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A DC-link voltage compensation method for a photovoltaic (PV) generation system with energy storage system(ESS) is presented. When PV power is oscillated, the DC-link voltage is also influenced. And this fluctuation of DC-link critically affects the load voltage when the ESS is operated in stand alone mode. In conventional method, huge capacitor bank is necessary to reduce the fluctuation. In this...
In this paper, a smart distribution transformer which addresses power quality issues in the electrical power distribution system is presented. The proposed system is comprised of a line frequency transformer connected to a power electronic converter that is ‘auto-connected’ on the secondary side. The auto-connection is facilitated by the use of a high-frequency (HF) / medium frequency (MF) transformer...
A modular three-phase voltage regulator with a fictitious dc-link is proposed. The proposed scheme is the combination of three single-phase modules while each one of the single-phase module is a three-leg ac voltage regulator. Therefore, the proposed voltage regulator reduces the number of main switches and compensates the voltage of each phase independently. Furthermore, a small film ac capacitor...
For medium/high voltage high-power neutral-point-clamped (NPC) three-level converters, narrow pulses appear usually when modulation waves are close to ±1 and 0. To ensure reliable switching and the safety, a long narrow pulse limit time needs to be set. Narrow pulse problems will become prominent. Meantime, neutral-point voltage balance problem of three-level NPC converters is a key issue that should...
Recent developments show that renewable energy sources are considerably contributing to the electrical power generation and offer a future-oriented, sustainable and environmental-friendly alternative to fossil energy sources. Wind energy in particular has experienced a rapid growth over the past decades, so that wind energy conversion systems (WECS) will occupy an important role in the power generation...
Increasing penetration of PV sources in LV grids is introducing new challenges to the quality of voltage. Variability of solar radiation can cause power ramps of up to the nominal power of the plant in one second, which directly induces voltage fluctuations on distribution feeders. To mitigate this impact on power quality, we investigate the introduction of dc micro-grids interfaced to the ac grid...
This paper presents a nonlinear controller for a permanent-magnet synchronous generator (PMSG) wind turbine system in the framework of port-controlled Hamiltonian system. For the simplification, this work focuses on the nonlinear control law of the grid side converter (GSC) that is directly connected to the grid and affected during network disturbances. The proposed controller is designed through...
The Fault Ride Through (FRT) capability of renewable energy sources (RES) for providing support to the power grid under several disturbances allows us to consider them not only as passive elements in the power system network, but also as ancillary services for the mitigation of evolving contingencies. In this paper, an investigation of the FRT operation of RES according to current grid regulations...
Voltage sags being inherent disturbances to power systems, equipment should be characterized by tolerance curves and grid operators are compelled to report voltage sags. Furthermore, voltage sag responsibility curves are currently being discussed by regulators. This paper condenses relevant information on these subjects, and presents three case-studies. The description and reporting of voltage sags...
In this paper, a new hybrid unified power quality conditioner (HUPQC) is proposed to improve current and voltage imperfections in distribution systems. The proposed HUPQC is comprised of the shunt hybrid active power filter (SHAPF), the dynamic voltage restorer (DVR) and the isolated bi-directional DC-DC converter. The main contribution of the study is a new HUPQC topology that enables the reduction...
With increasing penetration of grid-connected photovoltaic (PV) power generation, the grid codes about low-voltage ride-through (LVRT) of PV plants and their interface inverters have been established. Under a grid voltage sag, the underlying reasons may cause overcurrent of the grid-connected inverter and failure in ride-through. In this paper, a positive-sequence current injection with feedforward...
This paper presents a 95VAC-120VAC mains powered converter-free LED driver for general lighting application. A quasi-constant power control scheme is proposed to significantly reduce the low-frequency-flicker, combined with a valley fill circuit to maintain good power factor performance. The driver achieves 88.2% efficiency and 0.92 PF with only 18% flicker at 110VAC 60Hz input and does not require...
This paper proposes a hybrid control algorithm to maximize utilization and functionality of distribution static compensator (DSTATCOM). This control algorithm combines the different aspects of DSTATCOM operation and tries to mitigate the voltage and current harmonics, balance the source currents, improve the power factor, compensate for voltage disturbances such as sag and swell, reduce the losses...
Issues related to power quality have become more critical in recent times due to the increased penetration of renewables into the power grid. Voltage sags and swells are amongst the most important issues associated with a power grid, and extensive research has been directed towards the mitigation of these issues. In the DVR control strategies discussed so far in literature, complex vector control...
A rapid grid synchronization technique is proposed for enhanced low voltage ride-through (LVRT) operation of voltage source inverter based distributed energy resource (DER). The proposed synchronization method aims at enhancing the LVRT capability by providing fast information of the fundamental positive and negative sequence components of the grid voltage vector. This is achieved by a novel pre-filter,...
Existing voltage control schemes of cascade on-load tap changers (OLTCs) have been developed considering unidirectional power flow. However, in recent years, integration of distributed generation such as solar and wind power to the grid has created possibility for bidirectional power flow resulting in inefficiency of previous voltage control methods of cascade OLTCs. In this paper, an effective method...
Dynamic voltage restore (DVR) is a well established power device able to compensate voltage disturbances, in especial voltage sags and swells, in the power system. Its main goal is to protect sensitive loads against these disturbances. For this purpose, the precise computation of the DVR compensation voltage reference is a important issue. One of the effective techniques for the reference generation...
This paper presents a new proposal of combining a FACTS device with the fixed speed wind turbine (FSWT) to meet the restrictions found in upcoming grid codes. The applied FACTS device is based on the control strategy of the Dual Unified Power Quality Conditioner - the iUPQC. The power stage of the iUPQC consists of two converters connected back-to-back. One of them is connected in series and the other...
In this paper, a new controller approach for unified power flow controller (UPFC) is proposed to improve the low-voltage-ride-through (LVRT) capability of a DFIG-based WECS during voltage sag. The shunt and series converters of the UPFC are controlled using a hysteresis current controller (HCC) and proportional integral controllers (PI), respectively. Detailed simulation is carried out using MATLAB/SIMULINK...
This paper presents a predictive current control strategy for Active Front End (AFE) rectifier supplying active and reactive power to the electric system during unsymmetrical voltage fault conditions without the use of a Phase Locked Loop (PLL) or Frequency Locked Loop (FLL). For a given active and reactive power and supply voltage, the strategy generates the required reference currents. A predictive...
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