A flying capacitor type multi-level converter with automatic capacitor voltage balancing

Abstract

The present invention provides a flying capacitor type multi-level converter with automatic capacitor voltage balancing, which is used to solve the technical problem that the voltage balancing effect is poor or even cannot be balanced when the output is unloaded when the existing flying capacitor type multi-level converter realizes the voltage balancing of the flying capacitor through software, or the technical problem that the voltage balancing of the flying capacitor can only meet the voltage balancing in one direction when the uncontrollable unidirectional conducting power device is used to realize the voltage balancing of the flying capacitor. The flying capacitor type multi-level converter with automatic capacitor voltage balancing of the present invention uses the original switch tube, adds a small number of switch tubes, and can realize the automatic balancing of the voltage of each sub-flying capacitor and the bus capacitor through the drive of the original switch tube, without the need for additional driving circuits and complex control algorithms, and avoids the design of the sampling circuit of the capacitor voltage. The voltage balancing speed is faster and more accurate than the software algorithm, which greatly improves the voltage balancing reliability and can be easily expanded to converters of more levels.

Description

Technical Field

[0001] The invention relates to a flying capacitor type multi-level converter, in particular to a flying capacitor type multi-level converter with automatic capacitor voltage balancing. Background Art

[0002] As the voltage of power electronic converters becomes higher and higher and the size becomes smaller and smaller, it is difficult for traditional two-level converters to meet the requirements, and multi-level converters are increasingly widely used. Among them, flying capacitor type multi-level converters have been widely used because of the small number of power devices and the fact that they can be applied to ACDC and DCDC situations. The voltage balancing of the flying capacitors in existing flying capacitor type multi-level converters mostly relies on software implementation, but the way to achieve voltage balancing through software is heavily dependent on the direction of the output current. When the output is unloaded, the voltage balancing effect is not good or even cannot be balanced. At present, some flying capacitor type multi-level converters also use hardware to achieve voltage balancing of the flying capacitors, such as Figure 1 As shown, a flying capacitor type three-level converter adopts an uncontrollable unidirectional conducting power device, but this method can only meet the voltage balance in one direction. Summary of the invention

[0003] The purpose of the present invention is to provide a flying capacitor type multi-level converter with automatic capacitor voltage balancing, in order to solve the technical problem that the voltage balancing effect of the existing flying capacitor type multi-level converter is poor or even cannot be balanced when the output is unloaded, or the voltage balancing of the flying capacitor can only be satisfied in one direction when an uncontrollable unidirectional conducting power device is used to achieve the voltage balancing of the flying capacitor.

[0004] In order to achieve the above purpose, the technical solution provided by the present invention is as follows:

[0005] A flying capacitor type multi-level converter with automatic capacitor voltage balancing comprises N serially connected bus capacitors, N groups of switch tubes and N-1 flying capacitors, wherein N+1 is the number of levels of the multi-level converter, and N≥2; each group of switch tubes comprises a switch tube VA and a switch tube VB which are complementary and turned on; the N switch tubes VA are serially connected in sequence, the other ends of the first switch tube VA and the first switch tube VB are connected to the output high end, and the other ends of the Nth switch tube VA and the first bus capacitor are connected to the bus capacitor. The high-voltage end of the voltage, the other end of the Nth switch tube VB and the Nth bus capacitor are both connected to the low-voltage end of the bus voltage and the output low end; the i-th flying capacitor includes i series-connected sub-flying capacitors, i=1,2,…,N-1, one end of the first sub-flying capacitor in the i-th flying capacitor is connected between the i-th switch tube SA and the i+1-th switch tube SA, and the other end of the i-th sub-flying capacitor is connected between the i-th switch tube SB and the i+1-th switch tube SB; its special feature is that it also includes N-1-level voltage balancing units;

[0006] The first-stage voltage balancing unit includes a switch tube SA and a switch tube SB which are complementary to each other, one end of the switch tube SA and the switch tube SB are respectively connected to the two ends of the first-stage flying capacitor, and the other ends of the switch tube SA and the switch tube SB are both connected between the two sub-flying capacitors of the second-stage flying capacitor;

[0007] The second to N-1th voltage balancing units respectively include a switch tube SA and a switch tube SB that are complementary conductive, and one or two switch tubes S; one end of the switch tube SA and the switch tube SB in the second to N-1th voltage balancing units are respectively connected to the two ends of the corresponding flying capacitor; the other end of the switch tube SA in the second to N-2th voltage balancing units is connected between the first sub-flying capacitor and the second sub-flying capacitor of the next flying capacitor, and the other end of the switch tube SB is connected between the i-1th sub-flying capacitor and the i-th sub-flying capacitor of the next flying capacitor; the other end of the switch tube SA in the N-1th voltage balancing unit is connected between the first bus capacitor and the second bus capacitor, and the other end of the switch tube SB is connected between the N-1th bus capacitor and the Nth bus capacitor;

[0008] When there is one switch tube S in the second to N-1th voltage balancing units, one end of the switch tube S is connected to the other end of the switch tube SA or the switch tube SB in the previous voltage balancing unit, and the other end is connected to the other end of the corresponding switch tube SA or the switch tube SB in the voltage balancing unit; when there are two switch tubes S in the second to N-1th voltage balancing units, one end of the two switch tubes S is respectively connected to the other end of the switch tube SA and the switch tube SB in the previous voltage balancing unit, and the other end is respectively connected to the other end of the corresponding switch tube SA and the switch tube SB in the voltage balancing unit.

