Jong Pil Lee

A Novel Topology for Photovoltaic DC/DC Full-Bridge Converter With Flat Efficiency Under Wide PV Module Voltage and Load Range

In this paper, a novel topology for a photovoltaic (PV) dc/dc converter that can dramatically reduce the power rating and increase the efficiency of a PV system by analyzing PV module characteristics is proposed. Based on the analysis, in the proposed topology, only 30.7% power of the total PV system is needed for a dc/dc converter. Furthermore, the dc/dc converter efficiency curve is flat under wide PV module voltage and all load ranges. In particular, the converter efficiency at the lower duty range is dramatically improved. The total PV system is implemented for a 250-kW PV power conditioning system (PCS). This system has only three dc/dc converters with a 25-kW power rating. It is only one-third of the total PV PCS power. The 25-kW prototype PV dc/dc converter is introduced to experimentally verify the proposed topology. In addition, an experimental result shows that the proposed topology exhibits a good performance.

Input-Series-Output-Parallel Connected DC/DC Converter for a Photovoltaic PCS with High Efficiency under a Wide Load Range

This paper proposes an input-series-output-parallel connected ZVS full bridge converter with interleaved control for photovoltaic power conditioning systems (PV PCS). The input-series connection enables a fully modular power-system architecture, where low voltage and standard power modules can be connected in any combination at the input and/or at the output, to realize any given specifications. Further, the input-series connection enables the use of low-voltage MOSFETs that are optimized for a very low RDSON, thus, resulting in lower conduction losses. The system costs decrease due to the reduced current, and the volumes of the output filters due to the interleaving technique. A topology for a photovoltaic (PV) dc/dc converter that can dramatically reduce the power rating and increase the efficiency of a PV system by analyzing the PV module characteristics is proposed. The control scheme, consisting of an output voltage loop, a current loop and input voltage balancing loops, is proposed to achieve input voltage sharing and output current sharing. The total PV system is implemented for a 10-㎾ PV power conditioning system (PCS). This system has a dc/dc converter with a 3.6-㎾ power rating. It is only one-third of the total PV PCS power. A 3.6-㎾ prototype PV dc/dc converter is introduced to experimentally verify the proposed topology. In addition, experimental results show that the proposed topology exhibits good performance.

Active Frequency with a Positive Feedback Anti-Islanding Method Based on a Robust PLL Algorithm for Grid-Connected PV PCS

This paper proposes an active frequency with a positive feedback in the d-q frame anti-islanding method suitable for a robust phase-locked loop (PLL) algorithm using the FFT concept. In general, PLL algorithms for grid-connected PV PCS use d-q transformation and controllers to make zero an imaginary part of the transformed voltage vector. In a real grid system, the grid voltage is not ideal. It may be unbalanced, noisy and have many harmonics. For these reasons, the d-q transformed components do not have a pure DC component. The controller tuning of a PLL algorithm is difficult. The proposed PLL algorithm using the FFT concept can use the strong noise cancelation characteristics of a FFT algorithm without a PI controller. Therefore, the proposed PLL algorithm has no gain-tuning of a PI controller, and it is hardly influenced by voltage drops, phase step changes and harmonics. Islanding prediction is a necessary feature of inverter-based photovoltaic (PV) systems in order to meet the stringent standard requirements for interconnection with an electrical grid. Both passive and active anti-islanding methods exist. Typically, active methods modify a given parameter, which also affects the shape and quality of the grid injected current. In this paper, the active anti-islanding algorithm for a grid-connected PV PCS uses positive feedback control in the d-q frame. The proposed PLL and anti-islanding algorithm are implemented for a 250kW PV PCS. This system has four DC/DC converters each with a 25kW power rating. This is only one-third of the total system power. The experimental results show that the proposed PLL, anti-islanding method and topology demonstrate good performance in a 250kW PV PCS.

A Novel Topology for Photovoltaic Series Connected DC/DC Converter with High Efficiency Under Wide Load Range

The paper proposes a new topology for photovoltaic DC/DC converter with high efficiency under wide input voltage range is proposed. Photovoltaic DC/DC is a very crucial part of power conditioning system(PCS). Considering that output characteristic of photovoltaic cell has wide voltage range, depending on the operating conditions of photovoltaic cell, the DC/DC converter also needs to have wide input voltage range to regulate the constant output voltage. In addition, a high rated voltage of power switch (MOSFET) for DC/DC converter is necessary in order to be compatible with the high maximum output voltage of photovoltaic cells maximum output voltage. Also photovoltaic power conditioning system should have a high efficiency under operation condition. To satisfy PV PCS condition series connected non-isolated DC/DC converter topology is proposed. This paper examines the proposed topology employing four modules and shows that it dramatically enhances the energy efficiency from low load to high load condition by reducing the required power level for DC/DC converter by one-third of conventional DC/DC converter. A case of 20 kW prototype as the PV DC/DC converter is introduced to experimentally verify the proposed topology.

