A common ground type switched capacitor multi-level inverter with reduced capacitance

Abstract

The present invention belongs to the technical field of power converters, and discloses a common ground type switch capacitor multi-level inverter capable of reducing capacitance. The present invention comprises a DC input terminal, a multi-level AC output terminal, a power switch tube S1, a power switch tube S2, a power switch tube S3, a power switch tube S4, a power switch tube S5, a power switch tube S6, a power switch tube S7, a diode D1, a diode D2, a capacitor C1, and a capacitor C2; a sinusoidal pulse width modulation method is adopted to control each power switch tube and capacitor, and capacitors C1 and C2 are alternately charged and discharged according to the pulse width modulation frequency, and the capacitor voltage ripple is inversely proportional to the switching frequency, and the capacitance value of the capacitor can be reduced by increasing the switching frequency. The present invention can solve the leakage current problem in the photovoltaic system, shorten the capacitor discharge time, reduce the inverter volume, and has high power density and reliability.

Description

Technical Field

[0001] The invention belongs to the technical field of power converters, and in particular relates to a common ground type switched capacitor multi-level inverter capable of reducing capacitance. Background Art

[0002] The switched capacitor multi-level inverter has a flexible structure and has many combinations of capacitors and switches. It has a strong boost capability and often only requires a DC voltage source to achieve boost. The multi-level output can reduce THD and improve power quality. It is widely used in electric vehicles, renewable energy generation, microgrids, distributed generation, etc.

[0003] At the same time, in the application of photovoltaic power generation systems, the common ground type switched capacitor multi-level inverter can eliminate the leakage current caused by stray capacitance, improve the overall efficiency of the system, and avoid safety accidents caused by leakage current.

[0004] The capacitors in the common ground type switched capacitor multi-level inverter often need to be discharged continuously for a long time during operation. In order to reduce the capacitor ripple and improve the output voltage quality, large capacitors (above millifarad level) need to be used. Such large capacitors need to be electrolytic capacitors, but such capacitors have a short life and large size, which will seriously affect the power density. Therefore, how to reduce the capacitance of the capacitor is a key issue to improve the performance of the common ground type switched capacitor multi-level inverter. Summary of the invention

[0005] The purpose of the present invention is to provide a common ground type switched capacitor multi-level inverter with reduced capacitance to address the deficiencies of the prior art, thereby solving the leakage current problem in the photovoltaic system, shortening the capacitor discharge time, reducing the inverter size, and having higher power density and reliability.

[0006] Specifically, the present invention is implemented by adopting the following technical solutions.

[0007] The present invention provides a common ground type switch capacitor multi-level inverter capable of reducing capacitance, comprising a DC input terminal, a multi-level AC output port , power switch tube , power switch tube , power switch tube , power switch tube , power switch tube , power switch tube , power switch tube ,diode ,diode ,capacitance ,capacitance ;

[0008] The positive end of the DC input terminal and the power switch tube The first end of the power switch tube The negative end of the DC input terminal and the power switch tube The second end of the power switch tube The second end of the diode The second end, multi-level AC output port The negative end of the DC input terminal is grounded; the power switch tube The second end and the power switch tube The first end of the capacitor The first end of the capacitor is connected; The second end of the diode The first end of the power switch tube The first end of the power switch tube is connected to The second end of the diode The first end of the power switch tube is connected to The first end and the power switch tube The first end of the diode The second end of the capacitor The first end of the power switch tube is connected to The second end and the power switch tube The second end of the capacitor The second end of the power switch tube is connected; The second end and the power switch tube The first end, multi-level AC output port is connected to a first end of

[0009] The on and off of each power switch tube is controlled by sinusoidal pulse width modulation.

[0010] Furthermore, the output voltage of the common-ground type switched capacitor multi-level inverter capable of reducing capacitance has five voltage levels, namely, zero level, positive level 1, positive level 2, negative level 1, and negative level 2;

[0011] Among them, the zero level is 0V and the positive level is , the positive second level is , the negative level is , the negative second level is , is the voltage at the DC input terminal.

[0012] Further, the zero level has two working modes, which are switched when the positive and negative cycles of each sinusoidal pulse are switched;

[0013] In the first working mode, the power switch tube , , and the diode The power switch tube is turned on; , , , and the diode Disconnect; the capacitor Charging; Capacitor Hanging;

[0014] In the second working mode, the power switch tube , , and the diode The power switch tube is turned on; , , , and the diode Disconnect; the capacitor Charging; Capacitor Hanging.

[0015] Furthermore, when the output voltage is at a positive level, the power switch tube , , , and the diode The power switch tube is turned on; , , and diode Disconnect; Capacitor Charging; Capacitor Discharge; connect capacitor in series with DC input , to the capacitor Charge to , while giving the load powered by;

[0016] When the output voltage is at the positive second level, the power switch tube , , and the diode The power switch tube is turned on; , , , and the diode Disconnect; the capacitor Charging; the capacitor Discharge; the DC input terminal and the capacitor In parallel, give capacitor Charge to ,capacitance Give load powered by;

[0017] When the output voltage is at a negative level, the power switch tube , , , and diode The power switch tube is turned on; , , and diode Disconnect; the capacitor Charging; the capacitor Discharge; Capacitor Connect the DC input terminal in series to the capacitor Charge to , while giving the load powered by;

[0018] When the output voltage is at the negative second level, the power switch tube , , and the diode The power switch tube is turned on; , , , and the diode Disconnect; the capacitor Charging; the capacitor Discharge; DC input terminal and capacitor In parallel, give capacitor Charge to ,capacitance Give load powered by.