[0009] Furthermore, the first-stage voltage balancing unit further includes a current limiting resistor, and the second to N-1-th-stage voltage balancing units further include two current limiting resistors respectively;

[0010] The other ends of the switch tube SA and the switch tube SB in the first-stage voltage balancing unit are connected between the two sub-flying capacitors of the second-stage flying capacitor through a current limiting resistor;

[0011] The other end of the switch tube SA in the second to N-2th voltage balancing units is connected between the first sub-flying capacitor and the second sub-flying capacitor of the next-stage flying capacitor through a corresponding current limiting resistor, and the other end of the switch tube SB is connected between the i-1th sub-flying capacitor and the ith sub-flying capacitor of the next-stage flying capacitor through a corresponding current limiting resistor;

[0012] The other end of the switch tube SA in the N-1th level voltage balancing unit is connected between the first bus capacitor and the second bus capacitor through a corresponding current limiting resistor, and the other end of the switch tube SB is connected between the N-1th bus capacitor and the Nth bus capacitor through a corresponding current limiting resistor;

[0013] When there is one switch tube S in the second to N-1th level voltage balancing units, one end of the switch tube S is connected to the other end of the current-limiting resistor connected to the corresponding switch tube SA or switch tube SB in the previous level voltage balancing unit, and the other end is connected to the other end of the corresponding switch tube SA or switch tube SB in the voltage balancing unit; when there are two switch tubes S in the second to N-1th level voltage balancing units, one end of the two switch tubes S is respectively connected to the other end of the current-limiting resistor connected to the corresponding switch tube SA and switch tube SB in the previous level voltage balancing unit, and the other end is respectively connected to the other end of the corresponding switch tube SA and switch tube SB in the voltage balancing unit.

[0014] Furthermore, the switch tube VA, the switch tube VB, the switch tube SA, the switch tube SB and the switch tube S are all MOSFETs;

[0015] Alternatively, the switch tube VA, the switch tube VB, the switch tube SA, the switch tube SB and the switch tube S are all IGBTs.

[0016] Furthermore, the switch tube VA, the switch tube VB, the switch tube SA, the switch tube SB and the switch tube S are all NMOS tubes;

[0017] The drains and sources of N switch tubes VA are connected in sequence, and the sources and drains of the corresponding N switch tubes VB are connected in sequence; the source of the first switch tube VA and the drain of the first switch tube VB are both connected to the high end of the output, the drain of the Nth switch tube VA is connected to the high end of the bus voltage, and the source of the Nth switch tube VB is connected to the low voltage end of the bus voltage and the low end of the output;

[0018] One end of the i-th flying capacitor is connected to the source of the i+1-th switch tube VA, and the other end is connected to the drain of the i+1-th switch tube VB;

[0019] The drain of the switch tube SA and the source of the switch tube SB in the first-stage voltage balancing unit are respectively connected to the two ends of the first-stage flying capacitor, and the source of the switch tube SA and the drain of the switch tube SB are both connected to one end of the corresponding current limiting resistor;

[0020] The drain of the switch tube SA and the source of the switch tube SB in the second to N-1th voltage balancing units are respectively connected to the two ends of the corresponding flying capacitor, and the source of the switch tube SA and the drain of the switch tube SB are respectively connected to one end of the two current limiting resistors in the voltage balancing unit;

[0021] There is one switch tube S in the second to N-1th level voltage balancing units, and the source is connected to one end of the current limiting resistor connected to the switch tube SB in the voltage balancing unit, and the drain is connected to the other end of the corresponding current limiting resistor in the previous level voltage balancing unit.

[0022] Furthermore, the switch tube SA and the switch tube S are controlled by a driving signal of the switch tube VB, and the switch tube SB is controlled by a driving signal of the switch tube VA.

[0023] Furthermore, the switch tube SA, the switch tube SB and the switch tube S are all controlled by an enable signal.

[0024] Furthermore, diodes are connected in parallel to the switch tube VA, the switch tube VB, the switch tube SA, the switch tube SB and the switch tube S respectively.

