Abstract: Principles of operation 1 - threshold voltage principles of operation 2 - static characteristics principles of operation 3: transient and high-frequency behavior fabrication and reliability dissipation and heatsink design parallel and series operation gate drive circuits the power MOSFET as a switch automotive applications power supplies motor drives PWM inverters high-frequency applications linear applications MOSFETs and bipolar transistors packaging, testing, reliability and handling modeling power MOSFETs special-purpose MOSFETs other MOS power devices

Abstract: Acoustic noise in an inverter-driven AC electric machine can be reduced by avoiding the concentration of harmonic energy in distinct tones. One method to spread out the harmonic spectrum without the use of programmed PWM (pulse-width modulation) is to cause the switching pattern to be random. It is proposed that the switching pattern can be randomized by modulating the triangle carrier in sinusoidal PWM (pulse-width modulation) with bandlimited white noise. All the advantages of sinusoidal PWM are preserved with this technique. These include real-time control, linear operation, good transient response, and a constant average switching frequency. By controlling the bandwidth and RMS value of the pink noise modulation, it is shown that the instantaneous variation in switching frequency as well as the bandwidth of the energy spectrum in the machine can be specified within predetermined limits. Experimental results show the absence of acoustic noise concentrated at specific tones which is present with conventional sinusoidal modulation. >

Abstract: Multiple pulse position modulation (MPPM) is proposed as a modulation method to improve the band-utilization efficiency in optical pulse position modulation (PPM). Optical PPM gives higher transmission efficiency (bit/photon) in optical communications but degrades band-utilization efficiency. The proposed method reduces the required transmission bandwidth in optical PPM to about half with the same transmission efficiency, thus increasing band-utilization efficiency. While in conventional optical PPM, only one optical pulse is transmitted in every signal block, multiple pulses are transmitted using this method. Information is represented by different combinations of the positions of these pulses. The principle of bandwidth reduction applied, the transmission characteristics of the proposed method, and examples of improvement in band-utilization efficiency are also shown. >

Abstract: It is well known that a PWM-controlled rectifier can offer advantages of reduced low-order harmonics and unity input power factor when compared to a conventional thyristor converter. However, theoretically optimum PWM strategies are often difficult to implement physically or are not easily extended to regenerative operation. The authors propose an alternative PWM strategy based on AC-AC matrix converter theory, which generates only high-order switching harmonics, presents a unity power factor load to the supply, implicitly extends to regeneration (and operation with a center tapped DC output), and is feasible to physically implement for real-time output voltage control. Both the theory and physical simulation results are presented. >

Abstract: A buck pulsewidth modulated zero-current switching quasi-resonant converter (buck PWM ZCS QRC) operating at constant frequency is discussed. Operating principle and design-oriented analysis are presented with normalized design curves, design procedure, design example, simulations, and experimental results. The new topology, which can be considered as a particular one, is compared with the well-established buck frequency-modulated zero-current switching quasi-resonant converter (buck FM ZCS QRC) proposed by Fred C. Lee (1988). >

Abstract: Rectifier control schemes for use in AC-DC-AC voltage-sourced resonant link converters with controlled rectifiers are discussed. Resonant link converters require the use of discrete pulse modulation. Control of the AC-to-DC converter by means of averaging methods or duty-cycle control is not inherent with this type of modulation. However, it is shown that the voltage-sourced rectifier cannot be operated solely on the basis of instantaneous quantities. A bang-bang control scheme is developed which independently controls the angle and the magnitude of the AC line current vector. The magnitude of the current is controlled using a linear combination of the link voltage error and the current magnitude error. The current reference is derived by the use of load torque estimation. In addition, the current vector that satisfies the sliding-mode criteria and results in the lowest voltage ripple is chosen to further minimize the size of the link capacitor. >

Abstract: The nonlinear switching mechanism in pulsewidth-modulated (PWM) and quasi-resonant converters is that of a three-terminal switching device which consists only of an active and a passive switch. An equivalent circuit model of this switching device describing the perturbations in the average terminal voltages and current is obtained. Through the use of this circuit model the analysis of pulsewidth modulated and quasiresonant converters becomes analogous to transistor circuit analysis where the transistor is replaced by its equivalent circuit model. The conversion ratio characteristics of various resonant converters and their relationship to a single function, called the quasi-resonant function, is easily obtained using the circuit model for the three-terminal switching device. The small-signal response of quasi-resonant converters to perturbations in the switching frequency and input voltage is determined by replacing the three-terminal switching device by its small-signal equivalent circuit model. >

