46results about How to "Stable DC side voltage" patented technology

The invention belongs to the field of applied superconducting power electronics, and in particular relates to a synchronizing current and voltage decoupling control method of a voltage-source-type unit power factor high-temperature superconducting energy storage system converter. The control method is characterized by comprising the following steps: designing a voltage outer ring control module at a direct-current side and a current inner ring control module at an alternating-current side respectively with respect to a mathematical model of a superconducting energy storage system converter under dq synchronizing rotary coordinates; controlling an 'H'-shaped bidirectional DC-DC (direct-current to direct-current) chopper based on an SPWM (sinusoidal pulse width modulation) technology by adopting a hysteresis loop PI current closed-loop control method in a charge mode and a hysteresis loop PI voltage closed-loop control method in a discharge mode; and finally implementing the synchronizing current and voltage double-fed control method of a voltage-source-type SMES (superconducting energy storage system) converter according to the active current requirement and the current value of a superconducting magnet under the power grid unit power factor. The control method provided by the invention has the advantages of multi-stage current decoupling control, rapid response speed, easy implementation of control algorithm and the like, and the method is especially suitable for the application occasions for improving the electricity energy quality of a power grid and inhibiting the low-frequency oscillation of a power system and the like.

The invention discloses a control and switch method for redundant submodules of a modular multilevel converter. The converter monitors a voltage value of a redundant submodule support capacitor in the normal running process. When voltage of two ends of the redundant submodule support capacitor of a phase of bridge arm is larger than or equal to a first preset value and smaller than or equal to a second preset value, the redundant submodules are in a switch-out state; when the voltage of two ends of the redundant submodule support capacitor is smaller than the first preset value, the on-off states of a first switch tube and a second switch tube are determined according to a modulation mode and a submodule direct voltage balance control strategy; and till the voltage of two ends of the redundant submodule support capacitor is equal to the second preset value, the second switch tube is connected for afterflow, otherwise, a message of a overvoltage fault of the redundant submodules is sent, so that the protection action is executed. According to the control and switch method, the redundant submodules can be connected to bridge arms at the highest speed to replace fault submodules, so that the stability of voltage of the direct current side of the converter is maintained, the balance in voltage between capacitors of the submodules of the upper bridge arm and the lower bridge arm is kept, the reliability is improved, and the availability ratio is increased.

The invention provides a method for controlling low-voltage ride through of a cascaded photovoltaic grid-connected inverter. The method is based on two common mathematical models of grid-side voltage under the condition of an unbalanced grid fault, and the laws between the three-phase grid-side voltage amplitude and phase under different fault conditions are summarized. A method for controlling a cascaded photovoltaic grid-connected inverter under different fault conditions is derived based on the laws. By setting the on-off state of an H-bridge power device, a bypass power unit controls low-voltage ride through of a cascaded photovoltaic grid-connected inverter. When a bypass is generated, the optimal modulation ratio of a normal operation unit is recalculated, and a carrier phase shift module is adjusted to produce a new PWM pulse signal. The method can ensure that a photovoltaic grid-connected inverter outputs symmetrical three-phase current during grid-side voltage failure and enable the photovoltaic grid-connected inverter to run under unit power factor, and is of great significance to ensuring safe and stable operation of the power grid after large-scale photovoltaic power integration.

The invention discloses a fractional order-based adaptive fuzzy sliding-mode control method for an active power filter. The method specifically comprises the following steps: (1) building a mathematic model of the active power filter as shown in the specification; and (2) designing a fractional order-based adaptive fuzzy sliding-mode controller as shown in the specification. The fractional order-based adaptive fuzzy sliding-mode control method can ensure real-time tracking on a harmonic current, strengthens the dynamic performance of a system, improves the robustness of the system and can still keep good performance when an external load changes; the condition that the active power filter runs along a sliding-mode track is ensured through designing a sliding-mode variable controller; the fractional order-based adaptive fuzzy sliding-mode controller is designed for approaching the nonlinear part in the active power filter; real-time tracking on an instructional current can be ensured and the robustness of the system can be strengthened by designing an adaptive fuzzy controller; a fractional order module is introduced to the sliding-mode controller and the adaptive controller; and compared with an integral order, a tunable item is added, so that the overall performance of the system is improved.