[0019] Furthermore, the capacitor The calculation formula of capacitance is

[0020] ;

[0021] capacitance The calculation formula of capacitance is

[0022] ;

[0023] in, is the output current The maximum value of is the DC input voltage, is the maximum allowed capacitor voltage ripple ratio, is the switching frequency.

[0024] Furthermore, the common-ground type switched capacitor multi-level inverter capable of reducing capacitance further includes a switched capacitor unit;

[0025] The switch capacitor unit includes port 1', port 2', port 3', port 4', a power switch tube , power switch tube , power switch tube , power switch tube , power switch tube ,capacitance The port 1' and the power switch tube The first end of the capacitor The first end of the diode The second end of the power switch tube The first end is connected to the port 2' and the power switch tube The second end of the capacitor The second end of the power switch tube The second end of the power switch tube is connected; The second end and the power switch tube The first end of the power switch tube The second end of the power switch tube is connected; The first end and the power switch tube The second end of the power switch tube The first end of the power switch tube is connected to The first end and the capacitor The first end, the port 3', the power switch tube The first end of the power switch tube is connected to The second end and the capacitor The second end, the port 4', the power switch tube The second end is connected.

[0026] Furthermore, the output voltage of the common-ground type switched capacitor multi-level inverter capable of reducing capacitance has seven voltage levels, namely, zero level, positive level 1, positive level 2, positive level 3, negative level 1, negative level 2, and negative level 3;

[0027] Among them, the zero level is 0V and the positive level is , the positive second level is , positive three-level is , the negative level is , the negative second level is , negative three-level , is the voltage at the DC input terminal;

[0028] The zero level has two working modes, which are switched when the positive and negative cycles of each sinusoidal pulse are switched;

[0029] In the first working mode, the power switch tube , , , , , , and the diode The power switch is turned on. , , , , and the diode Disconnect; the capacitor Charging; Capacitor , Hanging;

[0030] In the second working mode, the power switch tube , , , , , , and the diode The power switch tube is turned on; , , , , and the diode disconnect, the capacitor Charging; Capacitor , Hanging.

[0031] Furthermore, when the output voltage is at a positive level, the power switch tube , , , , , , , and the diode The power switch is turned on. , , , and diode Disconnect; the capacitor Charging; the capacitor Charging; the capacitor Discharge; connect capacitor in series with DC input , to the capacitor , Charge to , while giving the load powered by;

[0032] When the output voltage is at the positive second level, the power switch tube , , , , , , and the diode The power switch is turned on. , , , , and the diode Disconnect; the capacitor Charging; the capacitor Charging; the capacitor Discharge; the DC input terminal and the capacitor In parallel, give capacitor Charge to ,capacitance With capacitor Connect to load in parallel powered by;

[0033] When the output voltage is positive three-level, the power switch tube , , , , , , and the diode The power switch is turned on. , , , , and the diode Disconnect; the capacitor Charging; the capacitor Discharge; the capacitor Discharge; connect capacitor in series with DC input , to the capacitor Charge to , DC input terminal and capacitor Connect in series to the load powered by;

[0034] When the output voltage is at a negative level, the power switch tube , , , , , , , and the diode The power switch is turned on. , , , and the diode Disconnect; the capacitor Charging; the capacitor Charging; the capacitor Discharge; Capacitor Connect the DC input terminal in series to the capacitor , Charge to , while giving the load powered by;

[0035] When the output voltage is at the negative second level, the power switch tube , , , , , , and the diode The power switch is turned on. , , , , and the diode Disconnect; the capacitor Charging; the capacitor Charging; the capacitor Discharge; DC input terminal and capacitor In parallel, give capacitor Charge to ,capacitance With capacitor Connect to load in parallel powered by;

[0036] When the output voltage is negative three-level, the power switch tube , , , , , , and the diode The power switch is turned on. , , , , and the diode Disconnect; the capacitor Charging; the capacitor Discharge; the capacitor Discharge; connect capacitor in series with DC input , to the capacitor Charge to , DC input terminal and capacitor Connect in series to the load powered by.

[0037] Furthermore, the common-ground type switched capacitor multi-level inverter capable of reducing capacitance value further includes a switched capacitor unit;

[0038] The switch capacitor unit includes port 1', port 2', port 3', port 4', a power switch tube , power switch tube , power switch tube , power switch tube , power switch tube , power switch tube ,capacitance The port 1' and the power switch tube The first end of the power switch tube The first end of the capacitor The first end of the diode The second end of the power switch tube The first end is connected to the port 2' and the power switch tube The first end of the power switch tube The second end of the power switch tube is connected; The second end and the power switch tube The second end of the power switch tube is connected; The second end and the power switch tube The second end of the power switch tube is connected; The second end and the power switch tube The first end of the capacitor The second end, port 4', the power switch tube The second end of the power switch tube is connected; The first end and the power switch tube The first end of the capacitor The first end, the port 3', the power switch tube is connected to the first end.