Abstract: A boost convertor power supply comprising an electronic switch controlling current through a boost inductance, rectifier means for charging capacitor means which accumulate the resulting boost charge from the boost inductance, and means for repeatedly switching the electronic switch. Pulse width modulation means vary the relative on/off period of each cycle of switching to cause the peak switch current to follow a variable amplitude wave of shape corresponding to the input voltage applied to the boost convertor and amplitude controlled by an error amplifier and multiplier thereby regulating the output voltage. A ramp signal generator provides for pulse width stability. Means correct for the difference between average current in the boost inductor and peak switch current to modify the pulse width modulation means to reduce distortion of the line current waveform.

Abstract: High dynamic performance of pulse-width-modulated (PWM) inverter-fed induction motor drives was achieved by using the method of field-oriented control. This method requires the actual value of the rotor time constant as essential system information, based on how the magnitude and the position of the rotor flux are calculated. An online identification technique for the rotor time constant and for other machine parameters is described. The identification is based on an evaluation of the stator current trajectory, which is the dynamic response of the induction motor to the PWM-switching sequence. An analytical machine model is operated in parallel to the actual machine, having the stator voltages and the mechanical speed of the induction motor as input signals. The coincidence of the two stator current trajectories of the model and the machine serves as an error indicator for the parameter identification scheme, permitting repetitive updates of the model parameters. >

Abstract: A pulse-width-modulated (PWM) high-frequency link series-parallel resonant converter operating with fixed frequency is proposed. A simple analysis and design procedure are presented. The proposed configuration has a number of desirable features, such as high efficiency for very wide load variations with a narrow range of duty-cycle ratio control, and load short-circuit capability. Detailed experimental results obtained from a 48 V output, 500 W experimental converter are presented to verify the concept. >

Abstract: A three-phase synchronous solid-state VAr compensator (SSVC) system that uses a three-phase pulsewidth-modulated (PWM) voltage-source inverter is presented and analyzed. The proposed SSVC system can compensate for leading and lagging displacement power factor. Pulsewidth modulation is used as a means of reducing the size of reactive components. The SSVC system is analyzed under self- and independently-controlled DC bus voltage operating conditions. Other areas of investigation include the design of SSVC filter components for both approaches and the closing of the loop around the reactive power command signal. Predicted results are verified experimentally for the case of the SSVC working with a self-controlled DC bus. >

Abstract: A pulse-width modulation (PWM) control technique for forced commutated cycloconverters is presented. The technique is based on the space vector representation of the voltages in the complex plane. It is shown that with the allowable switching combinations, six output voltage space vectors with varying amplitudes can be obtained, in addition to the zero vector. The variation is compensated by adapting the standard modulation technique. The technique permits space vector synthesis of a three-phase, nonsymmetrical, nonsinusoidal output voltage, even under non-steady-state conditions, which is essential for the control of AC servo drives. A detailed explanation of the modulator principles and the switch control as well as simulation results for the time- and frequency domain analysis is given. The results are compared with the results obtained using the standard modulation technique. A possible microprocessor implementation of the modulator is also proposed. >

Abstract: The authors discuss a number of issues involved in designing a current source inverter system for a large induction motor drive. Using two modulation techniques-selected harmonic elimination in the upper frequency range and trapezoidal modulation in the lower frequency range-control of voltage, current, and torque harmonics is achieved while limiting the GTO switching frequency to 180 Hz. Each modulation range is divided into a number of subranges to exploit the available switching capacity and to avoid harmonic resonances involving the capacitor and the motor inductance. In addition to the development of basic principles, the authors include simulation waveforms and test results from a laboratory experimental system. >

Abstract: Different strategies for series and parallel connections of hysteresis current-controlled PWM rectifier have been investigated by experiments, computer simulations, and analyses. Each rectifier unit delivers near-sinusoidal current waveforms at unity (or even leading) power factor. Of particular concern are the questions of: (i) system stability; (ii) the capability of the modular units to share voltage (series connection) and current (parallel connection) under steady-state and transient operation; and (iii) sensitivity of performance characteristics to component tolerances. Experiments were made on 1 kW bipolar transistor modular units. Two configurations, having independent local control (type A) and common switching control (type B), respectively, were studied. The study shows that type B is more economical than type A and appears to give a satisfactory performance. >

