54results about How to "Realize low voltage ride through" patented technology

The invention discloses an improved positive-negative sequence component separation method. By adopting the method, bigger errors which are caused by a 'one-quarter cycle delay' method used in a one-quarter cycle after the happening and the ending of unsymmetrical faults are avoided, and the advantages of simplicity, high detection performance and the like of the 'one-quarter cycle delay' method are well used. The invention also discloses a method realizing low voltage ride through of a single-stage photovoltaic grid-connected inverter by using the improved positive-negative sequence component separation method. By adopting the methods, low voltage sag of an electric network can be quickly detected, the influence caused by unsymmetrical sag negative sequence components is inhibited, reactive power is provided, the voltage of a support grid connection point is recovered, and the requirement on the low voltage ride through of a high-power grid-connected inverter is met.

The invention discloses a photovoltaic grid-connected inverter low-voltage ride through method based on reactive current injection. The method is based on a low-voltage ride through strategy supported by reactive current voltage, is aimed at an photovoltaic grid-connected inverter, switches voltage and current double-loop control of an inverter circuit into current single-loop control, switches an maximum power point tracking (MPPT) of a boost circuit into voltage stability control, and finally achieves low-voltage ride through of the photovoltaic grid-connected inverter. The method is simple and practical. When a power grid breaks down and the voltage of the power grid is reduced, the photovoltaic grid-connected inverter can be made to achieve low-voltage ride through by switching the control strategy of the photovoltaic grid-connected inverter, and the voltage of the power grid is supported to recover.

The invention provides a dynamic reactive current direct control method by a doubly-fed wind turbine generator set during a grid fault. The method includes the following steps: a, judging whether a doubly-fed wind turbine generator enters a low voltage ride through mode or not, b, in normal operation, adopting a double closed loop control mode with the power on the outer loop and the current on the inner loop for the wind turbine generator set, c, if a protective action is not triggered during the fault, performing direct current control by the wind turbine generator after the wind turbine generator enters the LVRT mode, and d, if the grid fault causes the overcurrent of a rotor current converter or the overvoltage of a direct current capacitor, after the current converter enters a lockout state, performing protective action by a crowbar to bypass the current converter until the set engaged time is over and a frequency converter is controlled again. The dynamic reactive current direct control technology by the doubly-fed wind turbine generator set during the grid fault can achieve that during the fault, the wind turbine generator set injects a reactive current into a power grid fast and provides voltage support, and helps the wind turbine generator set to achieve low-voltage riding through.

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 utility model provides a wind farm super capacitor energy storage type unified power quality conditioner which comprises a compensation transformer, a series connection compensator, a parallel connection compensator, a current limiting circuit, a super capacitor group, a bidirectional DC/DC chopper circuit, a signal acquisition conditioning circuit, a control circuit and a driving circuit. The conditioner has two control modes which are a power regulating mode and a low voltage ride through mode. In the power regulating mode, the wind power unit assembly output power quality can be improved, in the low voltage ride through mode, namely in a fault condition, the blower outlet voltage can be maintained and is not reduced, and the current influence on a blower system is avoided until the voltage is recovered and the low voltage ride through is realized. Electric energy generated by the blower in a fault stage can be stored in the super capacitor group, the energy is transmitted to the power grid after a power grid is recovered to a normal state, and the waste of the electric energy is avoided. The conditioner has versatility and can be applied to wind farms of various blower generations of a fixed speed induction generator (FSIG), a permanent magnet synchronous generator (PMSG) and a double-fed induction generator (DFIG).

The invention relates to a double-fed wind driven generator system and a low-voltage through control method. According to the double-fed wind driven generator and the low-voltage through control method on the basis of a Crowbar circuit and a battery energy storage device, the low-voltage through capability can be effectively improved under the condition of large-range voltage drop, the double-fed wind driven generator system can be still kept to be connected with a power grid, and the stability of a wind power system is improved.

The invention discloses a low-voltage crossing method of two-stage type photovoltaic grid connected system of variable power tracking path, which belongs to the field of new energy electric power system and micro power grid technology. Under the prerequisite that the original configuration of a two-stage three phase photovoltaic grid connected system is not changed and no auxiliary device is added, the power tracking path can be adjusted through the feed-forward control of the falling amplitude of voltage, the voltage at the photovoltaic cell end can be changed in a real-time manner, and the output of the photovoltaic cell power can be rapidly and effectively controlled, and the balance of power at two sides of an inverter can be realized. Through the cooperative control with a grid connected inverter, it can be guaranteed that under the prerequisite that the grid connected output of current of the inverter is not out of limit, active power and reactive power can be provided for the power grid as more as possible, the recovery of power grid voltage can be supported to the most extent, and the zero-voltage crossing of the photovoltaic grid connected system can be realized. Comparedwith the conventional control method, the invention is advantageous in that no additional device is required; safe and stable running of the system can be realized; the cost of the photovoltaic powergeneration system can be reduced, and practicality is better.

