Multi-level converter circuit with flying capacitor

Abstract

A multi-level conversion circuit with a flying capacitor includes: a first bridge arm including a plurality of switching devices connected in series; a second bridge arm including a flying capacitor including a plurality of switching devices connected in series, wherein the midpoint between the second and first bridge arms is connected to a first current limiting circuit, a power supply, and an inductor to form a series branch; a DC bus capacitor connected in parallel with the first and second bridge arms; a rectifier circuit having an input coupled to the power supply; at least one first auxiliary power supply having an input coupled to the output of the rectifier circuit; and a controller coupled to the at least one first auxiliary power supply and the plurality of switching devices in the second bridge arm. After the controller is activated, the controller is configured to control the corresponding switching devices in the second bridge arm to conduct, and the power supply charges the flying capacitor through the corresponding switching devices in the first bridge arm, the corresponding switching devices in the second bridge arm, and the first current limiting circuit. The present invention can effectively avoid the risk of damage to the switching devices due to overvoltage before the controller is activated.

Description

Technical Field

[0001] The present invention relates to the field of power electronics, and in particular to a multi-level conversion circuit with a flying capacitor. Background Art

[0002] For the Power Factor Correction (PFC) circuit, its startup sequence is that the power supply is powered on, the DC bus capacitor is charged through the switching device of the PFC circuit, and when the voltage of the DC bus capacitor reaches a certain preset value, the auxiliary power supply connected in parallel to the DC bus capacitor starts to work and supplies power to the controller, and then the PFC circuit starts to work normally.

[0003] When a PFC circuit uses a multi-level converter circuit with a flying capacitor, a switching device with a low withstand voltage is typically selected as the circuit's main power device. During the power-up phase of the multi-level converter circuit and the charging of the DC bus capacitor, the flying capacitor, its external switching device, and the DC bus capacitor form a loop. Because the flying capacitor's voltage is zero, the DC bus capacitor's voltage is applied to the switching device outside the flying capacitor, posing a risk of damage to the switching device outside the flying capacitor. Furthermore, after the multi-level converter circuit begins normal operation, the controller controls the switching devices to charge the flying capacitor. Because the flying capacitor's initial voltage is zero, when the controller turns on a switching device outside the flying capacitor, the DC bus capacitor's voltage is applied entirely to another switching device outside the flying capacitor, potentially damaging that switching device. Therefore, when using a flying capacitor multi-level conversion circuit, the switching devices outside the flying capacitor must be protected before the controller works, and the flying capacitor must be pre-charged before the multi-level converter with the flying capacitor works normally to prevent the switching devices outside the flying capacitor from being damaged by overvoltage and ensure the normal operation of the multi-level conversion circuit with the flying capacitor. Summary of the Invention

[0004] An object of the present invention is to provide a multi-level conversion circuit with a flying capacitor, which can solve one or more defects of the prior art.

[0005] To achieve the above-mentioned purpose, according to one embodiment of the present invention, the present invention provides a multi-level conversion circuit with a flying capacitor, comprising: a first bridge arm, comprising a plurality of switching devices connected in series; a second bridge arm with a flying capacitor, comprising a plurality of switching devices connected in series, and the midpoint of the second bridge arm and the midpoint of the first bridge arm are connected to a first current limiting circuit, a power supply and an inductor to form a first series branch; a DC bus capacitor, connected in parallel with the first bridge arm and the second bridge arm; a rectifier circuit, the input end of the rectifier circuit being coupled to the power supply; at least one first auxiliary power supply, the input end of the at least one first auxiliary power supply being coupled to the output end of the rectifier circuit; and a controller, coupled to the at least one first auxiliary power supply and the plurality of switching devices of the second bridge arm. After the controller is started, the controller is used to control the corresponding switching devices of the second bridge arm to be turned on, and the power supply charges the flying capacitor through the corresponding switching devices of the first bridge arm, the corresponding switching devices of the second bridge arm and the first current limiting circuit.

[0006] In one embodiment of the present invention, before the controller is started, the initial voltages of the flying capacitor and the DC bus capacitor are 0.

[0007] In one embodiment of the present invention, an input terminal of the at least one first auxiliary power supply is connected in parallel with the DC bus capacitor via an anti-reverse diode.

[0008] In one embodiment of the present invention, when the voltage of the DC bus capacitor is greater than the output voltage of the rectifier circuit, the at least one first auxiliary power supply is powered by the DC bus capacitor.

[0009] In one embodiment of the present invention, at least one second auxiliary power supply is further included, and an input end of the at least one second auxiliary power supply is connected in parallel with the DC bus capacitor.

[0010] In one embodiment of the present invention, the output power of the second auxiliary power supply is greater than the output power of the first auxiliary power supply.

[0011] In one embodiment of the present invention, after the controller is started and before the first current limiting circuit is turned on, the controller is configured to control the corresponding switching device of the second bridge arm to be turned on.

[0012] In one embodiment of the present invention, the power supply charges the DC bus capacitor through corresponding switching devices of the first bridge arm, corresponding switching devices of the second bridge arm, and the first current limiting circuit.

[0013] In one embodiment of the present invention, the multi-level conversion circuit further includes a third bridge arm including a plurality of switching devices connected in series; the third bridge arm is connected in parallel with the first bridge arm, and a midpoint of the third bridge arm is connected to the first series branch;

[0014] Wherein, after the controller is started, the power supply charges the flying capacitor through the corresponding switching device of the second bridge arm, the corresponding switching device of the first bridge arm and the first current limiting circuit; or the power supply charges the flying capacitor through the corresponding switching device of the second bridge arm, the corresponding switching device of the first bridge arm, the first current limiting circuit and the corresponding switching device of the third bridge arm.

[0015] In one embodiment of the present invention, the power supply charges the DC bus capacitor through the corresponding switching devices of the first bridge arm, the corresponding switching devices of the second bridge arm and the first current limiting circuit; and / or the power supply charges the DC bus capacitor through the corresponding switching devices of the first bridge arm, the first current limiting circuit and the corresponding switching devices of the third bridge arm.

[0016] In one embodiment of the present invention, the multi-level conversion circuit is a three-level converter circuit, the second bridge arm includes a first switching device, a second switching device, a third switching device and a fourth switching device connected in series; the flying capacitor is connected across the first switching device and the fourth switching device.

[0017] In one embodiment of the present invention, when the voltage of the flying capacitor reaches a first preset value, the flying capacitor completes charging; the controller is used to control the corresponding switching device of the second bridge arm to disconnect, and the power supply continues to charge the DC bus capacitor; when the voltage of the DC bus capacitor reaches a second preset value, the DC bus capacitor completes charging.

[0018] In one embodiment of the present invention, the first preset value is half of the second preset value.

[0019] In one embodiment of the present invention, the multi-level conversion circuit is an n-level conversion circuit, where n is a positive integer greater than 3, the first bridge arm includes a plurality of switching devices connected in series; the second bridge arm includes (2n-2) switching devices connected in series; the flying capacitor includes (n-2) flying capacitors, wherein the i-th flying capacitor is connected across the i-th switching device and the (2n-1-i)-th switching device of the second bridge arm, where i=1, 2,…, n-2.

[0020] In one embodiment of the present invention, when the voltage of the i-th flying capacitor reaches (n-1-i) / (n-1) times the second preset value, the i-th flying capacitor completes charging, and the controller is used to control the corresponding switching device of the second bridge arm to disconnect; when the (n-2) flying capacitors complete charging, the power supply continues to charge the DC bus capacitor; when the voltage of the DC bus capacitor reaches the second preset value, the DC bus capacitor completes charging.

[0021] In one embodiment of the present invention, the first current limiting circuit includes a first switch, a second switch and a snubber resistor, wherein the first switch and the snubber resistor are connected in series to form a second series branch, and the second switch is connected in parallel to the second series branch.

[0022] In one embodiment of the present invention, before the controller is started, the first switch and the second switch are both disconnected; after the controller controls the corresponding switching device of the second bridge arm to turn on, the first switch is turned on, and the power supply charges the flying capacitor through the corresponding switching devices of the first bridge arm and the second bridge arm, and the snubber resistor.

