Three-phase

About: Three-phase is a research topic. Over the lifetime, 16801 publications have been published within this topic receiving 159477 citations.

Active and Reactive Power Injection Strategies for Three-Phase Four-Wire Inverters During Symmetrical/Asymmetrical Voltage Sags

Abstract: Electric grid codes are expected to change in near future to accommodate an increased number of distributed generation units in the distribution power system without impairing its power quality. It is desired that the generators remain connected during voltage sags and provide ancillary services, such as voltage and reactive power control, ensuring the operational stability of the power system. This paper explores how the existing strategies for active and reactive power injection impact the operation of grid-tied inverters in terms of required power, current flowing, and reduction of active power delivery during the voltage sags. Such inputs are relevant to properly size converters for operation under fault events. In addition, this paper contributes to devise: 1) constant peak current control, 2) constant active current control, and 3) constant average active power control strategies for three-phase four-wire grid-tied inverters considering the natural (abc ) reference frame. The design and implementation of the investigated power injection strategies are discussed, and their effectiveness and technical viability are analyzed through dynamic computational simulations under symmetrical/asymmetrical voltage sags, and variation of the short-circuit ratio.

Apparatus for sensing short circuit faults in alternating current supply lines

Abstract: Apparatus is provided for sensing and responding to short circuit faults, in particular in three phase alternating current supply lines for direct-on-line starting three phase squirrel cage induction motors. Line current in each line is sensed by a respective current transformer and signals representing both the amplitude and phase of each line current are produced. Line-to-line or line-to-neutral voltage for each phase is also sensed, by photo-electric isolator circuitry, and signals produced representative of the respective phases of these voltages. Logic circuitry is used to produce from the signals representative of current and voltage phases three phase difference signals in the form of currents each varying substantially directly with the difference between the respective current and voltage phases of the respective line. The relationships between these difference signals and the respective current amplitude signals are compared with the relationship which corresponds to conditions from starting to normal running of the motor, and an output signal is produced representing whether there is correspondence or not between the compared relationships. If lack of correspondence is indicated, a circuit breaker is operated to break the supply lines upstream of the sensing equipment.

Development and Analysis of a Sensitivity Matrix of a Three-Phase Voltage Unbalance Factor

Abstract: Unbalanced phase voltages in electricity networks prevent efficient and stable delivery of power and energy services from utility companies to end-users, and vice versa. While variations in voltage magnitude and power loss have been studied extensively, little attention has been paid to the development of linearized expressions to account for the variation in voltage unbalance. Using a standard definition of the voltage unbalance factor (VUF), this study is the first, to the best knowledge of the authors, in which a VUF sensitivity matrix is mathematically developed and analyzed with respect to variations in three-phase (3- ph ) voltages and, consequently, 3- ph unbalanced load demand. To demonstrate its utility, we performed simulation case studies and compared the estimates made using the matrix to those from a power flow calculation algorithm. The VUF sensitivity matrix is expected to have a variety of practical applications for power systems, such as optimal scheduling and real-time control, which enables improvement in network power quality.

Direct Torque Control for Three-Phase Open-End Winding PMSM With Common DC Bus Based on Duty Ratio Modulation

Abstract: This article introduces the classical direct torque control (DTC) to a three-phase open-end winding permanent magnet synchronous motor with common dc bus for the first time. The electromagnetic torque and the stator flux are controlled at the same time. However, the zero-sequence current is not suppressed, and the ripples of the electromagnetic torque and stator flux are large. To improve the operation performance of this drive system, a DTC based on a duty ratio modulation (DRM-DTC) is proposed. First, a deadbeat zero-sequence current controller is proposed in the DRM-DTC to suppress the zero-sequence current. Second, another strategy, which is based on a graphical analysis method and a simple deadbeat direct torque and flux controller, is proposed to optimize the duty ratio of the active voltage vector. Thus, the electromagnetic torque and stator flux ripples can be reduced. Finally, an optimized pulsewidth modulation implementation strategy is proposed in the DRM-DTC to further reduce the switching frequency of inverters. The classical DTC and the proposed DRM-DTC are compared through simulation and experiment, and the results verify the effectiveness of the proposed strategy.

Three-phase zero-current-transition (ZCT) inverters and rectifiers with three auxiliary switches

Abstract: Zero current transition (ZCT) topologies are presented for three-phase inverters and rectifiers. Such devices are used for example in AC adjustable speed drives for so-called zero-emission vehicles (i.e., electric and hybrid combustion/electric automobiles). Compared to existing three-phase ZCT techniques, the number of auxiliary switches is reduced from six to three, while not altering the necessary device rating. Correspondingly, the number of gate-drivers for the auxiliary switches is also reduced to three. Meanwhile, the merits of the existing three-phase ZCT techniques are still retained, i.e., all the main switches and the auxiliary switches are turned on and turned off under zero-current conditions, and the independent commutation for each main switch is achieved. The desired soft-switching features are achieved. Therefore, this invention will contribute to more cost-effective, reliable, and efficient high-performance three-phase inverters and rectifiers.