A seven-level inverter based on switched capacitor

Abstract

The application discloses a seven-level inverter based on a switched capacitor, and a topology structure uses one direct-current voltage source, two capacitors, one diode and ten switch tubes to realize seven-level alternating current output. dc The application has three times boosting capacity, and the capacitor voltage can be self-balanced without an auxiliary circuit, and the respective voltage is maintained at V dc ; compared with other seven-level inverters, the application reduces the total number of devices used, has lower topology total voltage stress, simple structure, small size and cost saving.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power electronics, and particularly relates to a seven-level inverter based on a switching capacitor. BACKGROUND

[0002] Renewable energy has the advantages of wide distribution, safety and reliability, rich reserves and easy development. In a renewable energy power generation system, an inverter is a key link of electric energy conversion and transmission, and has an important influence on the working performance, conversion, efficiency and reliability of the whole system. In inverters, a multi-level inverter has the advantages of simple control mode, low total harmonic distortion (THD), high power density and small volume, and has been widely used in recent years. Traditional multi-level inverters include a neutral point clamped (NPC) type, a flying capacitor (FC) type and a cascaded H-bridge (CHB) type. Among them, the NPC type uses a number of clamping diodes which is approximately proportional to the square of the number of levels, and with the increase of the number of levels, the demand for the number of devices also increases dramatically, and the multi-level circuit needs to ensure the voltage balance of the DC side capacitor, greatly improving the complexity of control; the FC type needs a large number of capacitors with the increase of the number of levels, causing the increase of volume and weight; the CHB type uses a large number of switching tubes with the increase of the number of levels, and needs multiple DC voltage power supplies, increasing the system cost and floor area.

[0003] In recent years, switching capacitor multi-level inverters have been widely used in the field of renewable energy. The switching capacitor type inverter does not use any inductive element, and the main devices of the switching capacitor module are switching tubes and capacitors, having the advantages of high boost capability, small volume, high power density, high conversion rate and easy integration. However, the existing switching capacitor multi-level inverters generally have the problems of large number of devices, large total voltage stress of topology, complex structure and high cost. SUMMARY

[0004] The application aims to provide a seven-level inverter based on a switching capacitor.

[0005] The technical solution for achieving the application is as follows: a seven-level inverter based on a switching capacitor, comprising one DC voltage source, two capacitors, one diode and ten switching tubes.

[0006] The anode of the DC voltage source V dc is connected to the anode of the first diode D and the collector of the sixth switching tube S6; the cathode of the DC voltage source V dc is connected to the emitter of the second switching tube S2, the emitter of the eighth switching tube S8 and the emitter of the tenth switching tube S 10The positive pole of the first capacitor C1 is connected to the emitter of the fifth switch tube S5, and the negative pole of the first capacitor C1 is connected to the emitter of the sixth switch tube S6 and the collector of the seventh switch tube S7. 10 The positive pole of the second capacitor C2 is connected to the collector of the fourth switch tube S4 and the collector of the ninth switch tube S9.

[0007] The positive pole of the inverter output is connected to the emitter of the ninth switch tube S9 and the emitter of the tenth switch tube S 10 The negative pole of the inverter output is connected to the emitter of the first switch tube S1 and the collector of the second switch tube S2. 10 The positive pole of the load is connected to the emitter of the ninth switch tube S9 and the emitter of the tenth switch tube S dc The negative pole of the load is connected to the emitter of the first switch tube S1 and the collector of the second switch tube S2.

[0008] Compared with the prior art, the significant advantages of the present application are:

[0009] (1) The topology structure of the present application uses one direct current voltage source, two capacitors, one diode and ten switch tubes to realize seven-level alternating current output; the topology has three times voltage boosting capability, and the capacitor voltage can be self-balanced without auxiliary circuit, and each voltage is maintained at V dc .

[0010] (2) Compared with other seven-level inverters, the present application reduces the total number of devices used, has lower topology total voltage stress, simple structure, small size and cost saving under the same output voltage level. BRIEF DESCRIPTION OF DRAWINGS

[0011] Figure 1 It is a schematic diagram of the seven-level inverter topology structure based on switch capacitor of the present application.

