A high voltage/ultrahigh voltage direct current transmission inverter side frequency control implementing method includes: transmitting a deviation between the inverter side power grid frequency and rated frequency to the inverter side frequency controller, wherein the frequency controller regulates and outputs a modulation quantity by adopting self-adaptive parameters according to different operation conditions; when the interstation communication is normal, the modulation quantity output of the inverter side frequency controller causes the rectifier side and the inverter side to form a new power/current order through the interstation communication; when the interstation communication is abnormal, converting the inverter side to current control from voltage control and converting the rectifier side to voltage control from current control; superposing the modulation quantity output of the inverter side frequency controller to the power/current order of the inverter side, changing the size of the transmission power to realizing the inverter side frequency control.

A high voltage/ultrahigh voltage direct current transmission inverter side frequency control implementing method includes: transmitting a deviation between the inverter side power grid frequency and rated frequency to the inverter side frequency controller, wherein the frequency controller regulates and outputs a modulation quantity by adopting self-adaptive parameters according to different operation conditions; when the interstation communication is normal, the modulation quantity output of the inverter side frequency controller causes the rectifier side and the inverter side to form a new power/current order through the interstation communication; when the interstation communication is abnormal, converting the inverter side to current control from voltage control and converting the rectifier side to voltage control from current control; superposing the modulation quantity output of the inverter side frequency controller to the power/current order of the inverter side, changing the size of the transmission power to realizing the inverter side frequency control.

A system, including: a plurality of load commutated inverters (LCIs) connected in parallel, wherein each LCI includes: a source bridge for converting an alternating current (AC) voltage to a direct current (DC) voltage, wherein the source bridge includes at least one current switching device; a load bridge for converting the DC voltage from the source bridge to a variable frequency AC voltage; and a DC link coupling the source bridge to the load bridge; wherein each LCI includes a respective current regulator for controlling the at least one current switching device in the source bridge of the LCI to generate a current in the DC link.

A system, including: a plurality of load commutated inverters (LCIs) connected in parallel, wherein each LCI includes: a source bridge for converting an alternating current (AC) voltage to a direct current (DC) voltage, wherein the source bridge includes at least one current switching device; a load bridge for converting the DC voltage from the source bridge to a variable frequency AC voltage; and a DC link coupling the source bridge to the load bridge; wherein each LCI includes a respective current regulator for controlling the at least one current switching device in the source bridge of the LCI to generate a current in the DC link.

Disclosed are a soft start method, device, and system of a hybrid distribution transformer (HDT) based on unbypassing its voltage-compensating converter, which belong to the technical field of transformer control. According to the method, through a grid-side current controller, a DC-link voltage controller, a split-capacitor voltage balance controller, and a load voltage controller, a start process of the HDT is divided into an uncontrolled rectification stage and a PWM rectification stage. According to the present disclosure, an anti-parallel thyristor of the voltage-compensating converter is closed without a bypass in a process of energization. A DC-link capacitor is charged by respective converters of two transformers of the HDT simultaneously, and thus an energization flow is simpler. In addition, an inrush current at an initial phase of the PWM rectification stage can be effectively mitigated by improving an existing steady-state control strategy.

Disclosed are a soft start method, device, and system of a hybrid distribution transformer (HDT) based on unbypassing its voltage-compensating converter, which belong to the technical field of transformer control. According to the method, through a grid-side current controller, a DC-link voltage controller, a split-capacitor voltage balance controller, and a load voltage controller, a start process of the HDT is divided into an uncontrolled rectification stage and a PWM rectification stage. According to the present disclosure, an anti-parallel thyristor of the voltage-compensating converter is closed without a bypass in a process of energization. A DC-link capacitor is charged by respective converters of two transformers of the HDT simultaneously, and thus an energization flow is simpler. In addition, an inrush current at an initial phase of the PWM rectification stage can be effectively mitigated by improving an existing steady-state control strategy.