[0025] Furthermore, the switch tube SA, the switch tube SB and the switch tube S are respectively replaced by two switch tubes connected in reverse series.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1. The present invention provides a flying capacitor type multi-level converter with automatic capacitor voltage balancing. The original switch tube is used and a small number of switch tubes are added. The original switch tube is driven to realize automatic balancing of the voltages of each sub-flying capacitor and the bus capacitor. No additional driving circuit or complex control algorithm is required. At the same time, the design of a sampling circuit for the capacitor voltage is avoided. The voltage balancing speed is faster and more accurate than the software algorithm, which greatly improves the voltage balancing reliability. The present invention is simple to expand and has a wide applicability, and can be easily expanded to converters of more levels.

[0028] 2. The present invention provides a flying capacitor type multi-level converter with automatic capacitor voltage balancing, which can achieve flying capacitor balancing when the output is unloaded or loaded, effectively solving the technical problem that the voltage balancing effect is poor or even cannot be balanced when the output is unloaded (output small current).

[0029] 3. The present invention uses the switch tubes and bus capacitors of the original flying capacitor type multi-level converter to participate in voltage balancing. The number of newly added switch tubes is relatively small, and the voltage stress borne by the added switch tubes SA and SB is the same as that of the original switch tubes VA and VB, which greatly reduces the requirements for power devices.

[0030] 4. The present invention adds a current limiting resistor in each voltage balancing unit, which can effectively reduce the instantaneous current passing through each sub-flying capacitor, bus capacitor and each power device during voltage balancing, greatly extending the service life of each device in the converter. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 A circuit topology diagram of an existing flying capacitor type three-level converter using an uncontrollable unidirectional conducting power device for voltage balancing;

[0032] Figure 2 A circuit topology diagram of a first embodiment of a flying capacitor type multi-level converter with automatic capacitor voltage balancing according to the present invention;

[0033] Figure 3 Schematic diagram of the control circuit of each switch tube in the first embodiment of the present invention;

[0034] Figure 4 The switch state when the switch tubes V2B, V3B, and V4B are turned on and V2A, V3A, and V4A are turned off in the first embodiment of the present invention;

[0035] Figure 5 The switch states of the switch tubes V2A, V3B, and V4B when they are turned on and V2B, V3A, and V4A when they are turned off in the first embodiment of the present invention;

[0036] Figure 6 The switch states of the switch tubes V2B, V4B, and V3A when they are turned on and V3B, V2A, and V4A when they are turned off in the first embodiment of the present invention;

[0037] Figure 7 The switch states of the switch tubes V2B, V3B, and V4A when they are turned on, and V4B, V2A, and V3A when they are turned off in the first embodiment of the present invention;

[0038] Figure 8 The switch states of the switch tubes V4B, V2A, and V3A when they are turned on and V2B, V3B, and V4A when they are turned off in the first embodiment of the present invention;

[0039] Fig. 9 The switch states of the switch tubes V3B, V2A, and V4A when they are turned on and V2B, V4B, and V3A when they are turned off in the first embodiment of the present invention;

[0040] Fig.10The switch states of the switch tubes V2B, V3A, and V4A when they are turned on and V3B, V4B, and V2A when they are turned off in the first embodiment of the present invention;

[0041] Fig.11 The switch state when the switch tubes V2A, V3A, and V4A are turned on and V2B, V3B, and V4B are turned off in the first embodiment of the present invention;

[0042] Fig.12 It is a circuit topology diagram when the switch tube S is connected to the switch tube SA based on the first embodiment of the present invention;

[0043] Fig.13 for Fig.12 The control circuit diagram corresponding to each switch tube;

[0044] Fig.14 It is a circuit topology diagram when two switch tubes S are connected to the switch tube SA and the switch tube SB respectively based on the first embodiment of the present invention;

[0045] Fig.15 for Fig.14 The control circuit diagram corresponding to each switch tube;

[0046] Fig.16 The voltage waveforms of each sub-flying capacitor, each bus capacitor and the output bridge port when the dead time is inconsistent are simulated by using a traditional flying capacitor type five-level converter without voltage balancing;

[0047] Fig.17 The flying capacitor type five-level converter according to the first embodiment of the present invention is used to simulate the voltage waveforms of each sub-flying capacitor, each bus capacitor and the output bridge port when the dead time is inconsistent;

[0048] Fig.18 A circuit topology diagram of a second embodiment of a flying capacitor type multi-level converter with automatic capacitor voltage balancing;

[0049] Fig.19 Schematic diagram of the control circuit of each switch tube in the second embodiment of the present invention;

[0050] Fig. 20 The circuit topology diagram is a diagram in which S1A and S1B in the second embodiment of the present invention are replaced by two switch tubes connected in reverse series;

[0051] Fig.21 for Fig. 20 The control circuit diagram corresponding to each switch tube;

[0052] Fig. 22 The switch state when the switch tube V2B is turned on and V2A is turned off in the second embodiment of the present invention;

[0053] Fig.23 This is the switch state when the switch tube V2A is turned on and V2B is turned off in the second embodiment of the present invention. DETAILED DESCRIPTION

[0054] The flying capacitor type multi-level converter with automatic capacitor voltage equalization of the present invention can be applied to three-level and more-level flying capacitor voltage equalization. In order to make the advantages and features of the present invention clearer, the present invention is further described in detail below with five-level and three-level as examples and in conjunction with the accompanying drawings.

