• Journal of Power Electronics
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• 제12권2호
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• pp.326-332
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• 2012

This paper proposes a simple active damping algorithm for small-scale wind power systems with an LCL filter. Compared to an L filter or an LC filter, an LCL filter can decrease the harmonics induced by low switching frequencies and produce a satisfactory grid-side current using a comparatively low inductance. Additional active damping of the filter resonance is necessary when an LCL filter is used. This paper introduces an active damping method using a Discrete Fourier Transform (DFT) filter to improve performance without additional sensors or complexity. Experimental results are shown to verify the validity of the proposed algorithm as an active damping method.

• KIEE International Transaction on Electrical Machinery and Energy Conversion Systems
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• 제4B권3호
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• pp.134-145
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• 2004

This paper presents and analyses protection schemes for a series active compensator, which consists of a Unified Power Quality Conditioner (UPQC) or a hybrid active power filter. The proposed series active compensator operates as a high impedance "k(D)" for the fundamental components of the power frequency during over current conditions in the distribution system. Two control strategies are proposed in this paper. The first strategy detects the fundamental source current using the p-q theory. The second strategy detects the fundamental component of the load current in the Synchronous Reference Frame (SRF). When over currents occur in the power distribution system momentarily, the proposed schemes protect the series active compensator without the need for additional protection circuits, and achieves excellent transient response. The validity of the proposed protection schemes is investigated through simulation and compared with experimental results using a hybrid active power filter systems.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제55권5호
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• pp.258-264
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• 2006

This paper presents an integrative control scheme for series-type active power filters combined with shunt passive filters not only to compensate for the source voltage unbalance and current harmonics but also to correct the power factor. To reduce the power capacity of the active filters, passive filters are connected in parallel. Diode rectifiers are replaced by the PWM converters in order to feed the real power back to the source. Power factor control is performed by changing the phase of the load voltage so that the phase of the source current coincides with that of the source voltage. The resultant voltage reference is the addition of the voltage component compensating for the source voltage unbalance and harmonic currents and the voltage component correcting the power factor. The validity of the proposed algorithm has been verified by experimental results.

• 전기학회논문지
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• 제61권9호
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• pp.1289-1295
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• 2012

An active resonance damper for a DC Distributed Power System(DPS) with parallel loads is presented. Each pulse power load in a DC DPS comprises both a resistive power load and a step-up converter. The step-up converter behave as constant power load(CPL) when tightly regulated and usually cause a negative impedance instability problem. Furthermore, when an input filter is connected to a large constant power load, the instability of DC bus voltage. In this paper, a bidirectional DC/DC converter with a reduced storage capacitor quantitatively are proposed as a active resonance damper, to mitigate the voltage instability on the bus. The validity of the proposed method was confirmed by simulation and experimental works.

• Journal of Power Electronics
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• 제17권3호
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• pp.788-797
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• 2017

The power quality of AC electric railways has become an issue worthy of more and more concern. Many active compensators based on power converters have been proposed, but with complex transformers or coupled branches. This paper presents a single-phase cascaded H-bridge multilevel active power filter (APF), which can directly connect to the 27.5-kV power supplies to deal with power quality problems. According to field measured data, the load characteristics are analyzed, and the system configuration and control system are designed based on the load characteristic analysis. Finally, simulation and experimental results verify the effectiveness of the proposed APF system, considering some problems such as the supply voltage fluctuations and transient inrush currents in AC electric railway systems.

• 전기학회논문지
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• 제57권11호
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• pp.1954-1961
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• 2008

Microgrid usually consists of a cluster of distributed generators(DGs), energy storage systems and loads, and can operate in the grid-connected mode and the islanded mode. This paper presents detailed descriptions of two different options for controlling the active power of DGs in the microgrid. One is regulating the power injected by the unit to a desired amount(Unit output power control) and the other is to regulate the flow of active power in the feeder where the unit is installed to a constant(Feeder flow control). Frequency-droop characteristics are used to achieve good active power sharing when the microgrid operates in the islanded mode. The change in the frequency and the active power output of DGs are investigated according to the control mode and the configuration of DGs when the microgrid is disconnected from the main grid. From the analysis, this paper proposes a method to determine the droop constant of DGs operating in the feeder flow control mode. Simulation results using the PSCAD/EMTDC are presented to validate the approach, which shows good performance as opposed to the conventional one.

• International Journal of Aeronautical and Space Sciences
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• 제17권4호
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• pp.631-640
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• 2016

A dual-mode power management for a hybrid-electric UAV with a cruise power of 200W is proposed and empirically verified. The subject vehicle is a low-speed long-endurance UAV powered by a solar cell, a fuel cell, and a battery pack, which operate in the same voltage bounds. These power sources of different operational characteristics can be managed in two different methods: passive management and active management. This study proposes a new power management system named PMS2, which employs a bypass circuit to control the individual power sources. The PMS2 normally operates in active mode, and the bypass circuit converts the system into passive mode when necessary. The output characteristics of the hybrid system with the PMS2 are investigated under simulated failures in the power sources and the conversion of the power management methods. The investigation also provides quantitative comparisons of efficiencies of the system under the two distinct power management modes. In the case of the solar cell, the efficiency difference between the active and the passive management is shown to be 0.34% when the SOC of the battery is between 25-65%. However, if the SOC is out of this given range, i.e. when the SOC is at 90%, using active management displays an improved efficiency of 6.9%. In the case of the fuel cell, the efficiency of 55% is shown for both active and passive managements, indicating negligible differences.

• Journal of Electrical Engineering and information Science
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• 제2권4호
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• pp.46-52
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• 1997

In this paper th use of compensation based on a combination of active plus reactive power at distribution model system is proposed. The basic voltage-power relationships for the linearized case on an infinite bus are used and the compensation angle is defined based on the voltage magnitude response to small power injection. Compensation is supplied at several locations, and the system is subjected to varying fault scenarios, with its response observed under different system conditions. As number of control issues for a storage-based active/reactive power compensator as a bus voltage regulator are explored to compare the effectiveness of active/reactive again reactive-only compensation.

• 전기학회논문지
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• 제57권5호
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• pp.789-796
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• 2008

This paper describes a single-phase active power filter based on a newly developed digital controller. The developed controller utilizes FFT(Fast Fourier Transform) algorithm to extract the reference signal from the load current, considering the phase-angle delay of each order of harmonics. Optimized technique was applied for whole control algorithm to implement the real-time operation of developed controller. The performance of developed controller for a single-phase active power filter was verified through computer simulations with PSCAD/EMTDC. The feasibility of hardware implementation was confirmed by building and testing a prototype. The developed digital controller for a single-phase active power filter can compensate the harmonic current generated by the power supply for digital equipment.

• 대한전기학회논문지:전기기기및에너지변환시스템부문B
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• 제54권8호
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• pp.377-386
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• 2005

This paper presents the control algorithm of single-phase hybrid active power filter for the compensation of harmonic current components in nonlinear R-L load with passive active Power filters. To construct two phase system, an imaginary second phase was made. In this proposed method, the new signal which is the delayed through the filtering by the phase-delay property of low-pass filter is used as the secondary phase. Because two-phases have the different phase, the instantaneous calculation of harmonic current is possible. In this paper, a reference voltage is created by multiplying the coefficient k by the compensation current using the rotating reference frame synchronized with the source-frequency, not applying to instantaneous reactive power theory which has been used with the existing fixed reference frames In order to verify the validities of the proposed control methods, experiments are carried out with the prototypes of single-phase hybrid active power filter.