102 results about "Ac frequency" patented technology

The invention relates to the technical field of micro-grid control, and discloses an AC / DC micro-grid layered distributed control method and system, and the method comprises the steps: obtaining a DC voltage outputted by a distributed power supply in a DC micro-grid and an AC frequency outputted by a distributed power supply in an AC micro-grid, and carrying out the normalization processing; according to the voltage normalization value and the frequency normalization value, a finite time consistency algorithm is adopted to calculate a primary active power reference value of the interconnected converter; compensating the primary active power reference value according to a distributed secondary controller to obtain a secondary active power reference value; and generating a control signal of each interconnected converter according to the secondary active power reference value. Through hierarchical distributed control, the purposes that the total power sent by the direct current micro-grid and the alternating current micro-grid is proportionally distributed according to respective rated capacities and the active power transmitted by all the interconnected converters is proportionally distributed according to the transmission capacities are achieved, and the operation safety and stability of the alternating current and direct current micro-grid are effectively improved.

In an example, an electrochemical monitoring system for determining one or more parameters of interest of an electrochemical cell can include measurement circuitry, which can be configured to obtain, for a plurality of specified alternating current (AC) frequencies: (1) a first AC voltage measurement across nodes which can be coupleable to the electrochemical cell, and (2) a second AC voltage measurement across a sensing impedance which can be elicited in response to the AC stimulus. The sensing impedance can be coupled in series with the electrochemical cell. The electrochemical monitoring system can also include a controller circuit, which can be configured to jointly estimate model parameters corresponding to an equivalent circuit model (ECM) of a combination of the electrochemical cell and the sensing impedance, such as using the first and second AC voltage measurements for the plurality of specified AC frequencies.

A horticultural lighting device includes an LED array with multiple LED channels of different wavelengths, each having one or more LEDs. A voltage regulator supplies at least one LED channel with a constant voltage. A processor produces a PWM signal for a driving circuit coupled with the LED channels. In some cases the processor operates a tuning circuit to adjust the constant voltage thereby adjusting an intensity of the one or more LEDs of the one or more LED channels. A lighting system has multiple lamps, each with a zero cross detector that generates a timing signal based on an AC input signal. The PWM signal of each lamp has a frequency that is a multiple of the AC frequency. A method for lighting a facility includes generating a light recipe based on sensor data with an AI engine with one or more neural networks.

Provided is a battery module and battery rack having enhanced fire safety features. The battery module includes a swelling / pressure sensor that detects swelling of a battery cell. An output signal of the sensor is used to halt operation of a battery rack / battery system containing the battery module and prevent charging and discharging of the battery module. In an embodiment, the battery module uses an AC-to-AC power supply to provide AC frequency power for balancing battery cells of the battery module. In an embodiment, the battery rack includes an internal water fire suppression system that provides battery cooling in the event of a battery cell fire to prevent the spread and / or reigniting of the fire.

The present invention is a power coordination control method for an AC / DC hybrid power distribution system based on a solid-state transformer. The system includes a main grid, a solid-state transformer and an AC / DC microgrid. The solid-state transformer is a three-level structure of a low-voltage level, an isolation level and a medium-voltage level. The control method is composed of a low-voltage level, an isolation level, a medium-voltage level control strategy and a pre-synchronization control strategy. The low-voltage level associates the low-voltage AC frequency and the low-voltage DC voltage representing the power state of the AC / DC microgrid, and realizes power coordination between AC / DC microgrids without communication. The isolation level and the medium-voltage level establish a connection between the medium-voltage AC frequency and the low-voltage DC voltage, and realize the power exchange between renewable energy and the medium-voltage AC bus according to its own state. The pre-synchronization control strategy enables seamless switching of various modes. Under the premise of no communication and no switching control strategy, the present invention realizes stable operation and seamless switching of various modes, improves system reliability, and enhances the level of renewable energy consumption.

