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

An uninterruptible power supply (UPS) system includes an AC power input configured to receive AC power from a single-phase AC power source or a multi-phase AC power source, a DC power source, an output circuit including a power output, a controllable switch configured to selectively couple at least one of the AC power input and the DC power source to the output circuit, and a processor coupled and configured to affect operation of the output circuit depending upon which of single-phase and multi- phase operation of the UPS is indicated.

A method of converting a direct voltage generated by a decentralized power supply system into three-phase alternating voltage by means of a plurality of single-phase inverters (WR1-WR3), said alternating voltage being provided for supplying an electric mains, is intended to avoid inadmissible load unbalances using single-phase inverters. This is achieved in that, upon failure of one inverter (WR1-WR3), an asymmetrical power supply distribution is reduced by limiting the output of the other inverters. The method makes it possible to simplify three-phase voltage monitoring.

The invention relates to a method and device for performing on-load scheduling on a single-phase load in the intelligent power grid field. A master controller is mounted at an input end of a three-phase wire, a secondary controller is mounted at each single-phase branch of the wire, and the master controller exchanges information with the secondary controllers through communication interfaces. When the wire power unbalanced degree is over limit, the master controller optimizes and formulates a control scheme to operate the secondary controllers to convert the single-phase load between the phases; in the conversion process, the load is free from instant power off, and the power grid is free from impact and interference; and therefore, the distribution circuit dynamically runs in a load balance state, the unbalanced consumption problem of the circuit is completely solved.

The invention discloses a self-healing control method for operation of an urban distribution network, which is used in an operated urban distribution network. The method adopts an integrative coordination control mode of the urban distribution network based on the self-healing control technology; the process of signals and the generation of control strategies have self adaptability; the method automatically finishes a control process without external intervention, coordinates the action behaviors of a relay protection device, a switch, a safe automatic device and an automatic adjusting device, and carries out coordination control on the relay protection device, the switch, the safe automatic device and various automatic adjusting devices and parameters thereof so as to realize the technical proposal of stable, safe, reliable and economic operation of the urban distribution network; and the method belongs to the application field of cross technology of power system theory, control theory and artificial intelligence.

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.

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.

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.

An apparatus for providing phase rotation for a three-phase AC circuit. The apparatus comprises three phase input terminals and three phase output terminals, where a first phase input terminal is coupled with a third phase output terminal; a second phase input terminal is coupled with a first phase output terminal; and a third phase input terminal is coupled with a second phase output terminal.

The invention relates to a method for controlling a wind park comprising several wind power installations to feed electrical power into an electrical AC grid at a point of common coupling (PCC). The method comprises feeding a 3-phase current at a point of common coupling, identifying a grid voltage on the point of common coupling, comparing the grid voltage that was identified on point of common coupling with at least one predetermined set point value, determining set point values for wind power installations depending on a comparison conducted to meet a stability criterion on point of common coupling, passing the determined set point values to plant control units of the individual wind power installations, and producing electrical current at each of the wind power installations depending on the predetermined set point values to be jointly fed in on point of common coupling.

The invention discloses a power quality comprehensive compensation system of an electric railway and a control method thereof. The system comprises a railway static power controller RPC and two sets of thyristor switched capacitors TSC. The thyristor switched capacitors bear a large proportion of reactive power compensation, RPC performs active power compensation, harmonic suppression and a remained small proportion of reactive power compensation for two power supply arms, therefore, the capacity of RPC is effectively reduced, and negative sequence, harmonic and reactive comprehensive compensation are realized. The control method comprises a cooperative control policy of RPC and TSC, reference current detection based on reactive separation, a reactive power distribution method and an RPC control method. The power quality comprehensive compensation system of the electric railway greatly improves the power quality of the electric railway with low cost, and the corresponding control method effectively coordinates the operation of RPC and TSC and ensures that the system has good compensation performance and favorable application prospect.

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.

Disclosed are an automatic three-phase unbalanced load compensation experimental device and its control method. The experimental device comprises an automatic compensation device, a load simulation part, and detection, display and control parts. The automatic compensation device comprises power capacitors and intelligent grouping compound switches; the detection, display and control part comprises current transformers, molded case circuit breakers, a three-phase digital display ammeter, a three-phase electric power monitoring instrument, a protocol conversion module, 485 buses, Ethernet cables and an upper computer; the load simulation part comprises phase A, B and C loads which are in star connection and are same in component and circuit connection, an analog output module and a relay output module. Power monitoring instrument and digital ammeter are connected to the grid by circuit breaker and current transformer. The automatic compensation device and load simulation part are connected to the grid in parallel.

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.

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.

The invention relates to an electric energy adjustment device for active and reactive power adjustment of a high-voltage system, which belongs to the field of electric and electronic technology. The device realizes high-voltage synchronization by adopting a mode of cascading a plurality of shingle-phase full-bridge inversion units, adjusts reactive power and instantaneous active power output by the device, or compensates for phenomena, such as low voltage and three-phase unbalance at a synchronization position, by controlling the charge and discharge of a big capacitor on the direct-current bus of each inversion unit, and adjusts the stable active power output or stored by the device by using an assembled battery unit on the direct-current bus of each inversion unit. The adjustment device of the invention integrates functions of active power adjustment and reactive power adjustment, has strong dynamic adjustment capability, needs no transformers, occupies a small area, has no harmonic wave of output, is simple in maintenance and has relatively comprehensive functions and outstanding cost performance.

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.

