Controlling the Machine

Methods for controlling PMSM drives, connected to different types of converters, have been developed both for steady state operation and high performance servo control. This thesis discusses theservo control of the PMSM but a small discussion of the steady state behaviour of the machine can be found in Section 2.4.

The most advanced type of control of electrical machines is known as vector control. The term vector control includes many different control methods but they all use different types of feedback mechanisms for improved control. The standard laboratory setup of a vector controlled PMSM is shown in Figure 1.1.

Grid

Grid

Figure 1.1: Basic principle of vector control.

The PMSM is fed by the voltage source inverter (VSI), which is powered by the grid through an AC/DC converter. For the hybrid electric case, the VSI is fed by a DC source, such as batteries. The VSI is controlled by a digital signal processor (DSP). A combination of a fast DSP and a modern VSI can control the voltage in the three phases of the PMSM very accurately. Note also the feedback devices, which consist of current measuring devices and rotor position detection. The rotor position detection usually consists of Hall sensors or a resolver. The term sensorless control usually implies that the rotor position and/or rotor speed is not measured but estimated from the currents fed to the machine. Using vector control, various parameters can be controlled, for example rotor speed, angular position and torque on the shaft. The torque on the shaft is controller in hybrid electric vehicle applications.

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