For a low voltage IPMSM used in a hybrid drive system of a consumer car, it is of the highest importance to design a torque controller circuit that produces an accurate torque at the shaft. The accurate torque is needed to distribute the load between the combustion engine, or the manual break, and the electrical drive. As the capacitance of the batteries used in this type of car is usually very small, the control of the batteris state of charge and its output current is quite critical. Therefore, a precise torque control is elementary. Temperature changes have a large impact on the IPMSM internal parameters. Especially the permanent magnet flux and the stator resistance are affected by temperature changes. There are techniques to observe and calculate the temperature variation of these parameters. This contribution describes a method to handle the influence of temperature variation on the actual torque at the shaft, by correcting the current commands of the open loop controller.
For an efficient operation of a low voltage PMSM an optimized voltage usage is very important. Because of the relation between the low voltage and the high currents in this type of machine, a large voltage reserve is needed to compensate the influence of parameter mismatches and to guarantee a stable current control. As the power is limited by the low voltage in this type of hybrid drive systems, optimizing the voltage usage is also required to maximize the power and the torque availability. This paper describes a closed loop flux control to maximize the voltage usage. The controller feedback is used to estimate and maximize the available torque for each operating point.