945 results about "Circulating current" patented technology

The invention relates to the technical field of cable fault monitoring, in particular to an intelligent cable fault monitoring and early warning method and system, and the method comprises the steps: detecting a sheath circulation phase angle, adjusting the frequency through offset threshold exceeding, extracting de-noising data, injecting pulses, measuring the time delay, correcting the temperature, inverting a carbonization path, matching a conductivity abrupt change generation map, and measuring the attenuation rate to update the carbonization depth. And calculating a correlation factor to trigger early warning. According to the invention, through dynamic detection of circulation phase angle offset, frequency modulation anti-interference data extraction, noise suppression, signal-to-noise ratio improvement, combination of temperature gradient and dielectric correction delay, compensation of signal temperature influence, accurate inversion of a carbonization starting point, and joint analysis of multi-band signal attenuation rate and propagation time, complex working conditions are adapted; a coupling model is established through dynamic comparison of correlation factors and threshold values, layered early warning is performed, phase correction, temperature compensation and multi-band collaborative analysis are fused, and the positioning precision and the evaluation reliability are improved.

The invention discloses a cable sheath ring current fault positioning in-loop simulation method and system based on LABVIEW. The method comprises the following steps: collecting ring current data of cable sheath monitoring points in real time under the control of LABVIEW, and carrying out digital display and graphical display; decomposing circulation data to obtain a wavelet coefficient and calculating features, and inputting a classification model to obtain a fault type when the features are abnormal; calculating a compensation coefficient considering the influence of the electromagnetic field, and calculating the position of a fault point in combination with a double-end traveling wave method; the operation model switches a typical working condition simulation mode, prediction of a Bayesian reasoning correction model is carried out, and the full-life-cycle operation state of the cable is simulated; and performing fault early warning through the LSTM model and risk assessment. The method can effectively improve the cable operation and maintenance efficiency and reliability, and is widely applied to cable fault detection and guarantee of safe and stable operation of a power system.

A method for testing sheath impedance in a high-voltage cable cross-bonding system. Three-phase current data and three-phase grounding circulating current data from a first cable body segment and a last cable body segment in cross-bonding units, and three-phase current data, three-phase grounding circulating current data, and three-phase induced voltage data from a cable body at a cross-bonding box are detected and collected, thereby directly calculating three-phase sheath impedance of the three cable segments and determining whether the three-phase sheath impedance is abnormal (step 5), thus determining whether the tested cross-bonding units have a defect. The present invention involves a simple operation, achieves an accurate testing result, and can achieve energized testing without an external excitation source. By performing real-time testing on the cross-bonding units and calculating the sheath impedance of the three cable segments in the cross-bonding units in real time, the states of the cross-bonding units can be determined in real time, which makes it possible to detect a cable fault immediately, thereby preventing a loss caused due to the cable fault.

The invention provides a high-frequency circulating current calculation method for a motor simulator cascade coupling parallel structure, and the method comprises the following steps: building an equivalent decoupling circuit model of each branch in the cascade coupling parallel structure based on the voltage relation of each branch in the motor simulator cascade coupling parallel structure, wherein the equivalent decoupling circuit of each branch comprises an equivalent voltage source and an equivalent leakage inductor which are connected in series, and the equivalent leakage inductor is determined based on self-inductance and mutual inductance of a choking coil of each branch; a plurality of duty ratio intervals are divided between 0 and 1, and the number of the duty ratio intervals is equal to the number of the branches in the cascade coupling parallel structure; and using the equivalent decoupling circuit model to calculate the high-frequency circulation of each corresponding branch when the duty ratio of the modulation signal of the motor simulator is in each duty ratio interval. According to the method provided by the invention, the high-frequency circulating current of the cascade coupling parallel structure of the motor simulator can be accurately calculated, and effective support is provided for targeted design of a high-frequency circulating current suppression scheme.

