40 results about "Neutral point voltage" patented technology

The invention provides a data-driven multi-target control method, device and system based on model prediction, is applied to a three-phase three-level neutral point clamped converter, and aims to realize dual accurate control of switching frequency and neutral point voltage. According to the method, a switch weight factor and a neutral point voltage weight factor are used as inputs, and an average switch frequency in a fixed sliding window time and a neutral point voltage maximum value in another fixed sliding window time are used as outputs; and constructing an equivalent dynamic linearization data model under each dynamic working point of the closed-loop system by adopting a tight-format dynamic linearization method. Based on the data model, a data driving controller is elaborately designed to realize accurate regulation and control of the switching frequency and the maximum value of the neutral point voltage. The method has a high practical value and a wide application prospect in typical application scenes of power electronics and power transmission, such as grid connection and motor driving.

Adjustable frequency drives (AFDs) and methods of operating the same are described. An AFD includes a plurality of inverters having first terminals that are coupled to respective phases of a motor and having AC output terminals connected to one another at an AC neutral node. A voltage at the AC neutral node is detected. A root-mean-squared (RMS) voltage measurement is generated from the detected voltage. A potential ground fault is identified responsive to the generated RMS measurement. The AFD is controlled responsive to identification of the ground fault. Identifying a potential ground fault responsive to the generated RMS voltage measurement may include comparing the RMS voltage measurement to a reference value.

The present application relates to the technical field of small current grounding line selection, and provides a small current grounding line selection auxiliary increment device and method, a grounding transformer module for providing a neutral point for a target power system; the target power system is a system without grounding of the neutral point; a neutral point voltage detection module for detecting the voltage of the neutral point when a grounding fault occurs; an auxiliary increment module for selecting a corresponding input resistor according to the size of the voltage of the neutral point when the grounding fault occurs, so as to obtain an increment current matched with the voltage of the neutral point; the input resistor is used for connecting the neutral point; and a zero sequence current detection module for judging the grounding fault according to the increment current matched with the voltage of the neutral point. Through the above technical solution, the problem that the grounding line selection cannot be accurately judged according to the zero sequence current in the related art is solved.

The invention provides an overvoltage tuning method and system based on parallel cooperation of a resistor and an arc suppression coil. The method comprises the following steps: judging an event type according to a neutral point voltage; when the event type is that the operation mode is changed, performing first tuning based on a first preset rule, and judging whether the neutral point voltage after the first tuning is greater than a threshold value or not; if the neutral point voltage after the first tuning is greater than the threshold value, performing secondary tuning based on a second preset rule, and judging whether the neutral point voltage after the secondary tuning is less than the threshold value; if the voltage of the neutral point after secondary tuning is larger than or equal to the threshold value, a second preset rule continues to be executed until the voltage of the neutral point after secondary tuning is smaller than the threshold value, and if the voltage of the neutral point after secondary tuning is smaller than the threshold value, it is judged that damping succeeds, and the resistance grounding device is reset. According to the invention, a unified zero-sequence impedance regulation and control strategy is established through cooperation of arc suppression coil operation and damping, so that the probability of occurrence of tuning overvoltage is reduced.

The application discloses a four-bridge-arm driving permanent magnet synchronous motor parameter identification method based on d-axis current injection, which comprises the following steps: obtaining a q-axis current reference value according to a rotating speed ring; calculating a d-axis current reference value, an electric frequency of a base frequency required by a resonance controller and a phase compensation value, calculating a current d-axis and 0-axis control cycle resonance controller output, and injecting a d-axis current by setting the d-axis current reference value; calculating a reference voltage by FOC and performing inverter nonlinear compensation; calculating a reference value of three-phase voltage relative to a neutral point voltage, and further obtaining a driving signal; identifying resistance, inductance and a base wave flux linkage in real time based on an FFRLS algorithm; calculating a term containing third harmonic flux linkage information through a low-pass filter; and finally obtaining the third harmonic flux linkage through the FFRLS algorithm. The parameter identification method has the advantages of low cost, simplicity and the like.

