Clamping type multi-level converter and control method

Abstract

The invention discloses a clamping type multi-level converter and a control method, relates to the field of clamping, and aims to enable the voltage of a flying capacitor in the multi-level converter to be 1 / (N-1), 2 / (N-1)... (N-2) / (N-1) times of Vbus voltage (bus voltage) even if the voltage of the flying capacitor is in a steady state. The number of the clamping units is the same as that of the flying capacitors, and each flying capacitor is connected in series with the equivalent capacitors of the corresponding number of bus capacitors through the corresponding clamping unit when the multi-level converter switching tube is closed, so that each flying capacitor is clamped through the voltage of the corresponding number of equivalent bus capacitors; and the voltage of the flying capacitor in the multi-level converter can be ensured to be in a steady state without closed-loop control.

Description

Technical Field

[0001] The present invention relates to the field of clamping, and in particular to a clamping type multi-level converter and a control method. Background Art

[0002] As an important type of multi-level converter, the flying capacitor multi-level converter has the highest power density and efficiency, can greatly reduce the voltage stress of the switching device, and has small output voltage and current harmonics, and its advantages are very obvious. However, in order to ensure that the voltage across the flying capacitor in the existing flying capacitor multi-level converter is stable within a preset range, even if the voltage of the flying capacitor is in a steady state, it is necessary to ensure that the voltage of the flying capacitor must be 1 / (N-1), 2 / (N-1)...(N-2) / (N-1) times the Vbus voltage (bus voltage) to ensure that the stress of the switch tube is evenly distributed. In the prior art, the voltage of the flying capacitor is collected in real time, and then the PWM (Pulse Width Modulation) duty cycle or phase shift angle of the switch tube is closed-loop controlled based on the voltage value of the flying capacitor to realize the feedback control of the flying capacitor voltage. It can be seen that the prior art needs to collect the voltage of the flying capacitor in real time and needs to perform closed-loop control, the control strategy is relatively complex, and the reliability is low. Summary of the invention

[0003] The object of the present invention is to provide a clamped multi-level converter and a control method. In this scheme, N clamping units are additionally provided, and the number of the clamping units is the same as the number of flying capacitors. Each flying capacitor is connected in series with an equivalent capacitor of a corresponding number of bus capacitors through a corresponding clamping unit when a switch tube of the multi-level converter is closed, so that each flying capacitor is clamped by the voltage of the corresponding number of equivalent bus capacitors, and the voltage of the flying capacitor in the multi-level converter can be ensured to be in a steady state without closed-loop control.

[0004] In order to solve the above technical problems, the present invention provides a clamped multilevel converter, comprising: a multilevel converter and N clamping units, the number of the clamping units is the same as the number of flying capacitors in the multilevel converter, and N is a positive integer greater than 1;

[0005] Each of the clamping units is connected in parallel with the N flying capacitors in the multi-level converter in a one-to-one correspondence, and each of the clamping units is connected correspondingly to the M equivalent bus capacitors of the multi-level converter through the corresponding remaining clamping units, and is used to control each of the flying capacitors to be connected in series with a corresponding number of the equivalent bus capacitors when the switch tube in the multi-level converter is closed, and the number of each of the equivalent bus capacitors is the same as the difference between the number of levels of the multi-level converter minus 1.

[0006] Optionally, when the multi-level converter is a five-level converter, the clamp-type multi-level converter comprises: a first clamp unit, a second clamp unit and a third clamp unit;

[0007] The first clamping unit is connected in parallel with the first flying capacitor of the five-level converter, the first clamping unit is respectively connected to the first end of the first equivalent capacitor of the second flying capacitor of the five-level converter and the first end of the second equivalent capacitor of the second flying capacitor, the second end of the first equivalent capacitor is respectively connected to the second end of the second switch tube of the five-level converter and the first end of the third switch tube of the five-level converter, the second end of the second equivalent capacitor is respectively connected to the first end of the sixth switch tube of the five-level converter and the second end of the seventh switch tube of the five-level converter, the first equivalent capacitor and the second equivalent capacitor have the same capacitance, and the sum of the capacitances of the first equivalent capacitor and the second equivalent capacitor is equal to the capacitance of the second equivalent capacitor;

[0008] The second clamping unit is connected in parallel with the first equivalent capacitor and the second equivalent capacitor connected in series, and the second clamping unit is respectively connected to the first end of the fourth equivalent capacitor of the bus capacitor of the five-level converter and the first end of the fifth equivalent capacitor of the bus capacitor;

[0009] The third clamping unit is connected in parallel with the five-level converter. The third clamping unit is respectively connected to the first end of the third equivalent capacitor of the bus capacitor, the second end of the fourth equivalent capacitor, the second end of the fifth equivalent capacitor, the first end of the sixth equivalent capacitor of the bus capacitor, the first end of the first equivalent capacitor and the first end of the second equivalent capacitor. The second end of the third equivalent capacitor is connected to the second end of the fourth switch tube of the five-level converter, and the second end of the sixth equivalent capacitor is connected to the first end of the eighth switch tube of the five-level converter. The capacitances of the third equivalent capacitor, the fourth equivalent capacitor, the fifth equivalent capacitor and the sixth equivalent capacitor are all equal, and the sum of the capacitances of the third equivalent capacitor, the fourth equivalent capacitor, the fifth equivalent capacitor and the sixth equivalent capacitor is equal to the capacitance of the bus capacitor.

[0010] Optionally, the first clamping unit includes:

[0011] A first unidirectional conduction module, wherein an input end of the first unidirectional conduction module is connected to an output end of the second unidirectional conduction module, a first end of the first equivalent capacitor, and a first end of the second equivalent capacitor, and an output end of the first unidirectional conduction module is connected to a second end of a first switch tube of the five-level converter, a first end of the second switch tube, and a first end of the first flying capacitor;

[0012] The second unidirectional conduction module, the input end of the second unidirectional conduction module is respectively connected to the first end of the fifth switch tube of the five-level converter, the second end of the sixth switch tube and the second end of the first flying capacitor.

[0013] Optionally, the second clamping unit includes:

[0014] a third unidirectional conduction module, wherein the input end of the third unidirectional conduction module is respectively connected to the output end of the fourth unidirectional conduction module, the first end of the fourth equivalent capacitor and the first end of the fifth equivalent capacitor, and the output end is respectively connected to the first end of the third switch tube, the second end of the second switch tube and the second end of the first equivalent capacitor;

[0015] The fourth unidirectional conduction module, the input end of the fourth unidirectional conduction module is respectively connected to the first end of the sixth switch tube, the second end of the seventh switch tube and the second end of the second equivalent capacitor.

[0016] Optionally, the third clamping unit includes: a fifth unidirectional conduction module, a sixth unidirectional conduction module, a seventh unidirectional conduction module and an eighth unidirectional conduction module;

[0017] The input end of the fifth unidirectional conduction module is respectively connected to the output end of the sixth unidirectional conduction module, the second end of the fourth equivalent capacitor and the first end of the third equivalent capacitor, and the output end is connected to the first end of the third flying capacitor of the five-level converter;

[0018] The input end of the sixth unidirectional conduction module is respectively connected to the output end of the seventh unidirectional conduction module, the first end of the first equivalent capacitor and the first end of the second equivalent capacitor;

[0019] The input end of the seventh unidirectional conduction module is respectively connected to the output end of the eighth unidirectional conduction module, the second end of the fifth equivalent capacitor and the first end of the sixth equivalent capacitor;

[0020] The input end of the eighth unidirectional conduction module is respectively connected to the second end of the third flying capacitor, the first end of the seventh switch tube, and the second end of the eighth switch tube.

