Abstract: Analytical solutions of pulsewidth-modulation (PWM) strategies for multilevel inverters are used to identify that alternative phase opposition disposition PWM for diode-clamped inverters produces the same harmonic performance as phase-shifted carrier PWM for cascaded inverters, and hybrid PWM for hybrid inverters, when the carrier frequencies are set to achieve the same number of inverter switch transitions over each fundamental cycle. Using this understanding, a PWM method is then developed for cascaded and hybrid inverters to achieve the same harmonic gains as phase disposition PWM achieves for diode-clamped inverters. Theoretical and experimental results are presented in the paper.

Abstract: This paper comprehensively analyzes the relationship between space-vector modulation and three-phase carrier-based pulse width modulation (PWM). The relationships involved, such as the relationship between modulation signals (including zero-sequence component and fundamental components) and space vectors, the relationship between the modulation signals and the space-vector sectors, the relationship between the switching pattern of space-vector modulation and the type of carrier, and the relationship between the distribution of zero vectors and different zero-sequence signal are systematically established. All the relationships provide a bidirectional bridge for the transformation between carrier-based PWM modulators and space-vector modulation modulators. It is shown that all the drawn conclusions are independent of the load type. Furthermore, the implementations of both space-vector modulation and carrier-based PWM in a closed-loop feedback converter are discussed.

Abstract: Part I: PWM Converters: Topologies and Control 1 Power Electronic Converters 2 Resonant dc Link Converters 3 Fundamentals of the Matrix Converter Technology 4 Pulse Width Modulation Techniques for Three-Phase Voltage Source Converters Part II: Motor Control 5 Control of PWM Inverter-Fed Induction Motors 6 Energy Optimal Control of Induction Motor Drives 7 Comparison of Torque Control Strategies Based on the Constant Power Loss Control System for PMSM 8 Modeling and Control of Synchronous Reluctance Machines 9 Direct Torque and Flux Control (DTFC) of ac Drives 10 Neural Networks and Fuzzy Logic Control in Power Electronics Part III: Utilities Interface and Wind Turbine Systems 11 Control of Three-Phase PWM Rectifiers 12 Power Quality and Adjustable Speed Drives 13 Wind Turbine Systems Index

Abstract: A direct rotor-field-oriented control of a dual-three phase induction motor drive is described in this paper. The induction machine has two sets of stator three-phase windings spatially shifted by 30 electrical degrees. The stator windings are fed by a current-controlled pulsewidth-modulation (PWM) six-phase voltage-source inverter. Three key issues are discussed: (1) the machine dynamic model is based on the vector space decomposition theory; (2) the PWM strategy uses the double zero-sequence injection modulation technique which gives good results with low computational and hardware requirements; and (3) to eliminate the inherent asymmetries of the drive power section, a new current control scheme is proposed. Experimental results are presented for a 10-kW dual three-phase induction motor drive prototype.

Abstract: The driver circuit for light emitting diodes (LEDs) of the present invention provides power to LEDs using pulse width modulation (PWM). The driver circuit 100 uses current feedback to adjust power to LED arrays 54 and provides a full light and a dim mode.

Abstract: The performance of a dynamic voltage restorer (DVR) in improving the quality of power supply is examined. It is shown that the existing open-loop control strategy used in the DVR to regulate load voltage can produce poorly damped response due to the presence of the switching harmonic filter in the restorer. Damping is shown to be improved if the proposed multiloop controller is used. Furthermore, the new control scheme permits a closer tracking of the reference load voltage under varied load conditions. The analysis of the proposed method is then validated by simulation studies and laboratory experimental tests which show the efficacy of the new control scheme.

Abstract: In three-level neutral-point-clamped voltage-source inverters, proper modulation allows the average voltages of the DC-link capacitors to be kept at one-half the level of the DC-link voltage. However, in some operating conditions, a low-frequency ripple appears in the neutral-point potential and its frequency is three times that of the output voltages. As a result, the output voltages also have low-frequency distortion, which includes even and odd multiples of the fundamental. In this paper, a new space-vector pulsewidth-modulation strategy is presented to avoid that low-frequency output voltage distortion. This modulation method tries to balance the voltages of the capacitors by using only three vectors per modulation cycle. The duty ratios are directly calculated from the space-vector diagram, even when balance is not achieved. For all cases, the result is a balanced set of three AC output voltages. Some simulated and experimental results are given to validate the method.

