and 2017, respectively, where he is currently working toward Ph.D. degree in power electronics and power transmission. Now he is a joint Ph.D. student supported by the China Scholarship Council with the School of Electrical and Electronic Engineering of Nanyang Technological University. His research interests include distributed micro-grid, and power-electronic enabled power network.
Abstract-To regulate the DC-link voltage of three-phase AC/DC converters, an enhanced state observer (ESO)-based controller is presented in this letter. The proposed controller, contrary to the traditional ones, does not require the DClink current measurement and offers a "plug and play" capability, a rather high disturbance rejection ability and robustness against the DC-link capacitance parameter variation. The design procedure of the suggested controller is discussed, and its effectiveness is verified using experimental results.
This paper presents a reduced-order generalized proportional-integral observer (RGPIO) based resonant super-twisting sliding mode controller (RST-SMC) for the three-phase AC/DC converters. On the contrary to utilizing the proportional-integral (PI) controller in regulating the DC-link voltage, which may cause large undershoot/overshoot under the disturbance, the proposed voltage control strategy for the DC-link has high disturbance rejection ability and the settling time has been greatly reduced. In addition, the proposed RST-SMC in the current control loop not only preserve the merits of the sliding mode controller but also achieve the current tracking without steady-state error in the stationary − frame. The effectiveness of the proposed method has been verified by a lab-constructed experimental prototype.
In this paper, a DC-link voltage protection (DCVP) control method is proposed to address the DC-link overvoltage issue due to power back-feeding in parallel Uninterruptible Power Supply (UPS) system. The proposed control method is able to protect the inverter against the excessive DC-link voltage, which increases the system reliability and robustness. Moreover, a current sharing control strategy is proposed by online regulating the virtual resistance of each UPS module. The proposed current sharing control strategy is able to address the circulating fundamental and harmonic current caused by the line impedance mismatching or power back-feeding issue in the UPS system. In addition, an improved consensus-based distributed controller is proposed to alleviate the overshoot issue during the transient process in voltage amplitude and frequency restoration. Finally, the feasibility of the proposed methods are verified by experimental results from the parallel UPS prototypes. Index Terms-Uninterruptible Power Supply(UPS), DC link voltage protection, current sharing, consensus control, Anti-windup. I. INTRODUCTION RIVEN by the increasing importance of the Uninterruptible Power Supply (UPS) in the industry including enterprise IT, commercial telecom, data center and cloud computing area [1], the global market for the UPS system is projected to soar dramatically in the next few years. Meanwhile, the strong need for the UPS system to provide more reliable, efficient and secure electrical power supply for the modern digital equipment propels the UPS technology advancement by engineers and academic researchers [2]. According to the European Standard EN 62040-3 [3], the UPS systems are divided into on-line, off-line and lineinteractive UPSs. In an on-line UPS system, the load is always powered by the inverter regardless of the grid condition; the only exception is that when the overloading occurs and the bypass switch closes to connect the load with the grid. In offline and line-interactive UPS systems, however, the load power is supplied from the grid or a combination of the inverter and the grid, respectively [4]. The on-line UPS system is the most
To enhance the robustness and disturbance rejection ability of an on-line uninterruptible power supply (UPS) system, an Internal Model Control (IMC)-based DC-link voltage regulation method is proposed in this paper. Furthermore, the multi-mode operations of the on-line UPS system are investigated and their corresponding control strategies are proposed. The proposed control strategies are capable of achieving the seamless transition in traditional normal mode, PV-aided normal mode, enhanced eco-mode and burn-in test mode. Meanwhile, the uninterruptible load voltage is promised during the mode transition. The small signal analysis is also conducted to investigate the stability of enhanced eco-mode and burn-in test mode. Finally, extensive experimental results are provided to validate the effectiveness of the proposed methods.
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