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This paper presents a method for improving the control design for a high-power induction motor (IM) drive employing rotor-flux-based orientation. An offline genetic-algorithm routine is used to estimate the electrical and mechanical parameters of the machine using only speed transient measurements. This routine is applied to a range of operating conditions to obtain an accurate knowledge of the IM parameters as a function of the d-axis motor current [i.sub.d]. The information acquired is then employed, together with an enhanced control design obtained by optimizing speed and current transient responses, to increase the performance of the vector control algorithm. The effectiveness of this design method is demonstrated through a wide range of simulations using Matlab--Simulink and experimental results at power levels up to 230 kW. Index Terms--Genetic algorithms (GAs), induction motors (IMs), parameter estimation, rotor-flux control.

This paper describes the development of a highfrequency resonant-power converter for high-energy physics (CW) applications. The proposed converter topology has been demonstrated by the construction of a laboratory demonstrator that produces 25 kV with less than 1% ripple at 1 A (25 kW). The converter is a direct converter topology operating without the use of a dc link, significantly reducing the size and weight of the converter and resulting in a relatively high-energy density converter. A high-frequency (20 kHz) resonant circuit is employed which provides inherent short-circuit protection of the converter from the output, while reducing the turns ratio of the transformer. The transformer is integrated into the resonant circuit and operates at the same frequency as the resonant circuit (20 kHz). To achieve high-frequency and high-flux operation of the transformer, an amorphous (nanocrystalline) core is used, further reducing the physical size of the converter. Use of the resonant circuit also allows for soft switching of the IGBTs. High-frequency operation allows for a reduction in size of both the transformer and output filters, thereby removing the need for operation with a crowbar. All of the techniques implemented in the prototype converter may be extended to higher voltage higher power systems. Index Terms--HF transformers, modulators, predictive control, resonant-power conversion.

In this paper, a new control system to regulate the reactive power supplied by a variable-speed wind energy conversion system (WECS), based on an induction generator fed by a matrix converter (MC), is presented. The control system discussed in this paper is based on an input current observer, implemented using an estimation of the modulation matrix, and a nonlinear control loop that regulates the displacement angle at the MC input. The reactive power capability of the proposed system is also investigated. The work presented in this paper demonstrates that, for the proposed WECS, the maximum reactive power supplied to the grid is about 40% of the nominal value. Experimental results obtained from an experimental prototype are presented in this paper. The performance of the system using a wind turbine emulator and typical wind profiles is discussed in this paper. Index Terms--Current control, power generation, reactive power control, wind power generation.

Recently, considerable interest has been shown in direct (matrix) converter topologies as an alternative to conventional motor drives. In general, when compared with existing three-phase motor drives (rectifier--inverter types), these topologies offer advantages, such as reduced space and weight (due largely to the removal of the large electrolytic capacitor), four-quadrant operation, and high-quality current waveforms. Consequently, there is now considerable interest regarding direct converters in areas such as aerospace, where issues such as the size and weight of the converter are important. The work presented in this paper capitalizes on these advantages in power conversion for high-power radio-frequency supplies, such as those used in high-energy physics research and associated applications. Index Terms--Accelerator RF systems, power conditioning, predictive control, resonant power conversion.

This letter presents an improved harmonic injection method for determination of inverter-induced harmonic power loss across a range of induction motors rated at 1.1, 7.5, 15, and 30 kW. Techniques to obtain the necessary experimental precision and repeatability are investigated in detail. The harmonic injection method allows the machine to be tested under normal operating conditions while a range of selected harmonics are superimposed on the fundamental frequency of the pulse width modulation (PWM) waveform. This technique is validated by direct loss measurement using a specially built calorimeter capable of detecting power loss as low as a few watts in induction motors of up to 30 kW. Comparisons of segregated losses by IEEE 112 method B for the machines operating on sinusoidal and inverter-fed supplies show a good correlation between high frequency PWM harmonic loss and core loss. Core loss is not a constant proportion of total loss for any machine and neither is harmonic loss independent of machine design. Index Terms--Harmonic analysis, induction motors, loss measurement, power conversion harmonics, pulse width modulated inverters, variable speed drives.

