60 results about "Phase angle difference" patented technology

The invention discloses a transformer area electric leakage fault diagnosis method and device based on fault recording and a storage medium, and relates to the technical field of electric leakage fault diagnosis. The method comprises the steps of calculating a fundamental wave phase angle difference between a residual current and each phase current in a first analysis window based on event recording data, and calculating a phase angle consistency score based on the fundamental wave phase angle difference; judging whether the corresponding phase is a leakage phase or not according to the phase angle consistency score; on the basis of the instantaneous value of each electrical quantity, generating a statistic sequence in which each electrical quantity in the second analysis window is aggregated according to a fixed time period; according to the statistical magnitude sequence, calculating a mean value transition amount of the residual current, a synchronization parameter of the residual current and the total amount of the three-phase current, and duration of the residual current exceeding a threshold value; and judging the electric leakage type according to the mean value transition amount, the synchronization parameter and the duration time. According to the method, the defect that a traditional amplitude correlation method is easily influenced by sampling deviation is overcome, phase positioning is more stable and accurate, and wiring errors and insulation damage are effectively distinguished.

The present invention discloses a transient synchronous stability control method for a meshed SVG based on AC / DC voltage hybrid control, comprising: calculating the internal potential phase angle of the meshed SVG system based on operating parameter data of the meshed SVG system based on a DC voltage self-synchronous control module; judging whether the phase angle difference between the phase angle at a port of the meshed SVG system and the internal potential phase angle is less than 2°, and judging that the meshed SVG system is stable when the phase angle difference is less than or equal to 2°; implementing AC voltage stability enhancement control on the meshed SVG system when the phase angle difference exceeds 2°, and calculating the output current of the meshed SVG system; judging whether the output current reaches a preset current limit value; if the output current is greater than or equal to the current limit value, judging that the current of the meshed SVG system is saturated and there is a risk of instability, and implementing DC voltage stability enhancement control on the meshed SVG system.

A kind of single-phase grounding fault single-end impedance ranging method and system of DG-containing distribution line, method includes: input parameter and DG distribution to equipment, when single-phase grounding fault occurs in distribution network, the zero sequence voltage of equipment rises, it is judged that single-phase grounding fault occurs, and fault ranging calculation is started;Using symmetrical component method to obtain the sequence components of voltage and current at bus, DG access, load access and fault point;On the basis of the sequence components of voltage and current at fault point, the phase angle difference between line fault phase voltage and current is obtained, and the fault distance is calculated according to the phase angle difference.The ranging effect of the method of the application is very good, and it has practicality.

The invention provides a vacuum circuit breaker inrush current suppression method and system based on a voltage phase angle, and relates to the technical field of power system protection. Calculating a voltage phase angle difference value and analyzing historical data to obtain characteristic parameters; inputting the phase angle difference, the voltage amplitude, the system frequency and the historical characteristic parameters into a double-hidden-layer neural network, and outputting an optimal switching-on moment and a protection trigger sequence; when a switching-on instruction is received, the protection assembly is triggered immediately or in a delayed manner according to the optimal moment; after all the multi-stage protection assemblies are conducted, the circuit breaker body is controlled to be switched on; and adding the actual inrush current data to the historical data, optimizing the neural network model, and realizing continuous inrush current suppression.

The invention provides a signal denoising method and device for optical fiber sensing vibration monitoring. The method comprises the following steps: collecting vibration data of a to-be-detected optical fiber, and judging the type (signal or noise) of the to-be-detected optical fiber according to a mahalanobis distance; then, eliminating signal data, filling noise data by using an interpolation method, and generating a noise signal; thirdly, amplitude and phase angle sequences of noise and vibration signals are calculated through Fourier transform, and then an amplitude difference and a phase angle difference are obtained; and finally, calculating a de-noised frequency spectrum according to the difference values, and obtaining a de-noised vibration monitoring signal through inverse Fourier transform. The method is small in calculation amount and rapid, the output signal-to-noise ratio and the algorithm accuracy can be improved, the false alarm rate and the missing report rate are reduced, and the engineering application requirement is met.

