Jung-Muk Choe

Current feedback with decoupling scheme for single-phase UPS using a single current sensor

This paper proposes an inductor current feedback plus load current decoupling scheme for single-phase uninterruptible power supply (UPS) applications using a single current sensor. At first, the inductor current feedback with and without load current decoupling are compared in the view point of the output voltage control performance. The output impedance of the entire control system is analytically compared by using the derived model. From this analysis, it is shown that using the load current decoupling is better than not using the load current decoupling in voltage regulation performance. In addition to this analysis, a current sensing technique is proposed to measure the inductor and load current with a single current sensor. The proposed sensing method is shown that a load current and a branch current are simultaneously sampled by using a single current sensor at both the peak and valley point of the pulse-width modulation (PWM) carriers regularly, and then the inductor current and load current are reconstructed with the proposed algorithm in a single PWM cycle. Accordingly, the number of sensor and potential current sensing error can be reduced.

A capacitor current control for stand-alone inverters using an inductor current observer

This paper discussed an inductor current observer design that employs a capacitor current control model for single-phase stand-alone inverters. The single-phase stand-alone inverter is analyzed via modeling. The proposed solution is able to guarantee a fast dynamic response and also a precise compensation of a distortion load. Moreover, with a proper design of observer parameters, it is possible to build a precise inductor current information without the inductor current sensor. The simulation and experimental results show that the performance of the proposed controller.

Load Disturbance Compensation for Stand-alone Inverters Using an Inductor Current Observer

A control scheme for stand-alone inverters that utilizes an inductor current observer (ICO) is proposed. The proposed method measures disturbance load currents using a current sensor and it estimates the inductor current using the ICO. The filter parameter mismatch effect is analyzed to confirm the ICO’s controllability. The ICO and controllers are designed in a continuous-time domain and transferred to a discrete-time domain with a digital delay. Experimental results demonstrate the effectiveness of the ICO using a 5-kVA single-phase stand-alone inverter prototype. The experimental results demonstrate that the observed current matches the actual current and that the proposed method can archive a less than 2.4% total harmonic distortion (THD) sinusoidal output waveform under nonlinear load conditions.

A Performance Comparison of the Current Feedback Schemes with a New Single Current Sensor Technique for Single-Phase Full-Bridge Inverters

In this paper, a single current sensor technique (SCST) is proposed for single-phase full-bridge inverters. The proposed SCST measures the currents of multiple branches at the same time, and reconstructs the average inductor, capacitor, and load current in a single switching cycle. Since all of the branches’ current in the LC filter and the load are obtained using the SCST, both the inductor and the capacitor current feedback schemes can be selectively applied while taking advantages of each other. This paper also analyzes both of the current feedback schemes from the view point of the closed-loop output impedance. The proposed SCST and the analysis in this paper are verified through experiments on a 3kVA single-phase uninterruptible power supply (UPS).

Test and analysis of 3kW PV battery energy storage system

This paper discussed a 3kW PV Battery Energy Storage System (BESS) for conserving electrical energy and ensuring load leveling. The system targeted involved a PV unit capable of generating 3 kW of power and a 3 kW h lithium polymer battery. The proposed system was implemented in order to determine its effectiveness with respect to load leveling and energy saving. An office was selected for testing, which lasted an entire year. The results show operation profiles and the daily total reduction.

Asymmetrical loosely coupled transformer for wireless laptop charger with higher misalignment tolerance