Abstract: This paper presents a novel discrete-time sliding-mode control algorithm for an uninterruptible power supply (UPS) inverter design. The approach offers a dual-loop design, in which a current predictor utilizes the tracking error of output voltage to estimate the desired inductor current, while a current controller is adopted to regulate the inductor current and, thus, produces a control command to the pulsewidth modulation inverter. An explicit condition for stable controller design is derived. The efficacy of this scheme is validated via a successful implementation on a digital-signal-processor-based UPS inverter. The proposed scheme has shown its robustness on low output voltage distortion, excellent voltage regulation, and it is insensitive to load variation, even under nonlinear loads. Experimental studies were performed to further validate the effectiveness of this scheme.

Abstract: This paper presents a simple control method for balancing the DC-link voltage of three-level neutral-point-clamped inverters, while providing enhanced ride-through and common-mode voltage (CMV) elimination. The method uses DC-DC power converter technology on the DC link for balancing and ride-through enhancement, and a modified pulsewidth-modulation switching algorithm for CMV elimination. Simulation and experimental results are supplied to confirm the validity of the proposed method, which includes full digital signal processor control.

Abstract: We propose a circuit for generation of modified Hermite polynomial functions for use in impulse radio communications. Simultaneous generation of pulses of differing order is developed, reducing circuit complexity. Pulses are produced by applying modifications to Hermite polynomials. Pulses have the properties of orthogonality and not changing their pulse width and pulse bandwidth significantly dependent on pulse order, or under the differentiation effect of the transmitter or receiver antenna. The usefulness of these pulses applied to a multi-user system by orthogonal pulse modulation is shown by comparison with conventional pulse position modulation by computer simulation.

Abstract: The main goal of the paper is to perform a complete analysis and a comparative study of different digital pulsewidth modulation (PWM) techniques for dual three-phase induction machine drives. Six different digital PWM strategies are considered: four of them are present in the literature, the other two have been introduced by the authors in this paper. The comparison between the modulation strategies is based on several criteria: current harmonic minimisation, hardware and software implementation complexity with low cost fixed-point DSP platforms. Simulation results are provided to emphasize the advantages and disadvantages of each method. Experimental tests have been carried out to validate the most promising strategy which gives satisfactory results in terms of current harmonic minimisation and low implementation complexity.

Abstract: Electrolytic capacitors are used in nearly all adjustable-speed drives, and they are one of the components most prone to failure. The main failure mechanisms include loss of electrolyte through outgassing and chemical changes to the electrolyte and oxide layer. All the degradation mechanisms are exacerbated by ripple current heating. Since the equivalent series resistance of electrolytic capacitors is a very strong function of frequency it must be properly modeled to accurately calculate the power loss. In this paper, a method to reduce the ripple current in a constant Volts/Hertz pulse-amplitude-modulation (PAM)/pulsewidth-modulation (PWM) converter driving an induction motor is investigated. The dc-bus voltage amplitude is reduced in proportion to speed by a buck or current stiff rectifier and the PWM modulation index is maintained at a high level to achieve a reduced ripple current below base speed. By comparison with a diode-bridge-fed PWM voltage stiff inverter, it is shown that the PAM/PWM mode of operation can lead to a significant reduction in capacitor power loss leading to increased capacitor lifetime or decreased capacitor size. The capacitor heating is analyzed using numerical and analytical techniques. Experimental results are provided to verify the analytical results.

Abstract: A sequential burst mode regulation system to deliver power to a plurality of loads. In the exemplary embodiments, the system of the present invention generates a plurality of phased pulse width modulated signals from a single pulse width modulated signal, where each of the phased signals regulates power to a respective load. Exemplary circuitry includes a PWM signal generator, and a phase delay array that receives a PWM signal and generates a plurality of phased PWM signals which are used to regulate power to respective loads. A frequency selector circuit can be provided that sets the frequency of the PWM signal using a fixed or variable frequency reference signal.

Abstract: Pole-phase modulation adjusts the pole-phase ratio of an induction machine and requires a multileg, multiphase inverter. This paper analyzes an n-leg, n-phase inverter, and presents techniques for n-phase space vector pulse width modulation (SVPWM). In particular, nine-phase SVPWM is developed and implemented on a nine winding induction machine. The nine-phase SVPWM is compared to nine phase sine-triangle PWM in terms of DC bus utilization.

Abstract: A novel zero-voltage and zero-current-switching (ZVZCS) full-bridge pulse-width-modulated (PWM) converter is proposed to improve the previously proposed ZVZCS full-bridge PWM converters. By employing a simple auxiliary circuit with neither lossy components nor active switches, soft-switching of the primary switches is achieved. The proposed converter has many advantages such as simple auxiliary circuit, high efficiency, low voltage stress of the rectifier diode and self-adjustment of the circulating current, which make the proposed converter attractive for the high voltage and high power applications. The principles of operation and design considerations are presented and verified on the 4 kW experimental converter operating at 80 kHz.

