Lyapunov-based control for three-phase PWM AC/DC voltage-sourceconverters

The three-phase pulsewidth modulation (PWM) AC/DC voltage-source converter with the control laws proposed so far is not only unstable against large-signal disturbances, but also has the problem that its stability depends on the circuit parameters such as the DC-output capacitance. This paper describes a new control law based on Lyapunov's stability theory. It is shown that the converter can be stabilized globally for handling large-signal disturbances. The resulting closed-loop system not only guarantees a sufficient stability region (independent of the circuit parameters) in the state space, but also exhibits good transient response both in the rectifying and regenerating modes. Also, a new simulation technique is introduced which increases the speed of the simulation process considerably. Computer simulations are presented to confirm the effectiveness of the proposed control strategy and the validity of the simulation technique. Experimental results are also presented to verify the theoretical and simulation studies     

Power electronic converters for switched reluctance drives

A number of power electronic converter circuits exist for switched reluctance motor (SRM) drives which are generally applicable to most loads. A larger number of circuits exist which are suitable for particular niche applications, but which have the potential to be the most cost-effective within that niche. Due to the variable methods of operation of these circuits and the rapid progress in this field, comparisons of these circuits have so far been limited. This paper attempts to bring together the sum total of power converter topologies so far published for SRM drives. A novel classification methodology is presented. The power converters are compared using a straightforward total semiconductor VA per phase sum, and the relative cost of the drive system elements is considered     

Angle controlled current regulated rectifiers for AC/AC converters

Rectifier control schemes for use in AC/DC/AC voltage-sourced resonant link converters with controlled rectifiers are discussed. It is shown that the voltage-sourced rectifier cannot be operated solely on the basis of instantaneous quantities. A bang-bang control scheme that independently controls the angle and the magnitude of the AC-line current vector is developed and simulated. 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 which satisfies the sliding mode criteria and results in lowest voltage ripple is chosen to further minimize the size of the link capacitor     

Robotics and automation applications of drives and converters

The current design limits of power electronics have a significant effect on robotics and automation applications of drives and converters. This paper treats the major design limits that include dynamic range, reliability of power electronics, precision engineering and reliability, productivity and reliability, and drive motion control standards. For each of these limits, the paper identifies and discusses the salient issues and relates them to promising new technologies and, thus, to the future challenges in power electronic systems     

A space vector-based rectifier regulator for AC/DC/AC converters

A voltage-sourced rectifier control scheme for use with AC/DC/AC variable speed drives is presented. A control scheme is derived that directly calculates the duration of time spent on the zero state and on each switching state adjacent to the reference vector, over a constant switching interval, in order to drive the line current vector to the reference vector. In addition, under transient conditions, when deadbeat control is not possible, a control scheme is presented that ensures that the line current vector is driven in the direction of the reference current vector. The current reference for the rectifier controller is derived from the bus voltage error and a feedforward term based on the estimated converter output power. The proposed space vector-based rectifier regulator is shown to exhibit improved harmonic and transient performance over existing per-phase duty cycle prediction methods, especially at modulation indices near unity. The deadbeat control of the rectifier input current is accomplished every half-cycle with constant switching frequency while still symmetrically distributing the zero state within the half-cycle period     

Advanced regular-sampled PWM control techniques for drives andstatic power converters

Regular-sampled PWM techniques have been developed to reproduce the harmonic-elimination and harmonic minimization PWM power convertor characteristics. These new regular-sampled PWM control strategies significantly reduce the computational requirements for real-time microprocessor-based PWM implementation. This results in simplified and more efficient microprocessor software/hardware requirements, leading to real-time PWM generation with minimized harmonics, suitable for drives and uninterruptible power supplies     

A direct control method for matrix converters

Until now, direct control methods have been mainly investigated and used in conjunction with voltage source converters. In this paper, the authors develop a direct current control method for matrix converters. There are two objectives for the direct current control: the desired current has to be impressed into the load, and the current, drawn from the mains, should be in phase with the voltage and should be (nearly) sinusoidal. This implies active damping of the 400 Hz resonance or the line filter. The method is implemented on a DSP and tested on a 10 kVA matrix converter     