[0023] In one embodiment of the present invention, after the first switch is turned on, the controller controls the corresponding switching device of the second bridge arm to be turned on, and the power supply charges the flying capacitor through the corresponding switching devices of the first bridge arm and the second bridge arm, and the snubber resistor.

[0024] In one embodiment of the present invention, the multi-level conversion circuit further includes a second current limiting circuit coupled between the power supply and the rectifier circuit; the second current limiting circuit includes a third switch and a current limiting resistor, wherein the third switch and the current limiting resistor are connected in parallel.

[0025] In one embodiment of the present invention, before the controller is started, the third switch is disconnected, and the power supply supplies power to the at least one first auxiliary power supply through the current limiting resistor and the rectifier circuit.

[0026] In one embodiment of the present invention, after the controller is started, the third switch is turned on, and the power supply supplies power to the at least one first auxiliary power supply through the third switch and the rectifier circuit.

[0027] In one embodiment of the present invention, when a fault occurs in the multi-level conversion circuit, the first switch and the second switch are disconnected.

[0028] In one embodiment of the present invention, when the voltage of the DC bus capacitor reaches a second preset value, the controller is configured to control all switching devices of the second bridge arm to be disconnected, the second switch to be turned on, and the first switch to be disconnected.

[0029] In one embodiment of the present invention, when a fault occurs in the multi-level conversion circuit, the third switch is disconnected.

[0030] Based on the existing technology, the present invention establishes an independent power supply circuit for the auxiliary power supply, so that the power supply has corresponding technical characteristics, effectively avoiding the risk of damage to the switching device due to overvoltage before the controller is started. At the same time, it can completely cut off the circuit for charging the flying capacitor and the DC bus capacitor in a fault state, and actively connect the first current limiting circuit after the fault is eliminated, thereby improving the fault response capability of the multi-level conversion circuit.

[0031] The present invention proposes a multi-level conversion circuit with a flying capacitor. After the power supply is powered on, the rectifier circuit can provide electrical energy to at least one first auxiliary power supply, so that the power supply can establish an operating voltage to provide electrical energy to the controller. After the controller starts working, it controls the corresponding switching device of the second bridge arm to turn on, thereby establishing a circuit for charging the flying capacitor and the DC bus capacitor. Because the initial voltages of the flying capacitor and the DC bus capacitor are both zero before the controller is started, when the power supply charges the DC bus and the flying capacitor, the two switching devices connected in series on the outside of the flying capacitor will not be damaged by overvoltage. At the same time, at least one first auxiliary power supply is connected in parallel with the DC bus capacitor through an anti-reverse diode. When the voltage of the DC bus capacitor is higher than the output voltage of the rectifier circuit, the DC bus capacitor supplies power to the at least one first auxiliary power supply through the anti-reverse diode. The auxiliary power supply may also include at least one second auxiliary power supply, coupled in parallel across the DC bus capacitor, having a high output power and used to provide power to the entire multilevel conversion circuit after the multilevel conversion circuit is operating normally. Furthermore, at least one first auxiliary power supply, coupled to the output of the rectifier circuit, serves as an auxiliary power supply independent of the multilevel conversion circuit, having a lower output power and primarily used to provide power to the controller, etc., in the event of a multilevel conversion circuit fault and during the charging of the flying capacitor and DC bus capacitor. Furthermore, the first auxiliary power supply can completely shut down the charging circuit for the flying capacitor and DC bus capacitor in the event of a fault, and actively connect the first current limiting circuit after the fault is eliminated, thereby improving the fault response capability of the multilevel conversion circuit.

[0032] Additional aspects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the accompanying drawings.

[0034] Figure 1 The topology of the three-level conversion circuit with flying capacitors according to the first preferred embodiment of the present invention is as follows;

[0035] Figure 2A and Figure 2B Respectively in Figure 1 In the embodiment shown, after the controller is started and begins to work, the controller controls the switching device to form a positive and negative half-cycle charging circuit;

[0036] Figure 3 The topology of the 4-level conversion circuit with flying capacitors according to the second preferred embodiment of the present invention is as follows;

[0037] Figure 4A and Figure 4B Respectively in Figure 3 In the embodiment shown, after the controller is started and begins to work, the controller controls the switching device to form a positive and negative half-cycle charging circuit;

[0038] Figure 5 The topology of the n-level conversion circuit with a flying capacitor according to the third preferred embodiment of the present invention is as follows;

[0039] Figure 6A and Figure 6B Respectively in Figure 5 In the embodiment shown, after the controller is started and begins to work, the controller controls the switching device to form a positive and negative half-cycle charging circuit;

[0040] Figure 7A and Figure 7B Respectively in Figure 5 In the embodiment shown, after the controller is started and begins to work, the controller controls the switching device to form a positive and negative half-cycle of another charging circuit;

[0041] Figure 8 A topology of an n-level converter circuit with a flying capacitor according to a fourth preferred embodiment of the present invention, wherein a single auxiliary power supply is used for operation;

[0042] Figure 9 The topology of the n-level converter circuit with a flying capacitor according to the fifth preferred embodiment of the present invention is implemented by using multiple auxiliary power supplies.

[0043] Figure 10A and Figure 10B Respectively in Figure 1In the embodiment shown, after the controller is started and begins to work, the controller controls the switching device to form a schematic diagram of the inductive energy storage circuit and the flying capacitor charging circuit in the positive half cycle;

[0044] Figure 11A and Figure 11B Respectively in Figure 1 In the embodiment shown, after the controller is started and begins to work, the controller controls the switching device to form an inductive energy storage circuit and a flying capacitor charging circuit in the negative half cycle;

[0045] Figure 12 This is a topology of a three-level conversion circuit with flying capacitors according to another preferred embodiment of the present invention. DETAILED DESCRIPTION

[0046] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be embodied in many forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete and will fully convey the concepts of the example embodiments to those skilled in the art. Like reference numerals in the figures represent like or similar structures, and thus their detailed description will be omitted.

[0047] When introducing the elements / components / etc. described and / or illustrated herein, the terms "a," "an," "the," "said," and "at least one" are used to indicate that there are one or more elements / components / etc. The terms "comprising," "including," and "having" are used to indicate an open-ended inclusiveness and mean that additional elements / components / etc. may be present in addition to the listed elements / components / etc. Relative terms may be used in the embodiments, such as "upper" or "lower" to describe the relative relationship of one component of the illustration to another component. It is understood that if the device of the illustration is turned over so that it is upside down, the component described on the "upper" side will become the component on the "lower" side. In addition, the terms "first," "second," etc. in the claims are used only as labels and are not numerical limitations on their objects.

[0048] like Figure 1 As shown in FIG, it shows a circuit topology of a preferred multi-level conversion circuit 100 with flying capacitors of the present invention. Figure 1 In the embodiment shown, a three-level conversion circuit is used as an example, but the present invention is not limited thereto. In the present invention, the multi-level conversion circuit 100 may include a first bridge arm 10, a second bridge arm 20, a DC bus capacitor C p, rectifier circuit 30, auxiliary power supply 40 and controller (not shown). The first bridge arm 10 may include a plurality of switch devices 11 connected in series. The second bridge arm 20 may include a plurality of switch devices 21 connected in series and have a flying capacitor 22. In addition, the midpoint a of the second bridge arm 20 and the midpoint b of the first bridge arm 10 are connected to the first current limiting circuit 61 and the power supply V ac and the inductor L form a first series branch 101. The DC bus capacitor C p The input end of the rectifier circuit 30 is coupled to the power supply V ac . The input end of the auxiliary power supply 40 is coupled to the output end of the rectifier circuit 30. The controller is coupled to the output end of the auxiliary power supply 40 and the multiple switching devices 21 of the second bridge arm 20, wherein the switching device 11 includes a diode, or a controllable switch and a diode anti-parallel to the controllable switch, and the switching device 22 may include a controllable switch and a diode anti-parallel to the controllable switch. In some embodiments, the controller is connected to the control end of the controllable switch in the switching device, and the controller is used to control the conduction or shutdown of the switching device. Specifically, the controller is used to control the conduction or shutdown of the controllable switch in the switching device. For example, when the multiple switching devices 11 of the first bridge arm 10 include a controllable switch and a diode anti-parallel to the controllable switch, the controller can also be connected to the control end of the controllable switch in the multiple switching devices 11 to control the conduction or shutdown of the multiple switching devices 11.