The invention provides a modularized multi-level converter current control method based on feedforward analysis. The deviation between the direct-current side voltage and the reference value is stably monitored in real time based on the direct-current bus voltage, a first waveform signal is dynamically generated, and the direct-current side voltage fluctuation range is limited. According to the circulating current interphase voltage sharing, the dynamic deviation between the actual value and the rated value is calculated by collecting the capacitor voltage actual value of the bridge arm sub-module, and a second waveform signal is generated to balance the circulating current distribution of each phase of bridge arm. The loop current suppression based on feedforward analysis generates a third waveform signal to compensate for high-frequency loop current interference through real-time comparison of theoretical modeling and actual loop current components. In the modulation wave generation process, information in all aspects is integrated to accurately control the on-off state of the sub-module, so that the operation effect of the system is improved under the complex working condition, and the real-time performance and predictability of control are considered through combination of closed-loop adjustment and feed-forward compensation, so that the effectiveness of control is improved.

The invention discloses a zero common-mode voltage control method and system for two parallel converters based on single vector predictive control, and the method comprises the steps: building a prediction model and an evaluation function with parallel current, three-phase circulating current and common-mode voltage as control targets, and achieving the comprehensive control of output current and three-phase circulating current while guaranteeing the zero common-mode voltage; on the basis of the mapping relation between zero common-mode voltage and switch state combinations, 20 switch combinations with the common-mode voltage being 0 are selected, and an alternative switch combination library is formed; and a common-mode voltage penalty term considering a commutation process and a system parameter error is introduced into the evaluation function, and according to current polarity determination, alternative vectors generating common-mode voltage are rejected online, so that accurate control of zero common-mode voltage is realized. The invention provides an efficient and reliable common-mode voltage suppression scheme, and the common-mode voltage of the two parallel converters is successfully eliminated.

The invention discloses a source network load storage coordination control system and method for high-capacity multi-network energy storage combined transportation. The system comprises a master station layer which is responsible for receiving a superior scheduling instruction, issuing an emergency control instruction, and performing economic optimization scheduling and rapid coordination control on photovoltaic and energy storage resources; the substation layer is responsible for accessing photovoltaic, load and energy storage resource information and decomposing and issuing superior instructions to realize a local frequency voltage control function; and the terminal layer is used for receiving a generator tripping command or a power regulation command issued by the emergency state monitoring device. The system can effectively improve the network-related performance of a new energy station, enhance the stability and reliability of a power grid, improve the absorption capability of new energy, and optimize the economical efficiency of the system. Through combined operation of the network construction type energy storage equipment and the new energy, effective support for the power grid is realized, the problem of coordination control of parallel operation of multiple voltage sources is solved, oscillation and circulation are avoided, and the overall performance and the power supply guarantee capability of the system are improved.

The invention relates to the technical field of cable fault diagnosis and positioning, in particular to a cable fault positioning method and system based on multi-source data space-time correlation, and the method comprises the steps: obtaining partial discharge, traveling wave and temperature multi-source monitoring data from a high-voltage cable-overhead line hybrid power transmission network; on the basis of space-time correlation analysis of partial discharge and temperature data, heat-electricity associated defect points are calibrated; comparing traveling waves of the cable and the overhead line, and identifying and inhibiting cross-domain propagation interference; positioning the traveling wave data which are not identified to obtain temporary coordinates, judging fault characteristics by fusing information such as sheath ring current and the like, and comparing the temporary coordinates with defect points to generate matching identification; and inputting multi-dimensional information such as fault features, defect matching identification and temperature into the fusion model, calculating the confidence coefficient of a fault mode, and outputting a cross validation positioning result. According to the invention, high-reliability positioning of mixed line faults and active early warning of insulation defects are realized by carrying out space-time correlation and fusion decision on multi-source monitoring quantities such as traveling waves, partial discharge, circulation, temperature and the like.

The present invention relates to the technical field of energy storage. Disclosed is a wired parallel operation method applied to grid connection and grid disconnection of an energy storage system. The energy storage system comprises a plurality of inverters, a communication module, an electric meter and a load. The inverters are connected in parallel, each inverter being connected to the communication module, and each inverter being connected to a battery; the electric meter is connected to one of the inverters, and the electric meter is connected to the load. The method comprises: each inverter determines whether the inverter itself is a master inverter or a slave inverter according to the communication state with the electric meter; the master inverter sends a synchronization signal to each slave inverter, such that the switching frequency and the working mode of each slave inverter are synchronized with that of the master inverter; the master inverter communicates with the electric meter to acquire load power consumption information and outputs same to the communication module; and the communication module communicates with the master inverter and the slave inverters to acquire battery information, and adjusts the battery charge and discharge power according to the load power consumption information and the battery information. The present application ensures a reasonable distribution of power among inverters, thus avoiding the phenomenon of high-frequency circulating currents.