High efficient interleaved input-series-output-parallel-connected DC/DC converter for photovoltaic power conditioning system

In this paper, a novel topology is proposed for an input-series and output-parallel connected DC/DC converter, which consists of two DC/DC converter modules connected in series at the input and in parallel at the output, is an attractive solution for the photovoltaic system application. The proposed topology employ interleaving between two basic DC/DC modules which can be reduce inductor filter size and ratings. Also it shows that dramatically enhances the energy efficiency from low load to high load condition by reducing the required power level for DC/DC converter by one-third of conventional DC/DC converter. A case of 3.6kW prototype as the PV DC/DC converter is introduced to experimentally verify the proposed topology.

A new topology for PV DC/DC converter with high efficiency under wide load range

The paper proposes a new topology for photovoltaic DC/DC converter with high efficiency under wide input voltage range is proposed. Photovoltaic DC/DC is a very crucial part of power conditioning system (PCS). Considering that output characteristic of photovoltaic cell has wide voltage range, depending on the operating conditions of photovoltaic cell, the DC/DC converter also needs to have wide input voltage range to regulate the constant output voltage. In addition, a high rated voltage of power switch (MOSFET) for DC/DC converter is necessary in order to be compatible with the high maximum output voltage of photovoltaic cells maximum output voltage. Also photovoltaic power conditioning system should have a high efficiency under operation condition. To satisfy PV PCS condition series connected non-isolated DC/DC converter topology is proposed. This paper examines the proposed topology employing four modules and shows that it dramatically enhances the energy efficiency from low load to high load condition by reducing the required power level for DC/DC converter by one-third of conventional DC/DC converter. A case of 20 kW prototype as the PV DC/DC converter is introduced to experimentally verify the proposed topology.

Analysis and Design of Coupled Inductors for Two-Phase Interleaved DC-DC Converters

Multiphase dc-dc converters are widely used in modern power electronics applications due to their advantages over single-phase converters. Such advantages include reduced current stress in both the switching devices and passive elements, reduced output current ripple, and so on. Although the output current ripple of a converter can be significantly reduced by virtue of the interleaving effect, the inductor current ripple cannot be reduced even with the interleaving PWM method. One way to solve this problem is to use a coupled inductor. However, care must be taken in designing the coupled inductor to maximize its performances. In this paper, a detailed analysis of a coupled inductor is conducted and the effect of a coupled inductor on current ripple reduction is investigated extensively. From this analysis, a UU core based coupled inductor structure is proposed to maximize the performance of the coupled inductor.

1.5MVA grid-connected interleaved inverters using coupled inductors for wind power generation system

In this paper, grid-connected interleaved voltage source inverters for PMSG wind power generation system with coupled inductors is introduced. In parallel operation, the undesirable circulating current flows between inverters. There are some differences in circulating currents according to source configuration. It is mathematically analyzed and simulated for the verification of analysis. In case of interleaved inverters, the uncontrollable circulating current in switching frequency level flows between inverter modules regardless of source configuration such as common or separated if filter inductance which is placed between inverters is significantly low. In order to suppress high frequency circulating current, the coupled inductors are employed in each phase. A case of 1.5MVA grid-connected interleaved inverters using coupled inductors prototype for the PMSG wind power generation Back To Back converters in parallel are introduced and experimentally verified the proposed topology.

A new topology for photovoltaic 4 series dc/dc converter with high efficiency under wide load range

The paper proposes a new topology for photovoltaic DC/DC converter with high efficiency under wide input voltage range is proposed. Photovoltaic DC/DC is a very crucial part of power conditioning system (PCS). Considering that output characteristic of photovoltaic cell has wide voltage range, depending on the operating conditions of photovoltaic cell, the DC/DC converter also needs to have wide input voltage range to regulate the constant output voltage. In addition, a high rated voltage of power switch (MOSFET) for DC/DC converter is necessary in order to be compatible with the high maximum output voltage of photovoltaic cellpsilas maximum output voltage. Also photovoltaic power conditioning system should have a high efficiency under operation condition. To satisfy PV PCS condition series connected non-isolated DC/DC converter topology is proposed. This paper examines the proposed topology employing four modules and shows that it dramatically enhances the energy efficiency from low load to high load condition by reducing the required power level for DC/DC converter by one-third of conventional DC/DC converter. A case of 25 kW prototype as the PV DC/DC converter is introduced to experimentally verify the proposed topology.

A seamless transfer algorithm based on active frequency detection with feedforward control method in distributed generation system

This paper proposes a control strategy for grid-interactive Power Conditioning System (PCS) with feedforward control method based on active frequency detection. PCS should supply the power to critical loads continuously regardless of grid condition. Hence, PCS detects grid condition fast and transfers between two operation modes smoothly. In addition, it also important to detect its operating condition accurately for safety. In most of cases, PCS can detect its operation mode. However, when PCS operates in Non-Detection Zone (NDZ) condition, power gap between PCS and load is almost same, it cannot detect its operation mode precisely. Hence, other technique is needed to escape NDZ condition. This paper proposes using an active frequency method to get out of NDZ condition and a feedforward control to detect grid condition rapidly for seamless transfer. Controllers are composed of a current controller with a feedforward voltage controller. Each of the controllers checks power components independently, Hence, it helps restore the load voltage quickly when grid fault occurs. In NDZ condition, active frequency method helps PCS escape this condition. Proposed seamless transfer control strategy is verified by the experimental results.