Prof. Dr. Joachim Holtz
Editor-in-Chief
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Prof. Dr. Joachim Holtz |
IEEE Transactions on Industrial
Electronics
Volume 45, Number 5, October 1998
Special Section on PWM Current Regulation
Abstract - The aim of this paper is to present a review of recently used current control techniques for three-phase Voltage Source Pulse Width Modulated (VS-PWM) converters. Various techniques, different in concept, have been described in two main groups: linear and nonlinear. The first includes PI (stationary and synchronous) and state feedback controllers, and predictive techniques with constant switching frequency. The second comprises bang-bang (hysteresis, delta modulation) controllers and predictive controllers with on line optimization. New trends in the current control - neural networks and fuzzy logic based controllers - are discussed as well. Selected oscillograms accompany the presentation in order to illustrate properties of the described controller groups.
Abstract - Current control in voltage-source inverters with random pulse width modulation (RPWM) is investigated. The random modulation is introduced to alleviate the undesirable acoustic, vibration, and EMI effects in inverter-fed AC drive systems. A novel RPWM digital technique with dithering of the switching frequency and compensation of the processing time is described. Design of the current control loop is discussed. Results of investigation of an experimental drive system are presented, proving the feasibility of the proposed solutions.
Abstract - Active compensation of torque harmonics in high-performance synchronous PM motor drives requires high-bandwidth current control. It is demonstrated that PI current control exhibits performance limits even when feedforward compensation of the rotor induced voltage and the stator inductance drop is used. High bandwidth requirements are satisfied using a digital deadbeat current controler. Sampling time delays are eliminated to the extent possible by means of a current predictor. The current controler and the predictor refer to a model of the parasitic effects of the PM synchronous machine that is acquired and adapted to parameter changes in real-time. Stator current distortions due to deviations from the sinusoidal flux linkage distribution are thus eliminated. The control system facilitates compensation of high-frequency torque ripple of the machine.
Abstract - This paper presents the comparative evaluation of the performance of three state-of-the-art current control techniques for active filters. The linear rotating frame current controller, the fixed frequency hysteresis controller and the digital dead-beat controller are considered. The main control innovations, determined by industrial applications, are presented; suitable criteria for the comparison are identified and the differences in the performance of the three controllers, in a typical parallel active filter set-up, are investigated by simulations
Abstract - The system performance of an AC variable speed drive directly depends on the current regulation. In this paper, a novel space-vector current regulation scheme for field oriented controller(FOC) is developed. Motor currents are regulated by generating appropriate inverter output voltage vectors via software implemented comparators and switching table. Switching table based on angular coordinate enables the inverter to generate optimal voltage vectors. With introducing an additional triangular carrier signal to the output of original hysteresis comparators, a user-selectable high and fixed switching frequency can be obtained, this further improves the driver performance. Experiments are made to verify the effectiveness and correctness of this proposed method. According to the experimental results, both simple hardware design and good current response can be attained.
Abstract - In this paper, a new current controller that guarantees the fastest transient response is proposed. The basic concept is to find the optimal control voltage for tracking the reference current with minimum time under the voltage limit constraint. The generalized solution of the minimum time current control in the systems are presented in this paper. With the generalized solution, the minimum time current controller can be easily applied to all the 3-phase balanced system. Through the simulation and the experiment, it is observed that the proposed controller has much less transient time than the conventional synchronous PI regulator.
Abstract - The structure of current control loop of an induction machine drive determines decisively the dynamic performance of the overall system. Fast current control is a prerequisite for dynamic decoupling between the torque and the flux linkage state variables. Standard solutions are well established for drives in the low and medium power range. The low switching frequency of the high-power PWM inverters calls for a trade-off in controller design between the low harmonic losses and the torque ripple in the steady-state on one hand, and fast dynamic response during the transients on the other. In order to meet these conflicting aims: a good steady-state performance at constant frequency and fast current control during transients, a variable structure current control is proposed.
Abstract - In this paper, an improved space-vector-based hysteresis current controller (SVBHCC) is proposed. The controller determines a set of space vectors from a region detector and applies a space voltage vector selected according to the main hysteresis current controller. A set of space vectors including the zero voltage vector to reduce the number of switchings is determined from the information of the wider current errors than those of the main hysteresis current controller. A simple hardware implementation is proposed and the good experimental results of the space-vector-based hysteresis current controller are also shown.
Abstract - Shunt active power filters are connected in parallel with the electricity supply network. If the AC mains has a neutral conductor it is desirable to compensate the mains harmonic currents zero sequence components. This can be achieved with a four wire PWM voltage converter connected to the AC mains. In this case the three-phase and the neutral AC currents must be controlled. A generalization of the space vector based current controller in the ab0 coordinate system is presented in this paper. With this current controller all the current harmonic systems of positive, negative and zero sequence can be injected by the converter and thus compensated on the AC mains. The system is also useful to compensate unbalanced currents of fundamental frequency. A useful benefit of this system is that it is possible to control the converter four-wire currents with equal hysteresis errors. Simulation and experimental results are presented.