This paper addresses the analysis and performance of several model reference adaptive system (MRAS) observers for sensorless vector control of doubly-fed induction machines. Small signal models allow the formal analysis of the observers for a given dynamic. The performance of each MRAS observer is analyzed, considering grid-connected and stand-alone operation. The MRAS observers are implemented in a 3.5 kW experimental prototype composed of a doubly-fed induction generator and a wind turbine emulator. Experimental results validate the predictions of the small signal models and demonstrate the performance of the sensorless methods during both steady state and variable speed wind energy generation. Index Terms--Adaptive observers, induction generators, power generation control.

In this paper, the modeling and control strategy of a wind-diesel generation system are discussed. In the proposed topology, the diesel engine and the wind turbine are both variable-speed machines, allowing maximum fuel efficiency and optimal energy capture from the wind. A vector-controlled doubly fed induction generator is used in each generation system to provide fixed voltage and frequency to the load. The diesel unit balances the system power and changes the speed according to the power demand in order to minimize the fuel consumption. The electrical torque of the wind system generator is regulated to maximize the energy capture of the wind turbine. The advantages of operating a diesel engine at variable speed are discussed. The dynamic and steady-state operation of the wind-diesel system, including voltage and frequency control, active power balancing, and control of the reactive power supplied to the grid/load are analyzed in this paper. Experimental results, from a 3-kW experimental prototype are presented in this paper. Index Terms--Diesel-driven generators, induction generator, induction motor drives, wind energy.

The paper considers a solution for integration of large offshore doubly fed induction generator-based wind farms with a common collection bus controlled by a STATCOM into the main onshore grid using line-commutated high-voltage dc connection. A design procedure is described and the controlled system is validated using PSCAD/EMTDC simulations confirming high performance of the proposed control strategy in both normal operation conditions and faults. Engineering issues related to STATCOM capacitor sizing and reduction of STATCOM rating are considered and their effectiveness is confirmed. Index Terms--Controller design, doubly fed induction generator (DFIG), frequency, high-voltage dc (HVdc) transmission, stability, STATCOM, voltage, wind energy.

This paper quantifies the extra harmonic losses in an induction motor that are associated with the use of a matrix converter topology as a motor drive. These extra losses are compared to the harmonic losses associated with an inverter-based motor drive. The technique employed in the determination of the harmonic losses is described. For the matrix converter, the extra harmonic losses associated with two commonly used modulation techniques are calculated and compared. The impact of these extra losses on the cooling requirements and operation of the motor is considered. Index Terms--AC/AC power converters, calorimeter, harmonic losses, induction motors, matrix converters.

This paper presents a new sensorless method for the vector control of Doubly-Fed Induction Machines (DFIMs) without using speed sensors or rotor position measurements. The proposed sensorless method is based on the Model Reference Adaptive System (MRAS) estimating the rotor position and speed from the machine rotor currents. The method is appropriate for both stand-alone and grid-connected operation of variable speed DFIMs. To design the MRAS observer with the appropriate dynamic response, a small signal model is derived. The sensitivity of the method for variation in the machine parameters is also analyzed. Speed catching on the fly and synchronization of the Doubly-Fed Induction Generator with the utility are also addressed. Experimental results obtained from a 3.5-kW prototype are presented and fully analyzed. Index Terms--AC generators, induction motors, sensorless control, wind power generation.

This paper describes the control analysis and design of an ac-to-ac three-phase mobile utility power supply using a matrix converter capable of high-quality 50-, 60-, and 400-Hz output voltage and reduced input harmonic distortion. Instead of the traditional structure employing a diode bridge rectifier, a dc link and a pulsewidth-modulated inverter, a three-phase-to-three-phase direct ac-ac (matrix) converter has been used as the power-conditioning core of the system, working in conjunction with input and output LC low-pass filters. An optimizing control design method using a genetic algorithm approach has been used, which yields designs to minimize a cost function, taking into account transient and steady-state output voltage performance targets, together with robustness to different operative conditions and system parameters drift. Simulation and experimental tests have demonstrated that the system meets the power-quality requirements of the application. Index Terms--AC power supply, digital control, genetic algorithms (GAs), matrix converters.

