CN115276404A - Multilevel converter - Google Patents

Multilevel converter Download PDF

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Publication number
CN115276404A
CN115276404A CN202210960529.2A CN202210960529A CN115276404A CN 115276404 A CN115276404 A CN 115276404A CN 202210960529 A CN202210960529 A CN 202210960529A CN 115276404 A CN115276404 A CN 115276404A
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voltage
converter
isolated
basic
flying
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齐雨
范高
陈威
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Hangzhou Silergy Semiconductor Technology Ltd
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Hangzhou Silergy Semiconductor Technology Ltd
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    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M3/00—Conversion of dc power input into dc power output
    • H02M3/02—Conversion of dc power input into dc power output without intermediate conversion into ac
    • H02M3/04—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters
    • H02M3/06—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using resistors or capacitors, e.g. potential divider
    • H02M3/07—Conversion of dc power input into dc power output without intermediate conversion into ac by static converters using resistors or capacitors, e.g. potential divider using capacitors charged and discharged alternately by semiconductor devices with control electrode, e.g. charge pumps
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H—ELECTRICITY
    • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
    • H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
    • H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
    • H02M7/02—Conversion of ac power input into dc power output without possibility of reversal
    • H02M7/04—Conversion of ac power input into dc power output without possibility of reversal by static converters
    • H02M7/12—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
    • H02M7/21—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
    • H02M7/217—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only
    • H02M7/25—Conversion of ac power input into dc power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only arranged for operation in series, e.g. for multiplication of voltage

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  • Engineering & Computer Science (AREA)
  • Power Engineering (AREA)
  • Dc-Dc Converters (AREA)

Abstract

The invention discloses a multilevel converter, which realizes voltage-sharing control on flying capacitors by clamping each flying capacitor to fixed voltages with different values through hardware and abandons the traditional mode of regulating voltage-sharing based on regulating duty ratios of different modules or carrier phase shift angles, thereby improving the response speed of a system, reducing the difficulty and cost of a control system and having obvious advantages in high-power multilevel application occasions.

Description

Multilevel converter
Technical Field
The invention relates to the technical field of power electronics, in particular to a multilevel converter.
Background
The existing multi-level technical scheme of the flying capacitor can greatly reduce the volt-second product on the inductor, thereby reducing the volume of the inductor, and being widely applied. However, the problem of voltage sharing of each flying capacitor has been a major difficulty restricting large-scale application thereof. The method for realizing the voltage sharing of the flying capacitor by simply utilizing the control means has various defects of complex operation, complex sampling circuit, non-real-time calculation and the like, so that the cost and the benefit are not in direct proportion.
FIG. 1 is a block diagram of a conventional flying capacitor topology multilevel converter, which includes N-1 basic modules, each of which includes a pair of MOS transistors and a capacitor, twoThe MOS tube is controlled by a complementary conduction mode. The modules are controlled by a carrier phase shifting method. From v of the voltage on the capacitor C1 To v C(N-1) In turn is
Figure BDA0003789214920000011
Figure BDA0003789214920000012
The voltage resistance of the MOS transistor in each unit is the voltage difference of the capacitances of two adjacent modules, i.e.
Figure BDA0003789214920000013
Therefore, the voltage stress of the power tube is greatly reduced through the topology of the flying capacitor, and the application requirement of a high-voltage occasion can be met by using a low-voltage component. However, the topological voltage-sharing effect of the flying capacitor has a great influence on the system performance, and if the voltage-sharing effect is not good, the stress of the MOS tube is increased, so that the MOS tube is damaged and fails. Therefore, a relatively complex active control strategy is usually required to adjust the voltage sharing of the flying capacitor. The traditional control scheme adjusts voltage equalization based on adjusting the duty ratio of different modules or the carrier phase shift angle, but the scheme needs to increase a sampling circuit and the complexity of control, and reduces the reliability of the system.
Disclosure of Invention
In view of this, the present invention provides a multilevel capacitor converter to solve the problem that a voltage equalizing scheme of a flying capacitor in the prior art is complex.