The present invention relates to a method for setting a synchronous system constant value of an idling grid-connected phase regulator, comprising the following steps: Step S1: obtaining a phase regulator frequency variation curve under an idling condition; Step S2: selecting the phase regulator rated frequency ±Δ f Partial linearization is performed to measure the frequency change rate of the phase regulator; step S3: considering that the phase regulator voltage rotates at least 360 degrees relative to the grid voltage after the frequency difference constant is satisfied, a calculation model for the minimum frequency difference setting value is obtained in combination with the measured frequency change rate; step S4: using the measured synchronous closing lead time, considering the synchronous grid connection condition under the maximum frequency difference, a calculation model for the phase angle difference setting value of the synchronous check relay is obtained in combination with the measured frequency change rate; step S5: based on the minimum frequency difference obtained by the minimum frequency difference setting value calculation model and the relay phase angle difference obtained by the synchronous check relay phase angle difference setting value calculation model, the synchronous parallel connection of the phase regulator and the grid is achieved. The present invention effectively reduces the impact of grid connection and meets the requirement of 100% grid connection probability.

The invention discloses an intelligent control method and system for real-time switching of a frequency converter, and relates to the field of real-time switching control of the frequency converter, and the method comprises the steps: analyzing the change slope of a frequency deviation time sequence through linear regression based on the phase angle and frequency value of the current output voltage of the frequency converter; meanwhile, the phase angle difference value variation between adjacent sampling points is calculated; the method comprises the following steps of: establishing a state machine of transfer logic, entering a phase angle monitoring state after the frequency is continuously converged, and generating a switching ready signal after judging that a frequency deviation trend and a phase angle difference trend both meet a stable approaching condition; after switching is completed, the switching stability is analyzed through the fluctuation amplitude of the output current and the change trend of the instantaneous rotating speed change rate, a closed-loop correction mechanism is started when the switching stability is detected to be abnormal, the optimal switching moment of the frequency converter is determined, and it is guaranteed that the motor runs stably before and after switching.

The invention provides a novel power distribution system pilot impedance protection method and system considering an unmeasurable T-connection inverter power supply, and belongs to the technical field of power system relay protection. According to the method, a unified current phase angle interval of different types of inverter power supplies under a positive sequence network is established, and an impedance model is uniformly represented under a negative sequence network, so that multi-source fault characteristic decoupling is realized; under a symmetric fault, constructing a dynamic threshold criterion of a positive sequence differential current and a voltage phase angle difference before a T contact fault, and breaking through a metal fault dead zone limit; for an asymmetric fault, a negative sequence impedance phase angle accumulation and multiplicative polarity discrimination mechanism is provided, the protection speed is improved, and the influence of transition resistance is prevented.

The invention discloses a system strength control method and system for a new energy power system in a disturbance state, and relates to the technical field of new energy power systems, and the method comprises the steps: determining a multi-infeed dynamic system according to a power factor, a phase angle difference and the new energy power system; according to the disturbance factors of the new energy power system and the multi-infeed dynamic system, the corresponding dynamic mode is determined, and the accuracy of the dynamic mode is ensured. Therefore, a corresponding feature function and a feature subsystem are matched based on the dynamic mode; in the characteristic subsystem, a corresponding quantitative index is determined based on the power factor and the phase angle difference, and the system strength of the new energy power system in the disturbance state is presented by the quantitative index, so that quantitative control of the power factor and the phase angle difference is realized, and quantitative expression is performed aiming at the system strength of the new energy power system in the disturbance state; and the system strength control accuracy of the new energy power system in the disturbance state is ensured.

The invention belongs to the technical field of power system measurement and control, and relates to a fundamental wave zero-sequence current detection method based on a time domain CPT theory, which comprises the following steps: obtaining a time domain current signal and a voltage signal based on an actual power grid; based on the time domain current signal and the voltage signal, obtaining a physical quantity based on a CPT theory; the physical quantities based on the CPT theory comprise homologous voltage, active power, reactive power and basic apparent power; calculating the physical quantity based on the CPT theory to obtain a fundamental current effective value, a fundamental current voltage phase angle difference and a fundamental current phase; substituting the physical quantity, the voltage signal, the fundamental current effective value and the fundamental current phase based on the CPT theory into a zero-sequence current calculation formula to obtain fundamental zero-sequence current information; the fundamental wave zero-sequence current information comprises a fundamental wave zero-sequence current instantaneous value and a fundamental wave zero-sequence current effective value and amplitude; therefore, fundamental wave zero-sequence current detection which works stably under the conditions of harmonic distortion and three-phase imbalance is realized.