[0039] Furthermore, the output voltage of the common-ground type switched capacitor multi-level inverter capable of reducing capacitance has seven voltage levels, namely, zero level, positive level 1, positive level 2, positive level 3, negative level 1, negative level 2, and negative level 3;

[0040] Among them, the zero level is 0V and the positive level is , the positive second level is , positive three-level is , the negative level is , the negative second level is , negative three-level , is the voltage at the DC input terminal;

[0041] The zero level has two working modes, which are switched when the positive and negative cycles of each sinusoidal pulse are switched;

[0042] In the first working mode, the power switch tube , , , , , , and the diode The power switch tube is turned on; , , , , , and the diode Disconnect; the capacitor Charging; Capacitor , Hanging;

[0043] In the second working mode, the power switch tube , , , , , , and the diode The power switch tube is turned on; , , , , , and the diode Disconnect; the capacitor Charging capacitor , Hanging.

[0044] Furthermore, when the output voltage is at a positive level, the power switch tube , , , , , , , and the diode The power switch is turned on. , , , , and the diode Disconnect; the capacitor Charging; the capacitor Charging; the capacitor Discharge; connect capacitor in series with DC input , to the capacitor , Charge to , while giving the load powered by;

[0045] When the output voltage is at the positive second level, the power switch tube , , , , , , and the diode The power switch is turned on. , , , , and the diode Disconnect; the capacitor Charging; the capacitor Charging; the capacitor Discharge; the DC input terminal and the capacitor In parallel, give capacitor Charge to ,capacitance With capacitor Connect to load in parallel powered by;

[0046] When the output voltage is positive three-level, the power switch tube , , , , and the diode The power switch is turned on. , , , , , , , and the diode Disconnect; the capacitor Charging; the capacitor Discharge; the capacitor Discharge; connect capacitor in series with DC input , to the capacitor Charge to , DC input terminal and capacitor Connect in series to the load powered by;

[0047] When the output voltage is at a negative level, the power switch tube , , , , , , , and the diode The power switch is turned on. , , , , and the diode Disconnect; the capacitor Charging; the capacitor Charging; the capacitor Discharge; Capacitor Connect the DC input terminal in series to the capacitor , Charge to , while giving the load powered by;

[0048] When the output voltage is at the negative second level, the power switch tube , , , , , , and the diode The power switch is turned on. , , , , , and the diode Disconnect; the capacitor Charging; the capacitor Charging; the capacitor Discharge; DC input terminal and capacitor In parallel, give capacitor Charge to ,capacitance With capacitor Connect to load in parallel powered by;

[0049] When the output voltage is negative three-level, the power switch tube , , , , and the diode The power switch is turned on. , , , , , , , and the diode Disconnect; the capacitor Charging; the capacitor Discharge; the capacitor Discharge; connect capacitor in series with DC input , to the capacitor Charge to , DC input terminal and capacitor Connect in series to the load powered by.

[0050] The beneficial effects of the common-ground type switched capacitor multi-level inverter capable of reducing capacitance of the present invention are as follows:

[0051] In the common ground type switched capacitor multi-level inverter capable of reducing capacitance of the present invention, the capacitor ,capacitance The capacitor voltage ripple is inversely proportional to the switching frequency by alternately charging and discharging at the pulse width modulation frequency. By increasing the switching frequency, the capacitance value of the capacitor can be reduced, thereby improving the power density and reliability of the multi-level inverter.

[0052] The capacitance-reducing common-ground type switched capacitor multi-level inverter of the present invention can not only solve the leakage current problem in the photovoltaic system, but also avoid the long-term capacitor discharge problem of the previous common-ground type switched capacitor inverter, thereby shortening the capacitor discharge time.

[0053] The capacitance-reducing common-ground switching capacitor multi-level inverter of the present invention selects and uses a plurality of smaller chip capacitors in parallel, which reduces the size of the inverter and improves the life and power density of the inverter compared to using electrolytic capacitors.

[0054] The common ground type switched capacitor multi-level inverter capable of reducing capacitance of the present invention has an experimental prototype manufactured and experiments have been carried out, and the experimental results all show that the common ground type switched capacitor multi-level inverter can work normally and discharge the load. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 It is a circuit diagram of embodiment 1 of the present invention.

[0056] Figure 2 Schematic diagram of output waveform under sinusoidal pulse width modulation mode of an embodiment of the present invention.

[0057] Figure 3 It is a schematic diagram of a first working mode in which the output voltage of Embodiment 1 of the present invention is at zero level.

[0058] Figure 4 It is a schematic diagram of the second working mode in which the output voltage of the embodiment 1 of the present invention is zero level.

[0059] Figure 5 1 is a schematic diagram of a working mode in which the output voltage of Embodiment 1 of the present invention is at a positive level.

[0060] Figure 6 1 is a schematic diagram of a working mode in which the output voltage of Embodiment 1 of the present invention is a positive two-level output voltage.

[0061] Figure 7 1 is a schematic diagram of a working mode in which the output voltage of Embodiment 1 of the present invention is at a negative level.

