Multistage conversion device

Abstract

An embodiment of the present disclosure relates to a multi-stage conversion apparatus, comprising: a controllable DC power supply configured to regulate an output voltage of the controllable DC power supply; and a multi-stage flying capacitor converter connected to the output of the controllable DC power supply and having one or more flying capacitors; wherein the multi-stage conversion device is configured such that the pre-charge voltage increases and the pre-charge current decreases during a pre-charge state of the one or more flying capacitors.

Description

Technical Field

[0001] This invention relates to electric fields, and more particularly to multi-stage conversion devices. Background Technology

[0002] The demands of the electric vehicle charging and energy storage markets are becoming increasingly stringent. One such requirement is high voltage and a wide output range, which forces related power semiconductor switches and power converter systems to operate under harsh conditions. Multi-segment and multi-stage topologies are finding increasingly widespread application in various settings to meet these requirements due to their advantages.

[0003] Among multi-segment and multi-stage converters, the multi-stage flying capacitor converter (MLFC) has been used for many years due to its advantages of high efficiency, low power semiconductor voltage stress and small size. Summary of the Invention

[0004] This invention is defined by the claims.

[0005] According to one aspect of this disclosure, a multi-stage conversion device is provided. The multi-stage conversion device includes: a controllable DC power supply configured to regulate the output voltage of the controllable DC power supply; and a multi-stage flying capacitor converter connected to the output of the controllable DC power supply and having one or more flying capacitors; wherein the multi-stage conversion device is configured such that during a pre-charge state of the one or more flying capacitors, the pre-charge voltage increases while the pre-charge current decreases.

[0006] Through the aforementioned multi-stage conversion device, those skilled in the art will understand that the pre-charging time of one or more flying capacitors can be reduced, and simultaneously, the voltage stress across the power switches in the multi-stage flying capacitor converter can be alleviated. Therefore, a better balance can be achieved between the pre-charging time and voltage stress of the power semiconductor switches.

[0007] In some embodiments, the controllable DC power supply is configured to regulate the output voltage of the controllable DC power supply from zero to a specified voltage level during a pre-charge state.

[0008] In some embodiments, the multi-stage conversion device further includes: a discharge circuit connected to the output of a controllable DC power supply and in parallel with the multi-stage flying capacitor converter, and having a discharge switch such that when the discharge switch is turned on, one or more flying capacitors discharge through the discharge circuit.

[0009] In some embodiments, the controllable DC power supply is a DC / DC or AC / DC converter.

[0010] In some embodiments, a multi-stage flying capacitor converter is an N-stage flying capacitor converter, where N is an integer greater than or equal to 3.

[0011] In some embodiments, the output of the multistage flying capacitor converter is connected to the load via an inductor, and a buck or boost circuit may be formed by a portion of the multistage flying capacitor converter and the inductor.

[0012] In some embodiments, the multi-stage flying capacitor converter is a single-cell, interleaved multi-cell, serial, or parallel structure.

[0013] In some embodiments, the power switches in the multi-stage flying capacitor converter are selected from the group consisting of Si MOSFETs, SiIGBTs, SiC MOSFETs and GaN MOSFETs.

[0014] In some embodiments, the discharge circuit includes a resistor connected in series with the discharge switch.

[0015] In some embodiments, the discharge switch includes at least one power switch or magnetic relay.

[0016] In some embodiments, at least one power switch is selected from the group consisting of Si MOSFET, Si IGBT, SiC MOSFET and GaN MOSFET.

[0017] In some embodiments, the controllable DC power supply is configured as a CLLC circuit.

[0018] In some embodiments, the multi-stage conversion device further includes a sampling circuit for sampling the voltage of one or more flying capacitors.

[0019] In some embodiments, the multi-stage conversion device further includes a drive circuit for controlling a plurality of power switches in the multi-stage flying capacitor converter.

