262 results about "Unified power flow controller" patented technology

A method for calculating power flow solution of a power transmission network with unified power flow controllers is adapted to calculate the power flow on a large-scale power transmission network. The unified power flow controller has a series transformer, a series converter, a direct current coupling capacitor, a shunt converter, and a series transformer. The shunt transformer is connected electrically to a sending-end bus. The series transformer is connected electrically to the sending-end bus and a receiving-end bus. The unified power flow controller is represented by equivalent active and reactive loads on the sending-end and receiving-end buses of the power transmission network.

The invention discloses a unified power flow controller. The unified power flow controller comprises a plurality of series side converters, a plurality of transformers connected in series, a plurality of primary side winding by-pass switches, a parallel side converter, a parallel transformer and a wire incoming switch. The alternating-current ends of all the series side converters are connected with corresponding secondary side windings of the transformers connected in series, primary side windings of the transformers connected in series are connected with the corresponding primary side winding by-pass switches in parallel, and the primary side winding by-pass switches are connected into corresponding circuits in series. The direct-current ends of all the series side converters are connected in parallel and jointly connected with the direct-current end of the parallel side converter, the alternating-current end of the parallel side converter is connected with one end of the parallel transformer, and the other end of the parallel transformer is connected with an alternating-current bus of a multi-loop circuit through the wire incoming switch. The topological structure can achieve multiple operation modes and save a plurality of parallel side converters and transformers, has good economical efficiency and flexibility. The invention further discloses a control method of the unified power flow controller.

The invention discloses a start-stop method for a unified power flow controller. A start process comprises the steps of placing a parallel-side transformer into a parallel-side converter for charging and then unlocking the parallel-side converter to control the direct current voltage to be stable; unlocking a serial-side converter, and controlling the current of a by-pass switch of the serial-side converter to be close to zero; disconnecting the by-pass switch to connect a serial-side transformer to a line in series, wherein the serial-side converter enters a normal operation mode when the line stably runs; and during stop, switching the control mode of the serial-side converter firstly to enable the by-pass switch to be switched on in vicinity of zero current, controlling the current of the serial-side transformer to be gradually reduced into zero and stop the serial-side transformer, and then locking the serial-side converter and the parallel-side converter and stopping the parallel-side transformer. By the start-stop method for the unified power flow controller, the direct current overvoltage and overcurrent of the converter can be effectively inhibited when the serial-side transformer is switched off, the compact of current oscillation of an alternating current line to the serial-side transformer is reduced, and stable start and stop of the unified power flow controller are realized.

The invention relates to a unified power flow controller based on a modular multilevel converter structure. The unified power flow controller comprises a static synchronous compensator and a static synchronous series compensator, wherein positive and negative buses of the static synchronous compensator are connected with positive and negative buses of the static synchronous series compensator; and an output end of the static synchronous compensator and an output end of the static synchronous series compensator are respectively connected with a power grid. According to the invention, as a modular-mode cascaded form is adopted, the requirements on components are reduced; a modular design is realized, the integrated level is high, and the design is convenient; through a design on a bridge arm, an effect of individual-phase control is achieved; through using a redundancy technique, a fault unit can be bypassed, thereby improving the operation reliability of a device; in an original technique, for reducing the outputting of harmonic waves, a scheme of connecting IGBT (insulated gate bipolar translator) devices in series is usually high in switching frequency, therefore, the loss of the device is large; in the invention, a modular multilevel technique is adopted, so that the switching frequency of each component is low, but an effect of extremely high external equivalent switching frequency can be achieved, and the outputting of harmonic waves is reduced, therefore, the device is low in running loss.

The invention relates to a multi-port power electronic convert for energy internet, and belongs to the technical field of power electronic converters. According to the invention, the converter is composed of one static synchronous series compensator, one static synchronous compensator, one DC-DC converter and one three-phase DC-AC inverter. The static synchronous series compensator and the static synchronous compensator are both formed on the basis of a modular multi-level converter. The DC-DC converter is formed by a plurality of isolated DC-DC converters which are subject to input series and output series, and shares a high-voltage DC bus with the static synchronous series compensator and the static synchronous compensator. According to the invention, the converter integrates the functions of a unified power flow controller and the functions of a power electronic transformer, thus having complementary advantages of the unified power flow controller and the power electronic transformer and reducing cost; the converter is modularized, is easy to expand and set with a backup, and has important application potential in future energy internet.

