Jaeho Choi | Chungbuk National University (original) (raw)

Papers by Jaeho Choi

Energies, 2018

This paper proposes a multi-functional Photovoltaic (PV) inverter based on the Unified Power Qual... more This paper proposes a multi-functional Photovoltaic (PV) inverter based on the Unified Power Quality Conditioner (UPQC) configuration. Power quality improvement is a difficult issue to solve for isolated areas or islands connected to the mainland through long submarine cables. In the proposed system, the line voltage is compensated for by the series inverter while the shunt inverter delivers the PV generating power to the grid. Depending on the technical conditions of power quality and system environment, it has five different operating modes. Especially during poor power quality conditions, the sensitive load is separated from the normal load to provide a different power quality level by using the microgrid conception. In this paper, the control method and the power flow for each mode are described, and the operational performance is verified through a PSiM simulation so that it can be applied to the power quality improvement of weak grid power systems such as in isolated areas or ...

The Transactions of the Korean Institute of Power Electronics, 2010

This paper describes the PSIM simulator for the analysis of the series type HEV operation. The tr... more This paper describes the PSIM simulator for the analysis of the series type HEV operation. The traction force of the series type HEV of which engine is electrically coupled with a traction motor is supplied from the traction motor only. The rating of each power train components, such as gear, motor, ESS, ICE/generator, is designed with the Energy-Based Modeling method and the Electrical Peaking Hybrid(ELPH) method. Under driving cycle, the designed series HEV is evaluated with the developed PSIM simulator. A comparison between the conventional braking and the regenerative braking is performed with the average motor input power. And the fuel economy analysis is carried out on the basis of the simulation results.

Proceedings. International Conference on Power System Technology

Abstract-. This paper presents a new method for the determination of nehvork observability of the... more Abstract-. This paper presents a new method for the determination of nehvork observability of the power system using the neural networks. The nehrark observability problem, related to the power system c<mIiguration or network topology, called as the topological observability, ...

The Transactions of the Korean Institute of Power Electronics, 2016

Applied Sciences, 2020

The main contents of this paper are to verify the environmental factors affecting the power gener... more The main contents of this paper are to verify the environmental factors affecting the power generation of floating photovoltaic systems and to present the power generation prediction model considering environmental factors by using regression analysis and neural networks studied during the last decade. This study focused on a comparative analysis of which model is best suited for the power generation prediction of the floating photovoltaic (PV) system. To compare the power generation characteristics of a floating and a land-based PV system, two identical 2.5 kW PV systems were installed—one on the water surface in the Boryeong Dam, Korea, and the other nearby on dry land—and their performances were compared. The solar irradiance of the floating PV system was 1.1% lower than that of the land-based PV. Nevertheless, the floating PV module temperature was 4.9% lower than that of the land-based PV, generating approximately 3% more power. Using the correlation analysis of data mining tec...

2000 IEEE Power Engineering Society Winter Meeting. Conference Proceedings (Cat. No.00CH37077)

ABSTRACT This paper presents an experimental study of high efficiency energy conversion and drive... more ABSTRACT This paper presents an experimental study of high efficiency energy conversion and drives for flywheel energy storage system using the high temperature superconductive magnetic bearings and permanent magnet synchronous motor. This described flywheel energy storage system is designed to replace of the conventional EMB (electromechanical battery) system. To realize the high efficiency and to minimize the torque ripple, the waveform of the converter output current is controlled to be sinusoidal and in phase or inverse phase with the electro-motive voltage in motoring mode and regeneration mode, respectively. The actual performance of the mechanical and electrical characteristics of the proposed HTS magnet flywheel energy storage system is well described in this paper and its validity is verified through the simulation and experimental results

Implementation of fuzzy controller for the rotor side converter of a utility-connected double-fed... more Implementation of fuzzy controller for the rotor side converter of a utility-connected double-fed induction generator (DFIG) for wind power generation systems (WPGS) described in this paper. In the control schemes, real and reactive powers (PQ) at the stator side of DFIG are strictly controlled to supply the power to the grid. A TMS320VC33 DSP is selected as the controller of this system.

