Current-controlled Converter Research Articles

Vector Control Schemes for Tandem-Converter Fed Induction Motor Drives

The tandem converter is an arrangement of two inverters connected in parallel: a high-power pulse-amplitude modulated current-source inverter and a low-power pulse-width modulated voltage-source inverter. In comparison with an equivalent single voltage-source inverter, this structure offers several advantages, significant reduction of switching losses in particular. Results of experiments with a tandem inverter, and those of computer simulations of induction motor drives with that converter, are presented. Three vector control schemes for such drives were investigated: a) rotor-flux orientation with a voltage-controlled tandem converter, b) rotor-flux orientation with a current-controlled tandem converter, and c) stator-flux orientation with a voltage-controlled tandem converter. Performance characteristics of the described control schemes are discussed.

A Theoretical minimum DC-link capacitance in PWM converter–inverter systems

In the PWM converter-inverter system, if the converter current control is fast enough to match the inverter power at all instants, then no current flows through the DC-link capacitor, making the DC-link voltage constant, even with a very small DC-link capacitance. A matching control method making the capacitor current zero suggests the possibility of using a tiny DC-link capacitor. However, in practice, a certain amount of capacitance is required, since the matching control itself is not perfect and there are one-step delays in the PWM. In this work, the authors investigate a theoretical low bound of the DC-link capacitance, considering an extreme case in which the DC-link voltage rises to a maximum value in a single PWM period. Utilising the optimisation technique, the theoretical minimum capacitance is found to be the one that limits the voltage rise below a certain threshold value. Analytical calculation results are compared with MATLAB simulation results.

A study of composite resonance in AC/DC converters

Control-system errors and imbalances in the AC system may generate and magnify abnormal harmonics in the AC-bus voltages and the DC current. In this paper, a technique based on harmonic impedance matrices has been used to simulate the steady-state response of AC/DC converters. The technique allows the computation of converter impedances or admittances viewed from the DC or AC bus. At any operating point, a linear circuit may represent the converter and harmonic magnification factors are calculated. High harmonic magnification indicates the possibility of composite resonance. The impact of a small negative-sequence imbalance in the AC system voltages is shown for a six-pulse current-controlled converter.

A soft-switched current-controlled converter for induction machine drives

The paper proposes a current controlled inverter operating in zero voltage switching (ZVS) mode for an induction machine drive. Operation with no voltage stress in the DC link bus is achieved. Together with the soft switching operation, a fixed frequency bang-bang current control technique is also implemented to allow for an accurate shaping of sinusoidal currents to feed the motor. As a result, a ripple free torque profile in steady state operation is achieved. With the soft switching technique it is possible to operate conventional IGBTs at 40 kHz. A detailed analysis of the circuit operation is presented. The feasibility of the proposed scheme is experimentally verified on a prototype.

A feedback linearizing control scheme for a PWM converter-inverter having a very small DC-link capacitor

This paper addresses a control method of reducing the size of the DC-link capacitors of a converter-inverter system. The main idea is to utilize the inverter operation status in the current control of the converter. Specifically, the information on the load power is incorporated in synthesizing the converter current control input so that a proper DC voltage level is maintained. We describe the dynamics of load current and apply feedback linearization theory to obtain an input output linearized system. Theoretically, this control strategy is effective in regulating the DC voltage level, even though the DC-link capacitor is arbitrarily small and load varies abruptly. The superior performance is demonstrated through simulation and experiment. An experiment was performed with a 9-kW pulsewidth modulation converter-vector inverter system having a 75-/spl mu/F DC-link capacitor.

Power supply design considerations for maintaining a minimum sustaining current in a vortex water wall high-pressure argon arc lamp

Vortex water wall high-pressure argon arc lamps are used to generate intense light and are capable of operating at radiative efficiencies greater than 50%. These lamps are being considered for use in a pulsed DC mode of operation in the next generation of rapid thermal processing applications. The results of a series of experiments have shown that the breakdown to arc transition consists of a prethermionic electrode emission phase and a prethermal ionization phase. The large dynamic voltage and current range between the breakdown phase and the arc phase necessitates the use of three different power circuit topologies. A high-voltage ignition circuit is connected in series with an arc-sustaining power source. The series connection ensures that the arc-sustaining power supply is isolated from the high-voltage ignition circuit. The arc-sustaining current source power source consists of a step-down hysteresis-current-controlled DC/DC converter cascaded with a constant off-time output-voltage-controlled step-up DC/DC converter. The current-controlled converter supplies the minimum arc-sustaining current, whereas the step-up converter provides the minimum post-ignition prethermal ionization voltage. The inclusion of a shorting switch allows one to reduce the current ratings of the high-voltage circuit components. Finally, experimental verification of a simplified circuit model of the ignition to arc transition, the circuit operation, a power supply design procedure, and a design example are provided.

Series equivalence/operation of current-controlled boost-type single-phase voltage source converters for bidirectional power flow

Single-phase voltage source power converters (VSCs) under consideration are AC-DC current-controlled boost-type power converters with bidirectional power-handling capability. Equivalence between two series-connected two-level power converters and a single three-level power converter is considered here. Further considered is the series operation of three-level power converters. Simulation results and experimental verification for both are provided. Economical configurations of three-level power converters leading to multilevel waveforms are presented thereafter.

