Showing papers on "Pulse-width modulation published in 2002"

Multilevel inverters: a survey of topologies, controls, and applications

Abstract: Multilevel inverter technology has emerged recently as a very important alternative in the area of high-power medium-voltage energy control. This paper presents the most important topologies like diode-clamped inverter (neutral-point clamped), capacitor-clamped (flying capacitor), and cascaded multicell with separate DC sources. Emerging topologies like asymmetric hybrid cells and soft-switched multilevel inverters are also discussed. This paper also presents the most relevant control and modulation methods developed for this family of converters: multilevel sinusoidal pulsewidth modulation, multilevel selective harmonic elimination, and space-vector modulation. Special attention is dedicated to the latest and more relevant applications of these converters such as laminators, conveyor belts, and unified power-flow controllers. The need of an active front end at the input side for those inverters supplying regenerative loads is also discussed, and the circuit topology options are also presented. Finally, the peripherally developing areas such as high-voltage high-power devices and optical sensors and other opportunities for future development are addressed.

Multicarrier PWM strategies for multilevel inverters

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.

Relationship between space-vector modulation and three-phase carrier-based PWM: a comprehensive analysis [three-phase inverters]

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.

Control in Power Electronics: selected problems

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

Digital field oriented control for dual three-phase induction motor drives

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.

LED driver circuit with PWM output

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.

Monocycle shapes for ultra wideband system

Abstract: Ultra wideband (UWB) is a promising technique for wireless communications. It is a carrier-free (base-band) technique, which can greatly reduce the complexity and cost of the transceiver. In contrast with conventional communication systems using the "sine wave", UWB information is carried in a very short pulse, which covers an extremely wide spectrum bandwidth. Several candidate monocycle (narrow pulse) shapes are investigated, their spectrum characteristics and BER performance in AWGN using pulse position modulation (PPM) are simulated, and the results are compared. Their performances in the fading multipath channel are also investigated.

A vector control technique for medium-voltage multilevel inverters

Abstract: This paper presents a switching strategy for multilevel cascade inverters, based on the space-vector theory. The proposed switching strategy generates a voltage vector with very low harmonic distortion and reduced switching frequency. This new control method is an attractive alternative to the classic multilevel pulsewidth modulation techniques considering the following aspects: (1) voltage and current total harmonic distortion; (2) range of linear operation; and (3) number of commutations.

Performance improvement of the dynamic voltage restorer with closed-loop load voltage and current-mode control

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.

New feedforward space-vector PWM method to obtain balanced AC output voltages in a three-level neutral-point-clamped converter

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.

Ultracapacitors + DC-DC converters in regenerative braking system

Abstract: An ultracapacitor system for an electric vehicle has been implemented. The device allows higher accelerations and decelerations of the vehicle with minimal loss of energy and minimal degradation of the main battery pack. The system uses a DC-DC power converter, which is connected between the ultracapacitor and the main battery pack. The design has been optimized in weight and size, by using water-cooled heat sinks for the power converter, and an aluminum coil with air core for the smoothing inductance. The ratings of the ultracapacitor are: nominal voltage: 300 Vdc; nominal current: 200 Adc; capacitance: 20 Farads. The amount of energy stored allows us to have 40 kW of power during 20 seconds, which is enough to accelerate the vehicle without the help of the traction batteries. The vehicle uses a brushless DC motor with a nominal power of 32 kW and a peak power of 53 kW. A control system based on a Digital Signal Processor (DSP) manipulates all the aforementioned variables and controls the Pulse Width Modulation (PWM) switching pattern of the converter transistors. The car used for the implementation of this system is a Chevrolet LUV truck.

Multiple pulse generator for ultra-wideband communication using Hermite polynomial based orthogonal pulses

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.

UPS inverter design using discrete-time sliding-mode control scheme

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.

A multilevel inverter approach providing DC-link balancing, ride-through enhancement, and common-mode voltage elimination

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.

Sequential burst mode activation circuit

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.