[0055] Embodiment 1

[0056] like Figure 2 As shown, this embodiment is a flying capacitor type five-level converter capacitor voltage automatic equalization circuit, which includes four bus capacitors, four groups of switch tubes, three flying capacitors and three voltage equalization units. The four groups of switch tubes are the original switch tubes of the five-level converter, each group includes a switch tube VA and a switch tube VB, and the switch tube VA and the switch tube VB in each group are complementary. The three-level voltage equalization unit is an added part in this embodiment, which is used to realize the automatic equalization of the flying capacitor voltage at each level, wherein the first-level voltage equalization unit includes a switch tube SA, a switch tube SB and a current limiting resistor, the second-level voltage equalization unit and the third-level voltage equalization unit respectively include a switch tube SA, a switch tube SB, a switch tube S and two current limiting resistors, and the switch tube SA and the switch tube SB in each voltage equalization unit are complementary.

[0057] The switch tube VA, the switch tube VB, the switch tube SA, the switch tube SB and the switch tube S may be MOSFET, IGBT or other types of switch tubes. In this embodiment, the switch tube VA, the switch tube VB, the switch tube SA, the switch tube SB and the switch tube S are all NMOS tubes. At the same time, each of the VA, the switch tube VB, the switch tube SA, the switch tube SB and the switch tube S is respectively connected in parallel with a diode for freewheeling of the switch tube.

[0058] In order to facilitate the later description, the four switch tubes VA are respectively recorded as V1A, V2A, V3A, and V4A, the four switch tubes VB are respectively recorded as V1B, V2B, V3B, and V4B, the switch tubes SA in the three-stage voltage balancing unit are respectively recorded as S11A, S21A, and S31A, the switch tubes SB are respectively recorded as S11B, S21B, and S31B, the switch tubes S in the second and third voltage balancing units are respectively recorded as S22 and S32; the current limiting resistor in the first-stage voltage balancing unit is recorded as R11, and the two current limiting resistors in the second-stage voltage balancing unit are recorded as R21. The current limiting resistors are denoted as R21 and R22 respectively, and the two current limiting resistors in the third-stage voltage equalizing unit are denoted as R31 and R32 respectively; the four bus capacitors are denoted as Cbus1, Cbus2, Cbus3, and Cbus4 respectively; the first-stage sub-span capacitor includes only one sub-flying capacitor, which is denoted as Cf11, the second-stage flying capacitor includes two sub-flying capacitors connected in series, which are denoted as Cf21 and Cf22 respectively, and the third-stage flying capacitor includes three sub-flying capacitors connected in series, which are denoted as Cf31, Cf32, and Cf33 respectively.

[0059] The bus capacitors Cbus1, Cbus2, Cbus3, and Cbus4 are connected in series in sequence, the other end of Cbus1 is connected to the high voltage end Bus+ of the bus voltage, and the other end of Cbus4 is connected to the low voltage end Bus- of the bus voltage.

[0060] The drain of switch tube V1A is connected to the source of V2A, the drain of V2A is connected to the source of V3A, the drain of V3A is connected to the source of V4A, and the drain of V4A is connected to the other end of Cbus1; the source of switch tube V1B is connected to the drain of V2B, the source of V2B is connected to the drain of V3B, the source of V3B is connected to the drain of V4B, and the source of V4B is connected to the other end of Cbus4 and the output low end Out-; the source of V1A and the drain of V1B are both connected to the output high end Out+. One end of Cf11 is connected to the source of V2A, and the other end is connected to the drain of V2B, the other end of Cf21 is connected to the source of V3A, the other end of Cf22 is connected to the drain of V3B, the other end of Cf31 is connected to the source of V4A, and the other end of Cf33 is connected to the drain of V4B.

[0061] In this embodiment, an RC filter circuit is further provided between the output high end Out+ and the output low end Out- for output filtering. Specifically, the RC filter circuit includes an inductor Lo and a capacitor Co. The source of V1A and the drain of V1B are both connected to one end of the inductor Lo, and the other end of the inductor Lo is connected to the output high end Out+. The capacitor Co is connected in parallel between the other end of the inductor Lo and the source of V4B.