A thermal impedance monitoring process for a power module of a power converter for converting a DC current to an AC current, or converting an AC circuit to a DC current, where a semiconductor dissipates asymmetric losses between two half cycles of an AC frequency f of the AC current, said power module comprising at least a semiconductor die, a semiconductor die is attached to a stack of materials of layers for heat dissipation and / or electrical connection thereof, the process comprising: sampling and measuring a signal related to a junction temperature Tj of the semiconductor die at a frequency higher than twice the AC frequency of the AC current, calculating a duration [Delta] t = tTjmax-tTjmin between a moment tTjmax at which the junction temperature of the semiconductor die is at a maximum value and a moment tTjmin at which the junction temperature is at a minimum value in one cycle of the AC current, and storing the duration [Delta] t in a memory, repeating the step of sampling and measuring said signal and the step of calculating said duration at different times tx = t0 to tm during the operating life of the power module to provide a series of durations [Delta] t0 to [Delta] tm, and comparing the values of said durations [Delta] t0 to [Delta] tm for monitoring the evolution of said duration [Delta] t, and determining the evolution of the degradation of the thermal impedance of the power module.

A measuring system includes a vibration-type transducer and electrically coupled measuring system electronics unit for controlling the transducer and evaluating vibration measurement signals provided by the transducer. The exciter arrangement has a vibration exciter which is positioned and aligned such that a drive offset is no more than 0.5% of the tube length. The measuring system electronics are configured to supply electrical power to the vibration exciter by means of an electrical drive signal having a temporally variable electrical current and to provide the drive signal at least intermittently with a sinusoidal second useful current having a second AC frequency, in order to monitor a quality of the measured substance based upon a corresponding second useful signal component of at least one of the vibration measurement signals.

The present invention relates to the field of microgrid control technology, and discloses a hierarchical distributed control method and system for an AC-DC microgrid, including obtaining the DC voltage output by distributed power sources in the DC microgrid and the AC frequency output by distributed power sources in the AC microgrid, and performing normalization processing; according to the voltage normalization value and the frequency normalization value, adopting a finite-time consensus algorithm to calculate the primary active power reference value of the interconnected converters; compensating the primary active power reference value according to a distributed secondary controller to obtain a secondary active power reference value; and generating control signals for each interconnected converter according to the secondary active power reference value. Through hierarchical distributed control, the present invention realizes the goal of proportional distribution of the total power generated by the DC microgrid and the AC microgrid according to their respective rated capacities, and proportional distribution of the active power transmitted by all interconnected converters according to the transmission capacity ratio, effectively improving the safety and stability of the operation of the AC-DC microgrid.

This application discloses an islanding detection method and apparatus. The method includes: monitoring the AC frequency of an inverter, which fluctuates within a preset range when the inverter is in normal control mode; when the instantaneous offset value of the AC frequency exceeds the preset range, the frequency before the instantaneous offset is taken as the first frequency; if the frequency in the first frequency data within a first preset time range is only greater than or only less than the first frequency, the AC frequency at the end of the first preset time is taken as the second frequency; continuously adjusting the output power of the inverter based on the change of the current AC frequency; and when the frequency in the second frequency data within a second preset time range is only greater than or only less than the second frequency, the inverter can be promptly instructed to report the islanding status. By using a two-step judgment method, the method distinguishes between islanding and normal load switching, avoiding the inverter actively adjusting the system voltage or frequency and improving the accuracy of islanding detection.

This application provides a control method for an energy storage system, comprising: determining the state parameters corresponding to each individual battery cell; determining a multi-dimensional control factor corresponding to each individual battery cell based on different state dimensions indicated by the state parameters at preset calculation cycles; sorting multiple individual batteries cells according to the charge / discharge state of the energy storage system and the multi-dimensional control factor; determining the output demand voltage corresponding to the energy storage system based on the peak reference voltage and AC frequency corresponding to the energy storage system; and controlling the access state of each individual battery cell in the next AC cycle by applying the nearest level approximation method based on the sorting result, the output demand voltage, and the maximum supply voltage corresponding to each individual battery cell in the next AC cycle. This application controls the energy storage units connected to the charge / discharge circuit of the energy storage system and their access time through multi-dimensional control factors calculated from multiple dimensions, thereby achieving full utilization of the energy of the energy storage units.