A comparative study of carrier-frequency modulation techniques for conducted EMI suppression in PWM converters

Abstract: A rigorous mathematical analysis and a comparative study of carrier-frequency modulation (CFM) techniques for the conducted electromagnetic interference (EMI) suppression in pulsewidth-modulated converters is presented. CFM techniques dither the switching period with a small amplitude variation around the nominal value, so that the harmonic power is redistributed over the spectrum of concern. Two types of dithering signals, including the periodic and random signals, are investigated in this paper. The operational characteristics as well as the input and output power spectra of the converters with the two modulating signals are compared. In particular, their characteristics in the low- and high-frequency harmonic power redistribution will be depicted. It is shown that random CFM (RCFM) gives a more effective way to disperse the harmonics around the switching frequency than the periodic CFM (PCFM) with the same frequency deviation. However, RCFM introduces higher low-frequency harmonics than the PCFM at the converter output. Furthermore, effects of the resolution filter bandwidth in the electromagnetic compatibility analyzer on conducted EMI measurement is discussed. The validity of the analyses is confirmed experimentally by using a dc/dc buck converter operating in continuous conduction mode.

Space Vector PWM Control of Dual Inverter Fed Open-End Winding Induction Motor Drive

Abstract: The technique of space vector PWM control of dual voltage source inverter fed three phase open-end winding induction motor is presented in this paper. A space vector PWM technique is developed based on the combination of space vectors from dual inverters feeding the induction motor from both ends (open-end winding without neutral point). A total of 64 voltage space vector combinations are available for PWM voltage control of the inverter fed machine with open-end winding A space phasor based PWM scheme is proposed with minimum number of switching in a cycle per inverter coupled with equal number of switching for each inverter. All the voltage space vector combinations are utilized for generating the reference voltage vector to cover the entire speed range. The open-end winding structure can have significant third harmonic currents unless suitable third harmonic filters are used to suppress it. The third harmonic currents are suppressed by using isolated transformers for both inverters.

Multiphase space vector pulse width modulation

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.

Method and apparatus for controlling ultrasonic transducer

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.

Complete analysis and comparative study of digital modulation techniques for dual three-phase AC motor drives

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.

A Novel UWB Pulse Shape Modulation System

Abstract: In this paper novel modified Hermite polynomial functions for use in impulse radio (ultra-wideband) communications are proposed. With these functions pulse shapes which are orthogonal and have nearly constant pulse width regardless of the pulse order are generated. These properties hold under the effects of differentiation. An M-ary communication system is constructed using these pulse shapes. A Matlab model for generating the pulses is designed and the effect of timing jitter on the performance of the system is investigated by computer simulation.

Compensated synchronous PI current controller in overmodulation range and six-step operation of space-vector-modulation-based vector-controlled drives

Abstract: Overmodulation enhances the power utilization of the installed capacity of a voltage-source inverter. A space-vector strategy is used for constant-switching-frequency inverters. In order to achieve the overmodulation, a modified reference signal with nonuniform angular velocity is generated using a preprocessor. Such a reference wave produces low-frequency harmonics in currents. The presence of current harmonics restricts the bandwidth of the synchronous proportional plus integral current controller in the overmodulation range. A compensating current control is presented to allow for high-bandwidth current control in synchronous coordinates during overmodulation and six-step. The proposed scheme allows for an easy upgrade of a conventional vector control scheme to include overmodulation and, thus, reduce the design-to-market time.

Novel zero-voltage and zero-current-switching (ZVZCS) full-bridge PWM converter using coupled output inductor

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.

Reduction of DC bus capacitor ripple current with PAM/PWM converter

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.

Digital signal processor enhanced pulse width modulation amplifier

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.

AC voltage and current sensorless control of three-phase PWM rectifiers

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.

Two novel synchronized bus-clamping PWM strategies based on space vector approach for high power drives

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.

Decreasing spin up time in a disk drive by adjusting a duty cycle of a spindle motor PWM signal to maintain constant average input current

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.

A nonlinear control of the instantaneous power in dq synchronous frame for PWM AC/DC converter under generalized unbalanced operating conditions

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.

Analysis of power and power spectral density in PWM inverters with randomized switching frequency

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.