• 전력전자학회논문지
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• 제15권1호
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• pp.43-51
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• 2010

본 논문에서는 고전압 전동기 가변속 장치인 H-브릿지 멀티레벨(H-Bridge Multi-Level; HBML) 인버터를 이용한 유도 전동기 벡터 제어시 인버터의 출력 전압 위상 지연 현상을 해석하고 전류 제어기의 보상 기법을 제시하였다. Phase-Shifted Pulse Width Modulation (PSPWM) 기법을 적용한 HBML 인버터는 개별 인버터 모듈이 독립적으로 동작할 수 있어서 확장성과 모듈화 능력이 향상되는 장점이 있다. 그러나 이러한 PSPWM을 적용한 HBML 인버터는 기준 전압과 실제 전압 사이에 위상 차이가 있기 때문에 출력 주파수에 대한 샘플링 주파수의 비율이 충분하지 않은 고속 영역에서 전류 제어기를 불안정하게 하는 원인이 된다. 전류 제어기의 불안정성은 기준 전압과 출력 전압의 위상 차이를 보상하는 제안된 방법을 추가함으로써 제거하였다. 본 방법은 인버터의 스위칭 주파수가 낮고, 전동기 속도가 높은 조건에서 PSPWM을 이용한 HBML 인버터 시스템에 효과적이며, 13레벨로 구성된 HBML 인버터로 구동되는 6,600[V] 1,400[kW] 유도전동기 실험을 통해 제안된 방법의 타당성을 입증하였다.

• Journal of Electrical Engineering and Technology
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• 제11권1호
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• pp.241-246
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• 2016

This paper presents a method that can improve the performance of permanent magnet synchronous motor current control by minimizing the measured current phase delay caused by the Low Pass Filter(LPF) used to cut off the noises that flowed in when feedback currents are measured. Although existing methods that change the Cutoff Frequency of the LPF can minimize phase delays during high speed rotations, their noise cutoff effects are much lower and this may lead to the decline of control performance. Therefore, in this study, an algorithm that can compensate current phase delays through relatively simple calculations from the synchronous motor d-q axis coordinate transformation matrix and the inverse transformation matrix is proposed and the validity of the proposed method is verified by comparing the waveform of the calculated current with the waveform of actual currents through simulations and experiments.

• Journal of Power Electronics
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• 제10권4호
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• pp.412-418
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• 2010

This paper proposes a new algorithm to generate a reference signal for an active power filter using a sliding-window FFT operation to improve the steady-state performance of the active power filter. In the proposed algorithm the sliding-window FFT operation is applied to the load current to generate the reference value for the compensating current. The magnitude and phase-angle for each order of harmonics are respectively averaged for 14 periods. Furthermore, the phase-angle delay for each order of harmonics passing through the controller is corrected in advance to improve the compensation performance. The steady-state and transient performance of the proposed algorithm was verified through computer simulations and experimental work with a hardware prototype. A single-phase active power filter with the proposed algorithm can offer a reduction in THD from 75% to 4% when it is applied to a non-linear load composed of a diode bridge and a RC circuit. The active power filter with the proposed reference generation method shows accurate harmonic compensation performance compared with previously developed methods, in which the THD of source current is higher than 5%.

• Journal of Electrical Engineering and Technology
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• 제3권1호
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• pp.94-100
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• 2008

This paper presents a new control method of single-phase active power filter (APF) for the compensation of harmonic current components in nonlinear loads. To facilitate the possibility of complex calculation for harmonic current detection of the single phase, a single-phase system that has two phases was constructed by including an imaginary second-phase giving time delay to the load current. The imaginary phase, which lagged the load current T/4 (Here T is the fundamental cycle) is used in the conventional method. But in this proposed method, the new signal as the second phase is delayed by the filter. Because this control method is applied to a single-phase system, an instantaneous calculation was developed by using the rotating reference frames synchronized to source-frequency rather than by applying instantaneous reactive power theory that uses the conventional fixed reference frames. The control scheme of single-phase APF for the current source with R-L loads is applied to a laboratory prototype to verify the proposed control method.

• 한국통신학회논문지
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• 제37A권10호
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• pp.895-902
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• 2012

본 논문에서는 비선형 전력증폭기(PA:power amplifier)의 AM/PM 비선형 왜곡특성을 포함하는 군 지연을 보상하는 새로운 등화기를 제안한다. 군 지연 특성은 각 주파수 성분에 따라 서로 다르게 나타나는 상수가 아닌 비선형 시간지연이다. 전력증폭기에서 발생되는 AM/PM 특성으로 인한 위상 왜곡 현상은 군 지연을 증가시키는 주요한 요인이다. 이러한 군 지연 왜곡으로 신호 성상도에서 신호는 퍼지면서 회전하게 된다. 위와 같은 문제점을 고려하여 각 주파수 성분에 따라 다르게 나타나는 비선형 시간지연을 정적인 군지연으로 구분하고, PA의 AM/PM 특성인 입력신호 크기에 따라서 위상 천이가 다르게 발생하는 것을 동적인 군 지연으로 구분한다. 정적인 군 지연은 주파수 영역에서 Type-Based 방법으로 위상 왜곡을 추정 및 보상하고 동적인 군 지연은 시간영역에서 위상회전을 보상한다. 제안된 군 지연 보상기법으로 전력증폭기의 AM/PM 특성을 포함한 군 지연 특성을 충분히 보상할 수 있음을 확인하였다.

