A true ZCZVT commutation cell for PWM converters

This paper introduces a true zero-current and zero-voltage transition (ZCZVT) commutation cell for DC-DC pulsewidth modulation (PWM) converters operating with an input voltage less than half the output voltage. It provides zero-current switching (ZCS) and zero-voltage switching (ZVS) simultaneously, at both turn on and turn off of the main switch and ZVS for the main diode. The proposed soft-switching technique is suitable for both minority and majority carrier semiconductor devices and can be implemented in several DC-DC PWM converters. The ZCZVT commutation cell is placed out of the power path, and, therefore, there are no voltage stresses on power semiconductor devices. The commutation cell consists of a few auxiliary devices, rated at low power, and it is only activated during the main switch commutations. The ZCZVT commutation cell, applied to a boost converter, has been analyzed theoretically and verified experimentally. A 1 kW boost converter operating at 40 kHz with an efficiency of 97.9% demonstrates the feasibility of the proposed commutation cell     

Improvements in estimating the spectra of random PWM waveforms

Accurate estimates of the power spectral density of random-pulse-width-modulated waveforms (RPWM) are essential in reducing the perceived acoustic emissions from modern motor control drives. It is shown that by refining the estimate of the autocorrelation function of the phase of the RPWM waveform about the origin, the resulting power spectral density is greatly improved, giving excellent agreement with the observed spectrum.<>     

A new method of analysis for PWM switching power converters

A new method of analysis for pulse-width modulation (PWM) switching power converters is presented. It allows one to find an approximate periodic solution for the converter vector state variable. The converter is modelled by a differential equation with periodic coefficients. This equation is substituted by an equivalent system of linear differential equations with constant coefficients. Only the forced (steady-state) solutions should be found for each equation of this system. The equations are solved in sequence. The final steady-state solution of the PWM differential equation is obtained as the sum of these forced solutions. The method allows one to find the converter dc transfer function and efficiency, to evaluate their frequency dependences, and to find the critical frequency and ripple. The first three equations of the equivalent system are usually adequate for practical purposes, and these equations are obtained by an easy formal procedure. One can also obtain the dynamic equation of the state variable dc component, and calculate the converter line to output and duty cycle to output transfer functions. A boost converter is used as an example to confirm the analytical results by numerical simulation.     

A unified analysis of PWM converters in discontinuous modes

Three discontinuous operating modes of PWM (pulsewidth modulated) converters are considered: the discontinuous inductor current mode (DICM), the discontinuous capacitor voltage mode (DCVM), and a previously unidentified mode called the discontinuous quasi-resonant mode (DQRM). DC and small-signal AC analyses are applicable to all basic PWM converter topologies. Any particular topology is taken into account via its DC conversion ratio in the continuous conduction mode. The small-signal model is of the same order as the state-space averaged model for the continuous mode, and it offers improved predictions of the low-frequency dynamics of PWM converters in the discontinuous modes. It is shown that converters in discontinuous modes exhibit lossless damping similar to the effect of the current-mode programming     

A 3-D generalized direct PWM algorithm for multilevel converters

A three-dimensional (3-D) generalized direct pulse width modulation (PWM) algorithm is proposed for multilevel converters in a three-phase, four-wire system. It is proved to be equivalent to the newly proposed generalized 3-D space vector modulation (SVM). However, the direct PWM greatly simplifies the calculation process and is much easier to implement in digital controllers. The direct PWM can be used in all applications needing a 3-D control vector, such as active filters, uninterruptible power supplies, etc. Simulation and experimental results are given to show the validity of the proposed control strategy.     

A carrier-based PWM method for three-phase four-leg voltage source converters

In this paper a voltage modulation method based on a triangular carrier wave for the three-phase four-leg voltage source converter is described. The four-leg converter can produce three output voltages independently with one additional leg. The proposed modulation method for the four-leg converter can be implemented with a single carrier by a simple but useful "offset voltage" concept. The method is equivalent to the so called three-dimensional space vector PWM method, but its implementation is much easier. The maximum magnitude of the balanced three-phase voltage and the maximum magnitude of zero sequence voltage, which can be synthesized simultaneously, are derived. The feasibility of the proposed modulation technique is verified by computer simulation and experimental results. These results show that a proposed carrier-based pulsewidth modulation (PWM) technique can be easily implemented without conventional computational burden.     