A method compensates for an undesired switching state-specific change in a neutral point voltage of an intermediate circuit when an operating point-specific output voltage is modulated. The method includes determining an operating point-specific switching pattern from at least four voltage vectors, wherein at least two of the voltage vectors are produced by different switching states of a 3-level inverter redundantly but with an opposite influence on a neutral point voltage; predicting, based on the determined switching pattern, a current load of the neutral point connection causing the undesired change in the neutral point voltage; determining, based on the predicted current load, an equalization current compensating for the current load within a modulation period; and determining a temporal weighting of the redundant voltage vectors by which at least a portion of the compensating equalization current is provided when the output voltage is modulated.

This invention discloses an improved method for controlling the midpoint voltage balance of a three-level bidirectional DC-DC converter, comprising the following steps: sampling the upper arm supporting capacitor voltage, the lower arm supporting capacitor voltage, and the inductor current respectively; selecting a switching transistor with an adjusted duty cycle based on the relationship between the upper and lower arm supporting capacitor voltages and the direction of the inductor current to control the balance of the midpoint voltage of the three-level bidirectional DC-DC converter; the inductor current can also be selected from the input current or output current in the DC-DC converter circuit to control the balance of the midpoint voltage of the three-level bidirectional DC-DC converter; by reasonably selecting the switching transistor with an adjusted duty cycle, the problem of midpoint voltage runaway caused by factors such as zero drift in the current detection circuit is avoided.

The application discloses a general reconfigurable simulation system of a power electronic converter, comprising: a dynamic element module, which is used for solving a dynamic element state equation according to a forward Euler method to obtain a dynamic element state variable, and sending the dynamic element state variable to a switch module according to a preset selection instruction; the switch module is used for constructing a general matrix model for a bridge arm switch of the converter, processing the dynamic element state variable through the general matrix model, and generating a switch voltage and a switch state instruction; a neutral point voltage solving module, which is used for constructing a neutral point voltage model for a three-phase rectification or inversion circuit according to the switch voltage and the switch state instruction, and solving to obtain a neutral point voltage; and a power supply module, which is used for providing different power supply voltages for the neutral point voltage solving module, wherein the power supply voltages include three-phase alternating voltages and a direct current voltage. The technical problems that the simulation adjustment flexibility is poor in different scenes, the modeling is complicated due to the increase of system element complexity, and the simulation compilation is time-consuming in the prior art are solved.

The invention provides a three-level converter neutral-point imbalance seven-segment control method and electronic equipment, and relates to the technical field of power equipment. The three-level converter midpoint imbalance seven-segment control method comprises the following steps: acquiring three-phase power grid voltage and three-phase power grid current, and determining reference voltage vector coordinates according to the three-phase power grid voltage and the three-phase power grid current; determining a small sector where the reference voltage vector coordinates are located; and positive bus capacitor voltage and negative bus capacitor voltage are obtained, the action duration of each target control vector is determined according to the positive bus capacitor voltage, the negative bus capacitor voltage and the small sector where the reference voltage vector coordinates are located, and seven-segment SVPWM control is carried out. According to the method, the redundant small vector is reasonably selected, the neutral point voltage is adjusted through the redundant vector by adopting the seven-section SVPWM, the current ripple is smaller, and the control is simple.

The application discloses a non-isolated flexible interconnection equipment control method and system, and belongs to the technical field of power system distribution network fault control. The method comprises the following steps: starting fault detection based on zero sequence voltage ratio; distinguishing the fault side and the healthy side through zero sequence instantaneous power; inputting a zero sequence suppression strategy of the healthy side converter to eliminate cross-zone interference; injecting a 300Hz high-frequency signal into the fault side converter to realize parameter-independent fault phase selection; switching a proportional-resonance controller based on the phase selection result to execute an arc extinction strategy, controlling the neutral point voltage to be the negative value of the fault phase voltage, and reducing the fault point voltage to below 0.2kV. The application breaks through the limitation of traditional arc extinction devices relying on the neutral point, solves the zero sequence transmission problem of the non-isolated topology, realizes the full-automatic and rapid disposal of single-phase grounding faults, and has a 100% arc extinction success rate, and is suitable for intelligent distribution network construction.

