120 results about "Voltage flicker" patented technology

The invention discloses a power compensation method and a system for a wind power system, wherein the method comprises the following steps: detecting the voltage and current of a power grid belonging to the wind power system in real time; determining the power requirement quantity of the wind power system according to the voltage and current of the power grid, wherein the power requirement quantity comprises reactive power requirement quantity and/or active requirement quantity; and controlling an SVC (static var compensator) device and/or an energy storage unit to regulate so as to compensate the reactive power/or active power of the wind power system. According to the invention, through the compensation device combined by the SVC device and the energy storage unit, not only can the reactive power required in the wind power system be compensated smoothly, rapidly and accurately, but also harmonic wave can not be generated in the compensation process, at the same time, the active power can be provided, the output of the wind power system can be stablized, the voltage flicker is inhibited effectively, and the stability of the power grid is ensured.

The invention discloses a method for extracting power grid voltage flicker envelope parameters. According to the method, power grid voltage flicker waveforms are sampled at a constant sampling frequency, a flicker envelope amplitude modulated wave component is obtained through energy calculation of an improved Teager energy operator, a cosine window is added to conduct Chirp-Z conversion, the flicker envelope amplitude modulated wave frequency and a correction factor of an amplitude modulated wave amplitude value are extracted by improving the Chirp-Z conversion, and the flicker envelope amplitude modulated wave amplitude value is corrected through the correction factor and accurately obtained; through the combination of the improvement on the energy operator and the improvement on the Chirp-Z conversion, the energy operator is improved, the flicker envelope demodulation calculation process by the energy operator is improved, the noise resistance is improved; by improving the Chirp-Z conversion, the flicker frequency analysis range is flexible and adjustable, and frequency spectrum leakage generated under the condition of asynchronous sampling and errors caused by a picket fence effect are effectively avoided; the correction factor of the amplitude modulated wave amplitude value reduces the errors caused by the energy operator, and the power grid voltage flicker envelope parameters can be accurately measured in real time.

The invention discloses a voltage flicker detection method based on windowing interpolation short-time Fourier transform. The method mainly comprises the steps that 1) voltage signals are sampled discretely to obtain a sampling sequence U(n) of N points; 2) a Blackman-Harris triangular convolution window is used to weight the sampling sequence U(n) and carry out short-time Fourier transform to obtain an amplitude matrix P (i, j) of the singals; 3) a polynomial fitting method is applied to solve an amplitude expression yj(k) of each column of the matrix P (i, j); 4) according to the expression yj(k), a voltage signals envelope frequency fm(j) is calculated; 5) according to the envelope amplitude ymax(j) and the envelope frequency fm(j), characteristic quantities V1, V2, V3, V4, V5 and V6 are extracted; and 6) the characteristic quantities V1, V2, V3, V4 and V5 are used to calculate a signal flicker coefficient T, and compared with a threshold corresponding to V6, and a detection result is provided. The method is based on the windowing interpolation short-time Fourier transform, characteristic quantities are extracted, calculation is simple, the extracted characteristic quantities are fewer, the recognition is high, and requirement for rapid flicker detection in the power system can be met.

The invention discloses a control method for switch tube of a PFC circuit. The control method comprises the steps of obtaining an input current, an input voltage and a busbar voltage of the PFC circuit based on each control cycle of the switch tube; obtaining output quantity of a voltage loop based on a deviation control on the voltage loop based on a difference value between a set value of the busbar voltage and the practical value of the busbar voltage; determining a reference value of an electric current loop in the current cycle based on output quantity of the voltage and a reference value changing threshold value of the electric current loop; obtaining output quantity of an electric current loop by conducting deviation control on the electric current loop based on the differential value of the reference value of the electric current loop and the value of the input electric current; adding the output quantity of the electric current loop with a feedforward quantity to obtain a duty ratio signal which can control conduction and blockage of a switch tube of the PFC circuit. The control method for the switch tube of the PFC circuit can effectively eliminate phenomena of overcurrent or overvoltage and undervoltage of the generatrix caused due to voltage flicker in the PFC circuit and guarantee stability of the PFC device, therefore the method is safe and effective.