[0020] According to another aspect of this disclosure, a power supply circuit is provided, including the multi-stage conversion device as described above. Attached Figure Description

[0021] In the accompanying drawings, similar / identical reference numerals throughout the various views generally denote similar / identical parts. The drawings are not necessarily drawn to scale. Instead, the focus is on illustrating the principles of the invention. In these drawings: Figure 1 A traditional multi-stage conversion device is schematically shown; Figure 2 A conceptual circuit diagram of an improved multi-stage conversion device according to the present disclosure is shown schematically. Figure 3a A first exemplary multi-stage conversion device with a TLFC converter according to an embodiment of the present disclosure is schematically shown; Figure 3b schematically shown Figure 3a The pre-charging path of the multi-stage conversion device; Figure 3c schematically shown Figure 3a The discharge path of the multi-stage conversion device; Figure 4a A second exemplary multi-stage conversion device with an FLFC converter according to an embodiment of the present disclosure is schematically illustrated; Figure 4b schematically shown Figure 4a The first pre-charge path of a flying capacitor in a multi-stage conversion device; Figure 4c schematically shown Figure 4a The second pre-charge path of another flying capacitor in the multi-stage conversion device; Figure 4d schematically shown Figure 4a The discharge path of the multi-stage conversion device; Figure 5 An example of a multi-stage conversion device according to an embodiment of the present disclosure is schematically shown, wherein a CLLC circuit is used as the first stage and a multi-stage flying capacitor converter is used as the second stage; and Figure 6 It shows Figure 5 Voltage or current waveforms of a multi-stage conversion device during pre-charge and discharge states. Detailed Implementation

[0022] Embodiments of this disclosure will be described in more detail with reference to the accompanying drawings. Although the drawings illustrate some embodiments of this disclosure, it should be understood that this disclosure can be implemented in various ways and should not be construed as limited to the embodiments explained herein. Rather, embodiments are provided to provide a more thorough and complete understanding of this disclosure. It should be understood that the drawings and embodiments of this disclosure are for illustrative purposes only and are not intended to limit the scope of protection of this disclosure.

[0023] In the description of embodiments of this disclosure, the term "comprising" and variations thereof are to be interpreted as open-ended terms meaning "including but not limited to". The term "based on" is to be interpreted as "at least partially based on". The terms "one embodiment" and "this embodiment" are to be interpreted as "at least one embodiment". The following text may also include other explicit and implicit definitions.

[0024] As previously mentioned, multistage flying capacitor converters (MLFCs) have been used for many years. As is known in the art, one challenge of MLFC converters is balancing the pre-charge time with the voltage stress of the power semiconductor switches. Typically, the flying capacitors of the MLFC should be charged to a specified voltage before the power semiconductor switches begin switching, and should remain within a safe voltage range in the event of a fault.

[0025] like Figure 1 As can be seen, traditional multi-stage conversion devices with flying capacitors typically achieve the pre-charging function of the flying capacitor through a series of passive resistors.

[0026] like Figure 1 As shown, a conventional multistage converter 10 typically includes a DC power supply 11 with a fixed voltage output and a multistage flying capacitor converter 12, wherein the multistage flying capacitor converter 12 is configured to be connected to the output of the DC power supply 11 and applies an output voltage to a load RL via an output circuit. Specifically, the multistage flying capacitor converter 12 may be a three-stage flying capacitor (TLFC) converter, which includes four power semiconductor switches connected in series and a flying capacitor C connected in parallel with the two innermost power semiconductor switches. FC Furthermore, a passive pre-charge resistor circuit 14 with multiple passive resistors Rc1, Rc2, and Rc3 connected in series can also be connected to the output of the DC power supply 11, and the intermediate resistor Rc2 can be connected to the flying capacitor C. FC Parallel connection.

[0027] However, it has been found that this design of the aforementioned conventional multi-stage converter 10 may result in a trade-off between the power loss of the passive resistor and the pre-charge time of the flying capacitor. Furthermore, there is no discharge circuit under fault conditions.

[0028] In view of the above, this disclosure proposes an improved multi-stage conversion device comprising a controllable DC power supply configured to regulate the output voltage of the controllable DC power supply; and a multi-stage flying capacitor converter connected to the output of the controllable DC power supply and having one or more flying capacitors; wherein the multi-stage conversion device is configured such that during a pre-charge state, the pre-charge voltage of the one or more flying capacitors increases while the pre-charge current of the one or more flying capacitors decreases. Those skilled in the art will understand that using this improved multi-stage conversion device, the pre-charge time can be reduced, while simultaneously reducing the voltage across the power switch in the multi-stage flying capacitor converter.

[0029] To better understand the concepts of this disclosure, Figure 2A conceptual circuit diagram schematically showing an improved multi - stage conversion device according to the present disclosure is shown.