Abstract: Method and apparatus for implementing ultrasonic systems that maximize efficiency by dynamically detecting and maintaining peak operational resonance frequency. In one embodiment, the invention dynamically sweeps the output frequency range to locate the peak load current. The resonance frequency corresponding to the peak load current is used as a reference frequency in a control loop. The control loop includes a voltage-controlled oscillator (VCO) that is controlled by a loop controller and operates to lock onto the dynamically sensed reference frequency. In response to the VCO output, a pulse-width modulator (PWM) circuit drives a pair of switches that adjust transducer current to maintain the circuit locked on the resonance frequency at a substantially constant current.

Abstract: In this paper, a novel control scheme of three-phase PWM rectifiers eliminating both the AC input voltage and current sensors is proposed. The phase angle and the magnitude of the source voltage are estimated by controlling the deviation between the rectifier current and its model current to be zero. The input currents can be reconstructed from switching states of the PWM rectifier and the measured DC link currents. To eliminate the calculation time delay effect of the microprocessor, the currents ahead one sampling period are estimated by a state observer and then are used for feedback control. The proposed control scheme reduces the system cost and improves its reliability. The feasibility of the proposed AC sensorless technique for three-phase PWM rectifiers has been verified through experiments using a high performance DSP chip.

Abstract: A pulse width modulator (PWM) audio power amplifier (10) with a switch mode power converter (206) is provided that may adjust the duty of the switch mode power converter (206) based on output current. The PWM audio power amplifier (10) may include a digital signal processor (18) to process an input signal and control the switch mode power converter (206) to minimize distortion in an amplified output signal. The control within the PWM audio power amplifier (10) may include digital feed forward open loop control or may combine digital feed forward open loop control with analog negative feedback closed loop control to minimize distortion in the output signal.

Abstract: Two synchronized bus-clamping pulse width modulation (PWM) strategies based on the space vector approach are proposed for high-power induction motor drives. The two strategies together can produce PWM waveforms with any odd pulse number, preserving the waveform symmetries. The proposed strategies operate upto the six-step mode, maintaining the proportionality between the reference magnitude and the fundamental voltage generated throughout. These two strategies lead to lesser harmonic distortion as well as lesser peak current over the conventional space vector strategy (CSVS) in the high speed ranges of constant V/F drives. The reduction in the harmonic distortion over CSVS subject to a given maximum switching frequency (F/sub SW(MAX)/) of the inverter is demonstrated theoretically as well as experimentally for F/sub SW(MAX)/=750 Hz and 450 Hz, both with and without overmodulation. The best reduction in the distortion is as high as 30% to 50% in the different cases considered. Further, these two PWM strategies are also useful in reducing the switching frequency of the inverter over sine-triangle PWM and CSVS subject to an upper limit on the harmonic distortion.

Abstract: A novel method for accurate calculation of power spectra of the pulsewidth modulation (PWM) voltage-source inverter with randomized switching frequency is presented. The case of a limited pool of switching frequencies, convenient and adequate for technical purposes, is considered, and a mathematical background for this type of random PWM (RPWM) is provided. It is shown that the limited-pool RPWM gives rise to not only a continuous spectrum, but, also, under certain circumstances, pure power spectral components (harmonics), typical for the deterministic PWM. Criteria for the existence of harmonics are given, and formulae for both the power and the power spectral density are derived and verified experimentally.

Abstract: This paper proposes a new control scheme for regulating the instantaneous power for PWM AC/DC type rectifiers under generalized unbalanced operating conditions. By nullifying the oscillating components of instantaneous power at the poles of the converter instead of the front-end through solving a set of nonlinear control equations in real time, the harmonics in the output DC voltage can be eliminated more effectively under generalized unbalanced operating conditions on the AC input side. The control scheme allows the PWM rectifier to generate a DC output without substantial even-order harmonics and to maintain nearly unity power factor under generalized unbalanced operating conditions, which makes it possible to reduce the size of the DC-link capacitor and AC inductors leading to the possibility of reduced total cost. Simulation results along with experimental results under the two examples of the unbalanced operating conditions confirm the feasibility of the new control method.

Abstract: This paper investigates the use of a three-leg voltage source inverter topology for supplying two-phase induction motors. The paper also presents two pulse width modulation techniques for voltage control and a quasi time-invariant model to describe an unbalanced two-phase machine. The correctness of the proposed drive system was demonstrated through experimental results obtained with a laboratory prototype.

