Modeling, Simulation and Control of Electrical Drives
2: Danfoss Power Electronics A/S Denmark, Copenhagen, Denmark
Thanks to advances in power electronics device design, digital signal processing technologies and energy efficient algorithms, ac motors have become the backbone of the power electronics industry. Variable frequency drives (VFD's) together with IE3 and IE4 induction motors, permanent magnet motors, and synchronous reluctance motors have emerged as a new generation of greener highperformance technologies, which offer improvements to process and speed control, product quality, energy consumption and diagnostics analytics. Primarily intended for professionals and advanced students who are working on sensorless control, predictive control, direct torque control, speed control and power quality and optimisation techniques for electric drives, this edited book surveys state of the art novel control techniques for different types of ac machines. The book provides a framework of different modeling and control algorithms using MATLAB®/Simulink®, and presents design, simulation and experimental verification techniques for the design of lower cost and more reliable and performant systems.
Inspec keywords: sensorless machine control; machine vector control; PWM power convertors; synchronous motor drives; torque control; PWM invertors; machine control; closed loop systems; permanent magnet motors; induction motor drives
Other keywords: induction motor drives; torque control; PWM power convertors; PWM invertors; closed loop systems; permanent magnet motors; machine vector control; synchronous motor drives; sensorless machine control; machine control
Subjects: Control of electric power systems; Asynchronous machines; Drives; General electrical engineering topics; Power electronics, supply and supervisory circuits; Mechanical variables control; General and management topics; Synchronous machines
 Book DOI: 10.1049/PBCE118E
 Chapter DOI: 10.1049/PBCE118E
 ISBN: 9781785615870
 eISBN: 9781785615887
 Page count: 741
 Format: PDF

Front Matter
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1 Introduction to electric drives
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The basic elements of electric drive systems are introduced in this Chapter. The knowledge base comprising several disciplines that interact and encompass the selection of diverse components that go into a drive system for an application are brought out. Typical drive structures and control hierarchies that guide the designer to build an inherently reliable and wellprotected drive system are discussed.

2 Electric machines, dynamic models and sensors in drive systems
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This chapter gives an overview of three widely used machines of the full range of power spectrum. Steadystate torquespeed boundaries in all four quadrants within and above the base speed for the major types of conventional DC and AC machines are introduced first, followed by the dynamic models of these machines. A limited, by no means complete, analysis of the two dominant types of AC machine (the AC induction and the synchronous) dynamics is included with a view to guide the reader to appreciate the necessity for transformations of voltages and currents and flux linkages of a threephase machine to one of the rotating axes, in order to appreciate how current controls are used for controlling the torque and flux linkages independently of each other. The logical control structures, the RFOC, for these machines then follow for each machine type. This is followed by a brief description of sensor technologies and associated hardware. Finally an overview of recent developments in the AC induction and PM synchronous machines is included.

3 Converters for drives
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This chapter presents the most popular dc ac inverter topologies, two level and three level NPC inverter, used for the electric drives. It focuses on the SPWM and SVPWM methods for the two level and three level NPC inverters. The emphasis is given to the implementation aspect of these PWM methods. It is shown that the SVPWM method can be implemented in the same way as the SPWM method with small modification in the sinusoidal reference signals. Furthermore, the problem of neutral point voltage unbalance associated with the three level NPC inverter is discussed. A popular method to balance the neutral point voltage is also discussed.

4 DC motor drives
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This chapter is intended to provide insight on the design and development of controllers for DC motors, their classification and issues related to the control, power quality improvement and sensors reduction for various domestic, commercial and industrial applications.

5 Synchronous motor drives
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This chapter deals with the development of model, simulation and hardware implementation of the synchronous motor (SM) drive under various operating conditions. In the modeling of vectorcontrolled PMSM drive, the complete model of the SM drive system is developed for different types of speed controllers with a view to improving the performance of the drive. The simulations of PMSM drive are carried out in MATLAB ® environment with Power System Blockset (PSB) and fuzzy logic control (FLC) toolboxes. The hardware of vectorcontrolled PMSM drive system includes control circuit, interfacing circuit and the power circuit. The control circuit is implemented in DSP ADMC401 and the power circuit consists of the voltage source inverter (VSI) and the PMSM. The interfacing circuit is required for feedback signals in the form of motor winding currents and position as well as rotational speed of the rotor. The DSPbased software algorithm is used to obtain the performance of the drive for starting, speed reversal, load perturbation and steadystate response for different types of closedloop speed controllers. The simulated results are presented in this chapter along with DSPbased implementation results of developed prototype of drive to validate both the model and the control algorithms.

