Seven-level inverter based on switched capacitor

Abstract

The invention discloses a seven-level inverter based on switched capacitors. According to a topological structure, seven-level alternating-current output is achieved through one direct-current voltage source, two capacitors, one diode and ten switching tubes. According to the invention, the three-time boosting capability is realized, and the capacitor voltage can be self-balanced without an auxiliary circuit, and the respective voltages are respectively maintained at Vdc and 2Vdc; compared with other seven-level inverters, under the same output voltage level, the seven-level inverter has the advantages that the total number of used devices is reduced, the topology total voltage stress is low, the structure is simple, the size is small, and the cost is saved.

Description

Technical Field

[0001] The invention belongs to the technical field of power electronics, and in particular relates to a seven-level inverter based on switched capacitors. Background Art

[0002] Renewable energy has the advantages of wide distribution, safety, reliability, abundant reserves and easy development. In the renewable energy power generation system, the inverter is the key link of power conversion and transmission, and has an important impact on the performance, conversion, efficiency and reliability of the whole system. Among the inverters, the multi-level inverter has the advantages of simple control, low total harmonic distortion (THD), high power density and small size, and has been widely used in recent years. Traditional multi-level inverters include neutral point clamped type (NPC), flying capacitor type (FC) and cascaded H-bridge type (CHB). Among them, the number of clamping diodes used in the neutral point clamped type is approximately proportional to the square of the number of levels. As the number of levels increases, the demand for the number of devices also increases sharply, and the multi-level circuit needs to ensure the DC side capacitor voltage equalization, which greatly increases the complexity of control; the flying capacitor type requires a large number of capacitors as the number of levels increases, resulting in an increase in volume and weight; the cascaded H-bridge type will use a large number of switch tubes as the number of levels increases, and it requires multiple DC voltage power supplies, which increases the system cost and floor space.

[0003] In recent years, switched capacitor multi-level inverters have been widely used in the field of renewable energy. Switched capacitor inverters do not use any inductive components. The main components of their switched capacitor modules are switch tubes and capacitors. They have the advantages of high boost capability, small size, high power density, high conversion rate, and easy integration. However, existing switched capacitor multi-level inverters generally have problems such as a large number of components, large total topology voltage stress, complex structure, and high cost. Summary of the invention

[0004] The purpose of the present invention is to provide a seven-level inverter based on switched capacitors.

[0005] The technical solution for achieving the purpose of the present invention is: a seven-level inverter based on switched capacitors, including a DC voltage source, two capacitors, a diode and ten switching tubes;

[0006] DC voltage source V dc The positive electrode is connected to the anode of the first diode D and the collector of the sixth switch tube S6; the DC voltage source V dc The cathode of the switch is connected to the emitter of the second switch tube S2, the emitter of the eighth switch tube S8, and the emitter of the tenth switch tube S 10The positive electrode of the first capacitor C1 is connected to the emitter of the fifth switch tube S5; the negative electrode 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; the positive electrode 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; the negative electrode of the second capacitor C2 is connected to the emitter of the seventh switch tube S7 and the collector of the eighth switch tube S8; the collector of the first switch tube S1 is connected to the cathode of the first diode D, the collector of the third switch tube S3, and the collector of the fifth switch tube S5; the emitter of the first switch tube S1 is connected to the collector of the second switch tube S2; the emitter of the third switch tube S3 is connected to the emitter of the fourth switch tube S4; the emitter of the ninth switch tube S9 is connected to the cathode of the first diode D, the collector of the third switch tube S3, and the collector of the fifth switch tube S5; the emitter of the first switch tube S1 is connected to the collector of the second switch tube S2; the emitter of the third switch tube S3 is connected to the emitter of the fourth switch tube S4; the emitter of the ninth switch tube S9 is connected to the cathode of the tenth switch tube S 10 The collector;

[0007] The positive electrode 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 electrode of the inverter output is connected to the emitter of the first switch tube S1 and the collector of the second switch tube S2; the positive electrode of the load is connected to the emitter of the ninth switch tube S9 and the collector of the tenth switch tube S 10 The negative electrode 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 present invention has the following significant advantages:

[0009] (1) The topological structure of the present invention uses 1 DC voltage source, 2 capacitors, 1 diode and 10 switch tubes to achieve a seven-level AC output; the topology has a 3-fold boost capability and without the need for an auxiliary circuit, the capacitor voltage can achieve self-balancing, and each voltage is maintained at V dc , 2V dc .

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

[0011] Figure 1 The figure is a schematic diagram of the topological structure of a seven-level inverter based on switched capacitors according to the present invention.

[0012] Figure 2 The waveform diagram of output voltage and output current of the seven-level inverter topology based on switched capacitors in the simulation experiment of the present invention.