Abstract: A parallel-resonant DC link (PRDCL) circuit topology is presented as a way to realizing zero-switching-loss, DC-AC high switching frequency power conversion. The circuit is used as an interface between DC voltage supply and the voltage-source PWM (pulse-width-modulated) inverter. It provides a short zero-voltage period in the DC link of the inverter to allow zero-voltage switching to take place in the PWM inverter. The peak voltage stress on the PWM inverter switches is limited to the DC supply voltage. Another significant advantage of the proposed circuit is that the inverter can be controlled by the conventional PWM strategy. The circuit is systematically analyzed, and its operation principle is explained in detail. Design considerations and formulae are also presented. A complete zero-voltage-switching DC-AC converter system consisting of the proposed circuit and the PWM inverter is simulated on computer. >

Abstract: High-performance, high-frequency inverter systems for UPS (uninterruptible power system) applications cannot be easily realized using conventional hard-switched PWM inverter topologies. Adoption of typical soft-switched inverters such as the resonant DC link inverter, require the use of discrete pulse modulation strategies. New controller structures are necessary to cope with stringent voltage regulation and distortion constraints in the presence of unbalanced and nonlinear loads. A controller that utilizes a load current feedforward strategy with a cost function current regulator to achieve excellent transient performance characteristics is presented. Voltage regulation is ensured using a synchronous frame regulator. Detailed simulation and experimental results verifying the concepts are presented. Although this work focuses on soft-switching inverters, the control concepts can be applied to conventional hard-switching inverters as well. >

Abstract: In a switch mode power supply, a first switching transistor is coupled to a primary winding of a transformer for generating pulses of a switching current. A secondary winding of the transformer is coupled via a switching diode to a capacitor of a control circuit for developing a control signal in the capacitor. The control signal is applied to a mains coupled chopper second transistor for generating and regulating supply voltages in accordance with pulse width modulation of the control signal. During standby operation, the first and second transistors operate in a burst mode that is repetitive at a frequency of the AC mains supply voltage such as 50 Hz. In the burst mode operation, during intervals in which pulses of the switching current occur, the pulse width and peak amplitude of the switching current pulses progressively increase in accordance with the waveform of the mains supply voltage to provide a soft start operation in the standby mode of operation within each burst group.

Abstract: The authors present an analytical technique by which the on-state losses in the devices in a PWM inverter may be calculated. The authors take the regular type of symmetrical double-edge sinusoidal modulation, assume that the load current is sinusoidal, and show that the inherent Bessel Function solution can be reduced to a simple algebraic form when the frequency ratio is greater than about ten. It is assumed that the on-state voltage drop across an active device and a free-wheel diode is made up of a constant component plus a component that is linearly dependent upon current. The results are, therefore, applicable to most semiconductor devices. Experimental results are presented and are shown to be in good agreement with predictions.

Abstract: A description is given of a highly stable, triple-integration two-stage noise-shaping technique and a precise differential pulse-width modulation (PWM) output method which permits greater accuracy in monolithic audio digital-to-analog (D-to-A) converters (DACs) without trimming. Based on these techniques and using 1.5 mu m CMOS technology, a 17 bit 20 kHz bandwidth DAC LSI chip with digital filters was developed. A signal-to-noise ratio (S/(N+THD)) of 101 dB and a total harmonic distortion (THD) of 0.0007% at full-scale input were obtained. >

Abstract: A novel concept for a static three-phase to three-phase power converter for an AC drive with a unity power factor and reduced harmonics on the line side is presented. The power circuit comprises two back-to-back connected six-pulse bridges having no energy storage elements in the DC link. This permits pulse-width modulation (PWM) control in both bridges while requiring active turn-off semiconductor switches in only one bridge. The line-side harmonics are suppressed by a three-phase second-order filter. The method of predictive optimization is used for the control of the power converter. The complex control structure of the system is based on an online prediction of space vector trajectories. The steady-state operation of the system is exemplified by simulation results. >

Abstract: A resonant DC link scheme for soft-switched inverters, where the link oscillation can be synchronized with inverter modulation, is proposed. The scheme is able to operate with reduced commutation losses at a high switching frequency. Synchronization capability allows development of suitable modulation techniques that ensure improved waveform accuracy. The system performance and control strategies were verified by simulation and by experimental tests, and the interesting features of the proposed scheme were confirmed. >