The invention relates to a static var compensator (SVC) reactive prediction and compensation method for a rectifier load. The method comprises the following steps of: 1) calculating a triggering angle and simultaneously calculating reactive power to be generated by a load by using a rectifier controller and transmitting the reactive power of the rectifier load to an SVC controller; 2) receiving prediction reactive power transmitted by the rectifier controller by using the SVC controller, acquiring the on-off state of a branch breaker of a filter, simultaneously acquiring a power grid current signal and a power grid voltage signal used for the calculation of a reactive compensation amount, and finally realizing trigger control compensation in a triggering angle manner; and 3) after predicting and compensating, compensating a deviation caused by the calculation of the reactive power through a proportion integration (PI) regulation link. The method has the advantages that: effective compensation of a large amount of rapid reactive power in the working process of the load can be realized by an SVC device; and the SVC device has short response time, can fulfill the aim of reactive power rapid compensation, can effectively inhibit the impact of the power grid caused by the reactive power, and eliminates a voltage flicker.

The invention relates to an energy storage-containing arc furnace energy-supply power system and a control method thereof. The system comprises a power grid access and measuring unit, a network-side variable flow unit, a direct current bus, an energy storage power control unit, a high power energy storage device, an inverter unit and a main controller. According to the method, the power supply of an arc furnace is kept stable when a power grid is abnormal, the impact on the power grid is reduced, and the problems that the power factor of power grid access points is low and three phases are imbalanced caused by the arc furnace are solved. When the power grid voltage flickers and power fails in a short time, the power can be uninterruptedly and stably supplied to the arc furnace, so that the furnace temperature is stabilized and the quality of metallurgical products is ensured; meanwhile, the adverse effects on the power grid caused by factors of power fluctuation and low power factor of the arc furnace can be reduced.

A voltage flicker demodulation method is provided, which relates to a method for demodulating voltage flicker modulation wave. The invention can solve the problems that: the existing demodulation method is easily affected by fundamental voltage and fundamental frequency, additional filter needs to be designed, the arithmetic is complex and is not suitable to use in digital measurement device. The steps of the method in the invention are that: step 101 is to set the number of points sampled N and sampling frequency fs; step 102 is to get voltage sampling value serial u(n) through voltage sample circuit; step 103 is to get voltage successive value Z(k) by discrete Fourier transform of u(n); step 104 is to calculate U(k) according to voltage successive value; step 105 is to get analytic signal z(n) of u(n) by discrete Fourier transform of Z(k); step 106 is to calculate Hilbert of u(n) and transform u(n); step 107 is to calculate the module sequence |z(n)| of z(n) with the formula of |z(n)|=u< 2 >(n)+u< 2 >(n); step 108 is to have discrete Fourier transform to |z(n)|, filter direct-current component and get voltage flicker modulation signal a(n) and the amplitude and frequency.

The invention relates to a method for measuring IEC (International Electrical Commission) standard voltage flicker. The method includes initializing a measuring system, collecting voltage peak, preprocessing data, processing data based on a table look-up algorithm, processing data based on a frequency compensation algorithm, calculating short-time voltage flicker value, and calculating long-time voltage flicker value. With the simplified calculating process, RAM storage space occupancy rate is reduced, sampling continuity is guaranteed, and measurement accuracy is ensured.

The invention belongs to the technical field of electric energy quality control of a power distribution network, and specifically relates to an active and passive combined electrical load three-phaseimbalance adjusting device. The device mainly comprises an alternating current power grid, a non-linear load, a capacitance separate compensation circuit, a capacitance common compensation circuit, anIGBT compensating circuit, a protection circuit and an electric energy quality adjusting intelligent controller. The device is characterized in that the capacitance separate compensation circuit, thecapacitance common compensation circuit and the IGBT compensating circuit are separately connected to the alternating current power grid in parallel, and the electric energy quality adjusting intelligent controller is separately connected with the capacitance separate compensation circuit, the capacitance common compensation circuit and the IGBT compensating circuit in a controlled manner. Fusingprotection apparatuses are correspondingly and respectively arranged between the capacitance separate compensation circuit, the capacitance common compensation circuit and the IGBT compensating circuit, and the alternating current power grid, a zero-crossing switch array is controlled to perform dynamic switching on a capacitor core group, appropriate PWM switch signals are simultaneously outputto an IGBT module, and smooth adjustment of three-phase imbalance can be realized; reactive compensation and three-phase imbalance adjustment can be both realized; the response speed is fast, and voltage flicker and fluctuation can be avoided; and harmonic current pollution is avoided, the security is higher, and the reliability is better.