[0062] In the first-stage voltage-equalizing unit, the drain of S11A is connected to one end of Cf11, the source of S11B is connected to the other end of Cf11, the source of S11A and the drain of S11B are both connected to one end of R11, and the other end of R11 is connected between Cf21 and Cf22. In the second-stage voltage-equalizing unit, the drain of S21A is connected to the other end of Cf21, its source is connected to one end of R21, and the other end of R21 is connected between Cf31 and Cf32; the source of S21B is connected to the other end of Cf22, the drain of S22 is connected to the other end of R11, the drain of S21B and the source of S22 are both connected to one end of R22, and the other end of R22 is connected between Cf32 and Cf33. In the third-level voltage balancing unit, the drain of S31A is connected to the other end of Cf31, and its source is connected to one end of R31, and the other end of R31 is connected between Cbus1 and Cbus2; the source of S31B is connected to the other end of Cf33, the drain of S32 is connected to the other end of R22, the drain of S31B and the source of S32 are both connected to one end of R32, and the other end of R32 is connected between Cbus3 and Cbus4. In this embodiment, the current limiting resistors R11, R21, R22, R31, and R32 are preferably configured.

[0063] In order to facilitate the enabling and disabling of each voltage balancing unit, the switch tube SA, switch tube SB and switch tube S of each voltage balancing unit can be controlled by the enable signal EN, or the drive signal of the original switch tube can be directly borrowed. The control circuit of each switch tube is as follows: Figure 3 In this embodiment, the driving signal of the original switch tube is used for explanation, that is, S11A and V2B share a driving signal control, S11B and V2A share a driving signal control, S21A, S22 and V3B share a driving signal control, S21B and V3A share a driving signal control, S31A, S32 and V4B share a driving signal control, S31B and V4A share a driving signal control.

[0064] In the five-level circuit of this embodiment, the switching action of V1A and V1B does not affect the voltage balance. The other three groups of switch tubes have a total of 8 switching states. The energy flow diagram between the capacitors in each switching state is as follows: Figures 4 to 11 shown.

[0065] When the switch tube V2B is turned on and V2A is turned off, S11A is turned on and S11B is turned off. Figure 4 , Figure 6 , Figure 7 , Fig.10 As shown, the sub-flying capacitors Cf22 and Cf11 are connected together through the switch tube S11A, V2B, and the current limiting resistor R11. The capacitor with a high voltage will charge the capacitor with a low voltage until the voltages are equal. When the switch tube V2A is turned on and V2B is turned off, S11B is turned on and S11A is turned off. Figure 5 , Figure 8 , Fig. 9 , Fig.11 As shown, the sub-flying capacitors Cf21 and Cf11 are connected together through the switch tube S11B, V2A, and the current limiting resistor R11, and the capacitor with a higher voltage will charge the capacitor with a lower voltage until the voltages are equal. In this way, the voltage of the first-stage flying capacitor and the second-stage flying capacitor is balanced, and the voltage of Cf21 and Cf22 in the second-stage flying capacitor is equalized.

[0066] The present invention adds S22 in the second-stage voltage balancing unit to balance the voltages of the sub-flying capacitors in the third-stage flying capacitor, and adds S32 in the third-stage voltage balancing unit to balance the voltages of the four bus capacitors. In other embodiments of the present invention, Fig.12 As shown, the source of S22 can also be connected to R11, and the drain is connected to the source of the switch tube S21A, and the source of S32 is connected to R21, and the drain is connected to the source of the switch tube S31A; accordingly, the control circuit of each switch tube is as shown Fig.13 It is also possible to add two S22 in the second-stage voltage balancing unit, that is, to add S22A and S22B that are complementary, and to add two S32 in the third-stage voltage balancing unit, that is, to add S32A and S32B that are complementary. The connection topology is shown in Fig.14 As shown, the source of S22A and the drain of S22B are both connected to the other end of R11, the drain of S22A is connected to the source of S21A, and the source of S22B is connected to the drain of S21B; the source of S32A is connected to the other end of R21, and its drain is connected to the source of S31A, the drain of S32B is connected to the other end of R22, and its source is connected to the drain of S31B; accordingly, the control circuit of each switch tube is as shown Fig.15 As shown. Fig.14 The circuit topology is more complicated, but the effect is the same, so we continue with Figure 2 The circuit topology is analyzed.

[0067] When the switch tube V3B is turned on and V3A is turned off, S21A and S22 are turned on, and S21B is turned off. Figure 4 , Figure 5 , Figure 7 , Fig. 9As shown, the sub-flying capacitor Cf33 and Cf22 are connected together through the switch tube S22, V3B, and the current limiting resistor R22, and the capacitor with a high voltage will charge the capacitor with a low voltage until the voltages are equal. Since the voltage of Cf22 has been controlled to the voltage of Cf11 by the previous level balancing circuit, the voltage of Cf33 will also be balanced to the voltage of Cf11. At this time, the sub-flying capacitor Cf32 and Cf21 are connected together through the switch tube S22, S21A, and the current limiting resistor R21, and the capacitor with a high voltage will charge the capacitor with a low voltage until the voltages are equal. Since the voltage of Cf21 has been controlled to the voltage of Cf11 by the previous level balancing circuit, the voltage of Cf32 will also be balanced to the voltage of Cf11.