A novel current-control method for three-phase PWM AC/DCvoltage-source converters

This paper presents a novel current-control-based control strategy, obtained in stationary frame, for a three-phase pulsewidth-modulated AC/DC voltage-source converter. In this control strategy, an error voltage is produced from the comparison of the output DC voltage with a DC reference voltage. This error voltage is then utilized by a proportional plus integral controller to generate a command signal for the input line current amplitude and is automatically controlled to the desired value. Therefore, there is no need to measure the input line currents. Stability analysis of the closed-loop system is made, and the stability region for proportional and integral gains which makes the operating point stable is also found. The resulting closed-loop system not only exhibits good transient response, but also provides sinusoidal line currents and unity power factor, both in the rectifying and regenerating modes. Experimental results are presented and compared with simulations     

A unified SPICE compatible average model of PWM converters

A simple, unified, and topology-independent model of basic pulse-width modulated (PWM) power converters is developed using the switched inductor approach presented by S. Ben-Yaakov (1989). The model is compatible with SPICE or other similar general-purpose electronic circuit simulators. It can be used to simulate DC, small signal, and transient behavior of PWM converters operating in both discontinuous conduction mode (DCM) and continuous conduction mode (CCM). During simulation, the model automatically follows the CCM and DCM operation, with fewer convergence problems compared to previous simulation models. An effective measurement technique using the HP3562A dynamic signal analyzer (DSA) is presented and applied to compare simulation runs with experimental data. The two were found to be in good agreement     

A COMPUTER-AIDED UNIFIED APPROACH TO MODELING PWM AND RESONANT CONVERTERS

This letter puts forward a method of modeling for the steady-state and small signal dynamic analysis on PWM, quasi-resonant and series/（parallel） resonant switching converters based on pulse-waveform integral approach. As an example, PWM and quasi-resonant converters are used to discuss the principle of the approach. The results are compared with those in the relative literatures. Computer aided analysis are made to confirm the correctness.     

A refined nonlinear averaged model for constant frequency currentmode controlled PWM converters

A refined, duo-mode model for current programmed buck power converters is presented. The refined model uses a form of the current mode control law which is truly invariant with respect to operating conditions. That is, it is valid for both transient and steady-state operating conditions regardless of the converter operating mode, which could be either continuous conduction mode (CCM) or discontinuous conduction mode (DCM). The large-signal transient response predicted using the refined average model is shown to be virtually indistinguishable, in an average sense, from that predicted using a pulse-by-pulse simulation. The refined model is shown to exhibit improved high-frequency accuracy in both time and frequency domains. The model has been implemented in SPICE 2G6 and runs with default analysis options     

A quasioptimal on-line control of AC/DC PWM converters

An approximate procedure for on-line computing the loss-optimal values of the switching angles in a class of pulse width modulated converters is presented. The proposed technique is independent of the constants of the circuit and allows one to obtain a given power in the DC load with minimum loss of energy in the AC and DC filters. This corresponds to have a quasisinusoidal supply current with minimum ripple on the output load. Simulation and experimental results confirm the practical feasibility of the method     

Analysis and passivity-based control of zero-voltage-transition PWM converters

A zero-voltage-transition pulse-width modulation (ZVT-PWM) converter composed of a conventional PWM circuit and a resonant tank to achieve zero-voltage switching, resulting in low voltage and current stresses and zero capacitive turn-on losses. In this paper, the analysis and passivity-based control of the ZVT-PWM buck converter are presented. A generalized state space average model of the ZVT-PWM buck converter is derived. The controller design is carried out using the derived model and follows the "energy shaping plus damping injection" ideas of the passivity-based approach. Both direct and indirect output voltage regulation schemes are addressed. Simulation results are presented to illustrate the features of the proposed controllers.     

A SPICE model for current mode PWM converters operating undercontinuous inductor current conditions

A SPICE simulation model of current-mode pulse-width modulation (PWM) converters operating in the continuous mode is described and tested against analytical expressions and experimental data for buck and boost converters. The simulation model is also used to compare an earlier average model to a recently suggested modification and to examine the effect of the gain factor in the current feedback path     

A comparison of nondeterministic and deterministic switchingmethods for DC-DC power converters

