Control of Synchronous Machine Drives
This chapter deals with field-oriented, model based control of synchronous machines. Field-oriented control has become common choice for many servo drive applications due to the availability of accurate models and affordable digital signal processors (DSP
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Control of Synchronous Machine Drives
This chapter deals with field-oriented, model based control of synchronous machines. Field-oriented control has become common choice for many servo drive applications due to the availability of accurate models and affordable digital signal processors (DSPs) that execute the model based control algorithms in real time. This chapter builds on the machine models introduced in the previous chapter and extends the electromagnetic torque control principle introduced in Sect. 4.2.1. Controls are derived for both non-salient and salient synchronous machines. The operation in field weakening with constant stator flux linkage and with unity power factor is analyzed. At the end of the chapter, the controls are interfaced with a current-controlled and a voltage-controlled converter. A set of tutorials is provided to interactively illustrate the concepts and the proposed control strategies.
7.1 Controller Principles The drive structure of a synchronous machine under field-oriented control is shown in Fig. 7.1. It consists of a field-oriented control module, a converter with a current control unit, and a synchronous machine which is connected to a mechanical load [1]. In case the machine is not permanently excited, an additional single-phase converter is connected to the excitation winding of the machine. For current control, any of the methods outlined in Chap. 3 can be used. Input to the field-oriented control module is the reference torque Te∗ which is either set by the user or by a superimposed controller (e.g., speed regulator). From the reference torque Te∗ and the mechanical rotor angle Θm , the field-oriented control module generates the c , i c , and i c and calculates the control angle θ c . The rotor or command currents isd sq f shaft angle Θm is provided by a shaft encoder which is attached to the machine shaft. In an ideal case the control angle matches the shaft angle θ c = θm = p Θm .
© Springer Nature Switzerland AG 2020 R. W. De Doncker et al., Advanced Electrical Drives, Power Systems, https://doi.org/10.1007/978-3-030-48977-9_7
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7 Control of Synchronous Machine Drives
Fig. 7.1 Drive structure of a field-oriented controlled, separately excited synchronous machine Fig. 7.2 Space vector diagram for rotor-oriented control
The field-oriented control module uses an orthogonal control grid formed by the direct axis d and the quadrature axis q, as shown in Fig. 7.2. The d-axis is aligned with the flux linkage vector ψ f , giving the field-oriented control its name. In a synchronous machine, the flux linkage vector ψ f has a fixed orientation relative to the rotor, such that the rotor reference system (xy) matches the rotor-oriented reference system (dq). This is why this type of control is also referred to as rotor flux- or rotor-oriented control. Rotor-oriented control is most suited for synchronous drives because it has the benefit of easily decoupling the direct and quadrature currents in non-salient machines as discussed in Sect. 6.1.3. Given the above, rotor
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