360 results about "Point of common coupling" patented technology

A wind turbine generator control system is provided for controlling output of a plurality of tightly-coupled windfarms connected at a point of common coupling with a power system grid. A master reactive control device employs algorithms whose technical effect is to coordinate the real power, reactive power and voltage output of the multiple windfarms. The controller incorporates a reactive power regulator that can be used to regulate reactive power, power factor or voltage at the point of common coupling and an active power regulator that can be used to regulate real power at the point of common coupling; such that each windfarm is not asked to contribute or violate its own operating capability.

A power system having a plurality of power converters coupled together at a point of common coupling (PCC). The power converters are coupled to a load and provide a combined power converter output to the load. A switch is coupled in series between the PCC and an external grid. When the switch is closed, the power system is in a grid-tied configuration and when the switch is open, the power system is in a microgrid configuration. A control system coupled to the power converters enables the switch to open and close in response to a signal received from one or more sensors monitoring the external grid, enables the power converters to operate in a current control mode when the switch is closed, and transitions the power converters from grid-tied mode to microgrid mode and synchronize the power converters such that the converters share the load.

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.

A system and method for controlling voltage at a point of common coupling of a wind farm including a plurality of wind turbines is provided. The method includes: calculating a first voltage error value, which is a difference between a reference voltage value of the point of common coupling and an actual voltage value of the point of common coupling; calculating a compensation reference voltage value based on the first voltage error value; calculating a second voltage error value by subtracting a voltage value of an output terminal of a wind turbine from a sum of a reference voltage value of the wind turbine and the compensation reference voltage value; calculating a reactive power compensation value corresponding to the second voltage error value; and injecting a reactive current corresponding to the reactive current compensation value into a power grid.

The invention discloses a method for island detection by adopting intermittent two-sided reactive power disturbance. A frequency of a voltage of a common coupling point is out of allowance range after an island occurs by introducing the intermittent two-sided reactive power disturbance into the output reactive power of a grid-connected inverter, so that the aim of the island detection is fulfilled. By the method, an island phenomenon can be detected immediately and effectively, and grid-connected power factors are less influenced.

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.

The invention relates to a method for detecting islanding by frequency deviation applying pulse current interference, which comprises the steps of: selecting an AFD method of which the chopping rate cf is equal to 0.01 to perform small-range deviation on the frequency of a point of common coupling; if detecting that the frequency of the point of common coupling fluctuates continuously towards a direction, considering that the failure of a power grid possibly exists, and aiming at completing islanding detection and disconnecting synchronization before high-speed reclosing, applying current amplitude interference with an appropriate period; once discovering that the possibility of the failure is removed, revoking the current interference; and when detecting that voltage frequency exceeds the limit of OVP/UVP and OFP/UFP, performing anti-islanding protection. The method can accelerate the detection of the failure and reduce detection dead zones, and has the small influence on the power grid. The detection method can make up the defects caused by independent use of the two methods, judge the occurrence of the failure accurately and quickly, and provide guarantee for the safe and reliable operation of the power grid by adopting corresponding measures.

The invention discloses a grid-connected inverter island detection method based on wavelet transform and a neural network. The method is characterized in that the method comprises the following steps: firstly, gathering voltage values of a distributed grid-connected power generation system at a point of common coupling at island state and non-island state and the output current value of an inverter, then performing wavelet transform on the gathered voltage values and the output current value of the inverter and exacting high-frequency component wavelet coefficients to be processed, and finally taking processed signals as input signals of the neural network, and taking corresponding island state and non-island stage as output signals to train the neural network, so as to ensure that the system obtains recognition capability to the island state and the non-island state, and to adopt corresponding island protection measures when the distributed grid-connected power generation system is at the island state. The method can not only overcome the disadvantages of the existing passive island detection method that the detection blind area is large and the detection time is long, but also can solve the problem that the active island detection method affects the power supply quality of the distributed grid-connected power generation system, and rapidly accomplish island detection and island protection.