International Journal of Renewable Energy Research, 2015

This paper describes a LCL filter design method for a grid connected NPC three-level inverter. By... more This paper describes a LCL filter design method for a grid connected NPC three-level inverter. By analyzing the ripple current according to the switching of NPC three-level inverter, the inverter side inductor is designed without any information about the modulation index. After considering the r elation between the inductance ratio of inverter inductor to grid inductor and the filtering effect at the switching frequency, the relation between the inductance ratio and the attenuation of output ripple, and the current ripple of inverter side inductor, the optimized value of LCL filter is designed to meet the design criteria. Finally, the proposed design method is validated through the simulation and experimental results.

Energies

This paper proposes the grid synchronization method of inverter using a quasi Proportional+Multi ... more This paper proposes the grid synchronization method of inverter using a quasi Proportional+Multi Resonant (P+MR) control-based voltage controller a stationary reference frame. The inverter supplies a non-linear load under the islanded mode. In islanded mode, the inverter is defined as a voltage source to supply the full local load demand without a connection to the grid. On the other hand, if the grid is restored from a previous fault or the strategic islanding is unnecessary, the inverter needs to be synchronized with the phase of the grid before the transfer from islanded mode to grid-connected mode. When the system is modeled and controlled based on the stationary reference frame control, the AC reference voltage, which has a constant voltage and frequency in islanded mode, is substituted to the AC grid voltage. Significant error can occur due to the large phase differences between the phase of reference and that of the measured value. This error also can cause severe voltage dynamic problems. In addition, if any nonlinear local load is connected to the output of the inverter, it becomes more serious due to the harmonics generated from the loads. In this paper, the PR control under a stationary reference frame is used for voltage control under islanded mode considering the harmonic effects from the nonlinear load. The seamless grid synchronization method based on this PR control is proposed to solve the aforementioned problems. The validity of the proposed seamless grid synchronization method is verified through PSiM simulations and experimental results.

Journal of Power Electronics

This study examines a P+multi resonant-based voltage control for voltage harmonics compensation u... more This study examines a P+multi resonant-based voltage control for voltage harmonics compensation under the islanded mode of a microgrid. In islanded mode, the inverter is defined as a voltage source to supply the full local load demand without the connection to the grid. On the other hand, the output voltage waveform is distorted by the negative and zero sequence components and current harmonics due to the unbalanced and nonlinear loads. In this paper, the P+multi resonant controller is used to compensate for the voltage harmonics. The gain tuning method is assessed by the tendency analysis of the controller as the variation of gain. In addition, this study analyzes the slight voltage magnitude drop due to the practical form of the P+multi resonant and proposes a counter method to solve this problem by adding the PI-based voltage restoration method. The proposed P+multi resonant controller to compensate for the voltage harmonics is verified through the PSIM simulation and experimental results.

Journal of Astronomy and Space Sciences

A satellite power system should generate and supply sufficient electric power to perform the sate... more A satellite power system should generate and supply sufficient electric power to perform the satellite mission successfully during the satellite mission period, and it should be developed to be strong to the failure caused by the severe space environment. A satellite power system must have a high reliability with respect to failure. Since it cannot be repaired after launching, different from a ground system, the failures that may happen in space as well as the effect of the failures on the system should be considered in advance. However, it is difficult to use all the hardware to test the performance of the satellite power system to be developed in order to consider the failure mechanism of the electrical power system. Therefore, it is necessary to develop an accurate model for the main components of a power system and, based on that, to develop an accurate model for the entire power system. Through the power system modeling, the overall effect of failure on the main components of the power system can be considered and the protective design can be devised against the failure. In this study, to analyze the failure mode of the power system and the effects of the failure on the power system, we carried out modeling of the main power system components including the solar array regulator, and constituted the entire power system based on the modeling. Additionally, we investigated the effects of representative failures in the solar array regulator on the power system using the power system model.