The invention belongs to the technical field of design and application of new energy grid-connected detecting systems, and particularly relates to a wind turbine flickering simulation testing system and a method based on virtual power grid simulation. The system comprises a current transformer, a data acquirer, an industrial personal computer or a PC (Personal Computer) and simulation software Matlab or LabVIEW for performing flickermeter simulation, wherein an output port of the current transformer is connected with a data interface of the industrial personal computer through the data acquirer; current signals (numbers) are equivalent to controllable voltage sources in a virtual power grid which is built by the industrial personal computer; and the voltage sources are processed as voltage flickering values by a simulation tester, and can correspond to report forms or patterns. The system and the method have the advantages of simple and reliable structure and strong practicability, are conducive to reducing hidden troubles which are brought by wind power integration to the power grid, can reduce equipment investments, and are simple in testing process and suitable for promotion and application.

The invention discloses a voltage flicker evaluation and detection method for a power grid access point of a photovoltaic station. The voltage flicker evaluation and detection method comprises the steps of collecting environment data, and establishing a voltage flicker comprehensive environment factor model of an access point of a large-scale photovoltaic station; performing modeling on the photovoltaic station based on PSCAD; establishing a power grid side model; and establishing a voltage flicker evaluation and detection model. By adoption of the voltage flicker evaluation and detection method, the voltage flicker, caused by sudden drop of solar assembly efficiency due to the factors of shadow, fragments, battery board aging and short circuit, disconnecting, mist shielding and the like of a large-scale photovoltaic base, of the power grid access point of the station can be evaluated and detected, so that safe and economical operation, and overhaul and maintenance of a photovoltaic power generation system can be facilitated; and in addition, a photovoltaic output prediction result can assist power grid dispatching to operate a control strategy, so that the stability of the photovoltaic power generation power grid can be improved.

The invention relates to a detection method of a voltage flicker. The detection method specifically comprises the steps of: acquiring a grid voltage, acquiring a high-sampling-rate grid voltage effective value sequence XH and a low-sampling-rate grid voltage effective value sequence XL; calculating original frequency spectra of the XH and the XL by utilizing windowing FFT separately, and correcting frequencies and amplitude values of the original frequency spectra by utilizing a frequency spectrum correction algorithm to obtain corrected frequency spectra SH' and SL'; and calculating a short-term flicker value and a long-term flicker value by utilizing the corrected frequency spectra SH' and SL' obtained in the step 2. By adopting double-sampling-rate Fourier analysis, the detection requirements for low-frequency flicker signals is satisfied by means of Fourier analysis of the low-sampling-rate sequence, and the analysis requirements for high-frequency flicker signals is satisfied by means of Fourier analysis of the high-sampling-rate sequence, thereby significantly reducing the voltage flicker calculation load and requirements for storage space. In addition, by adopting a method of carrying out interpolation fitting on dominant frequency and the short-term flicker value, the voltage flicker measurement precision is improved.

The invention provides a voltage flicker detecting and control method based on battery energy storage system; the method comprises the steps: step (1) acquiring a single-phase voltage signal at a PCC (Program-controlled Computer) and changing the phase to obtain three-phase voltage and current signals; step (2), transforming the three-phase voltage and current signals obtained in the step (1) and obtaining instant active power and reactive power; step (3), filtering the obtained instant active power and extracting a DC component to calculate a voltage flicker enveloping signal; step (4) calculating voltage flicker parameters, including an amplitude value and a frequency; and step (5) solving a compensation command of the battery energy storage system and compensating active and reactive power to public nodes. The provided voltage flicker detecting and control method is capable of accurately detecting the corresponding parameters of the voltage flicker; the calculation method is simple and the engineering is easy in realization. The battery energy storage system is applied to a power distribution network to compensate the voltage flicker; in combination of the provided control method, the active and reactive power can be compensated at the same time and the voltage flicker in the power distribution network is restrained effectively.