[0049] The power supply V ac After power is turned on, the rectifier circuit 30 can provide power to the auxiliary power supply 40, so that the auxiliary power supply 40 can establish a voltage and be used to provide power to the controller. Before the controller is started, the first current limiting circuit 61 is open; after the controller is started, it is used to control the corresponding switch device 21 of the second bridge arm 20 to be turned on, and then the first current limiting circuit 61 is turned on, so that the power supply V ac The flying capacitor 22 can be charged by the corresponding switch device 11 of the first bridge arm 10, the first current limiting circuit 61 and the corresponding switch device 21 of the second bridge arm 20; and the power supply V ac The DC bus capacitor C can also be supplied with current through the corresponding switch device 11 of the first bridge arm 10, the first current limiting circuit 61, and the corresponding switch device 21 of the second bridge arm 20. p At this time, the flying capacitor 22 and the DC bus capacitor C pThe initial voltages of the first and second current limiting circuits 61 are both 0, and the switching devices S4 and S3 connected in series on the outer sides of the flying capacitor 22 are not at risk of damage due to overvoltage. It should be noted that the first current limiting circuit 61 being turned on means that the first current limiting circuit 61 can provide a flow path for current.

[0050] It should be noted that, if the first current limiting circuit 61 is turned on before the controller controls the corresponding switch device 21 of the second bridge arm 20 to turn on, the power supply V ac The DC bus capacitor C can be firstly supplied with current through the corresponding switch device 11 of the first bridge arm 10, the first current limiting circuit 61 and the corresponding switch device 21 of the second bridge arm 20. p During charging, if the switch device 21 of the second bridge arm 20 controlled by the controller operates slowly, the switch devices S4 and S3 connected in series on the outside of the flying capacitor 22 may be damaged due to overvoltage.

[0051] In some other embodiments, if it can be ensured that before the controller controls the corresponding switch device 21 of the second bridge arm 20 to be turned on, the DC bus capacitor C p When the voltage of the power supply V ac First, the DC bus capacitor C is supplied with current through the corresponding switch device 11 of the first bridge arm 10, the first current limiting circuit 61, and the corresponding switch device 21 of the second bridge arm 20. p Charging; the power supply V ac The flying capacitor 22 is then charged through the corresponding switch device 11 of the first bridge arm 10 , the first current limiting circuit 61 , and the corresponding switch device 21 of the second bridge arm 20 .

[0052] In some embodiments, the first current limiting circuit 61 can be turned on before or after the corresponding switching device 21 of the second bridge arm 20 is turned on, depending on the specific situation, but the first current limiting circuit 61 must be turned on during the charging process of the flying capacitor and the DC bus capacitor.

[0053] exist Figure 1 In the embodiment of the three-level conversion circuit shown, the number of the plurality of switch devices 11 of the first bridge arm 10 may be two, for example, including switch devices S connected in series. a and switching device S b The number of the plurality of switch devices 21 of the second bridge arm 20 may be four, for example, including a first switch device S4, a second switch device S2, a third switch device S1 and a fourth switch device S3 connected in series. The flying capacitor 22 may include, for example, one flying capacitor C fly1, which is connected across the first switch device S4 and the fourth switch device S3. The rectifier circuit 30 may include, for example, a diode rectifier bridge 31, but it is understood that the present invention is not limited thereto. A capacitor C may also be connected in parallel between the input end of the auxiliary power supply 40 and the output end of the rectifier circuit 30. aux The load 90 can be coupled to the DC bus capacitor C p output terminal.

[0054] In some embodiments, after the first current limiting circuit 61 is turned on, when the flying capacitor C fly1 The voltage of the flying capacitor C reaches the first preset value. fly1 After charging is completed, the controller can be used to control the corresponding switch device 21 of the second bridge arm 20 to be disconnected, and the power supply V ac Continue to add the DC bus capacitor C p When the DC bus capacitor C p When the voltage of the DC bus capacitor C reaches a second preset value, the DC bus capacitor C p In some embodiments, due to the voltage drop of devices and lines, the second preset value is slightly smaller than the peak voltage V between the midpoint b of the first bridge arm 10 and the midpoint a of the second bridge arm 20. ab_peak .

[0055] In some embodiments, the first preset value is half of the second preset value.

[0056] In some embodiments, before the controller is started, the flying capacitor 22 and the DC bus capacitor C p The initial voltage is 0.

[0057] In some embodiments, the input end of the auxiliary power supply 40 is connected to the DC bus capacitor C through the anti-reverse diodes D1 and D2. p When the DC bus capacitor C of the 3-level conversion circuit is connected in parallel. p After the flying capacitor 22 is fully charged, the 3-level conversion circuit operates normally. At this time, if the DC bus capacitor C p The voltage of the rectifier circuit 30 is greater than the output voltage of the auxiliary power supply 40, and the auxiliary power supply 40 can be supplied by the DC bus capacitor C p Provide power supply.

[0058] In some embodiments, the multi-level conversion circuit 100 may further include a third bridge arm 50, which may include a plurality of switching devices 51 connected in series. In some embodiments, the switching device 51 may be, but is not limited to, a diode. The third bridge arm 50 is connected in parallel with the first bridge arm 10, and the midpoint of the third bridge arm 50 is connected to the first series branch 101, for example, it may be connected to the power supply V acand the inductor L. The controller can control the corresponding switch device 21 of the second bridge arm 20 to be turned on. The corresponding switch device 21 of the second bridge arm 20, the flying capacitor 22, the corresponding switch device 11 of the first bridge arm 10, the power supply V ac , and the inductor L constitute the charging circuit of the flying capacitor 22, that is, the power supply V ac The flying capacitor 22 can be charged through the inductor L, the corresponding switch device 21 of the second bridge arm 20, the corresponding switch device 11 of the first bridge arm 10, and the first current limiting circuit 61. Alternatively, the corresponding switch device 21 of the second bridge arm 20, the flying capacitor 22, the corresponding switch device 11 of the first bridge arm 10, the power supply V ac , and the corresponding switch 51 of the third bridge arm 50 constitute the charging circuit of the flying capacitor 22, that is, the power supply V ac The flying capacitor 22 can be charged through the corresponding switching device 21 of the second bridge arm 20 , the corresponding switching device 11 of the first bridge arm 10 , the first current limiting circuit 61 , and the corresponding switching device 51 of the third bridge arm 50 .

[0059] In some embodiments, when the first current limiting circuit 61 is turned on, the corresponding switch device 11 of the first bridge arm 10, the first current limiting circuit 61, the power supply V ac , the inductor L, the corresponding switch device 21 of the second bridge arm 20 and the DC bus capacitor C p It forms the DC bus capacitor C p Charging circuit; that is, the power supply V ac The DC bus capacitor C can also be supplied with current through the inductor L, the corresponding switch device 11 of the first bridge arm 10, the first current limiting circuit 61, and the corresponding switch device 21 of the second bridge arm 20. p Charging. And / or the corresponding switch device 11 of the first bridge arm 10, the first current limiting circuit 61, the power supply V ac , the corresponding switch device 51 of the third bridge arm 50, and the DC bus capacitor C p It forms the DC bus capacitor C p Charging circuit; that is, the power supply V ac The DC bus capacitor C can also be supplied with current through the corresponding switch device 11 of the first bridge arm 10, the first current limiting circuit 61, and the corresponding switch device 51 of the third bridge arm 50. p Charging. DC bus capacitor C p The choice of charging circuit is related to the voltage drop in the charging circuit, such as the diode D s1 and D s2The voltage drop of the diode in the switching device is 2V, and the voltage drop of the diode in the switching device is 0.7V. Then, when the first current limiting circuit 61 is turned on, the charging circuit composed of the corresponding switching devices of the first bridge arm 10 and the corresponding switching devices of the second bridge arm 20 will be selected; then when the switching device of the second bridge arm 20 is selected as GaN, since the equivalent body diode voltage drop of GaN is related to the current flowing through it, when the first current limiting circuit 61 is turned on, the charging circuit composed of the corresponding switching devices of the first bridge arm 10 and the corresponding switching devices of the third bridge arm 80 will be selected.