The invention relates to the technical field of converter power averaging and circulating current suppression, in particular to a power averaging and circulating current suppression method for parallel operation of a plurality of grid-forming type energy storage converters, which averages power through communication interaction and generates frequency and voltage compensation quantity by adopting a first regulator and a second regulator to realize accurate power averaging; meanwhile, the total current is measured locally, and virtual impedance feedforward control is adopted, so that rapid suppression of the high-frequency circulating current is realized. According to the invention, high-precision active power and reactive power equalization is realized, the capacity utilization rate is improved, high-frequency circulating current is effectively suppressed, loss and thermal stress are reduced, dynamic performance and system reliability are considered, a cooperative control architecture with complementary advantages is formed, adaptability to complex working conditions and system stability are enhanced, and engineering applicability is improved.

The invention discloses an MMC sub-module fault processing method, device and equipment and a storage medium, and the method comprises the steps: obtaining the capacitor voltage value of a sub-module of an MMC and the bridge arm current value of the sub-module, the MMC comprises six bridge arms of three phases, each bridge arm comprises a plurality of sub-modules, the capacitor of each sub-module is connected with an equivalent series resistor in series, and further, the equivalent series resistor is connected with the capacitor voltage value of the sub-module of the MMC; the resistance value of an equivalent series resistor in the sub-module is monitored through the capacitor voltage value and the bridge arm current value, if the resistance value of the equivalent series resistor is higher than a preset resistance value, it is determined that the capacitor of the sub-module fails, fault-tolerant control is carried out on the sub-module through a voltage-sharing and circulating current suppression algorithm, a three-phase switching signal is output, and the three-phase switching signal acts on the MMC. Therefore, the circulating current fundamental frequency component and the double frequency component caused by fault-tolerant control after the fault can be eliminated through the circulating current suppression strategy, the effect of circulating current suppression is achieved, and the stability of system fault operation is improved.

The invention discloses a carrier synchronization method and device, an inverter and a storage medium, and relates to the technical field of carrier control, and the method comprises the steps: transmitting a host competition signal to a carrier bus in a system when a slave inverter in an inverter parallel system cannot acquire a carrier signal transmitted by a master inverter in the system and reaches a first preset duration, and then transmitting the host competition signal to the carrier bus in the system; all slave inverters in the system respond to the host competition signal to send a first identification number to the bus, and monitor a bus identification number transmitted in the bus at the same time, when a certain slave inverter finds that the first identification number sent by the slave inverter is matched with the bus identification number, it is confirmed that host competition succeeds, and the slave inverters send the first identification number to the bus. The main inverter sends carrier signals to the bus, the other slave inverters acquire the carrier signals to perform carrier synchronization, and the slave inverters establish a master-slave structure of the system through competition of the host, so that the carrier synchronization function of the system is established or recovered, the carrier synchronization stability of the system is improved, and the circulating current of the system can be efficiently inhibited.

The invention relates to the technical field of parallel three-level converter control, and provides a parallel three-level converter model prediction control method and system, and the method comprises the steps: enabling a parallel three-level converter to be modeled as a series connection of an equivalent voltage source and an equivalent filter inductor according to the Thevenin theorem, enabling the parallel three-level converter to be equivalent to a five-level converter, and enabling the parallel three-level converter to be connected in parallel; a three-layer optimization control strategy is adopted; in the first layer, a candidate vector closest to a reference voltage vector is selected as an optimal five-level basic vector so as to track a parallel total output current; in the second layer, a redundant five-level voltage vector is selected to balance the neutral-point voltage; and in the third layer, selecting the candidate switching state which enables the circulating current suppression value function to be the minimum as the optimal redundant three-level switching state so as to suppress the circulating current. The method can effectively reduce output current harmonics under low switching frequency, and balance of neutral-point voltage and effective suppression of circulating current are realized to ensure safe and stable operation of a parallel converter system.