The invention provides a high-voltage ride-through method for a double-fed wind turbine generator set. The high-voltage ride-through method comprises the following steps of 1, collecting a three-phase voltage U<abc> of a grid-connection point of the double-fed wind turbine generator set, and calculating a fundamental wave positive sequence voltage U1 according to the three-phase voltage U<abc>; and 2, determining whether the generator end voltage of the double-fed wind turbine generator is increased or not according to the value of the fundamental wave positive sequence voltage U1, if so, enabling a rotor side current convertor to start a reactive voltage compensation control strategy, and enabling a grid side current converter to start a direct current side voltage control strategy so as to realize high-voltage ride-through of the double-fed wind turbine generator set. Compared with the prior art, a hardware protection circuit is not required to be added within a 130%Un range by adoption of the high-voltage ride-through method for the double-fed wind turbine generator set provided by the invention; and the high-voltage ride-through of the double-fed wind turbine generator set can be realized by only coordinative control of the rotor side current convertor and the grid side current converter of the double-fed wind turbine generator set.

The invention relates to a UPQC for flexibility power transmission and distribution of a power system, in particular to a high-capacity UPQC and a control method of the high-capacity UPQC. The high-capacity UPQC is applied to the parallel-connection side of the UPQC by using the structure that a secondary side of a multi-winding transformer is connected with an H-bridge convertor. Three phases on the parallel-connection side are equivalent to three single-phase rectifier models connected to line voltage in a cross mode. As being controlled independently, each H-bridge rectifier is not affected by unbalance of three-phase voltage, and the stability of voltage across the direct current side of the UPQC when network voltage fluctuates is facilitated. A control method based on virtual orthogonal coordinate conversion is adopted, the single-phase rectifier models on the parallel-connection side of the UPQC are equivalent to a three-phase rectifier model, the functions of the controllable power factor and harmonic suppression of a three-phase rectifier are achieved, and all functions of the three-phase rectifier on the condition of the symmetric system voltage can be completely achieved.

The invention discloses a control method of the DC bus voltage of cascading multi-level power quality conditioners. The control method is verified by simulation through a simulink module in a MATLAB (Matrix Laboratory), meanwhile, a small experimental prototype with the capacity of 30 kVA and formed by connecting two single-phase full bridge unit modules in series is set up in the laboratory, and the control method is verified by experiments. Both simulation results and experiment results can verify that the control method can well stabilize the DC side voltage of the single-phase full bridge unit modules to equal to a given value, increase the utilization rate of the DC bus voltage and provide a good reference value for engineering application.

The invention provides a three-level four-leg active filter compensation distribution network neutral current control method. The method includes the steps of extracting harmonic waves and the sum of negative sequence components and zero sequence components of a line current as a command current of the controlling; setting the alternating current side three-phase current of an active filter and a neutral current as feedback currents, and performing feedforward decoupling control and dq0-abc conversion on each current component of dq0 axis for outputting three-phase voltage after respectively performing abc-dq0 conversion on the command current and the feedback currents; separately performing compensation control on the neutral current. The purpose of direct current side voltage balance and stability can be achieved through direct current side voltage stability and balance control. The three-level four-leg active filter compensation distribution network neutral current control method can effectively solve the problems such as overcurrent of a neutral line due to load imbalance in a three-phase four-wire system and is quick in response of a control system, capable of achieving dynamic real-time compensation and good in control effects.