[0021] Optionally, the five-level converter includes: the first switch tube, the second switch tube, the third switch tube, the fourth switch tube, the fifth switch tube, the sixth switch tube, the seventh switch tube, the eighth switch tube, the first flying capacitor, the second flying capacitor, the third flying capacitor, and the bus capacitor, the second flying capacitor includes the first equivalent capacitor and the second equivalent capacitor, and the bus capacitor includes the third equivalent capacitor, the fourth equivalent capacitor, the fifth equivalent capacitor, and the sixth equivalent capacitor;

[0022] The first switch tube, the second switch tube, the third switch tube and the fourth switch tube are connected in series in sequence, the first common end of the series connection is respectively connected to the power supply and the first end of the fifth switch tube, and the second common end of the series connection is connected to the second end of the third equivalent capacitor;

[0023] The fifth switch tube, the sixth switch tube, the seventh switch tube and the eighth switch tube are connected in series in sequence, the first common end of the series connection is respectively connected to the power supply and the first end of the first switch tube, and the second common end of the series connection is connected to the second end of the sixth equivalent capacitor.

[0024] Optionally, the first switch tube is a first NMOS tube, a source of the first NMOS tube is a first end of the first switch tube, a drain of the first NMOS tube is a second end of the first switch tube, and a gate of the first NMOS tube is a control end of the first switch tube;

[0025] Correspondingly, the second switch tube is a second NMOS tube, the source of the second NMOS tube is the first end of the second switch tube, the drain of the second NMOS tube is the second end of the second switch tube, and the gate of the second NMOS tube is the control end of the second switch tube;

[0026] The third switch tube is a third NMOS tube, the source of the third NMOS tube is the first end of the third switch tube, the drain of the third NMOS tube is the second end of the third switch tube, and the gate of the third NMOS tube is the control end of the third switch tube;

[0027] The fourth switch tube is a fourth NMOS tube, the source of the fourth NMOS tube is the first end of the fourth switch tube, the drain of the fourth NMOS tube is the second end of the fourth switch tube, and the gate of the fourth NMOS tube is the control end of the fourth switch tube;

[0028] The fifth switch tube is a fifth NMOS tube, the source of the fifth NMOS tube is the first end of the fifth switch tube, the drain of the fifth NMOS tube is the second end of the fifth switch tube, and the gate of the fifth NMOS tube is the control end of the fifth switch tube;

[0029] The sixth switch tube is a sixth NMOS tube, the source of the sixth NMOS tube is the first end of the sixth switch tube, the drain of the sixth NMOS tube is the second end of the sixth switch tube, and the gate of the sixth NMOS tube is the control end of the sixth switch tube;

[0030] The seventh switch tube is a seventh NMOS tube, the source of the seventh NMOS tube is the first end of the seventh switch tube, the drain of the seventh NMOS tube is the second end of the seventh switch tube, and the gate of the seventh NMOS tube is the control end of the seventh switch tube;

[0031] The eighth switch tube is an eighth NMOS tube, the source of the eighth NMOS tube is the first end of the eighth switch tube, the drain of the eighth NMOS tube is the second end of the eighth switch tube, and the gate of the eighth NMOS tube is the control end of the eighth switch tube.

[0032] Optionally, also include:

[0033] A filter device is connected to the power supply, the first end of the first switch tube and the first end of the fifth switch tube respectively.

[0034] In order to solve the above technical problems, the present invention further provides a clamped multi-level converter control method, which is applied to the clamped multi-level converter as described above, comprising:

[0035] Determine the rated PWM wave of the upper bridge arm and the rated PWM wave of the lower bridge arm of the upper bridge arm switch tube and the lower bridge arm switch tube in the multi-level converter in a unit switching cycle respectively;

[0036] Determine, according to the upper bridge arm rated PWM wave, a first phase of a first switch tube in the multilevel converter, a second phase of a second switch tube in the multilevel converter, a third phase of a third switch tube in the multilevel converter, and a fourth phase of a fourth switch tube in the multilevel converter;

[0037] Controlling any one of the first phase, the second phase, the third phase, or the fourth phase to advance a preset phase deviation angle, controlling any one of the remaining phases of the first phase, the second phase, the third phase, or the fourth phase to lag behind the preset phase deviation angle, and generating a new upper bridge arm PWM wave, and determining a new lower bridge arm PWM wave according to the new upper bridge arm PWM wave and the lower bridge arm rated PWM wave;

[0038] Based on the new upper bridge arm PWM wave and the new lower bridge arm PWM wave, the upper bridge arm switch tube and the lower bridge arm switch tube in the multi-level converter are controlled to be turned on and off.

[0039] Optionally, after controlling the turning on and off of the upper bridge arm switch tube and the lower bridge arm switch tube in the multi-level converter based on the new upper bridge arm PWM wave and the new lower bridge arm PWM wave, the method further includes:

[0040] Collecting the charge and discharge amounts corresponding to N flying capacitors in the multi-level converter after a preset time, where N is a positive integer greater than 1;

[0041] Determine whether the discharge amount corresponding to each of the flying capacitors is greater than the charge amount corresponding to each of the flying capacitors;

[0042] If the discharge amount corresponding to each of the flying capacitors is greater than the charge amount corresponding to each of the flying capacitors, it is determined that each of the flying capacitors is in an undercharged state;

[0043] If the discharge amount corresponding to each of the flying capacitors is not greater than the charge amount corresponding to each of the flying capacitors, it is determined that each of the flying capacitors is not in an undercharged state, and a corresponding alarm is issued.

[0044] The object of the present invention is to provide a clamped multilevel converter and a control method. In order to make the voltage of the flying capacitor in the multilevel converter 1 / (N-1), 2 / (N-1) ... (N-2) / (N-1) times the Vbus voltage (bus voltage), even if the voltage of the flying capacitor is in a steady state, the present solution additionally provides N clamping units, and the number of the clamping units is the same as the number of the flying capacitors. Each flying capacitor is connected in series with an equivalent capacitor of a corresponding number of bus capacitors through a corresponding clamping unit when the switch tube of the multilevel converter is closed, so that each flying capacitor is clamped by the voltage of the corresponding number of equivalent bus capacitors, and the voltage of the flying capacitor in the multilevel converter can be ensured to be in a steady state without closed-loop control. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0046] Figure 1 A schematic diagram of the structure of a clamped multi-level converter provided by the present invention;

[0047] Figure 2 A schematic diagram of the structure of a clamped five-level converter provided by the present invention;

[0048] Figure 3 A schematic diagram of the structure of a five-level converter provided by the present invention;

[0049] Figure 4 A schematic diagram of a clamping circuit provided by the present invention;

[0050] Figure 5 A schematic diagram of another clamping circuit provided by the present invention;

[0051] Figure 6 A schematic diagram of another clamping circuit provided by the present invention;

[0052] Figure 7 A schematic diagram of another clamping circuit provided by the present invention;

[0053] Figure 8 A schematic diagram of another clamping circuit provided by the present invention;

[0054] Fig. 9 A schematic diagram of another clamping circuit provided by the present invention;

[0055] Fig.10 A schematic diagram of another clamping circuit provided by the present invention;

[0056] Fig.11 A schematic diagram of another clamping circuit provided by the present invention;

[0057] Fig.12 A schematic diagram of a phase-shift PWM waveform with a duty cycle of [0, 1 / 4] provided by the present invention;