The invention discloses a modular high-voltage SVG circulating current suppression method. The method comprises the steps of obtaining and preprocessing module circulating current, voltage and state data; constructing an enhanced phase space fused with multiple physical quantities, extracting circulating current phase features and generating dynamic trend prediction data; calculating optimal feed-forward and feedback virtual impedance parameters based on phase characteristics and trend prediction; and generating a module control voltage correction value and a PWM control signal by applying a multi-time scale hybrid control strategy. Through hybrid control of phase space reconstruction of topology perception, multi-dimensional entropy analysis and stability guarantee, efficient suppression of the circulating current is realized, and the stability and robustness of the SVG system are improved.

This invention discloses a method and system for suppressing capacitor voltage fluctuations in SiC MMC submodules, belonging to the field of electronic power technology. Based on the analysis results of the optimal broadband harmonic circulating current injection boundary and order for SiC MMC submodules, an optimized model for submodule capacitor voltage fluctuations is determined that simultaneously injects 2nd, 4th, and 8th harmonic circulating currents and 3rd harmonic voltages, which can fully utilize the higher control bandwidth characteristic of SiC MMC. By solving the optimized model for submodule capacitor voltage fluctuations, the amplitude and phase of the reference values ​​of the 2nd, 4th, and 8th harmonic circulating currents to be injected, as well as the amplitude and phase of the corresponding 3rd harmonic voltage, are determined. Then, by injecting 2nd, 4th, and 8th harmonic circulating currents and jointly injecting the 3rd harmonic voltage, broadband harmonic joint injection is achieved, reducing the capacitor voltage fluctuations of the submodule and realizing a method for suppressing capacitor voltage fluctuations in SiC MMC submodules with high suppression effect.

Provided in the present disclosure are a converter system of a wind turbine generator system, and a wind turbine generator system and an offshore wind farm. The converter system comprises: a voltage source converter and a current source converter; and a converter control apparatus, which is configured to control the operation of the voltage source converter and the current source converter by means of taking into account an internal circulating current of a wind turbine generator system in voltage outer-loop control of the voltage source converter and by means of taking into account the internal circulating current in active and reactive power control stages of the current source converter.

The invention provides a super-capacitance multi-branch equalization method and system for a network-forming type static synchronous phase modifier. The method comprises the following steps: acquiring current data of each super-capacitance branch in the network-forming type static synchronous phase modifier; based on the current data of each super-capacitance branch, outputting voltage drop data of each super-capacitance branch by using a proportional-integral controller; according to the voltage drop data of each super-capacitance branch, generating a correction modulation wave of each super-capacitance branch; according to the correction modulation waves of all the super-capacitance branches, voltage control is carried out on the net-forming type static synchronous phase modifier; according to the invention, the voltage control is carried out on the network-forming type static synchronous phase modifier through the correction modulation wave generated according to the branch voltage drop data output by the proportional-integral controller, and the dynamic adjustment can be respectively carried out for the voltages of different super-capacitance branches, thereby facilitating the reduction of a circulation phenomenon caused by voltage imbalance, and improving the reliability of the network-forming type static synchronous phase modifier. And unnecessary energy loss and overheating can be avoided, and the service life of equipment is prolonged.

The invention discloses an enhanced SVG low voltage ride through method, and belongs to the technical field of electrical automation equipment, and the method comprises the steps: carrying out the three-phase voltage synthesis of a self-built voltage amplitude and a self-built voltage phase, and obtaining a current reference value through an electromagnetic square; according to the self-built voltage phase and the current reference value, a bridge arm differential mode voltage modulation wave is obtained through inner loop current control; obtaining a main circuit commutation actual value of the enhanced SVG, and obtaining a bridge arm common-mode voltage modulation wave through circulating current suppression control in combination with the self-built voltage phase; actual energy and rated energy of the enhanced SVG are obtained, and an energy modulation signal is obtained through an energy control ring; and after modulation is carried out according to the bridge arm differential mode voltage modulation wave, the bridge arm common mode voltage modulation wave and an energy modulation signal, a switching signal is generated to control the enhanced SVG, and low voltage ride through is realized. According to the invention, the problem that the enhanced SVG fails or is off-network under the condition of low voltage can be solved.