In a first aspect, the present invention provides a level converter, comprising:
a switched capacitor circuit comprising at least one base module, each said base module comprising a flying capacitor and two transistors, wherein one terminal of one transistor is connected to one terminal of the other transistor through said flying capacitor; and the number of the first and second groups,
and the voltage equalizing circuit is used for respectively clamping the voltages at two ends of the flying capacitor to a fixed voltage with a corresponding value so as to realize voltage equalizing control on the flying capacitor.
Preferably, the voltage-sharing circuit comprises at least one voltage-sharing module, and the voltage-sharing modules correspond to the base modules one to one; the input end of the voltage equalizing module is coupled to a voltage stabilizing source, and the output end of the voltage equalizing module outputs the fixed voltage, wherein the voltage stabilizing source is configured to be related to the direct current voltage of the first end or the direct current voltage of the second end of the switched capacitor circuit, and the first end of the switched capacitor circuit is one end close to the inductance device.
Preferably, the voltage equalizing module is configured as an isolated DC-DC converter and the isolated DC-DC converter is configured to generate the fixed voltage.
Preferably, the transformation ratio of the isolated DC-DC converter is determined according to the voltage of the corresponding flying capacitor and the voltage of the input end connection point of the isolated DC-DC converter.
Preferably, when the multilevel converter is a DC-DC converter, the input terminal of at least one isolated DC-DC converter corresponding to the basic module receives the DC voltage at the first terminal or the DC voltage at the second terminal of the switched capacitor circuit to implement voltage-sharing control on the flying capacitor.
Preferably, when the multilevel converter is an AC-DC converter, an input terminal of at least one isolated DC-DC converter corresponding to the basic module receives a direct-current voltage at an output terminal of the switched capacitor circuit to implement voltage-sharing control of the flying capacitor.
Preferably, in an N-level converter, input terminals of N-2 isolated DC-DC converters corresponding to N-2 basic modules respectively receive a direct-current voltage at a second terminal of the switched capacitor circuit to generate N-2 fixed voltages with different values, respectively, so as to clamp flying capacitors in the N-2 basic modules respectively.
Preferably, the transformation ratio of the isolated DC-DC converter corresponding to the basic module of the nth stage is N/(N-1), wherein N is a positive integer not greater than N-2.
Preferably, in one N-level converter, input terminals of N-2 isolated DC-DC converters respectively corresponding to N-2 basic modules are respectively connected to two ends of the flying capacitor in the basic module of the respective next stage, so as to respectively generate N-2 fixed voltages with different values, so as to respectively clamp the flying capacitors in the N-2 basic modules, wherein the input terminal of the isolated DC-DC converter corresponding to the basic module of the last stage receives the direct-current voltage at the second end of the switched capacitor circuit, and the basic module closest to the inductance device is the 1 st stage.
Preferably, the transformation ratio of the isolated DC-DC converter corresponding to the basic module of the nth stage is N/(N + 1), wherein N is a positive integer not greater than N-2.
Preferably, in an N-level converter, input terminals of N-2 isolated DC-DC converters corresponding to N-2 basic modules respectively are connected to two ends of a flying capacitor in any stage of the basic module or a second end of the switched capacitor circuit or a first end of the switched capacitor circuit respectively, so as to generate N-2 fixed voltages with different values respectively, so as to clamp the flying capacitors in the N-2 basic modules respectively.
Preferably, the input terminal of at least one isolated DC-DC converter corresponding to the base module receives the DC voltage of the first terminal or the DC voltage of the second terminal of the switched capacitor circuit.
Preferably, when the input terminal of the isolated DC-DC converter corresponding to the basic module of the nth stage is connected to both ends of the flying capacitor in the basic module of the mth stage, the transformation ratio of the isolated DC-DC converter corresponding to the basic module of the nth stage is N/m, where m is a positive integer no greater than N-2, and N is not equal to m.
Preferably, in an N-level converter, input terminals of N-2 isolated DC-DC converters corresponding to N-2 basic modules respectively receive a direct-current voltage at an input terminal of the switched capacitor circuit to generate N-2 fixed voltages with different values, respectively, so as to clamp flying capacitors in the N-2 basic modules respectively.
