Dong-Wook Yoo

High boost converter using voltage multiplier

With the increasing demand for renewable energy, distributed power included in fuel cells have been studied and developed as a future energy source. For this system, a power conversion circuit is necessary to interface the generated power to the utility. In many cases, a high step-up DC/DC converter is needed to boost low input voltage to high voltage output. Conventional methods using cascade DC/DC converters cause extra complexity and higher cost. The conventional topologies to get high output voltage use flyback DC/DC converters. They have the leakage components that cause stress and loss of energy that results in low efficiency. This paper presents a high boost converter with a voltage multiplier and a coupled inductor. The secondary voltage of the coupled inductor is rectified using a voltage multiplier. High boost voltage is obtained with low duty cycle. Theoretical analysis and experimental results verify the proposed solutions using a 300 W prototype.

A Novel Grid Synchronization PLL Method Based on Adaptive Low-Pass Notch Filter for Grid-Connected PCS

The amount of distributed energy resources (DERs) has increased constantly worldwide. The power ratings of DERs have become considerably high, as required by the new grid code requirement. To follow the grid code and optimize the function of grid-connected inverters based on DERs, a phase-locked loop (PLL) is essential for detecting the grid phase angle accurately when the grid voltage is polluted by harmonics and imbalance. This paper proposes a novel low-pass notch filter PLL (LPN-PLL) control strategy to synchronize with the true phase angle of the grid instead of using a conventional synchronous reference frame PLL (SRF-PLL), which requires a d-q-axis transformation of three-phase voltage and a proportional-integral controller. The proposed LPN-PLL is an upgraded version of the PLL method using the fast Fourier transform concept (FFT-PLL) which is robust to the harmonics and imbalance of the grid voltage. The proposed PLL algorithm was compared with conventional SRF-PLL and FFT-PLL and was implemented digitally using a digital signal processor TMS320F28335. A 10-kW three-phase grid-connected inverter was set, and a verification experiment was performed, showing the high performance and robustness of the proposal under low-voltage ride-through operation.

Novel zero-voltage and zero-current-switching full bridge PWM converter using transformer auxiliary winding

A novel zero voltage and zero current switching (ZVZCS) full bridge (FB) pulse width modulation (PWM) converter is proposed to improve the demerits of the previously presented ZVZCS-FB-PWM converters, such as use of lossy components or additional active switches. A simple auxiliary circuit which includes neither lossy components nor active switches provides ZVZCS conditions to primary switches, ZVS for leading-leg switches and ZCS for lagging-leg switches. Many advantages including simple circuit topology, high efficiency, and low cost make the new converter attractive for high power (>2 kW) applications. The operation, analysis, features and design considerations are illustrated and verified on a 2.5 kW, 100 kHz insulated gate bipolar transistor (IGBT) based experimental circuit.

A New Topology With High Efficiency Throughout All Load Range for Photovoltaic PCS

In this paper, a new topology is proposed that can significantly reduce the converter rated power and increase the efficiency of total photovoltaic (PV) system. Since the output voltage of PV module has very wide operating range, in general, the DC/DC converter is used to produce constant high-DC-link voltage for DC/AC inverter. According to the analysis of the proposed topology, only 20% of total PV system power is processed by the DC/DC power conversion stage. The DC/DC power conversion stage used in proposed topology has flat efficiency curve throughout all load range and very high efficiency characteristics. In the proposed topology, because the converter efficiency curve is almost flat throughout all load range, the total system efficiency at light load is dramatically improved. The proposed topology is implemented for 250-kW power conditioning system. This system has only three DC/DC power conversion stage with 24-kW rated power. It is only one-third of total system power. The experimental results show that the proposed topology has good performance.