[0062] Figure 8 1 is a schematic diagram of a working mode in which the output voltage of Embodiment 1 of the present invention is a negative second level.

[0063] Fig. 9 3 is a waveform diagram of the capacitor voltage waveform of Example 1 of the present invention.

[0064] Fig.10 4 is a waveform diagram of the output voltage waveform of Example 1 of the present invention.

[0065] Fig.11 1 is a waveform diagram of the experimental results under resistive load conditions displayed on the oscilloscope of Example 1 of the present invention.

[0066] Fig.12 It is a circuit diagram of embodiment 2 of the present invention. DETAILED DESCRIPTION

[0067] The present invention is further described in detail below in conjunction with embodiments and with reference to the accompanying drawings.

[0068] Embodiment 1:

[0069] One embodiment of the present invention is a common ground type switched capacitor multi-level inverter capable of reducing capacitance, such as Figure 1 As shown, it includes a DC input port and a multi-level AC output port , power switch tube , power switch tube , power switch tube , power switch tube , power switch tube , power switch tube , power switch tube ,diode ,diode ,capacitance ,capacitance .

[0070] The positive terminal of the DC input terminal and the power switch tube The first end of the power switch tube The negative end of the DC input terminal and the power switch tube The second end of the power switch tube The second end of the diode The second end, multi-level AC output port The negative end of the DC input terminal is grounded; the power switch tube The second end and the power switch tube The first end of the capacitor The first end of the capacitor is connected; The second end of the diode The first end of the power switch tube The first end of the power switch tube is connected to The second end of the diode The first end of the power switch tube is connected to The first end and the power switch tube The first end of the diode The second end of the capacitor The first end of the power switch tube is connected to The second end and the power switch tube The second end of the capacitor The second end of the power switch tube is connected; The second end and the power switch tube The first end, multi-level AC output port is connected to the first end.

[0071] Preferably, the power switch tube , power switch tube , power switch tube , power switch tube , power switch tube , power switch tube , power switch tube It is a fully controlled power switch device. Preferably, the inverter is selected to use multiple smaller chip capacitors in parallel, for example, chip capacitors of model FE2HX475M251LGL and C5750X6S2W225M250KA can be used. Compared with the use of electrolytic capacitors, this reduces the size of the inverter and increases the life and power density of the inverter.

[0072] Preferably, in another embodiment, the common-ground type switched capacitor multi-level inverter with reduced capacitance of the present invention uses a sinusoidal pulse width modulation method to control the on and off of each power switch tube. The output waveform of the common-ground type switched capacitor multi-level inverter with reduced capacitance of the present invention under the sinusoidal pulse width modulation method is as follows: Figure 2 shown.

[0073] The multi-level AC output port of the common-ground type switched capacitor multi-level inverter capable of reducing capacitance of the present embodiment The output voltage ( ) has five voltage levels, namely zero level (0V), positive level ( )、positive second level( )、Negative level( )、Negative second level( ), is the input DC voltage.

[0074] When the output voltage is at zero level, the common ground type switched capacitor multi-level inverter with reduced capacitance has two working modes, which are switched when the positive and negative cycles of each sinusoidal pulse are switched. In the first working mode, Figure 3 As shown, the power switch tube , , and diode Turn on; power switch tube , , , and diode Disconnect; Capacitor Charging. The DC input voltage is . DC power supply and capacitor In parallel, give capacitor Charge to ,capacitance Floating, capacitor Neither charging nor discharging, the power switch tube , Form a closed loop for the load Provides a freewheeling path to achieve zero-level output. In the second working mode, Figure 4 As shown, the power switch tube , , and diode Turn on; power switch tube , , , and diode Disconnect; Capacitor Charging. The DC power supply voltage is . DC power supply and capacitor In parallel, give capacitor Charge to ,capacitance Floating, capacitor Neither charging nor discharging, the power switch tube , and diode Form a closed loop for the load Provides a freewheeling path to achieve zero-level output.

[0075] When the output voltage is positive, Figure 5 As shown, the power switch tube , , , and diode Turn on; power switch tube , , and diode Disconnect; Capacitor Charging; Capacitor Discharge. Connect capacitor in series with DC input terminal , to the capacitor Charge to , while giving the load Power supply to achieve positive level output.

[0076] When the output voltage is positive level, Figure 6 As shown, the power switch tube , , diode Turn on; power switch tube , , , and diode Disconnect; Capacitor Charging; Capacitor Discharge. DC input terminal and capacitor In parallel, give capacitor Charge to ,capacitance Give load Power supply to achieve positive two-level output.

[0077] When the output voltage is negative one level, Figure 7 As shown, the power switch tube , , , and diode Turn on; power switch tube , , and diode Disconnect; Capacitor Charging; Capacitor Discharge. Capacitor Connect the DC input terminal in series to the capacitor Charge to , while giving the load Power supply to achieve negative level output.

[0078] When the output voltage is negative two levels, such as Figure 8 As shown, the power switch tube , , and the diode The power switch tube is turned on; , , , and the diode Disconnect; the capacitor Charging; the capacitor Discharge. DC input terminal and capacitor In parallel, give capacitor Charge to ,capacitance Give load Power supply to achieve negative second level output.