The invention relates to a non-liner switching control method of a single-phase shunt active power filter, comprising the following steps: 1) building an error model of a switching system; 2) calculating the liapunov function V=xTPX of each subsystem by the linear system theory, and judging: (1) judging whether each subsystem moves in the area, if yes, proving that the subsystem is convergent and the state variable of the system approaches to zero, and switching the switching system to a corresponding subsystem, wherein in the control input of the system, arg means that a subscript satisfying the expression is taken; (2) if two subsystems both move in the area, proving that two subsystems are convergent and can cause the state variable of the system to approach to zero, calculating the subsystem which causes the switching system to be switched to a control input decision, and ensuring the highest APF convergence rate; and 3) under the action of control input u(t), carrying out precise compensation on harmonic current in a power grid by the APF.

The invention discloses a parallel connection hybrid type active power filter and a control method thereof. The parallel connection hybrid type active power filter comprises an inverter, an output filter, a five-time passive filter, a seven-time passive filter and a shunt inductor. The five-time passive filter and the seven-time passive filter are directly connected in a grid in parallel. The seven-time passive filter and the shunt inductor are connected in series. The inverter is connected to the middle point of the seven-time passive filter and the shunt inductor after passing through the output filter. The control method is a recursive integral PI control method based on membership clouds. A membership cloud model is used for carrying out on-line adjustment on a proportionality coefficient and an integral coefficient of a recursive integral PI controller, and the response performance of a control system is improved. The parallel connection hybrid type active power filter and the control method thereof can be used for carrying out dynamic and real-time governance on each subharmonic current and reactive current, and have higher cost performance and engineering practicability.

The invention discloses a three-phase four-switch active electric power filter and a control method thereof. The active electric power filter comprises an inverter. The inverter comprises two switch arms and a DC capacitive branch. The two switch arms and the DC capacitive branch are connected in parallel. The two switch arms are respectively composed of two power switches which are connected in series. The inverter is parallelly connected between a three-phase electric network and a three-phase load through an output wave filter. The control method is an increment type PID control method based on a two-dimensional subordinated cloud model. The two-dimensional subordinated cloud module is utilized for performing on-line adjustment on proportion coefficient, integral coefficient and differential coefficient of an increment type PID controller, thereby improving response performance of a control system. The three-phase four-switch active electric power filter can perform dynamic real-time treatment on each sub-harmonic current and wattless current, thereby greatly improving compensation performance of the system, saving cost, and realizing higher engineering practicability.

The invention relates to a photovoltaic power generation system low voltage ride through reactive control method. The method comprises the following steps: (1) calculating and storing output active power Ppre of a photovoltaic grid-connected inverter before faults; (2) detecting whether actual voltage E of a grid-connected point drops, and 0.2EN<=E<=0.9EN, EN being nominal voltage of the grid-connected point, if yes, executing step (3), if no, using a grid-connected control method when network voltage is normal to control; (3) switching the photovoltaic grid-connected inverter to a low voltageride through reactive control mode, specifically including (31) obtaining maximum active power Pmax the photovoltaic grid-connected inverter allows to output, (32) if Ppre<=Pmax, making the photovoltaic grid-connected inverter work in a MPPT mode, otherwise, making the photovoltaic grid-connected inverter work in a non-MPPT mode; (4) returning to the step (2) and executing in a looping manner. Compared with the prior art, the method makes use of capacity of the photovoltaic inverter to the maximum extent, investment of reactive equipment is saved, and resources are saved.

The invention relates to a reactive compensation and vector control method for a doubly-fed wind turbine generator, and belongs to the technical field of operation and control of doubly-fed wind turbine generators in new energy power generation. In order to avoid off-grid operation of the doubly-fed wind turbine generator caused by voltage drop of a power grid, the output reactive power of a gridside is adjusted in a reactive power compensation mode by changing a grid side converter control method on the one hand; and on the other hand, in consideration of transient characteristics of a stator flux linkage during a voltage drop period, a rotor side converter adds a stator flux linkage change item caused by the voltage drop on the basis of the traditional vector control method, and the DCside overvoltage and the rotor side overcurrent are suppressed during the voltage drop period and after the fault is removed so as to help the recovery of the system voltage. For research of a grid-side and rotor-side converter cooperative control method, off-grid operation of the doubly-fed wind turbine generator caused by the voltage drop of the power grid can be effectively avoided, the systemfault voltage is helped to be recovered, and the stability of the power grid is maintained.

