• 로봇학회논문지
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• 제11권2호
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• pp.92-99
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• 2016

An electro-hydraulic actuator (EHA) is widely used in industrial motion systems and the increasing bandwidth of EHA position control is important issue. The model-inverse feedforward controller is known to extend the bandwidth of system. When the system has non-minimum phase (NMP) zeros, direct model inversion makes system unstable. To overcome this problem, an approximate model-inverse method is used. A representative approximate model inversion method is zero phase error tracking control (ZPETC). However, if zeros locate right half plane of z-plane, the approximate inverse model amplifies the high-frequency response. In this paper, to solve the problem of ZPETC, an adaptive model-inverse control is proposed. The adaptive algorithm updates feedforward term in real-time. The effectiveness of the proposed adaptive model-inverse position control strategy is verified by comparison with typical proportional-integral (PI) control and feedforward control by experiments. As a result, the proposed adaptive controller extends the bandwidth of EHA position control.

• Journal of Power Electronics
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• 제16권1호
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• pp.297-309
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• 2016

Grid-connected inverters (GCIs) with an LCL output filter have the ability of attenuating high-frequency (HF) switching ripples. However, by using only grid-current control, the system is prone to resonances if it is not properly damped, and the current distortion is amplified significantly under highly distorted grid conditions. This paper proposes a synchronous reference frame equivalent proportional-integral (SRF-EPI) controller in the αβ stationary frame using the parallel virtual resistance-based active damping (PVR-AD) strategy for grid-interfaced distributed generation (DG) systems to suppress LCL resonance. Although both a proportional-resonant (PR) controller in the αβ stationary frame and a PI controller in the dq synchronous frame achieve zero steady-state error, the amplitude- and phase-frequency characteristics differ greatly from each other except for the reference tracking at the fundamental frequency. Therefore, an accurate SRF-EPI controller in the αβ stationary frame is established to achieve precise tracking accuracy. Moreover, the robustness, the harmonic rejection capability, and the influence of the control delay are investigated by the Nyquist stability criterion when the PVR-based AD method is adopted. Furthermore, grid voltage feed-forward and multiple PR controllers are integrated into the current loop to mitigate the current distortion introduced by the grid background distortion. In addition, the parameters design guidelines are presented to show the effectiveness of the proposed strategy. Finally, simulation and experimental results are provided to validate the feasibility of the proposed control approach.

• 한국통신학회논문지
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• 제32권10C호
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• pp.1032-1041
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• 2007

위성 기반 측위 시스템은 (global navigation satellite system, GNSS) 위치 기반 기술의 핵심 기술로서, 통신 물리계층으로 직접수열 확산대역 (direct sequence spread spectrum, DS/SS) 시스템을 사용한다. DS/SS 시스템의 성능은 송수신기에서 사용하는 확산 부호의 정확한 동기에 따라 크게 좌우된다. 본 논문은 DS/SS 시스템의 동기기법 가운데 부호 추적 기법에 초점을 맞춘다. 가장 널리 알려진 부호 추적 기법은 이른-늦은 판별기를 사용하는 EL-DLL이다 (delay lock loop with early minus late discriminator). 이상적인 환경에서 EL-DLL은 최적 부호 추정기이다. 그러나 대역 제한된 다중경로 환경에서 EL-DLL은 추적을 통해 정확한 동기시점을 결정한 후에도 여전히 추적편이가 남게 된다. 본 논문에서는 대역 제한된 다중경로 환경에서 EL-DLL의 추적편이 특성 분석을 위해 상관 값이 나타나는 영역을 이른 상관시간 옵셋 영역과 (advanced offset range, AOR) 늦은 상관시간 옵셋 영역으로 (delayed offset range, DOR) 나누어 분석하였다. 분석 결과 대역 제한된 다중경로 환경에서 EL-DLL의 추적편이는 정확한 동기시점을 기준으로 AOR과 DOR에서 상관 값의 대칭성이 왜곡되어 발생하는 제 1형 추적편이와 최고 상관 값이 나타나는 시점이 정확한 동기시점에서 벗어나서 발생하는 제 2형 추적편이로 구별할 수 있으며, 이 가운데 제 2형 추적편이가 추적편이의 대부분을 차지함을 보였다. 또한 AOR과 DOR에서 상관 값 추이 분석을 통해 AOR에서의 상관 값이 DOR에서의 상관 값에 비해 다중경로신호에 의해 덜 왜곡되는 특성을 보였으며, 이를 바탕으로 대역 제한된 GNSS에 적합한 새로운 부호 추적편이 완화 기법을 제안하였다. 제안한 기법은 대역 제한된 다중경로 환경에서 EL-DLL에 비해 정확한 추적이 가능함을 보였다.

• Journal of Power Electronics
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• 제19권4호
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• pp.1000-1010
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• 2019

The use of internal-model-based linear controller, such as resonant controller, is a well-established technique for the current control of grid-connected systems. Attractive properties for resonant controllers include their two-sequence tracking ability, the simple control structure, and the reduced computational burden. However, in the case of continuous-designed resonant controller, the transient performance is inevitably degraded at a low switching frequency. Moreover, available design methods for resonant controller is not able to realize the direct design of transient performances, and the anticipated transient performance is mainly achieved through trial and error. To address these problems, the zero-order-hold (ZOH) characteristic and inherent time delay in digital control systems are considered comprehensively in the design, and a corresponding hold-equivalent discrete model of the grid-connected converter is then established. The relationship between the placement of closed-loop poles and the corresponding transient performance is comprehensively investigated to realize the direct mapping relationship between the control gain and the transient response time. For the benefit of automatic tuning and real-time adaption, analytical expressions for controller gains are derived in detail using the required transient response time and system parameters. Simulation and experimental results demonstrate the validity of the proposed method.