Showing papers in "IEEE Transactions on Power Electronics in 1990"

Zero-voltage switching technique in DC/DC converters

Abstract: A novel resonant switch operating under the principle of zero-voltage switching is presented. The basic configurations of the voltage-mode resonant switches are presented. The circuit's operating principles are described using a voltage-mode quasi-resonant boost converter. DC analysis of the converter is carried out. A new family of voltage-mode quasi-resonant converters are derived, and several members of this family are presented. The duality relationship between the zero-current switching technique and the zero-voltage switching technique is derived. These two techniques are compared using an example showing the duality between a current-mode quasi-resonant Buck converter and a voltage-mode quasi-resonant boost converter. The similarities and differences of the voltage-mode quasi-resonant converters and the Class-E converters are discussed. A 5 MHz 50 V to 5 V flyback converter employing the zero-voltage switching technique has been implemented. Design considerations and experimental results of this circuit are presented. >

Dead beat control of three phase PWM inverter

Abstract: A novel method for microprocessor control of three-phase sinusoidal-voltage pulse-width-modulated (PWM) inverters is proposed. First, the discretized state equations of the inverter main circuit on the d-q frame are derived. An algorithm for dead beat control with a current minor loop that constrains the inverter current within the safety limit is subsequently developed. To compensate the computing time delay, a second-order prediction method and a novel discretization method using twice the time of the sampling period have been adopted. This method is especially suitable for inverters using high-speed switching devices and digital signal processors. The validity of the control system has been demonstrated by precise simulation using a hybrid computer. >

A study of active power filters using quad-series voltage-source PWM converters for harmonic compensation

Abstract: An active power filter using quad-series voltage-source pulse-width-modulated (PWM) converters to suppress AC harmonics by injecting compensating currents into the AC system is described. The circuit used to calculate the compensating current references, the compensation characteristics, and the capability of the DC capacitor are discussed theoretically and experimentally. A control circuit for the DC capacitor voltage is proposed. The discussions focus on transient states, based on the instantaneous reactive power theory. A passive LC filter is designed to remove the switching voltage and current ripples caused by the PWM converters at the AC side. Some experimental results that illustrate the details of the study are shown. >

Phasor transformation and its application to the DC/AC analyses of frequency phase-controlled series resonant converters (SRC)

Abstract: A novel modeling technique based on phasor transformation that provides a unified model of series resonant converters (SRCs) is proposed. The approach gives explicit and simple equations that provide fruitful physical insight. When the switching frequency deviates from the resonant frequency, a first-order SRC model is obtained, and in the case of resonance a second-order model is obtained. It is shown that the frequency band of the second-order model is very narrow in practice. The time constant, small-signal gains, and system order are highly dependent on the switching frequency, load resistor, and output capacitor. >

High-frequency measurement techniques for magnetic cores

Abstract: Conventional techniques and new techniques based on digitizing instruments for making high-frequency B-versus-H loop and core-loss measurements on magnetic cores are presented and compared. Potential sources of measurement errors and their magnitudes, limitations imposed by the instrumentation, and thermal considerations are discussed. Circuits suitable for high-frequency sine-wave or square-wave core excitation are also discussed. The utility of such measurements is illustrated with sample data. >

Control characteristics and speed controller design for a high performance permanent magnet synchronous motor drive

Abstract: The theory of vector control is applied to the nonlinear model of a permanent magnet synchronous motor to develop a linear model for controller design purposes. The operation and relevant mathematics of a pseudo-derivative feedback controller are presented. Controller designs for three different speeds are then considered, and a comparative evaluation is made on the basis of their large and small-signal behavior. In order to test the large-signal response, the detailed nonlinear model of the machine and a real-time model of the inverter switches are used. Results indicate that a critically damped design done so as to ensure that all control and power signals never saturate gives an extremely poor result. Much better small and large-signal responses are achieved by avoiding this constraint and using Zener diodes instead to limit the commanded input into the inverter. Two designs using this technique are presented, an underdamped design with low speed overshoot and an overdamped design with no speed overshoot. The response of the underdamped design was much quicker than that of the overdamped. However the overdamped design has application when speed overshoot is intolerable. >