The invention provides a single-phase power factor correction circuit based on three-tube five-level topology. The circuit comprises switching tubes Q1, Q2 and Q3, one side of an AC power supply is connected with the anode of a diode D1 and the cathode of a diode D2, and the connection nodes form an end point b; the other side of the AC power supply AC is connected with one end of an inductor L, and the other end of the inductor L is connected with the anode of a diode D3 and the cathode of a diode D4 and the connection nodes form an end point a; the cathode of the diode D7 is connected with one end of a capacitor C1, and the connection node forms an end point p; the other end of the capacitor C1 is connected with one end of a capacitor C2, and the connection node forms an end point n; theother end of the capacitor C2 is connected with the anode of the diode D8, and the connection node forms an end point m; the drain electrode of the switching tube Q1 is connected with the cathode ofthe diode D1 and the anode of the diode D7 respectively, and the connection node forms an end point c; the source electrode of the switching tube Q3 is connected with the anode of the diode D2 and thecathode of the diode D8, and the connection node forms an end point d. The end point a, the end point c, the end point d and the end point n form four symmetrical ports. The correction circuit adoptsmultiple levels so as to have the advantage that the voltage stress of the switching tube is low.

The invention discloses a wind storage combined wind power converter and a control method thereof. The energy storage unit is arranged on the direct current side of the wind power converter, namely the energy storage unit is used for replacing a Chopper device in the prior art, so that the bidirectional regulation of the direct current side voltage of the wind power converter can be realized through the charging and discharging functions of the energy storage unit; therefore, the direct-current side voltage of the wind power converter is kept stable, and the stability of the wind power converter is improved. In addition, the energy storage unit can cooperate with the wind turbine generator to enable the wind storage combined wind power converter to have the function of achieving the powerauxiliary service control target, such as primary frequency modulation, energy transfer and power smoothing.

The invention discloses a high-speed railway negative-sequence and harmonic compensation system based on a two-phase three-wire system converter, comprising two single-phase reducing transformers and a two-phase three-wire system converter, wherein the primary sides of the two single-phase reducing transformers are connected with two single-phase power-supply arms arranged in a three-phase V / V tractive power-supply system, and both ends of the secondary sides of the two single-phase reducing transformers are connected correspondingly with the primary sides, thereby the secondary sides of the two single-phase reducing transformers form three wires; the two-phase three-wire system converter comprises three switch arms, wherein one switch arm is connected with two single-phase voltage sharedground wires, and the other two switch arms are respectively connected with the other two wires in the secondary sides of the two single-phase reducing transformers by an inductor. Compared with two common single-phase converters, the high-speed railway negative-sequence and harmonic compensation system reduces one switch arm and does not increase the current level of a switch device. Compared with the common three-phase converter, the high-speed railway negative-sequence and harmonic compensation system reduces one output inductor to save cost, and the voltage utilization of a direct currentside is one time higher.

The present invention discloses a microgrid energy storage converter control method. The method comprises three parts consisting of a microgrid energy storage converter, a voltage outer ring and a current inner ring. The present invention provides a grid voltage orientation double closed loop control strategy fusing feedforward decoupling control. On the basis of a three-phase voltage source converter (d, q) coordinate system mathematic model, grid voltage vector orientation and synchronous rotation are performed, the current inner ring employs the feedforward decoupling direct current control to decouple active current and reactive current so as to improve tracking speed and precision of the inner ring current and enhance the response speed of the outer ring voltage. A simulation result show that: the response speed of the converter system is fast, the grid-side current harmonic content is low, voltage at the direct current side is stable and the ripple voltage is small so that a unit power factor can be used for both-way operation. The provided control method is effective and feasible, and has an application reference value.