The invention provides a three-phase phase-locked loop method appropriate for photovoltaic grid connected low voltage ride through and relates to the field of solar power generation power supply, in particular to a three-phase phase-locked loop which has a function of low voltage ride through. The three-phase phase-locked loop method appropriate for the photovoltaic grid connected low voltage ride through solves the problems that an existing phaselock technique needs to consider influences of zero wander, and an existing detection method does not consider influences brought by measuring voltage deviation on voltage detection. The three-phase phase-locked loop method appropriate for photovoltaic grid connected low voltage ride through includes a first step of inputting network voltage v to a second-order orthogonal signal generator and outputting two sinusoidal signals v' and qv', wherein phases of the two sinusoidal signals differs by 90 degrees; a second step of calculating the signals v' and qv', obtaining line voltage amplitude VRMS, and converting the line voltage amplitude VRMS into phase voltage amplitude VP; a third step of inputting the signals v' and qv' into the phase-locked loop, locking a line voltage phase angle theta1, detecting the line voltage phase angle theta1, and converting the line voltage phase angle theta1 into phase voltage phase angle thetap; and a fourth step of conducting grid connection according to the phase voltage amplitude VP and the phase voltage phase angle thetap by means of an inverter current control strategy, and achieving the photovoltaic grid connected low voltage ride through. The three-phase phase-locked loop method appropriate for the photovoltaic grid connected low voltage ride through is appropriate for photovoltaic power stations.

Provided is an integrated low-voltage ride through regulation and control device of wind power generation. The integrated regulation and control device is used immediately that a voltage sag fault is detected in a low-voltage ride through system. An inverter obtains stable DC voltage from a DC energy storage device, a compensation voltage is generated by inversion, and the compensation voltage is connected in series to the system via a filter. The sum of the compensation voltage and the voltage after sag of the electrical network equals the voltage when the electrical network works normally, so that a generator end is kept in normal operation; and at the same time, a fixed capacitor implements reactive compensation, and an energy-consuming resistor consumes active power emitted by the generator end when the voltage is reduced transiently.

The invention provides an MMC-based low-voltage ride through control method and system of a photovoltaic grid-connected inverter. On the basis of traditional inner current loop and outer voltage loop double closed-loop vector control, when a grid-connected point voltage drop is detected, a reactive current instruction value as shown in the specification is redistributed by judging the voltage drop degree to achieve reactive current injection; the capacitor voltage fluctuation range of an MMC sub-module is adjusted by optimizing bridge arm current; a new active current instruction value is introduced to limit active current; and the active current is limited, so that low-voltage ride through is achieved and safe photovoltaic grid-connected operation is ensured. Through the system and the method, capacitor voltage fluctuation is suppressed by optimizing bridge arm loop current; output reactive power is increased; and the capacitor voltage fluctuation range of the sub-module is optimized by controlling reference voltage of the sub-module, so that the problem that the capacitor voltage fluctuation of the MMC sub-module is out of the limit during reactive injection is solved; and low-voltage ride through is smoothly achieved.

The invention discloses a power control device and method used for low voltage ride through of a direct-drive permanent magnetic synchronous wind driven generator. The device comprises a generator speed measuring module, a direct current voltage measuring module, a generator terminal voltage measuring module, a generator terminal current measuring module, a grid measurement voltage measuring module, a grid measurement current measuring module, a maximum power tracking and controlling module, a grid measurement power measuring module, a wind speed measuring module, a pitch angle measuring module and a power coordination control module. The invention further provides the power control method, active power and reactive power of a unit in a temporarily stable state period can be coordinated and controlled, so that the direct-drive wind driven generator effectively achieves low voltage ride through in a maximum power tracking area and a power limiting area, and the unit can provide dynamic reactive support for a power grid in a low-voltage transient state period. The power control device and method can use the control means of the direct-drive wind driven generator self sufficiently and reasonably without adding unloading hardware, and the power control method is easy to implement and remarkable in effect.