A system is provided for mitigating an electric unbalance of a three-phase current at a Point of Common Coupling being located between a wind farm having a plurality of wind turbines and a power grid. The system includes a measurement device and a central wind farm controller. The measurement device measures the electric unbalance at the Point of Common Coupling and provides a measurement signal being indicative for the measured electric unbalance. The central wind farm controller is coupled to the measurement device and controls the operation of the plurality of wind turbines. In response to the measurement signal the central wind farm provides a control signal for mitigating the electric unbalance at the Point of Common Coupling. Also provided is a corresponding method for mitigating an electric unbalance of a three-phase current and a computer program for controlling and/or for carrying out the mentioned method.

In a multiphase electrical power construction and assignment, a processor: determines a phase and voltage configuration for bi-directional power device pairs; determines a given bi-directional power device pair is to be coupled to a given phase connection based on the configuration; determines whether the given bi-directional power devices in the given bi-directional power device pair are to be coupled to each other; confirms that the given bi-directional power device pair is not coupled to any of the plurality of phase connections; couples the given bi-directional power device pair to the given phase connections, where power signals of the given bi-directional power device pair are synchronized with a power signal of the given phase connection; and in response to determining that the given bi-directional power devices are to be coupled to each other, couples each of the bi-directional power devices to a short bus.

Three phase power flow analysis of an unbalanced power distribution system decouples voltage changes resulting from nodal admittance matrix into one contribution from a real part, conductance matrix, and other contribution from an imaginary part, and a susceptance matrix. A first voltage change and second voltage change resulting from conductance and susceptance matrices are determined respectively. The voltages of a node of the power distribution system are determined as a combination of first and second voltages.

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.

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.

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.

The invention provides a modular multilevel converter (MMC) based solid-state transformer and a control method thereof. The solid-state transformer comprises a high-voltage AC/DC converter, an isolated DC/DC converter and a low-voltage DC/AC converter, wherein the high-voltage AC/DC converter is connected with the isolated DC/DC converter through a high-voltage DC bus, and the isolated DC/DC converter is connected with the low-voltage DC/AC converter through a low-voltage DC bus parallel module. In the MMC based solid-state transformer, a medium- and low-voltage DC side adopts a DC bus staggered parallel topological structure, so that the unbalanced mutual influence of a high-voltage side system and a low-voltage side system of the solid-state transformer is solved from structure, and the power supply reliability is automatically improved; with the mutually-balanced solid-state transformer based on an MMC structure, the influence of a three-phase unbalance on a power grid and the influence of three-phase unbalance occurring in the power grid on an AC load can be prevented by controlling the constant voltage of a high-voltage common DC bus.

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.

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.

Provided is an apparatus and method for providing to a differential relay an operational vector-group compensation setting pair that automatically provides correction for a phase shift occurring between currents of at least two windings of a power transformer. The method includes calculating a first and second plurality of phasors using secondary currents derived from respective first and second winding of the at least two windings. The method also includes selecting one pair of vector-group compensation settings based on operate current values calculated using different pair combinations of the vector-group compensation settings applied to the first and second plurality of phasors. The method further includes comparing phase angles of like-phase phasors to determine if the phase angles are within a pre-determined angle range, and enabling application of the selected pair of vector-group compensation settings as the operational vector-group compensation setting pair if the phase angles are within the pre-determined angle range.

A method for compensating dynamic three-phase unbalanced loadsand and its device characterizing in sampling values of line voltage and load line current of two sample points at the connecting place of the compensation device and the system to compute related sine signal basic wave symmetric component, then to calculate positive and negative sequential compensator threephase equal susceptance, thesum of which is the three-phase susceptance value for compensating load unbalance and providing reactive current for the load, the susceptance reference value to be converted to a control angle signal and an order of the thyristor switched capacitor to be sent to the pulse generation plate and the condenser zero-cross trigger plate for controlling two devices.

Systems and methods for balancing current from an AC source. The method includes determining a difference between a DC voltage output by a rectifier in an uninterruptible power supply (UPS) to a DC reference voltage. The method also includes determining an error between the DC voltage and the DC reference voltage based at least in part on the difference. After determining the error, the method includes filtering a second order harmonic from the error thereby generating a filtered error. The method may then include determining one or more switching signals for one or more switching components in the rectifier based at least in part on the filtered error and sending the switching signals to the rectifier.

The invention discloses a micro-grid multi-inverter parallel voltage unbalanced compensation method. The method relates to an unbalanced compensation ring, a power droop control ring and a voltage and current ring. On the basis of traditional power droop control, three-phase negative sequence voltages and currents are detected, the negative sequence reactive conductance Q-G unbalanced droop control ring is introduced, directive current reference values are synthesized and revised, and then unbalanced compensation of micro-grid voltage is achieved. Through P-f, Q-E and Q-G droop control, distributed power inverters can independently adjust and output fundamental wave frequency, voltage amplitude and unbalanced compensation conductance, and therefore active and reactive equilibrium distribution can be achieved among the inverters. Quasi-resonance PR control is adopted by the voltage and current control ring, astatic control of the voltage is achieved, dead-beat control is adopted, and then accurate control of currents in an inner ring is achieved. According to the method, the three-phase inverters in a micro-grid possess the unbalanced compensation capacity, and therefore micro-grid three-phase voltage balance is maintained.

The invention discloses a multifunctional power grid simulator and a control method thereof. The main circuit of the simulator is characterized in that three mutually independent back-to-back systems are provided; the mutually independent back-to-back systems have a structure form that the input sides are three-phase PWM (Pulse-Width Modulation) rectifier, and the output sides are controllable single-phase PWM inverters for outputting voltage; mains supply is connected to the three-phase PWM inverters after the isolation of a three-phase transformer; and the single-phase PWM inverters are outputted by an LC (Inductor-Capacitor) filter. The invention as a power grid voltage generating device in a distributed power generating synchronization research can be used for simulating to output standard grid voltage and the like, and provides a grid environment as real as possible for a distributed power generating system synchronization research so as to satisfy the requirements for distributed powder generating researches.