The invention provides a protection method and system for a unified power flow controller. The partitioning and layering method is adopted and includes the steps that the unified power flow controller is firstly partitioned according to the number of current converters; partition protection is carried out on each current converter area according to an alternating current protection area, a converter valve protection area and a direct current pole protection area; meanwhile, layered protection is carried out on the converter valve areas according to a converter valve layer and a valve element layer. The protection system is characterized in that according to the characteristic that a series connection side transformer is connected into a line in series, a PT is additionally arranged on the line to enable a series connection transformer primary winding to be arranged between the PT and a CT of an original line, a series connection transformer line side winding is brought into a line protection range, and meanwhile the additionally-arranged line PT is adopted for line protection. The protection method and system are simple and reliable, all areas of a UPFC device are covered, UPFC protection is matched with original alternating current system protection, the protected ranges are intersected, it is guaranteed that protected dead zones do not exist, and the motion reliability of the integral system is improved.

The invention relates to a method for restraining resonance mechanism low-frequency oscillation of a power system. The method is applied to a unified power flow controller in the system and includes the steps that at the measurement step, signal collection is performed on the system, and a bus power signal P in signals is sequentially processed in the blocking step, the proportion resonance control step, the phase compensation step and the amplitude limiting step, so that an output control signal Up is obtained; the control signal and a reference value corresponding to the unified power flow controller are superposed, so that a corresponding adjusting signal is obtained; difference operation is performed on the signal P and the adjusting signal, difference operation is performed on the multiple obtained signals at the measurement step and corresponding reference values, all difference value signals are sequentially processed at the first-order inertia step and the proportional integral step, so that current and voltage corresponding to an output q axis and an output P axis are obtained and then injected into the system, and the damp for restraining the resonance mechanism low-frequency oscillation in the system is increased. The method has the advantages of being capable of effectively decreasing the resonance oscillation magnitude value and restraining the resonance mechanism low-frequency oscillation.

A system and method for operating a Unified Power Flow Controller (UPFC) connected to a SCADA (Supervisory Control and Data Acquisition) are disclosed. The UPFC automatic operation system receives power system data from the SCADA system, automatically determines UPFC's optimum operation conditions according to power system states. The system includes: a UPFC acting as a serial / parallel FACTS to control variables of a power system; a SCADA for periodically acquiring line data of the power system and state data of the UPFC; and an upper controller for analyzing data received from the SCADA, and determining an UPFC's optimum operation mode for each power system condition and UPFC's optimum set-point control commands.

The invention discloses an addressing and capacity configuration method used for a UPFC. A UPFC addressing and capacity configuration model with transient stability constraints is established, a difference evolution algorithm serves as a framework, and the installation position and the capacity of the UPFC are optimized; in addition, a centrality correction interior point method is adopted for carrying out optimization and fitness assessment on continuous variables of each difference evolution unit. The difference evolution algorithm is simple in operation, high in searching capability, fewer in adjusting parameters and suitable for mixed optimization, and the interior point method is good in convergence and strong in robustness, so that the provided mixed algorithm can well solve the problems of UPFC addressing and capacity configuration, the method is highly efficient and convenient, and the application prospect is good.

The invention provides a convertible unified power flow controller. The convertible unified power flow controller comprises at least one parallel transformer, three current converters, at least two series transformers, at least a group of alternating current switches and three groups of direct current switches, wherein at least one side of each series transformer is connected with at least one group of bypass switches in parallel, alternating current sides of the three current converters are connected into an alternating current system after connected with the at least one parallel transformer through parallel side switches, the two current converters on the series side are respectively connected with at least one group of the series transformers, and then are connected with a power transmission line in series, and direct current sides of the three current converters are connected with one another through the direct current switches. By adopting the structure, multiple running modes can be achieved, unified power flow controller functions of a single circuit can still be achieved when a random current converter breaks down, and simultaneously the convertible unified power flow controller is small in occupied area and low in cost, and has good economical efficiency, flexibility and reliability.

The invention discloses a linear optimal power flow (LOPF) model containing a unified power flow controller (UPFC). DC optimal power flow (DCOPF) is the most popular OPF linear method so far, and is fast in solution speed but relatively low in calculation accuracy, and two electrical quantities of a node voltage amplitude value and a circuit reactive power cannot be solved; the UPFC can be used for improving the power supply capability of a regional power grid, the UPFC is introduced into a DCOPF model, thus, the problem complexity is improved, and the linear DCOPF is also converted to a non-linear model; on the basis, the invention proposes a novel LOPF model which is higher in accuracy and is more perfect; by the model, the voltage and the reactive power can be solved, a current source type steady-state model of the UPFC is processed and is equivalently embedded into a circuit, and thus, the novel LOPF model is applicable to the LOPF model proposed by the invention; and an example simulation result shows that the high efficiency of the linear model is maintained, the calculation result has relatively high accuracy, and moreover, power flow information which is more perfect than the DCOPF model can be figured out.