The invention discloses a STATCOM (static synchronous compensator) control system adopting a droop control strategy and a control method thereof. The STATCOM control system adopting the droop control strategy comprises a direct-current side capacitor, a three-phase inverter bridge and an inductance-capacitance filter, wherein the direct-current side capacitor and the three-phase inverter bridge are connected in parallel and then connected with the inductance-capacitance filter, and the inductance-capacitance filter is connected to a PCC (Point of Common Coupling) of a power grid by a three-phase switch K through a coupling transformer T. The control method disclosed by the invention comprises the steps of real-time signal collection, computation of active power reference value P*, computation of reactive power reference value Q*, computation of frequency reference value omega* and voltage modulation amplitude reference value E*, computation of phase reference value Delta* and computation of voltage modulation signals; and only one PI (proportional integral) regulator and two droop control coefficients need to be regulated, thus the whole control method is easy to realize, and further the power system can better supply power to users safely, excellently and economically.

The invention discloses a multi-fan grid-connected resonance analysis method. The method comprises the following steps: on the basis of an output impedance model of an inverter, establishing a grid-connected equivalent model of a wind power plant; establishing a cable equivalent model according to the cable distribution characteristic under a harmonic state, and establishing the equivalent impedance of fan output power at a PCC (Point of Common Coupling) according to a relationship between the absorption power of the PCC and the fan output power to obtain the total impedance of a distributed wind power grid-connected system. The multi-fan grid-connected resonance analysis method has the advantages that the total impedance is calculated by establishing a distributed wind power grid-connected system model recorded with the cable and fan output power; the system model more accords with practical situations and has an application value and a practical significance for the resonance problem in an accurate analysis system.

The invention discloses a comprehensive series compensation voltage ride-through device of a wind turbine generator. The comprehensive series compensation voltage ride-through device of the wind turbine generator is mounted on a three-phase circuit between a wind driven generator and a control device of the wind driven generator and a PCC (point of common coupling) of a power grid, and comprises a three-phase standard transducer, a series coupling transformer, a two-way charge-discharge circuit, a DC bus capacitor and a by-pass switch. With the adoption of a dynamic voltage restorer, a chopper circuit and a super capacitor with high-capacity energy storage in the power electronic technology, low voltage ride through, high voltage ride through and harmonic compensation are realized under the condition that generator terminal voltage drops off during power grid fault, generator terminal voltage rises due to excessive reactive power of the power grid and the harmonic content of the power grid is overlarge, the wind turbine generator is prevented from being separated from the grid, and harmful effects of harmonic are prevented; and moreover, a conventional wind turbine generator is not required to be transformed, and the device can be taken as an independent control module and added at the stator output port of the wind turbine generator and is convenient to mount.

The invention provides a verification method and an experimental device for grid impedance recognition. The experimental device comprises a voltage source inverter (10), a grid impedance unit (20) and a grid impedance recognition unit (30). The specific operation process for verifying grid impedance recognition by the experimental device comprises the following steps: a disturbing signal injection unit (301) injects disturbing signals into an inverter control system, current response signals iga, igb and igc and voltage response signals uga, ugb and ugc of a PCC (point of common coupling) are acquired respectively by a current sensor Hig and a voltage sensor Hug on a grid-connected side, acquired signals are input into a grid impedance calculation unit (305), and grid impedance is obtained through calculation. A grid impedance recognition method can be verified accurately and reliably by the experimental device, and adverse effect on power quality is avoided.

