Search

This paper proposes an energy management system (EMS) of direct current (DC) microgrid. In order to implement the proposed EMS, the control and operation method of EMS is presented in this work. While most of the studies have individually examined the grid-connected mode used in building and the stand-alone operation mode applicable to the island, the proposed EMS allows it to be used in both grid-connected mode and stand-alone mode with 10 modes. In order to determine each mode in EMS, not only the amount of generated power, load power, and the state of charge (SOC) of the battery, but also the rated power of the energy storage system (ESS) converter that performs charging and discharging operations is additionally considered. Thus, various uncertainties that may occur in the actual DC microgrid environment can be improved. A laboratory-scale DC microgrid is fabricated to conduct experimental validation of proposed EMS. Experiments of DC microgrid with proposed EMS were performed for each mode, and the experiment waveforms of each power conversion device are included in detail.

This paper proposes a new three-dimension (3-D) space vector pulse width modulation (SVPWM) for three-phase four-wire inverter under line-to-line (L-L) fault. To perform this method, we discussed coordinate transformation matrix to rotate the distorted voltage vector plane into a new coordinate system under L-L fault. In addition, this paper presented the selection of the output voltage vectors and mathematically analyzed the synthesis of the reference vector and calculation of the duty cycles. Through the above process, even though L-L fault occurs in distribution network, zero voltage can be supplied to the point of failure, and voltage can be supplied normally to the rest of the phases. The simulations and experimental results are provided to validate the effectiveness of the proposed method.

In this paper, increase in distributed power sources such as renewable energy sources, is increasing interest in microgrid that supply power by distributing. Research on various distribution network operation methods has been conducted. we adopted LabVIEW to design an interactive monitoring interface for EMS (Energy Monitoring System) operation of AC / DC hybrid microgrid. The provided monitoring interface works in conjunction with the reduced AC / DC microgrid experiment environment, allows operator to observe the impact on the system by input the change to the distribution system in addition to reading data from the distribution network. It will also be useful for testing various operational methods of microgrid system.

Active damping method and load current feedforward control method has been studied for control dc bus voltage in DC microgrid. Since load current feedforward control method requires information through communication, performance of controller is affected by communication time delay. This paper analyzes time delay performance of DC bus voltage variation with four control strategies based on the two control methods. DC bus voltage variation with four control strategies are simulated and analyzed considering three time delay cases.

This paper proposes energy management system (EMS) for power control in low voltage direct current (LVDC) distribution system. Since LVDC distribution system is connected to various distributed generators and power conversion devices, each situation of generated and load power should be considered for stable operation. Power control of LVDC distribution system must be required for its reliability and can be implemented by operation and control strategy of EMS. In this paper, proposed EMS defines each operation mode considering various conditions and each converter is controlled by centralized control based control strategy of EMS. Feasibility and stability of proposed EMS is verified by experiment results of LVDC distribution system including distributed energy resource such as wind turbine, photovoltaic array, battery and DC/AC load.

This paper proposes an artificial neural network (ANN)-based energy management system (EMS) for controlling power in AC–DC hybrid distribution networks. The proposed ANN-based EMS selects an optimal operating mode by collecting data such as the power provided by distributed generation (DG), the load demand, and state of charge (SOC). For training the ANN, profile data on the charging and discharging amount of ESS for various distribution network power situations were prepared, and the ANN was trained with an error rate within 10%. The proposed EMS controls each power converter in the optimal operation mode through the already trained ANN in the grid-connected mode. For the experimental verification of the proposed EMS, a small-scale hybrid AD/DC microgrid was fabricated, and simulations and experiments were performed for each operation mode.

This paper proposes a selective control algorithm to reduce switching losses of N-phase switching pole of 3-phase 4-leg interlinking converter (ILC) in AC/DC hybrid microgrid. Unbalanced load connected to 3-phase 4-leg ILC causes unbalanced voltage condition and this problems can be complemented by N-phase switching pole of 4-leg ILC. However, if the switching pole on N is operated constantly regardless of control decision due to unbalanced load conditions, switching loss on the N-phase switching pole will cause power loss in the entire topology. To compensate this problem, selective control algorithm considering voltage unbalance factor (VUF) for N-phase switching pole in ILC is proposed. Proposed algorithm decides switching operation of N-phase switching pole depending on unbalanced load voltage. When occurring unbalanced load condition, voltage unbalance factor can be reduced by proposed control algorithm. At the same time, the current flowing through the N-phase switch pole and switching losses can be reduced.