The application discloses a kind of water pump AC frequency converter energy-saving optimization control system, it is related to water pump energy-saving control technical field;Including: database, identification perception module, operation optimization module and control feedback module.Database acquires water pump operating parameter, and based on this and calculates lift, water pump efficiency and load rate;Identification perception module is based on lift, water pump efficiency and load rate deviation analysis constructs fusion deviation curve, and based on this obtains judging index to analyze curve area, to identify inefficient operation scene;Operation optimization module determines target flow, target lift according to end water demand and pipe network pressure demand, and obtains target frequency in combination with water pump similarity law and efficiency, lift deviation correction;Control feedback module implements frequency conversion control according to target operating parameter, and real-time feedback and secondary correction are carried out to execution result, form closed-loop optimization control, improve energy efficiency identification ability under low load condition, reduce water pump operating energy consumption.

A power supply device comprises a busbar, a circuit measurer, a temperature sensor and an operational circuit. The busbar is coupled to the inverter and the motor. The temperature sensor is used for measuring an initial temperature in an initial state. The circuit measurer is used for measuring voltage, current and alternating current frequency on the busbar. The arithmetic circuit is coupled to the circuit measurer and the temperature sensor. The operational circuit is configured to: calculate a resistance signal based on the AC frequency; calculating a first transient power of the busbar based on the current on the busbar and the resistance value signal; calculating a first temperature rise value of the busbar based on the first transient power; and adding the initial temperature and the first temperature rise value to obtain a first transient ideal temperature of the busbar. The invention further relates to a busbar temperature measuring method.

The utility model relates to electrical engineering and can be used to protect electromagnetic voltage transformers from ferroresonant oscillations occurring in voltage transformers in distribution networks with a voltage class of 6-10 kV, alternating current with a frequency of 50 Hz with an isolated neutral.In a device for protecting voltage transformers from ferroresonance phenomena, designed with the possibility of connecting to two terminals of auxiliary secondary windings of three single-phase transformers connected in an open-delta circuit, containing a series-connected RTS thermistor, a damping resistor and an electronic switching circuit with a threshold switching characteristic, which includes a switching element in the form of a triac, the control electrode of which is connected to a control circuit including a dinistor, two resistors and a capacitor, the control electrode of the triac is connected to the control circuit through a normally closed controlled key, the RTS thermistor is equipped with a temperature sensor connected to the controlled key, and the dinistor is selected to be symmetrical.Technical result: increasing the effective operating time of a device for protecting voltage transformers from ferroresonance phenomena in the presence of modes in the network accompanied by prolonged exposure to single-phase short circuits to ground by ensuring restoration of the original operating mode. 2 fig.

The utility model relates to an ARM microprocessor operation device for an alternating current frequency converter, and belongs to the technical field of alternating current frequency converter matching equipment.The ARM microprocessor operation device comprises an installation shell, a box door is hinged to the front face of the installation shell through hinges, and a wiring assembly used for wire arrangement is installed on the inner side of the installation shell; a ventilation assembly used for ventilation and heat dissipation is installed on the inner side of the installation shell, a water cooling assembly used for water cooling is installed on the outer side of the installation shell, a control panel used for control is fixedly installed on the outer side of the box door, and an alternating current frequency converter body is installed on the inner side of the installation shell. The inner side of the installation shell is provided with an ARM microprocessor main body used for controlling the AC frequency converter main body and an abnormal protection module used for detecting abnormal current. According to the ARM microprocessor operation equipment for the alternating current frequency converter, the equipment cannot be directly stopped when the current is unstable due to the abnormal phenomenon of the main power supply, the buffer time is provided for the equipment, and the heat dissipation effect can be ensured on the premise that the equipment is additionally arranged.