[0058] Fig.13 A schematic diagram of a phase-shift PWM waveform with a duty cycle of [1 / 4, 1 / 2) provided by the present invention;

[0059] Fig.14 A schematic diagram of a phase-shift PWM waveform with a duty cycle of 1 / 2 provided by the present invention;

[0060] Fig.15 A schematic diagram of a phase-shift PWM waveform with a duty cycle of (1 / 2, 3 / 4] provided by the present invention;

[0061] Fig.16 A schematic diagram of a phase-shift PWM waveform with a duty cycle of [3 / 4, 1] provided by the present invention;

[0062] Fig.17 A common duty cycle control modal diagram of a five-level converter provided by the present invention;

[0063] Fig.18 A duty cycle control modal diagram of a fixed phase deviation provided by the present invention;

[0064] Fig.19 A schematic diagram of a fixed phase bias PWM (the lower triangle wave and the upper waveform connected to the triangle wave) and an inductor current waveform with a duty cycle of [0, 1 / 4] provided by the present invention;

[0065] Fig. 20 A schematic diagram of a fixed phase bias PWM and inductor current waveform with a duty cycle of [1 / 4, 1 / 2] provided by the present invention;

[0066] Fig.21 A schematic diagram of a fixed phase bias PWM and inductor current waveform with a duty cycle of [1 / 2, 3 / 4] provided by the present invention;

[0067] Fig. 22 A schematic diagram of a fixed phase bias PWM and inductor current waveform with a duty cycle of [3 / 4, 1] provided by the present invention;

[0068] Fig.23 A clamping type five-level flying capacitor totem pole PFC circuit provided by the present invention;

[0069] Fig.24 The present invention provides a voltage-equalizing pre-charging experimental waveform of a flying capacitor under the action of a clamping diode. DETAILED DESCRIPTION

[0070] The core of the present invention is to provide a clamped multi-level converter and a control method. In this scheme, N clamping units are added, and the number of the clamping units is the same as the number of flying capacitors. Each flying capacitor is connected in series with the equivalent capacitors of a corresponding number of bus capacitors through the corresponding clamping unit when the switch tube of the multi-level converter is closed, so that each flying capacitor is clamped by the voltage of the corresponding number of equivalent bus capacitors, and the voltage of the flying capacitor in the multi-level converter can be ensured to be in a steady state without closed-loop control.

[0071] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0072] Please refer to Figure 1 , Figure 1A schematic diagram of the structure of a clamped multilevel converter provided by the present invention. The clamped multilevel converter comprises: a multilevel converter 1 and N clamping units 2, the number of the clamping units is the same as the number of flying capacitors in the multilevel converter 1, and N is a positive integer greater than 1;

[0073] Each clamping unit is connected in parallel with the N flying capacitors in the multi-level converter 1 in a one-to-one correspondence, and each clamping unit is connected to the M equivalent bus capacitors of the multi-level converter 1 through the corresponding remaining clamping units, and is used to control each flying capacitor to be connected in series with a corresponding number of equivalent bus capacitors when the switch tube in the multi-level converter 1 is closed, and the number of each equivalent bus capacitor is the same as the difference between the number of levels of the multi-level converter 1 and 1.

[0074] In the present invention, considering that in order to make each flying capacitor in the multilevel converter 1 in a steady state, it is necessary to make the voltage of the flying capacitor in the multilevel converter 1 1 / (N-1), 2 / (N-1) ... (N-2) / (N-1) times the Vbus voltage (bus voltage), so the present solution thinks of clamping the voltage of the flying capacitor in the multilevel converter 1 by the corresponding number of equivalent bus capacitors of the bus capacitor, so N clamping units 2 are provided, the number of each clamping unit is the same as the number of the flying capacitor in the multilevel converter 1, and each flying capacitor is connected in series with the equivalent capacitor of the corresponding number of bus capacitors through the corresponding clamping unit when the switch tube of the multilevel converter 1 is closed, that is, each flying capacitor is clamped by the voltage of the corresponding number of equivalent bus capacitors, and the voltage of the flying capacitor in the multilevel converter 1 can be ensured to be in a steady state without closed-loop control.

[0075] It should be noted that this scheme can achieve the clamping and equalizing of the flying capacitor by adding the least clamping devices, so as to improve the reliability of the flying capacitor circuit without affecting the power density and cost of the circuit. In addition, it can also achieve simpler bus capacitor pre-charging. For this reason, this scheme proposes a new type of clamping five-level converter and its self-equalizing control method with fixed phase shift angle. And the analysis of the pre-charging circuit when used as PFC.

[0076] It should also be noted that the topology proposed by the present invention is first introduced, such as Figure 2 The diode clamped flying capacitor five-level converter shown is also called a hybrid clamped five-level converter. Among them, S1a-S4a are the first switch tube to the fourth switch tube, S1b-S4b are the fifth switch tube to the eighth switch tube, Cf1 is the first flying capacitor, Cf2 is the second flying capacitor, Cf21 is the first equivalent capacitor, Cf22 is the second equivalent capacitor, Cf3 is the third flying capacitor, Cbus is the bus capacitor, and the four Vcells correspond to the voltage values ​​of the four equivalent capacitors of the bus capacitor. This topology is in the five-level flying capacitor (such as Figure 3 As shown in Figure 1, four pairs of clamping diodes D11D12, D21D22, D31D32, and D41D42 (corresponding to eight unidirectional conduction modules, respectively) are added, which will bring eight new clamping modes to the circuit:

[0077] Respectively Figure 4 As shown, during the conduction period of S4b, S4b, the flying capacitor Cf3, the clamping diode D31, and the 3Vcell in the bus capacitor form a clamping loop. According to the unidirectional conduction characteristic of the diode, the voltage Vcf3 of the flying capacitor will be clamped above the voltage of the bus capacitor 3Vcell;

[0078] like Figure 5 As shown, during the conduction period of S4a, S4a, the flying capacitor Cf3, the clamping diode D32, and the 3Vcell in the bus capacitor form a clamping loop. According to the unidirectional conduction characteristic of the diode, the voltage Vcf3 of the flying capacitor will be clamped above the voltage of the bus capacitor 3Vcell;

[0079] like Figure 6 As shown, during the period when S3b and S4b are turned on at the same time, S3bS4b, flying capacitor Cf2, clamping diode D21, and 2Vcell in the bus capacitor form a clamping loop. According to the unidirectional conduction characteristic of the diode, the voltage Vcf2 of the flying capacitor will be clamped above the voltage of the bus capacitor 2Vcell.

[0080] like Figure 7 As shown, during the period when S3a and S4a are turned on at the same time, S3aS4a, flying capacitor Cf2, clamping diode D22, and 2Vcell in the bus capacitor form a clamping loop. According to the unidirectional conduction characteristic of the diode, the voltage Vcf2 of the flying capacitor will be clamped above the voltage of the bus capacitor 2Vcell.

