60 results about "Grid synchronization" patented technology

The invention relates to a grid synchroniser for connecting an AC output of a power converter to the AC grid mains. In one aspect the invention provides a grid synchroniser comprising an inverter controller to control an AC output of the inverter, the controller including a receiver to receive grid data from a grid sensor location remote from said inverter. In another aspect we describe techniques for rapid removal of charge from a control terminal of a power switching device such as a MOSFET, IGBT or Thyristor using a particular driver circuit.

A small signal feedback loop or feed-forward loop having gain provides substantially unconditional instability in a phase locked loop when a reference phase signal is lost. The small signal feedback or feed-forward also modifies phase locked loop bandwidth when the reference phase signal is lost to increase rapidity of response to loss of reference phase signal while maintaining insensitivity to reference voltage amplitude change while the reference phase signal is present. The performance thus achieved is particularly suitable for rapid condition detection response and control of a grid connected power converter under islanding conditions.

The invention discloses a multi-terminal DC (Direct Current) power transmission system for combined synchronization of a wind power plant and a conventional power plant. The multi-terminal DC power transmission system comprises two rectification stations and an inversion station, wherein the wind power plant is connected to an AC (Alternating Current) bus side of one rectification station, the conventional power plant is connected to an AC bus side of the other rectification station, the inversion station is connected to a load center, DC buses of the two rectification stations, corresponding to the inversion station, are connected together by a DC power transmission line, thus the multi-terminal DC power transmission system is formed. According to the multi-terminal DC power transmission system disclosed by the invention, a matched conventional power plant does not need to be built near the wind power plant, and the multi-terminal DC power transmission system has no any requirements on a geographic position of the conventional power plant combined with the wind power plant; compared with a manner of AC power grid synchronization, the multi-terminal DC power transmission system does not need a local AC power grid near the wind power plant to level the power fluctuation of wind power; and compared with a scheme of synchronization of wind power plant through voltage source type DC power transmission, the multi-terminal DC power transmission system can enable the electricity transmission power of a single-circuit bipolar line to be 6,400MW or more by adopting the traditional mature ultra-high-voltage current conversion technology.

This invention presents a highly efficient harmonics free DC-AC power inverter using a pair of push-pull switches with feedback loop that acts as a voltage regulator. The feedback loop voltage regulator uses a series-shunt feedback amplifier to regulate the output voltage by amplifying the error signal between a pure sine wave referenced signal and the measured output voltage signal. A step-up low power transformer is used to step-up the triggering pulse at gates of the push-pull solid state switches to the desired rated output voltage so that the output voltage becomes harmonic free sine wave, but high voltage feedback amplifier, if feasible, maybe used without using the transformer. The reference signal may be synchronized with the grid for on grid applications, but it can also be used for stand alone loads. In order to optimally minimized the conduction power loss across the push-pull solid state switches of the DC-AC inverter, the positive voltage V+ and the negative voltage V− must be regulated and controlled, so that the voltage across the push-pull switches are minimized. Hence, two DC-DC converters are used to generate the regulated voltages V+ and V−. Each of those voltages is controlled using a feedback loop that drives the pwm of the DC-DC converter. At this point, the conduction power loss of the DC-AC push-pull solid state switches are optimally minimized, but the DC-DC converters are not. In order to minimize the conduction power loss of the DC-DC converters, two multilevel converters with n-array series voltage sources, or n-array series capacitors, are used. The voltage level at the top of each capacitor is carefully selected so that the overall conduction power loss of the DC-DC converters is minimized. The power conduction power loss proportional to the number of levels used but this comes at higher cost and complexity.