New time-discrete modulation scheme for matrix converters

While the known modulation strategies for matrix converters are based on pulsewidth modulation (PWM)-or vector modulation-this paper presents a novel time-discrete modulation method based on real-time prediction calculation to select the switching states. The decision about which switching state is to be set for the following sampling period is made by the use of a predictive quality function. Using this approach, unity displacement factor is seen at the supply side with minimum line current distortion while the load currents follow their reference values with good accuracy. The quality function is derived from a mathematical model of the matrix converter and the controlled system. Measurements taken on a model plant, consisting of a matrix converter and a standard induction machine with a rated output power of 11 kW, show that the matrix converter, equipped with the control method presented here, offers advantages over systems with conventional frequency converters, especially in terms of the input current distortion.     

Two-phase modulation technique for three-level inverter-fed AC drives

Two-phase dipolar and unipolar modulation techniques for three-level three-phase inverters are suggested and compared with conventional three-phase pulsewidth modulation (PWM) techniques. Two-phase PWMs with 60/spl deg/ (0/spl deg/ and /spl plusmn/30/spl deg/ shift) and 120/spl deg/ cycles are investigated from the point of view of harmonic losses, motor voltage spectra, and torque pulsations. It is shown that two-phase dipolar PWMs have no advantages in comparison with three-phase PWMs, while two-phase unipolar PWMs-in contrast with three-phase PWMs-considerably decrease the motor harmonic losses and torque pulsations in the whole motor voltage region. At the same time, the inverter neutral point control requires reversing to three-phase PWM technique for the duration of the control.     

A comparison of piezoelectric transformer AC/DC converters with current doubler and voltage doubler rectifiers

The objective of this study was to develop recommendations for an optimal design of piezoelectric transformer (PT) AC/DC converters. The paper presents a comprehensive comparison of the two commonly used rectifier topologies in a PT based power converters: current doubler and voltage doubler rectifiers. The advantages and disadvantages of the two rectifiers were investigated and the range of their applications with respect to output current, voltage, power capability, load resistance etc.-was delineated. Generic parameters are proposed and used to derive normalized and closed form equations that can help choosing a PT for a given set of requirements. Simulation and experimental results were found to be in a good agreement with the derivation of the theoretical analysis.     

Synthesis of input-rectifierless AC/DC converters

This paper discusses the basic construction procedure and topological possibilities of creating AC/DC converters out of simple DC/DC converters. It is shown that two separately controlled DC/DC converters are sufficient for producing a regulated DC output and shaping the input current, from an AC voltage source, without the need for input rectifiers. Some design constraints are discussed, emanating from the limitation of the conversion ratios that can be achieved by particular DC/DC converters. Selected topologies are verified experimentally. This kind of rectifierless converter find applications in airborne power supplies where zero-crossing distortions are significant because of the inevitable phase-lead effect of the input rectifier bridge.     

Novel real-time harmonic minimized PWM control for drives andstatic power converters

This paper shows how a novel harmonic minimized PWM control strategy, based on regular-sampling PWM techniques, can be used to significantly reduce the computational requirements for real-time microprocessor-based PWM implementation. This results in greatly simplified and more efficient microprocessor software/hardware requirements, leading to real-time PWM generation with minimized harmonics, suitable for all power-electronic PWM control applications     

Design,fabrication and application of organic power converters: Driving light-emitting electrochemical cells from the AC mains

The design, fabrication and operation of a range of functional power converter circuits, based on diode-configured organic field-effect transistors as the rectifying unit and capable of transforming a high AC input voltage to a selectable DC voltage, are presented. The converter functionality is demonstrated by selecting and tuning its constituents so that it can effectively drive a low-voltage organic electronic device, a light-emitting electrochemical cell (LEC), when connected to high-voltage AC mains. It is established that the preferred converter circuit for this task comprises an organic full-wave rectifier and a regulation resistor but is void of a smoothing capacitor, and that such a circuit connected to the AC mains (230 V, 50 Hz) successfully can drive an LEC to bright luminance (360 cd m⁻²) and high efficiency (6.4 cd A⁻¹).     