[0013] Figure 3 The waveform diagram of the voltage of the first capacitor C1 and the voltage of the second capacitor C2 during the simulation experiment of the seven-level inverter topology based on the switched capacitor of the present invention. DETAILED DESCRIPTION

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

[0015] like Figure 1 As shown, the seven-level inverter topology based on switched capacitor includes 1 DC voltage source, 2 capacitors, 1 diode and 10 switching tubes;

[0016] DC voltage source V dc The positive electrode is connected to the anode of the first diode D and the collector of the sixth switch tube S6; the DC voltage source V dc The cathode of the switch is connected to the emitter of the second switch tube S2, the emitter of the eighth switch tube S8, and the emitter of the tenth switch tube S 10 The positive electrode of the first capacitor C1 is connected to the emitter of the fifth switch tube S5; the negative electrode 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; the positive electrode 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; the negative electrode of the second capacitor C2 is connected to the emitter of the seventh switch tube S7 and the collector of the eighth switch tube S8; the collector of the first switch tube S1 is connected to the cathode of the first diode D, the collector of the third switch tube S3, and the collector of the fifth switch tube S5; the emitter of the first switch tube S1 is connected to the collector of the second switch tube S2; the emitter of the third switch tube S3 is connected to the emitter of the fourth switch tube S4; the emitter of the ninth switch tube S9 is connected to the cathode of the first diode D, the collector of the third switch tube S3, and the collector of the fifth switch tube S5; the emitter of the first switch tube S1 is connected to the collector of the second switch tube S2; the emitter of the third switch tube S3 is connected to the emitter of the fourth switch tube S4; the emitter of the ninth switch tube S9 is connected to the cathode of the tenth switch tube S 10 The collector.

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

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

[0019] The switch tubes are all equipped with anti-parallel diodes and have bidirectional current-carrying capability; the switch tubes are fully controlled 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 capacitors outputs different levels, the on-off state of each switch tube in the topology and the charging and discharging state of the capacitor are as follows:

[0021] The first working mode: 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 other switch tubes are turned off. The first diode D is turned off by the reverse voltage. At this time, the DC voltage source V dc Connected in series with the second capacitor C2 to supply power to the load, the inverter outputs +3V dc Level.

[0022] The second working mode: 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 other switch tubes are turned off. The first diode D is turned off by the reverse voltage. At this time, the DC voltage source V dc Connected in series with the first capacitor C1 to supply power to the load, the inverter outputs +2V dc level; at this time, the DC voltage source V dc Connected in series with the first capacitor C1 to charge the second capacitor C2 to 2V dc .

[0023] The third working mode: 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 other switch tubes are turned off. The first diode D is turned on by the forward voltage. At this time, the second capacitor C2 is reversely connected in 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 Connected in parallel with the first capacitor C1 to charge the first capacitor C1 to V dc .

[0024] Fourth working mode: 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 The first diode D is turned on, the other switches are turned off, and the first diode D is turned off by the reverse voltage. At this time, the inverter outputs 0 level; at this time, the DC voltage source V dc Connected in series with the first capacitor C1 to charge the second capacitor C2 to 2V dc .

[0025] The fifth working mode: 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 The other switches are turned off, and the first diode D is turned on by the forward voltage. dc To supply power to the load, the inverter outputs -Vdc level; at this time, the DC voltage source V dc Connected in parallel with the first capacitor C1 to charge the first capacitor C1 to V dc .

[0026] The sixth working mode: 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 The other switches are turned off, and the first diode D is turned off by the reverse voltage. dc Connected in series with the first capacitor C1 to supply power to the load, the inverter outputs -2V dc level; at this time, the DC voltage source V dc Connected in series with the first capacitor C1 to charge capacitor C2 to 2V dc .

[0027] The seventh working mode: 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 The other switches are turned off, and the first diode D is turned off by the reverse voltage. dc Connected in series with the second capacitor C2 to supply power to the load, the inverter outputs -3V dc Level.

[0028] Let "0" represent the switch is off, "1" represent the switch is closed, "C", "D" or "-" represent the capacitor is charged, discharged or unchanged, respectively. The switch status at each level is as follows:

[0029]

[0030] Among them, V o Represents the output voltage of the seven-level inverter based on switched capacitors.

[0031] The present invention is further described below in conjunction with specific embodiments and drawings.

[0032] Example

[0033] In this embodiment, the carrier in-phase disposition (IPD) modulation technology is used to obtain the control drive signals of 10 switch tubes. In this modulation strategy, the same amplitude A is vertically distributed from top to bottom. c , same frequency f s , 6 high-frequency carriers u1~u6 with the same phase and 1 with an amplitude of A ref Sine fundamental frequency modulation wave, modulation ratio M = A ref / 3A cEach time the modulated wave is compared with a carrier wave, the on / off state of some main control switches in the topology will be changed, causing the working mode cycle to change.

[0034] During the period when the sinusoidal 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 sinusoidal 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 sinusoidal 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 sinusoidal 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 The inverter output voltage is 0; when the sinusoidal 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 The inverter output voltage is -V dc During the period when the sinusoidal 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 Turn on, the inverter output voltage is -2V dc During the period when the sinusoidal 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 Turn on, the inverter output voltage is -3V dc ; Switching tube S1~S 10 The driving signals are all generated by logically combining the modulation wave and six carrier signals.