[0060] In some embodiments, in the charging loop of the flying capacitor and the charging loop of the DC bus capacitor, current flows through corresponding diodes, or a diode and a controllable switch.

[0061] In some embodiments, the first current limiting circuit 61 may include a first switch RL1, a second switch RL2 and a snubber resistor R s , wherein the first switch RL1 and the snubber resistor R s The second series branch 102 is formed by connecting the second switch RL2 in series. The second switch RL2 is connected in parallel with the second series branch 102. In the present invention, the multi-level conversion circuit 100 may further include a second current limiting circuit 62 connected to the input end of the rectifier circuit 30 and the power supply V ac The second current limiting circuit 62 may include, for example, a current limiting resistor R, which is connected to the diode rectifier bridge of the rectifier circuit 30 and the power supply V ac Connect the power supply V ac The DC bus capacitor C can be connected to the current limiting resistor R and the rectifier bridge 31. aux The battery is charged to supply power to the auxiliary power supply 40 .

[0062] In some other embodiments, such as Figure 12 As shown, the second current limiting circuit 62 may further include a current limiting resistor R and a third switch RL3. The third switch RL3 is connected in parallel with the current limiting resistor R. Before the controller is started, the third switch RL3 is disconnected, and the power supply V ac The DC bus capacitor C can be connected to the current limiting resistor R and the rectifier bridge 31. aux When the controller is started, the third switch RL3 is turned on, and the power supply V ac The DC bus capacitor C can be connected to the DC bus capacitor C through the third switch RL3 and the rectifier bridge 31. aux In some embodiments, the third switch RL3 may be controlled by a controller or other control device to be turned on or off.

[0063] In some embodiments, when a fault occurs in the multi-level conversion circuit, the third switch RL3 is disconnected.

[0064] In some embodiments, before the controller is started, the first switch RL1 and the second switch RL2 are both disconnected, so that the first current limiting circuit 61 is open, that is, the first current limiting circuit 61 blocks the current flow path in the charging circuit of the flying capacitor 22 and the charging circuit of the DC bus capacitor.

[0065] After the controller is started and used to control the corresponding switch devices of the second bridge arm 20 to be turned on, the first switch RL1 is turned on, so that the first current limiting circuit 61 is turned on. At this time, the first switch RL1 of the first current limiting circuit 61 and the snubber resistor R in the charging circuit of the flying capacitor 22 and the charging circuit of the DC bus capacitor are connected. s Provide a path for current to flow. Specifically, the power supply V ac The corresponding switch device 11 of the first bridge arm 10, the snubber resistor R s , the inductor L and the corresponding switch device 21 of the second bridge arm 20 to charge the flying capacitor 22; or the power supply V ac The corresponding switch device 21 of the second bridge arm 20, the corresponding switch device 11 of the first bridge arm 10, the snubber resistor R s , and the corresponding switch device 51 of the third bridge arm 50 charges the flying capacitor 22. At the same time, the power supply V ac The corresponding switch device 11 of the first bridge arm 10 and the slow-start resistor R s , the inductor L and the corresponding switch device 21 of the second bridge arm 20 to the DC bus capacitor C p Charging; and / or the power supply V ac The corresponding switch device 11 of the first bridge arm 10 and the slow-start resistor R s , and the corresponding switch device 51 of the third bridge arm 50 supplies the DC bus capacitor C p Charge.

[0066] In some other embodiments, the first switch RL1 is turned on first, and then the controller controls the corresponding switch device of the second bridge arm 20 to be turned on, and the power supply V ac The corresponding switch device 11 of the first bridge arm 10 and the slow-start resistor R s , the inductor L and the corresponding switch device 21 of the second bridge arm 20 to the DC bus capacitor C p Charging; and / or the power supply V ac The corresponding switch device 11 of the first bridge arm 10 and the slow-start resistor Rs , and the corresponding switch device 51 of the third bridge arm 50 supplies the DC bus capacitor C p Charging. At the same time, the power supply V ac Through the corresponding switch device 11 of the first bridge arm 10, the snubber resistor R s , the inductor L and the corresponding switch device 21 of the second bridge arm 20 to charge the flying capacitor 22; or the power supply V ac The corresponding switch device 21 of the second bridge arm 20, the corresponding switch device 11 of the first bridge arm 10, the snubber resistor R s , and the corresponding switching device 51 of the third bridge arm 50 charges the flying capacitor 22 .

[0067] When a fault occurs in the multi-level conversion circuit, the first switch RL1 and the second switch RL2 are disconnected.

[0068] When the DC bus capacitor C p When the voltage reaches a second preset value, the controller can control all the switch devices 21 of the second bridge arm 20 to be disconnected, and the first switch RL1 to be disconnected and the second switch RL2 to be turned on, so that the multi-level conversion circuit works normally.

[0069] In some embodiments, the first switch RL1 and the second switch RL2 may be controlled by a controller or other control device to be turned on or off.

[0070] The following will be combined Figure 1 The 3-level conversion circuit with flying capacitor is shown to describe and explain the principle of the present invention in detail.

[0071] like Figure 1 As shown, it shows a 3-level conversion circuit with flying capacitor clamping. ac After power-on, since the first switch RL1 and the second switch RL2 are disconnected, the flying capacitor 22 and the DC bus capacitor C p The voltage of the uncontrolled rectifier bridge 31 is coupled to the power supply V ac and set the power supply V ac The voltage is rectified into a DC voltage and applied to the capacitor C auxIt is used to supply power to the auxiliary power supply 40. The auxiliary power supply 40 starts and outputs an auxiliary voltage to supply power to the controller so that the controller starts and begins to work. After the controller starts, it controls the corresponding switch device 21 on the second bridge arm 20 to turn on, or controls the corresponding switch device 11 on the first bridge arm 10 and the corresponding switch device 21 on the second bridge arm 20 to turn on; and the first switch RL1 can be turned on before or after the corresponding switch device 21 of the second bridge arm 20 is turned on, depending on the actual situation, but in the process of charging the flying capacitor and the DC bus capacitor, the first switch RL1 must be turned on. Power supply V ac Through the snubber resistor R s , control the switch device 11 on the first bridge arm 10 and the switch device 21 on the second bridge arm 20 to supply power to the flying capacitor 22 and the DC bus capacitor C p Charging, the charging circuit of the positive and negative half cycles is as follows Figure 2A 、 2B shown.

[0072] like Figure 2A As shown, the power supply V ac In the positive half cycle, the controller controls the switch device S3 to turn on, and the first switch RL1 is turned on, the power supply V ac , inductor L, switch device S2, flying capacitor C fly1 , switching device S3, switching device S b And the snubber resistor R s Forming a flying capacitor C fly1 The charging circuit. Or the controller controls the switching device S b and / or S2 and S3 are turned on, and the first switch RL1 is turned on, the power supply V ac , inductor L, switch device S2, flying capacitor C fly1 , switching device S3, switching device S b And the snubber resistor R s Forming a flying capacitor C fly1 The first switch RL1 is turned on, and the power supply V ac , inductor L, switching devices S2 and S4, DC bus capacitor C p , switching device S b And the snubber resistor R s The DC bus capacitor C p The charging circuit. Or the controller controls the switching device S b and / or S2 and / or S4 are turned on, and the first switch RL1 is turned on, the power supply V ac , inductor L, switching devices S2 and S4, DC bus capacitor C p , switching device S b And the snubber resistor R s The DC bus capacitor Cp charging circuit.

[0073] like Figure 2B As shown, the power supply V ac In the negative half cycle, the controller controls the switch device S4 to turn on, and the first switch RL1 is turned on, the power supply V ac , inductor L, switching devices S1 and S3, flying capacitor C fly1 , switching device S4, switching device S a And the snubber resistor R s Forming a flying capacitor C fly1 The charging circuit. Or the controller controls the switching device S a and / or S1 and S4 are turned on, and the first switch RL1 is turned on, the power supply V ac , inductor L, switching devices S1 and S3, flying capacitor C fly1 , switching device S4, switching device S a And the snubber resistor R s Forming a flying capacitor C fly1 The first switch RL1 is turned on, and the power supply V ac , inductor L, switching devices S1 and S3, DC bus capacitor C p , switching device S a And the snubber resistor R s The DC bus capacitor C p Charging circuit; or controller controls the switching device S a and / or S1 and / or S3 are turned on, and the first switch RL1 is turned on, the power supply V ac , inductor L, switching devices S1 and S3, DC bus capacitor C p , switching device S a And the snubber resistor R s The DC bus capacitor C p charging circuit.

