Abstract: The present application provides a method for pre-charging a cascade converter and a cascade converter. The cascade converter includes a main transformer, multiple power units, a control unit and a precharge unit. Power units connected with the precharge unit are a first power unit group, and other power units are a second power unit group. The control unit controls first switch set in the precharge unit to be turned on, and low-voltage AC power supply in the precharge unit performs pre-charging for a bus capacitor through an inverter circuit in the first power unit group. When a voltage of the bus capacitor reaches a first voltage threshold, the control unit controls a rectifier circuit in the first power unit group to work to magnetize the main transformer, thereby performing pre-charging for bus capacitors in the second power unit group.

Abstract: A cascade converter and an online monitoring method are provided. The capacitor parameters of a bus capacitor of a cascade unit is acquired according to the voltage across the bus capacitor of the first target cascade unit, the cascade side current of the single-phase cascade module and a switching signal from the first target cascade unit. In such way, it is not necessary to increase the number of the current sensors. The capacitor parameters of the bus capacitor herein include the equivalent series resistance and the capacitance. Since the capacitor parameters of the bus capacitor are monitored constantly, the aging degree of the bus capacitor can be checked at any time.

Abstract: The present application provides a method for pre-charging a cascade converter and a cascade converter. The cascade converter includes a main transformer, multiple power units, a control unit and a precharge unit. Power units connected with the precharge unit are a first power unit group, and other power units are a second power unit group. The control unit controls first switch set in the precharge unit to be turned on, and low-voltage AC power supply in the precharge unit performs pre-charging for a bus capacitor through an inverter circuit in the first power unit group. When a voltage of the bus capacitor reaches a first voltage threshold, the control unit controls a rectifier circuit in the first power unit group to work to magnetize the main transformer, thereby performing pre-charging for bus capacitors in the second power unit group.

Abstract: A method of modulating a cascaded three-phase VFD, including: obtaining space voltage vectors according to states and output levels of switches of power units in each stage, and dividing the vectors into large vectors, medium vectors, small vectors and zero vectors according to their lengths; arranging the vectors into a vector space, and dividing the vector space into sectors, wherein each sector corresponds to a group of the large vector, the medium vector, the small vector and the zero vector; determining a sector in which a reference voltage vector is located, wherein the reference voltage vector is composed by the group of vectors; calculating action time of the vectors in the group; allocating an action order to the vectors; and generating a three-phase modulated wave signal based on the action orders and the action time.

Abstract: A cascade converter and an online monitoring method are provided. The capacitor parameters of a bus capacitor of a cascade unit is acquired according to the voltage across the bus capacitor of the first target cascade unit, the cascade side current of the single-phase cascade module and a switching signal from the first target cascade unit. In such way, it is not necessary to increase the number of the current sensors. The capacitor parameters of the bus capacitor herein include the equivalent series resistance and the capacitance. Since the capacitor parameters of the bus capacitor are monitored constantly, the aging degree of the bus capacitor can be checked at any time.

Abstract: A dead zone compensation circuit includes: a coordinate transformation module configured to perform a coordinate transformation on three-phase output currents of the three-phase frequency converter based on a given angle, for transforming the three-phase output currents from a three-phase static coordinate to a two-phase rotary coordinate to obtain a reactive current component of the three-phase output currents; a filter module configured to obtain a reactive current fluctuation amount; an error calculation module configured to calculate an error between the reactive current fluctuation amount and a zero value; a regulation and control module configured to regulate and control the reactive current fluctuation amount based on the error, for obtaining a voltage regulation variation; and a summing module configured to add the voltage regulation variation to a reference voltage, for obtaining a regulated voltage, the regulated voltage being used to generate a driving signal for the three-phase frequency converter

Abstract: A dead zone compensation circuit includes: a coordinate transformation module configured to perform a coordinate transformation on three-phase output currents of the three-phase frequency converter based on a given angle, for transforming the three-phase output currents from a three-phase static coordinate to a two-phase rotary coordinate to obtain a reactive current component of the three-phase output currents; a filter module configured to obtain a reactive current fluctuation amount; an error calculation module configured to calculate an error between the reactive current fluctuation amount and a zero value; a regulation and control module configured to regulate and control the reactive current fluctuation amount based on the error, for obtaining a voltage regulation variation; and a summing module configured to add the voltage regulation variation to a reference voltage, for obtaining a regulated voltage, the regulated voltage being used to generate a driving signal for the three-phase frequency converter