[0012] Figure 2 It is an output voltage and output current waveform diagram when the seven-level inverter topology based on switch capacitor of the present application is simulated.

[0013] Figure 3 It is a first capacitor C1 voltage and second capacitor C2 voltage waveform diagram when the seven-level inverter topology based on switch capacitor of the present application is simulated. Detailed Implementation

[0014] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings, but the scope of protection of the present invention is not limited to the embodiments described.

[0015] like Figure 1 As shown, the seven-level inverter topology based on switched capacitors includes one DC voltage source, two capacitors, one diode, and ten switching transistors.

[0016] DC voltage source V dc The positive terminal is connected to the anode of the first diode D and the collector of the sixth switch S6; DC voltage source V dc The negative terminal is connected to the emitter of the second switch S2, the emitter of the eighth switch S8, and the tenth switch S... 10 The emitter of the first switch S1 is connected to the emitter of the fifth switch S5; the cathode of the first switch S1 is connected to the emitter of the sixth switch S6 and the collector of the seventh switch S7; the anode of the second capacitor C2 is connected to the collector of the fourth switch S4 and the collector of the ninth switch S9; the cathode of the second capacitor C2 is connected to the emitter of the seventh switch S7 and the collector of the eighth switch S8; the collector of the first switch S1 is connected to the cathode of the first diode D, the collector of the third switch S3, and the collector of the fifth switch S5; the emitter of the first switch S1 is connected to the collector of the second switch S2; the emitter of the third switch S3 is connected to the emitter of the fourth switch S4; the emitter of the ninth switch S9 is connected to the tenth switch S8. 10 The collector.

[0017] The positive terminal of the inverter output is connected to the emitter of the ninth switch S9 and the tenth switch S1. 10 The collector of the inverter is connected to the emitter of the first switch S1 and the collector of the second switch S2; the positive terminal of the load is connected to the emitter of the ninth switch S9 and the collector of the tenth switch S1. 10 The collector of the first switch S1 and the collector of the second switch S2 are connected to the emitter of the first switch S1 and the collector of the second switch S2.

[0018] When the first capacitor C1 is fully charged, the voltage across it is equal to that of the DC voltage source, which is V. dc When the second capacitor C2 is fully charged, the voltage across it is twice that of the DC voltage source, i.e., 2V. dc .

[0019] Each of the switching transistors is equipped with an anti-parallel diode, which provides bidirectional current carrying capability. The switching transistors are fully controllable power electronic devices, which may be, but are not limited to, metal-oxide-semiconductor field-effect transistors (MOSFETs) or insulated-gate bipolar transistors (IGBTs).

[0020] When the seven-level inverter based on switched capacitor outputs different levels, the on-off state of each switch in the topology and the charge-discharge state of the capacitor are as follows:

[0021] The first working mode: the second switch S2, the sixth switch S6, the seventh switch S7 and the ninth switch S9 are turned on, the remaining switches are turned off, and the first diode D is turned off under reverse voltage. At this time, the DC voltage source V dc and the second capacitor C2 are connected in series to supply power to the load, and the inverter outputs +3V dc level.

[0022] The second working mode: the second switch S2, the third switch S3, the fourth switch S4, the fifth switch S5, the sixth switch S6, the eighth switch S8 and the ninth switch S9 are turned on, the remaining switches are turned off, and the first diode D is turned off under reverse voltage. At this time, the DC voltage source V dc and the first capacitor C1 are connected in series to supply power to the load, and the inverter outputs +2V dc level; at this time, the DC voltage source V dc and the first capacitor C1 are connected in parallel to charge the second capacitor C2 to 2V dc .

[0023] The third working mode: the first switch S1, the fifth switch S5, the seventh switch S7, the eighth switch S8 and the ninth switch S9 are turned on, the remaining switches are turned off, and the first diode D is turned on under forward voltage. At this time, the second capacitor C2 is connected in reverse series with the first capacitor C1 to supply power to the load, and the inverter outputs +V dc level; at this time, the DC voltage source V dc is connected in parallel with the first capacitor C1 to charge the first capacitor C1 to V dc .