The invention provides a power system cascading failure simulation method based on a unified power flow controller and belongs to the technical field of power system security and reliability protection. A computer is used for determining the installation position of the unified power flow controller in a power system firstly, determining an active power flow betweenness threshold value of each node of the power system, performing power system cascading failure simulation based on the unified power flow controller and finally calculating measurement index for reflecting severity of cascading failure through procedures. The power system cascading failure simulation method gives consideration to power flow directivity and the operation mode of the system, optimizes the installation position for installing the unified power flow controller, effectively performs line parameter regulation while meeting safe operation constraints of the power system, and can reflect the propagation process of the cascading failure of the power system actually. The power system cascading failure simulation method based on the unified power flow controller can be widely applied to the cascading failure simulation of the power system, is particularly suitable for the cascading failure simulation of a large-scale complicated power system, and provides a scientific basis for preventing occurrence of the cascading failure of the power system.

The invention relates to a unified power flow controller used for an unbalanced system. The unified power flow controller comprises a static synchronization compensator and a static synchronization series compensator. An upper part split capacitance and a lower part capacitance are arranged between the static synchronization compensator and the static synchronization series compensator. The upper part split capacitance and the lower part split capacitance are connected in series and then respectively connected with the static synchronization compensator and the static synchronization series compensator in parallel. The upper part split capacitance and the lower part split capacitance are connected in series and then a split capacitance branch circuit is formed. A midpoint of the split capacitance branch circuit is connected with a neutral point of the static synchronization series compensator. Output ends of the static synchronization compensator and the static synchronization series compensator are respectively connected with a power grid. The unified power flow controller is convenient to split-phase control and modularization design, small in running loss, good in voltage control capacity, good in zero-sequence current controlling, few in element quantity, low in cost and high in cost performance.

The invention relates to a node current injection method-based modeling method of a unified power flow controller. For the unified power flow controller, a power flow control model of the unified power flow controller is established by the following steps: step one, establishing an equivalent circuit of the unified power flow controller; step two, for the equivalent circuit obtained by the step one, establishing an equivalent model expressed by a node current injection method so as to obtain an injected current of a parallel side node s and an injected current of a serial side node m of the unified power flow controller; and using the equivalent model and a corresponding injected current computational formula to obtain the power flow control model of the unified power flow controller. The method has the high adaptability; and the bus voltage control effect is good.

The invention discloses a two-stage optimal power flow calculation method for a power supply containing a unified power flow controller. A UPFC (unified power flow controller) model is deduced based on a power injection method; a two-stage scheduling model is proposed; optimal power flow calculation models containing the UPFC are established separately; the volatility of intermittent energy is corrected through regulating the control parameters of the UPFC, and the coordinative cooperation between the wind power and the UPFC is realized. The two-stage optimal power flow calculation method has the beneficial effects that (1) the model initially formulates a unit output plane in an intraday rolling scheduling stage to optimize the running cost; then a control policy table of the unified power flow controller is obtained in a real-time scheduling stage according to wind power output predication error, the running plan is modified in real time and a scheduling evidence is provided for the running scheduling staff; and (2) the volatility and the uncertainty of the wind power output can be coordinated by the rapid regulation of the control parameters of the unified power flow controller based on the flexible control capability of the unified power flow controller, and the economical performance and the safety of the system are improved.

The invention relates to a mode recognition-based current transient state quantity direction protection method for a power transmission line with a unified power flow controller, and belongs to the technical field of power system relay protection. When the power transmission line with the unified power flow controller has a fault, data, which is obtained at a line measurement end, of line mode current containing a fault phase is subjected to principal component analysis, and a forward direction fault is distinguished from a back direction fault according to the projection of sample data on a first principal component axis. According to the invention, principal component cluster analysis directional protection of the line mode current containing the fault phase can reliably distinguish the forward direction fault from the back direction fault, also can judge that the forward direction fault is positioned at the left side or the right side of the unified power flow controller, and can reliably recognize a fault section. Therefore, criterions about property recognition of the forward direction fault and the backward direction fault have high reliability.