The present invention provides a seamless closed-loop power transfer device and a method for improving the waveform quality of the device, including: when the device is put into use, determining the phase angle difference between two AC bus voltages, where different phase angle differences correspond to different compensation voltages; determining the equivalent winding value of the secondary winding of the transformer required, adjusting the series-parallel relationship of the secondary winding to output the required compensation voltage; during the process of the device exiting, changing the conduction angle of the thyristor, so that the DC voltage output by the rectifier gradually decreases, the inversion modulation ratio of the inverter remains unchanged, the AC voltage output by the inverter gradually decreases, and the compensation voltage gradually decreases. After the DC voltage drops to a preset value, then reducing the inversion modulation ratio to make the compensation voltage continue to decrease, so that the amplitude of the AC bus voltage after power transfer remains unchanged. The present invention enables the inversion modulation ratio of the inverter to be maintained at a stable level through the series-parallel design of the secondary winding of the transformer and the control of the thyristor conduction angle, improving the waveform quality of the output of the seamless closed-loop power transfer device.

The invention belongs to the technical field of mechanical transmission systems, and particularly discloses a Halbach coupler torsional rigidity self-adaptive adjusting method and system.The method comprises the following steps that vibration signals of an inner ring and an outer ring of a Halbach coupler are collected and subjected to phase-locked loop analysis, and low-frequency information of the inner ring and the outer ring is obtained; comparing the low-frequency information of the inner and outer rings to calculate the phase angle difference delta phi of the inner and outer rings; a linear displacement sensor is used for converting and measuring a gap between an inner ring and an outer ring of the Halbach coupling, combining a phase angle difference delta phi, obtaining a real-time magnetic torsion rigidity value, calculating a real-time rigidity error delta K, carrying out self-adaptive calculation on the real-time rigidity error delta K and the phase angle difference delta phi, and combining self-adaptive PID control of a motor iteration step length. And obtaining an optimal motor step length delta s, and controlling the frameless motor to finely adjust the gap of the Halbach coupling. By the adoption of the technical scheme, the frameless motor is controlled to adjust the gap between the inner ring and the outer ring, quasi-zero rigidity adjustment is accurately achieved, and the torsional vibration damping performance of the torsional vibration buffer is improved.

Systems and methods for transferring a load between power sources may include monitoring voltage waveforms of power sources, in response to a power quality event affecting a first power source, switching a first switch device off to disconnect the load from the first power source, calculating a phase angle difference between the power sources based on the monitored voltage waveforms, selecting one of a first and second algorithms for transferring the load to a second power source based on the phase angle, selectively switching a second switch device using the selected one of the first algorithm and the second algorithm to transfer the load to the second power source. A controller may select the one of the first algorithm and the second algorithm based on the phase angle and a metric of the load transfer associated with the algorithms.

The invention discloses a high-voltage cable metal sheath grounding system fault rapid diagnosis method and system based on the same sheath loop phase angle difference absolute value and the sheath current effective value, and relates to the technical field of power system fault diagnosis. The method comprises the following steps: collecting sheath current data at the head end and the tail end of a high-voltage cable metal sheath loop in real time; phase and current effective value information in the sheath current data is extracted, and the phase angle difference absolute value of the head end and the tail end of a sheath loop and the standard effective value of current are calculated; and judging whether a fault exists and the fault type according to the change of the absolute value of the phase angle difference and the standardized effective value of the current. According to the invention, various faults in the high-voltage cable metal sheath grounding system can be quickly and accurately diagnosed.

The invention discloses a power transmission line double-end traveling wave fault positioning method and device independent of satellite time synchronization. The method comprises the steps that when it is determined that a power transmission line breaks down, fault initial traveling waves are acquired, and a first power frequency traveling wave phasor corresponding to a first fault detection device and a second power frequency traveling wave phasor corresponding to a second fault detection device are determined; determining an additional phase angle difference between the first power frequency traveling wave phasor and the second power frequency traveling wave phasor, the additional phase angle difference being used for representing clock asynchronism between the first fault detection device and the second fault detection device; the phase angle difference of the power frequency traveling wave phasor caused by the time difference of the fault initial traveling waves is detected by the first fault detection device and the second fault detection device; and determining the fault occurrence position of the power transmission line according to the additional phase angle difference, the line length of the power transmission line between the first fault detection device and the second fault detection device and the wave velocity of the traveling wave. According to the invention, accurate positioning of the fault occurrence position in the power transmission line can be realized without satellite time synchronization.