[0079] Table 1 gives Figure 1The common ground type switch capacitor multi-level inverter with reduced capacitance in the present invention can reduce the capacitance of the power switch tube and the diode when working at different levels, and the charging and discharging of the capacitor, so that each capacitor will not be discharged for a long time. The capacitors in the common ground type switch capacitor multi-level inverter with reduced capacitance of the present invention can be charged and discharged alternately according to the pulse width modulation frequency, and the capacitor voltage ripple is inversely proportional to the switching frequency. The capacitance of the capacitor can be reduced by increasing the switching frequency. The present invention can not only solve the leakage current problem in the photovoltaic system, but also avoid the problem of long-term discharge of the capacitor in the previous common ground type switch capacitor inverter, and shorten the capacitor discharge time.

[0080] Table 1 The on-off of the power switch tube and the diode and the charging and discharging of the capacitor when the embodiment 1 works at different levels

[0081]

[0082] capacitance The calculation formula of the capacitance value can be expressed as:

[0083] ;

[0084] capacitance The calculation formula of the capacitance value can be expressed as:

[0085] ;

[0086] In the above two formulas, is the output current The maximum value of is the DC input voltage, is the maximum allowed capacitor voltage ripple ratio, is the switching frequency.

[0087] The results obtained by PSIM simulation are as follows: Fig. 9 and Fig.10 shown. Fig. 9 is the capacitor voltage waveform, the capacitor ripple ratio is maintained within 5%, and the capacitor voltage is not powered off for a long time, which verifies that the capacitor ripple and capacitor capacitance of the common ground type switched capacitor multi-level inverter that can reduce the capacitance value of this embodiment can be reduced. Fig. 9 Medium V C1 is the voltage of capacitor C1, V C2 is the voltage of capacitor C2. Fig.10 is the output voltage waveform, the RMS value of the output voltage V orms The output voltage is 220V and the output frequency is 50Hz, which is consistent with the theoretical analysis, verifying the feasibility of the common-ground switched capacitor multi-level inverter with reduced capacitance in this embodiment.

[0088] Table 2 Experimental prototype working conditions

[0089]

[0090] The experimental prototype was made using the working conditions in Table 2. The experimental results obtained using the prototype are as follows: Fig.11 shown. Fig.11 The experimental prototype multi-level AC output port is shown The output voltage ( )、Current( ) and the capacitor voltage (V C1 、V C2 ). Fig.11 Medium output voltage The root mean square Vorms is 220V, the output frequency The frequency is 50Hz, and the capacitor voltage ripple is maintained within 5%, which is consistent with the theoretical analysis and verifies the feasibility of the structure.

[0091] Embodiment 2:

[0092] Fig.12 Another embodiment of the present invention is given. Figure 1 The common-ground type switched capacitor multi-level inverter with reduced capacitance in Example 1 is obtained by adding an extended structure, and two examples using switched capacitor units as extended structures are given. The switched capacitor unit of Example 1 or the switched capacitor unit of Example 2 can be used.

[0093] The switch capacitor unit of Example 1 includes: port 1', port 2', port 3', port 4', power switch tube , power switch tube , power switch tube , power switch tube , power switch tube ,capacitance . Port 1' and the power switch tube The first end of the capacitor The first end of the diode The second end of the power switch tube The first end is connected to the port 2' and the power switch tube The second end of the capacitor The second end of the power switch tube The second end of the power switch tube is connected; The second end and the power switch tube The first end of the power switch tube The second end of the power switch tube is connected; The first end and the power switch tube The second end of the power switch tube The first end of the power switch tube is connected to The first end and the capacitor The first end, the port 3', the power switch tube The first end of the power switch tube is connected to The second end and the capacitor The second end, the port 4', the power switch tube The second end is connected.

[0094] The switch capacitor unit of Example 2 includes: port 1', port 2', port 3', port 4', power switch tube , power switch tube , power switch tube , power switch tube , power switch tube , power switch tube ,capacitance The port 1' and the power switch tube The first end of the power switch tube The first end of the capacitor The first end of the diode The second end of the power switch tube The first end is connected to the port 2' and the power switch tube The first end of the power switch tube The second end of the power switch tube is connected; The second end and the power switch tube The second end of the power switch tube is connected; The second end and the power switch tube The second end of the power switch tube is connected; The second end and the power switch tube The first end of the capacitor The second end, port 4', the power switch tube The second end of the power switch tube is connected; The first end and the power switch tube The first end of the capacitor The first end, the port 3', the power switch tube is connected to the first end.

[0095] Compared with the original five-level inverter, the common-ground type switched capacitor multi-level inverter circuit structure of Example 2 with reduced capacitance obtained by using the switched capacitor unit shown in Example 1 or the switched capacitor unit shown in Example 2 has an output voltage with two more voltage levels, namely, positive three levels ( ) and negative three-level (- Table 3 gives Fig.11 The extended structure of the common ground type switched capacitor multi-level inverter with reduced capacitance in the embodiment of the present invention is the opening condition of the power switch tube and the diode and the charging and discharging condition of the capacitor when working at different levels. The circuit structure can still realize that each capacitor is alternately charged and discharged according to the pulse width modulation frequency, and the capacitor voltage ripple is inversely proportional to the switching frequency. By increasing the switching frequency, the capacitance of the capacitor can be reduced.

