Current Control of Generalized Load
The ability to control the currents in an electrical machine is essential for manipulating its mechanical torque and magnetic flux, as will become apparent in Chap. 4 . This chapter considers current control techniques for single- and three-phase voltage
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Current Control of Generalized Load
The ability to control the currents in an electrical machine is essential for manipulating its mechanical torque and magnetic flux, as will become apparent in Chap. 4. This chapter considers current control techniques for single- and three-phase voltage source converters which are connected to a generalized load as introduced in the previous chapter. The use of this type of load is instructive given that it reflects the electrical behavior of most electrical machines which are in use today. Consequently, the current control techniques discussed in this chapter may be applied for electrical machines discussed in this book. Attention has been given to the use of voltage source converters because these are widely used in low- and medium-power drive applications. However, for high power applications, current source converters are still deployed. These converters are considered outside the scope of this book. A bewildering variety of current control concepts have been developed. In this chapter two representative techniques for single- and three-phase converters will be considered. The two techniques in question are referred to as hysteresis and model based current control. Within these categories, different implementation techniques are possible. Two practical control techniques are introduced which have been used by the authors in electrical drive applications. The tutorial section at the end of this chapter deals with a range of simulation models which provide the reader with the ability to examine the control concepts explained in this chapter.
3.1 Current Control of Single-Phase Load 3.1.1 Hysteresis Current Control Prior to discussing this type of control it is helpful to define the so-called hysteresis concept with the aid of Fig. 3.1. Shown in Fig. 3.1 is a generic module with input © 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_3
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3 Current Control of Generalized Load
Fig. 3.1 Generic hysteresis module with hysteresis band x∗ and transfer function
Fig. 3.2 Single-phase converter with hysteresis current controller
x and output y. The output has two states, which in this example are taken to be −1 and 1, respectively, as is apparent from the transfer function shown in Fig. 3.1. The term hysteresis is used to describe a non-singular transitional process. If, for example, the output state y = −1, then the output will change to y = 1 when the condition x ≥ x/2 occurs. Vice versa, when the output is y = 1, a change to y = −1 will take place as soon as the condition x ≤ −x/2 occurs. The transitions exhibit a degree of “hysteresis” defined by the variable x∗, i.e., the hysteresis band, as shown in Fig. 3.1. In this section, a hysteresis based current control will be discussed with the aid of the half-bridge converter topology presented in Sect. 2.2. This topology is readily adapted to hysteresis type current control by adding a current controller module and a current
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