An analysis and experimental results of the random pulsewidth modulation (RPWM) and random pulse-position modulation (RPPM) methods for DC-DC converters are presented. The characteristics and performance of power converters under two randomized modulations are evaluated. The theoretical relationships of discrete harmonics, continuous noise, and output-voltage ripple of the RPWM and RPPM schemes are established and compared with those of a standard deterministic pulsewidth modulation (PWM) scheme in a buck converter. Limitations in the randomly switched DC-DC converters, which have not been addressed before, are highlighted. Randomized schemes generally have inherent problems in achieving low-output-voltage ripple due to the low-frequency continuous noise within the passband of the converter filter. The inherent low-frequency noise-induced voltage ripple problems of nondeterministic switching methods for DC converters are confirmed experimentally. The performance of the RPPM method is found to be closer to the standard PWM method than that of the RPWM method. For DC-DC power conversion, the RPPM method offers much better output-voltage performance than the RPWM method     

Averaged modeling of PWM converters operating in discontinuousconduction mode

Various aspects of averaged modeling of hard-switching pulse-width modulated (PWM) converters operating in the discontinuous conduction mode (DCM) are studied. A more streamlined modeling procedure is proposed which serves as a general framework for comparing different models. A duty ratio constraint that defines the diode conduction interval is identified to be the key to accurate prediction of high-frequency behavior. A new duty-ratio constraint is proposed that leads to full-order averaged models of DCM converters. Numerical analyses and experimental measurements confirm that the new models correctly predict the small-signal responses up to one third of the switching frequency and are more accurate than all previous models. Moreover, new analytical results are included to show the origin of the high-frequency pole in DCM operation and to explain why the full-order model is capable of accurately predicting it. Averaged circuit counterparts of the new models are developed in the form of averaged switch models to facilitate circuit simulation     

Modeling, control and implementation of three-phase PWM converters

Three-phase voltage- and current-source converters are the building blocks of a great number of power electronic systems. The origin of difficulties in the control of the above converters is in their nonlinear nature. In this paper, a novel modeling technique is introduced to derive the linear models of the converters from the nonlinear transformations of the conventional nonlinear models. Then, based on the derived linear models, a high-performance linear controller with satisfactory performances is designed. The bold feature of the new model is the independence of the controller design from the operating point. A DSP-based control system has been built in the lab to verify the performance of the new models and the control algorithm. The simulation and experimental results are in close agreement. The results show that the DC term and the AC-side reactive power can be controlled independently in less than one cycle.     

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

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     

A unified design criterion for ZVT DC-DC PWM converters with constant auxiliary Voltage source

This paper proposes a design criterion for calculating the resonant auxiliary elements of zero-voltage transition dc-dc pulsewidth-modulated (PWM) converters that use a dc auxiliary voltage source. The proposed criterion is based on stored energy in resonant auxiliary elements and takes into account the influence of the auxiliary voltage source value. Using this criterion, the reactive energy can be kept at a minimum level and a reduction of the auxiliary elements current ratings is achieved, which leads to lower conduction losses and improved converter efficiency. In addition, a reduction in size of auxiliary magnetic elements can be accomplished. To illustrate the usefulness of the proposed design criterion, the paper compares results obtained from the True-PWM Zero-Voltage Switching pole boost converter designed according to the proposed criterion, and from the original design guidelines. Experimental results show an efficiency gain of about 1% for a wide load range and 1.5% at full load. In addition, a reduction of about 52% in the auxiliary transformer volume for the implemented prototype was achieved, ensuring a reduction in overall converter size. Experimental results were obtained using a 1-kW 100-kHz laboratory prototype.     

A new family of zero-voltage-transition PWM converters with dual active auxiliary circuits

A new family of active auxiliary circuits that allow the power switch in single switch, pulsewidth modulated converters to operate with zero-voltage switching is proposed in this paper. The main feature of an auxiliary circuit belonging to this family is that the auxiliary switch can operate with a zero-current switching turn-on and turn-off without increasing the peak current stresses of the main switch. This is an improvement over previous proposed auxiliary circuits where either the auxiliary switch operates with a hard turn-off or the circuit itself increases the peak stresses of the main switch. In this paper, the fundamental principles behind the proposed family of active auxiliary circuits are explained. Based on these principles, an example auxiliary circuit is systematically derived and presented along with several other auxiliary circuits belonging to the new family. The operation of a boost converter operating with the example auxiliary circuit is discussed in detail, and general guidelines for the design and implementation of auxiliary circuits belonging to the new family are given. The feasibility of the example auxiliary circuit is confirmed by experimental results obtained from a 500-W, 100-kHz boost converter laboratory prototype.