Current-controlled boost-type single-phase voltage source converters for bidirectional power flow

A consolidation of existing as well as new configurations of voltage source power converters (VSCs) using gate turn-offs (GTOs) or a combination of GTOs and thyristors is considered. These VSCs are single-phase AC-DC current-controlled boost-type power converters with bidirectional power-handling capability. Both two-level and three-level power converters are presented along with a definitive classification. Experimental results are provided on a selective basis, confirming a 360/spl deg/ power angle range of the power converters.

Modelling and control of a three-phase current-controlled reversible AC-DC converter

A three-phase current-controlled AC-DC converter is presented, which uses only four active switches to simplify the circuit and achieve a unity power factor, sinusoidal input current and a bidirectional power flow capability. A small-signal model is derived and, in addition to feedback control, a three-phase instantaneous voltage detector is proposed for adaptive feed-forward control to achieve almost zero output impedance and zero audio susceptibility. A prototype circuit is constructed and experimental results are presented.

A method of designing ac/dc thyristor converter current control systems by using discrete time MRAC with deterministic disturbances

Two design methods of ac/dc thyristor converter current control systems with MRAC (Model Reference Adaptive Control) have been designed. To linearize the input/output relation of the systems, the constant term of the model is considered in different ways. In the first method, a linear transformation of the control input is made while in the second method, the constant term and compensated modeling error are neglected by integral adaptation. Computer simulations and experiments have shown that the control performances of the MRAC systems are much better than that of PI controllers. However, in the first method, since the variable vector is not persistently spanning, the convergence rate of estimated parameters is not as high as expected. The second method has better dynamic characteristics but its stability has not been proved in theory. This paper suggests a new design method in which the constant term is considered as a deterministic disturbance. The feature of this method is that by introducing an equality equation which makes the term of disturbances apparently unobservable, the effect of disturbances can be eliminated and the existing adaptive control scheme without disturbances whose stability has been proved theoretically can be used. Computer simulations and experiments show that the new method can obtain better responses than the old ones.

A Design Method of AC/DC Thyristor Converter Current Control Systems by using Discrete-Time MRAC with Deterministic Disturbances.

A Design Method of AC/DC Thyristor Converter Current Control Systems by using Discrete-Time MRAC with Deterministic Disturbances.

Residential Solar-Powered Air Conditioner.

The power demand in Japan yearly increases especially in summer, and becomes peak in the daytime. The main cause is the drastically increased load of air conditioners widely used in general homes. The load pattern of air conditioners is very similar to the output pattern of a photovoltaic (PV) array.Therefore, Sanyo has been developing two types of residential solar-powered air conditioner. One is a uni-directional system by using a DC/DC converter, which controls the voltage of a PV array at its optimal operation point and boosts the voltage up to the DC voltage of an inverter-type air conditioner. The other is a bi-directional system by using a bi-directional current-control converter, which regenerates surplus power into commercial system from a PV array, and suppresses the input current distortion of an air conditioner.In this paper, the configurations and experimental results are described and discussed.

A current-controlled quasi-resonant converter for switched-reluctance motor

A current-controlled quasi-resonant power converter suitable for switched-reluctance motor (SRM) feeding is presented. The converter operation is analyzed and its characteristics are determined in terms of the system parameters. The converter control strategy is studied for different operating conditions. Current control operation is considered and discussed. Theoretical predictions are verified and validated by experimental results obtained with a prototype SRM drive. >

Adaptive Identification and Thyristor Converter Control

The thyristor converter (TC) current control problem with use made of an ‘input-output’ model when affected by random disturbances in a measuring system is considered. It is shown that in the simplest case the current model may be presented in the form of a linear combination of exponential and harmonic terms with a priori unknown coefficients. It is noted that the obtained model is nonlinear relative to unknown parameters. To linearize it use is made of the differential transformation of current measurements which allows a linear combination of exponential terms to be selected from the initial model. It is emphasized that there is instability of calculations when identifying unknown parameters of the exponential component of the model. To improve stability there is suggested a method of natural regularization by selecting the current sensor sampling frequency and the number of measurements. Exponential smoothing of estimates of the electromagnetic time constant in a load circuit and the algorithmic filtration of current measurements with the use of spline functions are also advantageous.

New power supply method for air-conditioners using a bi-directional current control converter.

New power supply method for air-conditioners using a bi-directional current control converter.

On the Stability of Peak Current-Controlled Converters: Analysis, Simulation, and Experiments

Mathematical models are developed for the stability analysis of switching regulators operating in the current programmed, or Peak Current Control (PCC), mode. In this paper derivations are detailed for the necessary and sufficient conditions that the parameters of the PCC converter must satisfy in both the single-ended and the push-pull versions of the circuit. Furthermore, the effect of the stabilizing ramp on the steady-state performance is investigated; it is found that there is an optimum value for which the dc output error is truly zero independently of the input disturbance, and another value which results in a ``deadbeat'' response for disturbances of short duration. Finally, an interactive simulation program was developed for the single-ended version of the PCC converter, and implemented on a PDP-15 minicomputer. The results of these simulations agree closely with the predicted behavior, as well as with experimental observations.