16 results about "Third harmonic voltage" patented technology

The invention belongs to the technical field of power electronic conversion, and particularly discloses an MMC-STATCOM system direct optimization model prediction control method and system, and the method comprises the steps: respectively calculating a differential mode voltage and a common mode voltage between an upper bridge arm and a lower bridge arm of each phase; third harmonic voltage is injected into the upper bridge arm and the lower bridge arm of each phase to obtain upper bridge arm voltage and lower bridge arm voltage of a newly-added third voltage component of each phase; and based on the obtained voltage of the upper and lower bridge arms of the newly added three-time voltage component, determining the input number of the sub-modules of the upper and lower bridge arms of each phase by adopting a nearest level approximation modulation strategy, and determining the input sub-module of each bridge arm according to the capacitor voltage sequence of each sub-module of the bridge arms and the current direction. According to the method, on the basis of keeping a discrete control structure, direct injection of third harmonic voltage under an MPC framework is achieved, and higher real-time performance and expandability are achieved.

The invention discloses a generator stator grounding fault active arc extinction method based on double-loop quasi-PR control, and the method comprises the following steps: S1, monitoring the fundamental wave zero-sequence voltage and third harmonic voltage of a neutral point and a generator end of a generator, and carrying out the fault phase selection and positioning when a single-phase stator grounding fault occurs; s2, according to a fault positioning result, calculating a fault winding potential Ef, and setting a negative value-Ef of the fault winding potential Ef as a neutral point target compensation voltage; s3, a cascaded H-bridge converter is adopted as a topological structure of the active regulation and control device, and a double-closed-loop control framework composed of a voltage outer loop and a current inner loop is established; s4, setting quasi-PR control units for the fundamental wave component and the third harmonic component in the voltage outer ring and the current inner ring respectively; and S5, controlling the cascaded H-bridge converter to output a compensation voltage consistent with the target compensation voltage-Ef, and injecting the compensation voltage into the neutral point of the generator. The voltage regulation and control precision and the arc suppression speed in the active arc suppression process of the generator can be improved, and the operation safety and reliability of the generator are improved.

The application discloses a lightning arrester phase-to-phase coupling capacitor determination method and device, medium and equipment, relates to the electrical measurement field, and mainly aims to improve the low accuracy of the existing lightning arrester phase-to-phase coupling capacitor determination. Including: obtaining the fundamental wave voltage effective value, the third harmonic voltage effective value, the fundamental wave current effective value and the third harmonic current effective value of each phase target lightning arrester; based on the fundamental wave voltage effective value, the third harmonic voltage effective value, the fundamental wave current effective value and the third harmonic current effective value, constructing a first capacitive current relationship of each phase target lightning arrester under the interference of the fundamental wave phase-to-phase capacitor and a second capacitive current relationship of each phase target lightning arrester under the interference of the third harmonic phase-to-phase capacitor; based on the phase-to-phase coupling capacitor calculation model, the fundamental wave voltage effective value, the third harmonic voltage effective value, the fundamental wave current effective value and the third harmonic current effective value are calculated to obtain the phase-to-phase coupling capacitor between each phase target lightning arrester.

The invention belongs to the technical field of offshore wind power monitoring, and particularly relates to a monitoring method for an offshore wind power land converter station. And monitoring a voltage fault at the grounding position shared by the multiple transformers according to the third harmonic voltage, monitoring a starting resistor overheating damage fault according to the starting resistor current, and monitoring whether the energy consumption device has a fault according to the energy consumption device positive electrode current. According to the scheme, through real-time acquisition of the electrical quantity data of the key equipment in the land converter station, the operation state of the key equipment can be monitored, the precision is high, and the response is rapid. The method can achieve the comprehensive and precise monitoring of the operation state of key equipment in the land converter station, and improves the operation efficiency and safety of the converter station.

This invention belongs to the field of power electronic converter technology, specifically disclosing a direct optimization model predictive control method and system for an MMC-STATCOM system. The method includes: calculating the differential-mode voltage and common-mode voltage between the upper and lower arms of each phase; injecting third harmonic voltage into the upper and lower arms of each phase to obtain the upper and lower arm voltages of the newly added third voltage component for each phase; based on the obtained upper and lower arm voltages of the newly added third voltage component, determining the number of sub-modules to be engaged in each phase's upper and lower arms using a nearest-level approximation modulation strategy; sorting the sub-modules according to the capacitor voltage of each sub-module in the arm; and determining the engaged sub-modules for each arm according to the current direction. This invention, while maintaining the discrete control structure, achieves direct injection of third harmonic voltage under the MPC framework, exhibiting higher real-time performance and scalability.

