• Journal of Power Electronics
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• v.19 no.2
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• pp.580-590
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• 2019

The concept of virtual synchronous generators (VSGs) is a valuable means for improving the frequency stability of microgrids (MGs). However, a great virtual inertia in a VSG's controller may cause power oscillation, thereby deteriorating system stability. In this study, a small-signal model of an MG with two paralleled VSGs is established, and a control strategy for maintaining a constant inertial time with an increasing active-frequency droop coefficient (m) is proposed on the basis of a root locus analysis. The power oscillation is suppressed by adjusting virtual synchronous reactance, damping coefficient, and load frequency coefficient under the same inertial time constant. In addition, the dynamic load distribution is sensitive to the controller parameters, especially under the parallel operation of VSGs with different capacities. Therefore, an active power increment method is introduced to improve the precision of active power sharing in dynamic response. Simulation and experimental is used to verify the theoretical analysis findings.

• Proceedings of the KIPE Conference
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• 1998.10a
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• pp.176-181
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• 1998

The parallel inverter is popularly used because of its fault-tolerance capability, high-current outputs at constant voltages and system modularity. The conventional parallel inverter usually employs active and reactive power control of frequency and voltage droop control. However, these approaches have the disadvantages that the response time of parallel inverter control is slow against load and system parameter variation to calculate active, reactive power, frequency and voltage. This paper describes a novel control scheme for power equalization in parallel-connected inverter. The proposed scheme has a fast power balance control response, a simplicity of implementation, and inherent peak current limiting capability since it employees an instantaneous current/voltage control with output voltage and current balance and output voltage regulation. A design procedure for the proposed parallel inverter controller is presented. Furthermore, the proposed control scheme is verified through the experiment in various cases such as the system parameter variation, the control parameter variation and the nonlinear load condition.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.5
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• pp.533-540
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• 2013

Prime movers in engine rooms inherently are much affected by the adjustment of their governors for the steady state and transient properties, consequently requiring that marine engineers shall be well familiar with the way to manage governor dials for normal operation. The hydro-mechanical governors basically have different control characteristics and adjustment parameters of stability from digital governors. The former include compensation mechanism using dash pot while the control algorithm of the latter is usually based on the PID action. This study is for configuring a simulation module to let trainees practice how to adjust dials for stability on hydraulic governors in the view that the practice by real governors and engines is time consuming and high cost for operation. The governor module includes the adjusting points such as speed set, speed droop, needle valve and compensation pointer with engine module of $2^{nd}$ order coupled. The results of simulation showed satisfactory responses as a training tool for the adjustment of control parameters.

• The Transactions of the Korean Institute of Electrical Engineers A
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• v.54 no.11
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• pp.540-547
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• 2005

One of the roles of AGC is to regulate the frequency of power systems. AGC is also used to control the frequency of Korean Power System. AGC control strategies depend on system characteristics and the requirements of the systems to which those are applied. Korean Power System consists of one control area and does not have tie-lines. In this research, an AGC control strategy is suggested to avoid conflict with governor dynamics and to enhance frequency recovery It shows good performance for regulation and frequency recovery. This control strategy is expected to be applied to New EMS in KPX to get reasonable AGC regulation and frequency recovery performance.

• The Transactions of the Korean Institute of Power Electronics
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• v.24 no.5
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• pp.334-341
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• 2019

This study proposes the control strategy for the seamless mode transfer of indirect current controlled parallel grid-connected inverters. Under the abnormal grid condition, the grid-connected inverter can convert the operation mode from grid-connected to stand-alone mode to supply power to the local load. For a seamless mode transfer, the time delay problems caused by the accumulated control variable error must be solved, and the indirect current control method has been applied as one of the solutions. In this study, the design of control parameters for the proportional-resonant-based triple-loop indirect current controller and the control strategy for the seamless mode transfer of parallel grid-connected inverters are described and analyzed. The validity of the proposed mode transfer method is verified by the PSiM simulation results.

• Proceedings of the KIPE Conference
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• 2012.07a
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• pp.542-543
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• 2012

본 논문에서는 저항성 수하제어 방식과 단일루프 강인 전압 제어기를 적용하여 단상 UPS 인버터의 비통신선 방식 5-병렬 운전 결과를 기술한다. 단일 루프 강인 전압 제어기를 이용해 단상 3kVA UPS 인버터 5대로 병렬운전 환경을 구축하였고, 저항성 주파수-전압 강하 방식의 수하 제어를 이용하여 저항 부하와 선형 부하에 대한 전력분담 특성을 PSIM 시뮬레이션을 통하여 확인하였다.

• Proceedings of the KIPE Conference
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• 2016.11a
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• pp.184-185
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• 2016

본 논문에서는 직류 전기 선박의 발전시스템의 병렬 운전시 순환전류 저감 및 직류 전압유지에 효과적인 가변이득 드룹 제어 기법을 제시한다. PSIM을 이용한 시뮬레이션 결과를 보인다.

• Proceedings of the KIPE Conference
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• 2018.11a
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• pp.141-142
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• 2018

본 논문에서는 부하 분담, 신뢰성 및 효율 향상, 시스템 용량을 증가시키는 PCS 모듈 병렬 운전 방법을 제안한다. 병렬 운전을 할 때 모듈별 출력 전압, 전류 값들이 이상적으로 동일하지 않기 때문에 시스템 손실을 초래하는 순환전류가 필연적으로 발생하게 된다. 따라서 순환전류를 저감시키기 위해 모듈별 전력제어와 가상의 계수인 droop index를 이용하여 Load sharing이 잘 되는 제어 알고리즘을 이용하여 병렬 운전 방법의 타당성을 검증한다.

• Journal of Electrical Engineering and Technology
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• v.7 no.4
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• pp.459-467
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• 2012

In this paper, a grid connected microgrid with multiple inverter-based distributed generators (DGs) is considered. DG in FFC mode regulates the microgrid as a controllable load from the utility point of view as long as its output is within the capacity limit. The transition mode causes a change in frequency of microgrid due to the loss of power transferred between main grid and microgrid. Frequency deviation from the nominal value can exceed the limit if the loss of power is large enough. This paper presents a coordinated control method for inverter-based DGs so that the microgrid is always regulated as a constant load from the utility viewpoint during grid connected mode, and the frequency deviation in the transition mode is minimized. DGs can share the load by changing their control modes between UPC and FFC and stabilize microgrid during transition.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.6
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• pp.89-95
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• 2000

The engine idle speed mode becomes worse as one drives a vehicle for several years. This is due to ageing of engine and power-train parts. In this case, unstable idle conditions such as engine stall and droop are frequently experienced when the engine gets heavy torque loads due to power steering pump and air conditioning compressor. The objective of this paper is to study on the idle speed control using PID controller under load disturbances. The input of the PID controller is an error of rpm. The output of the PID controller is an ISCV duty cycle. The dSPACE Controller Boards are used to interface with engine. The on-vehicle test is realized using by SIMULINK and BLOCKSETS tools. The real time interface control panel supplied by Control Desk S/W is designed to have good results in engine idle speed control.