6 PM synchronous machine drives
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The purpose of this chapter is to discuss techniques for analyzing and controlling the electrical performance characteristics of permanent magnet (PM) synchronous machines (PMSMs) based on electrical equivalent circuit models for the machine derived in the synchronously rotating reference frame. Representation of the d and q axes components of the key machine variables as complex vectors provides a powerful means of graphically illustrating the amplitudes and spatial orientations of these key variables in the machine. This complexplane representation of the machinephase currents will be used to investigate the performance limits of the machine at high speeds when operating from a source that is restricted by maximum voltage and current limits.

7 Control of PM brushless DC motor drives
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Because of the simplicity in construction and in control, BLDCMs are found in a wide range of applications. This kind of motor suffers, however, a serious drawback in the torque ripple, due to sharp communications every 60° electrical. Various efforts have been made to reduce the torque ripple. Phase advance approach is a common practice for controlling the motors above the base speed. The working principle of the motor has been illustrated using the motor and electronics commutator association, in accordance with Hall effect sensors sequences. The mathematical modeling of the motor has been carried out. The practical block diagram of threephase motor has been built for the simulation purpose. Control of the BLDC drive was performed in MATLAB/Simulink environment and the analysis of torque ripples has been provided.

8 Switched reluctance motor drives
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9 Direct torque control of AC machines
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The DTC technology has been steadily developed for induction motors initially and now in a mature stage where its adaptation in commercial products has been accepted by industry. The development focus is now toward adaptation of DTC into complex applications requiring special motor types and drive topologies. The various technology areas are special machines for highspeed applications and multiphase machines with more than threephase windings. There are attempts to extend DTC strategies for advanced drive topologies like matrix converters, multilevel converter topologies, integrated line side converter control. The complexity in such topologies is coming from increased number of voltage vector combinations, which are available for switching, and thus, decisionmaking can be a complex and timeconsuming process. This is typical situation in even more complex multilevel converter fed multiphase machine architecture where the number of voltage vector combinations rises exponentially with machine phase and converter voltage levels.

10 Direct torque control of PM synchronous motor drives
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This chapter describes the direct torque control (DTC) technique for permanent magnet synchronous motors/machines (PMSMs). The DTC technique has evolved much since mid1980s when a less complex, cheaper and potentially faster method of torque and flux control than the preexisting rotor fluxoriented vector control (RFOCNC) for induction machines first emerged. The DTC technique is based on closedloop regulation of torque and stator flux linkage obtained from estimators using voltage vectors and currents in the stator reference frame and the machine model. Drive dynamics under DTC control is as fast and can be faster than that under RFOCNC in which rotor position sensing is used for exercising control in the rotor reference frame. This chapter starts with a brief review of the context of these developments, including the underlying theory (which had existed prior) and methods that have been used to apply DTC to PMSMs. Some comparative evaluations are included that may help researchers and engineers to further develop the method and apply it to highperformance PMSM drives in various applications.

11 Matrix converterdriven AC motor drives
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The matrix converter (MC) is an ACAC power converter topology. The MC topologies are classified into two types: direct MC (DMC) and the indirect MC (IMC) [I]. The IMC topology is composed of a rectifier with six bidirectional switches (BDSs) and a conventional voltage source inverter (VSI). The large energy storage elements are eliminated from the intermediate DClink in this topology. This chapter mainly focuses on direct torque control (DTC) for MC driven interior permanent magnet synchronous machine (IPMSM) drive. First of all, it gives a brief overview on the fundamentals of MC followed by the implementation of BDSs for MC. Two current commutation strategies based on input voltage sign and output current direction, respectively, are presented in this chapter. Some other practical issues of MC are also discussed in this chapter, in terms of input filter design and overvoltage protection. Different modulation strategies for MC are briefly reviewed in this chapter. Among these methods, the indirect space vector modulation (SVM) is demonstrated by considering the MC as a twostage converter, rectifier and inverter stages. The openloop and closedloop input power factor (IFF) compensation schemes are presented followed by the DTC schemes for MC drives.