[0081] Here we need to explain why S3bS4b or S3aS4a must have a mode of simultaneous conduction. This is determined by the characteristics of the phase shift PMW of the common duty cycle adopted by the flying capacitor control: Figure 12~Figure 16The figure shows the driving waveform of phase-shift PWM in a switching cycle at different duty cycle intervals, where the switches that are turned on at the same time are marked with shadows. We can find that when the duty cycle is in the interval of [0, 1 / 4] or [3 / 4, 1], the four switches of the upper bridge arm or the lower bridge arm are turned on at the same time. In this case, there must be a mode in which S3bS4b or S3aS4a is turned on at the same time; when the duty cycle is in the interval of [1 / 4, 1 / 2] or the duty cycle is in the interval of (1 / 2, 3 / 4] , there are three adjacent switch tubes in the upper or lower bridge arm that are turned on at the same time, so there must be a mode where S3bS4b or S3aS4a is turned on at the same time; when the duty cycle is 1 / 2, there are two adjacent switch tubes in the upper and lower bridge arms that are turned on at the same time, and there is also a mode where S3bS4b or S3aS4a is turned on at the same time. Therefore, in any duty cycle range, there must be a mode where S3bS4b or S3aS4a is turned on at the same time in a switching cycle, making Figure 6 and Figure 7 The clamping mode described can exist to realize the clamping voltage balancing of the circuit. This idea of ​​analyzing the minimum number of switch tubes that are turned on within the full duty cycle range is the main basis for the design and simplification of the clamping loop in the present invention. The common duty cycle control mode diagram of the five-level converter is shown in Fig.17 shown.

[0082] like Figure 8 As shown, during the conduction period of S2b, S2b, the flying capacitor Cf1, the clamping diode D11, and the flying capacitor Cf22 form a clamping loop. According to the unidirectional conduction characteristic of the diode, the flying capacitor voltage Vcf3 will be clamped above the flying capacitor Cf22 voltage;

[0083] like Fig. 9 As shown, during the conduction period of S2a, S2a, flying capacitor Cf1, clamping diode D12, and flying capacitor Cf21 form a clamping loop. According to the unidirectional conduction characteristic of the diode, the flying capacitor voltage Vcf3 will be clamped above the flying capacitor Cf21 voltage. Figure 7 and Figure 8 The clamping loop of Cf1 will be clamped at more than half of the total voltage of Cf2, that is, above the Vcell voltage.

[0084] like Fig.10 As shown, during the conduction period of S3a and S4a, S3aS4a, flying capacitor Cf21, and clamping diode D41 form a clamping loop. According to the unidirectional conduction characteristic of the diode, Cf21 will be clamped above the Vcell voltage. Fig.11As shown, during the conduction period of S3b and S4b, S3bS4b, flying capacitor Cf22, and clamping diode D42 form a clamping loop. According to the unidirectional conduction characteristic of the diode, Cf22 will be clamped above the Vcell voltage. These two clamping loops are mainly constructed to provide a pre-charging loop when the circuit is started, and their analysis is explained in the pre-charging part.

[0085] When the four capacitors of the busbar are voltage-equalized and voltage-divided, the voltages of the flying capacitors Cf1, Cf2, and Cf3 can be clamped above Vcell, 2Vcell, and 3Vcell, respectively, and Vcell, 2Vcell, and 3Vcell are just the ideal values ​​for the voltage equalization of the flying capacitors. To achieve voltage equalization of the flying capacitors, the flying capacitor voltages must always be stabilized at Vcell, 2Vcell, and 3Vcell. We define the undercharge state of the flying capacitor as the amount of charge charged into the flying capacitor voltage in each switching cycle is less than the amount of charge released. According to the ampere-second balance of the flying capacitor, the undercharge state means that the voltage of the flying capacitor will continue to fall. At this time, in conjunction with the clamping network that clamps the lower limit of the flying capacitor voltage, the flying capacitor voltage can always be clamped at the voltage-equalizing value.

[0086] It should also be noted that the undercharge control strategy based on fixed offset proposed in this scheme, such as Figure 19 to Figure 22 As shown, in the fixed phase bias control, we keep the duty cycle of S1a and S4a unchanged (still a common duty cycle), but let the overall phase of S1a slightly lead a certain phase angle α, and let the overall phase of S4a slightly lag a certain phase angle α. At this time, according to the shape of the inductor current, the current waveform flowing through the flying capacitor can be drawn as shown in the last row. At this time, due to the switching timing changes and mode changes caused by the phase bias, the inductor current flowing through the flying capacitor will be distorted, which can ensure that the charging charge is less than the discharging charge, achieving the effect of undercharging. For specific effects, please refer to Fig.18 , through fixed phase bias control, it can be clearly observed that the charging current area of ​​Cf1 and Cf2 is reduced, while the discharge current area of ​​Cf2 and Cf3 is increased, which has the effect of making the charging amount of Cf1, Cf2, and Cf3 less than the discharge amount during the switching cycle, so that all flying capacitors are in an undercharged state. Through calculation, it can be seen that when the phase bias angle is α, the discharge amount of the three flying capacitors in different duty cycle intervals is more than the charge amount:

[0087] ;

[0088] ;

[0089] ;

[0090] ;

[0091] in, are the difference between the charge and discharge of the flying capacitors Cf1, Cf2, and Cf3, respectively, α is the phase deviation angle, is the bus voltage, D is the duty cycle, Ts is the switching period of the switch tube, and L is the inductance value of the inductor at the input end of the five-level converter;

[0092] In the above formula, the positive or negative difference between the discharge amount and the charge amount is only related to α, and has nothing to do with the load conditions, etc. Therefore, when using fixed phase shift control, it is only necessary to control the leading phase deviation angle α>0 to basically ensure that the flying capacitor is undercharged.

[0093] The present embodiment provides a clamped multilevel converter. In order to make the voltage of the flying capacitor in the multilevel converter 1 1 / (N-1), 2 / (N-1) ... (N-2) / (N-1) times the Vbus voltage (bus voltage), even if the voltage of the flying capacitor is in a steady state, the present solution additionally provides N clamping units 2, and the number of the clamping units is the same as the number of the flying capacitors. Each flying capacitor is connected in series with the equivalent capacitors of the corresponding number of bus capacitors through the corresponding clamping unit when the switch tube of the multilevel converter 1 is closed, so that each flying capacitor is clamped by the voltage of the corresponding number of equivalent bus capacitors, and the voltage of the flying capacitor in the multilevel converter 1 can be ensured to be in a steady state without closed-loop control.

[0094] As an optional embodiment, when the multi-level converter 1 is a five-level converter, the clamping type multi-level converter includes: a first clamping unit, a second clamping unit and a third clamping unit;

[0095] The first clamping unit is connected in parallel with the first flying capacitor of the five-level converter. The first clamping unit is respectively connected to the first end of the first equivalent capacitor of the second flying capacitor of the five-level converter and the first end of the second equivalent capacitor of the second flying capacitor. The second end of the first equivalent capacitor is respectively connected to the second end of the second switch tube of the five-level converter and the first end of the third switch tube of the five-level converter. The second end of the second equivalent capacitor is respectively connected to the first end of the sixth switch tube of the five-level converter and the second end of the seventh switch tube of the five-level converter. The capacitance of the first equivalent capacitor is equal to that of the second equivalent capacitor. The sum of the capacitance of the first equivalent capacitor and the second equivalent capacitor is equal to the capacitance of the second equivalent capacitor.

[0096] The second clamping unit is connected in parallel with the first equivalent capacitor and the second equivalent capacitor connected in series, and the second clamping unit is respectively connected to the first end of the fourth equivalent capacitor of the bus capacitor of the five-level converter and the first end of the fifth equivalent capacitor of the bus capacitor;

[0097] The third clamping unit is connected in parallel with the five-level converter. The third clamping unit is respectively connected to the first end of the third equivalent capacitor of the bus capacitor, the second end of the fourth equivalent capacitor, the second end of the fifth equivalent capacitor, the first end of the sixth equivalent capacitor of the bus capacitor, the first end of the first equivalent capacitor and the first end of the second equivalent capacitor. The second end of the third equivalent capacitor is connected to the second end of the fourth switch tube of the five-level converter, the second end of the sixth equivalent capacitor is connected to the first end of the eighth switch tube of the five-level converter, the capacitances of the third equivalent capacitor, the fourth equivalent capacitor, the fifth equivalent capacitor and the sixth equivalent capacitor are all equal, and the sum of the capacitances of the third equivalent capacitor, the fourth equivalent capacitor, the fifth equivalent capacitor and the sixth equivalent capacitor is equal to the capacitance of the bus capacitor.

