Seong Ryong Lee

Application of voltage- and current-controlled voltage source inverters for distributed generation systems

Voltage source inverters (VSI) have been widely used in uninterruptible power supplies, unified power flow controllers or unified power quality conditioners, and distributed generation systems (DGS). VSIs are inherently efficient, compact, and economical devices used to control power flow and provide quality supply. VSIs can be classified as voltage-controlled VSIs (VCVSIs) and current-controlled VSIs (CCVSIs), depending on their control mechanism. In this paper, a detailed comparison of VCVSIs and CCVSIs for DGS applications is presented. This paper examines the advantages and limitations of each control technique in a single-phase DGS, without incorporating additional hardware and/or extra complex control techniques. Discussions on the concepts, hypotheses, and computer simulations of different VSIs in the presence of different loads and conditions are presented. The experimental results confirm the validity of the analysis and simulations outlined. The paper provides design recommendations for the use of VCVSIs and CCVSIs in various applications

Direct Energy Transfer for High Efficiency Photovoltaic Energy Systems Part I: Concepts and Hypothesis

This two-part paper presents a comprehensive comparative study on parallel power processing (PPP) and standard schemes in dc/dc converters for photovoltaic (PV) energy systems. It is demonstrated how PPP can improve direct energy transfer (DET), which results in PV systems operating at higher voltage and efficiency. Discussions of the concepts, hypotheses and computer simulations are presented in Part I. Part II provides the experimental results, which confirm the validity of the analysis and simulations.

Direct Energy Transfer for High Efficiency Photovoltaic Energy Systems Part II: Experimental Evaluations

This two-part paper presents a comprehensive comparative study on parallel power processing (PPP) and standard schemes in dc/dc converters for photovoltaic (PV) energy systems. It is demonstrated how PPP can improve direct energy transfer (DET), which results in PV systems operating at higher voltage and efficiency. Discussions of the concepts, hypotheses, and computer simulations are presented in Part I. Part II provides the experimental results, which confirm the validity of the analysis and simulations.

A grid current-controlling shunt active power filter

In this paper, the implementation of a three-phase shunt active power filter is presented. The filter is essentially three independent single-phase current-controlled voltage source inverters (CC-VSI) with a common DC bus. The CC- VSI is operated to directly control the AC grid current to be sinusoidal and in phase with the grid voltage. The APF consists of a current control loop, which uses polarized ramptime current control and a voltage control loop, which employs a simple Proportional Integral control. The experimental results indicate that the active filter is able to handle predominantly the harmonics, as well as the unbalance and reactive power, so that the grid currents are sinusoidal, in phase with the grid voltages and symmetrical.

Constant DC capacitor voltage control based strategy for active load balancer in three-phase four-wire distribution system

Three-phase four-wire distribution systems are widely used in many countries. These power distribution systems are used for both three-phase three-wire loads and single-phase two-wire consumer appliances in South Korea, Myanmar and other countries. Unbalanced load conditions always occur in three-phase four-wire distribution systems. These unbalanced load conditions cause unbalanced voltages for three-phase and single-phase loads, and increase the loss in the distribution transformer. In this paper, we propose an active load balancer (ALB) based on constant DC capacitor voltage control for three-phase four-wire distribution systems. Constant DC capacitor voltage control is always used in active power line conditioners. The proposed control algorithm does not require any computation blocks to calculate the active and reactive currents on the distribution system. Balanced source currents with a unity power factor are obtained without any calculation blocks of the unbalanced active and reactive components on the load sides. The basic principle of the constant DC capacitor voltage control based strategy for the ALB is discussed in detail and then confirmed by digital computer simulation using PSIM software. A prototype experimental model is also constructed and tested to validate the feasibility of the proposed control algorithm. Simulation and experimental results demonstrate that the proposed ALB can balance the source currents with a unity power factor for a three-phase four-wire distribution system.