Abstract: This paper presents an analytical approach for determining the spectral components of multilevel pulsewidth modulation (PWM) strategies, which avoids the problems of spectral leakage, roundoff, and subtle programming errors associated with the more usual approach of using discrete Fourier transforms of simulated switched waveforms. The approach uses a double Fourier integral formulation to analyze the inverter switched output, establishing the inner and outer integral limits of this formulation under conditions of natural sampling, regular sampling, and overmodulation. Closed-form and numerical integration solutions are presented for phase disposition PWM of a diode-clamped inverter to illustrate the technique, together with a comparison of theoretical and experimental spectral results for the naturally and asymmetric regularly sampled cases to confirm the validity of the approach.

Abstract: A benchmark system for studying the sinusoidal pulse-width-modulated distribution-static synchronous compensator (D-STATCOM) is proposed. A simple multifunction controller is provided to offer DC bus voltage control, power factor correction, and AC voltage control. Simulation results are presented and compared to experimental results obtained from a 10 kVA laboratory D-STATCOM. Excellent agreement between simulation and experimental results is obtained, validating the simulation output.

Abstract: A disk drive is disclosed comprising a spindle motor for rotating a disk, wherein the current applied to the spindle motor is controlled by adjusting a duty cycle of a pulse width modulated (PWM) signal. A current sensor generates a current sense signal representing a current flowing from a supply voltage. The current sense signal is integrated to generate an integration signal. The integration signal is compared to a threshold, and the result of the comparison is used to adjust the duty cycle of the PWM signal. In this manner the disk drive draws essentially constant average input current from the supply voltage which decreases the spin up time of the disk.

Abstract: The dual two level inverter fed open-end winding induction motor drive gives voltage space phasor locations similar to a three-level inverter fed induction motor drive. The dual inverter scheme renders advantages such as redundancy of the space vector combinations for the same number of space vector locations and the absence of neutral point fluctuations. In a dual inverter scheme, a total of 64 space vector combinations are distributed over 19 space vector locations compared to 27 space vector combinations distributed over the same number of locations in a three level inverter. The common mode voltages (the harmonics of the triplen order) need to be suppressed by transformer isolation or by the use of harmonic filters. In this paper, a space vector modulation scheme for the suppression of zero sequence currents (the harmonics of the triplen order) for a dual two level inverter fed open-end winding induction motor drive is described. The proposed scheme does not require bulky transformers or harmonic filters for the elimination of the zero sequence currents. The proposed space vector PWM is based on the observation that certain voltage space vector combinations in the dual inverter scheme do not contribute to the triplen harmonics and hence the PWM scheme that exclusively employs these combinations is used to eliminate the triplen harmonic currents

Abstract: A diffractive optical MEMS device for spatial and temporal light modulation is described that is capable of high-speed digital operation. The device contains electromechanical ribbons suspended flat above a silicon substrate by a periodic series of intermediate supports. When actuated electrostatically, the ribbons conform around the support substructure to produce a grating. The device has optical switching times of less than 50 nsec, sub-nanosecond jitter, high optical contrast and efficiency, and reliable actuation in contact mode. The fine gray levels needed for digital imaging systems are produced by pulse width modulation.

Abstract: Passive filters are conventionally used to suppress overvoltage in the motor terminal, either by reducing the voltage rise rate at the inverter output, or by decreasing the motor terminal impedance. We propose an overvoltage suppression scheme that renders the use of passive filters unnecessary. This approach differs from general filter methods, in that it is independent,of d/spl upsi//dt and does not try to reduce d/spl upsi//dt. Our scheme utilizes the middle voltage level V/sub DC//2 at each pulsewidth modulation voltage transition, where V/sub DC/ represents the DC-link voltage. The duration of the middle voltage level is controlled in such a way that reflected voltages are cancelled out at the motor terminal. Optimal cancellation is achieved when the duration of V/sub DC//2 is equal to twice the transport delay of the cable. Further, if reflection coefficients at the motor terminal and the inverter output are equal to /spl plusmn/1, no overvoltage takes place. The proposed scheme requires the use of six auxiliary insulated gate bipolar transistor switches. Simulation as well as experimental results are presented here.

Abstract: The performance and dynamic characteristics of a three-phase parallel active power filter (APF) with point of the common coupling (PCC) voltage compensation with consideration for an unbalanced load is presented and analyzed in this paper. The proposed scheme employs a pulse-width modulation (PWM) voltage-source inverter and has two operation modes. First, it operates as a conventional active filter with reactive power compensation when PCC voltage is within the 15% voltage drop range. Second, it operates as a voltage compensator when PCC voltage is not within the 15% voltage drop range. Both the APF and the voltage compensator compensate asymmetries caused by nonlinear loads. Finally, the validity of this scheme is investigated through the analysis of simulation and experimental results for a prototype APF system rated at 10 kVA.