[0096] Table 3 The on-off of the power switch tube and the diode and the charging and discharging of the capacitor when Example 2 works at different power levels

[0097]

[0098] When the common-ground type switched capacitor multi-level inverter capable of reducing capacitance adopts the switched capacitor unit of Example 1, the zero level has two working modes, which are switched when the positive and negative cycles of each sinusoidal pulse are switched;

[0099] In the first working mode, the power switch tube , , , , , , and the diode The power switch is turned on. , , , , and the diode Disconnect; the capacitor Charging; Capacitor , Hanging;

[0100] In the second working mode, the power switch tube , , , , , , and the diode The power switch tube is turned on; , , , , and the diode disconnect, the capacitor Charging; Capacitor , Hanging.

[0101] When the output voltage is at a positive level, the power switch tube , , , , , , , and the diode The power switch is turned on. , , , and diode Disconnect; the capacitor Charging; the capacitor Charging; the capacitor Discharge; connect capacitor in series with DC input , to the capacitor , Charge to , while giving the load powered by;

[0102] When the output voltage is at the positive second level, the power switch tube , , , , , , and the diode The power switch is turned on. , , , , and the diode Disconnect; the capacitor Charging; the capacitor Charging; the capacitor Discharge; the DC input terminal and the capacitor In parallel, give capacitor Charge to ,capacitance With capacitor Connect to load in parallel powered by;

[0103] When the output voltage is positive three-level, the power switch tube , , , , , , and the diode The power switch is turned on. , , , , and the diode Disconnect; the capacitor Charging; the capacitor Discharge; the capacitor Discharge; connect capacitor in series with DC input , to the capacitor Charge to , DC input terminal and capacitor Connect in series to the load powered by;

[0104] When the output voltage is negative one level, the power switch tube , , , , , , , and the diode The power switch is turned on. , , , and the diode Disconnect; the capacitor Charging; the capacitor Charging; the capacitor Discharge; Capacitor Connect the DC input terminal in series to the capacitor , Charge to , while giving the load powered by;

[0105] When the output voltage is at the negative second level, the power switch tube , , , , , , and the diode The power switch is turned on. , , , , and the diode Disconnect; the capacitor Charging; the capacitor Charging; the capacitor Discharge; DC input terminal and capacitor In parallel, give capacitor Charge to ,capacitance With capacitor Connect to load in parallel powered by.

[0106] When the output voltage is negative three-level, the power switch tube , , , , , , and the diode The power switch is turned on. , , , , and the diode Disconnect; the capacitor Charging; the capacitor Discharge; the capacitor Discharge; connect capacitor in series with DC input , to the capacitor Charge to , DC input terminal and capacitor Connect in series to the load powered by.

[0107] When the common-ground type switched capacitor multi-level inverter capable of reducing capacitance adopts the switched capacitor unit of Example 2, the zero level has two working modes, which are switched when the positive and negative cycles of each sinusoidal pulse are switched;

[0108] In the first working mode, the power switch tube , , , , , , and the diode The power switch tube is turned on; , , , , , and the diode Disconnect; the capacitor Charging; Capacitor , Hanging;

[0109] In the second working mode, the power switch tube , , , , , , and the diode The power switch tube is turned on; , , , , , and the diode Disconnect; the capacitor Charging capacitor , Hanging.

[0110] When the output voltage is at a positive level, the power switch tube , , , , , , , and the diode The power switch is turned on. , , , , and the diode Disconnect; the capacitor Charging; the capacitor Charging; the capacitor Discharge; connect capacitor in series with DC input , to the capacitor , Charge to , while giving the load powered by;

[0111] When the output voltage is at the positive second level, the power switch tube , , , , , , and the diode The power switch is turned on. , , , , and the diode Disconnect; the capacitor Charging; the capacitor Charging; the capacitor Discharge; the DC input terminal and the capacitor In parallel, give capacitor Charge to ,capacitance With capacitor Connect to load in parallel powered by;

[0112] When the output voltage is positive three-level, the power switch tube , , , , and the diode The power switch is turned on. , , , , , , , and the diode Disconnect; the capacitor Charging; the capacitor Discharge; the capacitor Discharge; connect capacitor in series with DC input , to the capacitor Charge to , DC input terminal and capacitor Connect in series to the load powered by;

[0113] When the output voltage is negative one level, the power switch tube , , , , , , , and the diode The power switch is turned on. , , , , and the diode Disconnect; the capacitor Charging; the capacitor Charging; the capacitor Discharge; Capacitor Connect the DC input terminal in series to the capacitor , Charge to , while giving the load powered by;

[0114] When the output voltage is at the negative second level, the power switch tube , , , , , , and the diode The power switch is turned on. , , , , , and the diode Disconnect; the capacitor Charging; the capacitor Charging; the capacitor Discharge; DC input terminal and capacitor In parallel, give capacitor Charge to ,capacitance With capacitor Connect to load in parallel powered by.

