37results about How to "Reduce the impact of power quality" patented technology

The invention discloses a hybrid island detection method based on the combination of wavelet neural network and SMS. The technical scheme of the method is: in the first stage, a voltage signal is obtained by detecting the voltage signal on the common coupling point in a period and performing wavelet transformation. The average value of the absolute value of the wavelet coefficients in the period is used as the input signal of the BP neural network, and finally the BP neural network is used for pattern recognition; the second stage introduces the phase disturbance in the SMS algorithm, so that whether the frequency of the common coupling point voltage exceeds Threshold, and through frequency detection to determine whether the islanding phenomenon really occurs, so as to take corresponding islanding protection measures when the grid-connected power generation system is in the islanding state. The invention greatly improves the reliability of the isolated island detection, and greatly reduces the influence of the detection method on the power quality of the system under the premise of ensuring the identification rate of the isolated island.

The invention relates to an alternating current and direct current hybrid power supply system and method. The system comprises current transformers C1, C2, C3, C4 and C5, diodes D1, D2 and D3, intelligent control switches S1, S2 and S3 and a direct current bus. A principle of prioritizing usage of a local DG is adopted, and a self-adaptive power control strategy based on direct current bus voltage signals is employed; the intelligent control switches S1, S2 and S3 for a three-phase alternating current power grid, the local DG and a local energy storage component are automatically controlled according to a state of the direct current bus voltage signals; supply and demand power balance between the three-phase alternating current power grid, the local DG as well as the local energy storage component and electricity consumption of loads can be effectively regulated and controlled. The method is well compatible with traditional alternating current systems; problems of alternating current stability, voltage and frequency synchronization, reactive power and the like caused by the local DG being connected to a power grid in an alternating current form can be prevented; continuous and high-reliability power supply for local loads can be realized; influence exerted on user side electric energy quality can be reduced, local DG energy utilization efficiency can be improved, and an environment friendliness property is fulfilled.

The invention relates to a self-adaptation positive sequence current quick break protection method for a distribution network containing inverter-based distributed generations (IBDGs), in particular to an island detection method suitable for a micro-grid including multiple inverter-based distributed generations (IBDGs). The island detection method includes the steps that segmented reactive power perturbations, frequency boundary values of the segmented reactive power perturbations and starting criteria used when the segmented reactive power perturbations are switched are set in an initialized mode, wherein the starting criteria comprise the first starting criterion which is set according to the situation that the first segment reactive power perturbations of the different IBDGs are synchronous, the second starting criterion which is set according to the situation that the first segment reactive power perturbations of the different IBDGs are not synchronous, but overlapping exists and the starting criterion which is set according to the situation that the first segment reactive power perturbations of the different IBDGs are not synchronous, and overlapping does not exist; whether system frequency meets the three starting criteria or not is detected, and the reactive power perturbations are exerted according to a detection result; whether the criteria for determining an island are met is detected. Reactive power perturbations when a system operates normally in a grid-connected mode are reduced.

The invention discloses a multi-target planning method for power grids of wind farms based on improved NSGA-II. The multi-target planning method includes the steps of building an output force model of the wind farms, calculating the flicker value of a wind turbine generator system at a common connection point, creating a target function with shortest line length and minimal flicker value of a wind farm at a common access point, and realizing multi-target planning of the power grid of the wind farm based on NSGA-II algorithm of NDX operators, the output force model and the target function. The multi-target planning method overcome the defects of subjectivity of conventional multi-target optimization and obtaining one solution in one time, enhances overall searching capability than routine NSGA-II algorithm, and improves convergence.

The invention discloses an islanding detecting method which comprises the following steps: acquiring a voltage waveform of a common coupling point and measuring a frequency value, calculating the average change rate in a certain period to obtain a judging signal, comparing the judging signal with the preset change rate threshold value, outputting a control signal, selecting an outputted reference signal of an inverter by the control signal, introducing reference current after phase deviation under the condition that islanding possibly exists by a frequency change rate detection method, realizing further detection according to a sliding mode frequency deviation method, otherwise, introducing non-deviation reference current, and achieving normal operation of the system. The islanding detecting method has the advantages of reducing detection blind zones and impact on the system power quality and increasing the detection speed.

The invention discloses an electric power supply inserting-connecting apparatus. The electric power supply inserting-connecting apparatus comprises a plug and a socket; the plug comprises a plug hand-held part, an inserting sheet box, a wedge-shaped block and inserting sheets; the inserting sheet box is fixedly mounted at the lower end of the plug hand-held part; an inserting sheet cavity is formed in the inserting sheet box; the inner top end of the inserting sheet cavity is elastically connected with the wedge-shaped block; the two ends of the wedge-shaped block are glidingly clamped with two inserting sheets through a key slot structure; the two inserting sheets run through the two ends of the inserting sheet box respectively; the inserting sheet box movably runs through a through holein the top end of the socket; a contact piece groove is formed in the socket at the lower end of the through hole; and contact pieces are fixed at the two ends of the contact piece groove. Through limiting rods, up and down movement of positioning blocks can be controlled; the limiting rods perform downward thrust on the positioning blocks under the effect of a torsional spring, wherein the thrustis greater than sum of elastic force provided by a spring and a compression spring, so that the positioning blocks can be tightly extruded and pressed at the top end of the socket, and sliding of theplug can be avoided; and therefore, only when the symmetrical limiting rods are pressed downwards, the plug can be inserted into the socket, so that a certain protection effect is achieved.