The invention discloses a grid-connected inverter island detection method based on parameter adaptive Sandia frequency shift (SFS). The method uses a digital correlation principle for detecting a phase difference angle between a common coupling point voltage and an inverter output current, initial chopped wave coefficient cf0 in the SFS is made to automatically adjust along with inverter frequency detection errors according to the detected phase difference angle, and meanwhile a positive feedback gain K in the SFS can be made to carry out adaptive modulation along with the difference of local loaded quality factors. The grid-connected inverter island detection method based on the parameter adaptive SFS overcomes the defect that a dilutive effect caused by traditional SFS due to frequency detection errors under a multi-inverter grid-connected condition can lead to the failure of island detection, solves the problem that the island detection is difficult and even can not be achieved when the local loaded quality factors are quite high, and quickly achieves the island detection and island protection under the condition that power supply quality of a distributed type power generation system is ensured.

The invention relates to an island detection method based on the wavelet packet energy spectrum. In the method, the wavelet theory is applied to decompose the signal into different frequency components, so that the fault information can be obviously displayed. The method is characterized by comprising the stages of signal processing and island identification and comprising the following specific steps: 1) directly measuring the voltage signal at the point of common coupling (PCC) and carrying out wavelet packet decomposition on the detected voltage signal; 2) reconfiguring the wavelet packet decomposition coefficient and extracting the signals in the frequency band ranges; 3) computing the energy characteristic value of each frequency band signal according to the energy expression shown in the specification; 4) constructing the fault characteristic vector T with number of dimensions being 2<j> by adopting the energy of the frequency band signals as the elements; 5) establishing a sample model and then determining the fault characteristic vector P according to the statistical average of the sample space; and 6) establishing mapping relationships between the energy characteristic vectors and the fault conditions, making a fault query table with the congruent relationships between the fault conditions and the parameter variation and storing the fault query table, identifying the faults based on the fault query table and simultaneously displaying the diagnosis results.

A method for controlling a wind turbine is proposed. The wind turbine is in a wind farm and connected to a point of common coupling that is connected to a utility grid. At least one quantity indicative of a short circuit ratio of the utility grid is measured. A control parameter of a control system controlling the wind turbine and the wind farm is adjusted. based on the measured value of the quantity.

The invention provides a quantitative analysis method of a harmonic voltage transmission level of a nonlinear load of a user terminal and a corresponding device. The method comprises the steps: sampling voltage and current in a common coupling point between a power supply terminal and the user terminal; obtaining several harmonic voltage phasors and current phasors according to sampling data; judging whether the nonlinear load of the user terminal is a main harmonic source or not; computing the harmonic impedance of the power supply terminal if the nonlinear load of the user terminal is the main harmonic source; and computing the harmonic voltage transmission level of the nonlinear load of the user terminal in a time interval according to the harmonic impedance of the power supply terminal and the current phasors in the common coupling point. By applying the method, the harmonic voltage transmission level of the nonlinear load of the user terminal can be easily and quantitively analyzed.

The invention provides a harmonic source identification method which comprises the following steps: performing responsibility allocation on harmonic pollution through the harmonic voltage emission level of a user, wherein the harmonic voltage emission level of the user at a time is represented through the variable quantity of harmonic voltage or current at a time at a point of common coupling before and after the user accesses to a power system; positioning an accurate point of a harmonic source through harmonic emission level evaluation to the maximum extent. The method has the benefits that an algorithm provided by the invention can quickly determine the harmonic source, is high in accuracy and practicality, and has very good project utilization values.

A method predicts a voltage collapse in a micro-grid connected to a power distribution network by measuring states at a point of common coupling of the micro-grid, and a connected bus of the power distribution network connected to the micro-grid through a connection link. Then, it is determined whether a reactive power generation limit of the micro-grid is reached based on the states, and if no, repeating the measuring, and otherwise determining parameters of the connection link using the measurements. A static voltage stability margin index is determined, and a voltage stability margin index is predicted using the static voltage stability margin index and a forecast of future load variations in the micro-grid. Then, it is determined whether the voltage stability margin index is smaller than a threshold, and if no, repeating the measuring, determining and predicting steps, and otherwise if yes, signaling a control action indicating the voltage collapse.