Preferably, when the switched capacitor circuit is configured as a Boost flying capacitor topology, the transformation ratio of the isolated DC-DC converter corresponding to the nth stage of the base module is N/((N-1) × (1-D)), where N is a positive integer no greater than N-2 and D is the duty cycle of the switched capacitor circuit.
Preferably, when the switched capacitor circuit is configured as a Buck flying capacitor topology, the transformation ratio of the isolated DC-DC converter corresponding to the nth stage of the base module is N/(N-1), where N is a positive integer no greater than N-2, and D is the duty cycle of the switched capacitor circuit.
Preferably, the multilevel converter is a two-stage topology, and includes the switched capacitor circuit, and an isolated converter cascaded with the switched capacitor circuit, and N-2 isolated DC-DC converters corresponding to the N-2 basic modules are configured to be magnetically integrated with the isolated converter.
Preferably, N-2 isolated DC-DC converters corresponding to N-2 basic modules each generate N-2 fixed voltages with different values by adding auxiliary windings with different turn ratios to a transformer of the isolated DC-DC converter, so as to clamp flying capacitors in N-2 basic modules, respectively.
The invention aims to provide a multilevel converter, each flying capacitor is clamped to fixed voltages with different values through hardware respectively to realize voltage-sharing control of the flying capacitors, and the traditional mode of adjusting the voltage sharing based on adjusting the duty ratios of different modules or carrier phase shift angles is abandoned, so that the system response speed is improved, the difficulty and the cost of a control system are reduced, and the multilevel converter has obvious advantages in high-power multilevel application occasions.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the embodiments or the prior art descriptions will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
Fig. 1 is a block diagram of a multilevel converter of a conventional flying capacitor topology;
FIG. 2 is a circuit schematic of a multi-level converter according to a first embodiment of the present invention;
FIG. 3 is a circuit diagram of a multilevel converter according to a second embodiment of the present invention;
FIG. 4 is a circuit schematic of a multilevel converter according to a third embodiment of the invention;
fig. 5 is a circuit diagram of a multilevel converter according to a fourth embodiment of the invention.
Detailed Description
The present invention will be described below based on examples, but the present invention is not limited to only these examples. In the following detailed description of the present invention, certain specific details are set forth. It will be apparent to one skilled in the art that the present invention may be practiced without these specific details. Well-known methods, procedures, flows, components and circuits have not been described in detail so as not to obscure the present invention.
Further, those of ordinary skill in the art will appreciate that the drawings provided herein are for illustrative purposes and are not necessarily drawn to scale.
Meanwhile, it should be understood that, in the following description, the "circuit" refers to a conductive loop constituted by at least one element or sub-circuit through electrical connection or electromagnetic connection. When an element or circuit is referred to as being "connected to" another element or element/circuit is referred to as being "connected between" two nodes, it may be directly coupled or connected to the other element or intervening elements may be present, and the connection between the elements may be physical, logical, or a combination thereof. In contrast, when an element is referred to as being "directly coupled" or "directly connected" to another element, it is intended that there are no intervening elements present.
Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense; that is, what is meant is "including, but not limited to".
In the description of the present invention, it is to be understood that the terms "first," "second," and the like are used for descriptive purposes only and are not to be construed as indicating or implying relative importance. In addition, in the description of the present invention, "a plurality" means two or more unless otherwise specified.
Fig. 2 is a circuit diagram of a multilevel converter according to a first embodiment of the present invention. A simpler topology will be described for the purpose of deriving the application of a multilevel converter, such as a three-level converter as shown in fig. 2.
As shown in fig. 2, the three-level converter is a flying capacitor topology, which includes a switched capacitor circuit 21 and a voltage-equalizing circuit 22.
The switched capacitor circuit 21 is configured to perform dc conversion on a voltage input thereto, and the switched capacitor circuit 21 includes a basic module, where the basic module includes a flying capacitor C1 and two transistors Q1 and Q2, where one end of the transistor Q1 is connected to one end of the transistor Q2 through the flying capacitor C1; the switched capacitor circuit 21 further includes a filter module, the filter module includes a filter capacitor Co and two transistors Q3 and Q4, the basic module is cascaded with the filter module, and the filter module is connected to the output terminal of the switched capacitor circuit 21.