12 An online parameter identification method for AC drives with induction motors
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The chapter describes how to implement an online identification method for induction motors within a fieldoriented control by using least squares (LS) methods. In particular, it focuses on how to develop the experimental rig by a stepbystep approach, where the different components of the setup are described to enable readers to have a reference on their own. Attention has been paid both to the connections of the sensors (current, voltage and rotor speed) to the digital signal processing (DSP) of the dSPACE platform and to the construction of the circuits and design of the signal processing part. Experimental results are then presented and discussed to assess the behaviour of the experimental rig with different LS methods to show the flexibility of the test setup.

13 Sensorless control of IM drives
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This chapter addresses the fundamental issues of sensorless vector control of induction motor drives. Starting from an historical overview of induction motor control in general, we revisit the two archetypical flux estimators known as the current model and voltage model, as well as their combination into a reducedorder observer. It is demonstrated not only that how speed estimation can be added to the observer but also how the flux estimator can be made inherently sensorless, i.e. the rotor speed no longer appears in the estimator equations. It is shown that all inherently sensorless flux estimators that are based on the reducedorder observer resemble a variant of the voltage model, called the statically compensated voltage model. Finally, theory is developed whereby the coefficients of the inherently sensorless flux estimator can be selected so that stability is obtained for all operating conditions, called complete stability. This includes the lowspeed regeneration region where often instability phenomena tend to occur.

14 Sensorless control of PMSM drives
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When compared to induction motors, permanent magnet synchronous motors (PMSMs) feature higher torque density, improved efficiency and increased constant power speed range. These distinct advantages have resulted in PMSMs being employed in a myriad of industrial applications. Traditionally, the open loop V/f control scheme has been the preferred method for PMSM drives owing to its inherent simplicity. Nevertheless, as this method is derived from the steadystate model of the machine and does not rely on any motor feedback information, it offers very poor dynamic performance and is susceptible to external disturbances. Thus, its adoption is limited to applications whose transients are relatively unimportant or occur over long intervals. If high torque and speed dynamic performance is required, the vector control method becomes a necessity.

15 Predictive torque control of induction motor drive
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This chapter summarizes the application of Model Predictive Control (MPC) technique to a twolevel inverter driven induction motor (IM) drive. There are two types of MPC: continuous control set MPC (CCSMPC) and finite control set MPC (FCSMPC). In CCSMPC, the controller generates a continuous output for a modulator, and the modulator generates the switching signals for the inverter to generate the required voltage. Conversely, in FCSMPC, the finite number of control actions available in the system  inverter switching states for motor drives  is evaluated against the desired control objectives. The outputs of the controller are discrete and are directly used to switch the power switches on/off in the inverter. The finitestate predictive torque control (FSPTC) of motor drives is an FCSMPC strategy. In FSPTC, torque and stator flux are predicted for the finite number of admissible switching states of a voltage source inverter (VSI). In this study, a twolevel VSI (2LVSI) is considered to produce the necessary voltage vectors. Experimental results illustrate that FSPTC algorithm yields good performance in terms of torque and flux ripple, stator current THD, robustness against load torque disturbance, step torque response and step speed response.

16 Multiphase machine drives
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Variablespeed AC drives are nowadays based on threephase electrical machines fed by power electronic converters acting as power interface between the electrical machine and AC or DC power sources. Nevertheless, in the last two decades the multiphase electrical drives have become an interesting alternative for particular applications. However, the application of multiphase drives is still limited, mainly due to their complexity and control that somehow make them more difficult to handle with respect to the conventional threephase counterparts. Therefore, this work intends to be a useful tool to disseminate the fundamental concepts of multiphase drives to students and application engineers.

17 Fractionalslot concentrated winding machines and drives
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Fractional slot concentrated wound AC machines have undergone intensive research and development recently due their compactness, ease of manufacturing and maintenance, and low cost compared to conventional AC machines. Many new applications in appliances, electric traction, and aerospace industries are already possible. These machines pose some control challenges due to the high number of poles, which can be taken advantage of in gearless drives, and the non sinusoidal nature of its stator MMF. This chapter is focused on the design and performance aspects of the fractionalslot concentratedwound machines.

Back Matter
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