The application provides a three-level converter neutral point potential control method and system, relates to the technical field of intelligent control, samples positive bus voltage and negative bus voltage, calculates voltage deviation, and generates an additional control quantity according to the voltage deviation and the sign of alternating current, wherein the additional control quantity is obtained through sign function and proportional control processing; the additional control quantity is subjected to amplitude limiting processing to obtain an amplitude-limited additional control quantity; the amplitude-limited additional control quantity is superimposed on a positive modulation wave, and the amplitude-limited additional control quantity is inverted and superimposed on a negative modulation wave to obtain final positive and negative modulation waves; the final positive and negative modulation waves are compared with a carrier wave to generate a driving signal of a power device; and the driving signal is used to control the on-off of the switching device, so that corresponding levels are output to realize neutral point potential balance. The application can simultaneously realize low-frequency fluctuation and DC offset suppression of the neutral point voltage.

A charging system for an electric vehicle and a method for controlling it are disclosed, wherein the charging system comprises a control unit that controls the duty cycles of a plurality of switching elements in an inverter based on a duty cycle command that causes the voltage of a neutral point of the motor to follow a preset neutral point voltage command when a charging current from an external current source is applied to the neutral point, and the duty cycle command is selectively compensated based on an error between the neutral point voltage command and the neutral point voltage.

The application discloses a capacitor bank online monitoring method and device, electronic equipment and a storage medium thereof. The method comprises the following steps: obtaining the bus voltage measurement value and the phase current measurement value of the capacitor bank; calculating the neutral point voltage according to the predicted three-phase equivalent impedance of the capacitor bank at the previous moment; obtaining the phase voltage according to the bus voltage measurement value and the neutral point voltage; and predicting the three-phase equivalent impedance of the capacitor bank according to the phase voltage and the current measurement value and by using the Kalman filtering algorithm. The application embodiment does not need to additionally increase sensors, can be implemented by using the existing equipment in the transformer substation, effectively reduces the implementation threshold and application cost, and improves the monitoring efficiency and accuracy of the frame capacitor bank by using the measurement data of the existing sensors.

The invention discloses a stator winding ripple current modeling and predicting method suitable for a fault asymmetric multi-phase motor system, and the method comprises the following steps: constructing an inductance matrix of a motor based on the self-inductance and inter-phase mutual inductance of each phase winding of the motor; performing elementary transformation on a motor voltage equation under a natural coordinate system based on the inductance matrix and a preset orthogonal matrix to obtain a motor voltage equation under a decoupling coordinate system, and obtaining an expression of a winding current slope based on an instantaneous voltage equation under a bridge arm open-circuit fault; on the basis of a motor voltage equation under a decoupling coordinate system and a forced constraint that a fault phase current is zero, representing a neutral point voltage of the motor as a weighted sum of a residual healthy bridge arm output voltage and mutual inductance and a rotor flux differential item; on the basis of the weighted sum expression of the output voltage and the neutral point voltage of the remaining healthy bridge arms, the instantaneous phase voltage of each phase winding is obtained through calculation; and based on the expression of the instantaneous phase voltage and the winding current slope, the ripple current of the motor is obtained through integral calculation.

The application discloses a multi-level inverter control method and system based on reinforcement learning sequential MPC, and relates to the technical field of power electronics control, and comprises the following steps: a three-layer sequential optimization structure of current tracking-flying capacitor voltage balance-neutral point potential voltage balance is constructed in turn; a multi-objective reward function is designed by taking system state as observation input, taking current tracking tolerance boundary and flying capacitor voltage balance tolerance boundary as action output, so that dynamic balance of current tracking, flying capacitor voltage and neutral point voltage is realized; multiple control targets of optimized current tracking, flying capacitor voltage balance and neutral point potential voltage balance are optimized, and each layer is independently optimized and controlled; meanwhile, based on autonomous learning of offline reinforcement learning, optimization of multi-objective tolerance boundary values is realized, and the key problems of low artificial parameter adjustment efficiency and existing parameter setting blind area in a multi-objective system are solved.