[0030] As Figure 2 shown, the multi - stage conversion device 20 may include a controllable DC power supply 21 and a multi - stage flying capacitor converter 22. Similar to Figure 1 that, the multi - stage flying capacitor converter 22 is also connected to the output of the DC power supply 11 and is configured to apply an output voltage to the load RL. However, the multi - stage conversion device 20 of the present disclosure is different from Figure 1 the multi - stage conversion device in that: the DC power supply is controllable, so the output voltage of the DC power supply can be adjusted, for example, from zero to a specified voltage level during the pre - charge state. In addition, in some alternative embodiments, a discharge circuit 24 may be connected to the output of the controllable DC power supply 21 and is in parallel with the multi - stage flying capacitor converter 22.

[0031] Those skilled in the art will understand that through the design of the multi - stage conversion device 20, a two - stage circuit structure can be formed, where the controllable DC power supply 21 will be the front - end stage of the multi - stage conversion device, and the multi - stage flying capacitor converter 22 will be the rear - end stage of the multi - stage conversion device 20. As a result, the regulated voltage from the controllable DC power supply 21 can be directly used as the input voltage of the multi - stage conversion device 20. In addition, through the control of the multi - stage conversion device 20, during the pre - charge state, the pre - charge voltage of one or more flying capacitors can be increased, while the pre - charge current of one or more flying capacitors can be decreased.

[0032] In some embodiments, the controllable DC power supply 21 may be a controllable DC / DC or AC / DC converter. In some embodiments, the controllable DC / DC or AC / DC converter may be a two - stage converter or a multi - stage converter. In some embodiments, the controllable DC / DC or AC / DC converter may be an isolated or non - isolated converter. By way of example only, the controllable DC power supply 21 may be a controllable CLLCDC / DC converter, as will be described in further detail.

[0033] As described above, in some alternative embodiments, a discharge circuit 24 may be included, where the discharge circuit 24 may include a discharge switch 241 and a discharge resistor Rdis connected in series. Generally, the discharge switch 241 may include a power switch or a magnetic relay. In some embodiments, the power switch may be a power semiconductor switch selected from the group consisting of Si MOSFET, Si IGBT, SiC MOSFET, and GaN MOSFET.

[0034] As will be described below, using discharge circuit 24, in the event of a fault, the charge stored in one or more flying capacitors of the multi-stage flying capacitor converter 22 can be discharged as needed through discharge circuit 24. In this way, operational safety can be improved.

[0035] In some embodiments, the multi-stage flying capacitor converter 22 may be an N-stage flying capacitor converter, where N is an integer greater than or equal to 3. In some embodiments, the multi-stage flying capacitor converter may be a single unit, an interleaved multi-unit structure, a serial structure, or a parallel structure.

[0036] Typically, a multistage flying capacitor converter 22 may have multiple power switches (e.g., power semiconductor switches), one or more flying capacitors, and an output connected to a node between two innermost adjacent power switches, wherein the one or more power switches may be connected in series, and each of the one or more flying capacitors may be connected in parallel with a portion of a power switch. In some embodiments, the power switches may be power semiconductor switches selected from the group consisting of Si MOSFETs, Si IGBTs, SiC MOSFETs, and GaN MOSFETs.

[0037] By way of example only, the multi-stage flying capacitor converter 22 can be a three-stage flying capacitor (TLFC) converter. Figure 3a A first exemplary multi-stage conversion apparatus with a TLFC converter according to an embodiment of the present disclosure is shown.

[0038] like Figure 3a As shown, the first exemplary multi-stage conversion device 20-1 may include a controllable DC power supply 21-1, a three-stage flying capacitor converter 22-1, and an optional discharge circuit 24-1.

[0039] The three-stage flying capacitor converter 22-1 may include four power semiconductor switches S1, S2, S3, and S4 connected in series, and a flying capacitor C connected in parallel with the two innermost power semiconductor switches S2 and S3. FC The output 25-1 is connected to the node between the two innermost adjacent power semiconductor switches S2 and S3. The output 25-1 of the three-stage flying capacitor converter 22-1 can be connected to the load RL via an LC circuit, wherein the inductor L is connected in series with the load RL and the output capacitor Cout is connected in parallel with the load RL.

[0040] The optional discharge circuit 24-1 may include a discharge switch 241-1 and a discharge resistor Rdis connected in series, and may be connected to the output of the controllable DC power supply 21-1 and in parallel with the three-stage flying capacitor (TLFC) converter 22-1.

[0041] During operation, four power semiconductor switches S1, S2, S3, and S4 can be controlled to allow the capacitor C to fly across. FC Pre-charge or discharge. Figure 3b It shows Figure 3a The pre-charge path of the multi-stage conversion device; and Figure 3c It shows Figure 3a The discharge path of the multi-stage conversion device.