[0074] When the bus capacitance C p The voltage is charged to the second preset value V Bulk When the DC bus capacitor C p Charging is completed. Considering the voltage drop of the circuit and the device, the second preset value V Bulk Should be slightly smaller than the voltage V between midpoint a and midpoint b ab The peak voltage V ab_peak When the flying capacitor C fly1 The voltage V Cfly1 When it is charged to the first preset value, there is a relationship V Cfly1 =V Cp , the controller controls the switch devices S3 and S4 to turn off, and the power supply V ac Continue to give bus capacitor Cp Charging, when the bus capacitor C p The voltage is charged to the second preset value V Bulk When the DC bus capacitor C p Complete charging. The first preset value is half of the second preset value. p After charging is completed, the controller controls all the switch devices 21 on the second bridge arm 20 to turn off, then turns on the second switch RL2 and turns off the first switch RL1, and then the controller starts to control the three-level conversion circuit to work normally.

[0075] like Figure 2A 、 2B As shown, the power supply V ac In the positive half cycle, when the power supply V ac At the same time, the flying capacitor C fly1 And the DC bus capacitor C p When charging, there is a relationship V S4 +V Cfly1 =V Cp . Flying capacitor C fly1 And the DC bus capacitor C p The initial voltage V Cfly1 =V Cp = 0, the switch device S4 does not have an overvoltage state, so no additional protection is required. ac In the negative half cycle, when the power supply V ac At the same time, the flying capacitor C fly1 And the DC bus capacitor C p When charging, there is a relationship V S3 +V Cfly1 =V Cp . Flying capacitor C fly1 And the DC bus capacitor C p The initial voltage V Cfly1 =V Cp = 0, the switch device S3 does not have an overvoltage state, so no additional protection is required. p The charging rate is faster than that of the flying capacitor C fly1 Fast, may make the switch devices S4 and S3 bear the corresponding voltage, but usually the DC bus capacitor C p When the capacitance is about hundreds of uF, the corresponding flying capacitor C fly1 The capacitance value is generally not more than 100uF, so the flying capacitor C fly1 The charging rate is faster and the switching devices S4 and S3 will not be subjected to a large voltage.

[0076] DC bus capacitor C p After charging is completed, the 3-level conversion circuit works normally. If the DC bus capacitor Cp The voltage V Cp If the output voltage of the uncontrolled rectifier bridge 31 is higher than the output voltage of the uncontrolled rectifier bridge 31, the auxiliary power supply 40 will be powered by the DC bus through the anti-reverse diodes D1 and D2. When the 3-level conversion circuit fails, the first switch RL1 and the second switch RL2 are disconnected. After the failure is resolved, the first switch RL1 is turned on again to supply the flying capacitor C fly1 And the DC bus capacitor C p Charging, or the second switch RL2 is turned on and the first switch RL1 is turned off, so that the three-level conversion circuit works normally.

[0077] In some embodiments, the multi-level conversion circuit 100 may also be an n-level conversion circuit, where n is a positive integer greater than 3, that is, for example, a 4-level conversion circuit (eg Figure 3 as shown) or more level conversion circuits (such as Figure 5 shown).

[0078] In the n-level conversion circuit of the present invention, the first bridge arm 10 may include a plurality of switching devices connected in series, for example, the switching devices S a and S b The second bridge arm 20 may include (2n-2) switching devices 21 connected in series; the flying capacitor 22 may include (n-2) flying capacitors, wherein the i-th flying capacitor is connected across the i-th switching device and the (2n-1-i)-th switching device of the second bridge arm 20, where i=1, 2, ..., n-2. For example, Figure 3 The 4-level PFC circuit 100-1 shown includes two flying capacitors, namely, flying capacitors C fly1 and C fly2 , where the first flying capacitor C fly1 It is connected across the first switch device S6 and the sixth switch device S5, and the second flying capacitor C fly2 It is connected across the second switch device S4 and the fifth switch device S3; Figure 5 The n-level PFC circuit 100-2 shown includes (n-2) flying capacitors, namely, flying capacitors C fly1 、C fly2 、C fly3 ,……,C fly(n-2) , where the first flying capacitor C fly1 It is connected across the first switching device S (2n-2) and the (2n-2)th switching device S (2n -3), ..., the (n-2)th flying capacitor C fly(n-2) It is connected across the (n-2)th switching device S4 and the (n+1)th switching device S3.

[0079] Before the controller is started, the first current limiting circuit 61 is open; when the controller is started and controls the corresponding switch device 21 of the second bridge arm 20 to be turned on, the power supply V ac The flying capacitor C is supplied with current through the corresponding switch device 11 of the first bridge arm 10, the first current limiting circuit 61, the corresponding switch device 21 of the second bridge arm 20 and the first current limiting circuit 61. fly1 、C fly2 、C fly3 ,……,C fly(n-2) Charging; and the power supply V ac The DC bus capacitor C is supplied with current through the corresponding switch device 11 of the first bridge arm 10, the first current limiting circuit 61, the corresponding switch device 21 of the second bridge arm 20 and the first current limiting circuit 61. p charging, where the power supply gives the flying capacitor C fly1 、C fly2 、C fly3 ,……,C fly(n-2) And the DC bus capacitor C p During the charging process, the first current limiting circuit 61 is turned on.

[0080] Preferably, the n-level conversion circuit may further include a third bridge arm 50, which may include a plurality of switch devices 51 connected in series. The midpoint of the third bridge arm 50 may be connected to the power supply V ac and the inductor L. When the controller starts and controls the corresponding switch device 21 of the second bridge arm 20 to turn on, the power supply V ac The flying capacitor C can be supplied with current through the corresponding switch device 21 of the second bridge arm 20, the corresponding switch device 11 of the first bridge arm 10 and the first current limiting circuit 61. fly1 、C fly2 、C fly3 ,……,C fly(n-2) Charging; or, the power supply V ac The flying capacitor C can be supplied with current through the corresponding switch device 21 of the second bridge arm 20, the corresponding switch device 11 of the first bridge arm 10, the first current limiting circuit 61 and the corresponding switch device 51 of the third bridge arm 50. fly1 、C fly2 、C fly3 ,……,C fly(n-2) Charging. Among them, the power supply gives the flying capacitor C fly1 、C fly2 、C fly3 ,……,C fly(n-2) During the charging process, the first current limiting circuit 61 is turned on.

[0081] In some embodiments, when the first current limiting circuit 61 is turned on, the power supply V ac The DC bus capacitor C can also be supplied with current through the corresponding switch device 11 of the first bridge arm 10, the first current limiting circuit 61 and the corresponding switch device 21 of the second bridge arm 20. p Charging; and / or the power supply V ac The DC bus capacitor C can also be supplied with current through the corresponding switch device 11 of the first bridge arm 10, the first current limiting circuit 61 and the corresponding switch device 51 of the third bridge arm 50. p Charge.

[0082] In some embodiments, when the i-th flying capacitor C flyi The voltage V Cflyi Reaching the second preset value V Bulk When the value of the switching element 21 of the second bridge arm 20 is (n-1-i) / (n-1) times, the controller may be used to control the corresponding switching device 21 of the second bridge arm 20 to be disconnected.

[0083] The following will be combined Figures 3 to 9 The n-level PFC circuit (where n is a natural number greater than 3) is shown to further describe and explain the principles of the present invention in detail.

[0084] like Figure 3 As shown, it shows a 4-level PFC circuit 100-1 with flying capacitor clamping according to the present invention. ac After power-on, since the first switch RL1 and the second switch RL2 are disconnected, the flying capacitor 22 and the DC bus capacitor C p The voltage on the power supply V ac The second current limiting circuit 62 and the uncontrolled rectifier bridge 31 are connected to the capacitor C aux The auxiliary power supply 40 starts and supplies power to the controller. The controller starts and starts working. The controller controls the switch device 21 on the second bridge arm 20 to operate and turns the power supply V ac Through the snubber resistor R s Connect to the charging circuit of the flying capacitor and the DC bus capacitor, the charging circuit of the positive and negative half cycles is as follows Figure 4A 、 4B shown.