[0024] The fourth working mode: the second switch S2, the third switch S3, the fourth switch S4, the fifth switch S5, the sixth switch S6, the eighth switch S8 and the tenth switch S 10 are turned on, the remaining switches are turned off, and the first diode D is turned off under reverse voltage. At this time, the inverter outputs 0 level; at this time, the DC voltage source V dc and the first capacitor C1 are connected in series to charge the second capacitor C2 to 2V dc .

[0025] The fifth working mode: the first switch S1, the fifth switch S5, the seventh switch S7, the eighth switch S8 and the tenth switch S 10 are turned on, the remaining switches are turned off, and the first diode D is turned on under forward voltage. At this time, the DC voltage source V dc supplies power to the load, and the inverter outputs -Vdc DC voltage source V dc parallel to the first capacitor C1 to charge the first capacitor C1 to V dc .

[0026] The sixth working mode: the first switch S1, the third switch S3, the fourth switch S4, the fifth switch S5, the sixth switch S6, the eighth switch S8 and the tenth switch S 10 are turned on, and the rest of the switches are turned off, and the first diode D bears a reverse voltage and is turned off. At this time, the DC voltage source V dc is in series with the first capacitor C1 to supply power to the load, and the inverter output is -2V dc . dc is in series with the first capacitor C1 to charge the capacitor C2 to 2V dc .

[0027] The seventh working mode: the first switch S1, the third switch S3, the fourth switch S4, the sixth switch S6, the seventh switch S7 and the tenth switch S 10 are turned on, and the rest of the switches are turned off, and the first diode D bears a reverse voltage and is turned off. At this time, the DC voltage source V dc is in series with the second capacitor C2 to supply power to the load, and the inverter output is -3V dc .

[0028] Set "0" to represent the switch being turned off, "1" to represent the switch being turned on, "C", "D" or "-" to represent the capacitor being charged, discharged or unchanged, respectively, and the switch state at each level is as follows:

[0029]

[0030] wherein V o represents the output voltage of the seven-level inverter based on the switched capacitor.

[0031] The present application will be further described below in conjunction with specific embodiments and drawings.

[0032] Embodiment

[0033] In this embodiment, the carrier in-phase disposition (IPD) modulation technology is adopted to obtain the control driving signals of the 10 switches. In this modulation strategy, there are 6 high-frequency carriers u1-u6 and 1 sinusoidal base frequency modulation wave with an amplitude of A c , a same frequency f s and a same phase vertically distributed from top to bottom, and the modulation ratio M=A ref / 3A ref . cThe modulation wave is compared with each carrier wave, and the on-off state of the main control switch tube in the topology is changed, so that the working mode changes regularly.

[0034] During the period when the sine modulation wave is greater than the first triangular carrier u1, the second switch tube S2, the sixth switch tube S6, the seventh switch tube S7 and the ninth switch tube S9 are turned on, and the inverter output voltage is +3V dc ; during the period when the sine modulation wave is greater than the second triangular carrier u2 and less than the first triangular carrier u1, the second switch tube S2, the third switch tube S3, the fourth switch tube S4, the fifth switch tube S5, the sixth switch tube S6, the eighth switch tube S8 and the ninth switch tube S9 are turned on, and the inverter output voltage is +2V dc ; during the period when the sine modulation wave is greater than the third triangular carrier u3 and less than the second triangular carrier u2, the first switch tube S1, the fifth switch tube S5, the seventh switch tube S7, the eighth switch tube S8 and the ninth switch tube S9 are turned on, and the inverter output voltage is +V dc ; during the period when the sine modulation wave is greater than the fourth triangular carrier u4 and less than the third triangular carrier u3, the second switch tube S2, the third switch tube S3, the fourth switch tube S4, the fifth switch tube S5, the sixth switch tube S6, the eighth switch tube S8 and the tenth switch tube S 10 are turned on, and the inverter output voltage is 0; during the period when the sine modulation wave is greater than the fifth triangular carrier u5 and less than the fourth triangular carrier u4, the first switch tube S1, the fifth switch tube S5, the seventh switch tube S7, the eighth switch tube S8 and the tenth switch tube S 10 are turned on, and the inverter output voltage is -V dc ; during the period when the sine modulation wave is greater than the sixth triangular carrier u6 and less than the fifth triangular carrier u5, the first switch tube S1, the third switch tube S3, the fourth switch tube S4, the fifth switch tube S5, the sixth switch tube S6, the eighth switch tube S8 and the tenth switch tube S 10 are turned on, and the inverter output voltage is -2V dc ; during the period when the sine modulation wave is less than the sixth triangular carrier u6, the first switch tube S1, the third switch tube S3, the fourth switch tube S4, the sixth switch tube S6, the seventh switch tube S7 and the tenth switch tube S 10 are turned on, and the inverter output voltage is -3V dc ; the driving signals of the switch tubes S1-S 10 are all generated by logical combination of the modulation wave and the six carrier signals.

