Improvement and Dynamic Simulation Test of a Power Electronic Device Applied to Phase Sequence Exchange Technology
Abstract : Phase sequence exchange (PSE) is a recently developed emergency control technology. PSE uses power electronic devices to switch the three-phase sequence, which reduces the power angle of the generator by 120 and prevents the system from losing stability. In this work, the structure of the PSE device is improved. Based on the original nine solid-state circuit breakers (SSCBs), three mechanical circuit breakers (MCBs) are added. Normally, the current flows through the MCBs, which greatly reduces the conduction loss of the PSE device. Once the generator is identified as being out-of-step, the MCBs quickly open to transfer the current to the SSCBs. When the power angle threshold of the PSE is reached, the SSCBs are switched to complete PSE. In this paper, the transient characteristics of the current transfer process and phase sequence exchange process are analyzed. Based on the RTDS platform, dynamic simulation tests of the improved PSE prototype are carried out under different conditions. Experiments and calculations demonstrate that the improved PSE device can meet the technical requirements of PSE, and that the conduction power loss is reduced by 96% on average.
? The AC power exchanged by the DSTATCOM is related with the DC bus power on an instantaneous basis in such a way that a power balance must exist between the input and the output of the inverter.
? As can be derived from the imaginary part of frequency characteristics of the SCES complex impedance, there exists a resonance frequency around 25 Hz below which the SCU behaviour is entirely capacitive.
? During more than ±1/2 decade of this resonance frequency, the imaginary component of the impedance magnitude is relatively flat and approximately zero, this demonstrating a purely resistive EDLC behaviour in this mid-frequency range
? The wide usage of nonlinear loads, such as personal computers, variable speed drives, UPS systems, and the other electronic equipment produce harmonics which represent a major problem in industrial and commercial power systems.
? These problems are facing electricity customers and suppliers so, one of the major concerns in electricity industry is power quality.
? The DVR is a fast, flexible and efficient solution to the voltage sag problems. It can restore the load voltage within a few milliseconds and hence avoiding any power disruption to that load.
? This work describes the DVR to improve the power quality problems such as voltage sags/swells, harmonics distortion and unbalanced voltages in distribution systems.
• The proposed DSTATCOM essentially consists of a three-phase voltage source inverter (VSI) built with semiconductors devices having turn-off capabilities.
• This device is shunt-connected to the distribution network by means of a coupling transformer and the corresponding line sinusoidal filter.
• The VSI structure proposed is designed to make use of a three-level twelve pulse pole structure, also called neutral point clamped (NPC), instead of a standard two-level six pulse inverter structure.
• The proposed DSTATCOM essentially consists of a three-phase three-level VSI built with semiconductors devices having turn-off capabilities.
? The control of the compensation voltage and harmonics cancellation in the DVR is based on Adaptive Noise Canceling (ANC) technique. Simulation results carried out by PSCAD/EMTDC to investigate the performance of the proposed method.
? Continuous development of high performance equipment: Such equipment are more susceptible to power disturbances.
? The auxiliary supply method is applied to increase the performance when the grid of the DVR is weak. In this topology, variable DC link voltage or constant DC link voltage types are applied.
? In no energy storage topology, the remaining voltage on supply side or load side is used to supply necessary power to the system if the DVR is connected to strong grid.
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