The invention discloses a back-stepping sliding-mode adaptive fuzzy control method of an active power filter. The method comprises the steps of (1) building a mathematic model of the active power filter; and (2) designing a fractional order-based back-stepping sliding-mode adaptive fuzzy controller. By the back-stepping sliding-mode adaptive fuzzy control method of the active power filter, real-time tracking of harmonic current can be ensured; the dynamic property of a system is strengthened; the robustness of the system is improved; and good property can still be kept when an external load changes. The condition that the active power filter runs along a sliding-mode track is ensured through designing a sliding-mode variable controller; aiming at the defects of the back-stepping control law, the fuzzy controller is adopted to approach a nonlinear part in the active power filter; real-time tracking of instruction current and strengthening of the robustness of the system can be ensured through designing the adaptive fuzzy controller; fractional order modules are introduced into the sliding-mode controller and the adaptive controller; and compared with an integer order, the fractional order has the advantage that a tunable item is added, so that the overall performance of the system is improved.

The invention relates to a one-cycle vector control-based SAPF control method and system. The method comprises the following steps of 1) obtaining three phases of voltage zero-sum components of a power supply separately, wherein each zero-sum component is a synthetic component of a positive sequence component and a negative sequence component; 2) performing regional division on a voltage cycle according to zero crossing points of the three phases of voltage zero-sum components into six regions in total; 3) obtaining a control equation based on the one-cycle vector control on each region according to a regional division result; 4) obtaining the working state of each phase of bridge arm switch on an SAPF inverter on each region according to the regional division result and the corresponding control equation based on the one-cycle vector control, and generating a corresponding switch driving signal according to the working state; and 5) ensuring the direct current side voltage stability of the SAPF inverter by adopting PSO-optimized PI control. Compared with the prior art, the control method and system have the advantages of circuit simplification, wide applicable range, loss reduction, optimization control and the like.

The invention discloses an improved control method and system for a STATCOM / BESS device in a microgrid, belonging to the field of power quality optimization. A STATCOM is connected between a power output end and a load of the power grid , and battery packs are connected in parallel at both ends of the voltage inverter in STATCOM to form STATCOM / BESS, and the power output end is sequentially connected with an instantaneous power calculation module, a power prediction module, and an SVPWM modulation module. The output end of the SVPWM modulation module outputs a target vector signal to drive the three-phase bridge arm in the STATCOM. The control method improves the STATCOM / BESS device in the microgrid, so that the STATCOM / BESS system has small output power fluctuation, stable DC side voltage, good power tracking control and fast power adjustment capability.

The invention discloses a control method for a permanent magnetic synchronous generator of an automobile. The permanent magnetic synchronous generator is driven to generate power by use of an automobile prime motor and stably outputs 42V DC voltages after passing through a PWM rectifier, and after an automobile storage battery is charged, power is supplied to an automobile load. The method has the following advantages: 1, the problem in the prior art is solved that rectifier control of a permanent magnetic synchronous generator needs a high-precision absolute position encoder and other devices for detecting the position of a rotor magnetic pole, the interference immunity of a system is improved, and the system cost is decreased; 2, the design is reasonable, the practicality is high, and the operation is simple; 3, weak-magnetic control of the generator at a high speed is realized through closed-loop control, and stability of DC-side voltages in case of the high speed is realized; and 4, DC drift caused by a pure integrator is effectively inhibited by replacing the pure integrator with a variable-frequency filter.

The invention relates to a unified power quality controller UPQC for flexible power transmission and distribution in a power system, in particular to a large-capacity unified power quality controller UPQC and a control method thereof. The structure of the unified power quality controller using the secondary side of the multi-winding transformer connected to the H-bridge converter is applied to the parallel side of the UPQC. The three-phase parallel side is equivalent to three single-phase rectifiers modeled across the line voltage. Since each H-bridge rectifier is independently controlled, it is not affected by the unbalanced three-phase voltage, which is beneficial to the stability of the DC side voltage of the UPQC when the grid voltage fluctuates, and a control method based on virtual orthogonal coordinate transformation is adopted to make the parallel side of the UPQC The single-phase rectifier device is equivalent to a three-phase rectifier model, which has the functions of controllable power factor and harmonic suppression of the three-phase rectifier, and can fully realize all the functions of the three-phase rectifier under the condition of symmetrical system voltage.