Abstract - In this paper a novel multivariable hysteresis current controller for three-phase inverters is presented. Hysteresis controllers are intrinsically robust to system parameters, exhibit very high dynamics and are suitable for simple implementation. The main drawback of hysteresis controller is a limited control on transistors' switching frequency. Very high switching frequency may result if three independent controllers are used. Multivariable solutions were proposed in the literature to solve the problem. In the paper, it is shown how the use of a sequential design for the multivariable controller can further contribute to transistors' switching frequency reduction, with no significant increase in the hardware implementation complexity. The proposed controller is illustrated and compared with other hysteresis controllers presented in the literature. The proposed sequential controller ensures a significant reduction of transistors' switching frequency with respect to the other tested controllers, under the same operating conditions. A prototype controller is also presented. The effects of noise captured by current sensors (especially Hall-Effect type), on performances of industrial hysteresis controllers are discussed. It is shown how the sequential design of the controller can help solving also this critical problem. Experimental results are reported to confirm the quality of the proposed controller. System stability condition is derived in Appendix.
Abstract - This paper proposes a new discrete fuzzy-tuning current-vector (FTC) control scheme for 3-phase PWM inverters. The proposed current control scheme can achieve fast transient responses and at the same time with very low total harmonics distortion (THD) in output current during steady-state operation. The proposed FTC control scheme generates quasi-optimum PWM patterns by using a closed-loop control technique with instantaneous current feedback. The proposed FTC control scheme has been realized using a single-chip digital signal processor (TMS320C14) from Texas Instruments. Experimental results are given to verify the proposed fuzzy-tuning current control strategy for 3-phase PWM inverters.
Abstract - The current control system of the three-phase voltage inverter used in the AC drive application is presented in the paper. This control system, operating in the rotating reference frame fixed to the motor flux, minimizes the switching frequency of the inverter transistors. The stator current is controlled by the space vector based method, so current vector is keeping within the tolerance band around the command current vector. The tolerance band which is square shaped and command current vector are stationary in the transient state. The optimal positions of the inverter output voltage vector are written in the EPROM memory as a function of the rotor positions, motor speed and motor load conditions. These optimal positions ensure the longest trajectory of the stator current vector moving within the tolerance band. The method of assigning the individual inverter output voltage vector position to the particular part of the tolerance band is based on the theoretical investigations discussed in the article. The results of the computer simulations and the laboratory model investigations show that in comparison to the conventional control system in which the stator currents are controlled individually for each phase by the hysteresis controllers, the switching frequency is significantly minimized. Depending on the motor speed and its load conditions the minimization level is between 15-90%. The proposed control system is very simple in practical realization and particularly useful for the field oriented control of the AC motor. The behavior of the practical system model in the steady and transient states of the motor work is presented in the paper.
Special Section Short Papers
Abstract - A new feedback current controller for three-phase PWM power inverters is presented. To achieve robustness, fast dynamical response, reduced switching frequency and simple hardware implementation, an improved three-level hysteresis sliding mode controller is used. All voltage vectors are accurately selected in order to minimize the current error.
Power Electronics
Abstract - The design and breadboard implementation of a constant-frequency, zero-voltage-switched (ZVS), full-bridge (FB) PWM converter delivering a 12 V at 1 kW output from a 350-450 VDC input bus is described. The ZVS characteristic is maintained over a wide operating range by utilizing the transformer magnetizing inductance as an energy storage element. Output voltage regulation is accomplished entirely on the secondary side through magamp control, thus simplifying the methods used for maintaining control and isolation.
Abstract - This paper presents a method of enhancing the performance of a four phase switched reluctance motor by using capacitors to produce additional supply voltage during the rise and fall periods of a motor phase current. The voltage rating of the inverter components increases and extra capacitor/ diode combinations are needed. the operation and analysis of a series voltage boost circuit are detailed for different modes of operation with a study of the effect of the boost capacitor voltage on the current waveform. Different voltage boost circuit configurations are compared. The predicted and measured results show that the boost circuit increases both torque and output power and, improves the efficiency of the machine, especially at high speeds.
Drive Control
Abstract - A mutual Model Reference Adaptive System (MARS) is proposed to implement a position sensorless field orientation control of an induction machine. The reference model and adjustable model used in the mutual MARS scheme are interchangeable. Therefore, it can be used to identify both rotor speed and the stator resistance of an induction machine. For the rotor speed estimation, one model is used as a reference model and another the adjustable model. Pure integration and stator leakage inductance are removed from the reference model, resulting in robust performance in both low and high speed ranges. For the stator resistance identification, the two models switch their roles. To further improve estimation accuracy of the rotor speed and stator resistance, a simple on-line rotor time constant identification is included. Computer simulations and experimental results are given to show it effectiveness.
Letters to the Editor
Abstract - A novel PWM buck-boost AC chopper using regenerative DC snubbers is proposed and analyzed. Compared to the previous buck-boost AC choppers, AC snubbers causing power loss are eliminated using regenerative DC snubbers. Experimental results show that the proposed scheme gives good steady state performances of the AC chopper and that they coincide with the theoretical results.