[0042] like Figure 3b As shown, in the pre-charge state, the two outermost power semiconductor switches (S1 and S4) can be turned on, while the two innermost power semiconductor switches (S2 and S3) can be turned off. Afterward, the controllable DC power supply 21-1 can connect to the flying capacitor C. FC The two ends are connected to directly connect to the flying capacitor C. FC Perform pre-charging.

[0043] like Figure 3c As shown, in the discharge state, all power semiconductor switches S1, S2, S3, and S4 are turned off, while discharge switch 241-1 is turned on. Afterwards, the flying capacitor C... FC The voltage on the circuit can be discharged through the body diodes of power semiconductor switches S1 and S4 and the discharge circuit 24-1.

[0044] As just another example, the multi-stage flying capacitor converter 22 could be a four-stage flying capacitor (FLFC) converter. Figure 4a A second exemplary multi-stage conversion apparatus with an FLFC converter according to an embodiment of the present disclosure is shown.

[0045] like Figure 4a As shown, the second exemplary multi-stage conversion device 20-2 may include a controllable DC power supply 21-2, a four-stage flying capacitor converter 22-2, and an optional discharge circuit 24-2.

[0046] The four-stage flying capacitor converter 22-2 may include six power semiconductor switches S1, S2, S3, S4, S5, S6 connected in series and two flying capacitors C. FC1 C FC2 The first flying capacitor C FC1 It is connected in parallel with the two innermost power semiconductor switches S3 and S4, and the second flying capacitor C FC2 It is connected in parallel with the four innermost power semiconductor switches S2, S3, S4 and S5.

[0047] The output 25-2 of the four-stage flying capacitor converter 22-2 is connected to the node between the two innermost power semiconductor switches (i.e., S3 and S4). The output 25-1 of the four-stage flying capacitor converter 22-1 can be connected to the load RL via an LC circuit, wherein the inductor L is connected in series with the load RL and the output capacitor Cout is connected in parallel with the load RL.

[0048] The optional discharge circuit 24-2 may include a discharge switch 241-2 and a discharge resistor Rdis connected in series, and may be connected to the output of the DC power supply 21-2 and in parallel with the four-stage flying capacitor converter 22-2.

[0049] During operation, six power semiconductor switches S1, S2, S3, S4, S5, and S6 can be controlled to allow the capacitor C to fly across. FC Pre-charge or discharge. Figure 4b It shows Figure 4a The first pre-charge path of a flying capacitor in a multi-stage conversion device; Figure 4c It shows Figure 4a The second pre-charge path of another flying capacitor in the multi-stage conversion device; and Figure 4d It shows Figure 4a The discharge path of the multi-stage conversion device.

[0050] In the pre-charge state, such as Figure 4b As shown, the four outermost power semiconductor switches (S1, S2, S5, S6) can be turned on, while the two innermost power semiconductor switches (S3, S4) can be turned off to turn on one of the two flying capacitors (e.g., C). FC2 Precharge to the specified voltage V2. Afterwards, as... Figure 4c As shown, the two outermost power semiconductor switches (S1 and S6) can remain on, while power switches S2 and S5 can subsequently be turned off to continue powering the flying capacitor C. FC1 Precharge to the specified voltage V1.

[0051] like Figure 4c As shown, in the discharge state, all power semiconductor switches S1, S2, S3, S4, S5, and S6 are off, while discharge switch 241-2 is on. In this situation, the two flying capacitors (i.e., C...) FC1 and C FC2 The voltage on the circuit can be discharged through the body diodes of the power semiconductor switches S1, S2, S5, and S6 and the discharge circuit 24-2.

[0052] Various embodiments are described regarding the pre-charge or discharge function of the multi-stage converter. It should be noted that, although not shown above, those skilled in the art will understand that multiple power switches can also be controlled, for example, via buck or boost circuits and / or filter circuits, to supply the voltage of one or more flying capacitors to the load RL. Typically, the buck or boost circuit can be formed by a portion of the switches of the multi-stage flying capacitor converter and an inductor connected to the output of the multi-stage flying capacitor converter 22.

[0053] In addition to the above, in some embodiments, the multi-stage conversion device may also include a sampling circuit for sampling the voltage of one or more flying capacitors.

[0054] In some embodiments, the multi-stage conversion device may further include a drive circuit for controlling a plurality of power semiconductor switches in the multi-stage flying capacitor converter.