[0098] In the present invention, since the existing flying capacitor circuit products rarely achieve five-level, this is because the five-level circuit topology is relatively complex and the control is also complex. Therefore, for the five-level converter, this solution sets three clamping units according to the number of flying capacitors in the five-level converter, namely the first clamping unit, the second clamping unit and the third clamping unit, and in order to successfully clamp the second flying capacitor of the five-level converter, this solution equates the second flying capacitor to the first equivalent capacitor and the second equivalent capacitor, and equates the bus capacitor to the third equivalent capacitor, the fourth equivalent capacitor, the fifth equivalent capacitor and the sixth equivalent capacitor, and clamps the voltages of the first flying capacitor, the second flying capacitor and the third flying capacitor of the five-level converter according to the equivalent capacitors equivalent to the bus capacitor, so that the voltage of the flying capacitor in the five-level converter can be ensured to be in a steady state without closed-loop control.

[0099] As an optional embodiment, the first clamping unit includes:

[0100] A first unidirectional conduction module, wherein the input end of the first unidirectional conduction module is respectively connected to the output end of the second unidirectional conduction module, the first end of the first equivalent capacitor and the first end of the second equivalent capacitor, and the output end is respectively connected to the second end of the first switch tube of the five-level converter, the first end of the second switch tube and the first end of the first flying capacitor;

[0101] The second unidirectional conduction module has an input end respectively connected to the first end of the fifth switch tube of the five-level converter, the second end of the sixth switch tube and the second end of the first flying capacitor.

[0102] In the present invention, considering any duty cycle interval of the switch tube of the five-level converter, there must be a situation in which the third switch tube and the fourth switch tube are turned on at the same time or the seventh switch tube and the eighth switch tube are turned on at the same time in one switching cycle, so it can be analyzed that at least two switch tubes of the five-level converter are turned on within the full duty cycle range. Based on this, the present solution adopts a first clamping unit having a first unidirectional conduction module and a second unidirectional conduction module. For example, when the third switch tube and the fourth switch tube in the five-level converter are turned on at the same time, the first flying capacitor can be connected in series with the third equivalent capacitor of the first unidirectional conduction module, the second unidirectional conduction module, the third switch tube and the fourth switch tube and the bus capacitor, so that the voltage of the first flying capacitor can be clamped to 1 / 4 of the bus voltage, so that the voltage of the first flying capacitor is in a steady state, thereby ensuring the reliability of the solution.

[0103] As an optional embodiment, the second clamping unit includes:

[0104] a third unidirectional conduction module, wherein the input end of the third unidirectional conduction module is respectively connected to the output end of the fourth unidirectional conduction module, the first end of the fourth equivalent capacitor and the first end of the fifth equivalent capacitor, and the output end is respectively connected to the first end of the third switch tube, the second end of the second switch tube and the second end of the first equivalent capacitor;

[0105] A fourth unidirectional conduction module, wherein the input end of the fourth unidirectional conduction module is respectively connected to the first end of the sixth switch tube, the second end of the seventh switch tube and the second end of the second equivalent capacitor.

[0106] In the present invention, considering any duty cycle interval of the switch tube of the five-level converter, there must be a situation in which the third switch tube and the fourth switch tube are turned on at the same time or the seventh switch tube and the eighth switch tube are turned on at the same time in one switching cycle, so it can be analyzed that at least two switch tubes of the five-level converter are turned on in the full duty cycle range. Based on this, the present solution adopts a second clamping unit having a third unidirectional conduction module and a fourth unidirectional conduction module. For example, when the seventh switch tube and the eighth switch tube in the five-level converter are turned on at the same time, the first equivalent capacitor and the second equivalent capacitor can be connected in series through the third unidirectional conduction module, the seventh switch tube, the eighth switch tube and the fifth equivalent capacitor and the sixth equivalent capacitor of the bus capacitor, and then the second flying capacitor, that is, the voltage sum of the first equivalent capacitor and the second equivalent capacitor is clamped to 2 / 4 of the bus voltage, so that the voltage of the second flying capacitor is in a steady state, thereby ensuring the reliability of the solution.

[0107] As an optional embodiment, the third clamping unit includes: a fifth unidirectional conduction module, a sixth unidirectional conduction module, a seventh unidirectional conduction module and an eighth unidirectional conduction module;

[0108] The input end of the fifth unidirectional conduction module is respectively connected to the output end of the sixth unidirectional conduction module, the second end of the fourth equivalent capacitor and the first end of the third equivalent capacitor, and the output end is connected to the first end of the third flying capacitor of the five-level converter;

[0109] The input end of the sixth unidirectional conduction module is respectively connected to the output end of the seventh unidirectional conduction module, the first end of the first equivalent capacitor and the first end of the second equivalent capacitor;

[0110] The input end of the seventh unidirectional conduction module is respectively connected to the output end of the eighth unidirectional conduction module, the second end of the fifth equivalent capacitor and the first end of the sixth equivalent capacitor;

[0111] The input end of the eighth unidirectional conduction module is respectively connected to the second end of the third flying capacitor, the first end of the seventh switch tube and the second end of the eighth switch tube.

[0112] In the present invention, considering any duty cycle interval of the switch tube of the five-level converter, there must be a situation in which the third switch tube and the fourth switch tube are turned on at the same time or the seventh switch tube and the eighth switch tube are turned on at the same time in one switching cycle, so it can be analyzed that at least two switch tubes of the five-level converter are turned on within the full duty cycle range. Based on this, the present solution adopts a third clamping unit having a fifth unidirectional conduction module, a sixth unidirectional conduction module, a seventh unidirectional conduction module and an eighth unidirectional conduction module. For example, when the fourth switch tube in the five-level converter is turned on alone, the third flying capacitor is connected in series with the fourth equivalent capacitor, the fifth equivalent capacitor and the sixth equivalent capacitor of the bus capacitor through the fifth unidirectional conduction module, thereby clamping the voltage of the third flying capacitor to 3 / 4 of the bus voltage, so that the voltage of the third flying capacitor is in a steady state, thereby ensuring the reliability of the solution.

[0113] It should be noted that, in actual applications, the first unidirectional conduction module to the eighth unidirectional conduction module can be a diode, a MOS tube (Metal-Oxide-Semiconductor Field-Effect Transistor, MOSFET, metal-oxide semiconductor field effect transistor) and other devices or device combinations with unidirectional conduction function, and this application does not make any special limitations here.

[0114] As an optional embodiment, a five-level converter includes: a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a fifth switch tube, a sixth switch tube, a seventh switch tube, an eighth switch tube, a first flying capacitor, a second flying capacitor, a third flying capacitor, and a bus capacitor, wherein the second flying capacitor includes a first equivalent capacitor and a second equivalent capacitor, and the bus capacitor includes a third equivalent capacitor, a fourth equivalent capacitor, a fifth equivalent capacitor, and a sixth equivalent capacitor;

[0115] The first switch tube, the second switch tube, the third switch tube and the fourth switch tube are connected in series in sequence, the first common end of the series connection is respectively connected to the power supply and the first end of the fifth switch tube, and the second common end of the series connection is connected to the second end of the third equivalent capacitor;

[0116] The fifth switch tube, the sixth switch tube, the seventh switch tube and the eighth switch tube are connected in series in sequence, the first common end of the series is connected to the power supply and the first end of the first switch tube respectively, and the second common end of the series is connected to the second end of the sixth equivalent capacitor.