The invention relates to the technical field of power supplies, in particular to a module power supply for communication equipment, which comprises an input filtering unit, at least two stages of power conversion units, an output voltage stabilization unit, an intelligent control module, a fault reconstruction unit and a composite heat dissipation structure, the input filtering unit is connected with the power conversion unit, the power conversion unit is connected with the output voltage stabilization unit, the output voltage stabilization unit is connected with a load end, and the input filtering unit, the power conversion unit, the output voltage stabilization unit, the fault reconstruction unit and the composite heat dissipation structure are respectively connected with the intelligent control module. The composite heat dissipation structure comprises a metal heat conduction substrate, a phase change material layer and a micro-channel liquid cooling module, the phase change material layer is arranged on the metal heat conduction substrate, the micro-channel liquid cooling module is arranged on the phase change material layer, and the metal heat conduction substrate is connected with the power device through heat conduction silica gel for heat conduction; when the fault reconstruction unit detects local failure, the damaged module is switched to be in a bypass state, current sharing parameters of the remaining modules are reconfigured, and the output power of the power supply is maintained to be not lower than 75% of a rated value. Compared with the prior art, the module power supply for the communication equipment has high-efficiency conversion and wide adaptability, and the efficiency is optimized in a full-load range; intelligent thermal management and reliability are enhanced, temperature rise control is obviously optimized, the phase change material layer absorbs transient thermal shock, temperature fluctuation is reduced, flow of the micro-channel liquid cooling module is adaptively adjusted, and power consumption is reduced; dynamic performance and stability are improved, multi-module parallel current sharing precision is improved, circulating current loss is reduced, and faults can be rapidly recovered.

The invention provides a carrier modulation method and modulation-demodulation system for an MMC circulation suppressor, and the method comprises the following steps: obtaining MMC operation log data, carrying out the spectrum analysis, and extracting the spectrum amplitude distribution characteristics; identifying a bridge arm circulation condition based on the amplitude distribution characteristics, and further detecting bridge arm load abnormity and unit energy abnormity conditions; identifying a circulating current frequency component according to an energy abnormal condition, performing electric energy quality attenuation detection and initial circulating current position tracing, and determining a circulating current generation mechanism; and finally, based on the risk assessment result and the generation mechanism data, constructing a modulation parameter, and generating an adaptive circulation suppressor carrier modulation strategy. Compared with the prior art, the method has the following beneficial effects: through modulation of the circulating current suppressor, modulation of the circulating current suppressor is more accurate, so that the problems of inaccurate analysis of a bridge arm circulating current generation mechanism and inaccurate analysis of an energy abnormal condition of the MMC unit existing in carrier modulation of a traditional circulating current suppressor are solved.

The invention relates to the technical field of battery management, in particular to a lithium ion battery power storage method and system based on a BMS architecture, and the method comprises the steps: carrying out the grouping specification division of a battery pack according to an internal resistance range, and collecting the internal resistance fluctuation amplitude and terminal voltage deviation rate of each cluster in real time under a constant charging current working condition; calculating the internal resistance sensitivity coefficient of each cluster under the corresponding group based on the parameters, so as to quantify the cluster-level circulating current risk level, and synchronously obtaining the number of batteries in the cluster, the internal resistance standard deviation and the charging current working condition; calculating a compensation priority index of the battery cluster by integrating the circulating current risk grade, the number of batteries in the cluster, the internal resistance standard deviation and the charging working condition; and the battery cluster with the highest priority is selected as a reference cluster, internal resistance difference compensation voltage regulation is performed on the non-reference cluster through the BMS, the terminal voltage of each cluster is dynamically balanced, the circulation effect is inhibited, and the stability and energy utilization efficiency of the battery pack in the power storage process are improved.