A comprehensive electrical prospecting method and device provided by the present invention, the method comprising: inputting an alternating current frequency signal with a preset bandwidth into the geological object to be measured in a frequency sweep manner, receiving the voltage data recorded by the measuring electrodes, and obtaining an amplitude-frequency response curve; finding the frequency corresponding to the amplitude attenuation position according to the amplitude-frequency response curve to obtain the response frequency of the geological object to be measured; obtaining the distribution characteristics of the water-richness of the geological object to be measured according to the difference between the response frequency of the geological object to be measured and the response frequency of a single medium; the present invention determines the distribution characteristics of the water-richness of coal and rock strata according to the difference between the response frequency of the geological object to be measured and the response frequency of a single medium. At the same time, by means of frequency sweep, the frequencies required for detecting the medium are covered, avoiding the omission situation existing in the current alternating current electrical method, so as to ensure the accuracy of the underground exploration results.

The invention discloses a servo system for a ship towing winch and a control method of the servo system. The servo system comprises a rectifying circuit, a three-phase full-bridge circuit, a braking circuit, a DSP control circuit, an output capacitor C, a brake control circuit and a rotary transformer decoding circuit. According to the servo driver, full electrification of releasing, recycling and zero-speed working condition maintaining of the ship winch is achieved, compared with a hydraulic driving device of a traditional winch, the defects that a hydraulic system is complex in structure, large in size and difficult to maintain are overcome, and an electric driving system is high in control precision, simpler to achieve and more convenient to operate. Compared with conventional alternating-current variable-frequency electric drive of an existing winch, servo drive is more suitable for the low-speed large-torque working condition, efficiency is higher, and cooperation of a PLC is not needed. Compared with a traditional speed loop and current loop control method, the control method for four-quadrant operation of the servo driver enables the winch to have an energy consumption braking function, and meanwhile the safety of the towing winch under the extreme working condition is guaranteed by being matched with a brake of the motor.

The invention discloses a frequency sensing and rapid supporting method for a wind power multi-terminal flexible direct current sending-out system. The method comprises the following steps that a fan side VSC control framework and a control framework and control rules of an alternating current power grid side flexible direct current converter station are constructed; an alternating-current power grid frequency-direct-current voltage-wind power plant power mapping model is constructed based on the characteristics of the converter station, and accurate sensing of the alternating-current frequency under the condition of no rapid communication is achieved; based on the mapping model, determining an improved frequency support strategy design scheme of the large-scale wind power multi-terminal flexible direct current sending-out system; and setting parameter constraint conditions for key parameters of the strategy. Accurate sensing of the alternating current frequency can be achieved under the condition of no rapid communication, the lowest frequency point after power disturbance is effectively raised, the frequency change rate is reduced, secondary falling of the frequency is avoided, meanwhile, different topological structures and line fault scenes are adapted, and safe and stable operation of an electric power system is guaranteed.

The utility model discloses a kind of amorphous alloy three-dimensional roll iron core annealing monitoring models, comprising: support, amorphous alloy three-dimensional roll iron core, high voltage coil, low voltage coil, insulating iron hoop, ac frequency modulation power supply, magnetized busbar and power analyzer, high voltage coil and low voltage coil are set in the upper yoke portion of amorphous alloy three-dimensional roll iron core;Insulating iron hoop is used to fix amorphous alloy three-dimensional roll iron core;Magnetized busbar is supported by insulating support plate and placed in the inner frame of the iron core;Ac frequency modulation power supply is electrically connected with high voltage coil;Voltage clamp and current clamp are electrically connected with low voltage coil respectively;Power analyzer is electrically connected with the voltage clamp and current clamp.

