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This paper presents a unified power quality conditioner (UPQC) and its control strategy for assisting the fault ride-through operation of large-scale photovoltaic (PV) power station. The output voltage of PV station can be controlled to its rated value with UPQC under high grid voltage fault condition. Moreover, it can absorb reactive power from the grid under high voltage condition to support the...
Since low voltage ride-through (LVRT) was proposed, its improvements have never been stopped, especially the improvements for operation under unbalanced faults. In this paper, an overall control strategy is proposed to solve the problem that the output current quality and dc-link voltage quality cannot be guaranteed at the same time. For this propose, a current control method is employed to guarantee...
The speed sensorless control method, which is based on the extended electromotive force (EEMF) model of interior permanent magnet synchronous motor, is difficult to make into use and its parameter dependence is strong. So a method to simplify the EEMF model was proposed and a simplified full order state and sliding mode observer (FOSSMO) was designed in order to achieve sensorless control. In addition,...
Short-circuiting in dc lines affects the security and reliability of dc microgrid greatly. A short-circuit current calculation method for low-voltage dc microgrid is proposed in this paper. To solve the calculation of short-circuit current, a line model of bipolar which includes π type equivalent circuits, solid-state bidirectional switches with snubber circuits and freewheeling branches is adopted...
The collective dynamics under different coupled strengths in the coupled synchronous reluctance motor drives is presented in this paper. With variation of the coupled strengths, the coupled system exhibits rich dynamical phenomena such as amplitude death, periodic anti-synchronization and complete synchronization. By the amplitude death the coupled synchronous reluctance motor drives can be stabilized...
This paper proposes a method for independent drive of two permanent magnet synchronous motors (PMSMs) fed by a single five-leg inverter (5LI) based on reducing peak current of common leg. The advantages of 5LI are reduced size, volume, reduced number of devices, and increased efficiency due to total lower losses. The conventional method that has been used for controlling two PMSMs sends a large amount...
This paper proposes an AC-AC converter, which consists of T-type three-level rectifier and inverter, for an on-line UPS. The switching loss of the proposed AC-AC converter is drastically reduced because the proposed converter is driven at a very low switching frequency which is six times of input side frequency. The T-type rectifier separates the maximum phase-voltage, medium phase-voltage and minimum...
Power sharing between inverters, microgrid modeling and stability analysis are hot research fields in microgrid research. Line impendence is an important parameter to improve accuracy of the power sharing and to improve the accuracy of the model of the microgrid system. Line impedance measure methods have been discussed in several papers. This paper summarized and analyzed each of these methods, identified...
To guarantee a smooth transition from islanding mode to grid-connected mode, synchronization is the first issue to be considered. This paper puts forward a new synchronizing strategy based on voltage-controlled inverter. It can easily and accurately make the voltage frequency and phase of the distributed generation system track the main grid even if it varies. At the same time, there is a very small...
The wireless power transfer (WPT) system for electric vehicles requires high efficiency, lightweight, compact and be suited to big air gap. The WPT system has low coupling coefficient, which is far different from the traditional transformer. Optimal parameters design approach for resonant converter with S-S compensation for WPT is investigated. 85kHz and 20kHz parameters design are introduced in the...
To promote the wide acceptance of electric vehicles (EVs), the charging facilities should satisfy with some basic requirements, such as high efficiency, low harmonic pollution, long lifetime, low cost, and ease of bulk construction. Therefore, a novel EV charging facility — dc charging spot and a lower stress zero current switch-pulse width modulation (ZCS-PWM) Superbuck converter suitable for output...
This paper presents a control strategy of star-connected cascade distribution static synchronous compensators (D-STATCOMs) operating under unbalanced conditions. By equivalent transformation, an accurate abc-frame mathematical model of the cascade D-STATCOM with unknown disturbances and parametric perturbation is proposed. Then a novel robust control with L2-gain performance based on the combination...
Due to the presence of the low-order background voltage harmonics in the grid, it will cause higher current harmonics in the AC side of the grid inverter with Selective Harmonic Elimination PWM (SHEPWM). Therefore the grid inverter with traditional SHEPWM has not prevailed since it is unable to overcome the background harmonics of the utility and satisfy the power quality requirement. In this paper,...
DC collection and transmission is a new trend for large scale offshore wind farms. In this paper, the output voltage of the wind farm is promoted by series connecting the wind turbines. Then, the wind power is collected by shunt connecting the wind turbine group. VSC-HVDC is a traditional method to connect offshore wind farm to onshore AC grid. However, big voltage variable ratio dv/dt is the main...
In order to improve the output-regulation accuracy of the switching converter with conventional constant off-time (CCFT) modulation, dual-edge constant off-time (DCFT) modulation for switching converter is proposed in this paper. The principle of switching converter with DCFT modulation, including leading-triangle constant off-time (LT-CFT) modulation and trailing-triangle constant off-time (TT-CFT)...
This paper proposes a new modeling method for buck converter. The new modeling method, named bi-switching status method (BSM), for buck converter is obtained via the propositional calculus and linear constrain. Based on the mixed logical dynamical (MLD) model, BSM model of buck converter is obtained. Compared with other modeling methods, such as MLD method and state-space averaging method, streamlined...
China Machinery Industry Standard (CMIS) GB/T 12326-2008 prescribed in the islanded operation mode, microgrid inverter (MGI) output voltage dynamic transient range is less than 10% when the resistive load is switched rapidly between 0% and 100%. The three-loop power virtual synchronous generator (VSG) control methods are commonly used in MGI units to share the loads among the parallel MGIs. However,...
A high efficiency high voltage step-up gain DC-DC converter is proposed and studied in this paper. The proposed converter consists of a boost converter cell and an isolated single-ended PWM resonant converter cell, with their outputs connected in series to achieve high voltage step-up gain. By using quasi-resonant technology, zero current switching (ZCS) for the diode on the secondary of transformer...
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