The invention belongs to the field of power system microgrid protection and control, and relates to a microgrid failure locating method. A static switch is arranged in a common coupling point, and a relay protection device is arranged in a synchronization place of lines including distributed power supplies. The microgrid failure locating method comprises the steps of: 1, carrying out real-time data sampling on a current by using a line protection device; 2, when detecting that some phase has current mutation and a mutation quantity absolute value is more than a set threshold for the first, turning into the step 3, otherwise, returning the step 1; 3, continuously carrying out real-time data sampling on the current, detecting whether some phase current mutation absolute value detected again within a time period t is more than the set threshold, if so, turning into the step 4, otherwise, judging that a failure is not caused or the failure occurs outside a line protection area, interlocking a protection, returning the step 1; and 4, judging that the failure occurs in the line protection area, and opening the protection. According to the invention, the failure occurring area can be accurately judged.

The global synchronous pulse width modulation system includes main control unit and plurality of grid-connected inverters located at different geographical locations, wherein each grid-connected inverter is connected with a distributed power supply; each grid-connected inverter is connected with a grid through a point of common coupling; main control unit communicates with all grid-connected inverters through communication channels; main control unit receives information of grid-connected inverters and respectively sends a global synchronous signal containing global synchronous strategy to grid-connected inverters after determining global synchronous strategy; grid-connected inverters regulate the phases of their own pulse width modulation waves through global synchronous signal to enable pulse width modulation waves of grid-connected inverters to satisfy a phase difference of harmonic counteraction, so as to counteract harmonic current injected by grid-connected inverters into grid. Advantages include eliminating the disordered superimposition problem of harmonic current of the inverters and mutually counteracting harmonic current between distributed inverters.

The invention relates to the field of power system and signal transmission and discloses an island effect detecting method of a grid-connected photovoltaic power system. Data of an inverter system and a public coupling point are used, and detecting is carried out based on a fuzzy neural network and wavelet transformation. The method comprises the steps that output current signals of the inverter system and voltage signals of the public coupling point are collected; the current signals and the voltage signals are subjected to wavelet transformation, and wavelet components in various dimensions are obtained; the wavelet components are subjected to mathematical treatment; and signals obtained after treating are used as a feature vector space to be provided for an input layer of the fuzzy neural network, and the fuzzy neural network judges whether an island happens according to input feature vectors. According to the technical scheme, detecting and early warning can be carried out on the island effect accurately, during stable operation, grid-connected current is not affected obviously, and the requirements of the NB/T32004-2013 standard are met.

A method controls a micro-grid connected to a power distribution system. The method determines parameters of a model of dynamics of the micro-grid using measurements of power flow at a point of common coupling (PCC) of the micro-grid with the power distribution system. The model is exponentially stable on a voltage set-point at the PCC and the method determines, using the parameters of the model, an amount of reactive power required to maintain the voltage at the PCC asymptotically stable on the voltage set-point. Next, the method controls a generator of the micro-grid to produce the amount of reactive power.

The invention relates to the electric energy quality comprehensive assessment, aims at providing an electric energy quality comprehensive assessment method of a distributed generating system and a micro power grid. The method comprises the following steps of: monitoring synchronized grid public coupling points to obtain monitoring data of each electric energy quality index; normalizing the data by using a maximin method; establishing a hierarchy assessment model and defining a corresponding sudden-change decision model; and obtaining the sudden-change grade of each layer from the lower layer to the top layer according to the sudden-change decision model, and finally obtaining the sudden-change grade of each synchronized grid public coupling point, that is, the electric energy quality comprehensive assessment index, wherein the greater the value is, the higher the grade of the corresponding electric energy quality is. The method provided by the invention has simple computation process and considers the nonlinear factor in the system, can provide the quantized index and basis for a power grid operator who fixes a price of the power to a distributed generating party according to the quality, and provides a reference target for the electric energy quality management. A corresponding compensating device can be mounted on the basis of the assessment method so as to flexibly customize the electric energy quality of the micro power grid.