Abstract: Two schemes for controlling the motor currents in PWM (pulse-width-modulated) inverters in synchronous motor drives are considered: hysteresis control and predictive control. It is pointed out that the system static and dynamic performance can be improved by selecting the control mode in an adaptive manner according to the operating conditions. In steady state, the predictive mode is selected to reduce current ripple and to obtain stable switching frequency. During large transients, such as during starting or load variations, the hysteresis mode is selected to provide fast response. The performance of the proposed controls scheme has been studied by simulation, and the results agree well with the prediction. This adaptive control scheme can be implemented using a high-performance 16-bit microcontroller supported by a mathematical coprocessor. >

Abstract: In an AC to DC power conversion circuit including a boost inductor connected in series between a full-wave rectifier and a DC load, a switch is connected to selectively shunt boost inductor current from the load. Switch conduction is controlled by a pulse width modulator generating switching pulses at a high fixed frequency. The pulse widths are automatically varied as a function of boost inductor current, load voltage, and an ideal sinusoidal waveform derived from the AC input voltage to force the boost inductor current to closely conform to the ideal sinusoidal waveform and thus minimize harmonic distortion, while achieving load voltage regulation and near unity power factor.

Abstract: A balanced transformer-less pulse width modulation amplifier circuit has two filter coils wound on the same core with the same polarity relative to the output. The arrangement reduces the possibility of magnetic saturation of the core and permits the cutoff frequency to be within the audio range.

Abstract: A reactive power compensation (RPC) system which uses a three-phase current-source force-commutated PWM (pulsewidth-modulated) rectifier is presented and analyzed Pulsewidth modulation is also investigated as a means of reducing the size of reactive components The proposed RPC system can compensate for leading and lagging displacement power factor Other areas of investigation include the selection of rectifier input and output filter components and the closing of the loop around the reactive power command signal finally, predicted results are verified experimentally >

Abstract: An introductory tutorial on chaotic behavior in DC-DC convertors is presented. Chaos is characterized by an emipirical spectrum which has a continuous component, and may even have no discrete components. Chaotic behavior frequently occurs when a power converter operates in a protective mode such as in a short-circuit or overload condition. Chaotic behavior in power converters is described in terms of phase-plane (state-space) trajectories. A description is given of a particular form of buck regulator circuit without PWM (pulse-width modulation) drive and without current sensing, i.e. a form of ripple-regulator. Simulation and experimental data for the circuit are presented and discussed. Two other similar circuits exhibiting chaotic behavior are also considered. >

Abstract: Harmonic elimination PWM strategies for voltage source inverter and current source inverter (VSI and CSI) drives have been developed using modified regular sampling techniques. These strategies can be generated online in real time using a simple microprocessor software algorithm and can be used over the complete voltage/frequency range of the drive up to and including the transition from PWM to quasi-square wave (QSW) operation. The implementation and generation of these techniques using the parallel processing INMOS transputer are discussed, and the concurrency programming ability of the transputer for PWM generation is emphasized. The implementation of the new PWM strategy can also be performed on any standard 8 or 16 b microprocessor using 4 or 1 timer implementations. Results from an experimental transputer-controlled PWM inverter drive are presented to demonstrate and confirm the special features of the new regular sampled harmonic elimination PWM control strategies. >

Abstract: The instability problems often experienced in PWM (pulsewidth modulation) inverter induction motor drive systems are discussed. Experimental results are presented on how the unstable regions and oscillating frequencies are dependent on dead time. It is noted that the experimental results can clarify the physical description of sources of the instability phenomena. It is shown that a switching-type inverter necessarily includes regenerative intervals. Its existence is the main source of unstable phenomena. It is also shown that a stable region can be determined by applying analytical results to a self-excited induction generator. >

Abstract: Topological constraints are obtained for pulse width-modulation (PWM) (under both continuous and discontinuous current modes) and quasi-PWM (including families of quasi-resonant and quasi-square wave) converters by identifying their three structures. Switching sequences of these converters and a classification of quasi-PWM power converters are presented. A dual circuit of an ideal diode and an ideal switch are proposed and used to obtain duals of the switching converters in one step. A procedure for the synthesis of quasi-PWM converters is presented. >