[0117] In the present invention, a five-level converter is provided with a first switch tube, a second switch tube, a third switch tube, a fourth switch tube, a fifth switch tube, a sixth switch tube, a seventh switch tube, an eighth switch tube, a first flying capacitor, a second flying capacitor, a third flying capacitor, and a bus capacitor. The second flying capacitor includes a first equivalent capacitor and a second equivalent capacitor. The bus capacitor includes a third equivalent capacitor, a fourth equivalent capacitor, a fifth equivalent capacitor, and a sixth equivalent capacitor. When the switch tube is normally closed, the flying capacitor in the five-level converter is connected in series with the equivalent capacitors of a corresponding number of bus capacitors through a corresponding clamping unit connected in parallel, so that the voltage of the flying capacitor in the five-level converter is in a steady state, thereby ensuring the reliability of the solution.

[0118] As an optional embodiment, the first switch tube is a first NMOS tube, the source of the first NMOS tube is the first end of the first switch tube, the drain of the first NMOS tube is the second end of the first switch tube, and the gate of the first NMOS tube is the control end of the first switch tube;

[0119] Correspondingly, the second switch tube is a second NMOS tube, the source of the second NMOS tube is the first end of the second switch tube, the drain of the second NMOS tube is the second end of the second switch tube, and the gate of the second NMOS tube is the control end of the second switch tube;

[0120] The third switch tube is a third NMOS tube, the source of the third NMOS tube is the first end of the third switch tube, the drain of the third NMOS tube is the second end of the third switch tube, and the gate of the third NMOS tube is the control end of the third switch tube;

[0121] The fourth switch tube is a fourth NMOS tube, the source of the fourth NMOS tube is the first end of the fourth switch tube, the drain of the fourth NMOS tube is the second end of the fourth switch tube, and the gate of the fourth NMOS tube is the control end of the fourth switch tube;

[0122] The fifth switch tube is a fifth NMOS tube, the source of the fifth NMOS tube is the first end of the fifth switch tube, the drain of the fifth NMOS tube is the second end of the fifth switch tube, and the gate of the fifth NMOS tube is the control end of the fifth switch tube;

[0123] The sixth switch tube is a sixth NMOS tube, the source of the sixth NMOS tube is the first end of the sixth switch tube, the drain of the sixth NMOS tube is the second end of the sixth switch tube, and the gate of the sixth NMOS tube is the control end of the sixth switch tube;

[0124] The seventh switch tube is a seventh NMOS tube, the source of the seventh NMOS tube is the first end of the seventh switch tube, the drain of the seventh NMOS tube is the second end of the seventh switch tube, and the gate of the seventh NMOS tube is the control end of the seventh switch tube;

[0125] The eighth switch tube is an eighth NMOS tube, the source of the eighth NMOS tube is the first end of the eighth switch tube, the drain of the eighth NMOS tube is the second end of the eighth switch tube, and the gate of the eighth NMOS tube is the control end of the eighth switch tube.

[0126] In the present invention, considering that the bus capacitor needs to be pre-charged during the actual operation of the five-level converter, in order to ensure the stable pre-charging, NMOS tubes need to be used as each switch tube, because the NMOS tube will be connected in parallel with a reverse diode, and on the basis of each unidirectional conduction module, the actual five-level converter can stably perform the pre-charging process of the bus capacitor when the switch tubes are not turned on, without applying any control, thereby improving the accuracy and practicality of the solution.

[0127] It should be noted that the simple pre-charge characteristics of the clamped five-level converter when used as PFC are explained. Fig.23 The five-level flying capacitor totem pole PFC circuit shown in the figure, when the circuit is started, as the bus voltage increases, the flying capacitor will be pre-charged for the positive and negative half cycles of the AC through the diode corresponding to the switch tube. Fig.24 As shown in the experimental waveform, the input voltage is 220V, 50Hz AC voltage to precharge the circuit. As the positive and negative half cycles of the input AC voltage alternate, the flying capacitor voltage gradually stabilizes and equalizes the voltage. This precharging process is completely realized by the clamping circuit composed of the clamping diode and the anti-parallel diode of the switch tube. Therefore, no control is required to achieve reliable precharging. At this time, it is only required that the capacitance of the discrete bus capacitor is 10 times larger than that of the flying capacitor to achieve a very good voltage equalization effect.

[0128] It should also be noted that this solution has the following advantages:

[0129] 1. Simplify the clamping circuit according to the phase-shift PWM characteristics and the voltage-sharing bus characteristics. The minimum number of switches that can be turned on simultaneously in the five-level phase-shift PWM in different duty cycle intervals is especially considered as the basis for constructing a clamping circuit that can turn on up to two switches at the same time;

[0130] 2. A fixed phase bias control method is proposed to achieve the effect of under-charging all flying capacitors in a switching cycle under any duty cycle control, thus ensuring the effectiveness of clamping;

[0131] 3. The idea of ​​using the voltage-equalizing busbar to provide a voltage-equalizing clamping reference for the flying capacitor voltage-equalizing;

[0132] 4. The idea of ​​using a diode to connect the bus capacitor to provide a flying capacitor pre-charging circuit.

[0133] Similarly:

[0134] 1. This solution uses fixed phase shift control, which can realize the undercharge state of the flying capacitor under various load conditions, realize the reliable clamping of the flying capacitor of the five-level circuit, and ensure the safety of the circuit operation. And it is very simple to realize the fixed phase shift using a single-chip microcomputer.

[0135] 2. The simplified clamping circuit only requires eight diodes to implement, which significantly reduces the complexity of the clamping, improves the circuit power density and reduces the circuit cost.

[0136] 3. The clamping diode can also provide a reliable path for pre-charging the flying capacitor, thereby reducing the complexity of the startup process when the flying capacitor is used in PFC (Power Factor Correction) applications.

[0137] It should also be noted that the actual circuit structure demonstration of the present application takes a five-level converter as an example to clamp the voltage of the flying capacitor of the five-level converter. Other levels can also use the idea of ​​the minimum number of switches that are simultaneously turned on in this phase-shift PWM control to construct a simplified flying capacitor clamping circuit. As long as the voltage of the flying capacitor can be clamped to the voltage of the equivalent capacitor of the corresponding number of bus capacitors, this solution does not limit the number of levels of the multi-level converter 1.

[0138] As an optional embodiment, it also includes:

[0139] The filter device is respectively connected to the power supply, the first end of the first switch tube and the first end of the fifth switch tube.

[0140] In the present invention, considering that in actual operation of the five-level converter, there may be stray inductance in the circuit, which will affect the current in the loop, a filter device is provided between the power supply and the five-level converter in this solution. The loop formed by the power supply and the five-level converter is filtered by the filter device to filter the influence of factors such as stray inductance, thereby improving the transmission efficiency and anti-interference of electric energy.