The application discloses a pumped storage full-power frequency converter power unit variable frequency control method and device, N power units are cascaded at an AC end to form a test valve, and M power units are cascaded at the AC end to form a test valve; the method is used for controlling the test valve to output several AC frequency target values, and the method comprises the following steps: pre-charging DC capacitors in the test valve and the test valve to target values; determining corresponding output current / power target values according to the AC frequency target values to be output; controlling the turn-on and turn-off time of the turn-off semiconductor of each power unit in the test valve and the test valve, so that the actual output current / power of the test valve is the output current / power target value, and the actual output frequency of the test valve is the AC frequency target value. The application can simulate the continuous speed regulation operation condition of the pumped storage full-power frequency converter power unit on the pumped storage unit.

The invention belongs to the technical field of power system synchronization, and particularly relates to a three-phase phase-locked loop control method and device. The method comprises the following steps: acquiring a q-axis power grid voltage sampling value of a three-phase power grid voltage sampling value under a two-phase rotating coordinate system; inputting the q-axis power grid voltage sampling value into a complex coefficient filtering sliding mode observer, extracting alternating current frequency multiplication disturbance brought by the distorted power grid voltage, and obtaining a q-axis voltage estimated value, a direct current estimated value in the alternating current frequency multiplication disturbance and a total alternating current estimated value in the alternating current frequency multiplication disturbance; the complex coefficient filtering sliding-mode observer is obtained by connecting a complex number filtering item of a complex coefficient filter in parallel in the sliding-mode observer; and calculating a phase angle estimation value of the three-phase phase-locked loop after feedback compensation based on the q-axis voltage estimation value, the direct current quantity estimation value in the alternating current frequency multiplication disturbance, the total alternating current quantity estimation value in the alternating current frequency multiplication disturbance and the power grid phase voltage amplitude. The control efficiency and accuracy of the phase-locked loop are improved, and the method has good stability and robustness.

The invention provides a wind power plant-multi-terminal flexible direct current system grid-source frequency mirror image control method, which comprises the following steps: based on a wind power plant-multi-terminal flexible direct current grid-connected system, adopting a grid frequency-active power-direct current voltage dual droop control strategy in converter stations, and analyzing power distribution characteristics and direct current voltage control characteristics of each converter station; deducing a design principle of a control coefficient; in a wind field-multi-terminal flexible direct-current grid-connected system, a positive and negative pole differential mode frequency transfer method is utilized to map power grid frequency change from direct-current voltage; based on a double droop control strategy of a wind field-multi-terminal flexible direct current grid-connected system and mapping of power grid frequency, a wind power plant side current converter obtains power grid frequency change by detecting direct current voltage and reflects the power grid frequency change on alternating current frequency of a wind power plant. The method solves the problems that when frequency mirroring from an onshore alternating current main network to an offshore alternating current power grid is achieved through droop control, a current converter is prone to overload, the mirroring precision is poor, and the frequency mirroring is prone to being disturbed by power fluctuation.

The invention discloses a control method and system of a ship alternating current and direct current hybrid power system based on a hybrid margin. The method comprises the following steps: collecting a direct current voltage of a direct current sub micro-grid and an alternating current frequency of an alternating current sub micro-grid in real time; for each energy storage unit in the DC sub-microgrid, adjusting the input and output power of the energy storage unit in different modes based on the operation margin corresponding to the state of charge; for each power supply in the AC sub-microgrid, adjusting the power supply output active power in different modes based on the power supply operation margin corresponding to the operation parameter; carrying out normalization processing on the direct-current voltage and the alternating-current frequency and calculating deviation values of the direct-current voltage and the alternating-current frequency; if the two deviation values are both in the margin range, the standby state of the interconnection converter is maintained, and the energy storage unit and the power supply autonomously complete power balance through a self droop control strategy; and if one of the two deviation values exceeds the margin range, power mutual assistance and distribution are performed on the DC sub-microgrid and the AC sub-microgrid through the interconnection converter based on a double-droop control strategy.

