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In the situation that the modular multilevel converter (MMC) needs to maintain a good current control performance within a wide scope of operations such as the intermittent new energy grid connection and electric locomotive, etc, this paper starts from the output current slope generated after the output voltage and system voltage of MMC converter are jointly acted on the equivalent coupling reactance...
Voltage sags can lead to abnormal operation of electric vehicle charging equipment, but the problem has not been paid more attention now. With the gradual increase in the application of electric vehicles, it is necessary to study the impacts of voltage sags on the electric vehicles charging. The simulation models of 6-pulse rectifier charger, 12-pulse rectifier charger and PWM rectifier charger are...
In this paper, improved solving method are proposed to calculate the maximum entropy probability distribution of negative sequence current. Negative sequence current is got from the process of the measured data obtained from power quality monitoring system first. Second, curve fitting method is used to calculate probability distribution of negative sequence current based on maximum entropy method...
In this paper, each harmonic value of harmonic sources is obtained in the process of the measured data obtained from power quality monitoring system first. And then, probability distribution of harmonic amplitude are achieved based on maximum entropy method. Considering that the phase distribution is associated with amplitude, a method of dividing amplitude into three parts by expectation and standard...
A battery energy storage system based on modular multilevel converter is proposed in this paper, which has many advantages, including easy expansibility, simple structure and high reliability. The system is capable of compensating active and reactive power simultaneously, applied for high capacity and high power situation. The mathematical model of system is built and its circulating current suppressing...
The location and size of distributed generations (DGs) can affect the power quality of distribution network, in order to solve the multi-objective optimization problem this paper focuses on four aspects: active power loss, harmonic distortion, voltage quality and voltage sag. Comprehensively the merits and faults of three algorithms are compared on application of solving DG locating and sizing problems,...
Energy storage technique is one of the most effective technique means for the regulation of wind power. Aiming at smoothing the fluctuation of wind power and maintaining bus voltage, this paper proposed a hybrid energy storage system (HESS) based on cascaded multilevel STATCOM, containing a battery and a super-capacitor. And the active and reactive power coordination control strategy was also developed...
The presence of unbalanced voltage sag in grid actual operation gives rise to the output power fluctuation of PV inverter, the increasing of output current harmonics and unbalanced current. The calculation of the output current reference is a key technology in the control of PV inverter and has important influence on the output of the PV inverter under unbalanced grid voltage. Base on the instantaneous...
The effective control of photovoltaic inverter under unbalanced grid voltages is very important for the grid-connected operation of the photovoltaic system. The calculation of the output current reference is a key technology in the control of photovoltaic inverter under unbalanced voltage. Base on instantaneous active-reactive control (IARC) and average active-reactive control (AARC), this paper proposed...
A switching method of capacitor banks with different reactance rates in harmonic case is proposed. The proposed method is combined with voltage and reactive power control (VQC). The total switching numbers of capacitor banks are determined by VQC, however, which branches should be switched is decided by harmonic conditions. The substation harmonics are divided into four cases according to the severity...
The modular simulation model of MW-level grid-connected photovoltaic (PV) power station is established at PSCAD/EMTDC. In this paper, simulation models according to different real engineering can be set up based on the modular flexible combinations. Next, power quality of PV power station and influence on distribution networks are studied. In addition taking a real system for example, the voltage...
Voltage sag is one of the most concerned power quality disturbances. The detection of voltage sag source is necessary for power quality troubleshooting, diagnosis, and mitigation strategy development. Moreover, the disputes about the major responsible party can be resolved fairly. This paper proposes an improved distance impedance method for voltage sag detection. By judging the rate of change of...
The compensation strategy of the dynamic voltage restorer (DVR) has significant impact on the compensation result. A new analysis method which is based on pre-sag load voltage is proposed in the paper. The new method chooses the pre-sag load voltage phasor as the reference phasor and put the centre of the limit compensation voltage circle at the terminal of the system voltage phasor. It not only has...
Three single-phase H-bridge DVR is a kind of dynamic voltage restorer (DVR) which is used very widely. The traditional analysis method of compensation strategy has some shortcomings so that it is not suitable for this kind of DVR. A new analysis method which could overcome the shortcomings of the tradition method is proposed in the paper. The new method not only has definite physical concept but also...
The losses of the transformer and the local temperature will increase because of the harmonic, so the efficiency and the service life of transformer will reduce. Therefore, it is significant to study the transformer's harmonic losses in energy conservation and economic operation. Firstly, methods to calculate the harmonic losses are summarized in the paper, which are improved parameter method, measurement...
Based on the waveform characteristic of virtual value by dq conversion, Wavelet Analysis and FFT, seven types of power quality disturbances are layered-recognized. Firstly, according to the size of voltage virtual value, the disturbances will be divided into two types, the first type includes voltage sag, swell and interruption. The second type includes the rest of the disturbances. Secondly, wavelet...
A novel stages compensation and control strategy suitable for a series power-quality regulator (SPQR) based on a voltage-source converter (VSC) inverter is proposed in which steady operation stage, overrun operation stage, and recovery operation stage are included. The presag voltage compensation, minimum energy compensation, and maximum energy compensation strategies are adopted to the three stages,...
Square demodulation and Root Mean Square (RMS) demodulation are noncoherent detections which are used in voltage fluctuation and flicker measurement. There are doubled frequency of the modulation signal and intermodulation distortion in the product of the square demodulation. The magnitude-frequency characteristic of RMS demodulation drops obviously with the increase of frequency of the modulation...
The high capacity active filter have the problem of high cost, high power loss, strong electromagnetic interference and so on, the compensation capacity of the device using in practical is limited, how to choose the right strategy to achieve optimal compensation plays an important role in the process of the device using in practical. This paper discussed strategy of shunt active filter compensation,...
A classification method of detecting the voltage sag sources based on Mamdani fuzzy inference is introduced in this paper. Three main sag reasons of short-faults, transformers energizing and large-capacity induction motor starting are analyzed. There are some different phenomena during the voltage sags caused by different sources. The characters of the balanced of the three phases, the changing trend...
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