[0055] In some embodiments, the multi-stage conversion device may further include some logic units for multiple MLFC power switches and discharge switches.

[0056] Typically, each of the above sampling circuits and logic units can be implemented using analog circuits, digital circuits, or functional modules integrated into a digital signal processor (DSP).

[0057] To verify the feasibility of this disclosure, Figure 5 An example of a multi-stage conversion device according to an embodiment of the present disclosure is illustrated schematically, wherein a controllable CLLC circuit is used as the first stage and a multi-stage flying capacitor converter is used as the second stage.

[0058] CLLC topologies are known in the art and are commonly used in battery integration. They offer current-current separation, the ability to integrate high-frequency transformers into resonant circuits, and the ability to operate over a wide voltage range. Furthermore, they ensure zero-voltage switching conditions for all switches and zero-current switching conditions for the secondary-side switches, enabling high efficiency. Additionally, it may be convenient to provide bidirectional converters with CLLC topologies.

[0059] like Figure 5 As shown, the multi-stage conversion device 20-3 may include a controllable DC power supply 21-3 as a first stage and a multi-stage flying capacitor converter 22-3 as a second stage, wherein the input of the multi-stage flying capacitor converter 22-3 is connected to the output of the DC power supply 21-3 and has a flying capacitor C7. Furthermore, the multi-stage conversion device 20-3 is configured with a discharge circuit 24-3.

[0060] Specifically, the controllable DC power supply 21-3 is configured as a CLLC circuit, and the multi-stage flying capacitor converter 22-3 is implemented by a three-stage flying capacitor converter. This allows for easy implementation of wide input and output voltage ranges and isolation requirements.

[0061] Since the output voltage of the controllable DC power supply 21-3 is the input voltage of the multi-stage flying capacitor converter 22-3, the multi-stage flying capacitor converter 22-3 can then be regulated with a defined PFM / PWM strategy and logic unit within an appropriate ramp-up time.

[0062] During the pre-charging phase, the controllable DC power supply 21-3 and the multi-stage flying capacitor converter 22-3 can then work together to complete the pre-charging task of the flying capacitor C7. As an example only, the controllable DC power supply 21-3 can, for instance, slowly regulate its output voltage from 0V to 950V, and FETD0 and FETD3 can be turned on until the flying capacitor C7 is charged to 450V, which is likely about half of the required input voltage. That is, even when the flying capacitor is pre-charged to its specified voltage, the input voltage of the multi-stage flying capacitor converter will continue to be controlled to ramp up to the required input voltage.

[0063] During the discharge phase, neither the controllable DC power supply 21-3 nor the multistage flying capacitor converter 22-3 should operate. For example, both the controllable DC power supply 21-3 and the multistage flying capacitor converter 22-3 will stop operating, and the discharge switch FETD12 (i.e., the discharge switch) can be turned on until the voltage of the flying capacitor is discharged to 0V to ensure safety under certain fault conditions.

[0064] Figure 6 It shows Figure 5 Voltage or current waveforms of a multi-stage conversion device during pre-charge and discharge states.

[0065] like Figure 6 As shown, during the pre-charge state, the pre-charge current used for the flying capacitor (in Figure 6 The so-called "CLLC resonant current" is controlled to gradually decrease, while the pre-charge voltage used for the flying capacitor (in Figure 6 The input voltage (referred to as "TLFC input voltage") is controlled to increase gradually or ramp up.

[0066] Through the control methods described above, those skilled in the art will understand that the voltage stress on the power switches in the multi-stage flying capacitor converter 22-3 can then be reduced. Furthermore, since the pre-charge current is set to be initially large, the total pre-charge time of the flying capacitors may also be reduced. A better balance can then be achieved between the pre-charge time and the voltage stress across the power switches. Additionally, power losses on the passive resistors can be reduced.

[0067] Furthermore, with the above-described configuration of this device, the discharge time can be controlled to a reasonable level.

[0068] Simulations show that by using the multi-stage conversion device 20-3, the pre-charging time can be reduced to less than 50ms, and the discharge time can be controlled to less than 500ms when the power loss on the discharge resistor is reasonable, thus verifying the feasibility of this disclosure.

[0069] In addition to the above, those skilled in the art will further understand that the above time-level sequence is very easy for digital signal processors (DSPs) or microcontrollers (MCUs) to process, which makes it easy to integrate sampling and processing modules into digital signal processors (DSPs) or microcontrollers (MCUs), and also greatly reduces cost and complexity.