The invention discloses a software phase locking method applicable to single-phase and three-phase power systems and belongs to the technical field of grid synchronization. The design thought mainly comprises the following steps: determining a single-phase or three-phase phase-locked loop mode by virtue of a state of a control switch K, and enabling a single-phase voltage to generate two paths oforthogonal signals such as u alpha and u beta by virtue of a phase-shifting algorithm or enabling a three-phase voltage to generate the u alpha and u beta by adopting Clark coordinate transformation;enabling the u alpha and u beta to pass through a positive-sequence component extraction link and a complex band-pass filter so as to obtain a network voltage fundamental positive-sequence component;performing Park transformation to obtain u d and u q, feeding the difference of the u q and 0 into a PI controller to be regulated, adding the output quantity of the PI controller and a rated angularfrequency omega f of the power grid so as to obtain a starting phase angle by using an integrator, and obtaining the final phase angle from the starting phase angle by using a comparator and a selector. The phase locking method provided by the invention can be applicable to the single-phase and three-phase power systems, and the frequency and phase angle of the network voltage can be accurately tracked under asymmetric distorted network voltages.

The invention discloses a grid synchronization harmonic phasor measurement method based on binary search. The method includes the steps: firstly, acquiring and preprocessing signals; secondly, performing search iterative operation for real frequency of harmonic by the aid of a bisection method, ensuring the correct iterative process by comparing and updating harmonic phasor values, performing repeated iterative calculation by taking preset error ratio accuracy as a standard, and approximating the real frequency of the harmonic; and finally, calculating a more accurate harmonic phasor estimation value in an iterative manner. Therefore, the accurate harmonic phasor estimation value is obtained by the aid of traditional Fourier transforming and transferring function amplitude frequency response characteristics. The method can approximate the real frequency and the phasor amplitude of the harmonic and is applied to grid harmonic measurement, positioning accuracy of a harmonic source can be improved, more accurate information is provided for suppressing grid harmonic, and harmonic suppression and management are facilitated.

The invention discloses a double-loop decoupling control method of an active power filter. The double-loop decoupling control method comprises the following steps of collecting relevant signals and converting the relevant signals into digital quantities; obtaining a reference voltage by double-loop decoupling control; and then obtaining a duty ratio signal of a switch tube according to sine pulse width modulation or space vector pulse width modulation, thereby controlling on and off of the switch tube of the active power filter. Grid synchronization and fundamental wave power control are achieved by an inner-loop controller while an outer-loop controller achieves fast and accurate tracking of a harmonic current. According to the control method, a harmonic current extraction process and a phase-locked loop can be omitted, and the calculating amount of a digital control system is greatly reduced. The double-loop decoupling control method plays an important role in reducing the system loss and ensuring safe and stable operation of the system. By the control method, the cost of the device can be reduced when the power quality is improved.

The invention relates to a three-phase photovoltaic inverter anti-islanding method based on phase angle deviation positive feedback, which comprises the steps as follows: carrying out disturbance to a power grid phase with T being used as a cycle, a disturbance phase angle for each time is delta theta under a grid synchronization condition of the inverter; and beginning to accumulate when a power grid voltage phase angle is 0 degree and assuming total accumulating n times within T, namely a current phase leading voltage is n*delta theta degrees, and calculating an error value delta f of the current frequency and the last periodic frequency of the power grid voltage, so that the error value is adopted as phase angle deviation positive feedback quantity. When islanding happens, the frequency of the current voltage is more than that of the last period, the delta f is positive, a control loop leads the plosive value into the positive feedback, the disturbance quantity is changed into n*delta theta+delta f at the moment, and equivalently, the forward disturbance is increased, so that the more the phase disturbance is, the more the voltage frequency deviation is, so as to form a forward deviation positive feedback system; and the system reports an overfrequency error until the frequency exceeds standard, so as to achieve the islanding protection purpose.

Systems, methods, and devices relating to the extraction of parameters for a grid voltage. A multi-block hybrid PLL or hybrid observer receives grid voltage. The grid voltage is received by a harmonic/noise decomposer block which separates the harmonic/noise component of the incoming voltage from the clean voltage signal. The clean voltage signal is then output from the PLL/observer. The clean voltage signal is also sent to an amplitude estimator block which estimates the amplitude of the clean voltage signal. The harmonic/noise component of the input voltage signal is sent, along with the clean voltage signal, to a frequency estimator block. The frequency estimator block then determines the phase angle of the incoming signal as well as the frequency of the incoming voltage signal.