The invention discloses a switching virtual circuit (SVC) feedforward feedback controlling method based on a high-power four-quadrant converter load. The SVC feedforward feedback controlling method based on the high-power four-quadrant converter load comprises steps as below: analyzing wire-connection and operation mode of a converter; building a reflecting internal memory network; calculating reactive power of the converter; collecting branch circuit state of a filter; importing network voltage feedback; achieving firing angle controlling; the SVC feedforward feedback controlling method quickly and accurately calculates reactive power the converter needing to waste soon to be used as a feedforward amount for load compensation according to the high-power converter load operation mode and real time data, meets requirements of load compensation quickness, at the same time gives consideration to indexes of electric power system compensation stability, enables reactive power compensation response time to be shorter than 4ms, effectively restrains impaction of reactive power to the electric power, eliminates occurrence of voltage flicker, and further improves stability of the electric power system.

The invention provides a low voltage loop-closing selective-tripping system, comprising auxiliary connection points of three air switches, a relay and a selective-tripping switch, wherein the relay comprises three normally open contacts; the selective-tripping switch comprises three groups of connection points, and moreover, only one group of connection points is located in the on-state; the auxiliary connection points of the three air switches are connected in series in order; the auxiliary connection point of the first air switch is connected with a live wire of a power supply source; the auxiliary connection point of the third air switch is connected in series with the first end of a coil of the relay; the second end of the coil of the relay is connected with a neutral wire of the power supply source; the three normally open contacts of the relay are connected with three input connection points in the three groups of connection points of the selective-tripping switch respectively; and three output connection points in the three groups of connection points of the selective-tripping switch are connected with opening coils of three opening loops of the three air switches respectively. With the adoption of the low voltage loop-closing selective-tripping system, the problem of voltage flicker of momentary interruption during the switching operation can be solved; the power can be supplied reliably; and the personal safety of operators can be guaranteed.

The invention discloses an integrated monitoring system for power transformer operation, and relates to the field of power distribution network automation. The integrated monitoring system aims to solve the problems of lack of a device simultaneously monitoring multiple operation data of a transformer and low monitoring precision at present. An intelligent measurement and analysis terminal is used to determine faults of overheat and insulation aging of a transformer according to change rules of oil temperature and oil pressure; and, if a change curve of the oil temperature or the oil pressure continues rising, the faults of the overheat and the insulation aging of the transformer occur, an alarm is given out. The intelligent measurement analysis terminal is further used to determine a seepage or oil-stealing problem of the transformer according to an oil level change rule; and, if an oil level change curve continues declining, the transformer has a seepage or oil-stealing fault, and an alarm is given out. The intelligent measurement analysis terminal is further used to compare an acquired three-phase current and voltage with a set three-phase current and voltage so as to determine whether a voltage flicker, sudden rise or sudden drop condition occurs, and, if the voltage flicker, sudden rise or sudden drop condition occurs, an alarm is timely given out. The intelligent measurement and analysis terminal is used to monitor faults occurring in the operation process of the transformer.

The invention relates to a voltage flicker measurement method for a power quality measurement instrument. According to acquired voltage effective value envelope data and a preset identification function, sliding convolution calculation is carried out to obtain an identification value. When positive and negative changes happen to the identification value, extreme values in a corresponding convolution calculation section and time corresponding to the extreme values are searched and acquired. According to a difference value of each two adjacent extreme values and the time corresponding to the extreme values, a flicker value in a measurement time period is calculated and obtained. The calculation method completely meets a definition that voltage of a power system is influenced by large load random switching by flicker according to a national standard, the method can be used for flicker calculation with periodic changes or random changes, and the measurement accuracy is high.

The invention provides a method and a device for detecting the voltage flicker of a grid-connected point of a wind turbine generator system. The method comprises the steps: sampling at an output end of a single fan to obtain a three-phase current signal and a three-phase voltage signal, separating and combining the obtained three-phase current signal and the three-phase voltage signal to obtain three ways of single-phase signals; respectively inputting the three ways of single-phase signals into a virtual power grid numerical value model and a virtual power grid circuit model, wherein the virtual power grid numerical value model is established according to a virtual power grid simulation phase voltage instantaneous value expression, the virtual power grid circuit model is established according to a virtual power grid phase diagraph and parallel resistors R are merged into two ends of a current source in the phase diagraph; measuring reference voltage us at a PCC point of the virtual power grid numerical value model and the voltage ud at a PCC point in the virtual power grid circuit model; measuring the flicker value pst1 of the reference voltage us at the PCC point and the flicker value pst2 of the voltage ud at the PCC point; and obtaining the flicker accuracy value of the voltage ud at the PCC point according to the flicker value pst1 and the flicker value pst2.