High powerACmotor drives: Status review and work at IISc

A variety of solutions are available today from industry for high power variable speed AC motor drive applications, starting from a power rating of a few 100 kW to several 10’s of Megawatts. These drives can be classified on the basis of the electrical motor, the power converter and the control technique. The main drive types are reviewed.The salient features of each type of drive are pointed out along with their industrial applications.Following this, some research at IISc which has applications in high power drives is described briefly

Space vector pulsewidth modulation — A status review

The technique of space vector pulsewidth modulation (SVM) is reviewed. The basic principle of SVM is derived and is compared with sine-triangle PWM. Operation in the overmodulation range is explained. Extension of SVM to other inverter-motor combinations such as three level inverters and split phase motors are discussed

Analytical Evaluation of Harmonic Distortion in PWM AC Drives Using the Notion of Stator Flux Ripple

This paper presents a method to evaluate harmonic distortion due to space vector-based PWM strategies for AC drives. The proposed method is general enough to deal with division of zero vector time as well as division of active vector time within a subcycle. The method is based on the notion of stator flux ripple, which is a measure of line current ripple. Expressions for RMS ripple over a subcycle are derived for six switching sequences in terms of magnitude and angle of the reference vector, and subcycle duration. The sequences considered include those involving division of active vector time within a subcycle. Further, analytical closed form expressions are derived for the total RMS harmonic distortion factor corresponding to six space vector-based synchronized PWM strategies, proposed recently, for high power drives. The square of the distortion factor turns out to be a quadratic polynomial in modulation index (M), and the coefficients differ with PWM strategies and pulse numbers. These expressions are validated through Fourier analysis as well as experimental measurements. The concept of stator flux ripple provides insight into current ripple as well as torque ripple corresponding to different sequences and strategies

Direct Torque Control Schemes for Split-Phase Induction Machine

In this paper, DTC (Direct Torque Control) algorithms for Split-phase Induction Machine (SPIM) are established. SPIM has two sets of three-phase stator windings, with a shift of thirty electrical degrees between them. The significant contributions of the present work are: a) Two new methods of DTC technique for SPIM are developed. They are called as Resultant Flux Control Method and Individual Flux Control Method. b) Advantages and disadvantages of both the methods are discussed. High torque ripple is a disadvantage for three-phase DTC. It is found that torque ripple in SPIM could be significantly reduced without increasing the switching frequency

Synchronised PWM strategies based on space vector approach. Part 1 : Principles of waveform generation

The authors deal with space-vector-based generation of synchronised three-phase PWM waveforms with three-phase, half-wave and quarter-wave symmetries. The necessary and sufficient conditions for synchronisation and the waveform symmetries are brought out in terms of the inverter states. These conditions are applied to the conventional and modified forms of space vector modulation to generate synchronised PWM waveforms with all the symmetries. Further, the necessary conditions governing the numbers of switchings of the different phases in any given sector to maintain the symmetries are identified. These rules are used to develop two new clamping strategies, namely the asymmetric zero-changing strategy and the boundary sampling strategy, which exploit the flexible features of space vector methods like double-switching of a phase and clamping of two phases in a sampling period. Typical waveforms corresponding to the different strategies are presented along with their theoretical and experimental spectra. The performance assessment of these strategies and their application to drives are dealt with in Part 2

Space vector based bus clamped PWM algorithms for three level inverters: implementation, performance analysis and application considerations

This paper describes the different types of space vector based bus clamped PWM algorithms for three level inverters. A novel bus clamp PWM algorithm for low modulation indices region is also presented. The principles and switching sequences of all the types of bus clamped algorithms for high switching frequency are presented. Synchronized version of the PWM sequences for high power applications where switching frequency is low is also presented. The implementation details on DSP based digital controller and experimental results are presented. The THD of the output waveforms is studied for the entire operating region and is compared with the conventional space vector PWM technique. The bus clamped techniques can be used to reduce the switching losses or to improve the output voltage quality or both.. Different issues dominate depending on the type of application and power rating of the inverters. The results presented in this paper can be used for judicious use of the PWM techniques, which result in improved system efficiency and performance

Rotor side control of grid-connected wound rotor induction machine

This paper deals with modeling, simulation and implementation of rotor side control strategies for a grid-connected wound rotor induction machine. In the system under consideration, the stator is directly connected to the constant frequency three-phase grid and the rotor is supplied by two back-to-back three-phase voltage source inverters with a common DC link. Such a configuration is attractive in large power applications with limited speed range of operation. The rotor currents are controlled at any desired phase, frequency and magnitude to control the active and reactive powers of the machine independently. A stator flux-oriented model of the doubly fed wound rotor induction machine is presented. The current controllers are designed in the field coordinates. Simulation waveforms exhibit excellent transient response of the current loops; the dynamics of the direct and quadrature axes are also observed to be decoupled. An experimental setup consisting of IGBT inverters and a TMS320F240 DSP-based digital controller is developed in the laboratory to implement the control algorithms. Relevant experimental waveforms are presented; they are observed to be in good agreement with the simulation results

A Simple Position-Sensorless Algorithm for Rotor-Side Field-Oriented Control of Wound-Rotor Induction Machine

A simple position-sensorless method for rotor-side field-oriented control of a wound-rotor induction machine is described in this paper. The algorithm is based on axis transformations. Compared to the previously proposed methods, it is more direct and the dependence on machine parameters is also largely reduced. The algorithm can be started on the fly without the knowledge of the initial rotor position. Operation at synchronous speed, corresponding to zero rotor frequency, is stable, thus making it suitable for variable speed constant frequency operations. Simulation and experimental results show excellent performance of the scheme

A Novel VSI- and CSI-Fed Active-Reactive Induction Motor Drive with Sinusoidal Voltages and Currents

Till date load-commutated inverter (LCI)-fed synchronous motor drive configuration is popular in high power applications (>10 MW). The leading power factor operation of synchronous motor by excitation control offers this simple and rugged drive structure. On the contrary, LCI-fed induction motor drive is absent as it always draws lagging power factor current. Therefore, complicated commutation circuit is required to switch off thyristors for a current source inverter (CSI)-driven induction motor. It poses the major hindrance to scale up the power rating of CSI-fed induction motor drive. Anew power topology for LCI-fed induction motor drive for medium-voltage drive application is proposed. A new induction machine (active-reactive induction machine) with two sets of three-phase winding is introduced as a drive motor. The proposed power configuration ensures sinusoidal voltage and current at the motor terminals. The total drive power is shared among a thyristor-based LCI, an insulated gate bipolar transistor (IGBT)-based two-level voltage source inverter (VSI), and a three-level VSI. The benefits of SCRs and IGBTs are explored in the proposed drive. Experimental results from a prototype drive verify the basic concepts of the drive