Kwan-Yuhl Cho

An MRAS-Based Diagnosis of Open-Circuit Fault in PWM Voltage-Source Inverters for PM Synchronous Motor Drive Systems

In this paper, a simple and low-cost open-circuit fault detection and identification method for a pulse-width modulated (PWM) voltage-source inverter (VSI) employing a permanent magnet synchronous motor is proposed. An open-circuit fault of a power switch in the PWM VSI changes the corresponding terminal voltage and introduces the voltage distortions to each phase voltage. The proposed open-circuit fault diagnosis method employs the model reference adaptive system techniques and requires no additional sensors or electrical devices to detect the fault condition and identify the faulty switch. The proposed method has the features of fast diagnosis time, simple structure, and being easily inserted to the existing control algorithms as a subroutine without major modifications. The simulations and experiments are carried out and the results show the effectiveness of the proposed method.

Nonlinearity estimation and compensation of PWM VSI for PMSM under resistance and flux linkage uncertainty

Generally, there exists a voltage distortion or nonlinear voltage gain between the reference and output voltages in a pulsewidth-modulation (PWM) voltage source inverter (VSI). Nonlinearity varies with operating conditions, such as the temperature, direct current (dc) bus voltage, and phase current level. Also, the nonlinearity affects the machine current distortion, torque pulsations, and degradation of control performance. In this paper, the nonlinearity in a PWM VSI is analyzed and a new online estimation method based on the model reference adaptive system is proposed to compensate the time varying voltage distortion, considering the parameter uncertainty caused by the temperature variation for a permanent magnet synchronous motor. The simulation and experimental results show the effectiveness of the proposed voltage difference estimator.

Torque Ripple Reduction of a PM Synchronous Motor for Electric Power Steering using a Low Resolution Position Sensor

MDPS (motor driven power steering) systems have been widely used in vehicles due to their improved fuel efficiency and steering performance when compared to conventional hydraulic steering. However, the reduction of torque ripples and material cost are important issues. A low resolution position sensor for MDPS is one of the candidates for reducing the material costs. However, it may increases the torque ripple due to the current harmonics caused by low resolution encoder signals. In this paper, the torque ripple caused by the quantized rotor position of the low resolution encoder is analyzed. To reduce the torque ripples caused by the quantization of the encoder signals, the rotor position and the speed are estimated by measuring the frequency of the encoder signals. In addition, the compensating q-axis current is added to the current command so that the 6th order torque harmonic is attenuated. The reduction of torque ripples by applying the estimated rotor position and the compensated q-axis current is verified through experimental results.

Novel PWM Method with Low Ripple Current for Position Control Applications of BLDC Motors

BLDC Motors are widely used in various speed control applications due to their ease of control and low cost. Generally, the unipolar PWM method is used for speed control applications. However, the unipolar PWM method has a current spike problem in the braking operation which can be a problem in speed reversal which generally happens in position control applications. However, the current spike problem can be solved by the conventional bipolar PWM method. Although the current spike problem can be solved, the conventional bipolar PWM method has the problem of a large current ripple. In this paper, a novel bipolar PWM method is proposed to solve this problem. The current ripple and the current spike problems are analyzed in this paper for the unipolar and bipolar PWM methods. At last, the merits of the proposed bipolar PWM method are proven by experiment.

Active damping of LCL filter without capacitor voltage sensors for three phase PWM inverter

In this paper, new sensorless active damping method of the grid-connected LCL filter for a three-phase PWM inverter is proposed. The resonance component of capacitor voltage of LCL filter is observed by a simple MRAS (Model Reference Adaptive System) observer without additional sensors or circuits. The active damping is implemented by feed-forward compensation of the observed capacitor voltage for current controller. The validity of the proposed method is verified by the simulation and experiment.

Design of LLC Resonant Converter having Enhanced Load Range for Communication Power

This paper deals with LLC resonant converter for communication power supply. Generally, the load range of communication power is very wide. However, voltage conversion ratio of LLC converter is highly dependent of load condition. So, it is not easy to design of robust power supply along with the wide load condition. Especially, it is not possible to meet the required low voltage conversion ratio for low output voltage with high input voltage under the light load condition. To solve this problem, in this paper, a new duty control interlinked with operational frequency has been proposed. To prove the usefulness of the proposed control method, the simulation and experiments were carried out. The simulation and experimental results show the usefulness of the proposed control method.

Single carrier wave comparison PWM for Vienna rectifier and consideration for DC-link voltage unbalance of offset voltage effects

This paper presents a new single carrier wave comparison PWM method for 3 level 3 phase Vienna type rectifier. The theoretical background for the single carrier wave comparison PWM is presented. The model for this Vienna rectifier is reviewed briefly and the voltage unbalance problem according to the offset duty is analyzed. Finally, the simulation and experimental results prove the effectiveness of the analysis results.

Analysis of LLC Resonant Converter with Current- Doubler Rectification Circuit

In this paper, LLC series resonant converter with current-doubler as a rectification circuit for secondary side is proposed. The current-doubler circuit is generally used for the high voltage input and low voltage output application to get high efficiency characteristics with reduced transformer turn ratio. However, an inductive circuit is not used in a secondary side for the LLC series resonant converter generally. When there is inductive circuit like current-double on the secondary side, the resonant characteristics are changed. In this paper, LLC converter with the current-doubler using coupled inductor is proposed. We verify that the secondary side current-doubler using coupled inductor is not affect to the resonant characteristic of primary LLC by the mathematical analysis. Finally, the analysis results are proved by the simulation and experiments.

Torque Ripple Reduction based on Flux Linkage Harmonics Observer for an Interior PM Synchronous Motor including Back EMF Harmonics

The mechanical vibration of a PM synchronous motor at low speeds due to the back emf harmonics may be serious problems in some application such as MDPS(Motor driven power steering), electric vehicles. In this paper, torque ripple reduction for an interior PM synchronous motor including back emf harmonics is proposed. The dq flux linkage harmonics of the permanent magnet are estimated on real time by using the dq currents of the real system and the model of the MRAS observer. Based on the estimated flux linkage harmonics, the dq harmonic currents for reducing the torque ripples are compensated on the dq reference currents. The estimation of the flux linkage harmonics by the MRAS observer and the torque ripple reduction of the proposed algorithm was verified by the simulation and experiment.

A carrier comparison PWM method for reducing input current THD of three-phase PWM rectifier

In this paper, a new PWM method is proposed to reduce input current THD of PWM Rectifier. In the carrier comparison PWM method for the PWM rectifier, a triangle wave is generally used as the carrier wave. However, large d-axis current ripple by this method can be a source of large input current THD. In this paper, new carrier comparison PWM method is proposed in which saw tooth wave is used as a carrier wave. Depending on the phase of the voltage commands, one of the rising or falling saw tooth wave is selected. Furthermore, switching losses are minimized by the selection of pole voltage on the proposed carrier comparison PWM method. The simulation results are shown and the usefulness of the proposed method is verified by the comparison of the performance between the conventional and proposed PWM methods.