Conversion system and conversion device

Abstract

An electrical conversion system includes: an inductor electrically connected to an alternating current (AC) power grid; a medium voltage direct current (MVDC) bus; a non-isolated AC/DC converter, provided with a first terminal electrically connected to the inductor and a second terminal electrically connected to the MVDC bus, wherein the non-isolated AC/DC converter is configured to output a bus voltage based on an input voltage from the AC power grid; a plurality of circuit branches connected in parallel, wherein each circuit branch is connected to the MVDC bus via a corresponding converter; and a filtering network disposed between the AC power grid and the MVDC bus and is grounded through at least one capacitor.

1 . An electrical conversion system, comprising:
 an inductor electrically connected to an alternating current (AC) power grid;   a medium voltage direct current (MVDC) bus;   a non-isolated AC/DC converter, provided with a first terminal electrically connected to the inductor and a second terminal electrically connected to the MVDC bus, wherein the non-isolated AC/DC converter is configured to output a bus voltage based on an input voltage from the AC power grid;   a plurality of circuit branches connected in parallel, wherein each circuit branch is connected to the MVDC bus via a corresponding converter; and   a filtering network, provided with a first terminal, a second terminal and a third terminal, wherein a first resistance-capacitance circuit is disposed between the first terminal and the third terminal of the filtering network, a second resistance-capacitance circuit is disposed between the second terminal and the third terminal of the filtering network, the first terminal of the filtering network is electrically connected to the AC power grid, the second terminal of the filtering network is electrically connected to the MVDC bus, and the third terminal of the filtering network is grounded through at least one capacitor.   
     
     
         2 . The system of  claim 1 , wherein each circuit branch comprises at least one selected from a group comprising:
 at least one of a DC load, a DC power supply, and a DC power storage, connected to the MVDC bus via at least one DC/DC converter; and   at least one of an AC load, an AC power supply, and an AC power storage, connected to the MVDC bus via at least one DC/AC converter.   
     
     
         3 . The system of  claim 2 , wherein the MVDC bus is connected to at least one of the circuit branches via at least two DC/DC converters or DC/AC converters, wherein input terminals of the DC/DC converters or DC/AC converters are connected in parallel and output terminals of the DC/DC converters or DC/AC converters are connected in series or in parallel. 
     
     
         4 . The system of  claim 2 , wherein the DC/DC converter comprises a plurality of isolated DC/DC conversion units with input terminals of the plurality of isolated DC/DC conversion units connected in series and output terminals of the plurality of isolated DC/DC conversion units connected in parallel. 
     
     
         5 . The system of  claim 1 , further comprising a controller and a DC circuit breaker corresponding to each circuit branch, wherein the DC circuit breaker is disposed between the non-isolated AC/DC converter and the corresponding converter of each circuit branch, and the DC circuit breaker is electrically connected to the controller, and part of operations of the DC circuit breaker is controlled based on a control signal sent by the controller. 
     
     
         6 . The system of  claim 1 , wherein the inductor comprises a common-mode and differential-mode integrated inductor, and is disposed between the AC power grid and the non-isolated AC/DC converter. 
     
     
         7 . The system of  claim 1 , wherein the inductor comprises a differential-mode inductor and a common-mode inductor, the differential-mode inductor is connected between the AC power grid and the non-isolated AC/DC converter, and the common-mode inductor is disposed on a circuit between the AC power grid and at least one of the circuit branches, wherein the circuit between the AC power grid and at least one of the circuit branches is between the first terminal and the second terminal of the filtering network. 
     
     
         8 . The system of  claim 1 , further comprising a plurality of the inductors and a plurality of the non-isolated AC/DC converters, wherein each inductor and each corresponding non-isolated AC/DC converter are connected in series, and a plurality of combinations of the series connected non-isolated AC/DC converter and inductor are connected in parallel. 
     
     
         9 . The system of  claim 8 , further comprising a controller configured to detect power of the circuit branches and control operation states of the at least two non-isolated AC/DC converters based on the power of the circuit branches. 
     
     
         10 . The system of  claim 9 , wherein when the circuit branches are half loaded or less, the controller controls part of the at least one non-isolated AC/DC converters to operate normally, and controls the remaining non-isolated AC/DC converters to stop operating. 
     
     
         11 . The system of  claim 1 , wherein the non-isolated AC/DC converter is an N-level AC/DC converter, and the non-isolated AC/DC converter comprises a plurality of switch bridge arms, wherein both an upper bridge arm and a lower bridge arm of each of the plurality of switch bridge arms of the non-isolated AC/DC converter include a plurality of semiconductor devices connected in series, and a rated withstand voltage Vsemi of each of the plurality semiconductor devices is greater than or equal to (Vbus*δ)/((N−1)*Nseries*λ), where Vbus represents the bus voltage, δ represents bus fluctuation, N represents a number of levels of the non-isolated AC/DC converter, λ represents a voltage derating coefficient of a respective semiconductor device of the plurality semiconductor devices, and λ≤1, and Nseries represents a number of semiconductor devices connected in series, and Nseries≥2. 
     
     
         12 . The system of  claim 2 , wherein the at least one DC/DC converter comprises at least one switch bridge arm, wherein both an upper bridge arm and a lower bridge arm of the at least one switch bridge arm of the DC/DC converter include a plurality of semiconductor devices connected in series. 
     
     
         13 . The system of  claim 2 , wherein the at least one DC/DC converter is a bi-directional DC/DC converter or a unidirectional converter. 
     