The application discloses a power converter, a control method and related devices, comprising: a direct current / direct current circuit and a three-phase power conversion circuit, each phase of the three-phase power conversion circuit comprising a four-switch Buck-Boost circuit, a direct current side of the three-phase power conversion circuit being used for connecting a direct current source, an alternating current side of the three-phase power conversion circuit being used for connecting a load, and the load being connected in a star type; a first end of the direct current / direct current circuit being used for connecting a positive pole of the direct current source, a second end of the direct current / direct current circuit being used for connecting a neutral point of the load, a third end of the direct current / direct current circuit being used for connecting a negative pole of the direct current source, and the direct current / direct current circuit being used for adjusting a voltage of the neutral point. Since the neutral point voltage is adjustable, the neutral point voltage will not be clamped by an input voltage of the direct current source, and the power converter can be normally operated under three-phase four-wire system.

Drive system comprising electric motor, inverter, energy storage device, wherein the electric motor can be powered by the inverter, which can be supplied from the energy storage device, wherein the inverter has upper and lower controllable semiconductor switches, wherein the electric motor is designed as a three-phase motor in star point connection, characterized in that current can be supplied to the star point of the electric motor from a rectifier, which is supplied by a secondary winding, wherein the secondary winding can be supplied from a primary winding, which is inductively coupled to the secondary winding, wherein the primary winding is inductively coupled to the secondary winding from outside the drive system, wherein the stator winding of the electric motor, as the inductor of a charging circuit designed as a buck converter or boost converter, charges the energy storage device, wherein the rectifier is directly connected to the energy storage device by means of a diode.that when a first critical value of the voltage at the neutral point is exceeded, the charging current is carried directly from the rectifier to the energy storage device(s) via a diode, in particular wherein the first critical value corresponds to the charging voltage for the energy storage device(s), wherein an additional inductor is arranged between the neutral point and the rectifier supplying it, wherein the inverter with the stator windings together with the additional inductor forms a boost converter, to which current from the rectifier is supplied and which provides charging current to the energy storage device, wherein, as protection against overcharging, one or more switches of the inverter switch the stator winding to the lower potential or a further switch is provided which connects the neutral point of the stator winding to the lower potential.

The embodiment of the invention provides a rectifier current zero crossing distortion processing method and device, electronic equipment, a medium and a program product, and the method comprises the steps: determining a plurality of preset intervals corresponding to three-phase current in a rectifier, determining the corresponding modulation duty ratios of a preset three-phase switch in the rectifier in the plurality of preset intervals, and adjusting the neutral point voltage difference based on the target values according to the preset variable and the target values of the preset variable in the plurality of preset intervals, so that the three-phase switch meets the corresponding modulation duty ratio in each preset interval, and current zero crossing point distortion of the rectifier is processed. Through the method provided by the invention, the system operation efficiency can be improved.

The invention relates to a power distribution network ground fault flexible intelligent arc extinguishing method, and belongs to the technical field of power distribution network ground fault flexible arc extinguishing. The method comprises the following steps: recording feeder line current and neutral point voltage when a system normally operates; after a grounding fault occurs, identifying a fault phase and a fault feeder line, and recording a fault feeder line current and a neutral point voltage after the fault; the method comprises the following steps of: controlling an active inverter to inject zero-sequence current to preliminarily suppress voltage and current of a fault point by taking control of voltage at a fault phase bus to be zero as a control target; and an intelligent optimization method is used to carry out on-line identification on the line voltage drop, a control given value of a current and voltage double-closed-loop controller is adjusted according to the identified line voltage drop, the voltage and current of a fault point are suppressed to smaller values, and the risk of fault arc reignition is reduced. The method is high in response speed, the optimization algorithm can be quickly converged, the voltage and current of a fault point can be further inhibited on the basis of traditional arc extinction, the arc reignition risk is reduced, and the method has good engineering application prospects.

The invention relates to a distribution line ground parameter online identification method based on RLS-MRAS, and the method comprises the steps: employing the neutral point voltage during the single-phase ground fault of a power distribution network and compensation current information injected by an active inverter (the active inverter in the abstract drawing takes a cascaded H bridge as an example); and taking a ground capacitance value with relatively high RLS identification precision as a known quantity in a variable model of the MRAS, identifying unknown quantities of ground leakage resistance and grounding transition resistance by utilizing an MRAS algorithm, continuously optimizing a final parameter identification result according to the deviation between a reference model and the variable model, and realizing multi-parameter accurate identification during the power distribution network grounding fault period. According to the method provided by the invention, the ground capacitance value identified by the RLS method is fed back to the variable model of the MRAS, and complementary advantages of the two algorithms are realized, so that the ground capacitance, the ground leakage resistance and the grounding transition resistance under the SPG fault working condition of the power distribution network are accurately identified.