[0070] Furthermore, those skilled in the art will understand that this disclosure is not limited to multi-stage conversion devices, but may also relate to power supply circuits including the multi-stage conversion devices described above.

[0071] In summary, this disclosure generally proposes a cost-effective multi-stage conversion device with a multi-stage flying capacitor (MLFC) converter, which can have the following advantages: - Reduced pre-charge and discharge times. This is because the device employs an active control strategy rather than a passive strategy for pre-charging or discharging the multi-stage flying capacitor (MLFC) converter, resulting in a relatively short and adjustable pre-charge time. This is particularly advantageous for fast-start and shut-down applications such as fast charging of electric vehicles. - Low circuit complexity, low cost, and high reliability. This is because the device adds very few external components to a traditional multistage flying capacitor (MLFC) converter.

[0072] Taking advantage of the above, those skilled in the art will understand that this application can be particularly applied to the following scenarios, including but not limited to: electric vehicle charging applications, solar energy system applications, industrial applications, consumer electronics applications, and other related applications.

[0073] By studying the accompanying drawings, this disclosure, and the appended claims, those skilled in the art can understand and implement other variations of the disclosed embodiments in practicing the claimed invention. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" ("a" or "an") does not exclude multiple. The mere fact that certain measures are recited in mutually different dependent claims does not mean that combinations of these measures cannot be used to exert advantages. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A multi-stage conversion device (20), comprising: A controllable DC power supply (21) is configured to regulate the output voltage of the controllable DC power supply (21); as well as A multi-stage flying capacitor converter (22) is connected to the output of the controllable DC power supply (21) and has one or more flying capacitors; The multi-stage conversion device (20) is configured such that during the pre-charge state of the one or more flying capacitors, the pre-charge voltage increases while the pre-charge current decreases.

2. The multi-stage conversion device (20) according to claim 1, wherein, The controllable DC power supply (21) is configured to regulate the output voltage of the controllable DC power supply (21) from zero to a specified voltage level during the pre-charge state.

3. The multi-stage conversion device (20) according to claim 1 or 2 further includes: The discharge circuit (24) is connected to the output of the controllable DC power supply and is in parallel with the multistage flying capacitor converter (22), and has a discharge switch (241) such that when the discharge switch (241) is turned on, the one or more flying capacitors discharge through the discharge circuit (24).

4. The multi-stage conversion device (20) according to claim 1 or 2, wherein, The controllable DC power supply (21) is a DC / DC or AC / DC converter.

5. The multi-stage conversion device (20) according to claim 1 or 2, wherein, The multi-stage flying capacitor converter (22) is an N-stage flying capacitor converter, where N is an integer greater than or equal to 3.

6. The multi-stage conversion device (20) according to claim 1 or 2, wherein, The output of the multi-stage flying capacitor converter (22) is connected to the load via an inductor (L), and The buck or boost circuit can be formed from a portion of the multi-stage flying capacitor converter (22) and the inductor (L).

7. The multi-stage conversion device (20) according to claim 1 or 2, wherein, The multi-stage flying capacitor converter (20) can be a single unit, an interleaved multi-unit structure, a serial structure, or a parallel structure.

8. The multi-stage conversion device (20) according to claim 1 or 2, wherein, The power switches in the multi-stage flying capacitor converter (22) are selected from the group consisting of Si MOSFET, Si IGBT, SiC MOSFET and GaN MOSFET.

9. The multi-stage conversion device (20) according to claim 3, wherein, The discharge circuit (24) includes a resistor connected in series with the discharge switch.

10. The multi-stage conversion device (20) according to claim 8, wherein, The discharge switch (241) includes at least one power switch or magnetic relay.

11. The multi-stage conversion device (20) according to claim 10, wherein, The at least one power switch is selected from the group consisting of SiMOSFET, Si IGBT, SiC MOSFET and GaN MOSFET.

12. The multi-stage conversion device (20) according to claim 1 or 2, wherein, The controllable DC power supply (21) is formed as a CLLC circuit.

13. The multi-stage conversion device (20) according to claim 1 or 2 further includes a sampling circuit for sampling the voltage of the one or more flying capacitors.

14. The multi-stage conversion device (20) according to claim 1 or 2 further includes a drive circuit for controlling a plurality of power switches in the multi-stage flying capacitor converter (22).

15. A power supply circuit, comprising: The multi-stage conversion device (20) according to any one of claims 1 to 14.

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