The invention provides a controlling method for a grid-connected photovoltaic system including a two-stage voltage inverter. The method comprises: step one, a direct-current-side voltage value and alternating-current-side three-phase voltage and current values of an inverter and an input voltage value of a boosted circuit of the inverter are collected; step two, according to practical measurement data, whether the direct-current-side voltage value of the inverter reaches the 1.1 times of a rated voltage is determined, and an input direct-current voltage of the inverter is controlled correspondingly or an outlet voltage of a photovoltaic array is controlled to be a maximum power point voltage; and step three, on the basis of the practical measurement data, whether a threshold determination system is in a normal or faulted state is calculated and determined; if the threshold determination system is in a normal state, dual-loop controlling is carried out on the inverter by ways of voltage outer loop controlling and current inner loop controlling and if the threshold determination system is in a faulted state, positive-sequence and negative-sequence controlling is carried out on the inverter. Under the circumstance that the system works normally, the photovoltaic array can work at a maximum power point; and the direct-current-side voltage of the inverter can be stabilized and a certain reactive power is sent based on the drop degree of the alternating-current-side voltage of the inverter, and thus the grid-side voltage is supported.

The invention discloses a control method of a backstepping controller based on a VIENNA rectifier. The control method comprises the following steps of acquiring the voltage and current parameters of the direct-current side, a direct-current side voltage expected value and a q-axis current expected control quantity of the VIENNA rectifier; performing dq conversion processing on the voltage and current parameters, and determining a d-axis current value, a q-axis current value, a d-axis voltage value and a q-axis voltage value; determining a d-axis current expected control amount according to thedirect-current side voltage expected value and the actual voltage value; according to the d-axis current expected control amount, the d-axis current value, the q-axis current value and the d-axis voltage value to determine the actual control amount of the d-axis voltage; according to the expected control amount of the q-axis current, the d-axis current value, the q-axis current value and the q-axis voltage value for determining the actual control quantity of the q-axis voltage; and generating SVPWM modulating signals according to the actual control quantity of the d-axis voltage, the actual control quantity of the q-axis voltage and the output angle theta of a phase-locked loop, and controlling the VIENNA rectifier. By adopting the control method, the stability of the d-q-axis current tracking and the direct-current side voltage can be realized.

The invention discloses a compound control method for compensating unbalanced harmonics, and relates to the technical field of electric energy quality governance. The method comprises the steps of calculating the reference quantity of the active and reactive power control in the improved DQ decoupling control according to the required phase information, and adding the improved DQ decoupling to generate a first modulation wave; calculating the active and reactive components of each harmonic according to the required phase information, and adding a specific harmonic control loop to generate a second modulation wave; and superposing and sending the first modulation wave and the second adjustment harmonic to a PWM modulation module to generate a switching signal required by a two-bridge-arm APF. Through the improved DQ decoupling control, the negative sequence and reactive reference quantities are added into the active and reactive components of traditional DQ control, so that the direct current side capacitor voltage can be stabilized, and the fundamental wave negative sequence current and reactive current are compensated; and meanwhile, the specific sub-harmonics in a traditional APF are introduced to be compensated into the two-bridge-arm APF, and the high-content harmonics are compensated, so that the method has good negative sequence, reactive power and harmonic compensation performances.