Energies

This paper describes the detailed analysis of a reactor application for a power plant to mitigate... more This paper describes the detailed analysis of a reactor application for a power plant to mitigate the voltage rise of a distribution line (DL) caused by the connection of distributed resources (DRs). The maximum capacity of renewable energy generators (REGs) that meets the acceptable voltage rise of a DL and the necessary capacity of the reactor to mitigate that voltage rise according to the different types of REGs are analyzed. The re-coordination of a protection relay and the loss of generation revenue as well as the installation location of a reactor are described. Finally, the ON/OFF conditions of the reactor, such as the magnitudes of the grid voltage and generator voltage, and the duration time of the voltage rise are analyzed. As the voltage rise is mitigated and self-limited in small power plants, it is confirmed that the capacity of the DRs connected to the DL can be increased through a field demonstration.

Journal of Power Electronics

This paper presents DG based droop controlled parallel inverter systems with virtual impedance co... more This paper presents DG based droop controlled parallel inverter systems with virtual impedance considering the unequal resistive-inductive combined line impedance condition. This causes a reactive power sharing error and dynamic performance degradation. Each of these drawbacks can be solved by adding the feedforward term of each line impedance voltage drop or injecting the virtual inductor. However, if the line impedances are high enough because of the long distance between the DG and the PCC or if the capacity of the system is large so that the output current is very large, this leads to a high virtual inductor voltage drop which causes reductions of the output voltage and power. Therefore, the line impedance voltage drops and the virtual inductor and resistor voltage drop compensation methods have been considered to solve these problems. The proposed method has been verified in comparison with the conventional droop method through PSIM simulation and low-scale experimental results.

Journal of Power Electronics, 2010

Journal of Power Electronics, 2012

This paper proposes the State-of-charge (SOC) estimator of a LiPB Battery using the Extended Kalm... more This paper proposes the State-of-charge (SOC) estimator of a LiPB Battery using the Extended Kalman Filter (EKF). EKF can work properly only with an accurate model. Therefore, the high accuracy electrical battery model for EKF state is discussed in this paper, which is focused on high-capacity LiPB batteries. The battery model is extracted from a single cell of LiPB 40Ah, 3.7V. The dynamic behavior of single cell battery is modeled using a bulk capacitance, two series RC networks, and a series resistance. The bulk capacitance voltage represents the Open Circuit Voltage (OCV) of battery and other components represent the transient response of battery voltage. The experimental results show the strong relationship between OCV and SOC without any dependency on the current rates. Therefore, EKF is proposed to work by estimating OCV, and then is converted it to SOC. EKF is tested with the experimental data. To increase the estimation accuracy, EKF is improved with a single dominant varying parameter of bulk capacitance which follows the SOC value. Full region of SOC test is done to verify the effectiveness of EKF algorithm. The test results show the error of estimation can be reduced up to max 5%SOC.

The Transactions of the Korean Institute of Power Electronics, 2016

Recently, the interest in DC systems to achieve more efficient connection with renewable energy s... more Recently, the interest in DC systems to achieve more efficient connection with renewable energy sources, energy storage systems, and DC loads has been growing extensively. DC systems are more advantageous than AC systems because of their low conversion losses. However, the DC-link voltage is variable during operation because of different random effects. This study focuses on DC voltage stabilization applied in stand-alone DC microgrids by means of voltage ranges, power management, and coordination scheme. The quality and stability of the entire system are improved by keeping the voltage within acceptable limits. In terms of optimized control, the maximum power should be tracked from renewable resources during different operating modes of the system. The ESS and VSDG cover the power shortage after all available renewable energy is consumed. Keeping the state of charge of the ESS within the allowed bands is the key role of the control system. Load shedding or power generation curtailment should automatically occur if the maximum tolerable voltage variation is exceeded. PSIM-based simulation results are presented to evaluate the performance of the proposed control measures.

Energies, 2016

Wind power systems are being integrated increasingly into the power grid because of their large c... more Wind power systems are being integrated increasingly into the power grid because of their large capacity and easy access to the transmission grid. The reliability of wind power plants is very important and the elimination of protective relay's malfunctions is essential to the mitigation of power quality problems due to the frequent starts and stops of high capacity wind generators. In this study, the problem of frequent false operations of the protective relays are analyzed using real data as line voltages, line currents, and wind speed. A new re-coordination of the overcurrent relay (OCR) based on the wind speed is proposed to avoid frequent operations of relays and tested for a grid-connected wind farm. This study verifies that the false actions by the OCRs that are not accompanied by actual electrical faults in the power grid or wind power system can be solved by the appropriate re-coordination of the OCR.

