DC Filter Capacitor Research Articles

Electric field evaluation and optimization of shielding electrodes for high voltage apparatus in ±1100 kV indoor DC yard

The indoor DC yard of the ±1100 kV UHVDC transmission project is preferred to the outdoor solution, and the rational design of shielding electrodes for the ±1100 kV apparatus becomes the key to system security. In this paper, the design requirements of indoor DC yards were described and the preliminary designs of the indoor shielding electrodes for the key ±1100 kV DC apparatus were proposed. The whole 3-D FEM model of one ±1100 kV indoor DC yard was established. An empirical formula of the critical E-field strength for the evaluation of relatively large shielding electrodes was proposed based on the corona tests of typical ball and ring electrodes. The electric field distribution of the whole indoor DC yard was calculated and the surface electric field strength of all the shielding electrodes for the key ±1100 kV apparatus was evaluated. The results show that after optimization, the maximum surface field strength on the shielding electrode of ±1100 kV DC filter capacitor decreased from 1507 V/mm to 1335 V/mm, lower than the critical value for evaluation, then the corona free design of all the ±1100 kV indoor shielding electrode could be predicted. The method of electric field evaluation and optimization could provide important references for the development of shielding electrodes in the ±1100 kV or other UHV indoor DC yards.

Design and Simulation of Grid-Connected Rectifier and Boost Control Circuit for Micro-Turbine

本文对微型燃气轮机并网整流与升压控制回路进行了设计与仿真。整流部分(Rectifier system)选用电压型PWM整流器(VSR)，所搭建模型主要包括输入滤波电感(Reactor)、整流桥(Three-Level Bridge Rectifier)、整流控制器(Rectifier Controller)和直流滤波电容(C1, C2)。本次研究课题的斩波电路选用的是升压Boost斩波电路，将电压调节器用作外环控制，电流内环则根据id*、iq*的值来控制电流，从而实现对交流侧电流的快速调节作用。Boost Controller模块主要是通过产生合适的控制脉冲信号来控制可控开关Mosfet的通断，最终实现调节输出电压的目的。仿真结果表明本文设计的整流电路与升压控制回路输出电压波形稳定性优良。 In this paper, the design and simulation of the micro-turbine grid-connected rectification and boost control circuit are carried out. Rectifier system selected voltage-type PWM rectifier (VSR), the proposed model includes input filter inductors (Reactor), rectifier bridge (Three-Level Bridge Rectifier), rectifier controller and DC filter capacitor (C1, C2). The chopping circuit of this research topic is the step-up Boost chopper circuit, the voltage regulator for the outer ring control, and current inner ring can be based on id*, iq* value to control the current, in order to achieve the ra- pid adjustment of the AC side of the current role. Boost Controller module is mainly through the generation of appropriate control pulse signal, thus controlling the control switch Mosfet off, and ultimately achieving the purpose of adjusting the output voltage. The simulation results show that the design of the rectifier circuit and the boost control circuit output voltage waveform stability is excellent.

Interrupting Short-Circuit Direct Current Using an AC Circuit Breaker in Series with a Reactor

This paper describes and demonstrates the principle and efficacy of a novel direct current fault interruption scheme using a reactor in series with a controlled rectifier and a conventional AC circuit breaker. The presence of the series reactor limits the capacitive discharge current from the DC filter capacitor at the output terminals of the phase-controlled rectifier. In addition, the series reactor along with the filter capacitor forms an underdamped series RLC circuit which forces the fault current to oscillate about zero. This synthetic alternating current can then be interrupted using a conventional AC circuit breaker. The selection criteria for the series reactor and overcurrent protection are presented as well. Using the proposed scheme for an example case, a DC fault current magnitude is reduced from 56 kA to 14 kA, while the interruption time is reduced from 44 ms to 25 ms.

Interactions within heterogeneous systems of uncontrolled rectifiers for aircraft electrical power systems

There is an increase in the use of multi-pulse, rectifier-fed motor-drive equipment on board more-electric aircraft. Motor drives with feedback control appear as constant power loads to the rectifiers, which can cause instability of the DC filter capacitor voltage at the output of the rectifier. This problem can be exacerbated by interactions between rectifiers that share a common source impedance. In order that such a system can be analysed, there is a need for average, dynamic models of systems of rectifiers. In this study, an efficient, compact method for deriving the approximate, linear, large-signal, average models of two heterogeneous systems of rectifiers, which are fed from a common source impedance, is presented. The models give insight into significant interaction effects that occur between the converters, and that arise through the shared source impedance. First, a 6-pulse and doubly wound, transformer-fed, 12-pulse rectifier system is considered, followed by a 6-pulse and autotransformer-fed, 12-pulse rectifier system. The system models are validated against detailed simulations and laboratory prototypes, and key characteristics of the two system types are compared.