In this paper, a new low-frequency predictive current control is proposed for a single-phase cascaded H-bridge multilevel rectifier. The control method has been fully investigated with theoretical analysis, simulation, and experiments on a laboratory prototype with five series-connected H-bridges. However, the analysis and technique are valid for any general N-level structure. The simulations and experimental results presented demonstrate the excellent performance of the predictive control in terms of ac current waveform quality, power factor, and reduced switching frequency of each bridge, in comparison to traditional control schemes. Index Terms--Active rectifiers, multilevel converters, predictive control, pulsewidth modulation (PWM).

This paper presents a complete method that is used to balance dc link voltages in a cascaded H-Bridge (CHB) multilevel rectifier. Recently, such converters have been the subject of extensive research due to their suitability for high-power applications. One requirement in using a multilevel active rectifier at high levels of power is to limit the switching losses by reducing the switching frequency to a minimum. Another requirement for these converters is to ensure that individual dc link capacitor voltages for each cell of the converter are always balanced to ensure controllability and to limit stress on the converter cells. This paper presents a complete method in solving both of these problems using a selective-harmonic-elimination pulsewidth-modulation scheme. The scheme utilizes a simple controller to track each cell dc link capacitor voltage magnitude and accordingly biases the power flowing into each cell to ensure that the voltages across each cell capacitor converge. This is the case even when the loads attached to the individual cells are not balanced. The theory is supported by both simulated results from Saber and by experimental results from a seven-level CHB single-phase multilevel rectifier. Index Terms--Multilevel converter, selective harmonic elimination (SHE), voltage balancing control.

Matrix converters are becoming a real alternative to traditional topologies for many ac-ac power conversion applications. One of the less well-known advantages is the potential for reduced waveform distortion that arise from device characteristics and commutation delays. This paper describes the origin of distortion effects for a matrix converter with current sign-based commutation and gives a novel approach to the method that can, in principle, eliminate the distorting effects to give a power converter having excellent linear behavior. The effectiveness of compensation techniques are illustrated for both an open-loop matrix converter driving a passive load and a matrix converter as part of a vector-controlled drive. Index Terms--Matrix converters, nonlinearity compensation, sensorless control.

The interest in using the matrix converter (MC) for motor drive applications and energy conversion systems is steadily increasing due to its main advantage of performing a direct coupling between two three-phase alternating current sources without the need of an intermediate direct current bus. This characteristic, together with the presence of inductance-capacitance input filters and the feedforward compensation of the input voltage variations, might yield unstable operation in electrical drives. In this paper, a theoretical analysis of MCs based on a large-signal model is presented with the aim to show which parameters may affect the stability and to explain the reason of this phenomenon. The theoretical analysis is supported by several experimental tests carried out on an MC prototype. Index Terms--Harmonic distortion, matrix converter (MC), stability.

The paper considers a control solution for integration of large offshore doubly fed induction generator based wind farms with a common collection bus, controlled by a static compensator, into the main onshore grid, using line-commutated high-voltage direct current connection. The paper's main focus is a mathematically grounded study of the power system interactions. That study produced an appropriate plant model for formal control design. A design procedure is described and the controlled system is validated using power systems computer-aided design/electromagnetic transient program simulations, which confirm the high performance of the proposed control strategy in both normal operation and fault conditions. Index Terms--Controller design, doubly fed induction generator (DFIG), frequency, high-voltage direct current (HVDC) transmission, stability, static compensator (STATCOM), voltage, wind energy.

This paper presents a novel power-balance control method for a wind-diesel generation feeding an isolated grid. The system is based on a variable-speed wind energy conversion system (WECS) connected to an ac load using a power converter. An energy storage system (ESS), connected to the ac load using an additional converter, is used to balance the power generated by the WECS with the load. In this paper, the vector control systems for both interfacing power converters are discussed; the control uses the WECS converter to regulate the ac load voltage and the ESS converter to regulate the power flow to achieve a power balance. A small signal model is used to design the control systems. Finally, the proposed control is implemented in a 2-kW experimental prototype and the experimental results are fully analyzed and discussed in the paper. Index Terms--Diesel engines, pulsewidth-modulated (PWM) power converters, wind-power generation.