[0068] When the switch tube V3A is turned on and V3B is turned off, S21B is turned on, and S21A and S22 are turned off. Figure 6 , Figure 8 , Fig.10 , Fig.11 As shown, the sub-flying capacitors Cf31 and Cf32 are connected in series, and Cf21 and Cf22 are connected in series through the switch tube S21B, V3A, and the current limiting resistor R22. The capacitor with a high voltage will charge the capacitor with a low voltage until the voltages are equal. Since the voltages of Cf21, Cf22, and Cf32 have been balanced to the voltage of Cf11, the voltage of Cf31 will also be balanced to the voltage of Cf11.

[0069] When the switch tube V4B is turned on and V4A is turned off, S31A and S32 are turned on, and S31B is turned off. Figure 4 , Figure 5 , Figure 6 , Figure 8 As shown, the bus capacitor Cbus4 and the sub-flying capacitor Cf33 are connected together through the switch tube S32, V4B, and the current limiting resistor R32, and the capacitor with a high voltage will charge the capacitor with a low voltage until the voltage is equal. Since the voltage of Cf33 has been balanced to the voltage of Cf11, the voltage of Cbus4 will also be balanced to the voltage of Cf11. At this time, the bus capacitors Cbus2 and Cbus3 are connected in series, and the sub-flying capacitors Cf31 and Cf32 are connected in series through the switch tube S32, S31A, and the current limiting resistor R31. The capacitor with a high voltage will charge the capacitor with a low voltage until the voltage is equal. Since the voltages of Cf31 and Cf32 have been balanced to the voltage of Cf11, the voltage of Cbus2 and Cbus3 after being connected in series will be balanced to twice the voltage of Cf11.

[0070] When the switch tube V4A is turned on and V4B is turned off, S31B is turned on, and S31A and S32 are turned off. Figure 7 , Fig. 9 , Fig.10 , Fig.11As shown, after the bus capacitors Cbus1, Cbus2, and Cbus3 are connected in series, the sub-flying capacitors Cf31, Cf32, and Cf33 are connected in series through the switch tube S31B, V4A, and the current limiting resistor R32. The capacitor with a high voltage will charge the capacitor with a low voltage until the voltages are equal. Since the voltages of Cf31, Cf32, Cf33, and Cbus4 have been balanced to the voltage of Cf11, the voltage of Cbus2 and Cbus3 in series will be balanced to twice the voltage of Cf11, so the voltage of Cbus1 will also be balanced to the voltage of Cf11. At this time, the sum of the voltages of Cbus1, Cbus2, Cbus3, and Cbus4 is 4 times the voltage of Cf11, so the voltage of Cf11 will be balanced to 1 / 4 of the bus voltage, and the voltages of other flying capacitors will also be balanced to the ideal voltage value.

[0071] In order to further illustrate the voltage balancing effect of the present invention, the capacitor voltages of a conventional flying capacitor type five-level converter without voltage balancing and a flying capacitor type five-level converter with a voltage balancing unit added to the present invention are compared below. Fig.16 As shown, it is a voltage waveform diagram of each sub-flying capacitor and each bus capacitor when the dead time is inconsistent when simulating a traditional flying capacitor type five-level converter without voltage balancing. Fig.17 The voltage waveforms of each sub-flying capacitor and each bus capacitor when the dead time is inconsistent when simulating the flying capacitor type five-level converter according to the first embodiment of the present invention are shown, wherein V(Cf11) is the voltage of Cf11, V(Cf21) is the voltage of Cf21, and so on, and VSW is the bridge port voltage of the flying capacitor type converter. It can be seen that the present invention effectively realizes the voltage balance of each sub-flying capacitor and each bus capacitor.

[0072] Embodiment 2

[0073] like Fig.18 As shown, this embodiment is a flying capacitor type three-level converter capacitor voltage automatic balancing circuit, which includes two bus capacitors, two groups of switch tubes, a flying capacitor and a voltage balancing unit. The two bus capacitors are respectively denoted as Cbus1 and Cbus2, the first group of switch tubes includes complementary conduction V1A and V1B, the second group of switch tubes includes complementary conduction V2A and V2B, the first flying capacitor includes only one sub-flying capacitor Cf1, the voltage balancing unit includes complementary conduction S1A, S1B, and a current limiting resistor R1.

[0074] The bus capacitors Cbus1 and Cbus2 are connected in series, the other end of Cbus1 is connected to the high voltage end Bus+ of the bus voltage, and the other end of Cbus2 is connected to the low voltage end Bus- of the bus voltage; the drain of V1A is connected to the source of V2A, the drain of V2A is connected to the other end of Cbus1, the source of V1B is connected to the drain of V2B, the source of V2B is connected to the other end of Cbus2 and the output low end Out-, the source of V1A and the drain of V1B are both connected to the output high end Out+; one end of Cf1 is connected to the source of V2A, and the other end is connected to the drain of V2B. The drain of S1A is connected to one end of Cf1, the source of S1B is connected to the other end of Cf1, the source of S1A and the drain of S1B are both connected to one end of R1, and the other end of R1 is connected between Cbus1 and Cbus2.