The invention discloses an inverter low voltage riding-through control method for a weak network far-end severe voltage failure. The method comprises the steps of when the weak network far-end severevoltage failure occurs, switching an active current control target quantity and a passive current control target quantity into zero in an inverter, then designing the active current control target quantity and passive current control target quantity input of the inverter, performing transient-state transition, optimizing phase-locked loop, current inner loop and voltage feed-forward parameters, and improving the stability and dynamic control performance of the inverter in low voltage riding-through. According to the inverter low voltage riding-through control method for the weak network far-end severe voltage failure, unstability of the inverter when the severe voltage drop failure occurs at the far end under a weak network can be avoided, the end voltage of the inverter can be effectivelyrecovered, certain active power can be injected into the inverter for supporting the power network frequency, and the method can be applied to achieving low voltage riding-though of an inverter system when the severe voltage failure occurs at a new energy power station grid-connected system far end with the inverter being an interface under the weak network.

The invention relates to the running control technique of wind power generation equipment, in particular to a low voltage ride through control method for a full-power high-speed permanent synchronous fan. The method is that mechanical load impact on a machine set when a power grid is in fault can be reduced by reducing machine side converter direct torque control reference preset orders Te* on the motor side of a wind power generation system, and simultaneously a crowbar circuit with an energy storage link is arranged on the direct current side to absorb and store redundant energy when the power grid is in fault to achieve low voltage ride through of the fan. The method can reduce load of a wind power generation set when the power grid is in fault, enables the machine set to run safely and stably and can absorb, store and utilize redundant energy when the power grid is in fault.

The invention provides a doubly-fed type wind-power-improved Crowbar circuit which is low in circuit cost, high in reliability, simple in structure and simple in control strategy. The improved Crowbar circuit meets the requirement of an existing Crowbar circuit for protecting a doubly-fed wind generator and overcomes the defect that in the voltage drop process, low voltage ride through can not be achieved through the existing Crowbar circuit. According to a doubly-fed wind generator low voltage ride through control method, the defect that a Crowbar protection circuit on the rotor side can not provide reactive power support for a power grid is mainly overcome by arranging the Crowbar protection circuit on the stator side. The doubly-fed wind generator low voltage ride through control method is mainly characterized in that control is achieved through rotor exciting voltage when the voltage drop amplitude is smaller than the limit value of rotor exciting voltage control; control is achieved through the combined action of the rotor exciting voltage and the Crowbar protection circuit when the voltage drop amplitude is larger than the limit value of rotor exciting voltage control. When the method is applied, the low voltage ride through capacity can be effectively improved under the condition of the wide-range voltage drop, a doubly-fed wind generator system can be kept connected with the power grid all the time, and stability of the wind generator system is improved.

The invention discloses a virtual synchronous generator low-voltage ride-through method and system based on virtual voltage drop. The method comprises the steps of: enabling a power control loop to be converted into a freezing mode from a conventional virtual synchronous mode when a power grid voltage drops, guaranteeing the stability of a system, through adding virtual fault voltage drop, enabling modulation waves to be equal to a difference value between the internal potential and the virtual fault voltage drop, suppressing an overcurrent when the fault occurs, and outputting reactive power meeting the national standard requirement by an inverter, thereby facilitating the recovery of the power grid voltage; and when the voltage returns to normal, converting the power control loop into a recovery mode from the freezing mode, and in order to suppress transient current during fault recovery, adding virtual recovery voltage drop, so that the modulation waves are equal to a difference value between the internal potential and the virtual recovery voltage drop. The strategy is suitable for a control structure with or without a current inner loop, and low voltage ride through of a virtual synchronous generator can be realized without mode switching.

The invention discloses a low-voltage ride-through method and device for a feed pump turbine power generation system. The low-voltage ride-through method comprises the following steps: detecting the voltage and current of a power grid; judging whether the power grid voltage and the power grid current exceed corresponding threshold values or not; and if the power grid voltage and the power grid current both exceed the corresponding threshold values, switching a direct-current voltage control outer ring of the power generation system to a first converter, and meanwhile, switching rotating speedcontrol outer rings of a water feeding pump, a steam turbine and a power generator to an air inlet valve of the steam turbine to realize low-voltage ride-through of the power generation system. According to the invention, the input active power can be rapidly reduced when the power grid has a low-voltage fault and the grid-connected power is reduced, so that the rotating speed of the power generation system is stabilized, the converter is prevented from being damaged by excess power or the rotating speed is prevented from rising, the robustness of the power generation system can be improved, the adjustment mode is simple, and the dynamic response of the control process is rapid.