Abstract: A method of modulating a cascaded three-phase VFD, including: obtaining space voltage vectors according to states and output levels of switches of power units in each stage, and dividing the vectors into large vectors, medium vectors, small vectors and zero vectors according to their lengths; arranging the vectors into a vector space, and dividing the vector space into sectors, wherein each sector corresponds to a group of the large vector, the medium vector, the small vector and the zero vector; determining a sector in which a reference voltage vector is located, wherein the reference voltage vector is composed by the group of vectors; calculating action time of the vectors in the group; allocating an action order to the vectors; and generating a three-phase modulated wave signal based on the action orders and the action time.

Abstract: The present invention discloses a cascade type power conversion device and a communication system for the same. Each phase of the cascade type power conversion device comprises a plurality of power modules connected in series and a communication system. The communication system comprises a plurality of low voltage communication units and a plurality of optical fibers. The plurality of low voltage communication units are connected in series and disposed in the plurality of power modules, respectively. And the plurality of optical fibers are connected between the low voltage communication units and a master control system of the cascade type power conversion device.

Abstract: Switching control systems and methods are presented for controlling power conversion systems to provide electrical power to a grid or other load in which a synchronous machine is driven by a wind turbine or other prime mover to provide generator power to a switching type current source converter (CSC), with a current source rectifier (CSR) of the CSC being switched to provide d-axis control of the synchronous machine current based on grid power factor feedback, and with a current source inverter (CSI) of the CSC being switched to provide leading firing angle control and selective employment of dumping resists to dissipate excess generator energy in a fault mode when a grid voltage drops below a predetermined level.

Abstract: Switching control systems and methods are presented for controlling power conversion systems to provide electrical power to a grid or other load in which a synchronous machine is driven by a wind turbine or other prime mover to provide generator power to a switching type current source converter (CSC), with a current source rectifier (CSR) of the CSC being switched to provide d-axis control of the synchronous machine current based on grid power factor feedback, and with a current source inverter (CSI) of the CSC being switched to provide leading firing angle control and selective employment of dumping resists to dissipate excess generator energy in a fault mode when a grid voltage drops below a predetermined level.

Abstract: Control systems, methods and power conversion systems are presented for controlling harmonic distortion, in which multi-sampling space vector modulation (SVM) is employed for controlling power converter switching devices, with a reference vector being sampled two or more times during each SVM period to update the SVM dwell times more than once during each SVM cycle.

Abstract: Power conversion apparatus and methods are presented for providing electrical power to a grid or other load in which a synchronous machine is driven by a wind turbine or other prime mover to provide generator power to a switching type current source converter (CSC), with a current source rectifier (CSR) of the CSC being switched to provide d-axis control of the synchronous machine current based on grid power factor feedback, and with a current source inverter (CSI) of the CSC being switched to provide leading firing angle control and selective employment of dumping resists to dissipate excess generator energy in a fault mode when a grid voltage drops below a predetermined level.

Abstract: Control systems, methods and power conversion systems are presented for controlling harmonic distortion, in which multi-sampling space vector modulation (SVM) is employed for controlling power converter switching devices, with a reference vector being sampled two or more times during each SVM period to update the SVM dwell times more than once during each SVM cycle.

Abstract: Power conversion apparatus and methods are presented for providing electrical power to a grid or other load in which a synchronous machine is driven by a wind turbine or other prime mover to provide generator power to a switching type current source converter (CSC), with a current source rectifier (CSR) of the CSC being switched to provide d-axis control of the synchronous machine current based on grid power factor feedback, and with a current source inverter (CSI) of the CSC being switched to provide leading firing angle control and selective employment of dumping resists to dissipate excess generator energy in a fault mode when a grid voltage drops below a predetermined level.