Paresh C. Sen

Electric motor drives and control-past, present, and future

A comprehensive review of the state of the art in the field of electric motor drives and control strategies is presented. It is pointed out that drive technology has seen impressive growth during the last three decades. Recent advances in semiconductor power electronics and microelectronics have made is possible to use AC motors in many variable-speed drive applications. Implementation of new control techniques, such as field-oriented control and variable-structure control with sliding-mode features, has made AC motors a viable alternative to DC motors in high-performance drive applications. The advent of microprocessors/microcontrollers/microcomputers has made it possible to implement these complex control techniques. >

High-Power Wind Energy Conversion Systems: State-of-the-Art and Emerging Technologies

This paper presents a comprehensive study on the state-of-the-art and emerging wind energy technologies from the electrical engineering perspective. In an attempt to decrease cost of energy, increase the wind energy conversion efficiency, reliability, power density, and comply with the stringent grid codes, the electric generators and power electronic converters have emerged in a rigorous manner. From the market based survey, the most successful generator-converter configurations are addressed along with few promising topologies available in the literature. The back-to-back connected converters, passive generator-side converters, converters for multiphase generators, and converters without intermediate dc-link are investigated for high-power wind energy conversion systems (WECS), and presented in low and medium voltage category. The onshore and offshore wind farm configurations are analyzed with respect to the series/parallel connection of wind turbine ac/dc output terminals, and high voltage ac/dc transmission. The fault-ride through compliance methods used in the induction and synchronous generator based WECS are also discussed. The past, present and future trends in megawatt WECS are reviewed in terms of mechanical and electrical technologies, integration to power systems, and control theory. The important survey results, and technical merits and demerits of various WECS electrical systems are summarized by tables. The list of current and future wind turbines are also provided along with technical details.

A Design Method for PI-like Fuzzy Logic Controllers for DC–DC Converter

This paper proposes a novel design procedure of proportional and integral (Pl)-like fuzzy logic controller (FLC) for DC-DC converters that integrates linear control techniques with fuzzy logic. The design procedure allows the small signal model of the converter and linear control design techniques to be used in the initial stages of FLC design. This simplifies the small signal design and the stability assessment of the FLC. By exploiting the fuzzy logic structure of the controller, heuristic knowledge is incorporated in the design, which results in a nonlinear controller with improved performance over linear PI controllers.

Control dynamics of speed drive systems using sliding mode controllers with integral compensation

The control dynamics and robustness improvement of vector controlled AC speed drive systems using a sliding mode control with integral compensation (SLMC-I) are described. The dynamics of step command speed and impact load disturbance under SLMC-I control are formulated and studied. Acceleration estimation techniques using observers and nonideal differentiators for the SLMC-I speed drive systems are outlined and compared. The control dynamics of SLMC-I with increased system order are discussed. The techniques of robustness improvement for the SLMC-I drives are presented. A method of control in which the sliding line is fed forward is developed to enhance the drive robustness. The control dynamics with this method of control are investigated. The effectiveness of the proposed scheme is demonstrated through computer simulations and experimental work.<<ETX>>

Decoupling control of induction motor drives

The decoupling control of induction machines is investigated. Three different schemes for decoupling-control methods based on stator flux, airgap flux, and rotor flux field regulation are developed. The control dynamics of each scheme are outlined and studied. Simulation results are presented to verify that these schemes provide decoupling control with excellent dynamic behavior. The transient and steady-state relationships between slip frequency and torque, under constant stator flux, airgap flux, and rotor flux operations, are simulated and compared. The sensitivity characteristics of the three methods of flux-control, machine fed by impressed currents and voltages, are also compared and studied. A prototype torque-drive system is implemented to demonstrate the decoupling control of a squirrel-cage induction machine. >

A new soft-switching technique for buck, boost, and buck-boost converters

A new soft switching technique for buck, boost and buck-boost converters using a coupled inductor is proposed in this paper. The principles of operation of these converters are analyzed in detail. An additional winding is added on the same core of the main inductor for the purpose of commutation. By using hysteresis current control, zero voltage switching (ZVS) conditions are ensured over wide load range. The main inductor current is kept in continuous conduction mode (CCM) with small ripple, which allows high output power and small filter parameters. Also, the switching frequency is kept constant when load changes. Prototypes of buck, boost, and buck-boost converters have been built to verify the proposed concept. The experimental results are presented and they verify the analysis.