[0035] In order to verify the correctness and feasibility of the switch capacitor-based seven-level inverter, a simulation experiment of the switch capacitor-based seven-level inverter is designed. The following conclusions are obtained through MATLAB simulation.

[0036] The simulation parameters of this embodiment are: input voltage Vdc =100V; capacitance C1=C2=4700 μF; output voltage frequency f0=50 Hz; carrier frequency is 10 kHz; load is resistive and inductive load, R=100 Ω, L=100 mH; modulation ratio M=1;

[0037] Figure 2 For the output voltage, output current waveform of the simulation experiment based on the switch capacitor seven-level inverter, the output voltage realizes seven-level AC output, the voltage gain is 3 times, the output current is approximately 50 Hz sine wave, which is consistent with the theoretical analysis, and verifies the feasibility of the structure.

[0038] Figure 3 For the first capacitor C1 voltage, the second capacitor C2 voltage waveform, the maximum ripple voltage of the first capacitor C1 is 1.98V, and the maximum ripple voltage of the second capacitor C2 is 1.58V, which shows that the capacitor voltage can realize self-balancing.

[0039] Finally, it should be noted that: the above only for the preferred embodiments of the present application, and not for limiting the present application, although the foregoing embodiments of the present application are described in detail, for those skilled in the art, it still can be modified, or equivalent replacement for part of the technical features recorded in the foregoing embodiments. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application, should be included in the protection scope of the present application.

