Kang-Soon Ahn

Robust DC-link voltage control scheme for photovoltaic power generation system PCS

A power conversion system (PCS) for photovoltaic power generation system is composed of the DC/DC converter and the DC/AC inverter. To maximize power generation, DC/DC converter operated with MPPT (Maximum Power Point Tracking) algorithm and the PCS has been developed by the method of transformer tab change. DC/AC inverter controls DC-link voltage and grid current. But, single phase grid has 120Hz (Grid voltage frequency is 60Hz.) power ripple which arise DC-link voltage ripple. This paper presents a robust DC-link voltage control scheme. The control scheme utilizes a widow averaged DC-link voltage as a feedback signal. Experiment performed with 3kW PCS and the results support the validity of the control scheme.

A carrier-based medium vector PWM strategy for three-level inverters in transformerless photovoltaic systems

This paper proposes a new carrier-based PWM strategy for three-level inverter in transformerless photovoltaic systems. The proposed modulation method completely eliminates leakage currents by employing only medium vectors and one zero vector which produce the same common mode voltage. Due to carrier-based scheme, the proposed PWM method can allow overmodulation and be intuitively understood and simply implemented with analog or digital hardware. To show the feasibility of the proposed PWM method, the simulation results are presented.

Adapter design using planar transformer for aircraft

Planar magnetic based design technologies have been widely applied to power design for better cooling and ease of fabrication. The planar transformer and the planar inductor have low profile characteristics compare to the conventional transformer which would be more cubical in volume. High frequency operation of magnetic components is a main key to achieve high power density of the power module. However, at a high frequency, the skin effect and the proximity effect have to be considered very significantly in magnetic design and also the parasitic in the converter cannot be ignored. This paper deals with the design and the experiment of planar integrated magnetic component. The optimal design for planar magnetic is summarized.

A new oven detection algorithm and control of IH-Jar achieved by DSP control

This paper suggests a new method for oven detection in those induction heating rice cooker (IH-Jar) circuits that are controlled by DSP. The designed control method calculates oven detection levels based on changes in input currents during oven detection time and averages the input voltages, input currents and outputs during oven detection time thereby enhancing the reliability of oven detection. This new method allows more stable oven detection under the dip or distortion of commercial power supply that may occur in actual field, particularly, in circuits with no separate power factor circuit. The topology of the circuits used in this paper is Quasi-Resonant ZVS-PFM Single-ended.

Clamp mode forward ZVS-MRC with self-driven synchronous rectifier

The clamped-mode (CM) forward zero-voltage-switching multi-resonant power converter (ZVS-MRC) with a self-driven synchronous rectifier is studied. The loss at the synchronous rectification stage of the power converter is analyzed and compared with the loss at the conventional Schottky diode rectification stage of the power converter. From the results of the analysis, it is known that the use of MOSFETs as a synchronous rectifier effectively reduces the loss at the rectification stage over the whole load range. In order to verify the validity of the analysis, the authors have built a 33 W (3.3 V/10 A) CM forward ZVS-MRC with a self-driven synchronous rectifier, with a switching frequency of 1 MHz, and tested its performance. From these experimental results, synchronous rectification achieved about a 3 W improvement in losses at the rectification stage and about 3% in the efficiency of the power converter as compared with conventional Schottky diode rectification.

Space vector PWM for common mode voltage reduction and neutral point voltage balancing in three-level converters

This paper proposes a new space vector pulse-width modulation (PWM) for common mode (CM) voltage reduction and neutral point (NP) voltage balancing in three-level converters. In case of unbalanced NP voltage, a group of the space vectors that increase or decrease the NP voltage is chosen to achieve the NP voltage balancing while the resultant CM voltage has not only the minimized amplitude but also the dominant low frequency. In case of NP voltage balancing, the only space vectors with the same CM voltage are used to completely eliminate the CM voltage variation. To show the feasibility of the proposed PWM method, the simulation results are presented.

A Study on a Carrier Based PWM having Constant Common Mode Voltage and Minimized Switching Frequency in Three-level Inverter

In this paper, a carrier-based pulse with modulation (PWM) strategy for three-phase three- level inverter is dealt with, which can keep the common mode voltage constant with minimized switching frequency. The voltage gain and the switching frequency in overall operating ranges including overmodulation are investigated and the analytic equations are presented. Finally, the leakage current reduction effect is confirmed by carrying out simulation and experiment. It will be pointed out that the leakage current cannot be perfectly eliminated because of the dead time.

Development of 125kW grid-tied PV inverter and research on efficiency vs. transformer turn ratio

This paper reviewed the development of a 3-phase 125kW grid connected PV inverter and changes in the conversion performance of the inverter based on the gain of the low frequency isolation transformer for isolation between solar and the grid. The 125kW PV inverter consists of a transformer with the grid frequency for isolation between input and output (galvanic isolation) and it has the output power of 60Hz, 3P 3W 380Vac. P&O technique was used for MPPT (Maximum Power Point Tracking) and Active Phase Shift technique was used through changes in reactive power to prevent a islanding operation. Inverter control was achieved based on 16-bit DSP. This paper discussed about the conversion performance of the 125kW inverter in relation to the system and the result of development of THD, MPPT etc and mentioned about the result of comparison of the conversion performance of the inverter based on the efficiency of the low frequency transformer.