[0085] like Figure 4A As shown, the power supply V ac In the positive half cycle, the controller controls the switch devices S3 and S5 to turn on, and the power supply V ac , inductor L, switch device S2, flying capacitor C fly2 , switching devices S3 and S5, switching device S b , snubber resistor R s Forming a flying capacitor Cfly2 The controller controls the switch device S5 to turn on, and the power supply V ac , inductor L, switching devices S4 and S2, flying capacitor C fly1 , switching device S5, switching device S b , snubber resistor R s Forming a flying capacitor C fly1 Charging circuit. Power supply V ac , inductor L, switching devices S2, S4 and S6, DC bus capacitor C p , switching device S b , snubber resistor R s The DC bus capacitor C p charging circuit.

[0086] like Figure 4B As shown, the power supply V ac In the negative half cycle, the controller controls the switch devices S4 and S6 to turn on, and the power supply V ac , inductor L, switch device S1, flying capacitor C fly2 , switching devices S4 and S6, switching device S a , snubber resistor R s Forming a flying capacitor C fly2 The controller controls the switch device S6 to turn on, and the power supply V ac , inductor L, switching devices S3 and S1, flying capacitor C fly1 , switching device S6, switching device S a , snubber resistor R s Forming a flying capacitor C fly1 Charging circuit. Power supply V ac , inductor L, switching devices S1, S3 and S5, DC bus capacitor C p , switching device S a , snubber resistor R s The DC bus capacitor C p charging circuit.

[0087] When the DC bus capacitor C p The voltage is charged to the second preset value V Bulk , considering the line and device voltage drop, the second preset value V Bulk Should be slightly smaller than the voltage V between midpoint a and midpoint b ab The peak voltage V ab_peak When the flying capacitor C fly2 The voltage V Cfly2 Reaching the second preset value V Bulk / 3, there is a relationship V Cfly2 =V Cfly1 =V Cp ; Flying capacitor Cfly2 After charging is completed, the controller controls the switch devices S3 and S4 to be disconnected. fly1 The voltage V Cfly1 Reach the preset value 2V Bulk / 3, there is a relationship V Cfly1 =V Cp ; Flying capacitor C fly1 After charging is completed, the controller controls the switch devices S5 and S6 to be disconnected. p The voltage V Cp Reach the preset value V Bulk When the DC bus capacitor C p After charging is completed, the controller controls all switch devices to turn off, then controls the second switch RL2 to turn on, and finally controls the first switch RL1 to turn off. The controller then starts to control the 4-level conversion circuit to operate normally.

[0088] like Figure 4A 、 4B As shown, the power supply V ac In the positive half cycle, the flying capacitor C fly2 In the charging circuit, there is a relationship V S6 +V Cfly1 =V Cp , due to the flying capacitor C fly1 and DC bus capacitor C p The initial voltage V Cfly1 =V Cp =0, so the switch device S6 does not have an overvoltage state and does not require additional protection; similarly, when the power supply V ac In the negative half cycle, the flying capacitor C fly1 In the charging circuit, there is a relationship V S5 +V Cfly1 =V Cp However, due to the flying capacitor C fly1 and DC bus capacitor C p The initial voltage V Cfly1 =V Cp = 0, so the switch device S5 does not have an overvoltage state and does not require additional protection. ac In the positive half cycle, the flying capacitor C fly2 In the charging circuit, there is a relationship V S4 +V Cfly2 =V Cfly1 , due to the flying capacitor C fly2 and DC bus capacitor C p The initial voltage V Cfly1 =V Cfly2 =0, so the switch device S4 does not have an overvoltage state and does not require additional protection; similarly, when the power supply Vac In the negative half cycle, the flying capacitor C fly2 In the charging circuit, there is a relationship V S3 +V Cfly2 =V Cfly1 , due to the flying capacitor C fly1 and DC bus capacitor C p The initial voltage V Cfly1 =V Cfly2 =0, so the switch device S3 does not have an overvoltage state and does not require additional protection.

[0089] DC bus capacitor C p After charging is completed, the 4-level conversion circuit works normally. If the DC bus capacitor C p The voltage V Cp Higher than the output voltage of the uncontrolled rectifier bridge 31, the auxiliary power supply 40 will be supplied by the DC bus capacitor C p Power is supplied through the anti-reverse diodes D1 and D2. When a fault occurs in the 4-level conversion circuit, the first switch RL1 and the second switch RL2 are disconnected. After the fault is resolved, the first switch RL1 is turned on again to supply power to the flying capacitor C fly1 、C fly2 And the DC bus capacitor C p Charging, or the second switch RL2 is turned on and the first switch RL1 is turned off, so that the 4-level conversion circuit works normally.

[0090] like Figure 5 As shown, it shows the flying capacitor clamped n-level PFC circuit 100-2 of the present invention. ac After power-on, since the first switch RL1 and the second switch RL2 are disconnected, the flying capacitor 22 and the DC bus capacitor C p The voltage on the power supply V ac The second current limiting circuit 62 and the uncontrolled rectifier bridge 31 are connected to the capacitor C aux As the auxiliary power supply 40 starts to power the controller, the controller starts and begins to work, and the controller controls the switching device to form a charging circuit, so that the power supply V ac Through the snubber resistor R s Give the flying capacitor 22 and the DC bus capacitor C p For charging, the charging circuit of positive and negative half cycles is as follows Figure 6A 、 6B shown.

[0091] like Figure 6A As shown by the dotted line, the power supply V ac In the positive half cycle, the control switch devices S3~S (2n-3) On, power supply V acThrough the inductor L, the switching device S b 、S2~S (2n-2) , switching devices S3~S (2n-3) , snubber resistor R s Give the flying capacitor C fly1 、C fly2 、C fly3 ,……,C fly(n-2) Charging, where when the i-th flying capacitor C flyi The voltage reaches the second preset value V Bulk When (n-1-i) / (n-1) times (i=1,2,3…n-2), the controller controls the corresponding flying capacitor C flyi The outer switching device S (2n-1-2i) and S (2n-2i) Shut down.

[0092] In some embodiments, the power supply V ac Through the inductor L, the switching device S b 、S2~S (2n-2) , snubber resistor R s To the DC bus capacitor C p Charge.

[0093] like Figure 6B As shown by the dotted line, the power supply V ac In the negative half cycle, the switching devices S2~S (2n-2) The controllable switch in must be turned on, and the switching device S a 、S1~S (2n-3) The controllable switch in the circuit can be turned on or off; the power supply V ac Through the inductor L, the switching device S a 、S1~S (2n-3) , switching devices S2~S (2n-2) , snubber resistor R s Give the flying capacitor C fly1 、C fly2 、C fly3 ,……,C fly(n-2) Charging, where when the i-th flying capacitor C flyi The voltage reaches the second preset value V Bulk When (n-1-i) / (n-1) times (i=1,2,3…n-2), the controller controls the corresponding flying capacitor C flyi The outer switching device S (2n-1-2i) and S (2n-2i) Shut down.

[0094] In some embodiments, the power supply V ac Through the inductor L, the switching device S a 、S1~S (2n-3), snubber resistor R s To the DC bus capacitor C p Charge.

[0095] Among them, when the DC bus capacitor C p After charging is completed, the controller controls all switch devices to turn off, the second switch RL2 to turn on, and the first switch RL1 to turn off, and the controller starts to control the n-level conversion circuit to start normal operation.

[0096] Consider that the n-level conversion circuit has a third bridge arm 50, wherein the third bridge arm 50 includes a plurality of switching devices 51 connected in series, for example, a diode D s1 and D s2 By setting the third bridge arm 50 in the n-level conversion circuit, the power supply V ac Through the snubber resistor R s Give the flying capacitor 22 and the DC bus capacitor C p For charging, the charging circuit of positive and negative half cycles is as follows Figure 7A 、 7B shown.