The proposed inductive power transfer (IPT) system for laptop charging consists of three parts: a high frequency power supply from a full-bridge inverter with frequency modulation, a LLC resonant tank that incorporates a loosely coupled transformer (LCT) and a resonant capacitor series connected with the primary winding, and a rectification output circuits that uses a full-bridge diode rectifier. Due to the relatively large air gap, the magnetic coupling coefficient of the IPT system is significantly lower than that with tightly coupled transformer. As a result, the efficiency of the IPT system is always a major concern for applications with possible misalignment variation condition. To ensure high power transfer efficiency, the IPT system should have high tolerance for different misalignment conditions. In this paper, the effect of coupling coefficient deviation to compensation network efficiency is analyzed, and asymmetrical LCT which has significant higher misalignment tolerance is proposed. By using finite element analysis (FEA) simulation method, the performance of different transmitter and receiver coil dimensions are compared. In order to validate the performance of the proposed design, a 100-W hardware prototype with two sets of LCT is built and the corresponding experiments are carried out. As compared to the symmetrical LCT architecture, the proposed asymmetrical LCT prototype improves the coupling coefficient reduction from 70% to 12.5% when the misalignment ranges from 0 to 40 mm. Therefore, the efficiency deviation for the asymmetrical LCT is maintained nearly constant over the entire tested misalignment variation ranges.

High-Performance Voltage Controller Design Based on Capacitor Current Control Model for Stand-alone Inverters

This study proposes high-performance voltage controller design that employs a capacitor current control model for single-phase stand-alone inverters. The single-phase stand-alone inverter is analyzed via modeling, which is then used to design the controller. A design methodology is proposed to maximize the bandwidth of the feedback controller. Subsequently, to compensate for the problems caused by the bandwidth limitations of the controller, an error transfer function that includes the feedback controller is derived, and the stability of the repetitive control scheme is evaluated using the error transfer function. The digital repetitive controller is then implemented. The simulation and experimental results show that the performance of the proposed controller is high in a 1.5 kW singlephase stand-alone inverter prototype.

Parallel PCS Interconnection Current Surge Elimination Technique Using a Coupled Inductor

In this paper, coupled inductor method in parallel operation of PCS is proposed. In coupled inductor the primary and secondary currents flow in the same direction, the total flux total inductance is cancelled. However, when the currents flow in the opposite direction, each flux becomes an individual inductor. Aforementioned characteristic is adopted in parallel operation of PCS. Abnormal current is blocked by coupled inductor which is barred to connect grid code. A design guide is suggested by PCSs capacity and the circulation current duration time. The proposed design is verified through the hardware implementation and experimental results that show the effectiveness of variance reduction.

Nonisolated Single-Switch Two-Channel LED Driver with Simple Lossless Snubber and Low-Voltage Stress

In two-channel light-emitting diode (LED) driver, capacitive-current-balancing method is the simplest and the most effective way to equally balance the current in each channel due to its simplicity. As a result, the capacitive balancing method was used with flyback or tapped-boost converters in low-power LED applications. Since flyback and tapped-boost converters suffer from a snubber loss and a high-voltage stress on the switching devices, conventional approaches use additional passive components, resulting in the limitations on the cost and power density. In this paper, a new converter topology for low-power two-channel LED application has been proposed. The proposed converter uses the blocking capacitor and the output capacitor as a snubber capacitor so that it has a low-voltage stress without using the additional components. Although the blocking capacitor plays a role as a snubber capacitor, the current balancing characteristic is still preserved. Furthermore, the proposed converter has a high efficiency since it minimizes the number of semiconductor components in the current paths. The effectiveness of the proposed converter has been verified with an offline 3.3 Vdc input and 11.55 W rated output prototype.

Design of a state-space controller employing a deadbeat state observer for ups inverters

The design of a digital state-space controller employing a deadbeat state observer is presented for uninterruptible power source (UPS) inverter applications with inductor-capacitor (L-C) filters. Conventionally, the inductor current and capacitor voltage values are utilized as the measured feedback variables for the controller, and the load current is either measured or estimated. In the proposed method, the inductor current sensor is not used, and an output load current sensor is used. The proposed state-space controller utilizes the estimated current and voltage states from an observer as the feedback values, and the measured output load current information as the feedforward value. The advantage of the proposed method is that the measured load current information accurately compensates the observer and control system pole deviation due to the load current variation, and thus it increases the overall system robustness with only one current sensor. The proposed control scheme exhibits low total harmonic distortions and fast transient responses. Experiments are performed on a UPS prototype to demonstrate the effectiveness of the proposed scheme.