The invention discloses an SAI phase-locked loop method applicable to a non-ideal power grid. The method comprises steps of: extracting three-phase power grid voltage, transforming the power grid voltage to a [alpha][beta] coordinate system through Clarke transform, extracting the positive sequence fundamental wave of the voltage transformed to the [alpha][beta] coordinate system by using an SAI regulator, subjecting the extracted positive sequence fundamental wave to Park transform in order to transform the same to a dq coordinate system, passing the output of a q axis through a PI regulatorto obtain the synchronous angular frequency of the power grid, and obtaining the phase angle of the power grid after integration. The method not only can accurately track the phase under the balance state of the power grid, but also can accurately obtain a power grid synchronization signal under non-ideal power grid environments such as three-phase imbalance, voltage sag or swell, harmonic pollution and frequency jump, greatly expands the application of the phase-locked loop, and improves tracking accuracy of the power grid synchronization signal.

The invention discloses an on-grid/off-grid seamless switching control method for a photovoltaic micro grid. By controlling the power of a tie line at a specified target value, the transient transition time is reduced, and smooth switching from an on-grid mode to an off-grid mode is realized. Full-automatic and reliable switching from an off-grid mode to an on-grid mode is realized by using a micro grid on-grid synchronization protection device. For operation from an on-grid mode to an off-grid mode, the method includes the following steps: (1) refreshing the background data of an energy management system; (2) calculating and acquiring a required active power adjustment compensation value; (3) calculating the adjustable potential range of the external exchange power of an energy storage unit; (4) controlling the power of a tie line at a constant value; and (5) adjusting the power of the tie line to a target value. For switching from an off-grid mode to an on-grid mode, the method includes the following steps: S1, the micro grid operates stably in an off-grid operation mode; S2, the energy management system receives a micro grid grid-connection closing instruction issued by a dispatcher; S3, the synchronization protection device judges the grid connection conditions; and S4, the switching from an off-grid mode to an on-grid mode is completed.

The invention discloses a cable partial discharge positioning method and system based on active synchronization. The method comprises the following steps of: wrapping the outer sheath of the cable with an annular metal plate to form a coupling capacitor; covering both ends of the cable range to be tested with shielding magnetic ring to form a traveling wave boundary; injecting a high frequency pulse into the cable shielding layer as a synchronization signal through a coupling capacitor at one end of the cable range to be detected; extracting a partial discharge pulse signal and a synchronization signal at both ends of the cable range to be detected; and positioning and computing the cable partial discharge source based on the time difference of partial discharge pulse and the synchronization pulse at both ends of the cable range to be detected. The cable partial discharge positioning method and system based on active synchronization use an external annular metal plate to form a coupling capacitor to solve the problem of synchronous injection of the pulse signal, use the time difference between the synchronization signal and the cable partial discharge pulse to complete the local discharge source positioning. Compared with the traditional satellite timing synchronization and fiber synchronization method, it is convenient to implement in the field, and basically eliminates the additional error caused by time synchronization.

An integrated device having energy feedback and blackout emergent functions is composed of an energy feedbacker, a storage battery controller and a storage battery (group). The energy feedbacker is based on the theory of active inversion phase width control, uses lock phase ring technology to track grid synchronization to determine inversion output voltage phase angle and amplitude as PWM controlamount, ensures to feedback electricity to the grid with unit power factor, and supplies electricity in an independent power generation manner when the grid is cut off. The storage battery controlleris based on separated DC/DC conversion to recharge the storage battery (group) and supply electricity to DC bus from the storage battery when the grid is cut off. The energy feedbacker begins to generate electricity within half cycle of blackout of the grid, for the elevator system, the power supply is no different from power supply of the grid. The invention has the following characteristics: 1.the increase of the system cost is small; 2. average system energy saving is over 30%; 3. system wiring is almost unchanged and reliability is not influenced; and 4. emergency security is vastly improved, and the elevator is more humane as a special device.