[0141] In order to solve the above technical problems, the present invention further provides a clamped multi-level converter control method, which is applied to the above clamped multi-level converter, comprising:

[0142] Determine the upper bridge arm rated PWM wave and the lower bridge arm rated PWM wave of the upper bridge arm switch tube and the lower bridge arm switch tube in the multilevel converter 1 in a unit switching cycle respectively;

[0143] Determine the first phase of the first switch tube in the multilevel converter 1, the second phase of the second switch tube in the multilevel converter 1, the third phase of the third switch tube in the multilevel converter 1, and the fourth phase of the fourth switch tube in the multilevel converter 1 according to the rated PWM wave of the upper bridge arm;

[0144] Control any one of the first phase, the second phase, the third phase, or the fourth phase to advance a preset phase deviation angle, control any one of the remaining phases of the first phase, the second phase, the third phase, or the fourth phase to lag behind a preset phase deviation angle, and generate a new upper bridge arm PWM wave, and determine a new lower bridge arm PWM wave according to the new upper bridge arm PWM wave and the rated PWM wave of the lower bridge arm;

[0145] Based on the new upper bridge arm PWM wave and the new lower bridge arm PWM wave, the upper bridge arm switch tube and the lower bridge arm switch tube in the multi-level converter 1 are controlled to be turned on and off.

[0146] In the present invention, since the most commonly used device for the unidirectional conduction module is a diode, and the diode has the characteristic that it will be conducted only when the anode voltage is greater than the cathode voltage, it is necessary to keep the flying capacitor in the five-level converter in an undercharged state, so that the voltage of the flying capacitor is less than the voltage of the equivalent capacitor of the bus capacitor, so that the diode is forward-conducted, and then the voltage corresponding to the flying capacitor is successfully clamped. This solution adjusts the phase of the switch tube in the rated PWM wave of the upper bridge arm and generates a new upper bridge arm PWM wave, and determines a new PWM wave according to the new upper bridge arm PWM wave and the rated PWM wave of the lower bridge arm (the PWM wave of the upper bridge arm is always complementary to the PWM wave of the lower bridge arm), so as to ensure that the flying capacitor is kept in an undercharged state in each working cycle, thereby ensuring that the voltage of the flying capacitor is always in a steady state.

[0147] As an optional embodiment, after controlling the turning on and off of the upper bridge arm switch tube and the lower bridge arm switch tube in the multi-level converter 1 based on the new upper bridge arm PWM wave and the new lower bridge arm PWM wave, the method further includes:

[0148] Collecting the charge and discharge amounts corresponding to N flying capacitors in the multilevel converter 1 after a preset time, where N is a positive integer greater than 1;

[0149] Determine whether the discharge amount corresponding to each flying capacitor is greater than the charge amount corresponding to each flying capacitor;

[0150] If the discharge amount corresponding to each flying capacitor is greater than the charge amount corresponding to each flying capacitor, it is determined that each flying capacitor is in an undercharged state;

[0151] If the discharge amount corresponding to each flying capacitor is not greater than the charge amount corresponding to each flying capacitor, it is determined that each flying capacitor is not in an undercharged state, and a corresponding alarm is issued.

[0152] In the present invention, considering that the purpose of adjusting the PWM wave of the upper bridge arm to always be consistent with the PWM wave of the lower bridge arm is to make the flying capacitor of the adjusted five-level converter always in an undercharged state, so after controlling the opening and closing of the upper bridge arm switch tube and the lower bridge arm switch tube in the multi-level converter 1 based on the new upper bridge arm PWM wave and the new lower bridge arm PWM wave, the scheme will also collect the charge and discharge amounts corresponding to the N flying capacitors in the multi-level converter 1 after a preset time, because the relationship between the charge and discharge amounts of the flying capacitors determines whether the flying capacitors are in an undercharged state, if the discharge amounts corresponding to the flying capacitors are all greater than the charge amounts corresponding to the flying capacitors, it is determined that the flying capacitors are all in an undercharged state; on the contrary, if the discharge amounts corresponding to the flying capacitors are not all greater than the charge amounts corresponding to the flying capacitors, it is determined that the flying capacitors are not all in an undercharged state, proving that the PWM wave after the above phase adjustment does not make the flying capacitors all in an undercharged state, so it is necessary to issue a corresponding alarm for the fault condition after the phase adjustment, so that the user or maintenance personnel can adjust the phase adjustment or repair the five-level converter, thereby improving the reliability of the scheme.

[0153] It should be noted that, in this specification, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "comprise", "include" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device. In the absence of further restrictions, an element defined by the statement "comprises a ..." does not exclude the presence of other identical elements in the process, method, article or device including the element.

[0154] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present invention. Various modifications to these embodiments will be apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present invention. Therefore, the present invention will not be limited to the embodiments shown herein, but rather to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A clamped multilevel converter, characterized in that: include: A multilevel converter and N clamping units, the number of the clamping units is the same as the number of flying capacitors in the multilevel converter, and N is a positive integer greater than 1; Each of the clamping units is connected in parallel with the N flying capacitors in the multi-level converter in a one-to-one correspondence, and each of the clamping units is connected correspondingly to the M equivalent bus capacitors of the multi-level converter through the corresponding remaining clamping units, and is used to control each of the flying capacitors to be connected in series with a corresponding number of the equivalent bus capacitors when the switch tube in the multi-level converter is closed, and the number of each of the equivalent bus capacitors is the same as the difference between the number of levels of the multi-level converter minus 1.

2. The clamped multilevel converter according to claim 1, wherein: When the multi-level converter is a five-level converter, the clamp-type multi-level converter comprises: a first clamp unit, a second clamp unit and a third clamp unit; The first clamping unit is connected in parallel with the first flying capacitor of the five-level converter, the first clamping unit is respectively connected to the first end of the first equivalent capacitor of the second flying capacitor of the five-level converter and the first end of the second equivalent capacitor of the second flying capacitor, the second end of the first equivalent capacitor is respectively connected to the second end of the second switch tube of the five-level converter and the first end of the third switch tube of the five-level converter, the second end of the second equivalent capacitor is respectively connected to the first end of the sixth switch tube of the five-level converter and the second end of the seventh switch tube of the five-level converter, the first equivalent capacitor and the second equivalent capacitor have the same capacitance, and the sum of the capacitances of the first equivalent capacitor and the second equivalent capacitor is equal to the capacitance of the second equivalent capacitor; The second clamping unit is connected in parallel with the first equivalent capacitor and the second equivalent capacitor connected in series, and the second clamping unit is respectively connected to the first end of the fourth equivalent capacitor of the bus capacitor of the five-level converter and the first end of the fifth equivalent capacitor of the bus capacitor; The third clamping unit is connected in parallel with the five-level converter. The third clamping unit is respectively connected to the first end of the third equivalent capacitor of the bus capacitor, the second end of the fourth equivalent capacitor, the second end of the fifth equivalent capacitor, the first end of the sixth equivalent capacitor of the bus capacitor, the first end of the first equivalent capacitor and the first end of the second equivalent capacitor. The second end of the third equivalent capacitor is connected to the second end of the fourth switch tube of the five-level converter, and the second end of the sixth equivalent capacitor is connected to the first end of the eighth switch tube of the five-level converter. The capacitances of the third equivalent capacitor, the fourth equivalent capacitor, the fifth equivalent capacitor and the sixth equivalent capacitor are all equal, and the sum of the capacitances of the third equivalent capacitor, the fourth equivalent capacitor, the fifth equivalent capacitor and the sixth equivalent capacitor is equal to the capacitance of the bus capacitor.

