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1408results about "Polyphase network asymmetry elimination/reduction" patented technology

Control method for enhancing asymmetrical fault ride-through capability of wind power system

The invention discloses a control method for increasing asymmetrical fault ride-through capability of a wind power system. In the method, a super capacitance energy storage system is assessed between a machine side rectifier and a net side inverter on the basis of the prior art. On the control aspect, besides the control for the machine side rectifier and the net side inverter, the control for a super capacitance energy storage system is additionally provided in the method. Through controlling the coordination of the machine side rectifier and the net side inverter, a unit can realize the maximum wind energy tracking, grid-connected active and reactive power adjusting and grid-connected three-phase current symmetry and the stability of the voltage for a direct-current busbar between the machine side rectifier and the net side inverter when a power grid is normal is assured. The additionally provided super capacitance energy storage system is further controlled, the voltage stability of the direct-current busbar of the unit while the power grid has asymmetrical faults is assured, especially the grid-connected three-phase current symmetry is assured and the double power frequency ripple wave of the voltage of the direct-current busbar while the power grid has asymmetrical faults is removed so that the asymmetrical fault ride-through capability of the wind power system is enhanced.
Owner:CHONGQING UNIV

Power compensation method for unbalanced direct power control of voltage controlled grid-connected inverter

The invention discloses a power compensation method for unbalanced direct power control of a voltage controlled grid-connected inverter, which is suitable for direct power control (the conventional direct power control) without synchronous speed rotational coordinate transformation. The method comprises the following steps of extracting negative sequence voltage signals and positive sequence current signals by collecting voltage and current signals of a three-phase electric network; and computing compensation items of active and reactive power according to selected control targets. In the method of the invention, the compensation items of active and reactive power are injected in the power reference signals of the conventional direct power control according to required control targets so as to respectively eliminate negative sequence current, double frequency fluctuation of the active power and double frequency fluctuation of the reactive power in the electric network, caused by unbalanced voltage in the electric network, and fit different application situations. The invention has the advantages of enhancing the capabilities of control and uninterrupted operation of the voltage controlled grid-connected inverter when the electric network is in an unbalanced fault.
Owner:ZHEJIANG UNIV

Electric locomotive non-power-off neutral section passing-electric energy quality comprehensive compensation device and method

The invention relates to an electric locomotive non-power-off neutral section passing-electric energy quality comprehensive compensation device and method, which belongs to the technical field of railway transport equipment and electric electronics. The device comprises a controllable transfer switch, a single-phase step down transformer, a single-phase step down transformer with a middle tap, a two-phase back-to-back converter sharing a DC-side capacitor, a circuit breaker switch, four position sensors and three electric quantity sensors. In the method, when the electric locomotive passes the neutral section, the controllable transfer switch is turned off, and the device works in a non-power-off neutral section passing mode to perform control on amplitude and phase of the neutral section voltage and enable the electric locomotive to pass the neutral section with load in a non-power-off manner. Without locomotive passing, the controllable transfer switch is closed, and the device works in an electric energy quality comprehensive compensation mode and has functions of active power transfer as well as inactive power and harmonic compensation. Through the device, the problems relating to electric energy quality of a traction substation and neutral section can be comprehensively solved based on the traditional traction power supply mode.
Owner:TSINGHUA UNIV +1

Low-voltage power grid three-phase imbalance adjustment method based on phase-change switch

The invention discloses a low-voltage power grid three-phase imbalance adjustment method based on a phase-change switch. A difference between average current and the inter-phase maximum current is calculated, an average current fixed value and an inter-phase maximum current fixed value for starting imbalance adjustment is calculated according to transformer capacity and a load rate, three-phase transfer load is calculated, a load transfer direction is determined, the phase actually needs to transfer load out if the load which needs to be transferred is positive, the phase actually needs to receive load if the load which needs to be transferred is negative or zero, a phase-change switch which needs load transfer and a transferred target phase are determined according to the phase and the actual load of each phase-change switch, a phase-change switch action queue is generated, the phase-change switches are sequentially controlled to perform load transfer until all phase-change switches complete load transfer, and the system thus achieves the best balance state in the current condition. The method is used for low-voltage power grid three-phase imbalance treatment, the three-phase imbalance degree is reduced, voltage drop is reduced, power supply voltage treatment is improved, and line loss is reduced.
Owner:NARI TECH CO LTD +1

Low-voltage ride through (LVRT) control system of photovoltaic inverter and method thereof