The voltage equalizing circuit 22 is configured to implement voltage equalizing control on the flying capacitor C1 by clamping the voltage of the flying capacitor C1 in the basic module to a fixed voltage, which is a desired voltage on the flying capacitor C1.
Here, the voltage equalizing circuit 22 is an isolated DC-DC converter having a transformation ratio of 1. Specifically, the transformation ratio of the isolated DC-DC converter is determined according to the voltage of the corresponding flying capacitor and the voltage of the input end connection point of the isolated DC-DC converter. Since the switched capacitor circuit 21 and the inductor L form a Boost flying capacitor topology, specifically, the circuit structure itself determines the voltage across the flying capacitor C1 to beHalf of the voltage at the two ends of the filter capacitor Co, the voltage at the two ends of the filter capacitor Co is a relatively fixed DC voltage V DC So that the DC voltage V is applied DC The output voltage obtained after the voltage conversion of the isolated DC-DC converter with the output voltage and the input voltage having the transformation ratio of 1 DC The voltage across the flying capacitor C1 is clamped by this voltage to realize voltage-sharing control of the flying capacitor C1.
It should be noted that the selection of the input voltage of the isolated DC-DC converter in the voltage equalizing circuit 22 is not limited to the DC voltage V across the filter capacitor Co in this embodiment DC . When the three-level converter is a DC-DC converter, the input end of the isolated DC-DC converter receives the direct-current voltage V at the two ends of the filter capacitor Co DC Or the direct-current input voltage Vin of the multi-level converter is used for realizing voltage-sharing control over the flying capacitor C1; when the three-level converter is an AC-DC converter, the input end of the isolated DC-DC converter receives the DC voltage V at the two ends of the filter capacitor Co DC So as to realize voltage-sharing control of the flying capacitor C1. Therefore, the flying capacitor can be clamped to realize voltage-sharing control by selecting a stable fixed voltage and converting the stable fixed voltage through a proper transformation ratio.
Fig. 3 is a circuit diagram of a multilevel converter according to a second embodiment of the invention. As shown in fig. 3, the four-level converter is a flying capacitor topology, which includes a switched capacitor circuit 31 and a voltage-equalizing circuit 32.
The switched capacitor circuit 31 comprises two basic modules, the first basic module comprises a flying capacitor C1 and two transistors Q1 and Q2, the second basic module comprises a flying capacitor C2 and two transistors Q3 and Q4, the switched capacitor circuit 31 further comprises a filtering module, the filtering module comprises a filtering capacitor Co and two transistors Q5 and Q6, the basic modules are sequentially connected in a cascade mode and then connected with the filtering module in a cascade mode, and the filtering module is connected with the output end of the switched capacitor circuit 31.
The voltage equalizing circuit 32 is used for equalizing and controlling the flying capacitor C1 by clamping the flying capacitor C1 in a basic module to a fixed voltage, and for equalizing and controlling the flying capacitor C2 in another basic module to another fixed voltage. The fixed voltage is the desired voltage on each respective flying capacitor.
Here, the voltage equalizing circuit 32 includes one isolated DC-DC converter 321 having a transformation ratio of 1. The isolated DC-DC converter 321 and the isolated DC-DC converter 322 correspond to the flying capacitor C1 and the flying capacitor C2, respectively, and are configured to output fixed voltages with different values to clamp the flying capacitor accordingly, so as to implement voltage-sharing control on the corresponding flying capacitor.
Specifically, the transformation ratio of the isolated DC-DC converter is determined according to the voltage of the corresponding flying capacitor and the voltage of the input end connection point of the isolated DC-DC converter. Since the switched capacitor circuit 31 and the inductor L form a Boost flying capacitor topology, specifically, the circuit structure itself determines the voltages at the two ends of the flying capacitor C1, the flying capacitor C2, and the filter capacitor Co in turn to be 1/3V DC 、2/3V DC 、V DC 。
The voltage at the two ends of the filter capacitor Co is a relatively fixed direct current voltage V DC So that the DC voltage V is applied DC The output voltage obtained after the voltage conversion of the isolated DC-DC converter with the output voltage and the input voltage having the transformation ratio of 2 DC The voltage across the flying capacitor C2 is clamped by this voltage to realize voltage-sharing control of the flying capacitor C2. As shown in fig. 3, an isolated DC-DC converter having a transformation ratio of 2. When there is a more constant DC voltage 2/3V between CDs DC In the process, an isolated DC-DC converter with the output voltage and input voltage conversion ratio of 1 DC The voltage at the two ends of the flying capacitor C1 is clamped by the voltage, so as to implement voltage-sharing control on the flying capacitor C1.