A resonant converter has a transformer having a primary winding and a secondary winding magnetically coupled to the primary winding via a transformer core, a controllable primary-side switching element electrically coupled to the primary winding via a primary-side resonant circuit, and a controllable secondary-side switching element electrically coupled to the secondary winding, the primary-side switching element is used for connecting the primary winding with a primary-side alternating current voltage with a predeterminable alternating current frequency, and the secondary-side switching element is used for guiding a secondary-side alternating current with an alternating current frequency through the secondary winding. The transformer has, on the secondary side, a separate secondary-side synchronous winding magnetically coupled to the primary winding for generating a secondary-side synchronous signal, and has a control device. The control device is designed to receive the secondary-side synchronization signal, to detect a zero value of the secondary-side AC current on the basis of the secondary-side synchronization signal, and to determine a time difference between a sign change of the primary-side AC voltage and reaching the zero value.

The application provides a sparse modular multilevel matrix converter topology, a design method and a control method, and the topology has three-phase symmetry on the input and output sides. The design method is for the purpose of reserving the functions and performance of a conventional M3C and reducing the cost, and comprises the following steps: setting the input side and the output side AC frequency of the matrix converter as an integer frequency division relationship; improving the utilization rate of the DC voltage and reducing the modulation amplitude of each bridge arm through a two-side phase coordination control method; and determining the number of bridge arm sub-modules to be less than the number of bridge arm sub-modules of the conventional M3C based on the modulation amplitude. Through the phase coordination technology, the number of bridge arm sub-modules is reduced on the basis of reserving the functions and performance of the conventional M3C, so that the cost is reduced, and the operation efficiency is improved to a certain extent.

The invention provides an off-grid hydrogen production system comprehensive efficiency optimization method based on alternating current frequency modulation, and belongs to the technical field of new energy hydrogen production. Comprising the following steps: establishing an electrolytic cell performance evaluation system; obtaining a performance index weight; dividing a working interval by an improved TOPSIS method; aC frequency information transmission and electrolytic cell power adaptive control are carried out. Compared with the prior art, the system state information is transmitted through the frequency signals, communication does not need to be depended on, and the problem that communication faults affect the system stability is solved. In addition, a hydrogen production power self-adaptive control strategy is designed in combination with the working interval of the electrolytic cell, the influence of the working state of the electrolytic cell is considered, and the method is suitable for various weather conditions.

The application discloses a DC link capacitor configuration method for a ship hybrid power station energy storage system, and the method comprises the following steps: constructing a ship hybrid power station energy storage system model containing an energy storage frequency modulation system and an AC power supply system, setting an inertia time constant and a damping coefficient of a VSG, and calculating an inertia frequency modulation required power; in an online stage, according to an actually measured AC frequency fluctuation and an energy storage output power considering a power ramping constraint, a DC link capacitor is calculated with the target of maintaining a DC voltage fluctuation in a safe range under a maximum frequency step fluctuation. The application quantitatively analyzes the frequency modulation required power / energy, the battery ramping power / energy and the link capacitor power / energy, uses the DC link capacitor energy as a fast frequency modulation resource in the energy storage inertia frequency modulation system, and makes up the difference between the energy storage system ramping power output and the VSG inertia frequency modulation power requirement. According to the power and energy conservation, the DC link capacitor size under the best frequency modulation power requirement of the ship comprehensive power system is obtained, the method is suitable for different types of energy storage systems and system frequency modulation requirements under different disturbances, and the inertia frequency modulation capability and the stable operation capability of the system under multiple working conditions are effectively improved.