[0097] like Figure 7A As shown by the dotted line, the power supply V ac In the positive half cycle, the controller controls the switch devices S3 to S (2n-3) and S2~S (2n-2) On, power supply V ac Through the diode D s1 , switching devices S3~S (2n-3) and S2~S (2n-2) , switching device S b , snubber resistor R s Give the flying capacitor C fly1 、C fly2 、C fly3 ,……,C fly(n-2) Charging, where when the i-th flying capacitor C flyi The voltage reaches the second preset value V Bulk When (n-1-i) / (n-1) times (i=1,2,3…n-2), the controller controls the corresponding flying capacitor C flyi The outer switching device S (2n-1-2i) and S (2n-2i) Shut down.

[0098] In some embodiments, the power supply V ac Through the inductor L, the switching device S b 、S2~S (2n-2) , snubber resistor R s To the DC bus capacitor C p Charging; and / or power supply V ac Through the diode Ds1 , switching device S b , snubber resistor R s To the DC bus capacitor C p Charging, when the DC bus capacitor C p The voltage V Cp Reaching the second preset value V Bulk When the DC bus capacitor C p Charging is complete.

[0099] like Figure 7B As shown by the dotted line, the power supply V ac In the negative half cycle, the controller controls the switch devices S3 to S (2n-3) and S2~S (2n-2) On, power supply V ac Through the diode D s2 , switching devices S3~S (2n-3) and S2~S (2n-2) , switching device S a , snubber resistor R s Give the flying capacitor C fly1 、C fly2 、C fly3 ,……,C fly(n-2) Charging, where when the i-th flying capacitor C flyi The voltage reaches the second preset value V Bulk When (n-1-i) / (n-1) times (i=1,2,3…n-2), the corresponding switching device S (2n-1-2i) and S (2n-2i) Shut down.

[0100] In some embodiments, the power supply V ac Through the inductor L, the switching device S a 、S1~S (2n-3) , snubber resistor R s To the DC bus capacitor C p Charging; and / or power supply V ac Through the diode D s2 , switching device S a , snubber resistor R s To the DC bus capacitor C p Charging, when the DC bus capacitor C p The voltage V Cp Reaching the second preset value V Bulk When the DC bus capacitor C p Charging is complete.

[0101] Among them, when the DC bus capacitor C pAfter charging is completed, the controller controls all switch devices to turn off, the second switch RL2 to turn on, and the first switch RL1 to turn off, and the controller starts to control the n-level conversion circuit to start normal operation.

[0102] The DC bus capacitor C p After charging is completed, when the n-level conversion circuit is working normally, the DC bus capacitor C p The voltage V Cp If it is higher than the output voltage of the uncontrolled rectifier bridge 31, the auxiliary power supply will be supplied by the DC bus capacitor C p Power is supplied through the anti-reverse diodes D1 and D2. When the n-level conversion circuit fails, the first switch RL1 and the second switch RL2 are disconnected. After the failure is resolved, the first switch RL1 can be turned on again to supply power to the flying capacitor 22 and the DC bus capacitor C p or the second switch RL2 is turned on and the first switch RL1 is turned off, the controller controls the n-level conversion circuit to operate normally.

[0103] In some embodiments, the multi-level conversion circuit can use a single auxiliary power supply. Figure 5 As shown, a single auxiliary power supply 40 is used, and the auxiliary power supply 40 is connected to the DC bus through anti-reverse diodes D1 and D2. If the DC bus capacitor C p When the output voltage of the uncontrolled rectifier bridge 31 is higher than the output voltage of the uncontrolled rectifier bridge 31, the auxiliary power supply 40 will be supplied by the DC bus capacitor C p The auxiliary power supply 40 is fully connected to the multi-level conversion circuit through the anti-reverse diodes D1 and D2 for power supply.

[0104] like Figure 8 As shown, the multi-level conversion circuit, such as the n-level PFC circuit 100-3, can use a single auxiliary power supply 40, but the auxiliary power supply 40 and the DC bus capacitor C p No connection (ie no connection with the DC bus capacitor C p The auxiliary power supply 40 always works independently.

[0105] In some embodiments, the multi-level conversion circuit may further use multiple first auxiliary power supplies and multiple second auxiliary power supplies. Figure 9 As shown, the auxiliary power supply 40 may include at least one first auxiliary power supply 41 and at least one second auxiliary power supply 42, wherein the at least one first auxiliary power supply 41 is connected in parallel to the output end of the rectifier circuit 30 and coupled to the controller, as an auxiliary power supply independent of the multi-level conversion circuit, with a relatively small output power, mainly used to provide power to the controller when the multi-level conversion circuit fails and during the charging process of the flying capacitor and the DC bus capacitor. The input end of the at least one second auxiliary power supply 42 is connected to the DC bus capacitor Cp The second auxiliary power supply 42 is connected in parallel to provide power to the entire multi-level conversion circuit after the multi-level conversion circuit operates normally.

[0106] like Figure 1 、 10A As shown in FIG10B, after the controller is started and the power supply V ac In the positive half cycle, the controller can control the switching devices S1 and S3 of the second bridge arm 20 to be turned on, and the first switch RL1 to be turned on at the first preset moment, and the power supply V ac The controllable switches in the switching devices S1 and S3, the switching devices S b , and snubber resistor R s The controller can control the switch device S1 of the second bridge arm 20 to turn off at the second preset time, and control the switch device S3 to continue to turn on. ac It can also be achieved through the inductor L, the switch device S2, the switch device S3, the switch device S b , and snubber resistor R s The flying capacitor 22 is charged. Figure 10A and 10B Form a boost circuit to supply the flying capacitor C fly1 Fast charging.

[0107] like Figure 1 、 11A As shown in FIG11B, after the controller is started and the power supply V ac In the negative half cycle, the controller can control the switching devices S4 and S2 of the second bridge arm 20 to be turned on, and the first switch RL1 to be turned on at the first preset moment, and the power supply V ac Through the switch devices S4 and S2, the switch device S a , and snubber resistor R s The controller can control the switch device S2 of the second bridge arm 20 to turn off at the second preset time, and control the switch device S4 to continue to turn on, and the power supply V ac It can also be achieved through the inductor L, the switch device S1, the switch device S4, the switch device S a , and snubber resistor R s The flying capacitor 22 is charged. Figure 11A and 11B Form a boost circuit to supply the flying capacitor C fly1 Fast charging.

[0108] like Figures 10A-11B As shown, a 3-level converter constitutes a boost circuit for feeding the flying capacitor Cfly1 Fast charging, of course, for n-level conversion circuits (such as Figure 5 As shown) can also form a boost circuit to supply the flying capacitor C fly1 、C fly2 、C fly3 ,……,C fly(n-2) Fast charging.

[0109] In the above scheme, after the power supply is powered on, the rectifier circuit can provide electrical energy to at least one first auxiliary power supply, so that it establishes an operating voltage to provide electrical energy to the controller. After the controller starts working, it controls the corresponding switching device of the second bridge arm to turn on, thereby establishing a circuit for charging the flying capacitor and the DC bus capacitor. Because the initial voltages of the flying capacitor and the DC bus capacitor are both zero before the controller is started, when the power supply charges the DC bus and the flying capacitor, the two switching devices connected in series on the outside of the flying capacitor will not be damaged by overvoltage. At the same time, at least one first auxiliary power supply is connected in parallel with the DC bus capacitor through an anti-reverse diode. When the voltage of the DC bus capacitor is higher than the output voltage of the rectifier circuit, the DC bus capacitor supplies power to the at least one first auxiliary power supply through the anti-reverse diode. The auxiliary power supply may also include at least one second auxiliary power supply, coupled in parallel across the DC bus capacitor, having a high output power and used to provide power to the entire multilevel conversion circuit after the multilevel conversion circuit is operating normally. Furthermore, at least one first auxiliary power supply, coupled to the output of the rectifier circuit, serves as an auxiliary power supply independent of the multilevel conversion circuit, having a lower output power and primarily used to provide power to the controller, etc., in the event of a multilevel conversion circuit fault and during the charging of the flying capacitor and DC bus capacitor. Furthermore, the first auxiliary power supply can completely shut down the charging circuit for the flying capacitor and DC bus capacitor in the event of a fault, and actively connect the first current limiting circuit after the fault is eliminated, thereby improving the fault response capability of the multilevel conversion circuit.