The invention relates to an energy storage type MMC battery state-of-charge rapid equalization method. The method comprises the following steps: acquiring a power reference value, voltage and current parameters of the energy storage type MMC, and calculating the number of initial upper / lower bridge arm input sub-modules; sOC imbalance between phases and between bridge arms is calculated, and a circulating current instruction value is obtained through an adaptive equalization coefficient; obtaining an upper / lower bridge arm input sub-module quantity correction value through a circulation controller; virtual resistance of the in-arm energy storage sub-module is calculated through a virtual resistance controller; the sub-modules are divided into an input group and a cut-off group, and the number of the input sub-modules of the switching group is determined according to the initial number of the input sub-modules of the upper / lower bridge arm and the correction value of the number of the input sub-modules of the upper / lower bridge arm. According to the invention, the state of charge balance of the energy storage type MMC can be realized, and the SOC balance speed is improved.

The invention is suitable for the technical field of flexible power distribution of a power system, and discloses a modular multilevel converter multi-objective optimization method, system and device based on model predictive control and space vector modulation, and a medium. Obtaining an output current reference value and a circulating current reference value; obtaining a reference voltage vector based on the output voltage reference value, and screening out a plurality of groups of redundant voltage vector sequences through a space vector diagram; performing performance evaluation through rolling optimization by combining each redundant voltage vector sequence with a multi-target cost function to obtain an optimal voltage vector sequence; and on the basis of the optimal voltage vector sequence and the corresponding duty ratio, a switching signal for driving each sub-module switching device of the MMC is generated, and multi-target cooperative control is realized. The three targets of reference output current tracking, circulating current suppression and sub-module capacitor voltage balance are met, and the dynamic response capability, efficiency and reliability of MMC system operation are comprehensively improved.

The invention provides a three-phase four-wire parallel inverter system circulating current suppression method based on 3D-SVPWM (three-dimensional space vector pulse width modulation), and the method comprises the steps: changing a zero-sequence voltage difference through changing a difference value of zero-sequence duty ratios of two inverters through a 3D-SVPWM strategy, thereby suppressing the zero-sequence circulating current in the parallel inverter system, and achieving the purpose of suppressing the circulating current in the parallel inverter system. The parallel inverter system comprises a parallel inverter circuit module, a 3D-SVPWM modulation module and a closed-loop control module. According to the method, zero-sequence circulating current suppression of the three-phase four-leg parallel inverter system can be realized, the steps are simple, the system loss can be reduced, the efficiency and reliability of the parallel four-leg inverter system can be improved, the service life of the parallel four-leg inverter system can be prolonged, and a relatively good zero-sequence current suppression effect can be achieved.

The invention provides a grid-connected circulating current suppression method and device for a grid-forming type wind turbine generator. The grid-connected circulating current suppression method comprises the following steps: acquiring an active power reference value, an active power actual value, a reactive power reference value and a reactive power actual value of the grid-forming type wind turbine generator and a three-phase output voltage and a three-phase output current of the grid-forming type wind turbine generator; the method comprises the following steps: performing proportional integral operation on an active power reference value, an active power actual value, a reactive power reference value and a reactive power actual value of a network construction type wind turbine generator, and calculating to obtain a first reference voltage; inputting a three-phase output voltage and a three-phase output current of the grid-forming type wind turbine generator set into a virtual impedance module, and calculating to obtain a second reference voltage; and providing the difference between the second reference voltage and the first reference voltage as a voltage reference to a voltage and current loop of the grid-forming type wind turbine generator so as to suppress the grid-connected circulation of the grid-forming type wind turbine generator.

The invention relates to a direct-current circulating current suppression method and system for parallel operation of inverters and electronic equipment. The method comprises the following steps: acquiring a first current of a balance bridge circuit in an inverter, a second current output by a bus midpoint and a three-phase current direct-current component output by a three-phase bridge circuit based on a carrier cycle synchronized with a host; based on the first current and the second current, a first adjusting signal is generated to act on an upper bridge arm circuit and a lower bridge arm circuit of the balance bridge circuit, fluctuation interference currents in the first current and the second current are adjusted to offset each other, and therefore direct-current circulation between output zero lines caused by voltage difference between different parallel inverter buses is restrained; and based on the direct current component of each phase of current, generating a corresponding second adjusting signal to act on the three-phase bridge circuit, and adjusting the corresponding direct current component to suppress direct current circulation between output zero lines of each inverter caused by the direct current component of the three-phase current.