To convert the three-phase AC power to DC power, conventional power conversion system has a 2-stage configuration which consists of the AC/DC PFC and isolated DC/DC converter system. However, this configuration has the disadvantage that the volume of the system increases and the efficiency decreases due to two-times of the power conversion process. Therefore, in this paper, we propose a three-phase bridgeless PFC system with LLC resonant circuit for improvement of power factor, input current THD and efficiency through soft switching.

This paper proposes a novel dual integrated LLC resonant converter (DI-LRC) with a wide output voltage range using various switching patterns. The primary side of the proposed DI-LLC converter consists of two resonant tanks and six switches, while the secondary side consists of a six-pulse diode rectifier. Depending on the switching pattern of the primary switch, the DI-LRC converter is performed by single full-bridge operation with a voltage gain of 1, series-connected full-bridge operation with a voltage gain of 0.5, series-connected half bridge operation with a voltage gain of 0.25, and parallel-connected full-bridge operation with a voltage gain of 2. Accordingly, the proposed DI-LRC converter has four voltage gain curves with different variations and achieves a wider output voltage range than the conventional single voltage gain curve in a given operating frequency range. In this paper, the equivalent circuits derived for each switching pattern are proposed to analyze the operating characteristics of the proposed converter according to each switching pattern, and each Q factor and voltage gain are calculated based on the analyzed equivalent circuit. The performance of the proposed converter and switching pattern is verified using the simulation and experimental results of the prototype battery charger, which is designed to be 4-kW class.

In this paper, a modified droop control method is proposed to minimize variation of common bus voltage. The proposed control method models line impedance between load and auxiliary power supply to compensate for voltage drop of power line. The expected voltage drop of the modelled line impedance is mathematically analyzed and applied to the traditional droop curve to design the modified drop equation. The controller has a cascaded structure with inner current and voltage control loops and outer power control loop. A droop curve for power control is applied a modified droop equation to reduce the load voltage drop due to the line impedance. The validity of a modified droop control is verified using two 85kVA auxiliary power supply units connected in parallel.

Recently, Uninterruptible power supply(UPS) is spotlighted from concern about black out, due to reserve power problem caused by increased power consumption. When fault occurs on the grid, UPS system supplies power to loads instead of the grid. Also, it is an advantage of possible operation as Energy storage system(ESS). Bi-directional power control of AC/DC Pulse width modulation(PWM) converter is essential for grid-connected UPS system. And, mode transfer control has to be performed considering phase and dynamic characteristic under grid condition. In this paper, control of mode transfer and bi-directional power control of AC/DC PWM converter is proposed for UPS system. Also, it is verified by simulation and experimental results.

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.

In this paper, high efficiency control method for flyback inverter with synchronous rectifier(SR) based on photovoltaic AC modules is proposed. In this control method, the operation of SR is classified according to the voltage spike across main switch SP. When the voltage spike across SP is lower than the rating voltage of SP, the operation of active clamp circuit is interrupted for reducing the switching loss of auxiliary switch. In this time, the SR is operated for soft-switching of SP. When the voltage spike across Sp is higher than the rating voltage of SP, the operation of active circuit is activated for reducing the voltage spike. The SR is operated for reducing the conduction loss of secondary output diode. Thus, a switching loss of the main switch can be reduced in low power region, and weighted-efficiency can be improved. A theoretical analysis and the design principle of the proposed method are provided. And validity is confirmed through simulation and experimental results.

This paper presents design method of soft switching interleaved buck and boost converter for vehicle application. The soft switching interleaved buck and boost converter is composed of interleaved boost converter and resonant tank. The converter improve the problem of switching loss by employing the small size resonant tank compared with conventional interleaved buck and boost converter. The conditions of ZCS and ZVS of the converter are mathematically analyzed by using the mode analysis. Through the mode analysis, size of the resonant tank is optimized according to the rated power of converter. The design method is verified by simulation result.