The related renewable energy feedback interconnected circuit comprises: the input dc, a power unit with an absorption filter and level circuit in turns all paralleled between positive and negative bus-bar, an equalizing inductance, and the output ac. This invention can improve running efficiency, reduces cost, and has high power factor fit to wide application.

The invention relates to an interline power flow controller based on a modular multi-level converter structure. The interline power flow controller comprises a static synchronous compensator (1) and a static synchronous series compensator (2), the static synchronous compensator (1) comprises a converter (7) and a parallel transformer (8), the static synchronous series compensator (2) comprises a converter (9) and a series transformer (10), the converter (7) is connected into a power transmission line I in parallel through the parallel transformer (8), the converter (9) is connected in a power transmission line II in series through the series transformer (10), a unified power flow controller comprises a by-pass switch (4), and the by-pass switch (4) is connected with the series transformer (10) in parallel. The interline power flow controller avoids the technical difficulty of device series connection, facilitates split-phase control and modular design, can bypass a trouble unit through the redundancy technology, improves operational reliability of a device, and is low in device switching frequency and small in device operation loss.

The invention discloses an MMC-UPFC-based three-phase imbalance governance system and method of a power transmission line. The system comprises a modular multilevel-unified power flow controller MMC-UPFC, wherein the MMC-UPFC comprises a parallel side converter and a series side converter which are in back-to-back connection and share a same DC bus; the parallel side converter is connected with an AC side of a power grid through a parallel transformer; and the series side converter is connected with a power transmission line side through a series transformer. The system and the method disclosed by the invention have the beneficial effects that control on power flow of the power transmission line can be achieved while a three-phase imbalance problem of the power transmission line is solved, the problems of a light load and an overload of the power transmission line can be solved; the application function is expanded; and safe, economic and stable operation of a power system is ensured.

The invention discloses a UPFC reactive compensation method capable of reducing commutation failures, comprising the steps of setting up a detailed power grid model; separately performing transient simulation under various typical faults, and respectively calculating an inversion side converter station blow-out angle and a converter station AC bus voltage; according to conditions which may cause commutation failures, determining the constraint limits of the blow-out angle and the converter station bus voltage, and a fault set of commutation failures which may be caused by a current power grid; increasing a parallel side compensation reference value, and determining whether the parallel side compensation reference value exceeds an adjusting limit; and determining a new fault set, determining whether the fault set is empty, and finally obtaining a UPFC reactive compensation scheme applied to an actual power grid. The method performs simulation control on a current power grid to determine an appropriate UPFC compensation scheme, and can cover various faults, and reduce the AC power grid fault influence to extra-high voltage direct current, and fault lines which may cause commutation failures, thereby improving extra-high voltage DC access power grid safety and stability.

The invention provides a high-reliability unified power flow controller suitable for a double-circuit line. The high-reliability unified power flow controller comprises at least one parallel transformer, four converters, at least two series transformers, a parallel-side back brake loop, a series-side back brake loop and a direct-current public bus. At least one side of each series transformer is connected with at least one set of bypass switches in parallel. The alternating current side of at least one converter is connected with at least one series transformer through the series-side back brake loop to be connected into the line in series. The alternating current side of at least one converter is connected with the at least one parallel transformer through the parallel-side back brake loop to be connected into an alternating current system. The direct current sides of the converters are connected to the direct-current public bus through change-over switches. By means of the structure, multiple operation modes can be achieved, and when one converter breaks down, power flow of the double-circuit electric transmission line and the voltage of the parallel-side alternating current system can still be controlled; when two converters break down, control over the power flow of the double-circuit line can be achieved, and the good flexibility and the good reliability are achieved.

Dynamic power flow controllers are provided. A dynamic power flow controller may comprise a transformer and a power converter. The power converter is subject to low voltage stresses and not floated at line voltage. In addition, the power converter is rated at a fraction of the total power controlled. A dynamic power flow controller controls both the real and the reactive power flow between two AC sources having the same frequency. A dynamic power flow controller inserts a voltage with controllable magnitude and phase between two AC sources; thereby effecting control of active and reactive power flows between two AC sources.

A line power control method and system for a unified power flow controller includes outer loop line power control, inner loop valve side current control, and converter valve control. Series-side converter valve side current reference values Isedref and Iseqref are calculated by means of the outer loop line power control according to line power instructions Pref and Qref that are input, a measured line power UL, and measured line power Pline and Qline; a converter output voltage reference value Ucref is calculated by means of the inner valve side current control according to the valve side current reference values that are output by means of the outer loop power control, a measured valve side current, and a measured valve side voltage; and finally, a converter outputs, according to the voltage reference value, a corresponding voltage to control line power to achieve a reference value.