2015 IEEE 2nd International Future Energy Electronics Conference (IFEEC), 2015

This paper describes the cascaded current and voltage control for seamless transfer of microgrid ... more This paper describes the cascaded current and voltage control for seamless transfer of microgrid with harmonic compensation according to load location. DG based microgrid is defined as a current source in the grid-connected mode and a voltage source in the islanded mode, respectively. Hence, it needs a robust control to supply the high quality power under both modes of DG based microgrid. But a connection of non-linear load and/or distorted grid can cause the system power quality degradation due to the produced non-linear current and/or voltage. Therefore, the PR control based cascaded current and voltage control which can be used under both modes simultaneously has been considered with a deliberate control topology in this paper. According to the load location, it can meet both non-linear compensation and seamless transfer between two modes. Also, a simple voltage restoration method has been added to solve the magnitude degradation of output voltage due to the practical PR control limitation and sometimes grid frequency change. Finally, proposed control methods which supply the power to the non-linear load under both grid-connected mode and islanded mode are verified through the PSIM simulation.

In this paper, control schemes are developed for a propulsion system(Converter/Inverter) in elect... more In this paper, control schemes are developed for a propulsion system(Converter/Inverter) in electrical train. A robust controller for PWM converter is proposed. The converter controller consists of a PI controller for DC output voltage and a current controller using error-space approach for maintaining the sinusoidal current waveform and unity power factor. This proposed method is based on characteristic ratio assignment(CRA) method which has the advantage to design the optimal gain to meet the referenced response and overshoot within the limit range. Inverter system is controlled by vector control and slip frequency control. At low speed region, vector control scheme is applied to control instantaneous torque and slip frequency control is performed under overmodulation region and one pulse mode. Because output voltage of converter contains harmonics ripple at twice input ac line frequency, control scheme is developed to reduce the pulsating torque current. The performance of propulsion system will be verified by simulation and prototype experimental results.

Energies, 2018

This paper proposes a multi-functional Photovoltaic (PV) inverter based on the Unified Power Qual... more This paper proposes a multi-functional Photovoltaic (PV) inverter based on the Unified Power Quality Conditioner (UPQC) configuration. Power quality improvement is a difficult issue to solve for isolated areas or islands connected to the mainland through long submarine cables. In the proposed system, the line voltage is compensated for by the series inverter while the shunt inverter delivers the PV generating power to the grid. Depending on the technical conditions of power quality and system environment, it has five different operating modes. Especially during poor power quality conditions, the sensitive load is separated from the normal load to provide a different power quality level by using the microgrid conception. In this paper, the control method and the power flow for each mode are described, and the operational performance is verified through a PSiM simulation so that it can be applied to the power quality improvement of weak grid power systems such as in isolated areas or ...

The Transactions of the Korean Institute of Power Electronics, 2010

This paper describes the PSIM simulator for the analysis of the series type HEV operation. The tr... more This paper describes the PSIM simulator for the analysis of the series type HEV operation. The traction force of the series type HEV of which engine is electrically coupled with a traction motor is supplied from the traction motor only. The rating of each power train components, such as gear, motor, ESS, ICE/generator, is designed with the Energy-Based Modeling method and the Electrical Peaking Hybrid(ELPH) method. Under driving cycle, the designed series HEV is evaluated with the developed PSIM simulator. A comparison between the conventional braking and the regenerative braking is performed with the average motor input power. And the fuel economy analysis is carried out on the basis of the simulation results.

Proceedings. International Conference on Power System Technology

Abstract-. This paper presents a new method for the determination of nehvork observability of the... more Abstract-. This paper presents a new method for the determination of nehvork observability of the power system using the neural networks. The nehrark observability problem, related to the power system c<mIiguration or network topology, called as the topological observability, ...