The invention provides a control method for suppressing third harmonic current of a grid-constructing type converter, which is applied to a three-phase four-wire grid-constructing type converter, and the converter is connected in parallel with a generator containing a third harmonic voltage component. The method comprises the following steps: sampling an output voltage and an output current of the network-forming converter; performing coordinate transformation on the sampled output voltage to extract a zero-axis voltage component; third harmonic compensation voltage is generated through a quasi-resonance controller based on the zero-axis voltage component, and the resonant frequency of the quasi-resonance controller is set to be three times of the rated angular frequency of the system; and introducing the third harmonic compensation voltage into a zero-axis voltage and current double-closed-loop control loop of the network-forming converter to offset a third harmonic voltage component in the voltage feedback signal. Quasi-resonance control is added to the zero-axis voltage loop to obtain the third harmonic compensation voltage to offset third harmonic voltage feedback, and generation of third harmonic current is suppressed, so that the quality of output electric energy of the converter is improved.

The invention discloses a three-phase four-bridge-arm inverter system based on static coordinate system control and a control method thereof, the three-phase four-bridge-arm inverter system comprises four bridge arms which are connected in parallel, an auxiliary network and a control module, the auxiliary network comprises two filter capacitors which are connected in series and a filter inductor which is connected with the midpoint of the two filter capacitors; the filter inductor is connected with the midpoint of the fourth bridge arm, the two filter capacitors are connected with the four bridge arms in parallel, the control module comprises a first control module and a second control module, the first control module controls the first three bridge arms based on a phase voltage effective value ring, a phase voltage transient ring, an inductive current transient state and an injected third harmonic ring, and the second control module controls the second three bridge arms based on a phase voltage transient state. And the second control module controls the fourth bridge arm based on the modulation of the third harmonic voltage, the modulation of the zero sequence current and the modulation wave of the three-phase output voltage. The first three bridge arms realize independent control to suppress negative sequence influence, the fourth bridge arm eliminates zero sequence influence, and independent control is carried out on each phase voltage without coordinate transformation, so that the system stability is improved, and the calculated amount and complexity of a control strategy are reduced.

The application provides a method and device for distributed phase modifier third harmonic zero voltage stator grounding protection, the method comprising: collecting the closing position information of the circuit breaker and static var compensator at the generator end and the analog quantity information at the generator end; calculating the third harmonic components of the zero sequence voltage at the generator end and the neutral point zero sequence voltage, the reactive power and the frequency based on the analog quantity information; forming the operating condition with the adjustment criterion, and automatically switching the third harmonic voltage ratio fixed value before and after the grid connection based on the operating condition with the adjustment criterion; forming the power with the adjustment criterion, and determining the third harmonic voltage ratio calculation fixed value based on the power with the adjustment criterion; forming the grounding protection criterion, and judging whether the third harmonic zero voltage stator grounding protection action condition is met based on the grounding protection criterion. The application can quickly identify the operating condition of the unit, and automatically switch the corresponding protection fixed value, thereby improving the flexibility of the protection. The power with the adjustment criterion is braked by the reactive power unit value, thereby further improving the protection reliability under different operating conditions.

The invention relates to a five-phase motor real-time simulation method and device considering a third harmonic flux linkage equation based on an FPGA, and the method comprises the steps: receiving motor and inverter parameters and PWM signals through the FPGA, and generating a motor terminal voltage through a five-phase inverter model; fundamental wave / third harmonic coordinate transformation is carried out on a motor model based on dynamic decoupling, an improved Euler method is adopted to solve a current differential equation, and inverse transformation is carried out after integration to obtain stator current; and outputting an electromechanical state quantity in combination with the torque and the motion equation. The whole link of the FPGA adopts fixed-point number calculation, and the nanosecond-level simulation step length is realized by unifying the data scale through parameter pre-scaling and numerical value per unit. And when the third harmonic voltage component is zero, the model is degraded into a standard five-phase motor system, and adaptive compatibility of a harmonic injection mode and a standard driving mode is realized. Compared with the prior art, fine real-time simulation of the five-phase motor system considering the third harmonic is realized, and the real-time verification requirement of a high-dynamic scene can be met.

This invention discloses an active arc suppression method for generator stator grounding faults based on dual-loop quasi-PR control, comprising the following steps: S1. Monitoring the fundamental zero-sequence voltage and third harmonic voltage at the generator neutral point and terminals, and performing fault phase selection and location when a single-phase stator grounding fault occurs; S2. Calculating the fault winding potential based on the fault location results. E f And negative it – E f S3. Set the neutral point target compensation voltage; S4. Adopt a topology structure of cascaded H-bridge converters as active control devices, and establish a dual closed-loop control framework consisting of an outer voltage loop and an inner current loop; S5. Set quasi-PR control units for the fundamental and third harmonic components in the outer voltage loop and the inner current loop, respectively; S6. Control the output of the cascaded H-bridge converter to the target compensation voltage – E f A consistent compensation voltage is injected into the generator neutral point. This invention improves the voltage regulation accuracy and arc suppression speed during the active arc suppression process of the generator, thereby enhancing the safety and reliability of generator operation.

