Tae-Won Chun

Algorithms for Controlling Both the DC Boost and AC Output Voltage of Z-Source Inverter

This paper aims to achieve the good performances of both the DC boost control and AC output voltage control of the Z-source inverter. The algorithm to control linearly the capacitor voltage is suggested in order to improve the transient response for DC boost control of the Z-source inverter. The peak AC output voltage is used to control exactly the AC output voltage to its desired level. The proposed algorithms are verified with simulation and experiment with 32-bit DSP

Input Power Factor Compensation Algorithms Using a New Direct-SVM Method for Matrix Converter

An input filter is necessary for a matrix converter (MC) system to improve the input current quality with low harmonic components, as well as to reduce the input voltage distortion supplied to the MC. However, the input filters characteristics make the input power factor (IPF) obtained at unity only in the presence of high output loads, and the IPF degrades significantly under light-load conditions. In this paper, we propose a new direct space vector modulation (DSVM) method to achieve the required displacement angle between the input voltage and input current of the MC. A new switching strategy is introduced based on the maximum compensated angle. Then, power factor compensation algorithms using the new DSVM method to achieve the maximum IPF are presented, in which compensation algorithm I is based on using the input filter and power supply parameters to estimate the optimal compensated angle. Compensation algorithm II is subsequently proposed using a proportional-integral controller to overcome drawbacks presented in compensation algorithm I. Simulation and experimental results are shown to validate the effectiveness of the proposed compensation algorithms.

Sensorless Control of BLDC Motor Drive for an Automotive Fuel Pump Using a Hysteresis Comparator

This paper develops the brushless dc (BLDC) motor sensorless control system for an automotive fuel pump. The sensorless techniques that are based on a hysteresis comparator and a potential start-up method with a high starting torque are suggested. The hysteresis comparator is used to compensate for the phase delay of the back EMFs due to a low-pass filter (LPF) and also prevent multiple output transitions from noise or ripple in the terminal voltages. The rotor position is aligned at standstill for maximum starting torque without an additional sensor and any information of motor parameters. Also, the stator current can be easily adjusted by modulating the pulse width of the switching devices during alignment. Some experiments are implemented on a single chip DSP controller to demonstrate the feasibility of the suggested sensorless and start-up techniques.

Grid-connected PV System Using a Quasi-Z-source Inverter

This paper presents the MPPT (Maximum Power Point Tracking) and PCC (Point of Common Coupling) current control strategy for photovoltaic (PV) grid-connected generating system using the quasi-Z-source inverter (QZSI). At first, in order to explain the above controllers, the characteristic of QZSI is analyzed. And then, the MPPT control technique with a modified P&O method, the PCC current control one for the regulation of dc-link capacitor voltage, and the PWM methods for the proposed system are explained. The feasibility of the propose algorithm is verified through the simulation and experiment with 3kW system.

PLL-Based Seamless Transfer Control Between Grid-Connected and Islanding Modes in Grid-Connected Inverters

This paper proposes a phase-locked loop (PLL)-based seamless transfer control method between grid-connected and islanding modes in a three-phase grid-connected inverter. The PLL is used to synchronize the phase of the load voltage to a grid voltage in grid-connected operation, and to generate an angle with the desired frequency in islanding operation. The stability of both the grid current loop for grid-connected operation and the load voltage control loop for islanding operation is analyzed. The phase and magnitude of the load voltage are successively matched to the grid voltage for a seamless transfer from islanding to grid-connected operation. When grid voltage sag occurs, an operating sequence including a PLL operation is suggested in order to transfer smoothly to islanding operation and to provide a stable and seamless voltage to a sensitive load under the voltage sag condition. The simulation and experimental results are carried out to verify the effectiveness of the proposed algorithm.

A Novel Strategy of Efficiency Control for a Linear Compressor System Driven by a PWM Inverter

Linear compressors with a free piston driven by a linear motor have attracted wide attention in cooling apparatuses such as refrigerators due to their high efficiency. The method of using triacs as a linear motor drive is not satisfactory for improving the efficiency of linear compressors. In this paper, the performance of linear compressors using a pulsewidth modulation inverter is investigated, with emphasis on the efficiency and power factor along with variations of both mechanical and electrical resonant frequencies. The strategy for improving the efficiency of the linear compressor is suggested by controlling the average value of the product of the piston stroke and motor current to 0. The performance of both the stroke and efficiency controls of the linear compressor is verified through experiments under various gas pressure conditions.

Algorithms for controlling both the DC boost and AC output voltage of the Z-source inverter

This paper aims to achieve good performance for both the dc boost and the ac output voltage control of the Z-source inverter (ZSI). The algorithm to control linearly the capacitor voltage is suggested in order to improve the transient response for dc boost control of the ZSI. The peak value of the ac output voltage is used to control exactly the ac output voltage to its desired level. A modified space vector pulsewidth modulation scheme is applied to control the shoot-through time for boosting dc voltage. The proposed algorithms are verified with simulation and experiment with a 32-bit digital signal processor.

Power Conditioning System for a Grid Connected PV Power Generation Using a Quasi-Z-Source Inverter

This paper presents a grid connected photo-voltaic system using a quasi-Z-source inverter (QZSI) for power stage reduction. The power stage can be reduced because of an additional shoot-through stage which is a characteristic of QZSI. Therefore, by utilizing a QZSI the system’s efficiency can be increased. In this paper, for applying a QZSI to a PV system, control methods such as maximum power point tracking (MPPT), point of common coupling (PCC) current control and PWM are studied and verified through simulation and experiment. In order to explain the above controllers, the characteristics of a QZSI are first analyzed. Then the MPPT control technique with a modified P&O method, the PCC current control for the regulation of the dc-link capacitor voltage and the PWM methods for the proposed system are explained. The feasibility of the proposed algorithm is verified through simulation and experiment with a 3kW system.

Development of adaptive hysteresis band current control strategy of PWM inverter with constant switching frequency

Hysteresis current control is one of the simplest techniques used to control the magnitude and phase angle of motor current for motor drive systems. However the conventional fixed band hysteresis control has a variable switching frequency depending on motor speed and load. In this paper, the adaptive hysteresis band current control strategy is proposed, where the hysteresis band is controlled as variations of motor speed, load current, and neutral point voltage in order to hold the switching frequency constant at any operating conditions. The proposed current control strategy is introduced to the current controller of a vector controlled permanent magnet synchronous motor systems. The proposed strategy is verified by simulations and experiments.

AC Output Voltage Control with Minimization of Voltage Stress Across Devices in the Z-Source Inverter Using Modified SVPWM

The paper proposes the algorithms of ac output voltage control in the Z-source inverter while minimizing the voltage stress across the devices. A novel switching pattern in the SVPWM is used in order to boost easily the capacitor voltage by controlling a shoot through time. The possible operating region for obtaining a desired ac output voltage to dc input voltage is analyzed. The voltage stress across the switching devices can be so mush reduced at a given ac output voltage. The proposed methods are verified with the simulation studies and experiments with 32-bit DSP.