The invention discloses an automatic quasi-synchronization device and a synchronization verification blocking relay setting calculation method, and the setting calculation of the leading time, the switching-on and switching-off pulse width, the voltage difference, the frequency difference, the frequency modulation pulse width and the voltage regulation pulse width of the automatic quasi-synchronization device of a generator is carried out. And carrying out setting calculation on the maximum allowable phase angle difference, the voltage difference and the frequency difference of the synchronous verification blocking relay. By accurately calculating the setting parameters, coordination of the matching relation between the quasi-synchronization device and the synchronization verification blocking relay is ensured, the success rate and stability of generator parallel operation are improved, and the risk of power grid accidents is reduced. The method is suitable for the technical field of power system automation, and is especially suitable for parallel operation control of generators.

The invention relates to the technical field of power distribution and utilization, and discloses a synchronous switching-on phase angle difference calculation method and system, a storage medium and equipment, and the method comprises the following steps: obtaining two voltage signals at the same time at the two sides of switch equipment, and detecting and repairing an abnormal point; carrying out IIR mean filtering on the signal; judging whether the signal frequency is between 40Hz and 60Hz or not; carrying out direct current removal processing on the signal; judging whether the effective values of the signals are greater than 80% of a standard effective value or not; and calculating a signal phase angle difference and outputting a result. The method is simple and effective, when the sampling frequency of the feeder terminal device is low, the accuracy of a phase angle difference calculation result is improved through a designed algorithm, so that synchronous closing is controlled more accurately, and the method has very high engineering practicability.

The invention discloses a phase difference comparison-based state evaluation method for a lightning arrester with a series gap in a line. The method comprises the following steps of calculating a phase difference between voltages at the head end and the tail end of the line; collecting the sum of the horizontal spans of the towers of the whole line, and establishing an equation set to solve the phase angle difference of each span; and after the phase angle difference of each gear is obtained simultaneously, the sum of the phase angle difference from the head end to the target tower is subtracted by taking the bus voltage phase of the head end transformer substation as a reference, and the voltage phase of the target tower is obtained. Obtaining the total leakage current of the target tower lightning arrester, measuring the outer surface current by using a power taking ring, and subtracting the outer surface current from the total current to obtain a body current and a phase; and subtracting the target tower voltage phase from the body current phase to obtain a current-voltage phase difference, and carrying out expansion calculation on the phase difference of the same-phase lightning arresters of the whole line. And solving the average value of the phase differences, calculating the deviation value of each lightning arrester, and if negative deviation is abnormal, non-negative normal. The lightning arrester phase acquisition problem is solved, the state is evaluated by transversely comparing the phase difference, and a new thought and an implementation method are provided.

The invention discloses an initial phase angle high-precision measurement method and device based on automatic correction of a double-point angle difference value, and relates to the technical field of electric signal measurement of relay protection devices. In order to overcome the defects that an existing electric signal angle calibration device is limited by sampling frequency, large in difference estimation error and incapable of achieving dynamic compensation, an initial phase angle and cyclic wave data are measured through electric signal break variables; calculating an angle difference value between the second point and the first point according to the cyclic wave data; calculating a reference angle according to the number of sampling points, and calculating a compensation reference quantity; a compensation coefficient model is adopted to obtain an angle dynamic compensation coefficient, and the initial phase angle is dynamically compensated according to the angle difference value; and calibrating a real-time phase angle difference value, and calibrating an initial phase angle according to the real-time phase angle difference value. The method is mainly used for compensating the break variable of the electric signal.

The present invention relates to a method for monitoring a line break fault of an FTU, comprising the following steps: collecting electrical data of a line of the FTU through a preset electrical mutual inductor to obtain electrical data; wherein the electrical data includes voltage data and current data; performing phase angle calculation on the voltage data and the current data to obtain a phase angle difference; if the phase angle difference is not within a standard range, calling a database to obtain attributes of the line of the FTU; locating the line break based on the attributes of the line, the phase angle and the electrical data through a preset distributed parameter model to obtain a line break area; performing dynamic feature recognition on electrical parameters corresponding to the line break area to obtain dynamic fault features, performing fault type analysis on the line break area based on the dynamic fault features to obtain a fault type monitoring report. The method solves the technical problem that traditional fault monitoring methods rely on manual inspections and simple fault indicators, making it difficult to meet positioning accuracy and determine fault types.

