Dae-Woong Chung

Analysis and compensation of current measurement error in vector controlled AC motor drives

In this paper, the effects of current measurement error inherent in all categories of AC motor drives are discussed and a compensation method is proposed. Recently, as the higher performance of torque control is required, current measurement error classified as offset error and scaling error becomes considerable. It is demonstrated that the offset error causes the torque of a motor to oscillate at the stator electrical frequency, f/sub e/, and the scaling error, at the frequency, 2 f/sub e/, respectively. These torque ripples deteriorate the performance of speed control because they act as disturbance loads. The simulation and experimental results shows that the proposed compensation method can improve the performance of torque control by eliminating torque ripples effectively.

Minimum-loss strategy for three-phase PWM rectifier

In this paper, the conduction and switching losses of a voltage-fed three-phase pulsewidth modulation (PWM) rectifier are analyzed for various PWM schemes. On the basis of this result, a novel PWM strategy which minimizes the loss of a three-phase PWM rectifier is developed. This minimization result is derived from the following two factors: (1) less switching frequency ratio; and (2) the absence of switching in the vicinity of peak input current. As a result, it is anticipated that the switching loss of the rectifier is reduced by 46%, compared with continuous space-vector PWM rectifiers, and 20% compared with conventional discontinuous space-vector PWM rectifiers. Moreover, the proposed PWM scheme can produce the highest available output voltage because it is based on the concept of the voltage space vector. The effectiveness of the proposed PWM strategy is verified by experiments.

Direct torque control of induction machine with variable amplitude control of flux and torque hysteresis bands

In this paper, effects of the hysteresis bands on the direct torque control (DTC) of an induction machine are investigated, and a method to control the switching frequency of inverter by a variable amplitude of the hysteresis band is proposed for DTC of an induction machine. A major drawback of the conventional DTC is an unpredictable inverter switching frequency which varies due to operating speed, load condition and parameters of the induction machine. Therefore the amplitude of the hysteresis band should be large enough to avoid excessive inverter switching at any operating region, which inevitably causes relatively large torque ripple especially in the low speed region. This paper proposes an effective switching frequency regulation method which consists of hysteresis band controller and switching frequency command generator. The effectiveness of the proposed strategy is analyzed and compared with the conventional method.

Initial rotor position detection of PMSM at standstill without rotational transducer

This paper presents a new standstill rotor position detecting algorithm for nonsalient permanent magnet synchronous machine (PMSM) without any position sensor. By injecting high frequency current to the stator of the machine, the proposed algorithm provides the standstill rotor position with reasonable accuracy as well as the direction of magnetization. Though this paper focuses on the nonsalient PMSM, the proposed algorithm also works more effectively in the case of the salient machine such as an interior permanent magnet machine. From the experiments, the standstill rotor position is successfully detected within /spl plusmn/5/spl deg/ error in electrical degree.

Minimum-loss PWM strategy for 3-phase PWM rectifier

In this paper, the conduction and switching losses of a three-phase PWM rectifier are analyzed for various PWM schemes. On the basis of these results, a novel PWM strategy which minimizes the loss of a voltage-fed three-phase PWM rectifier is developed. This minimization results from the following two factors: (a) low switching frequency ratio; and (b) absence of switching in the vicinity of peak input current. The effectiveness of the proposed PWM strategy is verified by both simulation and experimental results.

Control of PWM current source converter and inverter system for high performance induction motor drives

In this paper, a novel control strategy for an induction motor driver fed by a PWM current source converter and inverter system is proposed. A multivariable state feedback control with feedforward control is applied for the improved control of both the converter input and inverter output currents, which gives fast transient responses. In addition, the modulation index control of the DC link current is carried out, which produces lower loss of switching devices and low current ripples in steady state. With the PWM converter, the source current is nearly sinusoidal and unity power factor control is obtained. Since the capacitor voltage control is incorporated in the inverter output current control, the decoupling control of the d-q current of the induction motor is well retained. To verify the validity of the proposed strategy, various simulation results are prepared.

Implementation of field oriented induction machine considering iron losses

Iron loss is a possible source of performance deterioration, especially for a torque regulation, in field oriented induction machine. In this paper, study on the model of an induction machine with iron losses, a flux estimation strategy, the design of direct and indirect field oriented controller, a precise torque regulation scheme and the determination of a core loss resistance are discussed. Simulation and experimental results are also included and show the effectiveness of the proposed analysis and the proposed control strategy.

A new high efficient 2-phase and 3-phase interleaved Power Factor Correction boost converter typed Intelligent Power Module with high switching capability for low power home appliances

This paper introduces a new high efficient 2-phase and 3-phase interleaved PFC (Power Factor Correction) boost converter typed IPM (Intelligent Power Module) specialized in low power home appliances such as an air-conditioner. This new CIPOS(Control Integrated Power System) PFC IPM integrates 650V rated TRENCHSTOP 5 IGBTs with 650V rated Rapid switching diodes and a SOI (Silicon On Insulator) gate driver in DIL (Dual-in-line) package of transfer molded type with DCB (Direct Copper Bond). It is optimized to provide unmatched performance in terms of efficiency for hard switching application. This paper describes key features and performance of the new CIPOS mini PFC.

Suppression of vibration for elevator system using dead-time compensation with current prediction

In this paper, a vibration suppression scheme is proposed for the riding comfort of elevator using dead-time compensation with an accurate current information. To obtain an accurate current information at switching instants, a current prediction is used. The prediction current at switching instant for dead-time compensation is calculated from the sampled current, which greatly reduces the polarity error of the current at switching instants and increases the compensation accuracy. Using the proposed dead-time compensation scheme, the torque ripple of 6 times harmonics and the corresponding elevator vibration are reduced. Experimental evaluation has been performed with an 11 kW induction machine and a medium-speed elevator system. The result obtained proves the feasibility of the proposed method.

A new dynamic overmodulation strategy for high performance torque control of induction motor

In this paper, a new dynamic overmodulation strategy is proposed for vector-controlled induction motor drive, and a comparison study with conventional schemes is described in an analytical manner. By considering voltage boundary of inverter and current dynamics of induction motor simultaneously, the proposed overmodulation scheme allocates the output voltage of the inverter so that synchronous d-axis voltage is diminished in proportion as reference voltage exceeds hexagon boundary. As a result, d-axis current of vector-controlled induction motor is decreased in the overmodulation region, which secures the control voltage margin and improves the dynamic performance of torque control. The conspicuous improvement of the proposed scheme over conventional ones is observed in both simulated and experimental results.