• 동력기계공학회지
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• 제19권4호
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• pp.89-96
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• 2015

This paper investigates some strategies to overcome the chattering problem of the conventional sliding mode observer (SMO) and to improve the rotor position estimation performance for full range sensorless control of a PMSM. An adaptive observer gain based on the Lyapunov's stability criterion and a cascade low pass filter with advanced phase delay compensation were proposed to reduce the chattering problem and to strengthen the filtering capability of the SMO. Several cases studies through experiments were carried out to confirm conventional SMO's problems and effectiveness of the proposed strategies. The experimental results show that the proposed method gives precise estimation on speed and rotor position when the motor rotates on 2% of its rated speed.

• Journal of information and communication convergence engineering
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• 제6권3호
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• pp.353-357
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• 2008

One objective in developing the next generation of wireless communication systems is to increase data rates and reliability. A promising way to achieve this is to combine multiple-input and multiple-output signal processing with a space-time coding scheme, which offers higher coding and diversity gains and improves the spectrum efficiency and reliability of a wireless communication system. It is noted, however, that time delay differences and phase differences among different channels increase symbol interference and degrade system performance. In this letter, we investigate phase differences and their effects on multiple-input and multiple-output systems, and propose a compensation algorithm for the Rayleigh fading model to minimize their effects.

• Journal of Power Electronics
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• 제16권5호
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• pp.1833-1842
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• 2016

In grid-connected converter control, grid voltage feedforward is usually introduced to suppress the influence of grid voltage distortion on the converter's grid-side AC current. However, owing to the time-delay in control systems, the suppression effect of the grid voltage distortion is seriously affected. In this paper, the positive effects of the grid voltage feedforward control are analyzed in detail, and the time-delay caused by the low-pass filter (LPF) in the voltage filtering circuits and digital control are summarized. In order to reduce the time-delay effect on the performance of the feedforward control, a voltage feedforward control strategy with time-delay compensation is proposed, in which, a leading correction of the feedforward voltage is used. The optimal leading step used in this strategy is derived from analyzing the phase-frequency characteristics of a LPF and the implementation of digital control. By using the optimal leading step, the delay in the feedforward path can be further counteracted so that the performance of the feedforward control in terms of suppressing the influence of grid voltage distortion on the converter output current can be improved. The validity of the proposed method is verified through simulation and experiment results.

• Journal of the Optical Society of Korea
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• 제17권5호
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• pp.415-422
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• 2013

White-light phase-shifting interferometry (WLPSI) is widely recognized as a standard method to measure shapes with high resolution over a long distance. In practical applications, WLPSI, however, is associated with some degree of ambiguity of its phase, which occurs due to a phase delay, which is the offset between the phase of the fringes and the fringe envelope peak position. In this paper, a new algorithm is proposed for the determination of a fringe order suitable for samples in which the phase delay mainly occurs due to noise, diffraction and a steep angle. The concepts of the decouple factor and the connectivity are introduced and a method for calculating the decouple factor and the connectivity is developed. With the phase-unwrapping procedure which considers these values, it is demonstrated that our algorithm determines the correct fringe order. To verify the performance of the algorithm, a simulation was performed with the virtual step height under noise. Some specimens such as step height standard and a column spacer with a steep angle are also measured with a Mirau interference microscope, after which the algorithm is shown to be effective and robust.

• Journal of Power Electronics
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• 제12권4호
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• pp.654-663
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• 2012

In this paper, a digital control strategy based on equivalent fundamental and odd harmonic resonators is proposed for single-phase DVRs. By using a delay block, which can be equivalent to a bank of resonators, it rejects the fundamental and odd harmonic disturbances effectively. The structure of the single closed-loop control system consists of a delay block, a proportional gain and a set of zero phase notch filters. The principle of the controller design is discussed in detail to ensure the stability of the system. Both the supply voltage and the load current feedforwards are used to improve the response speed and the ability to eliminate disturbances. The proposed controller is simple in terms of its structure and implementation. It has good performances in harmonic compensation and dynamic response. Experimental results from a 2kW DVR prototype confirm the validity of the design procedure and the effectiveness of the control strategy.