[0075] The control circuit of each switch tube in this embodiment is as follows: Fig.19 As shown. Similarly, the switch tubes S1A and S1B can be controlled by the enable signal EN, or S1A and V2B can share a drive signal control, and S1B and V2A can share a drive signal control. However, when the enable signal EN is not used, the capacitors may still exchange energy in a unidirectional manner through the diodes in the voltage balancing circuit. Therefore, Fig. 20 As shown, in this embodiment, it is preferred to replace S1A and S1B with two reverse series connected switch tubes to avoid the above situation. Fig.21 This method is also applicable to other multi-level circuits such as the first embodiment. When applied to other multi-level circuits, the switch tube SA, the switch tube SB and the switch tube S all need to be replaced accordingly.

[0076] In this embodiment Fig.18 In the three-level circuit shown in the figure, the switching action of V1A and V1B does not affect the voltage balance. V2A and V2B have two switching states. The energy flow diagram between the capacitors in the two switching states is as follows: Fig. 22 , Fig.23 shown.

[0077] When the switch tube V2B is turned on and V2A is turned off, S1A is turned on and S1B is turned off. Fig. 22 As shown, the bus capacitor Cbus2 and the sub-flying capacitor Cf1 are connected together through the switch tube S1A, V2B, and the current limiting resistor R1. The capacitor with a high voltage will charge the capacitor with a low voltage until the voltages are equal. When the switch tube V2A is turned on and V2V is turned off, S1B is turned on and S1A is turned off. Fig.23As shown, the bus capacitor Cbus1 and the sub-flying capacitor Cf1 are connected together through the switch tube S1B, V2A, and the current limiting resistor R1. The capacitor with a higher voltage will charge the capacitor with a lower voltage until the voltages are equal. At this time, the voltages of Cbus1, Cbus2, and Cf1 are equal, all half of the bus voltage, so as to achieve voltage balance of the flying capacitor.

[0078] The above description is only used to illustrate the technical solution of the present invention rather than to limit it. For ordinary professional and technical personnel in the field, the specific technical solution recorded in the above embodiment can be modified, or some of the technical features therein can be replaced by equivalents, and these modifications or replacements do not make the essence of the corresponding technical solution deviate from the scope of the technical solution protected by the present invention.

Claims

1. A flying capacitor type multilevel converter with automatic capacitor voltage balancing, comprising N bus capacitors connected in series, N groups of switch tubes and N-1 flying capacitors, N+1 is the number of levels of the multilevel converter, N≥2; each group of switch tubes comprises a switch tube VA and a switch tube VB which are complementary and turned on; N switch tubes VA are connected in series in sequence, N switch tubes VB are connected in series in sequence, the other ends of the first switch tube VA and the first switch tube VB are both connected to the high-end output, the other ends of the Nth switch tube VA and the first bus capacitor are both connected to the high-voltage end of the bus voltage, the other ends of the Nth switch tube VB and the Nth bus capacitor are both connected to the low-voltage end of the bus voltage and the low-end output; the i-th flying capacitor comprises i series-connected sub-flying capacitors, i=1, 2, ..., N-1, one end of the first sub-flying capacitor in the i-th flying capacitor is connected between the i-th switch tube SA and the i+1-th switch tube SA, and the other end of the i-th sub-flying capacitor is connected between the i-th switch tube SB and the i+1-th switch tube SB; characterized in that: It also includes an N-1 level pressure equalizing unit; The first-stage voltage balancing unit includes a switch tube SA and a switch tube SB which are complementary to each other, one end of the switch tube SA and the switch tube SB are respectively connected to the two ends of the first-stage flying capacitor, and the other ends of the switch tube SA and the switch tube SB are both connected between the two sub-flying capacitors of the second-stage flying capacitor; The second to N-1th voltage balancing units respectively include a switch tube SA and a switch tube SB that are complementary conductive, and one or two switch tubes S; one end of the switch tube SA and the switch tube SB in the second to N-1th voltage balancing units are respectively connected to the two ends of the corresponding flying capacitor; the other end of the switch tube SA in the second to N-2th voltage balancing units is connected between the first sub-flying capacitor and the second sub-flying capacitor of the next flying capacitor, and the other end of the switch tube SB is connected between the i-1th sub-flying capacitor and the i-th sub-flying capacitor of the next flying capacitor; the other end of the switch tube SA in the N-1th voltage balancing unit is connected between the first bus capacitor and the second bus capacitor, and the other end of the switch tube SB is connected between the N-1th bus capacitor and the Nth bus capacitor; When there is one switch tube S in the second to N-1th voltage balancing units, one end of the switch tube S is connected to the other end of the switch tube SA or the switch tube SB in the previous voltage balancing unit, and the other end is connected to the other end of the corresponding switch tube SA or the switch tube SB in the voltage balancing unit; when there are two switch tubes S in the second to N-1th voltage balancing units, one end of the two switch tubes S is respectively connected to the other end of the switch tube SA and the switch tube SB in the previous voltage balancing unit, and the other end is respectively connected to the other end of the corresponding switch tube SA and the switch tube SB in the voltage balancing unit.