The invention relates to a virtual synchronous machine low-voltage ride-through comprehensive control method. When a voltage drop fault occurs in a power grid, a positive-sequence d-axis component of the voltage of the power grid is fed forward to a VSG reactive power excitation voltage regulation equation of a differential-free link, so that the output voltage of the VSG can quickly follow the drop of the amplitude of the voltage of the power grid; the VSG output reactive power instruction value is increased according to the voltage drop depth, and meanwhile, the VSG output active power instruction value is reduced to avoid VSG steady-state output overcurrent; when the VSG output inductive current exceeds a set threshold value, a virtual resistor is input to suppress transient overcurrent; and when three-phase voltage asymmetric drop occurs in a power grid, VSG three-phase output current balance, VSG output active power frequency doubling pulsation suppression and VSG output reactive power frequency doubling pulsation suppression are realized by setting current instruction compensation values of different positive and negative sequence d-axis and q-axis current loops. According to the method, the low voltage ride-through capability of the VSG is improved, and the output electric energy quality of the VSG during the voltage fault of the power grid is improved.

The invention belongs to a wind power generation technology, and relates to a system and a method for controlling low voltage ride through of a high-power direct-driven permanent magnet wind power generation system. The system comprises a full power converter which is positioned between a wind power generator and a power grid and consists of a machine side converter and a grid side converter, and a Crowbar circuit is connected onto a direct current bus of the full power converter. According to the system and the method, protection for the converter can be realized well when the voltage of the direct-driven permanent magnet wind power generation system drops in the power grid, and the low voltage ride through can be realized well through the cooperation with a converter system.

A current converter control method for improving the low-voltage ride-through capability of a doubly-fed fan comprises the steps that after the voltage drops suddenly, the voltage of a direct-currentcapacitor and the current ir of a rotor are monitored constantly, and whether the voltage of the direct-current capacitor or the current of the rotor exceeds a limit value or not is judged; when the direct-current capacitor voltage or the rotor current ir exceeds a limit value, an active Crowbar protection circuit is triggered; when the direct current capacitor voltage and the rotor current are both lower than the limit value and no out-of-limit is kept in the two cycles, the active Crowbar protection circuit is exited, and PI control of the rotor side converter and the network side converterare switched into comprehensive interference suppression control at the same time; and after voltage drop is recovered, PI control is switched back, and the purpose of low-voltage ride through of thewind power plant under sudden power grid fault drop is achieved. Compared with a PI control strategy, the comprehensive LVRT control strategy designed by the invention can make full use of the outputcapability of the converter, has the better transient control performance in the voltage drop period, and can effectively meet the low-voltage ride-through requirement of the doubly-fed fan.

The invention discloses a reactor key electric valve motor low-voltage ride-through control method and a controller applied to low-voltage ride-through of a reactor key valve motor. For problems thatthe valve opening and closing actions of a traditional reactor valve control mode become slow under the condition that power grid voltage drops and the safety requirement of a system cannot be met, the invention proposes a valve motor low-voltage ride-through method adopting voltage closed-loop feedback weak magnetic compensation and the controller, theoretical analysis and experiments show that the control mode of the invention has obvious advantages compared with a traditional valve motor control mode, the rotating speed of the valve motor can be stabilized under the condition of voltage drop, and the low-voltage ride-through of the reactor key valve motor is achieved.

The invention discloses a wind power generation grid-connected system transient state stabilization control method based on automatic current adjustment. The method comprises the steps of: converting a three-phase voltage signal of a grid-connected point from a three-phase static coordinate system to a two-phase rotating coordinate system in a power grid voltage d-axis orientation mode if a system enters a low voltage ride-through mode, and obtaining two-phase DC values Usd and Usq; with the usq used as an input signal of a phase-locked loop, calculating the output angular frequency, the output angular frequency deviation and the additional self-adaptive q-axis current adjusting quantity of the phase-locked loop in sequence; calculating d-axis and q-axis output current instruction values of the wind power generation grid-connected system in the low-voltage ride-through period; and sequentially controlling the active and reactive current instruction values in the low-voltage ride-through period, so as to make the wind power generation grid-connected system have a balance point again and successfully realize low voltage ride through. The transient stability of a wind power generation system can be improved only by adaptively changing the control strategy of the q-axis current instruction of the wind power generation grid-connected system.