Disclosed are a control method and control system for a modular multilevel converter and a power transmission system. The control method includes calculating an actual capacitor voltage of the sub-module; calculating a reference capacitor voltage of the sub-module; dividing the plurality of sub-modules into a plurality of modules, reference capacitor voltages of the sub-modules in the same module are the same, and reference capacitor voltages of the sub-modules from different modules are different; sorting in the module to obtain a first voltage sequence; sorting among different modules to obtain a second voltage sequence; and determining the sub-modules to be switched on or switched off according to charging and discharging states of the sub-module, the first voltage sequence and the second voltage sequence, until an actual level of the bridge arm is consistent with a desired level, wherein the desired level changes using a first preset value as a step.

Disclosed are a control method and control system for a modular multilevel converter and a power transmission system. The control method comprises: calculating an actual capacitor voltage and a reference capacitor voltage of the sub-module; dividing the plurality of sub-modules into a plurality of modules, wherein reference capacitor voltages of the sub-modules in the same module are the same, and reference capacitor voltages of the sub-modules among different modules are different; obtaining a first voltage sequence and a second voltage sequence; and determining the sub-modules to be switched on or switched off according to charging and discharging states of the sub-modules, the first voltage sequence and the second voltage sequence, until an actual level of the bridge arm is consistent with a desired level, wherein the desired level changes taking an insert value selected from a combination of one or more elements in a collection {INTER.sub.k} as a step.

A power conversion device includes a plurality of leg circuits and a control device. The control device controls an output voltage at a first converter cell, which is controlled not based on the circulating current, based on a first voltage instruction value. The control device controls an output voltage at a second converter cell using a first value based on a deviation between a circulating current and a circulating current instruction value and a second value based on a deviation between a capacitor voltage and a capacitor voltage instruction value in the second converter cell. When the capacitor voltage at the second converter cell is less than a first threshold, the control device linearly combines an auxiliary voltage instruction value including at least one of a DC component and a fundamental AC component of the AC circuit with the first value and the second value.

A power conversion device includes a power conversion circuit unit including a plurality of leg circuits, and a control device. Each of the leg circuits includes a plurality of first converter cells each having a capacitor and connected in series to each other and a plurality of second converter cells each having the capacitor and connected in series to each other. The plurality of first converter cells are controlled not based on a circulating current circulating between the plurality of leg circuits, and the plurality of second converter cells are controlled based on the circulating current. The control device stops a switching operation of at least one second converter cell in the plurality of second converter cells when a voltage at the capacitor in the second converter cell becomes less than a first threshold.

A charging circuit of an electronic device having a three-level converter, and a method and a device for controlling balancing in a charging circuit are provided. The electronic device includes a battery, at least one processor, and a charging circuit. The charging circuit includes, as a three-level converter, a switching circuit including multiple switching elements and a flying capacitor, and a filter circuit including an inductor and a capacitor. The charging circuit includes, as a balancing circuit, a balancing control circuit configured to, during balancing corresponding to a designated a mode, based on whether the balancing corresponds to targeted balancing, generate an output for maintaining or switching a balancing control direction configured for the designated mode, and a switching control circuit configured to perform switching for the switching elements in a balancing control direction corresponding to the designated mode, based on an output of the balancing control circuit, or perform switching for the switching elements in a direction reverse to a balancing control direction corresponding to the designated mode.

An inverter circuit control method and a device thereof are provided. In the control method, after determining a DC bus voltage and an output leakage current of a target inverter circuit, a modulation harmonic wave to be injected into a SPWM signal is adjusted according to the DC bus voltage or the output leakage current if it is determined according to the DC bus voltage that the target inverter circuit satisfies a preset modulation condition, such that total harmonic distortion of a current of the target inverter circuit is within a preset range. The DC bus voltage and the output leakage current of the target inverter circuit are used as references for adjusting the modulation harmonic wave, ensuring total harmonic distortion of the current of the target inverter circuit to be within a preset range.

A multi-level inverter having one or more banks, each bank containing a plurality of low voltage MOSFET transistors. A processor configured to switch the plurality of low voltage MOSFET transistors in each bank to switch at multiple times during each cycle.

In an MMC-type power conversion device, a control device calculates an evaluation value representing the degree of variations in voltage of capacitors of individual converter cells. When this evaluation value exceeds a threshold value, the control device controls the converter cells as follows: (i) when current in a positive direction flows through a first converter cell with a voltage of the capacitor greater than a mean value, reducing an output time of positive voltage, (ii) when current in a negative direction flows through the first converter cell, increasing an output time of positive voltage, (iii) when current in the positive direction flows through a second converter cell with a voltage of the capacitor smaller than a mean value, increasing an output time of positive voltage, or (iv) when current in the negative direction flows through the second converter cell, reducing an output time of positive voltage.

An inverter includes a DC/DC converter which converts a direct current received from a DC voltage source into an intermediate circuit voltage of an intermediate circuit, a DC/AC converter which converts the intermediate circuit voltage into an AC voltage, and a monitoring unit which monitors capacitors of the intermediate circuit for protection against overvoltages. If an overvoltage occurs at one of the capacitors of the intermediate circuit the overvoltage unit decouples the DC voltage source from the intermediate circuit by actuating the DC/DC converter.

Systems and methods that facilitate multilevel hysteresis voltage control methods for cascaded multilevel voltage modulators having a plurality of power cells connected in series and has any positive integer number of output voltage levels to control any unipolar voltage on the load of the voltage modulator, and transfer electrical power from an electrical grid via AC/DC converters or directly from energy storage elements of the power cells to that load. A method of operational rotation of the power cells of a multilevel voltage modulator, which ensures an equal power sharing among the power cells and voltage balancing of the energy storage elements of the power cells of the modulator.