The Transactions of the Korean Institute of Power Electronics, 2016

Applied Sciences, 2020

The main contents of this paper are to verify the environmental factors affecting the power gener... more The main contents of this paper are to verify the environmental factors affecting the power generation of floating photovoltaic systems and to present the power generation prediction model considering environmental factors by using regression analysis and neural networks studied during the last decade. This study focused on a comparative analysis of which model is best suited for the power generation prediction of the floating photovoltaic (PV) system. To compare the power generation characteristics of a floating and a land-based PV system, two identical 2.5 kW PV systems were installed—one on the water surface in the Boryeong Dam, Korea, and the other nearby on dry land—and their performances were compared. The solar irradiance of the floating PV system was 1.1% lower than that of the land-based PV. Nevertheless, the floating PV module temperature was 4.9% lower than that of the land-based PV, generating approximately 3% more power. Using the correlation analysis of data mining tec...

2000 IEEE Power Engineering Society Winter Meeting. Conference Proceedings (Cat. No.00CH37077)

ABSTRACT This paper presents an experimental study of high efficiency energy conversion and drive... more ABSTRACT This paper presents an experimental study of high efficiency energy conversion and drives for flywheel energy storage system using the high temperature superconductive magnetic bearings and permanent magnet synchronous motor. This described flywheel energy storage system is designed to replace of the conventional EMB (electromechanical battery) system. To realize the high efficiency and to minimize the torque ripple, the waveform of the converter output current is controlled to be sinusoidal and in phase or inverse phase with the electro-motive voltage in motoring mode and regeneration mode, respectively. The actual performance of the mechanical and electrical characteristics of the proposed HTS magnet flywheel energy storage system is well described in this paper and its validity is verified through the simulation and experimental results

Implementation of fuzzy controller for the rotor side converter of a utility-connected double-fed... more Implementation of fuzzy controller for the rotor side converter of a utility-connected double-fed induction generator (DFIG) for wind power generation systems (WPGS) described in this paper. In the control schemes, real and reactive powers (PQ) at the stator side of DFIG are strictly controlled to supply the power to the grid. A TMS320VC33 DSP is selected as the controller of this system.

International Journal of Renewable Energy Research, 2015

This paper describes a LCL filter design method for a grid connected NPC three-level inverter. By... more This paper describes a LCL filter design method for a grid connected NPC three-level inverter. By analyzing the ripple current according to the switching of NPC three-level inverter, the inverter side inductor is designed without any information about the modulation index. After considering the r elation between the inductance ratio of inverter inductor to grid inductor and the filtering effect at the switching frequency, the relation between the inductance ratio and the attenuation of output ripple, and the current ripple of inverter side inductor, the optimized value of LCL filter is designed to meet the design criteria. Finally, the proposed design method is validated through the simulation and experimental results.

Energies

This paper proposes the grid synchronization method of inverter using a quasi Proportional+Multi ... more This paper proposes the grid synchronization method of inverter using a quasi Proportional+Multi Resonant (P+MR) control-based voltage controller a stationary reference frame. The inverter supplies a non-linear load under the islanded mode. In islanded mode, the inverter is defined as a voltage source to supply the full local load demand without a connection to the grid. On the other hand, if the grid is restored from a previous fault or the strategic islanding is unnecessary, the inverter needs to be synchronized with the phase of the grid before the transfer from islanded mode to grid-connected mode. When the system is modeled and controlled based on the stationary reference frame control, the AC reference voltage, which has a constant voltage and frequency in islanded mode, is substituted to the AC grid voltage. Significant error can occur due to the large phase differences between the phase of reference and that of the measured value. This error also can cause severe voltage dynamic problems. In addition, if any nonlinear local load is connected to the output of the inverter, it becomes more serious due to the harmonics generated from the loads. In this paper, the PR control under a stationary reference frame is used for voltage control under islanded mode considering the harmonic effects from the nonlinear load. The seamless grid synchronization method based on this PR control is proposed to solve the aforementioned problems. The validity of the proposed seamless grid synchronization method is verified through PSiM simulations and experimental results.

