Bong-Yeon Choi

Battery-Integrated Power Optimizer for PV-Battery Hybrid Power Generation System

Recently, hybrid generation systems combine multiple energy sources or storage components to optimize the characteristics of the individual energy sources. PV-battery hybrid systems usually combine photovoltaic (PV) generation of electricity with energy storage components (i.e. batteries). These systems are often configured as mini-grids in which the generation sources supply loads through a relatively small local distribution grid. In these systems, to improve the utilization of solar energy, the output power mismatch between PV modules due to the non-identical solar irradiance has to be considered. In this paper, a battery integrated PV power optimizer for PV-battery hybrid power generation system is proposed. Proposed system can be applied to the conventional PV hybrid power generation systems, as well as, the normal centralized PV generation systems. By integrating the batteries to the PV power optimizer, PV system using proposed topology can easily increase battery capacity and stabilize input power for central power conditioning system (PCS). Proposed battery integrated power optimizer is verified by simulation results.

Battery Balancing Algorithm for Parallel Operation of Single Phase UPS Inverters

A current sharing method considering battery state of charge (SOC) for single phase uninterruptable power supply (UPS) module is proposed. Each of UPS module system is consists of single master and multi slave modules. A master module performs output voltage control and current sharing algorithm considering the battery SOC of each of the UPS modules. In current sharing algorithm, current commands are generated for eliminating SOC difference of batteries of each modules. However, the slave modules control the only output current which is generated by master module. As the output load current is shared by battery SOC of UPS module, the utilization of the battery is increased in parallel UPS system. The validity of proposed method is verified by simulation results.

Flyback Inverter Using Voltage Sensorless MPPT for Photovoltaic AC Modules

A flyback inverter using voltage sensorless maximum power point tracking (MPPT) for photovoltaic (PV) AC modules is presented. PV AC modules for a power rating from 150 W to 300 W are generally required for their small size and low price because of the installation on the back side of PV modules. In the conventional MPPT technique for PV AC modules, sensors for detecting PV voltage and PV current are required to calculate the PV output power. However, system size and cost increase when the voltage sensor and current sensor are used because of the addition of the auxiliary circuit for the sensors. The proposed method uses only the current sensor to track the MPP point. Therefore, the proposed control method overcomes drawbacks of the conventional control method. Theoretical analysis, simulation, and experiment are performed to verify the proposed control method.

Economic dispatch algorithm considering battery degradation characteristic of energy storage system with PV system

In this paper, energy storage system(ESS) operation algorithm for economics considering battery degradation properties is proposed. Hourly electricity charge according to real-time pricing (RTP) and battery properties are analyzed for high profit through ESS operation. Especially, hourly electricity charge of Illinois State is analyzed. Characteristics of battery accounts for a high percentage of ESS configuration. Thus, degradation properties of the battery for the price considering the loss of battery usage is considered. The algorithm is proposed for the highest profit through analysis of the battery degradation properties and electricity charge, and the proposed algorithm is verified by mathematical analysis.

Power flow control strategy of PV hybrid module system with energy storage

In this paper, an power flow control strategy of a hybrid module type photovoltaic(PV) generation system with energy storage is presented. This system consists of the current source converters to perform the maximum power point tracking(MPPT), a grid connected H-bridge inverter and a bidirectional converter for energy storage. In this system, in order to improve the utilization of PV energy and stabilize the power control, the control strategy is in need of improving. This control strategy is designed by analyzing the residential power consumption and irradiance condition in a day. Through the theoretical analysis and simulation results, proposed control strategy for PV hybrid module system with energy storage is verified.

An Optimal Method to Design a Trap-CL Filter for a PV AC-Module Based on Flyback Inverter

The power factor and total harmonic distortion (THD) are important considerations when designing an output filter. In the case of the photovoltaic (PV) ac-module, the size and weight also have to be taken into consideration. This paper proposes an output filter to reduce size and weight, and provides the optimal design method for a PV ac-module. The proposed output filter consists mainly of a conventional CL filter with a trap filter. The trap filter is used to eliminate the harmonic at the switching frequency that contains most of the harmonics. Therefore, total inductance and the size of the filter can be reduced although the output filter components are increased. This paper presents analysis of the proposed filter characteristics in detail. Also, an optimal design method reducing the size of the output filter components including the damping resistor is proposed. The proposed methods are verified on the experimental prototype rated at 320 W with an ac-module based on the interleaved flyback inverter. The total filter inductance and volume are, respectively, reduced to 9.54% and 26.62% with the same performance.

Battery balancing algorithm for serial multi-module UPS system

In this paper, battery balancing algorithm for serial multi-module UPS system is proposed. The battery balancing algorithm is performed by the output power control of each UPS modules for eliminating SOC difference of batteries respectively. So, the coulomb counting method is used to estimate SOC of the batteries. The reference is compensated with SOC difference and according to magnitude order of SOC . Finally, the output voltage becomes sum of output voltage of UPS modules and the utilization of the battery is increased in serial UPS system. The validity of proposed battery balancing algorithm is verified by simulation results.

The predictive control of single-phase UPS system for fast dynamic characteristic

This paper presents the predictive control of single-phase UPS system for fast dynamic characteristic. When occurring grid fault, UPS system has to transfer UPS mode and supply power to the load. In PI controller, it has a disadvantage rather low dynamic characteristic, which is caused increasing transient time. To solve this problem, the predictive control is proposed. By adopting predictive control in UPS system, it is possible to decrease the transient time to load voltage when UPS system conducts mode transfer. In this paper, reference output current of load is calculated by formulating inductor current and capacitor voltage to apply the predictive control of single-phase UPS system. To verify validity of the proposed predictive control method, simulation and experiment are carried out based on 350W single off-line UPS system.

Current sharing algorithm for parallel operation of single phase UPS inverters using predictive current control

A current sharing method considering battery state of charge(SOC) for multi-module uninterruptable power supply(UPS) system is proposed. Modularized UPS system consists of a single master module and multi slave modules. A master module performs output voltage control and distributes current commands to slave modules. The current commands are generated by using the proposed current sharing algorithm to balance the SOC of each UPS module. Moreover, the UPS mode transfer time can be significantly reduced by using the predictive current control. The predictive current control method is mathematically verified by analyzing the UPS system. The validity of proposed balancing method and predictive control is verified by simulation results.

ESS operation algorithm for economics considering battery degradation properties

In this paper, Energy storage system(ESS) operation algorithm for economics considering battery degradation properties is proposed. Hourly electricity charge according to real-time pricing (RTP) and battery properties are analyzed for high profit through ESS operation. Especially, hourly electricity charge of Illinois State is analyzed. Characteristics of battery accounts for a high percentage of ESS configuration. Thus, degradation properties of the battery for the price considering the loss of battery usage is considered. The algorithm is proposed for the highest profit through analysis of the battery degradation properties and electricity charge, and the proposed algorithm is verified by mathematical analysis.