Single-phase power factor correction circuit based on three-tube five-level topology, involving the field of power factor correction circuits, including switching tube Q 1 , Q 2 , Q 3 , the AC side of the AC power supply is connected to the diode D 1 anode, diode D 2 Cathode, its connection node constitutes terminal b; the other side of the AC power supply AC is connected to one end of the inductor L, and the other end of the inductor L is respectively connected to the diode D 3 anode, diode D 4 Cathode, connected to node to form terminal a; diode D 7 Cathode connection capacitance C 1 One end, the connecting node constitutes the terminal p; the capacitance C 1 The other end is connected to the capacitor C 2 One end, the connecting node constitutes the terminal n; the capacitor C 2 The other end is connected to the diode D 8 The anode, its connection node constitutes the terminal m; the switch tube Q 1 The drains are connected to the diode D 1 cathode, diode D 7 Anode, its connection node constitutes terminal c; switching tube Q 3 The source is connected to the diode D respectively 2 anode, diode D 8 Cathode, whose connection nodes form terminal d. The endpoints a, c, d, n form a symmetrical four-port. The correction circuit of the present invention adopts multi-level, and has the advantage of small voltage stress of the switch tube.

The invention discloses a three-phase four-switch active electric power filter and a control method thereof. The active electric power filter comprises an inverter. The inverter comprises two switch arms and a DC capacitive branch. The two switch arms and the DC capacitive branch are connected in parallel. The two switch arms are respectively composed of two power switches which are connected in series. The inverter is parallelly connected between a three-phase electric network and a three-phase load through an output wave filter. The control method is an increment type PID control method based on a two-dimensional subordinated cloud model. The two-dimensional subordinated cloud module is utilized for performing on-line adjustment on proportion coefficient, integral coefficient and differential coefficient of an increment type PID controller, thereby improving response performance of a control system. The three-phase four-switch active electric power filter can perform dynamic real-time treatment on each sub-harmonic current and wattless current, thereby greatly improving compensation performance of the system, saving cost, and realizing higher engineering practicability.

The invention belongs to the field of applied superconducting power electronics, and in particular relates to a synchronizing current and voltage decoupling control method of a voltage-source-type unit power factor high-temperature superconducting energy storage system converter. The control method is characterized by comprising the following steps: designing a voltage outer ring control module at a direct-current side and a current inner ring control module at an alternating-current side respectively with respect to a mathematical model of a superconducting energy storage system converter under dq synchronizing rotary coordinates; controlling an 'H'-shaped bidirectional DC-DC (direct-current to direct-current) chopper based on an SPWM (sinusoidal pulse width modulation) technology by adopting a hysteresis loop PI current closed-loop control method in a charge mode and a hysteresis loop PI voltage closed-loop control method in a discharge mode; and finally implementing the synchronizing current and voltage double-fed control method of a voltage-source-type SMES (superconducting energy storage system) converter according to the active current requirement and the current value of a superconducting magnet under the power grid unit power factor. The control method provided by the invention has the advantages of multi-stage current decoupling control, rapid response speed, easy implementation of control algorithm and the like, and the method is especially suitable for the application occasions for improving the electricity energy quality of a power grid and inhibiting the low-frequency oscillation of a power system and the like.

The invention discloses a power coupling circuit in an unbalanced power grid and a control method, and the power coupling circuit comprises a power grid side circuit which is provided with a three-phase power supply in star connection and each phase is provided with a leakage inductor Lg; a main circuit which is provided with a first bridge arm, a second bridge arm and a third bridge arm which aresequentially connected in parallel, wherein each of the first bridge arm, the second bridge arm and the third bridge arm comprises two switching devices, and central points of the first bridge arm, the second bridge arm and the third bridge arm are respectively connected to a three-phase power grid; a power coupling circuit which is provided with a fourth bridge arm connected to the right side ofthe main circuit in parallel, wherein the coupling bridge arm comprises two switching devices, and a coupling inductor and a coupling capacitor are sequentially connected between the midpoint of thebridge arm and a ground wire in series; and a DC-side circuit having a DC-side capacitor and a load connected in parallel with the main circuit. Oscillation power generated due to imbalance of a powergrid can be completely transferred to the power coupling circuit, the DC-side voltage is maintained to be free of fluctuation, and the electric energy quality is improved.