Claims

1. A seven-level inverter based on switched capacitors, characterized in that, It includes one DC voltage source, two capacitors, one diode, and ten switching transistors; DC voltage source V dc The positive terminal is connected to the first diode. D anode, sixth switch tube S 6's collector; DC voltage source V dc The negative terminal is connected to the second switching transistor. S 2's emitter, the eighth switch S 8's emitter, tenth switch transistor S 10 The emitter; the first capacitor C The positive terminal of 1 is connected to the fifth switching transistor. S 5's emitter; first capacitor C The negative terminal of 1 is connected to the sixth switching transistor. S 6's emitter, the seventh switch S 7's collector; second capacitor C The positive terminal of 2 is connected to the fourth switching transistor. S 4's collector, the ninth switching transistor S 9's collector; second capacitor C The negative terminal of 2 is connected to the seventh switch. S 7's emitter, the eighth switching transistor S 8's collector; first switching transistor S The collector of 1 is connected to the first diode. D cathode, third switch tube S 3's collector, fifth switching transistor S 5's collector; first switching transistor S The emitter of transistor 1 is connected to the second switching transistor. S 2's collector; the third switching transistor S The emitter of transistor 3 is connected to the fourth switching transistor. S 4's emitter; the ninth switch transistor S The emitter of transistor 9 is connected to the tenth switching transistor. S 10 The collector; The positive terminal of the inverter output is connected to the ninth switching transistor. S 9's emitter, tenth switch transistor S 10 The collector of the inverter; the negative terminal of the inverter output is connected to the first switching transistor. S 1's emitter, second switch S The collector of transistor 2; the positive terminal of the load is connected to the ninth switching transistor. S 9's emitter, tenth switch transistor S 10 The collector of the load; the negative terminal of the load is connected to the first switching transistor. S 1's emitter, second switch S 2's collector; When the seven-level inverter outputs different levels, the on / off states of each switch and the charging / discharging states of the capacitors in the topology are as follows: First operating mode: Second switching transistor S 2. Sixth switching transistor S 6. Seventh switching transistor S 7 and the ninth switch S 9 is on, the other switches are off, and the first diode is on. D The DC voltage source is turned off when subjected to reverse voltage; at this time, the DC voltage source... V dc Second capacitor C Two inverters are connected in series to supply power to the load, and the inverter output is +3. V dc Level; Second operating mode: Second switching transistor S 2. Third switching transistor S 3. Fourth switching transistor S 4. Fifth switching transistor S 5. Sixth switching transistor S 6. Eighth switching transistor S 8 and the ninth switch S 9 is on, the other switches are off, and the first diode is on. D The DC voltage source is turned off when subjected to reverse voltage; at this time, the DC voltage source... V dc and the first capacitor C 1 is connected in series to power the load, and the inverter outputs +2 V dc Level; DC voltage source at this time V dc and the first capacitor C 1 is connected in series as the second capacitor C 2 charging to 2 V dc ; Third operating mode: First switching transistor S 1. Fifth switching transistor S 5. Seventh switching transistor S 7. Eighth switching transistor S 8 and the ninth switch S 9 is on, the other switches are off, and the first diode is on. D The second capacitor is turned on under forward voltage; at this time, the second capacitor... C 2 reverse series first capacitor C 1 supplies power to the load, inverter output + V dc Level; DC voltage source at this time V dc With the first capacitor C 1 is connected in parallel as the first capacitor C 1. Charge to V dc ; Fourth operating mode: Second switching transistor S 2. Third switching transistor S 3. Fourth switching transistor S 4. Fifth switching transistor S 5. Sixth switching transistor S 6. Eighth switching transistor S 8 and 10th switching transistors S 10 When the diode is turned on, the other switching transistors are turned off, and the first diode... D The inverter is shut off when subjected to reverse voltage; at this time, the inverter outputs a 0 level; at this time, the DC voltage source... V dc and the first capacitor C 1 is connected in series as the second capacitor C 2 charging to 2 V dc ; Fifth operating mode: First switching transistor S 1. Fifth switching transistor S 5. Seventh switching transistor S 7. Eighth switching transistor S 8 and 10th switching transistors S 10 When the diode is turned on, the other switching transistors are turned off, and the first diode... D It conducts under forward voltage; at this time, the DC voltage source... V dc The inverter outputs power to the load. V dc Level; DC voltage source at this time V dc With the first capacitor C 1 is connected in parallel as the first capacitor C 1. Charge to V dc ; Sixth operating mode: First switching transistor S 1. Third switching transistor S 3. Fourth switching transistor S 4. Fifth switching transistor S 5. Sixth switching transistor S 6. Eighth switching transistor S 8 and 10th switching transistors S 10 When the diode is turned on, the other switching transistors are turned off, and the first diode... D The DC voltage source is turned off when subjected to reverse voltage; at this time, the DC voltage source... V dc and the first capacitor C 1 is connected in series to supply power to the load, and the inverter outputs -2 V dc Level; DC voltage source at this time V dc and the first capacitor C 1 is a capacitor connected in series C 2 charging to 2 V dc ; Seventh operating mode: First switching transistor S 1. Third switching transistor S 3. Fourth switching transistor S 4. Sixth switching transistor S 6. Seventh switching transistor S 7 and 10 switch transistors S 10 When the diode is turned on, the other switching transistors are turned off, and the first diode... D The DC voltage source is turned off when subjected to reverse voltage; at this time, the DC voltage source... V dc With the second capacitor C 2 units are connected in series to power the load, and the inverter output is -3. V dc Level.

2. The seven-level inverter based on switched capacitors according to claim 1, characterized in that, The first capacitor C When fully charged, the voltage across it is equal to that of a DC voltage source. V dc Second capacitor C When fully charged, the voltage across 2 is twice that of a DC voltage source, i.e., 2 V dc .

3. The seven-level inverter based on switched capacitors according to claim 1, characterized in that, Each switching transistor is equipped with an anti-parallel diode, providing bidirectional current carrying capability.

4. The seven-level inverter based on switched capacitors according to claim 3, characterized in that, The switching transistor is a fully controllable power electronic device, which is a metal-oxide-semiconductor field-effect transistor or an insulated-gate bipolar transistor.

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