Journal of Power Electronics

This study examines a P+multi resonant-based voltage control for voltage harmonics compensation u... more This study examines a P+multi resonant-based voltage control for voltage harmonics compensation under the islanded mode of a microgrid. In islanded mode, the inverter is defined as a voltage source to supply the full local load demand without the connection to the grid. On the other hand, the output voltage waveform is distorted by the negative and zero sequence components and current harmonics due to the unbalanced and nonlinear loads. In this paper, the P+multi resonant controller is used to compensate for the voltage harmonics. The gain tuning method is assessed by the tendency analysis of the controller as the variation of gain. In addition, this study analyzes the slight voltage magnitude drop due to the practical form of the P+multi resonant and proposes a counter method to solve this problem by adding the PI-based voltage restoration method. The proposed P+multi resonant controller to compensate for the voltage harmonics is verified through the PSIM simulation and experimental results.

Journal of Astronomy and Space Sciences

A satellite power system should generate and supply sufficient electric power to perform the sate... more A satellite power system should generate and supply sufficient electric power to perform the satellite mission successfully during the satellite mission period, and it should be developed to be strong to the failure caused by the severe space environment. A satellite power system must have a high reliability with respect to failure. Since it cannot be repaired after launching, different from a ground system, the failures that may happen in space as well as the effect of the failures on the system should be considered in advance. However, it is difficult to use all the hardware to test the performance of the satellite power system to be developed in order to consider the failure mechanism of the electrical power system. Therefore, it is necessary to develop an accurate model for the main components of a power system and, based on that, to develop an accurate model for the entire power system. Through the power system modeling, the overall effect of failure on the main components of the power system can be considered and the protective design can be devised against the failure. In this study, to analyze the failure mode of the power system and the effects of the failure on the power system, we carried out modeling of the main power system components including the solar array regulator, and constituted the entire power system based on the modeling. Additionally, we investigated the effects of representative failures in the solar array regulator on the power system using the power system model.

Energies

This paper describes the detailed analysis of a reactor application for a power plant to mitigate... more This paper describes the detailed analysis of a reactor application for a power plant to mitigate the voltage rise of a distribution line (DL) caused by the connection of distributed resources (DRs). The maximum capacity of renewable energy generators (REGs) that meets the acceptable voltage rise of a DL and the necessary capacity of the reactor to mitigate that voltage rise according to the different types of REGs are analyzed. The re-coordination of a protection relay and the loss of generation revenue as well as the installation location of a reactor are described. Finally, the ON/OFF conditions of the reactor, such as the magnitudes of the grid voltage and generator voltage, and the duration time of the voltage rise are analyzed. As the voltage rise is mitigated and self-limited in small power plants, it is confirmed that the capacity of the DRs connected to the DL can be increased through a field demonstration.

Journal of Power Electronics

This paper presents DG based droop controlled parallel inverter systems with virtual impedance co... more This paper presents DG based droop controlled parallel inverter systems with virtual impedance considering the unequal resistive-inductive combined line impedance condition. This causes a reactive power sharing error and dynamic performance degradation. Each of these drawbacks can be solved by adding the feedforward term of each line impedance voltage drop or injecting the virtual inductor. However, if the line impedances are high enough because of the long distance between the DG and the PCC or if the capacity of the system is large so that the output current is very large, this leads to a high virtual inductor voltage drop which causes reductions of the output voltage and power. Therefore, the line impedance voltage drops and the virtual inductor and resistor voltage drop compensation methods have been considered to solve these problems. The proposed method has been verified in comparison with the conventional droop method through PSIM simulation and low-scale experimental results.

Journal of Power Electronics, 2010

Journal of Power Electronics, 2012

This paper proposes the State-of-charge (SOC) estimator of a LiPB Battery using the Extended Kalm... more This paper proposes the State-of-charge (SOC) estimator of a LiPB Battery using the Extended Kalman Filter (EKF). EKF can work properly only with an accurate model. Therefore, the high accuracy electrical battery model for EKF state is discussed in this paper, which is focused on high-capacity LiPB batteries. The battery model is extracted from a single cell of LiPB 40Ah, 3.7V. The dynamic behavior of single cell battery is modeled using a bulk capacitance, two series RC networks, and a series resistance. The bulk capacitance voltage represents the Open Circuit Voltage (OCV) of battery and other components represent the transient response of battery voltage. The experimental results show the strong relationship between OCV and SOC without any dependency on the current rates. Therefore, EKF is proposed to work by estimating OCV, and then is converted it to SOC. EKF is tested with the experimental data. To increase the estimation accuracy, EKF is improved with a single dominant varying parameter of bulk capacitance which follows the SOC value. Full region of SOC test is done to verify the effectiveness of EKF algorithm. The test results show the error of estimation can be reduced up to max 5%SOC.