[0115] When the output voltage is negative three-level, the power switch tube , , , , and the diode The power switch is turned on. , , , , , , , and the diode Disconnect; the capacitor Charging; the capacitor Discharge; the capacitor Discharge; connect capacitor in series with DC input , to the capacitor Charge to , DC input terminal and capacitor Connect in series to the load powered by

[0116] In the common ground type switched capacitor multi-level inverter capable of reducing capacitance of the present invention, the capacitor ,capacitance The capacitor voltage ripple is inversely proportional to the switching frequency by alternately charging and discharging at the pulse width modulation frequency. By increasing the switching frequency, the capacitance value of the capacitor can be reduced, thereby improving the power density and reliability of the multi-level inverter.

[0117] The capacitance-reducing common-ground type switched capacitor multi-level inverter of the present invention can not only solve the leakage current problem in the photovoltaic system, but also avoid the long-term capacitor discharge problem of the previous common-ground type switched capacitor inverter, thereby shortening the capacitor discharge time.

[0118] The capacitance-reducing common-ground switching capacitor multi-level inverter of the present invention selects and uses a plurality of smaller chip capacitors in parallel, which reduces the size of the inverter and improves the life and power density of the inverter compared to using electrolytic capacitors.

[0119] The common ground type switched capacitor multi-level inverter capable of reducing capacitance of the present invention has an experimental prototype manufactured and experiments have been carried out, and the experimental results all show that the common ground type switched capacitor multi-level inverter can work normally and discharge the load.

Claims

1. A common ground type switched capacitor multi-level inverter capable of reducing capacitance, characterized in that: Including DC input port, multi-level AC output port , power switch tube , power switch tube , power switch tube , power switch tube , power switch tube , power switch tube , power switch tube ,diode ,diode ,capacitance ,capacitance ; The positive end of the DC input terminal and the power switch tube The first end of the power switch tube The negative end of the DC input terminal and the power switch tube The second end of the power switch tube The second end of the diode The second end, multi-level AC output port The negative end of the DC input terminal is grounded; the power switch tube The second end and the power switch tube The first end of the capacitor The first end of the capacitor is connected; The second end of the diode The first end of the power switch tube The first end of the power switch tube is connected to The second end of the diode The first end of the power switch tube is connected to The first end and the power switch tube The first end of the diode The second end of the capacitor The first end of the power switch tube is connected to The second end and the power switch tube The second end of the capacitor The second end of the power switch tube is connected; The second end and the power switch tube The first end, multi-level AC output port The first end of the diode is connected; ,diode The first end of the diode is the anode. ,diode The second end is a cathode; The on and off of each power switch tube is controlled by sinusoidal pulse width modulation.

2. The common ground type switched capacitor multi-level inverter capable of reducing capacitance according to claim 1, characterized in that: Its output voltage has five voltage levels, namely zero level, positive level 1, positive level 2, negative level 1, and negative level 2; Among them, the zero level is 0V and the positive level is , the positive second level is , the negative level is , the negative second level is , is the voltage at the DC input terminal.

3. The common ground type switched capacitor multi-level inverter capable of reducing capacitance according to claim 2, characterized in that: The zero level has two working modes, which are switched when the positive and negative cycles of each sinusoidal pulse are switched; In the first working mode, the power switch tube , , and the diode The power switch tube is turned on; , , , and the diode Disconnect; the capacitor Charging; Capacitor Hanging; In the second working mode, the power switch tube , , and the diode The power switch tube is turned on; , , , and the diode Disconnect; the capacitor Charging; Capacitor Hanging.

4. The common ground type switched capacitor multi-level inverter capable of reducing capacitance according to claim 2, characterized in that: When the output voltage is at a positive level, the power switch tube , , , and the diode The power switch tube is turned on; , , and diode Disconnect; Capacitor Charging; Capacitor Discharge; connect capacitor in series with DC input , to the capacitor Charge to , while giving the load powered by; When the output voltage is at the positive second level, the power switch tube , , and the diode The power switch tube is turned on; , , , and the diode Disconnect; the capacitor Charging; the capacitor Discharge; the DC input terminal and the capacitor In parallel, give capacitor Charge to ,capacitance Give load powered by; When the output voltage is at a negative level, the power switch tube , , , and diode The power switch tube is turned on; , , and diode Disconnect; the capacitor Charging; the capacitor Discharge; Capacitor Connect the DC input terminal in series to the capacitor Charge to , while giving the load powered by; When the output voltage is at the negative second level, the power switch tube , , and the diode The power switch tube is turned on; , , , and the diode Disconnect; the capacitor Charging; the capacitor Discharge; DC input terminal and capacitor In parallel, give capacitor Charge to ,capacitance Give load powered by.

5. The common-ground type switched capacitor multi-level inverter capable of reducing capacitance according to any one of claims 1 to 4, characterized in that: capacitance The calculation formula of capacitance is ； capacitance The calculation formula of capacitance is ； in, is the output current of the common-ground type switched capacitor multi-level inverter capable of reducing capacitance The maximum value of is the DC input voltage, is the maximum allowed capacitor voltage ripple ratio, is the switching frequency.