The invention provides a low-voltage ride through (LVRT) control system of a photovoltaic inverter and a method thereof. The system comprises a solar cell panel, a photovoltaic inverter, a power grid and a controller, wherein the solar cell panel, the photovoltaic inverter and the power grid are sequentially connected; and the controller is respectively connected with the photovoltaic inverter and the power grid. The system and the method have the advantages that 1) when the power grid breaks down to cause power grid voltage balance sag, good dynamic response is provided, and grid-connected current can be steadily outputted by three phases of current sharing of the photovoltaic inverter; and 2) in unbalanced voltage sag, the positive and negative sequence voltage influence of the power grid can be eliminated by the control system, only the positive sequence current component is outputted, and the three-phase current sharing is ensured and has a lower harmonic component, so that the loss caused by the faults of the power grid is reduced, and the power supply reliability of the power grid is improved. The special situation of the unbalanced power grid is supported by the system, and the stable operation of the normal three-phase current sharing is guaranteed.
Owner:ZHEJIANG EIFESUN ENERGY TECH

Single-phase combined co-phased power supply and transformation structure

The invention discloses a single-phase combined in-phase power supply and transformation structure mainly comprising a traction transformer and a CPD. In the CPD, a high-voltage matching transformer primary side and a traction transformer primary side form an SCOTT connected group, a secondary side winding of the CPD is connected to the incoming end of an AC-DC-AC converter, and the outgoing end of the AC-DC-AC converter is connected with the primary side of a traction matching transformer. A secondary side winding of the traction transformer and the secondary side winding of the traction matching transformer are equal in voltage amplitude and phase and both connected with a traction busbar; traction load calculated capacity is equal to the sum of traction transformer calculated capacity and CPD calculated capacity, the traction transformer is responsible for main power supply, and the CPD calculated capacity is determined by the capacity of traction load which caused exceeding three-phase voltage unbalance. The single-phase combined in-phase power supply and transformation structure has the advantages that optima configuration of traction power supply resources is realized and energy conservation is better.
Owner:CHENGDU SHANGHUA ELECTRIC CO LTD

Reactive power compensation device based on novel modular multilevel topology and control method thereof

A reactive power compensation device based on novel modular multilevel topology and a control method thereof relate to a high-voltage and large-power reactive power compensation device. In the prior art, compensation in a high-voltage and large-power field is limited and an inhibiting ability to circulation is insufficient. The invention aims at solving the above problems. A three-phase alternating-current power supply, a resistance-inductance load, a MMC converter, a signal detection circuit, a control circuit and a driving circuit are included. The MMC converter comprises three bridge arms which share a same structure and are connected in parallel. Each bridge arm comprises an upper bridge arm and a lower bridge arm which are symmetrical about a middle point of the bridge arm and are connected in series. Each upper bridge arm comprises a resistor, an inductor, several half-bridge units and an H bridge unit which are connected in series. The inductor of each upper bridge arm and an inductor of each lower bridge arm are connected in series. The middle points of the three bridge arms of the converter are connected in parallel between the three-phase alternating-current power supply and the load through a lead. By using the device and the method in the invention, power-grid reactive power can be compensated; a three-phase imbalance problem of a system is solved; effects of supporting a power grid voltage and inhibiting the circulation are achieved.
Owner:HARBIN UNIV OF SCI & TECH

STATCOM unbalance compensation control method based on modular multilevel converter

The invention discloses a STATCOM unbalance compensation control method based on a modular multilevel converter (MMC). The method comprises a converter compensation current dead-beat control method and a converter interphase circular current active damping control method. A comprehensive compensation current dead-beat control part is used for compensating active loss in the MMC by controlling active current, reactive current and negative-sequence current which are output by the MMC so as to eliminate unbalance of the current of a power grid and compensate reactive power; the interphase circular current active damping control method is used for summing by detecting the bridge arm current of upper and lower bridge arms of each phase and multiplying by 0.5 to obtain the circular current of each phase, and superposing the output of three-phase current passing through an active damping controller to dead-beat control output so as to inhibit the alternating current component of the circular current, reduce the current stress of converter devices and reduce the loss of the converter. Through the adoption of the method provided by the invention, compensation of the negative-sequence current and reactive current of unbalanced load of the power grid is realized, inhibition of the interphase double frequency circular current of the MMC is simple, the response speed is high and the stability is high.
Owner:HUNAN UNIV

Grid power quality control system and method based on unified power quality conditioner