Novel Simple Reactive Power Control Strategy With DC Capacitor Voltage Control for Active Load Balancer in Three-Phase Four-Wire Distribution Systems

This paper proposes a novel, simple reactive power control strategy for the active load balancer (ALB) in three-phase four-wire distribution systems. The proposed reactive power control strategy is applicable for adjustment of the source-side power factor under the balanced load condition. Only DC capacitor voltage control is used in the proposed control strategy. Therefore, the calculation blocks of the active and reactive components of the load currents are not necessary. The authors, thus, offer the simplest control strategy to control reactive power under the balanced load condition on three-phase four-wire distribution feeders. The basic principle of DC capacitor voltage control based reactive power control strategy is discussed in detail, and then confirmed by digital computer simulation. A prototype experimental system was constructed and tested. Experimental results demonstrate that balanced source currents with reactive power control are achieved on three-phase four-wire distribution feeders. These experimental results also demonstrate that controlling the reactive power reduces the required power rating of the ALB compared to that of the existing control strategy, which achieves balanced source currents with unity power factor.

A constant DC-capacitor voltage control based strategy for current balancer in single-phase three-wire distribution systems

This paper proposes a constant dc-capacitor voltage control based strategy for a current balancer in single-phase three-wire distribution systems. The proposed control strategy only uses the constant dc-capacitor voltage control block commonly used in active power conditioners to calculate the compensation current. No calculation blocks to obtain the reactive and unbalanced-active components are necessary. Thus, we provide the simplest possible control strategy for the current balancer. The basic principle of the proposed control method is discussed in detail then its validity is confirmed by digital computer simulation using PSIM software. A prototype experimental model is constructed and tested. Experimental results demonstrate that balanced source currents with a power factor of unity are obtained on the secondary side of a pole-mounted distribution transformer while retaining unbalanced load current conditions with a lagging power factor.

Reactive power control strategy based on DC capacitor voltage control for active load balancer in three-phase four-wire distribution systems

This paper proposes a reactive power control strategy for the active load balancer (ALB) in three-phase four-wire distribution systems. The proposed reactive power control strategy is based on constant DC capacitor voltage control, which is always used in active power line conditioners. Therefore, the proposed reactive power control strategy does not require active, reactive calculation blocks of load currents for the reference source current calculation. Balanced source currents with a predefined power factor can be achieved without unbalanced active and reactive components detection of the load currents. The basic principle of the reactive power control strategy for the ALB is discussed in detail, and then confirmed by digital computer simulation using PSIM software. A prototype experimental model is constructed and tested to validate the feasibility of the proposed control algorithm. Simulation and experimental results demonstrate that balanced source currents with a predefined power factor are achieved in three-phase four-wire distribution systems.

Novel simple reactive power control with constant dc-capacitor voltage control for active load balancer on three-phase four-wire distribution feeders under distorted source voltage conditions

This paper addresses the compensation performance of the previously proposed reactive power control algorithm with the constant dc-capacitor voltage control for active load balancer (ALB) on three-phase four-wire distribution feeders under distorted source voltage conditions. The instantaneous power flows into the ALB is discussed in detail. This instantaneous power flows into the ALB show that the previously proposed reactive power control algorithm is applicable under the distorted source-voltage conditions. A computer simulation is implemented to confirm the reality of the previously proposed reactive power control algorithm with the constant dc-capacitor voltage control under the distorted source-voltage conditions. A prototype experimental model is constructed and tested. Simulation and experimental results demonstrate that sinusoidal and balanced source currents with the power factor of 0.9 are achieved on three-phase four-wire distribution feeders under the distorted source-voltage conditions.

Individual-phase reactive power control strategy with constant DC-capacitor voltage control for active load balancer on three-phase four-wire distribution feeders

This paper proposes an individual-phase reactive power control strategy for an active load balancer (ALB) in three-phase four-wire distribution systems. The authors offer the simplest method to control different amounts of individual-phase reactive power for each phase on three-phase four-wire distribution feeders. The basic principle of the proposed power factor adjustable reactive power control strategy is discussed in detail. Simulation and experimental results demonstrate that the amount of individual-phase reactive power can be controlled with the balanced active source-current conditions on three-phase four-wire distribution feeders with the proposed individual-phase reactive power control strategy.