Kyoung-Jun Lee

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.

Implementation of Fault Ride-Through Techniques of Grid-Connected Inverter for Distributed Energy Resources With Adaptive Low-Pass Notch PLL

The amount of distributed energy resources (DERs) has constantly increased worldwide. As the power ratings of DERs have become considerably high, the grid code requirements are necessary to secure reliable power generation and transmission for the public electric network. In order to follow grid codes of the various countries and optimize the function of grid-connected inverters for DERs, a robust phase-locked loop (PLL) is essential for extracting the grid phase information accurately, when the grid voltage is polluted by harmonics and unbalanced. This paper proposes fault ride-through techniques based on a low-pass notch (LPN)-PLL. The LPN-PLL has not only fast and smooth transient responses to a sudden transition of the grid voltage but also has robustness to the distorted and unbalanced grid conditions. Therefore, the stable performance in the grid fault conditions is expected without the system trip. Furthermore, a universal voltage sag generator for the various grid codes with six parameters is proposed for the verification of low voltage ride-through (LVRT) performance. Experimental verifications are presented to show the LVRT performance based on the LPN-PLL with a three-phase grid-connected inverter (10 kV·A) and a prototype of the voltage sag generator (10 kV·A).

Coupled inductors for parallel operation of interleaved three-phase voltage source grid-connected inverters

In this paper, coupled inductors for parallel operation of interleaved three-phase voltage source grid-connected inverters are introduced. When DC-link capacitors of each inverter are shared and interleaving method is employed, more severe circulating currents which are zero-sequence components are emerged than the other cases. In order to suppress carrier frequency zero-sequence components of circulating currents, the filter inductors of each same phase are coupled. Moreover, this technique has additional advantages; 1) Reduction of current ripples of both coupled inductors and outputs of coupled inductors; 2) Reduced size and weight of total filter inductors; 3) Efficiency improvement of conventional topology. The experimental results are shown to verify the advantages of proposed method.

Hybrid photovoltaic/diesel green ship operating in standalone and grid-connected mode in South Korea - Experimental investigation

The paper presents experimental results from the operation of a proto-type green ship in Geoje island, South Korea. After ground testing with a stand-alone PV generation system, this PV system was added to conventional diesel ship. Proto-type green ship is consisted of photovoltaic (PV) generation system, diesel engine, battery energy storage, hybrid control system, stand-alone and grid-connected inverter. The aim of the green ship is not only to minimize the fuel consumption but also to support the power grid as a distributed generation (DG) in the near future.

A Study on a Solar Simulator for Dye Sensitized Solar Cells

Dye-sensitized solar cells (DSSC) are emerging low-cost, simple alternatives to conventional solar cells. While there has been considerable study on improving the efficiency of DSSCs, there has not been sufficient research on a photovoltaic power conditioning system adaptable to DSSCs or on a solar simulator for DSSCs. When DSSCs are commercialized in the near future, the DSSC modules must be connected to an adaptable power conditioning system in order to manage the energy produced and provide a suitable interface to the load. In the process of developing a power conditioning system, a solar simulator with the characteristics of DSSCs is essential to show the performance of the maximum power point tracking. In this paper, a virtual DSSC is designed and simulated in PSIM. Irradiation factors, temperature and shadow effects are considered in dynamic link library block in PSIM which is linked to the external C routine. A 100 W converter is built to show the performance of a DSSC as the solar simulator controlled by a digital signal processor.

Experimental and Numerical Analysis of a Simple Core Loss Calculation for AC Filter Inductor in PWM DC-AC Inverters

This paper introduces a simple core loss calculation method for output filter inductor in pulse width modulation (PWM) DC-AC inverter. Amorphous C-core (AMCC-320) is used to analyze the core loss. In order to measure core loss of the output filter inductor and validate the proposed method, a single-phase half-bridge inverter and a calorimeter are used. By changing switching frequency and modulation index (MI) of the inverter, core loss of the AMCC-320 is measured with the lab-made calorimeter and the results are compared with calculated core loss. The proposed method can be easily extended to other core loss calculation of various converters.

Proposal of optimal process parameters for polymethylmethacryl plastic adhesion using a pulsed Nd:YAG laser

In this study, we propose a pulsed Nd:YAG laser system that uses a sequential charge and discharge circuit to adhere polymethylmethacryl (PMMA) plastics. Two PMMA plastics adhere to each other when the red one transmits the laser beam and the black one absorbs it. The optimal adhesion depends on several process parameters, such as the charging voltage of the capacitor, the pulse rate [in pulses per second (pps)], the velocity of the target, and the laser beam diameter. We try to optimize the adhesion process parameters from trial-and-error experiments. It has proposed that the optimal adhesion process parameters are a charging voltage of 650 V, a pulse rate of 11 pps, a target velocity of 4.20 mm/s, and a laser beam diameter of 4.00 mm in this pulsed Nd:YAG laser system. In addition, we generalize the optimal conditions for plastic adhesion, such as energy per pulse, peak power, and the velocity of the target.

Phase-locked loop algorithm using FFT concept for grid synchronization under unbalanced voltage sags

The amount of distributed energy resources (DERs) constantly increased recently all over the world. The power ratings of DERs have reached considerably high, being required by the new grid code requirement. Because the influence of DER system on the grid can`t be overlooked. Among the grid codes, the low voltage ride through (LVRT) requires the grid-connected inverter based on DERs to remain connected during grid voltage sags and support grid voltages. To meet the LVRT requirements, the grid-connected inverter have to inject active and reactive power without losing phase-locked loop (PLL). In this paper, the PLL method using FFT concept and improvement in performance during transient time are proposed to meet the LVRT requirements not to fail the support performance during different types of voltage sags. The proposed algorithms and control strategy is demonstrated using simulation program. A 10kW inverter is set and verification experiment is conducted using NF grid fault simulator.

A novel active power filter for selective harmonic suppression based on a robust PLL Algorithm

Distributed Generation (DG) based on renewable green energy is expected to grow at an unexpected rate. However increasing penetration of DG to the power grid has issued power quality of power system. Among the power quality problems, the harmonic current may corrupt the power system which is connected to the grid. Accordingly, the performance of DG systems must be improved to meet the grid codes in each country. In this paper, a novel selective harmonic suppression method based on a robust PLL Algorithm is proposed and demonstrated using PSIM. The proposed algorithm is applied over the harmonic current detection of a nonlinear load. Now 10kW prototype active power filter (APF) is set and verification experiment will be conducted with the nonlinear load.

A study on the performance of 10kW Grid-Connected Photovoltaic power conditioning system with characteristics variation in inductor core materials

Grid-Connected power conditioning system (PCS) is widely used for distributed generation system. In Grid-Connected PCS, the LC filter is essential to reduce the current harmonics injected to the grid. In this paper adequate inductor core materials are selected to analyze the performance of 10kW Grid-Connected Photovoltaic (PV) PCS. Core materials can be classified into three groups: power core, sheet core and ferrite core. For the experiment, Fe-3%Si core, Fe-6.5%Si (Super core) and Mega Flux core were chosen as a filter inductor core. Optimal condition for each inductor core is determined by the efficiency and THD.