Quote:
Originally Posted by SPL
If the ICE is burning fuel and providing motive power, then its torque vector is positive (upward in my diagrams). This means that the MG1 torque vector is downward (negative), since they must balance (Newton's third law: action = reaction). Then whenever MG1 is spinning backward (negative rpm) its power (torque x rpm) is positive, and so it is acting as a motor.
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Two corrections. First, the torques from the ICE, MG1, and the combination of MG1/wheels must balance. MG1 and the ICE can both be negative, as may be the case on a steep downhill in the B transmission setting. That is, this is a three way balance of torques through the planetary gear set, and not a two way as stated.
Second, motors are generators when the RPM times the motor constant Kv is greater than the voltage ***in either direction***. (Kv is reasonably constant over most of the operational speeds of any given motor, but I doubt that MG1 and MG2 have the same Kv value.) For example, at -1000 RPM with a Kv of 1000, if the voltage is less than (more negative) -1 volt (say -3.8 volts), then the motor is sucking current trying to go faster (towards a larger negative RPM, up to -3800 RPM at -3.8V). If the voltage is more than -1V (say, +2.5V), then the motor is generating current (and would continue to do so up to +2500 RPM, in this case). Neither the direction of rotation, nor the polarity of the voltage alone determines whether the motor is acting as a torque producing/current consuming motor or a torque consuming/current producing generator. That is determined by the simple relationship of the voltage to the product of the speed time the motor constant. (This assumes the phasing of the voltage on the three phase motor is always being maintained, as the inverter does, just as an armature does on a brushed DC motor.) The greater the difference between the RPM times Kv and the applied voltage, the greater the current flow.
The hybrid inverter controls whether MG1 and MG2 are acting as motors or generators by controlling the voltage applied to them, from -600V to +600V (I'm not sure what the voltage range of the inverters are, but I understand the motors are rated at up to 600V). It similarly controls whether the batteries are suppling current to power (one or both) motors, or being charged by the motors (generators) by raising or lowering the voltage applied to the batteries to be above (to charge) or below (to drain) the voltage of the batteries (which vary with the state of charge). The combined current flows to the two motors and battery pack must total zero.
-- Alan