Of course, it should be noted that the isolated DC-DC converter 3 in the voltage-equalizing circuit 32The input terminal of 21 may alternatively be not connected to the CD terminal, but also connected to the AB terminal across the filter capacitor Co. Will direct current voltage V DC The isolated DC-DC converter with the output voltage and the input voltage having the transformation ratio of 1 DC The voltage across the flying capacitor C1 is clamped by this voltage to realize voltage-sharing control of the flying capacitor C2.
Therefore, the multi-level converter can not only clamp the flying capacitor voltage by connecting the isolated DC-DC converter to the bus voltage, but also clamp the flying capacitor voltage by connecting the flying capacitors.
Fig. 4 is a circuit diagram of a multilevel converter according to a third embodiment of the invention. As shown in fig. 4, the N-level converter is a flying capacitor topology, and includes a switched capacitor circuit 41 and a voltage-equalizing circuit 42.
The switched capacitor circuit 41 is used for performing dc conversion on the voltage input thereto, and in the N-level converter, the switched capacitor circuit 41 includes N-2 basic modules M1 and a filter module. Each basic module M1 includes a flying capacitor and two transistors (a first transistor and a second transistor), where the first transistor, the flying capacitor, and the second transistor are sequentially connected in series between input terminals of the basic module, two ends of the flying capacitor are output terminals, that is, one end of one transistor is connected to one end of the other transistor through the flying capacitor, and the other ends of the two transistors are input terminals of the basic module. The two input ends of the first basic module are connected together and connected with an inductor L, the two input ends of the other basic modules are respectively connected with the output end of the previous basic module, the filtering module comprises a filtering capacitor Co and two transistors, and the basic modules are sequentially connected in a cascade mode and then connected with the filtering module in a cascade mode.
In practical application, any device capable of being used as a power switch tube can be selected as the transistor according to requirements. Two transistors in the same stage of basic module are complementarily conducted, and the basic modules at different stages are controlled by a carrier phase shifting method, namely, the switch control signals of the first transistors in the basic modules at different stages are sequentially staggered by a preset angle,the switch control signals of the second transistors in each level of basic modules are sequentially in phase-staggered with the preset angle; wherein N is a natural number of 3 or more. Since the switched capacitor circuit 41 and the inductor L form a Boost flying capacitor topology, the voltage on the flying capacitor is from the first stage (denoted as v) C1 ) To the N-2 th stage (denoted as v) C(N-2) ) To the filter capacitor Co, in turn
Figure BDA0003789214920000091
The withstand voltage of the transistor in each basic module is the voltage difference of the capacitors in two adjacent modules, i.e.
Figure BDA0003789214920000092
Therefore, the voltage stress of the power tube can be greatly reduced through the topology of the flying capacitor, so that the application requirement of a high-voltage occasion can be met by using a low-voltage component.
And a voltage equalizing circuit 42 for realizing voltage equalizing control of the flying capacitors by clamping the flying capacitors in each basic module to a fixed voltage of a corresponding value. Here, the voltage-equalizing circuit 42 includes N-2 voltage-equalizing modules because the number of voltage-equalizing modules needs to be identical to the number of basic modules, and the N-2 voltage-equalizing modules correspond to the N-2 basic modules one-to-one. The input terminal of the voltage equalizing module is coupled to a voltage regulator, and the output terminal outputs the fixed voltage, wherein the voltage regulator is configured to be related to the dc voltage of the first terminal or the dc voltage of the second terminal of the switched capacitor circuit 41, and here, the first terminal of the switched capacitor circuit 41 is configured to be close to one terminal of the inductor device L. In this embodiment, referring to fig. 4, the dc voltage at the first terminal of the switched capacitor circuit 41 is the dc input voltage V of the multilevel converter in The DC voltage at the second terminal of the switched capacitor circuit 41 is the DC voltage V at the two terminals of the filter capacitor Co DC 。
Preferably, the voltage equalizing module is composed of an isolated DC-DC converter, and the isolated DC-DC converter is used for generating a corresponding fixed voltage. Specifically, the transformation ratio of each isolated DC-DC converter is determined according to the voltage of the corresponding flying capacitor and the voltage of the input end connection point of the isolated DC-DC converter. The selection of the transformation ratio is based primarily on making the clamp voltage on the flying capacitor equal to its desired voltage.