The application discloses a three-phase four-bridge-arm inverter system based on a stationary coordinate system control and a control method thereof, which comprises four parallel bridge arms, an auxiliary network and a control module. The auxiliary network comprises two series filter capacitors and a filter inductor connected to the midpoint of the two filter capacitors. The filter inductor is connected to the midpoint of the fourth bridge arm, and the two filter capacitors are connected in parallel with the four bridge arms. The control module comprises a first control module and a second control module. The first control module controls the first three bridge arms based on a phase voltage effective value ring, a phase voltage transient ring, an inductor current transient and a third harmonic injection ring. The second control module controls the fourth bridge arm based on the modulation of a third harmonic voltage, the modulation of a zero sequence current and the modulation wave of a three-phase output voltage. The first three bridge arms realize independent control to inhibit the influence of negative sequence, and the fourth bridge arm eliminates the influence of zero sequence. The system stability is improved, and the calculation amount and complexity of the control strategy are reduced.

The application discloses a current constraint condition active and reactive comprehensive oscillation quantity minimization collaborative control method, analyzes an inverter side converter in a power grid voltage unbalanced state, quantifies double frequency fluctuation quantities of active power and reactive power caused by a negative sequence component; adopts a third harmonic voltage compensation method to suppress the negative sequence current, dynamically adjusts third harmonic voltage compensation quantities of the converter, regulates and controls three-phase current balance; based on active and reactive power fluctuation suppression of the negative sequence current compensation method, utilizes controllable negative sequence current compensation quantities to eliminate double frequency fluctuation quantities of the active and reactive power, constructs an optimization function with active and reactive comprehensive fluctuation quantity minimization as a target, and adopts a particle swarm optimization algorithm to solve an optimal negative sequence current compensation scheme in real time, realizes collaborative suppression of three-phase current balance and power oscillation, and significantly improves operation stability and power transmission capacity of the inverter side converter under an asymmetric fault under current limiting conditions.

This application provides a system and method for measuring the thermal conductivity of thin sheet materials based on 3ω harmonic detection, belonging to the field of thermal conductivity measurement technology. The system includes a PCB board, electrodes, a lock-in amplifier subsystem, and a vacuum thermostatic chamber subsystem. The PCB board is disposed within the vacuum thermostatic chamber subsystem and has a cutout area. The two ends of the electrodes overlap the PCB board, with the middle area of ​​the electrodes located above the cutout area. The thin sheet material to be measured is placed on the electrodes. The electrodes are connected to the lock-in amplifier subsystem located outside the vacuum thermostatic chamber subsystem. The method includes placing the thin sheet material to be measured on the electrodes, controlling the vacuum thermostatic chamber subsystem to reach a preset temperature and a preset vacuum level, obtaining a third harmonic voltage through the lock-in amplifier subsystem, and obtaining the thermal conductivity of the thin sheet material to be measured based on the third harmonic voltage using a calculation formula. This application reduces measurement errors, improves the accuracy of measurement results, and broadens the range of materials that can be measured.

The application discloses a kind of generator stator winding single-phase ground fault detection methods based on third harmonic voltage fault transient component, comprising the following steps: first, the zero-sequence voltage of generator neutral point and machine end side before and after fault is collected, and the fault transient component of machine end and neutral point is obtained;Second, using empirical wavelet decomposition (EWT) to extract fundamental zero-sequence voltage fault component and third harmonic zero-sequence voltage fault component;Then, based on neutral point and machine end side third harmonic voltage addition modulus to obtain action amount, subtraction modulus to obtain brake amount;Finally, using and calculating the spectral energy of action signal and brake signal in a cycle, obtain brake coefficient, construct detection criterion.The application is based on the characteristics of machine end and neutral point zero-sequence fundamental and third harmonic voltage fault transient component, and the brake coefficient is adaptively adjusted using the ratio of spectral energy, which improves the sensitivity of detection criterion.

The invention is suitable for the technical field of relay protection, and provides a generator stator grounding protection fixed value automatic setting method and protection equipment, and the method comprises the steps: obtaining a machine end third harmonic voltage vector and a neutral point third harmonic voltage vector of a generator under a preset normal operation condition; in response to an automatic setting instruction, calculating a balance coefficient to be downloaded based on the machine end third harmonic voltage vector and the neutral point third harmonic voltage vector; and performing downloading operation based on the to-be-downloaded balance coefficient, so as to enable the balance coefficient to be consistent in numerical value between the calculation side and the execution side of the protection equipment, thereby improving the setting accuracy and convenience, and enhancing the system reliability.

The embodiment of the invention discloses a distributed power supply island state detection method and related equipment, and the method comprises the steps: firstly determining a first characteristic frequency of a power grid side and a second characteristic frequency of a distributed power supply side; obtaining a first harmonic voltage ratio and a second harmonic voltage ratio according to the first harmonic voltage average value of the grid connection point and the second harmonic voltage average value of the distributed power supply side; a third harmonic voltage ratio is obtained according to the harmonic voltage average value of the grid-connected point under the first characteristic frequency before and after the grid fault occurs, and a fourth harmonic voltage ratio is obtained according to the harmonic voltage average value of the grid-connected point under the second characteristic frequency before and after the grid fault occurs; and comparing the different harmonic voltage ratios to obtain an island state detection result, so that the island state detection result can accurately reflect changes of the different harmonic voltage ratios before and after a power grid fault occurs, and the purpose of more accurately detecting the island state of the distributed power supply is achieved.