The invention relates to a transient energy protection method of a transmission line with a unified power flow controller, which belongs to the technical field of power system relay protection. When the transmission line with the unified power flow controller fails, according to current and voltage values measured by transformers on both ends of the line, transient energy values on both ends of the line are calculated. Through symbols of the transient energy values on both ends of the line, in region and out region failures are judged and distinguished. If the symbols of the transient energy on both ends of the line are respectively positive and negative, out region failures are judged. If the symbols of the transient energy values on both ends of the line are negative, in region failures are judged. According to the invention, instantaneous power transient energy polarity acquired through integrating can be determined; unconstant change of instantaneous power positive and negative polarity after a failure can be avoided; and the judgment reliability is improved.

The invention relates to the technical field of power electronics and discloses a unified power flow controller in the modular structure. A structurally modified modular multilevel converter is organically combined with a unified power flow controller so that direct-current voltage of the unified power flow controller is halved and the unified power flow controller is imparted with individual phase control capacity; a power electronic bypass switch on the serial side of the unified power flow controller provides higher safety, and the requirement on converter switching devices is lower. In addition, the unified power flow controller has the advantages of compact structure of the modular multilevel converter, flexibility in voltage and power level change, low switch frequency, low loss, low content of output waveform harmonic and the like.

The invention discloses a two-stage multi-target addressing method for a UPFC (unified power flow controller), and belongs to the technical field of operation and control of power systems. The method achieves the addressing of the UPFC at two stages based on an analytic hierarchy process, and comprises the steps: estimating the risk of each branch circuit through a branch circuit comprehensive load rate and the comprehensive vulnerability from the angle of system safety and stability, scoring each branch circuit, and preliminarily screening out an alternative branch circuit set of the UPFC; calculating the investment ratio of a UPFC and power grid construction replacement alternative scheme, the operation benefits of the UPFC, the control sensitivity and the damping gradient of the system after the UPFC is installed from the economic benefits and the safety benefits brought by the UPFC, obtaining the comprehensive score of each branch through combining with the scores of the alternative branch circuits at the first stage, and giving a recommended installation site of the UPFC. The method achieves the complete evaluation of the indexes, reduces the calculation scale through a stage dividing method, and can provide instructive advices for the addressing of the UPFC for a power grid planning worker.

The invention discloses a general power flow calculation method of a power system provided with a UPFC (unified power flow controller). According to the method, under a premise that the control objective of the UPFC is satisfied, a power injection model and Newton-Raphson method are combined so as to solve the power flow of the power system iteratively. The method is not only suitable for UPFCs of traditional structures, but also suitable to novel UPFCs of which the parallel sides and series sides are connected with different bas-bars or novel UPFCs provided with a plurality of series branches. The present invention also provides specific calculation steps and calculation formulas of power flow calculation. Thus, when the method of the invention is adopted to carry out power flow calculation, new state variables are not needed to be added, the dimensions of Jacobian matrix will not be increased in an iteration process; and the method is easy to implement and has an excellent convergence characteristic.

The invention discloses a unified power flow controller additional damping control system capable of restraining subsynchronous oscillation. The unified power flow controller additional damping control system comprises a subsynchronous damping controller, wherein the additional control signals are superimposed in current inner loop control instructions of reactive control circuits of a shunt-wound side converter and a series-wound side converter of the unified power flow controller; the subsynchronous damping controller comprises multiple subsynchronous modal control circuits; each subsynchronous modal control circuit comprises a modal filter, a proportion amplifying module and a phase shifter for realizing phase compensation separately; the output signals of each subsynchronous modal control circuit are subjected to signal superposition and amplitude limiting to form the additional control signals output by the subsynchronous damping controller; and the subsynchronous damping controller takes generator shaft system rotating speed deviation as the input control signal. The unified power flow controller additional damping control system provided by the invention is capable of restraining subsynchronous oscillation of the power system successfully and the normal and steady operation of the system and the unified power flow controller is not affected.

The invention relates to a unified power flow controller (UPFC) system based on a direct AC-converter hexverter-modular multilevel converter (H-MMC) and a passive control method thereof. A new hexagondirect AC-converter, Hexverter-Modular Multilevel Converter (H-MMC), is applied to a Unified Power Flow Controller (UPFC), and an Interconnection and Damping Assignment Passivity-Based Control (IDA-PBC) method is designed, thereby realizing active and reactive power flow distribution of a UPFC adjusting circuit and the function of voltage amplitude phase.