In the N-level converter of this embodiment, the input terminals of N-2 isolated DC-DC converters corresponding to the N-2 basic modules respectively receive the DC voltage V across the filter capacitor Co DC And N-2 fixed voltages with different values are respectively generated for clamping the flying capacitors in the N-2 basic modules. The transformation ratio of the isolated DC-DC converter corresponding to the nth stage basic module is N/(N-1), wherein N is a positive integer not greater than N-2. For example, level 1 is 1: an isolated DC-DC converter of N-1, wherein the 2 nd stage is 2: and the output ends of the N-2 isolated DC-DC converters are respectively connected to two ends of the corresponding flying capacitor.
In another embodiment, the input terminals of N-2 isolated DC-DC converters respectively corresponding to N-2 basic modules may also be respectively connected to two ends of the flying capacitors in the respective next basic module to respectively generate N-2 fixed voltages with different values, so as to respectively clamp the flying capacitors in the N-2 basic modules. Wherein, the DC voltage V at the input end of the isolated DC-DC converter and the two ends of the filter capacitor Co corresponding to the basic module of the last stage DC . In this case, as can be seen from the numerical relationship of the voltages at the flying capacitors of the respective stages, the conversion ratio of the isolated DC-DC converter corresponding to the nth stage basic module is n/(n + 1).
In another other embodiment, the input ends of N-2 isolated DC-DC converters respectively corresponding to the N-2 basic modules are respectively connected to both ends of the flying capacitors or both ends of the filter capacitor Co in any stage of basic module to respectively generate N-2 fixed voltages with different values for clamping the flying capacitors in the N-2 basic modules. Wherein, the input end of at least one isolated DC-DC converter corresponding to the basic module receives the DC voltage V at the two ends of the filter capacitor Co DC . In this case, when the input terminal of the isolated DC-DC converter of the nth stage is connected to the basic module of the mth stageWhen the flying capacitor is arranged at two ends of the flying capacitor, the transformation ratio of the isolation type DC-DC converter at the nth stage is N/m, wherein m is a positive integer not more than N-2, and N is not equal to m; when the input end of the isolated DC-DC converter of the nth stage is connected to two ends of the filter capacitor Co, the transformation ratio of the isolated DC-DC converter corresponding to the nth stage basic module is N/(N-1).
When the multilevel converter is a DC-DC converter, the input end of the isolated DC-DC converter can also selectively receive the direct-current input voltage V of the multilevel converter in So as to realize voltage-sharing control of the flying capacitor. Several voltage-based inputs V are set forth below in Case of clamping flying capacitor:
in one embodiment, the input ends of the N-2 isolated DC-DC converters all receive the direct-current input voltage V of the multilevel converter in And N-2 fixed voltages with different values are respectively generated for clamping the flying capacitors in the N-2 basic modules. When the switched capacitor circuit 41 is configured as a Boost flying capacitor topology, the transformation ratio of the isolated DC-DC converter of the nth stage is N/((N-1) × (1-D)), where D is the duty cycle of the switched capacitor circuit. When the switched capacitor circuit 41 is configured as a Buck flying capacitor topology, the transformation ratio of the isolated DC-DC converter of the nth stage is N/(N-1).
In another embodiment, the input terminals of the N-2 isolated DC-DC converters are respectively connected to two ends of the flying capacitor in the previous basic module to respectively generate N-2 fixed voltages with different values for clamping the flying capacitors in the N-2 basic modules, wherein the input terminal of the isolated DC-DC converter corresponding to the first basic module receives the DC input voltage V of the multilevel converter in . In this case, the isolated DC-DC converter of the nth stage has a transformation ratio of n/(n-1), n being greater than 1.