[0110] In summary, the multi-level conversion circuit with flying capacitors proposed in the present invention can meet the application requirements of 3-n level conversion circuits by simply adding a simple rectifier circuit, compared to existing technical solutions. The above embodiments are only used to illustrate the present invention. The structure, configuration, and corresponding modulation method of each circuit are subject to variation. Based on the technical solution of the present invention, any improvements and equivalent transformations of individual circuits based on the principles of the present invention should not be excluded from the scope of protection of the present invention.

[0111] While exemplary embodiments of the present invention have been particularly shown and described above, it should be understood that the present invention is not limited to the disclosed embodiments, but rather is intended to cover various modifications and equivalent arrangements encompassed within the spirit and scope of the appended claims.

Claims

1. A multi-level conversion circuit with a flying capacitor, characterized in that: include: A first bridge arm includes a plurality of switching devices connected in series; A second bridge arm having a flying capacitor includes a plurality of switching devices connected in series, and a midpoint of the second bridge arm and a midpoint of the first bridge arm are connected to a first current limiting circuit, a power supply, and an inductor to form a first series branch; a DC bus capacitor, connected in parallel with the first bridge arm and the second bridge arm; a rectifier circuit, wherein an input end of the rectifier circuit is coupled to the power supply; at least one first auxiliary power supply, wherein an input terminal of the at least one first auxiliary power supply is coupled to an output terminal of the rectifier circuit; as well as a controller coupled to the at least one first auxiliary power source and the plurality of switch devices of the second bridge arm; Wherein, after the controller is started, the controller is used to control the corresponding switching device of the second bridge arm to be turned on, and the power supply charges the flying capacitor through the corresponding switching device of the first bridge arm, the corresponding switching device of the second bridge arm and the first current limiting circuit.

2. The multi-level converter circuit with flying capacitor according to claim 1, wherein: Before the controller is started, the initial voltages of the flying capacitor and the DC bus capacitor are 0.

3. The multi-level converter circuit with flying capacitor according to claim 1, wherein: An input terminal of the at least one first auxiliary power supply is connected in parallel to the DC bus capacitor via an anti-reverse diode.

4. The multi-level converter circuit with flying capacitor according to claim 1, wherein: When the voltage of the DC bus capacitor is greater than the output voltage of the rectifier circuit, the at least one first auxiliary power supply is powered by the DC bus capacitor.

5. The multi-level converter circuit with flying capacitor according to claim 1, wherein: It also includes at least one second auxiliary power supply, and the input end of the at least one second auxiliary power supply is connected in parallel with the DC bus capacitor.

6. The multi-level converter circuit with flying capacitor according to claim 5, characterized in that: The output power of the second auxiliary power supply is greater than the output power of the first auxiliary power supply.

7. The multi-level converter circuit with flying capacitor according to claim 1, wherein: After the controller is started and before the first current limiting circuit is turned on, the controller is used to control the corresponding switching device of the second bridge arm to be turned on.

8. The multi-level converter circuit with flying capacitor according to claim 1, wherein: The power supply charges the DC bus capacitor through the corresponding switching devices of the first bridge arm, the corresponding switching devices of the second bridge arm, and the first current limiting circuit.

9. The multi-level converter circuit with flying capacitor according to claim 1, wherein: It also includes a third bridge arm, including a plurality of switching devices connected in series; the third bridge arm is connected in parallel with the first bridge arm, and the midpoint of the third bridge arm is connected to the first series branch; Wherein, after the controller is started, the power supply charges the flying capacitor through the corresponding switching device of the second bridge arm, the corresponding switching device of the first bridge arm and the first current limiting circuit; or the power supply charges the flying capacitor through the corresponding switching device of the second bridge arm, the corresponding switching device of the first bridge arm, the first current limiting circuit and the corresponding switching device of the third bridge arm.

10. The multi-level converter circuit with flying capacitor according to claim 9, wherein: The power supply charges the DC bus capacitor through the corresponding switching devices of the first bridge arm, the corresponding switching devices of the second bridge arm and the first current limiting circuit; and / or the power supply charges the DC bus capacitor through the corresponding switching devices of the first bridge arm, the first current limiting circuit and the corresponding switching devices of the third bridge arm.

11. The multi-level converter circuit with flying capacitor according to claim 1, wherein: The multi-level conversion circuit is a three-level converter circuit, the second bridge arm includes a first switching device, a second switching device, a third switching device and a fourth switching device connected in series; the flying capacitor is connected across the first switching device and the fourth switching device.

12. The multi-level converter circuit with flying capacitor according to claim 11, wherein: When the voltage of the flying capacitor reaches a first preset value, the flying capacitor completes charging; the controller is used to control the corresponding switch device of the second bridge arm to be disconnected, and the power supply continues to charge the DC bus capacitor; When the voltage of the DC bus capacitor reaches a second preset value, the DC bus capacitor is completely charged.

13. The multi-level converter circuit with flying capacitor according to claim 12, wherein: The first preset value is half of the second preset value.

14. The multi-level converter circuit with flying capacitor according to claim 1, wherein: The multi-level conversion circuit is an n-level conversion circuit, where n is a positive integer greater than 3, the first bridge arm includes a plurality of switching devices connected in series; the second bridge arm includes (2n-2) switching devices connected in series; the flying capacitor includes (n-2) flying capacitors, wherein the i-th flying capacitor is connected across the i-th switching device and the (2n-1-i)-th switching device of the second bridge arm, where i=1, 2,…, n-2.

15. The multi-level converter circuit with flying capacitor according to claim 14, characterized in that: When the voltage of the i-th flying capacitor reaches (n-1-i) / (n-1) times of the second preset value, the i-th flying capacitor is charged, and the controller is used to control the corresponding switch device of the second bridge arm to be disconnected; when the (n-2) flying capacitor is charged, the power supply continues to charge the DC bus capacitor; When the voltage of the DC bus capacitor reaches the second preset value, the DC bus capacitor is completely charged.

16. The multi-level converter circuit with flying capacitor according to claim 1, wherein: The first current limiting circuit includes a first switch, a second switch and a snubber resistor, wherein the first switch and the snubber resistor are connected in series to form a second series branch, and the second switch is connected in parallel to the second series branch.

17. The multi-level converter circuit with flying capacitor according to claim 16, wherein: Before the controller is started, the first switch and the second switch are both disconnected; after the controller controls the corresponding switching device of the second bridge arm to turn on, the first switch is turned on, and the power supply charges the flying capacitor through the corresponding switching devices of the first bridge arm and the second bridge arm, and the snubber resistor.

18. The multi-level converter circuit with flying capacitor according to claim 16, wherein: After the first switch is turned on, the controller controls the corresponding switch device of the second bridge arm to be turned on, and the power supply charges the flying capacitor through the corresponding switch devices of the first bridge arm and the second bridge arm and the snubber resistor.

19. The multi-level converter circuit with flying capacitor according to claim 1, wherein: Also included is a second current limiting circuit coupled between the power supply and the rectifier circuit; The second current limiting circuit includes a third switch and a current limiting resistor, wherein the third switch and the current limiting resistor are connected in parallel.

20. The multi-level converter circuit with flying capacitor according to claim 19, wherein: Before the controller is started, the third switch is turned off, and the power supply supplies power to the at least one first auxiliary power supply through the current limiting resistor and the rectifier circuit.

21. The multi-level converter circuit with flying capacitor according to claim 19, wherein: After the controller is started, the third switch is turned on, and the power supply supplies power to the at least one first auxiliary power supply through the third switch and the rectifier circuit.

22. The multi-level converter circuit with flying capacitor according to claim 16, wherein: When a fault occurs in the multi-level conversion circuit, the first switch and the second switch are disconnected.

23. The multi-level converter circuit with flying capacitor according to claim 16, wherein: When the voltage of the DC bus capacitor reaches a second preset value, the controller is used to control all the switch devices of the second bridge arm to be disconnected, the second switch to be turned on, and the first switch to be turned off.

24. The multi-level converter circuit with flying capacitor according to claim 19, wherein: When a fault occurs in the multi-level conversion circuit, the third switch is disconnected.

Images