The invention discloses a timing synchronization method used for an electromechanical transient simulation system and an electromagnetic transient simulation system. the method comprises the following steps: both the electromechanical transient simulation system and the electromagnetic transient simulation system receive first time reference, one of the two serves as the sending end to send synchronization signals transmitted via a first power line channel to the other serving as the receiving end, if a controller judges timing synchronization according to the transmission time of the synchronization signals, the receiving end sends first synchronization success signals to the sending end and the controller; if the controller judges false timing synchronization, the receiving end sends second synchronization success signals to the sending end and the controller after time is adjusted, and the sending end sends third synchronization success signals to the controller after the first or the second synchronization success signals are received. A middle adjuster and a synchronization signal carrying speed detection module are arranged between the sending end and the receiving end, and when the speed detection module detects that the speed of the synchronization signal exceeds the preset speed threshold, the middle adjuster carries out acceleration or deceleration processing.

The invention discloses a control method and system for solving grid-connected impulse currents. The control method includes that phase synchronization is guaranteed by compensating delay of a grid synchronization phase lock angle due to sampling and filtering; inverter vector control is performed through the real-time decomposition value namely the target control reference value of two voltage active and reactive components as well as the compensated grid synchronization phases lock angle to acquire the inverter voltage control vector, loop opening and delay starting are realized, and the amplitude and frequency are assuredly synchronized; in addition, judgment is made through the difference value of inverter line voltage and grid line voltage, and when the difference value is stabilized in a small range, a grid-connected relay is controlled to close, and instant impact current in closing of grids can be assuredly minimized even when three phrases are asymmetrical. With the control method, the phases, the amplitude and the frequency of the inverter voltage and the grid voltage can be strictly synchronized, the grid-connected impact current can be minimized, the impact current of the grid-connected inverter can be controlled during connecting and starting of the grids, and occurrence of the impact current is greatly reduced.

The invention discloses a reactive power compensation method of an intelligent energy storage and power generation system. The method can monitor the power generation device, load unit, energy storage device and SVG equipment in real time for the power fluctuation value of the energy storage and power generation system, and thereby Dynamically adjust the power of the energy storage device for the information source, so as to achieve smooth grid-connected power; it can realize the economical operation of the energy storage power generation system, and suppress voltage fluctuations. By collecting data from the energy storage power generation system, a network architecture model is established. Under the power control strategy, the power factor of the power generation device is guaranteed to be constant, and the economic operation is completed through reactive power regulation.

The invention relates to a harmonic detection method applied to a power distribution network. The method comprises the following steps of (1) obtaining harmonic data of all typical harmonic sources in the grid monitoring system; (2) showing the position of each harmonic source accessing the power system; (3) obtaining the voltage and current of the harmonic source, and analyzing the voltage and current of each harmonic source; (4) calculating the harmonic frequency according to the following formula, and drawing the harmonic curve according to the harmonic frequency of the harmonic source, and (5) judging the harmonic voltage level according to the harmonic frequency. The method has the advantages that the method is simple and quick in calculation and high in harmonic detection precision, the harmonic voltage level is analyzed by calculating the harmonic frequency, and the grid synchronization angle is not required, and the method can be used for single-phase, three-phase three-wire or three-phase four-wire systems for the detection of harmonic components.

A permanent-magnet wind power generation system grid synchronization method comprises three parts: voltage positive sequence component separation, a novel phase-locked loop and network-side converter control. The novel phase-locked loop used in the invention is a new method for separating the positive sequence components of the asymmetric grid voltage under the double synchronous rotational coordinates by using an all-pass filter and the mathematical operation and then extracting phases. The novel phase-locked loop is suitable for use in the grid synchronization of a direct-drive permanent-magnet wind power generation system, and has better performance in the case of unbalanced input voltage.