3. The clamped multilevel converter according to claim 2, wherein: The first clamping unit comprises: A first unidirectional conduction module, wherein an input end of the first unidirectional conduction module is connected to an output end of the second unidirectional conduction module, a first end of the first equivalent capacitor, and a first end of the second equivalent capacitor, and an output end of the first unidirectional conduction module is connected to a second end of a first switch tube of the five-level converter, a first end of the second switch tube, and a first end of the first flying capacitor; The second unidirectional conduction module, the input end of the second unidirectional conduction module is respectively connected to the first end of the fifth switch tube of the five-level converter, the second end of the sixth switch tube and the second end of the first flying capacitor.

4. The clamped multilevel converter according to claim 2, wherein: The second clamping unit comprises: a third unidirectional conduction module, wherein the input end of the third unidirectional conduction module is respectively connected to the output end of the fourth unidirectional conduction module, the first end of the fourth equivalent capacitor and the first end of the fifth equivalent capacitor, and the output end is respectively connected to the first end of the third switch tube, the second end of the second switch tube and the second end of the first equivalent capacitor; The fourth unidirectional conduction module, the input end of the fourth unidirectional conduction module is respectively connected to the first end of the sixth switch tube, the second end of the seventh switch tube and the second end of the second equivalent capacitor.

5. The clamped multilevel converter according to claim 2, wherein: The third clamping unit includes: a fifth unidirectional conduction module, a sixth unidirectional conduction module, a seventh unidirectional conduction module and an eighth unidirectional conduction module; The input end of the fifth unidirectional conduction module is respectively connected to the output end of the sixth unidirectional conduction module, the second end of the fourth equivalent capacitor and the first end of the third equivalent capacitor, and the output end is connected to the first end of the third flying capacitor of the five-level converter; The input end of the sixth unidirectional conduction module is respectively connected to the output end of the seventh unidirectional conduction module, the first end of the first equivalent capacitor and the first end of the second equivalent capacitor; The input end of the seventh unidirectional conduction module is respectively connected to the output end of the eighth unidirectional conduction module, the second end of the fifth equivalent capacitor and the first end of the sixth equivalent capacitor; The input end of the eighth unidirectional conduction module is respectively connected to the second end of the third flying capacitor, the first end of the seventh switch tube, and the second end of the eighth switch tube.

6. The clamped multilevel converter according to any one of claims 2 to 5, characterized in that: The five-level converter includes: the first switch tube, the second switch tube, the third switch tube, the fourth switch tube, the fifth switch tube, the sixth switch tube, the seventh switch tube, the eighth switch tube, the first flying capacitor, the second flying capacitor, the third flying capacitor, and the bus capacitor, the second flying capacitor includes the first equivalent capacitor and the second equivalent capacitor, and the bus capacitor includes the third equivalent capacitor, the fourth equivalent capacitor, the fifth equivalent capacitor, and the sixth equivalent capacitor; The first switch tube, the second switch tube, the third switch tube and the fourth switch tube are connected in series in sequence, the first common end of the series connection is respectively connected to the power supply and the first end of the fifth switch tube, and the second common end of the series connection is connected to the second end of the third equivalent capacitor; The fifth switch tube, the sixth switch tube, the seventh switch tube and the eighth switch tube are connected in series in sequence, the first common end of the series connection is respectively connected to the power supply and the first end of the first switch tube, and the second common end of the series connection is connected to the second end of the sixth equivalent capacitor.

7. The clamped multilevel converter according to claim 6, wherein: The first switch tube is a first NMOS tube, the source of the first NMOS tube is the first end of the first switch tube, the drain of the first NMOS tube is the second end of the first switch tube, and the gate of the first NMOS tube is the control end of the first switch tube; Correspondingly, the second switch tube is a second NMOS tube, the source of the second NMOS tube is the first end of the second switch tube, the drain of the second NMOS tube is the second end of the second switch tube, and the gate of the second NMOS tube is the control end of the second switch tube; The third switch tube is a third NMOS tube, the source of the third NMOS tube is the first end of the third switch tube, the drain of the third NMOS tube is the second end of the third switch tube, and the gate of the third NMOS tube is the control end of the third switch tube; The fourth switch tube is a fourth NMOS tube, the source of the fourth NMOS tube is the first end of the fourth switch tube, the drain of the fourth NMOS tube is the second end of the fourth switch tube, and the gate of the fourth NMOS tube is the control end of the fourth switch tube; The fifth switch tube is a fifth NMOS tube, the source of the fifth NMOS tube is the first end of the fifth switch tube, the drain of the fifth NMOS tube is the second end of the fifth switch tube, and the gate of the fifth NMOS tube is the control end of the fifth switch tube; The sixth switch tube is a sixth NMOS tube, the source of the sixth NMOS tube is the first end of the sixth switch tube, the drain of the sixth NMOS tube is the second end of the sixth switch tube, and the gate of the sixth NMOS tube is the control end of the sixth switch tube; The seventh switch tube is a seventh NMOS tube, the source of the seventh NMOS tube is the first end of the seventh switch tube, the drain of the seventh NMOS tube is the second end of the seventh switch tube, and the gate of the seventh NMOS tube is the control end of the seventh switch tube; The eighth switch tube is an eighth NMOS tube, the source of the eighth NMOS tube is the first end of the eighth switch tube, the drain of the eighth NMOS tube is the second end of the eighth switch tube, and the gate of the eighth NMOS tube is the control end of the eighth switch tube.

8. The clamped multilevel converter according to claim 6, wherein: Also includes: A filter device is connected to the power supply, the first end of the first switch tube and the first end of the fifth switch tube respectively.

9. A clamped multi-level converter control method, characterized in that: A clamped multilevel converter as claimed in any one of claims 1 to 8, comprising: Determine the rated PWM wave of the upper bridge arm and the rated PWM wave of the lower bridge arm of the upper bridge arm switch tube and the lower bridge arm switch tube in the multi-level converter in a unit switching cycle respectively; Determine, according to the upper bridge arm rated PWM wave, a first phase of a first switch tube in the multilevel converter, a second phase of a second switch tube in the multilevel converter, a third phase of a third switch tube in the multilevel converter, and a fourth phase of a fourth switch tube in the multilevel converter; Controlling any one of the first phase, the second phase, the third phase, or the fourth phase to advance a preset phase deviation angle, controlling any one of the remaining phases of the first phase, the second phase, the third phase, or the fourth phase to lag behind the preset phase deviation angle, and generating a new upper bridge arm PWM wave, and determining a new lower bridge arm PWM wave according to the new upper bridge arm PWM wave and the lower bridge arm rated PWM wave; Based on the new upper bridge arm PWM wave and the new lower bridge arm PWM wave, the upper bridge arm switch tube and the lower bridge arm switch tube in the multi-level converter are controlled to be turned on and off.

10. The clamped multi-level converter control method according to claim 9, wherein: After controlling the turning on and off of the upper bridge arm switch tube and the lower bridge arm switch tube in the multi-level converter based on the new upper bridge arm PWM wave and the new lower bridge arm PWM wave, the method further includes: Collecting the charge and discharge amounts corresponding to N flying capacitors in the multi-level converter after a preset time, where N is a positive integer greater than 1; Determine whether the discharge amount corresponding to each of the flying capacitors is greater than the charge amount corresponding to each of the flying capacitors; If the discharge amount corresponding to each of the flying capacitors is greater than the charge amount corresponding to each of the flying capacitors, it is determined that each of the flying capacitors is in an undercharged state; If the discharge amount corresponding to each of the flying capacitors is not greater than the charge amount corresponding to each of the flying capacitors, it is determined that each of the flying capacitors is not in an undercharged state, and a corresponding alarm is issued.

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