This invention discloses an energy coordination and neutral point balance control method applied to a bidirectional energy storage converter. Specifically, the difference between the voltage difference of the voltage divider capacitors and the standard deviation value (0) of the bipolar DC microgrid is subtracted, and this difference is used to generate a voltage equalization control signal after passing through a voltage regulator. This voltage equalization control signal is then subtracted from the neutral point current, and the result is used to generate an improved voltage equalization control signal through a current regulator. This improved voltage equalization control signal is added to the bus voltage control signal and transmitted to a PWM pulse signal generator to generate pulses that control the DC / DC converter. This invention employs a three-level bidirectional DC-DC energy storage converter method to suppress the neutral point voltage offset problem and proposes an improved current loop voltage equalization control loop. Compared with traditional voltage equalization control loops, the proposed voltage equalization strategy has a better effect on voltage imbalance problems.

The application discloses a kind of low voltage distribution network three-phase asymmetric power flow calculation methods containing doubly-fed wind turbine, comprising: 1 based on back-to-back converter steady-state constraint, the sequence component equivalent circuit of doubly-fed wind turbine DFIG is constructed, and the internal node power balance equation of unit under stator voltage asymmetry is established;2 using the node power balance equation when stator voltage is asymmetric, the internal flow of DFIG is calculated, and the output power of unit stator node is obtained;3 the unit is equivalent to PQ power supply, considering the influence of neutral point voltage, the three-phase asymmetric node power balance equation of distribution network is established, the power flow of low voltage distribution network is calculated, and the three-phase voltage of grid-connected point is obtained;4 according to the difference between DFIG grid-connected point and DFIG stator sequence voltage, the convergence of alternating iteration is judged, and if it is not converged, the internal flow of unit is recalculated and cyclic iteration is carried out.The application considers the influence of three-phase asymmetric node voltage of low voltage distribution network on the internal flow of DFIG, and improves the accuracy of power flow calculation of doubly-fed wind turbine into low voltage distribution network.

The disclosure discloses a measurement method for arc suppression coil grounding transformer tap adjustment imbalance, comprising: measuring the neutral point voltage of the grounding transformer; measuring the three-phase capacitance value and the total ground capacitance value of the grounding transformer; inquiring the reactance value, the inductance value and the damping resistance value of the arc suppression coil; calculating the first displacement voltage at the tap adjustment place when the arc suppression coil is connected in series with the grounding transformer; calculating the second displacement voltage at the tap adjustment place when the arc suppression coil is connected in parallel with the grounding transformer; judging whether the tap of the grounding transformer meets the compensation range of the arc suppression coil when the arc suppression coil is connected in series with the grounding transformer according to the first displacement voltage; judging whether the tap of the grounding transformer meets the compensation range of the arc suppression coil when the arc suppression coil is connected in parallel with the grounding transformer according to the second displacement voltage.

The invention relates to a phase selection and positioning method for a single-phase earth fault of a stator winding of a pumped storage generator motor, and belongs to the technical field of generator fault detection. On the premise of considering asymmetry of three-phase ground capacitance and ground conductance of a stator winding of the generator motor, real-time measurement of the three-phase asymmetric ground parameters is realized by measuring the fundamental wave and third harmonic component of the neutral point voltage. And then, a grounding fault phase judgment and grounding resistance calculation method is provided, and reliable positioning accurate to the stator slot position is realized by constructing a stator winding single-phase grounding fault position evaluation equation. And finally, the property of the ground fault is judged by measuring the size of the ground resistance for the second time, and the instantaneous ground fault and the permanent ground fault can be accurately distinguished. The method is simple, reliable, high in safety and easy to implement.