A control system for power smoothing using a switched reluctance machine (SRM) driving a flywheel is presented in this paper. Power smoothing is achieved by controlling the SRM to operate as a motor/generator, storing or retrieving energy from a rotating flywheel. In order to increase the rotational energy stored in the flywheel, the SRM operates at high rotational speed, and the machine phase current is controlled using single-pulse mode. To control the SRM output power, a two-dimensional lookup table is used to store the switching angles. The control strategies proposed in this paper have been experimentally implemented in a 2.5-kW prototype based on an 8/6 SRM. Experimental results are presented and discussed. Index Terms--Control systems, power quality, reluctance machines, wind-power generation.

This paper addresses the use of a matrix converter (MC) with high-frequency voltage injection for zero- and low-speed sensorless control of surface mount permanent magnet alternating current motors. This paper also proposes a dual compensation technique that can practically eliminate zero-current-crossing distortions in MCs, discusses the effect of such distortions on sensorless control using injection techniques, and presents experimental results that illustrate the enhanced low-speed sensorless performance that can be obtained from exploiting the effective linearity of the MC operation. Index Terms--Matrix converters (MCs), sensorless control, surface mount permanent magnet (SMPM) ac motors, zero-low speed.

This paper presents a novel control system for the operation of a switched reluctance generator (SRG) driven by a variable speed wind turbine. The SRG is controlled to drive a wind energy conversion system (WECS) to the point of maximum aerodynamic efficiency using closed loop control of the power output. In the medium and low speed range, the SRG phase current is requlated using pulsewidth-modulation (PWM) control of the magnetizing voltage. For high speeds the generator is controlled using a single pulse mode. In order to interface the SRG to the grid (or ac load) a voltage-source PWM inverter is used. A 2.5-kW experimental prototype has been constructed. Wind turbine characteristics are emulated using a cage induction machine drive. The performance of the system has been tested over the whole speed range using wind profiles and power impacts. Experimental results are presented confirming the system performance. Index Terms--Reluctance generators, variable-speed drives, wind energy, wind power generation.

This paper presents an analysis of a model reference adaptive system (MRAS) observer for the sensorless control of a standalone doubly fed induction generator (DFIG). The analysis allows the formal design of the MRAS observer of given dynamics and further allows the prediction of rotor position estimation errors under parameter mismatch. The MRAS observer analysis is experimentally implemented for the vector control of a standalone DFIG feeding a load at constant voltage and frequency. Experimental results, including speed catching of an already spinning machine, are presented and extensively discussed. Although the method is validated for a standalone generator, the proposed MRAS observer can be extended to other applications of the doubly fed induction machine. Index Terms--Induction generator, induction motor drives, wind energy.

High-frequency multimegawatt polyphase resonant power conditioning techniques have recently been realized as a result of key component developments, cooperative efforts, research and development funding contracts, and newly applied engineering techniques. The first generation 10-MW pulsed converter-modulators, implemented at Los Alamos National Laboratory, Los Alamos, NM, are now utilized for the Oak Ridge National Laboratory, Oak Ridge, TN, Spallation Neutron Source (SNS) accelerator klystron radio frequency amplifier power systems [1]. Three different styles of polyphase resonant converter-modulators were developed for the SNS application. The various systems operate up to 140-kV, or 11-MW pulses, or up to 1.1 MW average power, all from a direct current input of +/- 1.2 kV. The component improvements realized with the SNS effort coupled with new applied engineering techniques have resulted in dramatic changes in overall power conditioning topology. As all example, the 20-kHz high-voltage transformers are less than 1% the size and weight of equivalent 60-Hz versions. With resonant conversion techniques, load protective networks are not required. A shorted load de-tunes the resonance which results in limited power transfer. This provides for power conditioning systems that are inherently self-protective, with automatic fault 'ride-through' capabilities. By altering and iterating the Los Alamos design, higher power and continuous wave power conditioning systems can now be realized with improved performance and flexibility. This paper will examine the SNS engineering data, briefly review the underlying theory of polyphase resonant conversion techniques, and apply this knowledge to future system topologies. Index Terms--Insulated gate bipolar transistor (IGBT), modulator, nanocrystalline transformer, power conditioning, resonant converter.