Current phase control methods for permanent magnet synchronous motors

Abstract: Three types of current phase control methods are examined for the interior magnet motor and the surface magnet motor: (1) the i/sub d/=0 control method, (2) the cos phi =1 control method, and (3) the constant-flux-linkage control method. The control circuits for realizing these control methods were investigated and a drive test carried out. The most suitable current phase control method for the rotor geometry was examined by computer simulation and experimentation. It was found that in the i/sub d/=0 control method, high-performance torque control can be obtained as the torque is proportional to the armature current. In the cos phi =1 control method, the torque per armature current is small and the torque characteristic is nonlinear. Therefore, high-performance torque control cannot be expected. The constant-flux-linkage control method is desirable for interior magnet motors as the torque characteristic is almost linear and the required inverter capacity is comparatively small. >

Voltage angle lock loop control of the boost type PWM converter for HVDC application

Abstract: The advent of high-power, high-frequency, solid-state switches with fast gate turn-off capabilities suggests that pulse-width-modulated (PWM) techniques can soon be introduced into HVDC (high-voltage direct-current) applications. A boost-type PWM converter with voltage angle lock control that is tailored to the utility environment is described. Experimental test results for 1 kVA models show that the advantages are substantial. >

Delta modulation strategies for resonant link inverters

Abstract: The suitability of delta modulation strategies for resonant link inverters is explored in detail. The control and spectral characteristics of various delta modulators are examined in an effort to develop a model for the same. The more fundamental question of comparing delta modulation systems with conventional pulse-width-modulated (PWM) systems, given similar devices, is addressed, and it shown that the former provides a viable high-performance alternative. As the resonant DC link topology allows at least an order of magnitude increase in the switching frequency, Sigma Delta M systems using a given family of devices are capable of better spectral response than a conventional PWM inverter. >

Electrical terminal representation of conductor loss in transformers

Abstract: The formulation of a general, complete electrical terminal representation of eddy-current loss in transformer windings is presented. It is shown that the effects of mutual resistances must be considered in addition to the familiar winding resistances (self resistances) for a complete description of eddy-current loss. A simple two-foil winding structure is analyzed to display the features of the self- and mutual-resistance terms. The example illustrates that leakage resistance, i.e. resistance associated with opposing winding currents of equal amp turns, provides only a partial description of eddy-current loss. The analysis is extended to multiple windings, with a simple three-foil winding structure as an example. >

Diode forward and reverse recovery model for power electronic SPICE simulations

Abstract: A pn-diode micro-model representing forward and reverse recovery phenomena for power electronic simulation, especially simulations using SPICE2 is presented. The model is proposed to compensate the incompleteness of the diode model in current circuit simulation packages. In the forward recovery submodel, the diode bulk resistance modulation and its forward current dependence are included. In the reverse recovery submodel, the charge control equation for excess storage carriers is employed to simulate the detailed behavior. A procedure is described for extracting the model's physical parameters from data sheet information. The model is verified by a comparison of experimental results for several different tests with SPICE simulations. A discussion is given of extending the applicability of the micro-model to the simulation of p-i-n diode behaviour. >

Microprocessor based harmonic elimination in chopper type AC voltage regulators

Abstract: A control strategy for firing instances in pulse-width-modulated (PWM) AC voltage regulators is presented. In this type of regulator, output voltage is controlled by varying the on/off time ratios of a series-controlled switch. Using a microprocessor as a controller makes it possible to vary firing instances at will according to a predetermined timing regime. One of these regimes, proposed here, involves adjusting firing instances so that selected dominant lower-order harmonics can be eliminated. This in turn leads to improved system power factor and efficiency. The theoretical principles used in evaluating firing instances are described, and experimental results verifying the analysis are presented. >