The invention discloses a cooperative control method for neutral-point balance and circulation suppression of an inverter. The method comprises the following control steps: collecting three-phase current of a power grid side, and generating a three-phase bridge arm modulation signal through a grid-connected current control loop; collecting a lower half bus voltage and generating a first zero-sequence component through a neutral-point balance control loop; collecting three-phase current on the power grid side, and generating a second zero-sequence component through a circulating current suppression control loop; inputting the first zero-sequence component and the second zero-sequence component into a competition logic processing module, and generating a final zero-sequence component by using a competition mechanism based on dynamic weight distribution; and the final zero-sequence component is subjected to over-modulation processing and then superposed to a three-phase bridge arm modulation signal of a grid-connected current control loop, and then a control signal of the three-level inverter is obtained after PWM (Pulse-Width Modulation). The method has the advantages that by dynamically coordinating the midpoint balance and circulating current restraining requirements, efficient coordination of the midpoint balance and the circulating current restraining requirements can be achieved, the control complexity is reduced, and the method is suitable for low-cost industrial application scenes.

The invention discloses a dynamic virtual impedance control method for multi-machine parallel connection of a network construction type energy storage converter, and belongs to the technical field of power electronics. The method aims to solve the problem that accurate reactive power distribution, circulating current suppression, dynamic response and voltage precision are difficult to consider in a multi-machine parallel system through fixed parameter virtual impedance. A dynamic adjustable virtual impedance module is introduced into the voltage outer loop output end of each converter, and virtual resistance and virtual inductance are calculated in real time based on locally measured output current, bus voltage change rate and adjacent machine reactive power deviation information; and the average reactive power of the system is estimated through a phase synchronization mechanism under the condition of no communication so as to realize multi-machine cooperation. According to the method, the reactive power distribution error is less than 5%, the bus voltage drop is less than 3%, the high-frequency circulating current is controlled within 5% of the rated current under all working conditions, and the dynamic performance and robustness of the system are remarkably improved.

The invention discloses a loop current suppression and modulation method for a network-forming inverter of a heavy truck battery swap station, which comprises the following steps: after harmonic waves are suppressed by adopting a reduced-order resonance controller, converting a negative-sequence double frequency, a positive-sequence quadruple component and a frequency loop current harmonic wave component into third-order loop current harmonic waves, and considering a primary frequency modulation characteristic, carrying out secondary frequency modulation on the third-order loop current harmonic waves, and carrying out secondary frequency modulation on the third-order loop current harmonic waves; and a proportional resonance integral controller is connected in parallel to ensure harmonic suppression during frequency deviation, and meanwhile, suppressed harmonic is introduced into a hysteresis controller to correct a nearest level approximation modulation wave. Through a combined control method of direct inhibition and indirect inhibition of the circulating current, the purpose of inhibiting the circulating current is achieved. According to the invention, harmonic suppression after power frequency and frequency deviation is guaranteed, the influence of capacitor voltage ripples of the sub-modules is improved while modulation waves are corrected, and the control mode is simplified.

The embodiment of the invention discloses a photovoltaic system and a parallel operation circulating current suppression method thereof, the photovoltaic system comprises a plurality of power converters connected in parallel, each power converter comprises an inversion module, an output filter, a detection circuit and a controller, and the output filter comprises a variable inductor and / or a variable capacitor. The variable inductor comprises a first winding connected with the first switching circuit in series, and the controller can control the first switching circuit to be switched on or switched off according to the current value, detected by the detection circuit, flowing through the output filter so as to change the inductance value of the variable inductor. The variable capacitor is connected in series with the second switching circuit between the neutral line and the alternating current bus, and the controller can control the second switching circuit to be switched on or switched off according to the current value which is detected by the detection circuit and flows through the output filter so as to change the state that the variable capacitor is connected to the alternating current bus. By changing the inductance value and / or the capacitance value, the position of the resonant frequency point of the output filter can be changed, so that the parallel operation circulating current is inhibited.