Titanium matrix composites (TMCs) have several attractive characteristics including high temperature properties, wear resistance and oxidation resistance. In the case of metal matrix composites, it is generally desirable to select reinforcements that exhibit suitable interfaces with the matrix, high temperature stability, and similar coefficients of thermal expansion with respect to the matrix. Conventional candidates for reinforcements in TMCs include SiC, Si3N4, Al2O3, TiC, TiN, TiB, and TiB2. These materials have high temperature properties, fatigue strength, and wear and oxidation resistance. TMC manufacturing methods can be divided into powder metallurgy and the melting route approach. In the case of powder metallurgy, the processing steps are very complicated, and an agglomeration of reinforcements can cause the deterioration of mechanical properties. In the melting route approach, net-shape forming is hard to obtain due to a high affinity in the molten state, and low fluidity of the melts. However, the melting route approach can provide an economical and sound final casting. In this study, we used the investment casting process for economical considerations. In addition, an in situ synthesis method was also developed to ensure homogeneous distribution and a controlled interfacial reaction between the matrix and reinforcements. The friction and wear behavior of TMCs were investigated using a pin-on-disk wear tester under various conditions and were evaluated using scanning electron microscopy (SEM) analysis.

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.

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.

A DC-link voltage compensation method for a photovoltaic (PV) generation system with energy storage system(ESS) is presented. When PV power is oscillated, the DC-link voltage is also influenced. And this fluctuation of DC-link critically affects the load voltage when the ESS is operated in stand alone mode. In conventional method, huge capacitor bank is necessary to reduce the fluctuation. In this case, if the PV power is drastically changed, large capacitance as much as the whole PV system is required to reduce the DC-link fluctuation. Therefore, the DC-link voltage compensation method is applied to the DC-link control to reduce the DC-link voltage variation without using huge capacitor bank. The proposed control method is mathematically analyzed and verified by simulation results.

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.

In the photovoltaic (PV) AC-module system, the system size and weight are important design factors because AC-modules are installed to each PV panels. Since the most of harmonics occur at multiples of switching frequency, the harmonic elimination at switching frequency can be an effective technique for reducing the total filter size. To decrease output filter size, proposed output filter consists of trap filter to eliminate switching frequency harmonic and CL filter. In this paper, the trap-CL filter is analyzed, and its optimal design method is proposed. The validity of proposed filter and design method are verified by simulation and experimental results.

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.

In this paper, the uninterruptible power supply(UPS) mode transfer method of three-phase energy storage system (ESS) using the silicon-controlled rectifier(SCR) is applied. In the three-phase ESS using the SCR, the three-phase grid is not blocked because each-phase has a difference of 120 degree. Therefore, the ESS needs the UPS transfer method which is blocking the three-phase grid at the same time when the grid fault occurs. So the UPS mode transfer method which is blocking the SCR by changing the direction of the power flow is applied. The applied UPS mode transfer method is verified by simulation results using the PSIM ver.9.1.4.

In this paper, a control strategy of bidirectional converter for energy storage system in photovoltaic hybrid modules is proposed. The bidirectional converter for energy storage system (ESS) with battery is connected with DC link in parallel which is located between current source flyback converters and unfolding bridge. Because output currents which are generated by flyback converters are rectified sinusoidal waveform, suitable control strategy is required for bidirectional converter. In this paper, a theoretical analysis of the proposed control strategy is provided. And, validity is confirmed through simulation results.

In this paper, a control method for phase synchronous of each converter in photovoltaic (PV) hybrid module system (HMS) is proposed. A PV-HMS consists of a central inverter operated with a grid-line frequency and modularized converters installed backside of each PV module. In PV-HMS, the modularized converters has to operate with current-source converter using grid-line phase information because the central inverter is an unfolding bridge inverter which of switching frequency is equal to the grid-line. However, each modularized converter cannot get the grid-line phase information because these converters directly is not connected the grid-line. Therefore, this paper is proposed the control method for operation of each modularized converter through phase-lock-loop (PLL) DC-link voltage. The theoretical analysis of the proposed control method is verified by simulation results.

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.

The photovoltaic(PV) module has the nonlinear current-voltage characteristics. To track the maximum power in PV-module, maximum power point tracking(MPPT) algorithm is needed in PV power generation system. To use MPPT algorithm, the PV generation system is essential for PV-module's current and voltage. In this paper, a current sensorless MPPT algorithm is proposed for a photovoltaic generation system using AC-module type flyback inverter. The proposed method estimate the PV current without using current sensor. Thus, the cost of an AC-module type flyback inverter can be reduced. Theoretical analysis and simulation are performed in order to verify the proposed current sensorless MPPT method.

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.

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.