[0035] In order to verify the correctness and feasibility of the seven-level inverter based on switched capacitors, a simulation experiment of the seven-level inverter based on switched capacitors was designed. The following conclusions were obtained through MATLAB simulation.

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

[0037] Figure 2 To simulate the output voltage and output current waveforms of the seven-level inverter based on switched capacitor described in the experiment, the output voltage achieves seven-level AC output, the voltage gain is 3 times, and the output current is approximately a 50Hz sine wave, which is consistent with the theoretical analysis, verifying the feasibility of the structure.

[0038] Figure 3 : is the waveform of the voltage of the first capacitor C1 and the voltage of the second capacitor C2. 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 voltages can achieve self-balancing.

[0039] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A seven-level inverter based on switched capacitors, characterized in that: It includes 1 DC voltage source, 2 capacitors, 1 diode and 10 switch tubes; DC voltage source V dc The positive electrode is connected to the anode of the first diode D and the collector of the sixth switch tube S6; the DC voltage source V dc The cathode of the switch is connected to the emitter of the second switch tube S2, the emitter of the eighth switch tube S8, and the emitter of the tenth switch tube S 10 The positive electrode of the first capacitor C1 is connected to the emitter of the fifth switch tube S5; the negative electrode 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; the positive electrode 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; the negative electrode of the second capacitor C2 is connected to the emitter of the seventh switch tube S7 and the collector of the eighth switch tube S8; the collector of the first switch tube S1 is connected to the cathode of the first diode D, the collector of the third switch tube S3, and the collector of the fifth switch tube S5; the emitter of the first switch tube S1 is connected to the collector of the second switch tube S2; the emitter of the third switch tube S3 is connected to the emitter of the fourth switch tube S4; the emitter of the ninth switch tube S9 is connected to the cathode of the first diode D, the collector of the third switch tube S3, and the collector of the fifth switch tube S5; the emitter of the first switch tube S1 is connected to the collector of the second switch tube S2; the emitter of the third switch tube S3 is connected to the emitter of the fourth switch tube S4; the emitter of the ninth switch tube S9 is connected to the cathode of the tenth switch tube S 10 The collector; The positive electrode 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 electrode of the inverter output is connected to the emitter of the first switch tube S1 and the collector of the second switch tube S2; the positive electrode of the load is connected to the emitter of the ninth switch tube S9 and the collector of the tenth switch tube S 10 The negative electrode of the load is connected to the emitter of the first switch tube S1 and the collector of the second switch tube S2.

2. The seven-level inverter based on switched capacitor according to claim 1, characterized in that: When the first capacitor C1 is fully charged, the voltage on it is equal to the DC voltage source, which is V dc When the second capacitor C2 is fully charged, the voltage on it is twice that of the DC voltage source, i.e. 2V dc .

3. The seven-level inverter based on switched capacitor according to claim 1, characterized in that: The switch tubes are all equipped with anti-parallel diodes, which enable bidirectional current flow.

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

5. The seven-level inverter based on switched capacitor according to claim 1, characterized in that: When the seven-level inverter outputs different levels, the on-off state of each switch tube in the topology and the charging and discharging state of the capacitor are as follows: The first working mode: 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 other switch tubes are turned off. The first diode D is turned off by the reverse voltage. At this time, the DC voltage source V dc Connected in series with the second capacitor C2 to supply power to the load, the inverter outputs +3V dc Level; The second working mode: 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 other switch tubes are turned off. The first diode D is turned off by the reverse voltage. At this time, the DC voltage source V dc Connected in series with the first capacitor C1 to supply power to the load, the inverter outputs +2V dc level; at this time, the DC voltage source V dc Connected in series with the first capacitor C1 to charge the second capacitor C2 to 2V dc ; The third working mode: 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 other switch tubes are turned off. The first diode D is turned on by the forward voltage. At this time, the second capacitor C2 is reversely connected in 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 Connected in parallel with the first capacitor C1 to charge the first capacitor C1 to V dc ; Fourth working mode: 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 The first diode D is turned on, the other switches are turned off, and the first diode D is turned off by the reverse voltage. At this time, the inverter outputs 0 level. At this time, the DC voltage source V dc Connected in series with the first capacitor C1 to charge the second capacitor C2 to 2V dc ; The fifth working mode: 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 The other switches are turned on, and the first diode D is turned on by the forward voltage. At this time, the DC voltage source V dc To supply power to the load, the inverter outputs -V dc level; at this time, the DC voltage source V dc Connected in parallel with the first capacitor C1 to charge the first capacitor C1 to V dc ; The sixth working mode: 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 The other switches are turned on, and the first diode D is turned off by the reverse voltage. At this time, the DC voltage source V dc Connected in series with the first capacitor C1 to supply power to the load, the inverter outputs -2V dc level; at this time, the DC voltage source V dc Connected in series with the first capacitor C1 to charge capacitor C2 to 2V dc ; The seventh working mode: 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 The other switches are turned on, and the first diode D is turned off by the reverse voltage. At this time, the DC voltage source V dc Connected in series with the second capacitor C2 to supply power to the load, the inverter outputs -3V dc Level.

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