The Transactions of the Korean Institute of Power Electronics, 2016

Recently, the interest in DC systems to achieve more efficient connection with renewable energy s... more Recently, the interest in DC systems to achieve more efficient connection with renewable energy sources, energy storage systems, and DC loads has been growing extensively. DC systems are more advantageous than AC systems because of their low conversion losses. However, the DC-link voltage is variable during operation because of different random effects. This study focuses on DC voltage stabilization applied in stand-alone DC microgrids by means of voltage ranges, power management, and coordination scheme. The quality and stability of the entire system are improved by keeping the voltage within acceptable limits. In terms of optimized control, the maximum power should be tracked from renewable resources during different operating modes of the system. The ESS and VSDG cover the power shortage after all available renewable energy is consumed. Keeping the state of charge of the ESS within the allowed bands is the key role of the control system. Load shedding or power generation curtailment should automatically occur if the maximum tolerable voltage variation is exceeded. PSIM-based simulation results are presented to evaluate the performance of the proposed control measures.

Energies, 2016

Wind power systems are being integrated increasingly into the power grid because of their large c... more Wind power systems are being integrated increasingly into the power grid because of their large capacity and easy access to the transmission grid. The reliability of wind power plants is very important and the elimination of protective relay's malfunctions is essential to the mitigation of power quality problems due to the frequent starts and stops of high capacity wind generators. In this study, the problem of frequent false operations of the protective relays are analyzed using real data as line voltages, line currents, and wind speed. A new re-coordination of the overcurrent relay (OCR) based on the wind speed is proposed to avoid frequent operations of relays and tested for a grid-connected wind farm. This study verifies that the false actions by the OCRs that are not accompanied by actual electrical faults in the power grid or wind power system can be solved by the appropriate re-coordination of the OCR.

2015 IEEE 2nd International Future Energy Electronics Conference (IFEEC), 2015

This paper describes the cascaded current and voltage control for seamless transfer of microgrid ... more This paper describes the cascaded current and voltage control for seamless transfer of microgrid with harmonic compensation according to load location. DG based microgrid is defined as a current source in the grid-connected mode and a voltage source in the islanded mode, respectively. Hence, it needs a robust control to supply the high quality power under both modes of DG based microgrid. But a connection of non-linear load and/or distorted grid can cause the system power quality degradation due to the produced non-linear current and/or voltage. Therefore, the PR control based cascaded current and voltage control which can be used under both modes simultaneously has been considered with a deliberate control topology in this paper. According to the load location, it can meet both non-linear compensation and seamless transfer between two modes. Also, a simple voltage restoration method has been added to solve the magnitude degradation of output voltage due to the practical PR control limitation and sometimes grid frequency change. Finally, proposed control methods which supply the power to the non-linear load under both grid-connected mode and islanded mode are verified through the PSIM simulation.

In this paper, control schemes are developed for a propulsion system(Converter/Inverter) in elect... more In this paper, control schemes are developed for a propulsion system(Converter/Inverter) in electrical train. A robust controller for PWM converter is proposed. The converter controller consists of a PI controller for DC output voltage and a current controller using error-space approach for maintaining the sinusoidal current waveform and unity power factor. This proposed method is based on characteristic ratio assignment(CRA) method which has the advantage to design the optimal gain to meet the referenced response and overshoot within the limit range. Inverter system is controlled by vector control and slip frequency control. At low speed region, vector control scheme is applied to control instantaneous torque and slip frequency control is performed under overmodulation region and one pulse mode. Because output voltage of converter contains harmonics ripple at twice input ac line frequency, control scheme is developed to reduce the pulsating torque current. The performance of propulsion system will be verified by simulation and prototype experimental results.