The present application discloses a dual-current-based control method for a grid-connected power factor of a flyback inverter, and a controller. The method comprises: acquiring an working electrical signal of a target power grid; obtaining a first current modulation wave signal; obtaining a second current modulation wave signal; obtaining a waveform of a corrected modulation wave signal; and controlling a flyback inverter to output, to the target power grid or an electric device, a target alternating current corresponding to the waveform of the corrected modulation wave signal. The corrected modulation wave signal, which is generated by using a second half waveform of the first current modulation wave signal and a first half waveform of the second current modulation wave signal, has a signal having a phase and frequency consistent with those of the working electrical signal of the power grid, and also has a signal having a phase angle difference from the working electrical signal of the power grid. By using the corrected modulation wave signal of the present application to control the flyback inverter, the flyback inverter can accurately adjust the power factor during grid connection and the harmonic distortion rate is reduced.

The application discloses a kind of power system homologous switch quantity variable position time difference measurement method and system, it is related to the technical field of power system automation, including: respectively obtaining the fault recording file of protection device and intelligent recording device and homologous switch quantity variable absolute time;Respectively calculate the fault component value of fault recording file in homologous ac voltage channel, and determine fault component point position;Respectively in homologous ac voltage channel, find the zero-crossing time corresponding to the nearest zero-crossing point from fault component point position;In fault recording file intercepts fault section waveform;With the sampling rate of intelligent recording device, first fault section waveform is resampled;Calculate phase angle difference;Calculate the homologous switch variable position time difference of protection device and intelligent recording device.The application alleviates the technical problem that existing technology cannot accurately measure the homologous switch quantity variable position time difference of protection device and intelligent recording device when not connected to external public clock or external time service fails.

The invention relates to a rapid loop closing and opening method for a 30-degree phase angle difference distribution line. The method comprises the following steps: acquiring basic electrical parameters of a looped network system; a PSCAD simulation model is built; calculating loop closing impact current and operation current of the loop opening point switch; determining a main loop opening point switch protection constant value and a standby loop opening point switch protection constant value; judging whether the phase angle difference of the two sides of the interconnection switch is within a range allowing loop closing or not; and the controller sends a closing signal to the interconnection switch to monitor the voltage and current states of the distribution line in real time. According to the invention, during high-load operation of the distribution line or equipment maintenance, rapid loop closing and opening operation can be realized, the power failure time and frequency can be reduced, and the loop closing current duration can be obviously shortened, so that the requirements of safety and stability of the system and equipment can be met, and the risk of power grid fault caused by overlong loop closing current duration can be reduced; the application range of loop closing and opening operation is widened, and the requirement of a user for power supply reliability is met.

The application provides a voltage phase angle-based vacuum circuit breaker inrush current suppression method and system, relates to the technical field of power system protection, and comprises the following steps: obtaining a voltage signal and historical closing data of a circuit breaker; calculating a voltage phase angle difference value and analyzing historical data to obtain characteristic parameters; inputting the phase angle difference value, a voltage amplitude, a system frequency and the historical characteristic parameters into a double-hidden layer neural network to output an optimal closing time and a protection triggering sequence; when a closing instruction is received, deciding whether to immediately or delay trigger a protection component according to whether it is the optimal time; controlling the circuit breaker body to close after all multi-stage protection components are turned on; and adding actual inrush current data to the historical data to optimize the neural network model and realize inrush current continuous suppression.

The invention discloses a small current grounding system fault line selection method and system based on transient information fusion, and relates to the field of small current grounding system fault detection, and the method comprises the steps: carrying out the signal decomposition and reconstruction through employing a VMD algorithm, and calculating the transient energy of a reconstructed current signal; calculating a transient energy measure according to a transient energy value in a power frequency period; according to the second current decomposition result, the second voltage decomposition result, the first current decomposition result and the fundamental component, the fifth harmonic component and the seventh harmonic component corresponding to the first voltage decomposition result, the sum of admittance phase angle difference coefficients in a power frequency period is calculated, and the transient information fusion criterion measure is further calculated; and determining the fault power transmission line. According to the invention, the reliability of fault line selection criteria can be improved.