ActiveCN106451466AApplication advantages are obviousMany output levelsPolyphase network asymmetry elimination/reductionAc network voltage adjustmentTransformerStatic error
The invention provides a grid power quality control system and method based on a unified power quality conditioner. The system comprises a series MMC, a parallel MMC and a control circuit. The series MMC and the parallel MMC form a unified power quality conditioner (UPQC) topological structure based on MMC, and are connected to a grid side and a load side through a transformer respectively. The method comprises the following steps: carrying out transformation on an MMC module under an abc stationary coordinate system to obtain a differential equation matrix model under a dq rotating coordinate system; obtaining small-signal models of the series MMC and the parallel MMC under the dq rotating coordinate system; utilizing the parallel MMC to output an offset current and stabilize DC side voltage; and utilizing the series MMC to output an offset voltage. A fundamental wave positive sequence voltage component and a fundamental wave positive sequence current component adopt a PI regulator, and other components adopt a PR regulator to realize non-static-error control, so that compensation is carried out not only for the cases of distortion, harmonic wave and reactive power and the like, but also for the cases of unbalance power source voltage and unbalance load, and the load is allowed to obtain reliable power supply.
Owner:LIAONING TECHNICAL UNIVERSITY

Power load balancing system applied to low-voltage power distribution network

The invention discloses a power load balancing system applied to a low-voltage power distribution network. The device includes phase conversion devices and a control master station; three-phase input ends of the phase conversion devices are electrically connected with the low-voltage power distribution network; single-phase output ends of the phase conversion devices are electrically connected with electricity consumption terminals, so that the load information of the electricity consumption terminals can be transmitted to the control master station; the control master station performs computation processing, and determines electricity consumption terminals which are on phases with large total load information and require phase switching, and phase switching signals which enable the electricity consumption terminals to switch to phases with small total load information from the current phases, and transmits the phase switching signals to corresponding phase conversion devices; and the phase conversion devices switch the electricity consumption terminals and make the same connected into connection phases of the low-voltage power distribution network according to the phase switching signals, so that the load of the electricity consumption terminals can be re-distributed, and therefore, the load of the electricity consumption terminals can be uniformly distributed on the three phases of the low-voltage power distribution network. With the power load balancing system applied to the low-voltage power distribution network of the invention adopted, the distribution of the load of the electricity consumption terminals between three phases can be adjusted with continuous power supply ensured, and the three-phase load balance of the low-voltage power distribution network can be realized, and line loss can be effectively reduced, and power supply quality can be improved.
Owner:四川创能电力工程有限公司

Method for three-phase imbalance load distribution suitable for low-voltage distribution network

The invention discloses a method for three-phase imbalance load distribution suitable for a low-voltage distribution network. The method comprises the steps that according to the phenomenon of three-phase imbalance load often occurring in the low-voltage distribution network, electrical load data of users are extracted and the FCM arithmetic is used for conducting clustering analysis on user load features; according to a classification result, the users of different types are distributed in the low-pressure distribution network through the optimal algorithm, so that the three-phase imbalance of the low-voltage distribution network is restrained, and therefore the purposes that the consumption of the low-voltage distribution network is reduced and the reliability of the low-voltage distribution network is improved are achieved. Pattern classification is conducted on the user loads according to a daily load curve or a monthly load curve of each user and the best power grid connection phase sequence mode is searched for according to the user loads belonging to the same load pattern through the optimization algorithm, so that local classification and time sharing balance of a load side is achieved, and therefore the imbalance degree of the distribution network is reduced to the greatest extent from a source. The method is suitable for three-phase imbalance load distribution of the low-voltage distribution network.
Owner:STATE GRID JIANGXI ELECTRIC POWER CO LTD RES INST +1

Method for treating three-phase load imbalance of low-voltage distribution network

The invention discloses a method for controlling unbalanced three-phase loads of a low-voltage distribution network. The method uses a station area controller to collect three-phase current data on the low-voltage side of a distribution transformer, load data of an outlet leakage protection switch, and user power consumption data. The load data and the current and phase data of the commutation switch are analyzed and calculated to obtain the unbalance value of each outgoing line. When the unbalance is found to be greater than the set limit value, and the unbalance maintenance time exceeds the set adjustment time In this case, the optimal "unbalance adjustment method" is given, and the phase change switch is automatically controlled by remote control to adjust the load and complete the redistribution of the three-phase loads of each outgoing line, so that the three-phase loads of each outgoing line are in a basically balanced state, so as to achieve low-voltage line The three-phase load balance state. The invention realizes the redistribution of the single-phase load current by controlling the phase change switch installed on the side of the household meter box, so as to achieve the basic balance of each phase load.
Owner:BEIJING TELLHOW ELECTRIC POWER TECH CO LTD
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