is important because each phase of the 3-phase current must be switched on at the correct time to ensure proper motor operation.
The Voltage Converter Module (also part of the MDM) receives commands from the Motor Control Module, and switches the IGBT's appropriately to meet system demands.
During regeneration mode, current flows from the IMA Motor to the MDM. The motor generates true 3-phase Alternating Current, and that AC must be transformed into DC before it can be used to charge the Battery Module.
Diodes inside the Motor Power Inverter Module are used to rectify the AC power in the same way as they are used in a typical alternator.
It is very important to note that the IMA Motor is a permanent magnet type and will generate power whenever it is turning. If the engine were accidentally started with the IPU Compartment opened, the MDM cables will be hot - even when they are disconnected from the Junction Board. For this reason, the MDM cable terminals should be wrapped with electrical tape whenever they are disconnected from the Junction Board.