     
         14 . A conversion device, connected between an alternating current (AC) power grid and a circuit branch, the conversion device comprising:
 an inductor electrically connected to the AC power grid;   a medium voltage direct current (MVDC) bus;   a non-isolated AC/DC converter, provided with a first terminal electrically connected to the inductor and a second terminal electrically connected to the MVDC bus, wherein the non-isolated AC/DC converter is configured to output a bus voltage based on an input voltage from the AC power grid;   at least one isolated DC/DC converter, provided with a first terminal electrically connected to the MVDC bus and a second terminal electrically connected to the circuit branch, wherein the isolated DC/DC converter is configured to convert the bus voltage into an output voltage to the circuit branch; and   a filtering network, provided with a first terminal, a second terminal and a third terminal, wherein a first resistance-capacitance circuit is disposed between the first terminal and the third terminal of the filtering network, a second resistance-capacitance circuit is disposed between the second terminal and the third terminal of the filtering network, the first terminal of the filtering network is electrically connected to the AC power grid, the second terminal of the filtering network is electrically connected to the MVDC bus, and the third terminal of the filtering network is grounded through at least one first capacitor.   
     
     
         15 . The device of  claim 14 , wherein a second capacitor and a third capacitor are connected in series across the MVDC bus, and the second terminal of the filtering network is electrically connected between the second capacitor and the third capacitor. 
     
     
         16 . The device of  claim 14 , wherein the inductor comprises a common-mode and differential-mode integrated inductor, and is disposed between the AC power grid and the non-isolated AC/DC converter. 
     
     
         17 . The device of  claim 14 , wherein the inductor comprises a differential-mode inductor and a common-mode inductor, the differential-mode inductor is connected between the AC power grid and the non-isolated AC/DC converter, and the common-mode inductor is disposed between the differential-mode inductor and the non-isolated AC/DC converter, or the common-mode inductor is disposed between the non-isolated AC/DC converter and the at least one isolated DC/DC converter. 
     
     
         18 . The device of  claim 14 , wherein the first resistance-capacitance circuit comprises a first resistor and a fifth capacitor connected in series, and the second resistance-capacitance circuit comprises a second resistor and a sixth capacitor connected in series. 
     
     
         19 . The device of  claim 14 , wherein the at least one isolated DC/DC converter comprises a plurality of DC/DC converters with input terminals of plurality of the DC/DC converters connected in parallel and output terminals of the DC/DC converters connected in series or in parallel. 
     
     
         20 . The device of  claim 14 , wherein the at least one isolated DC/DC converter comprises a plurality of isolated DC/DC conversion units with input terminals of the plurality of isolated DC/DC conversion units connected in series and output terminals of the plurality of isolated DC/DC conversion units connected in parallel. 
     
     
         21 . The device of  claim 14 , wherein the non-isolated AC/DC converter comprises at least two AC/DC converters connected in parallel. 
     
     
         22 . The device of  claim 14 , further comprising at least one controller,
 wherein the at least one controller is configured to control operations of the non-isolated AC/DC converter and/or the at least one isolated DC/DC converter.   
     
     
         23 . A conversion device, connected between an alternating current (AC) power grid and a circuit branch, the conversion device comprising:
 an inductor electrically connected to the AC power grid;   a medium voltage direct current (MVDC) bus;   a non-isolated AC/DC converter, provided with a first terminal electrically connected to the inductor and a second terminal electrically connected to the MVDC bus, wherein the non-isolated AC/DC converter is configured to output a bus voltage based on an input voltage from the AC power grid;   at least one non-isolated DC/DC converter, provided with a first terminal electrically connected to the MVDC bus and a second terminal electrically connected to the circuit branch, wherein the non-isolated DC/DC converter is configured to convert the bus voltage into an output voltage to provide energy to the circuit branch; and   a filtering network, provided with a first terminal, a second terminal and a third terminal, wherein a first resistance-capacitance circuit is disposed between the first terminal and the third terminal of the filtering network, a second resistance-capacitance circuit is disposed between the second terminal and the third terminal of the filtering network, the first terminal of the filtering network is electrically connected to the AC power grid, the second terminal of the filtering network is electrically connected to the MVDC bus or the second terminal of the non-isolated DC/DC converter, and the third terminal of the filtering network is grounded through a first capacitor.   
     
     
         24 . The device of  claim 23 , wherein a fourth capacitor is connected across the MVDC bus. 
     
     
         25 . The device of  claim 23 , wherein the inductor comprises a common-mode and differential-mode integrated inductor, and is disposed between the AC power grid and the non-isolated AC/DC converter; or
 the inductor comprises a differential-mode inductor and a common-mode inductor, the differential-mode inductor is connected between the AC power grid and the non-isolated AC/DC converter, and the common-mode inductor is disposed on a circuit between the AC power grid and the circuit branch, wherein the circuit between the AC power grid and the circuit branch is between the first terminal and the second terminal of the filtering network.   
     
     
         26 . The device of  claim 23 , wherein the non-isolated DC/DC converter comprises a plurality of non-isolated DC/DC conversion units with input terminals of the plurality of non-isolated DC/DC conversion units connected in series. 
     
     
         27 . The device of  claim 23 , wherein the non-isolated AC/DC converter comprises at least two AC/DC converters connected in parallel. 
     
     
         28 . The device of  claim 23 , further comprising at least one controller, wherein the at least one controller is configured to control operations of the non-isolated AC/DC converter and/or the at least one non-isolated DC/DC converter.