The invention belongs to the technical field of power transformers, and particularly relates to a constant-flux medium-voltage regulation autotransformer based on neutral point voltage regulation. Comprising a main transformer body and an exciting winding body, the main transformer body comprises a first iron core, and a series winding, a common winding and a medium-voltage regulating winding which are wound on the first iron core; the medium-voltage regulating winding is arranged at a neutral point, and the medium-voltage regulating winding is connected with the voltage regulating switch and is used for realizing voltage regulation; the excitation winding body is connected in parallel with the medium-voltage regulating winding; the excitation winding body is connected in series between the common winding and the series winding; by arranging the medium-voltage regulating winding on the neutral point side of the common winding, the potential to ground and the inter-phase voltage difference of a voltage regulating loop are remarkably reduced, so that the insulation grade required by the tap switch is greatly reduced, and the cost, the size and the failure rate of switch equipment are effectively reduced. And a main power loop and a voltage regulation control loop are decoupled by adopting a double-body structure, so that the electromagnetic compatibility and the operation stability of the system are improved.

The invention discloses a relay protection parameter self-configuration method and device, a program product and a medium, and relates to the technical field of power systems. The method comprises the following steps: acquiring a three-phase voltage, a three-phase current and a neutral point voltage of a target generator in a preset time period; determining a phase angle difference based on the three-phase voltage and the three-phase current, and constructing a comprehensive state feature vector based on the phase angle difference and the neutral point voltage; classifying the operation conditions of the target generator to obtain a plurality of operation modes, and determining a corresponding health state track cluster according to the comprehensive state feature vector under each operation mode; and analyzing geometric features of each health state track cluster, and determining protection parameters of a relay protection device for protecting the target generator based on each geometric feature. The method has the effect of improving the effectiveness of the self-configuration protection parameters of the relay protection device.

The application discloses a kind of H-MMC motor drive system comprehensive control method of same frequency operation.The H-MMC motor drive system includes: H-MMC, permanent magnet synchronous motor and AC power grid;System comprehensive control method of same frequency operation is mainly composed of compensation phase angle calculation, motor side speed control, grid side power control, bridge arm submodule voltage stabilization and voltage equalization control and modulation wave calculation 5 parts;The application gives the topological structure of H-MMC motor drive system, adjusts motor phase angle by real-time calculation compensation phase angle, to control H-MMC bridge arm difference frequency power tends to zero;Greatly reduce the requirement of circulation and neutral point voltage, without increasing controller, to realize the stable operation of system under same frequency working condition, with the advantages of small submodule capacitor voltage ripple, small loss, relatively simple control when same frequency operation.

The application discloses a contactor structure, which comprises a shell and a moving iron core, an electromagnetic coil, a neutral line static contact, a neutral line moving contact, a phase line static contact and a phase line moving contact which are arranged in the shell; the neutral line moving contact and the phase line moving contact are fixedly arranged on the moving iron core; the neutral line static contact and the phase line static contact are arranged in the shell in correspondence with the neutral line moving contact and the phase line moving contact; one end of the neutral line static contact close to the neutral line moving contact and / or one end of the neutral line moving contact close to the neutral line static contact are elastically deformable structures; a first distance between the neutral line static contact and the neutral line moving contact is smaller than a second distance between the phase line static contact and the phase line moving contact; and the electromagnetic coil is arranged in correspondence with the moving iron core. The neutral point voltage drift problem caused by the neutral line being separated first or the neutral line being combined last compared with the other three phases is effectively avoided.

This invention discloses a fault-tolerant operation method for Active Power Filters (APFs) based on residual vectors, relating to harmonic mitigation and inverter control in power systems. The method includes: establishing a mathematical model of an active power filter (APF) with a T-type three-level topology; fault analysis based on fault characteristics using the DC-side capacitor voltage residual value; synthesizing a new virtual output vector from the residual voltage vector of the T-type three-level inverter to achieve fault-tolerant operation of the APF; and selecting different control strategies according to different fault types to improve harmonic compensation. This invention achieves improved harmonic compensation by selecting different control strategies based on different fault types. The control strategy eliminates the need to consider neutral point voltage balance, relying solely on hardware parameters. The virtual vector synthesized from the residual vector effectively participates in the inverter's vector output, thus reducing harmonics.