In another other embodiment, the input ends of N-2 isolated DC-DC converters are respectively connected to the two ends of the flying capacitor in the basic module of any stage or the direct current input end of the multilevel converter to respectively generate N-2 fixed-state DC-DC converters with different valuesConstant voltage for clamping flying capacitors in N-2 basic modules, wherein at least one input end of the isolated DC-DC converter corresponding to the basic module receives direct current input voltage V of the multilevel converter in 。
Therefore, the multilevel converter provided by the invention has the advantages that the voltage-sharing control of the flying capacitors is realized by clamping each flying capacitor to the fixed voltage with different values through hardware, and the traditional mode of regulating the voltage-sharing based on regulating the duty ratios of different modules or carrier phase shift angles is abandoned, so that the system response speed is improved, the difficulty and the cost of a control system are reduced, and the multilevel converter has obvious advantages in high-power multilevel application occasions.
Fig. 5 is a circuit diagram of a multilevel converter according to a fourth embodiment of the invention. The multilevel converter differs from the third embodiment in that it has a two-stage topology, and includes a switched capacitor circuit 51 at a front stage, and an isolated converter 53 at a rear stage in cascade connection with the switched capacitor circuit, where the isolated converter 53 includes an inverter bridge, a transformer T, and a rectifier circuit. The input terminals of the N-2 isolated DC-DC converters in the voltage-sharing circuit 52 all receive the DC voltage V across the filter capacitor Co DC And the isolated DC-DC converter in each grading module is configured to be magnetically integrated with the isolated converter 53.
Specifically, N-2 isolated DC-DC converters each generate N-2 fixed voltages with different values by adding N-2 auxiliary windings with different turn ratios to the transformer T of the isolated converter 53, so as to clamp the flying capacitors in N-2 basic modules, respectively. Thus, the voltage equalizing circuit 52 can multiplex the inverter bridge in the later-stage isolated converter 53, the magnetic core and the primary winding of the transformer, and then form N-2 isolated DC-DC converters with N-2 additional auxiliary windings with different turn ratios. Therefore, the scheme of the embodiment can save N-2 transformers, and the volume of the transformer is generally larger, so that the scheme of the embodiment of the invention can reduce the system volume to the greatest extent and improve the power density.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims (18)

1. A multilevel converter, comprising:
a switched capacitor circuit comprising at least one base module, each said base module comprising a flying capacitor and two transistors, wherein one terminal of one transistor is connected to one terminal of the other transistor through said flying capacitor; and the voltage equalizing circuit is used for respectively clamping the voltages at two ends of the flying capacitor to a fixed voltage with a corresponding numerical value so as to realize voltage equalizing control on the flying capacitor.
2. The multilevel converter according to claim 1, wherein the voltage-equalizing circuit comprises at least one voltage-equalizing block, and the voltage-equalizing block corresponds to the base block one to one; the input end of the voltage equalizing module is coupled to a voltage stabilizing source, and the output end of the voltage equalizing module outputs the fixed voltage, wherein the voltage stabilizing source is configured to be related to the direct current voltage of the first end or the direct current voltage of the second end of the switched capacitor circuit, and the first end of the switched capacitor circuit is one end close to the inductance device.
3. The multilevel converter of claim 2, wherein the voltage grading module is configured as an isolated DC-DC converter and the isolated DC-DC converter is configured to generate the fixed voltage.
4. The multilevel converter according to claim 3, wherein the transformation ratio of the isolated DC-DC converter is determined according to the voltage of the corresponding flying capacitor and the voltage of the input connection point of the isolated DC-DC converter.
5. The multilevel converter according to claim 3, wherein when the multilevel converter is a DC-DC converter, at least one input terminal of the isolated DC-DC converter corresponding to the basic module receives the direct-current voltage at the first terminal or the direct-current voltage at the second terminal of the switched capacitor circuit to realize voltage-sharing control of the flying capacitor.
6. The multilevel converter according to claim 3, wherein when the multilevel converter is an AC-DC converter, an input terminal of at least one isolated DC-DC converter corresponding to the basic module receives a direct-current voltage at an output terminal of the switched capacitor circuit to realize voltage-sharing control of the flying capacitor.