A Practical Switching Loss Model for Buck Voltage Regulators

In this paper, a review of switching loss mechanisms for synchronous buck voltage regulators (VRs) is presented. Following the review, a new simple and accurate analytical switching loss model is proposed for synchronous buck VRs. The model includes the impact of common source inductance and switch parasitic inductances on switching loss. The proposed model uses simple equations to calculate the rise and fall times and piecewise linear approximations of the high-side MOSFET voltage and current waveforms to allow quick and accurate calculation of switching loss in a synchronous buck VR. A simulation program with integrated circuit emphasis (Spice) simulations are used to demonstrate the accuracy of the voltage source driver model operating in a 1-MHz synchronous buck VR at 12-V input, 1.3-V output. Switching loss was estimated with the proposed model and compared to Spice measurements. Experimental results are presented to demonstrate the accuracy of the proposed model.

Circulating Current Minimization in High-Frequency AC Power Distribution Architecture With Multiple Inverter Modules Operated in Parallel

The control issue of multiple inverter modules operated in parallel is investigated for high-frequency alternative current (HFAC) power distribution architectures, where multiple high-frequency resonant inverters are connected in parallel to the high-frequency high-voltage low-current (HVLC) AC bus, to feed a number of point-of-use power supplies. The circulating current in the multiple inverter system is analyzed first. A novel control scheme is proposed based on the active and reactive current decomposition concept. In the proposed control, there are two loops: 1) the current sharing control loop and 2) the voltage feedback control loop. For the current sharing loop, the active current and reactive current are controlled separately. It is shown that the minimization of the circulating current can be achieved if both the active current and reactive current of the equivalent load are evenly distributed among activated inverter modules. This control method is superior to the scalar control where only the magnitudes of the currents are controlled. Performance is verified with both simulations and experiments on a prototype HFAC power distribution system where two two-stage resonant inverter modules of 500 kHz and 100 W are connected in parallel through small connection inductors to the 500-kHz 28-V rms HFAC bus.

A Current Source Gate Driver Achieving Switching Loss Savings and Gate Energy Recovery at 1-MHz

In this paper, a new current source gate drive circuit is proposed for power MOSFETs. The proposed circuit achieves quick turn on and turn off transition times to reduce switching loss and conduction loss in power MOSFETs. In addition, it can recover a portion of the CV gate energy normally dissipated in a conventional driver. The circuit consists of four controlled switches and a small inductor (typically 100 nH or less). The current through the inductor is discontinuous in order to minimize circulating current conduction loss. This also allows the driver to operate effectively over a wide range of duty cycles with constant peak current-a significant advantage for many applications since turn on and turn off times do not vary with the operating point. Experimental results are presented for the proposed driver operating in a boost converter at 1 MHz, 5 V input, 10 V/5 A output. At 5 V gate drive, a 2.9% efficiency improvement is achieved representing a loss savings of 24.8% in comparison to a conventional driver.

Digital control of switching power converters

The paper reviews the latest advance of the digital control technologies in DC-DC converters. The research on digital control is mainly focused on two areas. One is the methods to generate digital PWM (DPWM) signals to meet the output voltage accuracy requirement. Various dithering techniques have been developed to improve the output voltage resolution and at the same time to reduce the clock frequency requirement. The other is to develop new control methods that can utilize these advantages of the digital controller so as to improve the dynamic performance of the switching power converters. Several new digital control methods have been proposed and significant dynamic performance improvement has been achieved