Hyun-Keun Ku

Fault detection and tolerant control of 3-phase NPC active rectifier

Compared to conventional 2-level AC/DC PWM converter, the 3-phase NPC active rectifier has a high number of power semi-conductors. Hence the possibility of the open-switch faults is much higher. Due to the many number of active elements, the detection and the tolerant control of the open-switch faults are more complicated than the conventional 2-level converter. Furthermore, the open-switch faults give rise to imbalance of the AC input currents and the fluctuation DC-link voltage. This paper proposes the open-switch fault detection method and the tolerant control method. In particular, open-switch fault case of one switch among inner six switches of NPC active rectifier is analyzed. The usefulness of this paper is verified through the computer simulation and experimentations, respectively.

Multiple open-switch faults detection and fautls tolerant method of three-level three-phase NPC active rectifier

This paper presents multiple open-switch faults detection and faults tolerant methods for the 3-level 3-phase neutral point clamped (NPC) active rectifier. The 3-level 3-phase NPC active rectifier is comprised of many switching elements, which is increased the probability of open-switch faults compared to conventional 3-phase AC/DC PWM converter. These open-switch faults generate the imbalance of the input AC currents and output DC-link voltage pulsation. As a result, system performance and efficiency are reduced. Therefore, accurate and quick fault detection is required. Further fault tolerant is needed. In this paper suggests the multiple open-switch faults detection method and fault tolerant without additional component. The proposed faults detection method is getting by combination of grid angle and output DC-link voltage ripple component. The fault tolerant is implemented by changing voltage reference. The usefulness of the proposed methods is verified through the simulation results.

Full simulation modeling for electrical analysis of all electric ships with medium voltage DC power system

This paper presents the development of full simulation model for All Electric Ship (AES) based on medium voltage DC power system. AES is generally adopted Integrated Power Systems (IPS). AES has become popular both in commercial and military areas owing to the advantages of IPS. However, the configuration of IPS is complex and difficult to experimental verification. Therefore, a tool for effective analysis is highly required to have an insight into the ship electrical system. The proposed simulation model includes the mechanical and the electrical elements by using the MATLAB/Simulink tool. By using this model, proposed paper performs a comprehensive electrical analysis based on the different ship operating scenarios.

A Study Integrated-Power-System Simulation Model of All-Electric-Ship

The simulation model of All-Electric-Ship consists of electrical and mechanical systems. Running the total simulation requires considerable time and causes a lack of computer memory, because the two systems have different dynamic characteristics. Therefore, integrated simulation is practically impossible. This paper proposes the simplified model of electrical system to reduce simulation time significantly, compared to the detailed model. The validity of the proposed simplified model is verified by comparing detailed and simplified simulation results. Thus, the simplified models are applied to the integrated system. As a result, total system simulation can be implemented.

Current reconstruction method with single DC-link current sensor based on the PWM inverter and AC motor

This paper proposes the new current reconstruction method of three-phase currents in case of using dc-link shunt resistor for three-phase AC motor. When dc-link shunt resistor is used for the acquisition of phase currents, there are the immeasurable regions in the hexagon of Space Vector Pulse Width Modulation(SVPWM). The conventional methods used the shift of the switching patterns of SVPWM to extend the region of the measurable area from the immeasurable area. Thus, these methods cause the audible noise, the current distortion and deteriorate the control performance of the motor drive system. The proposed method uses the current equations of the combined equivalent circuits of the PWM inverter and AC motor according to the switching patterns of the PWM inverter. This method can reconstruct three-phase current without the shift of the switching pattern of SVPWM and producing the audible noise. The effectiveness of the proposed algorithm is verified through computer simulation and the experimental results.

Current reconstruction method for PMSM drive system with a DC link shunt resistor

For the cost reduction of the inverter system, a DC link shunt resistor can be used to obtain the phase current of the AC motor. However, the phase current cannot be obtained from the shunt resistor when the duration of the active vector is shorter than the minimum time to sample the DC link current accurately. Conventional methods to reconstruct the phase current have some problems such as the high THD (Total Harmonic Distortion), the acoustic noise and the inaccurate reconstruction of the phase current in the low modulation region. In this paper, the cause of the noise in the conventional method is analyzed. To solve the acoustic noise problem, current reconstruction method based on current estimation is proposed. Intermittent PWM shift method is also proposed to enhance the accuracy of the reconstructed current in the low modulation region. The effectiveness of the proposed methods is verified through the simulations and the experiments. The usefulness of the proposed method is also proven by measuring the sound in the anechoic room.

A PWM Control Strategy for Low-speed Operation of Three-level NPC Inverter based on Bootstrap Gate Drive Circuit

This paper proposes the pulse width modulation (PWM) control strategy for low-speed operation in the three-level neutral-point-clamped (NPC) inverters based on the bootstrap gate drive circuit. For the purpose of the cost reduction, several papers have paid attention to the bootstrap circuit applied to the three-level NPC inverter. However, the bootstrap gate driver IC cannot generate the gate signal to the IGBT for low-speed operation, because the bootstrap capacitor voltage decreases under the threshold level. To solve this problem, the dipolar and partial-dipolar modulation can be the effective solution. Nevertheless, these modulation have drawbacks in terms of the switching loss and THD. Therefore, this paper proposes the PWM control strategy to operate the inverter at low-speed and to minimize the switching loss and harmonics. The experimental results are presented to verify the validity on the proposed method.

A Study on the Cuf-off Speed of Small-scale Wind Power System for Battery Charging

Three phase PWM(Pulse Width Modulation) converter of the small-scale wind power system is able to charge battery under the rated wind speed regions. However, it is impossible to control output power of converter at the over win speed region because back-EMF(Electro Motive Force) of PMSG(Permanent Magnet Synchronous Generator) is higher than the battery terminal voltage of PMSG is reduced. However, the cut-off wind speed exists although battery charging algorithm is implemented by flux weakening control method. Therefore, this paper performs analysis of other factors which affects limitation wind speed. The validity of the analysis are verified through simulation.

The Analysis and Study on Operation Strategy of Grid-connected Series Small Wind Turbine System

This paper proposes an analysis and operation strategy of a grid-connected wind turbine system using a diode rectifier. The currents of generators are the same as that of a small wind turbine system. Therefore, the analysis of generator torque is required as opposed to an analysis of blade speed. In this paper, the appropriate MPPT control method is proposed to control generator torque. Usefulness of the proposed operation strategy is verified by simulations and experiments.

Lithium-ion Battery Energy Storage System for Power Quality Improvement in Electrical Propulsion Ships

This paper explained the application of a lithium-ion battery energy storage system to electric propulsion ships. The power distribution in electric propulsion ships has low power quality because of the variation in the power consumption of the propulsion motor. For proper operation of the ship, the power quality needs to be improved, and the battery energy storage system is used to solve power-quality problems. The simulation models of electric propulsion ship and battery energy storage systems are constructed on MATLAB/Simulink to verify the improvement in power quality. The proposed system is applied in various scenarios of the propulsion motor state. The power quality achieved by using the battery energy storage system in both voltage and frequency satisfies the standards set by IEC-60092/101.