This invention proposes a hybrid MMC fault clearing control method and apparatus with a low full-bridge ratio. The invention includes: when a DC fault is detected, the DC controller of the sending-end converter switches to fault mode, generates a fault DC internal potential through proportional control, and applies negative limiting to cut off the fault current; the AC controller switches to fault mode, adjusts the energy storage reference value of the full-bridge submodule, and generates an AC frequency deviation; the grid-side converter of the wind turbine sets the AC power reference value to zero, generates a wind turbine frequency deviation based on the power deviation, and updates the voltage phase; after the fault current returns to zero, each controller switches back to normal mode to restore power transmission. This method can quickly cut off the fault current, stabilize wind turbine operation, and ensure system fault ride-through and reliable recovery.

The invention relates to the technical field of mobile power supplies, man-machine interaction, transmission and the like, and provides a user-defined interaction method of a mobile power supply and the mobile power supply, the mobile power supply is arranged as a main device, when AC output is in a closed state and a power supply main switch button and an AC inverter switch button are pressed for a long time, a display screen flickers an AC voltage icon and an AC frequency icon at the same time, and the AC voltage icon and the AC frequency icon are displayed. The main device is prompted to enter an AC output voltage and frequency setting mode, the set values of the AC output voltage and frequency are increased once by clicking a power supply main switch button, the set values of the AC output voltage and frequency are continuously increased and displayed through an AC voltage icon and an AC frequency icon by pressing the power supply main switch button for a long time, and the set values of the AC output voltage and frequency are displayed through an AC inverter switch button by clicking an AC inverter switch button. The set value of the AC output voltage and the set value of the frequency are reduced at a time, the set value of the AC output voltage and the set value of the frequency are continuously reduced and displayed through the AC voltage icon and the AC frequency icon by pressing the switch key of the AC inverter for a long time, and therefore personalized management and use of the mobile power supply by a user are supported.

The invention relates to the technical field of converters, in particular to a bipolar AC-AC frequency converter and a control method thereof.The power frequency side of an AC-AC frequency converter body is connected to a power frequency power grid, the low frequency side of the AC-AC frequency converter body is connected to a low frequency power grid through a three-phase three-winding bipolar transformer, an A-B-C three-phase structure is adopted, and each phase comprises an upper bridge arm and a lower bridge arm; each bridge arm is formed by connecting n full-bridge sub-modules and a bridge arm inductor in series, but the inductance values of the three-phase bridge arm inductors are different. The phase three-winding bipolar transformer comprises a positive pole transformer and a negative pole transformer, the phase difference of corresponding port voltages of the positive pole transformer and the negative pole transformer is 180 degrees, and a symmetrical bipolar structure is formed; and neutral points of the two are interconnected to form a bipolar output loop. The unbalanced capacitor voltage caused by the inductance difference of the three-phase bridge arm is accurately adjusted, so that the working voltage of each module tends to be consistent, and the balanced operation of the system is ensured. Harmonic generation and electric energy fluctuation possibly caused by voltage imbalance are reduced, the electric energy quality is improved, and stable power supply of a power system is guaranteed.

The present invention discloses a half-wave shaping multilevel AC converter topology and control method suitable for AC-AC frequency conversion fields such as low-frequency power transmission. The converter comprises three phase units, each of which is connected to symmetrical converters on the 1st and 2nd sides via a DAHB isolation unit. Both converters consist of a multilevel shaping unit and a half-wave commutation unit, and are connected to AC systems of different frequencies. The multilevel shaping unit is composed of a cascade of half-bridge submodules, with the submodule capacitors consisting of two capacitors connected in series. The submodules and the DAHB isolation unit share a DC capacitor, which helps reduce the number of capacitors and improve power density. The half-wave commutation unit is a full-bridge circuit, with the bridge arm switches consisting of multiple devices connected in series, which are turned on and off according to the fundamental frequency cycle, flipping the multilevel sinusoidal half-waves modulated by the multilevel shaping unit into full sinusoidal waves. The control method for low-frequency power transmission of the present invention is as follows: the power frequency side adopts fixed module capacitor voltage control, the low-frequency side adopts fixed AC voltage control, and the DAHB adopts fixed low-frequency side module capacitor voltage control.