The present invention discloses a control method for improving the power pulsation characteristics of a boost converter with a DC / DC-IPOS structure. By connecting an AC / DC conversion link in series at the output and introducing a phase angle difference on the AC side, that is, adding an arbitrary angle to the given standard phase of any commutation branch, causing the two branches to commutate with a phase shift, the problem of power pulsation of the converter caused by the IPOS structure is suppressed, thereby improving the DC-side voltage waveform. The present invention adds a phase difference between the series branches on the output side, causing a phase difference in the voltage of the AC link of the converter, achieving the purpose of suppressing the series voltage ripple on the DC side, effectively improving the waveform of the series DC voltage output on the high-voltage side, and enabling the boost converter to achieve more excellent performance indicators. The present invention can effectively improve the problem of power pulsation of the input-parallel output-series structure of the DC / DC voltage converter for DC power transmission, can significantly improve the DC voltage waveform on the output side, and enhance the controllability of the system.

This invention discloses a method for on-site calibration of low-voltage smart switches, comprising the following steps: initiating meter search, initiating broadcast time synchronization, acquiring downstream devices through topology identification, synchronously freezing the low-voltage smart switch to be calibrated and each downstream device, transcribing the voltage, current, active power, and reactive power of the previously frozen data, performing voltage gain, current gain, and phase angle difference calibration for each phase, and performing power calibration for each phase after waiting for a freeze interval. Compared with existing technologies, the method disclosed in this invention can expand the applicability of on-site meter calibration and improve the accuracy of on-site meter calibration.

The invention relates to a single-phase earth fault section positioning method and system and a medium. The method comprises the following steps: detecting and extracting zero-sequence current of each section sampling point of a line; injecting a power frequency current signal into the neutral point, and detecting and extracting the zero-sequence current of each section sampling point of the line again; according to the zero-sequence current detected and extracted before and after the zero-sequence current signal is injected into the neutral point, calculating a phase angle # imgabs1 # formed by the ratio of the relative change of the zero-sequence current of each sampling point # imgabs0 # to the zero-sequence current before the zero-sequence current signal is injected; and calculating the phase angle difference value between the sampling points at the two ends of the section, and determining the section corresponding to the maximum value in all the phase angle difference values as the grounding fault section, so that the fault section can be quickly and accurately positioned.

A satellite-timing-independent double-ended traveling wave fault locating method and apparatus for a power transmission line. The method comprises: when it is determined that a fault occurs in a power transmission line, acquiring a fault initial traveling wave (S101); determining a first power-frequency traveling-wave phasor corresponding to a first fault detection apparatus and a second power-frequency traveling-wave phasor corresponding to a second fault detection apparatus (S102); determining an additional phase angle difference between the first power-frequency traveling-wave phasor and the second power-frequency traveling-wave phasor (S103), wherein the additional phase angle difference is used for representing a phase angle difference between the power-frequency traveling-wave phasors caused by clock asynchronization between the first fault detection apparatus and the second fault detection apparatus and a time difference between a moment at which the first fault detection apparatus detects the fault initial traveling wave and a moment at which the second fault detection apparatus detects the fault initial traveling wave; and on the basis of the additional phase angle difference, the length of the power transmission line between the first fault detection apparatus and the second fault detection apparatus, and the speed of the traveling wave, determining a fault occurrence location in the power transmission line (S104).

The present invention discloses a flexible low-frequency power transmission system considering frequency and phase angle optimization. The flexible low-frequency power transmission system of the present invention includes: a first-frequency AC power grid operating at a first frequency; a second-frequency AC power grid operating at a second frequency, where the second frequency is lower than the first frequency; a modular multilevel matrix converter, one side of which is connected to the first-frequency AC power grid through a first-frequency transformer, and the other side is connected to the second-frequency AC power grid through a second-frequency transformer to achieve the conversion between the first frequency and the second frequency; a second-frequency optimization value and a first-frequency and second-frequency AC power grid side voltage initial phase angle difference optimization value, under which conditions, to achieve the same steady-state voltage on the second-frequency AC power grid side, the single-bridge-arm voltage requirement value of the modular multilevel matrix converter is minimized, and the number of modules required for each bridge arm is minimized, thereby reducing the cost of the converter in the low-frequency power transmission system.