Do-Hyun Jang

Step-up/down AC voltage regulator using transformer with tap changer and PWM AC chopper

A step-up/down AC voltage regulator is proposed, in which a tap-changing transformer and a pulsewidth modulation (PWM) AC chopper are combined. The proposed regulator can step up or down the output voltage to input voltage. Also, the proposed regulator restrains more harmonics of output voltage compared to the conventional PWM regulator. The input current flows continuously in the proposed regulator, while it flows discontinuously in the conventional PWM regulator. Through digital simulation, several characteristics are investigated theoretically and then compared with those of conventional schemes. Practical verification of the theoretical predictions is presented to confirm the capabilities of the proposed regulator.

PWM methods for two-phase inverters

This article focuses on simple space-vector PWM (SPWM) methods for two-leg, three-leg, and four-leg inverters that can be applied to three phase induction motor drives (TPIM). First, a carrier-based PWM method for a two-leg inverter was proposed on the basis of the conventional SPWM method. Second, a carrier-based PWM method for a four leg inverter that used a double triangular carrier wave was proposed. Third, a carrier-based PWM method for a three-leg inverter was proposed as a replacement for a conventional SVPWM method. Digital calculations using the PSIM software package are performed to investigate the effectiveness of the proposed PWM method

Voltage, frequency, and phase-difference angle control of PWM inverters-fed two-phase induction motors

A phase-difference angle (PDA) controlled pulsewidth-modulated (PWM) inverter is proposed for a two-phase induction motor adjustable speed drive. Output waveforms are fixed over the whole operating range of the motor. The motor torque is controlled not by the modulation of the phase voltage, but by the PDA. Based on the selected harmonic elimination (SHE) PWM technique, the commutation angles of the output voltage are calculated. Several characteristics of the two-phase induction motor driven by the PDA inverter are analyzed. A hybrid PWM inverter is also proposed to compensate for the degradation of the efficiency at small PDA. Not only the PDA but also the voltage amplitude and frequency are used as the parameters for controlling the torque of the motor in the hybrid inverter. The speed characteristics of the two-phase induction motor driven by the hybrid PWM inverter are more flexible than when the motor is driven by the conventional PWM inverter, which requires adjustable communication angles. >

Improvement of input power factor in AC choppers using asymmetrical PWM technique

An asymmetrical pulse width modulated (APWM) control technique for AC choppers is proposed to improve the input power factor. The switching function for the proposed technique is derived and hence converted into the asymmetrical PWM waveform for practical implementation of an AC chopper. Through digital simulation several characteristics are investigated theoretically and then compared with those of the conventional PWM control technique. The proposed strategy is simplified to an approximate APWM which can be realized by the analog circuit. Practical verification of the theoretical predictions is presented to confirm the capabilities of the proposed technique. >

Asymmetrical PWM technique with harmonic elimination and power factor control in AC choppers

This paper describes the asymmetrical pulse width modulated (APWM) control technique for single phase AC choppers, which improves the input power factor and eliminates the harmonics of the output voltage up to a specified order. This technique also enables linear control of the fundamental component of the output voltage. The APWM switching patterns at the specified phase angle are obtained by the Newton-Raphson method and can be implemented by a one-chip microprocessor. Theoretical comparisons are made with conventional PWM technique and the computed performance indicates the superiority of the proposed APWM technique. Practical verification of the theoretical predictions is presented to conform the capabilities of the new technique. >

Problems Incurred in a Vector-Controlled Single-Phase Induction Motor, and a Proposal for a Vector-Controlled Two-Phase Induction Motor as a Replacement

This paper presents several of the problems encountered with vector-controlled single-phase induction motor (SPIM), and discusses about the complex implementation of a vector controlled SPIM drive. The vector-controlled symmetrical two-phase induction motor (TPIM) is presented as a viable replacement for the vector-controlled SPIM. The implementation of the proposed vector-controlled TPIM is simple compared to the vector-controlled SPIM. All the TPIM parameters can be calculated simply and precisely. The proposed strategy for TPIM is derived from the indirect vector control strategy used for three-phase ac machines. Several differences between the vector control strategies for the TPIM and for three-phase ac motor are discussed. The validity of the proposed vector-controlled TPIM was verified by simulations and experiments.

A new control strategy for instantaneous voltage compensator using 3-phase PWM inverter

In a three-phase power system, unbalanced voltage with harmonics can be detected on the synchronous reference frame. Assuming that there is no neutral path in the power system, an unbalanced voltage with harmonic components has a DC component, a 2nd harmonic and the other harmonic components. Therefore, it is possible to compensate unbalanced voltage and harmonic voltage by cancelling the harmonic components, exclusive of the DC component on the d-q axis. In addition, by adjusting the value of the DC component obtained from positive sequences, the regulation of load voltage is achieved. This paper presents an algorithm performing compensation of unbalanced and harmonic voltage as well as maintaining the constant voltage in the load side. The compensating characteristics of the proposed instantaneous voltage compensator are also discussed.

Asymmetrical PWM method for AC chopper with improved input power factor

An asymmetrical pulsewidth modulated (APWM) control technique for AC choppers, which can improve the input power factor as well as the harmonic contents, is proposed. A switching scheme for the proposed technique is suggested. Using digital simulation, several characteristics are investigated theoretically and then compared with those of the conventional PWM one. Practical experimental results have good agreement with the calculated ones, proving the feasibility of the proposed technique.<<ETX>>

Signal Compensation for Analog Rotor Position Errors due to Nonideal Sinusoidal Encoder Signals

This paper proposes a compensation algorithm for the analog rotor position errors caused by nonideal sinusoidal encoder output signals including offset and gain errors. In order to achieve a much higher resolution, position sensors such as resolvers or incremental encoders can be replaced by sinusoidal encoders. In practice, however, the periodic ripples related to the analog rotor position are generated by the offset and gain errors between the sine and cosine output signals of sinusoidal encoders. In this paper, the effects of offset and gain errors are easily analyzed by applying the concept of a rotating coordinate system based on the dq transformation method. The synchronous d-axis signal component is used directly to detect the amplitude of the offset and gain errors for the proposed compensator. As a result, the offset and gain errors can be well corrected by three integrators located on the synchronous d-axis component. In addition, the proposed algorithm does not require any additional hardware and can be easily implemented by a simple integral operation. The effectiveness of the proposed algorithm is verified through several experimental results.

Speed control method for switched reluctance motor drive using self-tuning of switching angle

In this paper, a determination method of turn-off angle is realized by using a self-tuning control method. During the sampling time, a number of pulses from the encoder are checked by using a single-chip microprocessor and then compared with a pre-checked number of pulses. After calculating the difference between the two data, the turn-off angle moves forward or backward by the self-tuning method. By repeating such a process, the optimal turn-off angle is determined and the maximum torque is maintained. Though experiments, it is observed that motor speed is almost maintained if the turn-off angle is adjusted automatically by a self-tuning method when turn-on angle is changed.