A fast time-domain algorithm for the simulation of switching power converters

Abstract: An efficient algorithm for the simulation of switched-mode power converters is developed. A Chebyshev series expansion is used to effectively solve the differential equations describing the system in each topology. The power of the new simulation technique lies both in the simple, but accurate, polynomial approximation for the state transition matrices and in the ability to explicitly obtain the instants at which the switching of the circuit topology takes place. The simulation technique is illustrated with reference to a simple Buck converter operating at a constant frequency. The derivation of the new algorithm is presented and its performance is analyzed. The case of a rapidly varying input forcing function is analyzed. Examples illustrating the generality and the computational efficiency of the algorithm are presented. >

Theoretical and experimental studies of the LCC-type parallel resonant converter

Abstract: Using the state-plane approach, the steady-state analysis and design of a high-frequency LCC-type parallel resonant converter (LCC PRC) operating in the continuous conduction mode are carried out. On the basis of this analysis, a set of steady-state characteristic curves for the LCC PRC is plotted. Various design curves for component value selection and device ratings are also presented. A simple design procedure is given, and a design example for a 150 W, 140 kHz multioutput LCC PRC power supply is presented for illustrative purposes. A prototype unit has been built and verifies the theoretical results. >

A simple scheme for unity power-factor rectification for high frequency AC buses

Abstract: A simple scheme is proposed for offline unity power factor rectification for high-frequency AC buses (20 kHz). A bandpass filter of the series-resonant type, centered at the line frequency, is inserted between the line and the full-wave rectified load. The Q=Z/sub 0//R/sub L/ formed by the load and the characteristic impedance of the tank circuit determines the power factor, the boundary between continuous and discontinuous conduction modes, the peak stresses, and the transient response of the rectifier. It is shown that for Q>2/ pi the rectifier operates in continuous conduction mode and the output voltage is independent of the load. Also, it is shown that for Q>2 the line current is nearly sinusoidal with less than 5% third-harmonic distortion and the power factor is essentially unity. An increase in Q causes an increase in the peak voltages of the tank circuit and a slower transient response of the rectifier circuit. The DC, small-signal, and transient analyses of the rectifier circuit are carried out, and the results are in good agreement with simulation and experimental results. >

Large-signal stability analysis of spacecraft power processing systems

Abstract: The authors present a comprehensive large-signal stability analysis of a solar-array power system. The stability of the equilibrium points of a system with a typical nonlinear load characteristic is analyzed. Employing state-plane analysis techniques, the dynamic behavior of the system from an arbitrary initial condition is characterized, and the region of the desired stable operation is identified. The stability and transient response of the system operation near the solar array's maximum power point are evaluated. The dynamic response of the spacecraft power system operating in the shunt mode and battery-discharge mode is analyzed. >

Steady-state modeling, analysis, and performance of transistor-controlled AC power conditioning systems

Abstract: Steady-state modeling, analysis, and solution of transistor-controlled systems are developed and experimentally verified over a wide range of operation. General features of the system performance and the effects of the chopping frequency on the performance parameters and harmonic generation are thoroughly investigated. Over most of the control range, and for chopping frequencies in the order of several hundred hertz and higher, it is demonstrated that the harmonic contents of the load current are almost negligible, providing highly desired operating conditions for many applications where the fundamental current is the only useful component. >

Application of nonlinear design optimization for power converter components

Abstract: A computer-aided-design approach for power converter components is described. A designer with a minimum of programming and optimization experience can interface with nonlinear optimization routines to rapidly perform design trade-offs that would be impossible by hand. A power converter design using MOSFET and bipolar-junction-transistor (BJT) switches is shown to illustrate the power of optimization routines in power electronics. Realistic design values and available vendor components can be incorporated in a design without using an extensive database program structure. A practical example is given with experimental data to verify the accuracy and usefulness of optimization software. >