7. The multilevel converter according to claim 3, wherein in an N-level converter, the input terminals of N-2 isolated DC-DC converters corresponding to N-2 basic modules respectively receive the DC voltage of the second terminal of the switched capacitor circuit to generate N-2 fixed voltages with different values respectively for clamping the flying capacitors in the N-2 basic modules respectively.
8. The multilevel converter according to claim 7, wherein a transformation ratio of the isolated DC-DC converter corresponding to the base module of the nth stage is N/(N-1), where N is a positive integer not greater than N-2.
9. The multilevel converter according to claim 3, wherein in an N-level converter, input terminals of N-2 isolated DC-DC converters respectively corresponding to N-2 basic blocks are respectively connected to two ends of the flying capacitor in the basic block of the respective next stage to respectively generate N-2 fixed voltages with different values for respectively clamping the flying capacitors in the N-2 basic blocks, wherein the input terminal of the isolated DC-DC converter corresponding to the basic block of the last stage receives the DC voltage of the second end of the switched capacitor circuit, and wherein the basic block closest to the inductor device is the 1 st stage.
10. The multilevel converter according to claim 9, wherein a transformation ratio of the isolated DC-DC converter corresponding to the nth stage of the base module is N/(N + 1), where N is a positive integer not greater than N "2.
11. The multilevel converter according to claim 3, wherein in an N-level converter, input terminals of N-2 isolated DC-DC converters corresponding to N-2 basic blocks respectively are connected to both ends of the flying capacitor in the basic block of any stage or the second end of the switched capacitor circuit or the first end of the switched capacitor circuit respectively to generate N-2 fixed voltages with different values for clamping the flying capacitors in the N-2 basic blocks respectively.
12. The multilevel converter according to claim 11, wherein an input terminal of at least one isolated DC-DC converter corresponding to the basic module receives the DC voltage of the first terminal or the DC voltage of the second terminal of the switched capacitor circuit.
13. The multilevel converter according to claim 12, wherein when an input terminal of the isolated DC-DC converter corresponding to the basic module of the nth stage is connected to both ends of the flying capacitor in the basic module of the mth stage, a transformation ratio of the isolated DC-DC converter corresponding to the basic module of the nth stage is N/m, where m is a positive integer not greater than N "2, and N and m are not equal.
14. The multilevel converter according to claim 3, wherein in an N-level converter, the input terminals of N-2 isolated DC-DC converters corresponding to N-2 basic modules respectively receive the DC voltage at the input terminal of the switched capacitor circuit to generate N-2 fixed voltages with different values respectively for clamping the flying capacitors in the N-2 basic modules respectively.
15. The multilevel converter of claim 14, wherein when the switched capacitor circuit is configured as a Boost flying capacitor topology, the isolated DC-DC converter corresponding to the nth stage of the base module has a transformation ratio of
Figure FDA0003789214910000031
Here, N is a positive integer not greater than N-2, and D is a duty cycle of the switched-capacitor circuit.
16. The multilevel converter of claim 14, wherein when the switched capacitor circuit is configured as a Buck flying capacitor topology, a transformation ratio of the isolated DC-DC converter corresponding to the base module of the nth stage is N/(N-1), where N is a positive integer no greater than N-2 and D is a duty cycle of the switched capacitor circuit.
17. The multilevel converter of claim 7, wherein the multilevel converter is a two-level topology comprising the switched capacitor circuit and an isolated converter cascaded with the switched capacitor circuit, wherein N-2 of the isolated DC-DC converters corresponding to N-2 of the base modules are configured to be magnetically integrated with the isolated converter.
18. The multilevel converter according to claim 17, wherein N-2 of the isolated DC-DC converters corresponding to N-2 of the basic blocks each generate N-2 of the fixed voltages with different values by adding auxiliary windings with different turn ratios to a transformer of the isolated DC-DC converter for clamping flying capacitors in the N-2 of the basic blocks, respectively.
CN202210960529.2A 2022-08-09 2022-08-09 Multilevel converter Pending CN115276404A (en)

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