High voltage switch using series-connected IGBTs with simple auxiliary circuit

There is much need for high voltage solid-state-switches in a broad area of applications. To get a high voltage switch, the series-connection of a solid state device is usually used. The main problem in such high voltage switches is to guarantee the voltage balance across the device both at a static and dynamic transient state. This paper presents a simple and reliable voltage-balancing scheme of the high voltage switch stack using series-connected IGBTs. With the proposed method, using a simple voltage balancing circuit, high-voltage semiconductor switches are realized with working voltages of several orders of kilo-volts. The operation principle of the proposed circuit is explained and analyzed. Transient and static voltage balancing is tested on an experimental 20 kV/400 A switch with sixteen series-connected IGBT modules.

Survey of the Power Conditioning System for PV Power Generation

This paper is a survey on photovoltaic (PV) power conditioning systems (PCS) and their control strategies. Different inverter structures used in the PCSs are summarized. A novel Z-Source inverter based PCS is presented. The requirements and standards of PV PCS are also introduced.

Novel zero-voltage and zero-current-switching (ZVZCS) full bridge PWM converter using transformer auxiliary winding

A novel zero voltage and zero current switching (ZVZCS) full bridge (FB) PWM converter is proposed to improve the demerits of the previously presented ZVZCS-FB-PWM converters such as use of lossy components or additional active switches. A simple auxiliary circuit which includes neither lossy components nor active switches provides ZVZCS conditions to primary switches, ZVS for leading-leg switches and ZCS for lagging-leg switches. Many advantages including simple circuit topology, high efficiency, and low cost make the new converter attractive for high power (>1 kW) applications. The operation, analysis, features and design considerations are illustrated and verified on a 2.5 kW, 100 kHz IGBT based experimental circuit.

A novel grid-connected PV PCS with new high efficiency converter

In this paper, new topology is proposed that can dramatically reduce the converter power rating and increase the efficiency of total PV system. Since the output voltage of PV module has very wide voltage range, in general, the DC/DC converter is used to get constant high DC voltage. According to analysis of PV characteristics, in proposed topology, only 20% power of total PV system power is needed for DC/DC converter. DC/DC converter used in proposed topology has flat efficiency curve at all load range and very high efficiency characteristics. The total system efficiency is the product of that of converter and that of inverter. In proposed topology, because the converter efficiency curve is flat all load range, the total system efficiency at the low power range is dramatically improved. The proposed topology is implemented for 200 kW PCS system. This system has only three DC/DC converters with 20 kW power rating each other. It is only one-third of total system power. The experiment results show that the proposed topology has good performance.

Novel Single-Phase PWM AC–AC Converters Solving Commutation Problem Using Switching Cell Structure and Coupled Inductor

This paper presents novel single-phase pulse width modulation (PWM) ac-ac converters that can solve the commutation problem in single-phase direct PWM ac-ac converters without sensing the input voltage polarity. By using a basic switching cell structure and coupled inductors, the proposed ac-ac converters can be short- and open-circuited without damaging the switching devices. Neither lossy RC snubber nor dedicated soft commutation strategy is required in the proposed converter. By replacing the conventional phase-leg of the PWM ac-ac converters with the switching cell structure and the coupled inductor, three novel buck, boost, and buck-boost type PWM ac-ac converters are developed. Although two coupled inductors are required for the proposed converter, the input inductor of the proposed converter can be much smaller than that of the conventional PWM ac-ac converters. The volume of the magnetic components can be further reduced by increasing switching frequency of the converter because very fast recovery diodes can be selected externally. In order to verify performance and robustness of the proposed converter, a 200-W boost type prototype converter was built and tested with both mismatched gate signals and highly distorted input voltage.

Zero-voltage-transition isolated PWM boost converter for single stage power factor correction

A novel zero-voltage-transition (ZVT) isolated PWM boost converter for single stage power factor correction (PFC) is presented. A simple auxiliary circuit added in the secondary rectifier side provides zero-voltage-switching (ZVS) condition to all semiconductor devices without increasing additional device voltage and current stresses. The proposed converter gives both input power factor correction and direct conversion from AC line to DC output, which leads to high efficiency and high power density conversion. Operation principle, analysis, and features of the proposed converter are presented and verified by the computer simulation and experimental results from a 1.5 kW, 80 kHz laboratory prototype.