The effects of motor parameters on the performance of brushless DC drives

Abstract: A simulation model for predicting the transient performance of brushless DC drives is described. The model does not require assumptions of phase balance of either the power electronic converter or the motor, nor are idealized waveforms for the induced voltage or phase and mutual inductance terms necessary. The model is applied to drives for which neither equivalent-circuit nor d-q axis analyses are rigorously applicable. Test results establish the degree of correlation of the predictions with a practical example. The model is then used to conduct a sensitivity study that not only explores the degrees of model complexity necessary for adequate representation but also provides guidelines to system designers on the effects of certain practical configurations. The importance of the interaction of converter details, such as the pulse-width-modulated (PWM) technique, and motor parameters, such as the induced voltage waveform, is stressed in the approach considered. >

Modeling of control loop behavior of magamp post regulators

Abstract: Small signal-control models are presented for a magnetic amplifier switching-mode post regulator for SMPS applications. Two commonly used current reset schemes are considered; an external reset scheme and a self-reset scheme. It is mathematically shown that the open-loop gain is a two-pole, single-zero transfer function for continuous-mode operation and is a single pole transfer function for discontinuous mode operation. The equations for predicting the open-loop gains for both types of reset circuits are derived and verified experimentally. It is shown that the open-loop gain characteristics of a magnetic-amplifier regulator depends on power circuit parameters, the reset-circuit parameters, and the saturable reactor parameters. Models for both continuous mode and discontinuous modes of operation that provide designers with useful tools for designing a compensation network for the feedback error amplifier are presented. >

Qualitative analysis and control of a DC-to-DC boost converter operating in discontinuous mode

Abstract: The boost cell operating in discontinuous conduction mode based on an approximate discrete-time difference equation is investigated. A qualitative discussion of the steady-state and open-loop dynamical behavior is presented. A linearized small-signal equation that leads to a linear feedforward control law for regulating this type of converter is derived. The conventional linear scheme provides satisfactory control in the neighborhood of the operating point, but ceases to meet the requirement as soon as the small-signal assumption is violated. A nonlinear feedforward control law whose validity extends over a wider range of fluctuation of the variables about the operating point is proposed, along with some simulation results that confirm the superiority of the proposed nonlinear control over its linear counterpart. >

A multiprocessor-based fully digital control architecture for permanent magnet synchronous motor drives

Abstract: The design and implementation of a multiprocessor-based fully digital control architecture for permanent-magnet synchronous motor drives and an approach for designing advanced AC servo drives using currently available high-performance microprocessors are presented. The design of the architecture involves formulation of control algorithms for a current-regulated pulsewidth-modulated inverter and advanced vector-control strategies for speed and position loop. Under the vector-control framework, some recently developed robustness control results are applied to the design of speed-loop controllers. The implementation of the architecture integrates the control of current, speed, and position loop using the multiprocessor-based controller. Experimental case studies that correlate simulation and measurement results are provided. Experiments were conducted to compare the controller performance, including step speed and position responses, closed-loop frequency responses, the effect of field-weakening control, and disturbance-rejection performance. The experimental results validate the theoretical development. >

Megamp post regulators-practical design considerations to allow operation under extreme loading conditions

Abstract: Practical design equations and guidelines are established to allow magnetic amplifier (magamp) operation under extreme loading conditions. Three conditions are considered: shutdown of output, foldback of the output current, and operation under discontinuous inductor current mode. Design equations are derived for the three extreme operations, and their use is illustrated by numerical examples. The design equations provide the designers with tools for parameter trade-offs and lend themselves to computer-search design procedures. >

Steady state analysis of an inverter-fed induction motor employing natural commutation

Abstract: A steady-state analysis of a three-phase induction motor fed by a DC link inverter commutated by machine-induced EMF (electromotive force) is presented. The active power requirement of the motor is met by the DC link, and the necessary reactive power is supplied by a capacitor bank connected at the motor terminals. A generalized analytical model is developed for no-load as well as loaded conditions of the motor. The steady-state performance of the motor is numerically evaluated. The computed results are compared with corresponding experimental results for a 4 HP squirrel cage induction motor. The relevant oscillograms of voltage and current waveforms of the inverter and motor are presented and discussed. >