A Novel Control Scheme for Current-Source-Converter-Based PMSG Wind Energy Conversion Systems

A novel control scheme for permanent-magnet synchronous generator is proposed in this paper, where a current-source converter is employed as the bridge between the generator and the grid for high-power wind energy conversion systems. In these medium voltage (2.3-13.8 kV) level applications, current-source converters not only have inherent advantages, but also present some challenges for controller design due to the DC link choke and filter capacitors. The control strategy is developed to achieve better performances with improved dynamic response. By maintaining the grid-side converter modulation index at the highest possible level, the proposed control scheme reduces the DC link current to a minimum value to reduce converter conduction loss. The systempsilas dynamic performance is further improved by adopting generator-side power feedforward. Simulation and experimental results are provided to verify the proposed control scheme.

A Novel Control Scheme for Current-Source-Converter-Based PMSG Wind Energy Conversion Systems

A novel control scheme for permanent-magnet synchronous generator is proposed in this paper, where a current-source converter is employed as the bridge between the generator and the grid for high-power wind energy conversion systems. In these medium voltage (2.3-13.8 kV) level applications, current-source converters not only have inherent advantages, but also present some challenges for controller design due to the DC link choke and filter capacitors. The control strategy is developed to achieve better performances with improved dynamic response. By maintaining the grid-side converter modulation index at the highest possible level, the proposed control scheme reduces the DC link current to a minimum value to reduce converter conduction loss. The systempsilas dynamic performance is further improved by adopting generator-side power feedforward. Simulation and experimental results are provided to verify the proposed control scheme.

A Harmonic Analysis of Three-Phase Rectifier with a DC Filter Capacitor.

In most voltage-fed inverter drives, three-phase diode bridge rectifiers with a filter capacitor at the DC side are often used. In this type of rectifier, the harmonic levels of the line current are well known to be quite high. So far, a time simulation method has been used to analyze the harmonic current. This method is very accurate, but it requires a long computing time and a complicated algorithm.This paper proposes a practical new method to easily calculate the harmonic currents for both the continuous and discontinuous current conductions. The proposed method is based on the frequency domain method and the rectifier switching functions. Analytical equations for the harmonic currents on both the DC and AC sides are derived, taking into account the effects of filter capacitance and line reactance. All the calculations are conducted only by algebraic calculation with high accuracy. The effectiveness of the proposed method is confirmed by comparison with the results obtained by the simulation method.

Calculation of Uncharacteristic Harmonics Generated by Three-Phase Diode-Bridge Rectifier with DC Filter Capacitor.

Three-phase diode-bridge rectifiers are used to convert the AC input into DC voltage. A large capacitor is connected as a filter on the DC side, since in most applications, a low ripple in the DC output voltage is desirable. Unbalance in the supply conditions of a three-phase diode-bridge rectifier with a DC filter capacitor gives rise to uncharacteristic harmonics on both the AC and DC sides.This paper proposes a simplified method for calculating the uncharacteristic harmonic currents generated by the three-phase diode-bridge rectifier under unbalance, taking into account the effects of both the AC and DC side impedances. Analytical expressions for the harmonic currents are derived using the switching functions with overlap period the AC circuit theory. Therefore, the proposed method can be executed only with algebraic computation and its accuracy is quite high. The validity of the proposed method is demonstrated by comparison with the results of time simulation.

Harmonic analysis of a single‐phase rectifier with a DC filter capacitor

AbstractA single‐phase diode bridge rectifier with a filter capacitor on the dc side is often employed to convert ac input into a dc voltage. The input current of the rectifier contains harmonic currents which cause undesirable power line effects. Recently, a method using the time domain analysis has been proposed to calculate the harmonic currents of rectifier considering noninfinite capacitance, i.e., non‐zero dc side impedance. This method is very accurate, but it requires a long computing time and a complicated algorithm.This paper proposes a new method that makes it possible to easily calculate the harmonic currents taking into account the effects of the ac and dc side impedances of rectifier. The proposed method, which is based on the frequency domain method, can be executed only with the algebraic computation, and its accuracy is quite high. The validity of the proposed method is also demonstrated by comparison with the results of time simulation.