2. The flying capacitor type multi-level converter with automatic capacitor voltage equalization according to claim 1, characterized in that: The first-stage voltage balancing unit also includes a current limiting resistor, and the second to N-1-th-stage voltage balancing units also include two current limiting resistors respectively; The other ends of the switch tube SA and the switch tube SB in the first-stage voltage balancing unit are connected between the two sub-flying capacitors of the second-stage flying capacitor through a current limiting resistor; The other end of the switch tube SA in the second to N-2th voltage balancing units is connected between the first sub-flying capacitor and the second sub-flying capacitor of the next-stage flying capacitor through a corresponding current limiting resistor, and the other end of the switch tube SB is connected between the i-1th sub-flying capacitor and the ith sub-flying capacitor of the next-stage flying capacitor through a corresponding current limiting resistor; The other end of the switch tube SA in the N-1th level voltage balancing unit is connected between the first bus capacitor and the second bus capacitor through a corresponding current limiting resistor, and the other end of the switch tube SB is connected between the N-1th bus capacitor and the Nth bus capacitor through a corresponding current limiting resistor; When there is one switch tube S in the second to N-1th level voltage balancing units, one end of the switch tube S is connected to the other end of the current-limiting resistor connected to the corresponding switch tube SA or switch tube SB in the previous level voltage balancing unit, and the other end is connected to the other end of the corresponding switch tube SA or switch tube SB in the voltage balancing unit; when there are two switch tubes S in the second to N-1th level voltage balancing units, one end of the two switch tubes S is respectively connected to the other end of the current-limiting resistor connected to the corresponding switch tube SA and switch tube SB in the previous level voltage balancing unit, and the other end is respectively connected to the other end of the corresponding switch tube SA and switch tube SB in the voltage balancing unit.

3. The flying capacitor type multi-level converter with automatic capacitor voltage equalization according to claim 2, characterized in that: The switch tube VA, the switch tube VB, the switch tube SA, the switch tube SB and the switch tube S are all MOSFETs; Alternatively, the switch tube VA, the switch tube VB, the switch tube SA, the switch tube SB and the switch tube S are all IGBTs.

4. The flying capacitor type multi-level converter with automatic capacitor voltage equalization according to claim 3, characterized in that: The switch tube VA, the switch tube VB, the switch tube SA, the switch tube SB and the switch tube S are all NMOS tubes; The drains and sources of N switch tubes VA are connected in sequence, and the sources and drains of the corresponding N switch tubes VB are connected in sequence; the source of the first switch tube VA and the drain of the first switch tube VB are both connected to the high end of the output, the drain of the Nth switch tube VA is connected to the high end of the bus voltage, and the source of the Nth switch tube VB is connected to the low voltage end of the bus voltage and the low end of the output; One end of the i-th flying capacitor is connected to the source of the i+1-th switch tube VA, and the other end is connected to the drain of the i+1-th switch tube VB; The drain of the switch tube SA and the source of the switch tube SB in the first-stage voltage balancing unit are respectively connected to the two ends of the first-stage flying capacitor, and the source of the switch tube SA and the drain of the switch tube SB are both connected to one end of the corresponding current limiting resistor; The drain of the switch tube SA and the source of the switch tube SB in the second to N-1th voltage balancing units are respectively connected to the two ends of the corresponding flying capacitor, and the source of the switch tube SA and the drain of the switch tube SB are respectively connected to one end of the two current limiting resistors in the voltage balancing unit; There is one switch tube S in the second to N-1th level voltage balancing units, and the source is connected to one end of the current limiting resistor connected to the switch tube SB in the voltage balancing unit, and the drain is connected to the other end of the corresponding current limiting resistor in the previous level voltage balancing unit.

5. The flying capacitor type multi-level converter with automatic capacitor voltage equalization according to claim 4, characterized in that: The switch tubes SA and S are controlled by a driving signal of the switch tube VB, and the switch tube SB is controlled by a driving signal of the switch tube VA.

6. The flying capacitor type multi-level converter with automatic capacitor voltage equalization according to claim 4, characterized in that: The switch tube SA, the switch tube SB and the switch tube S are all controlled by an enable signal.

7. A flying capacitor type multi-level converter with automatic capacitor voltage equalization according to any one of claims 1 to 6, characterized in that: The switch tube VA, the switch tube VB, the switch tube SA, the switch tube SB and the switch tube S are respectively connected in parallel with a diode.

8. A flying capacitor type multi-level converter with automatic capacitor voltage equalization according to claim 1 or 2, characterized in that: The switch tube SA, the switch tube SB and the switch tube S are respectively replaced by two switch tubes connected in reverse series.

Images