DC machine models for SPICE2 simulation

Abstract: A four-level computer model is proposed for DC machine simulation using SPICE2 to meet different simulation requirements. The most complex model takes account of magnetic saturation, armature reaction, current dependence of winding circuit parameters, and eddy current effects. The models have been developed to enable designers to simulate the static and dynamic characteristics of a complete converter drive system including the DC machine more simply, practically, and reliably in one simulation run. Some simulations have been investigated to demonstrate the benefits of the SPICE2 machine models. >

Role of the amplifying gate in the turn-on process of involute structure thyristors

Abstract: The switching characteristics of involute thyristors with and without the amplifying gate structure are discussed. The effects of peak gate currents (10-100 A) on the anode current di/dt, switching delay, and energy loss in both types of devices are presented. The performance of the devices without the amplifying gate was far superior than that of the devices with the amplifying gate. A model is presented to explain this difference. Thyristors without the amplifying gate successfully switched anode currents on the order of 12.6 kA, at a di/dt of 100000 A/ mu s, from an anode voltage of 2 kV on a single-shot basis. >

Closed-form expressions for the frequency-domain model of the series resonant converter

Abstract: The steady-state analysis of the series resonant converter is presented using a novel frequency-domain model. Closed-form expressions are derived for the infinite Fourier series. The effects of load resistance, nonzero resistance of the inductor coil, and transistor and diode voltage drops are considered. The output current and voltage characteristics are plotted using the transistor conduction angle as the parameter. The operating point is easily obtained by superimposing on these characteristics a shifted load line that accounts for transistor and diode voltage drops. An example illustrating the solving procedures using the graphical and Newton-Raphson (N-R) methods is included. >

Comments, with reply, on "A new control philosophy for power electronic converters as fictitious power compensators" by J.H.R. Enslin and J.D. Van Wyk

Abstract: In the above titled paper (see ibid., vol.5, no.1 p.88-97, Jan. 1990) the authors develop concepts they suggested in an earlier paper (see IEEE Trans. Instrum. Meas., vol.IM-37, no.3, p.403-8, Sept. 1988). In these two papers, they draw conclusions regarding definitions of power quantities for systems with nonsinusoidal waveforms. They also show how the quantities suggested can be measured and compensated. The commenter points out that although the authors correct errors pointed out by himself and by P.S. Filipski in comments on the earlier paper, they repeat certain misconceptions in their definitions and add new ones. The commenter identifies these misconceptions. The authors refute the points raised by the commenters. >

Nonresonant and resonant coupled zero voltage switching converters

Abstract: Two zero-voltage switching power converters with nonresonant and resonant coupling are presented. These are high-order multiple resonant converters in which the circuit modes associated with the converter operation may have different resonant frequencies. The steady-state responses of these converters are derived in terms of state-plane diagrams by using proper state variable transformations. It is shown that the converters have all the desirable features for high-frequency applications and overcome the drawback of load-range limitation of zero-voltage switching associated with the conventional class-E converter. >

An approach for handling the nonlinearities of HVDC system for stability analysis

Abstract: An approach for linearizing the nonlinearities of the high voltage direct current (HVDC) system for analyzing the system stability over wide range of operation is presented. The nonlinearities can be linearized with +or-5% error over a wide range of system operation. It is shown that the nonlinearities introduced by the converter, real power, and reactive power equations can be linearized over a wide range by using the integral square error (ISE) method. The results are compared with standard techniques called small signal analysis. It is shown that the stability margin of the system predicted by the new technique is relatively smaller than what is predicted by small signal analysis. The system stability boundaries are determined by the AC voltage and the reactive current control. These two control schemes may provide the same stability margin, provided appropriate controller gains are selected. The power factor control modeling is discussed. >