Capacitor loss analysis method for power electronics converters

A capacitor is a major component that contributes to reducing the reliability of high-power density power electronics converters. The lifetime and reliability of capacitors are strongly influenced by temperature. An accurate loss measurement method is necessary to estimate temperature rise. However, practical capacitor loss measurement systems used in power electronics converters have not yet been developed because capacitor loss data provided by the manufacturer is usually measured under sinusoidal excitation, which is different from actual excitations of electronics converters. In this study, a capacitor loss measurement system for power electronics converters is proposed. The proposed measurement system can be used for fast capacitor loss measurement with high accuracy in a real circuit and capacitor loss analysis for each switching period of power electronics converters. To verify the accuracy of the loss measurement, the measured loss value of a filter capacitor used in a pulse width modulated inverter is compared with the calculated value. The experimental results show good agreement with the calculated capacitor loss.     

A rugged soft commutated PWM inverter for AC drives

A novel DC-DC power converter for variable-speed AC power drives using the zero-voltage switching technique is described. This converter combines the advantages of soft commutated inverters and those of conventional pulsewidth modulated (PWM) inverters. In the proposed scheme, the soft commutation reduces the constraints on the switches, and the PWM enables simple and efficient regulation of the power flow. Furthermore, the zero-voltage switching technique makes operation safe, and the switching of bipolar transistors at 20 kHz is easily achieved without compromising the efficiency of the system     

A series-resonant DC/AC inverter for impedance-load drives

A DC/AC inverter without cycloconversion configured by a half-bridge series-resonant inversion (HB-SRI) circuit is presented. The inverter is a series resonator with two auxiliary switches in shunt with the resonant capacitor so as to configure adaptively the output current suitable for impedance load. The output sinusoidal voltage is synthesized by a series of equal-amplitude quasisinusoidal pulses (QSPs) and the corresponding current is formed by unequal QSPs and adaptively phase-shifts to the impedance load. The presented HB-SRI is operated by frequency modulation with a constant-on time control. System modeling and waveform syntheses for the output sinusoidal voltage and its current are clearly derived, A typical design example of a 500 W HB-SRI inverter is examined to assess the system performance. The power efficiency is over 90% when the inverter output is above 200 W. The total harmonic distortions (THDs) for various impedance loads are all within 6%     

A novel soft-switched PWM inverter for AC motor drives

A novel soft-switched inverter topology is derived from the passively clamped quasi-resonant link (PCQRL) circuit. By introducing magnetic coupling between the two resonant inductors, the number of auxiliary switches can be reduced from two to one, and only a single magnetic core is required for the resonant DC link. An analysis of this novel PCQRL topology with coupled inductors is presented to reveal the various soft-switching characteristics. In comparison with the conventional passively clamped, continuously resonant DC link inverter, this soft-switched inverter can reduce voltage stresses from more than 2 per unit (pu) to 1.1-1.3 pu. It can also provide soft-switched pulse-width modulated (PWM) operation. Simulations and experiments are performed to backup the analysis     

Implementation of a PWM regular sampling strategy for AC drives

The regular sampling technique offers a feasible basis for the microprocessor control of inverters in pulse width modulated (PWM) AC drives. An implementation of this technique is presented for the speed control of an induction motor in the frequency range 5-105 Hz. Hardware and software design principles are outlined and discussed for an 8 b microprocessor. Spectral analyses of the sampling technique with a sinusoidal modulating function and with a third harmonic added to this function are derived, with emphasis on the fundamental and dominant components. Experimental and computed results are presented for the motor control in steady-state, and for transient current and speed in closed-loop operation, with excellent correlation     

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     

Benchmark of power packaging for DC/DC and AC/DC converters

This paper presents the first reported final results of a benchmarking project "StatPEP" which investigated the Status of Power Electronic Packaging used in commercial DC/DC and AC/DC switch mode power supplies. The methodology of the project is first described. Some of the salient results of a comprehensive benchmarking of DC/DC converters (rated power of 100 W) and AC/DC converters (rated power up to 576 W) are presented. Examples for figures-of-merit are presented. The results of the investigation are presented in a generic form, which does not identify individual products. A comparison of the performance of the units shows that the measured power density of the AC/DC units is approximately 10% that of the DC/DC while the thermal density based on footprint is 50%. Also the switching frequency of the AC/DC is 50% that of the DC/DC. Some of the reasons for these differences are discussed