6. The common ground type switched capacitor multi-level inverter capable of reducing capacitance according to claim 1, characterized in that: Also included is a switched capacitor unit; The switch capacitor unit includes port 1', port 2', port 3', port 4', a power switch tube , power switch tube , power switch tube , power switch tube , power switch tube ,capacitance The port 1' and the power switch tube The first end of the capacitor The first end of the diode The second end of the power switch tube The first end is connected to the port 2' and the power switch tube The second end of the capacitor The second end of the power switch tube The second end of the power switch tube is connected; The second end and the power switch tube The first end of the power switch tube The second end of the power switch tube is connected; The first end and the power switch tube The second end of the power switch tube The first end of the power switch tube is connected to The first end and the capacitor The first end, the port 3', the power switch tube The first end of the power switch tube is connected to The second end and the capacitor The second end, the port 4', the power switch tube The second end is connected.

7. The common ground type switched capacitor multi-level inverter capable of reducing capacitance according to claim 6, characterized in that: Its output voltage has seven voltage levels, namely zero level, positive level 1, positive level 2, positive level 3, negative level 1, negative level 2, and negative level 3; Among them, the zero level is 0V and the positive level is , the positive second level is , positive three-level is , the negative level is , the negative second level is , negative three-level , is the voltage at the DC input terminal; The zero level has two working modes, which are switched when the positive and negative cycles of each sinusoidal pulse are switched; In the first working mode, the power switch tube , , , , , , and the diode The power switch is turned on. , , , , and the diode Disconnect; the capacitor Charging; Capacitor , Hanging; In the second working mode, the power switch tube , , , , , , and the diode The power switch tube is turned on; , , , , and the diode disconnect, the capacitor Charging; Capacitor , Hanging.

8. The common ground type switched capacitor multi-level inverter capable of reducing capacitance according to any one of claims 6 or 7, characterized in that: When the output voltage is at a positive level, the power switch tube , , , , , , , and the diode The power switch is turned on. , , , and diode Disconnect; the capacitor Charging; the capacitor Charging; the capacitor Discharge; connect capacitor in series with DC input , to the capacitor , Charge to , while giving the load powered by; When the output voltage is at the positive second level, the power switch tube , , , , , , and the diode The power switch is turned on. , , , , and the diode Disconnect; the capacitor Charging; the capacitor Charging; the capacitor Discharge; the DC input terminal and the capacitor In parallel, give capacitor Charge to ,capacitance With capacitor Connect to load in parallel powered by; When the output voltage is positive three-level, the power switch tube , , , , , , and the diode The power switch is turned on. , , , , and the diode Disconnect; the capacitor Charging; the capacitor Discharge; the capacitor Discharge; connect capacitor in series with DC input , to the capacitor Charge to , DC input terminal and capacitor Connect in series to the load powered by; When the output voltage is at a negative level, the power switch tube , , , , , , , and the diode The power switch is turned on. , , , and the diode Disconnect; the capacitor Charging; the capacitor Charging; the capacitor Discharge; Capacitor Connect the DC input terminal in series to the capacitor , Charge to , while giving the load powered by; When the output voltage is at the negative second level, the power switch tube , , , , , , and the diode The power switch is turned on. , , , , and the diode Disconnect; the capacitor Charging; the capacitor Charging; the capacitor Discharge; DC input terminal and capacitor In parallel, give capacitor Charge to ,capacitance With capacitor Connect to load in parallel powered by; When the output voltage is negative three-level, the power switch tube , , , , , , and the diode The power switch is turned on. , , , , and the diode Disconnect; the capacitor Charging; the capacitor Discharge; the capacitor Discharge; connect capacitor in series with DC input , to the capacitor Charge to , DC input terminal and capacitor Connect in series to the load powered by.

9. The common ground type switched capacitor multi-level inverter capable of reducing capacitance according to claim 1, characterized in that: Also included is a switched capacitor unit; The switch capacitor unit includes port 1', port 2', port 3', port 4', a power switch tube , power switch tube , power switch tube , power switch tube , power switch tube , power switch tube ,capacitance The port 1' and the power switch tube The first end of the power switch tube The first end of the capacitor The first end of the diode The second end of the power switch tube The first end is connected to the port 2' and the power switch tube The first end of the power switch tube The second end of the power switch tube is connected; The second end and the power switch tube The second end of the power switch tube is connected; The second end and the power switch tube The second end of the power switch tube is connected; The second end and the power switch tube The first end of the capacitor The second end, port 4', the power switch tube The second end of the power switch tube is connected; The first end and the power switch tube The first end of the capacitor The first end, the port 3', the power switch tube is connected to the first end.

10. The common-ground type switched capacitor multi-level inverter capable of reducing capacitance according to claim 9, characterized in that: Its output voltage has seven voltage levels, namely zero level, positive level 1, positive level 2, positive level 3, negative level 1, negative level 2, and negative level 3; Among them, the zero level is 0V and the positive level is , the positive second level is , positive three-level is , the negative level is , the negative second level is , negative three-level , is the voltage at the DC input terminal; The zero level has two working modes, which are switched when the positive and negative cycles of each sinusoidal pulse are switched; In the first working mode, the power switch tube , , , , , , and the diode The power switch tube is turned on; , , , , , and the diode Disconnect; the capacitor Charging; Capacitor , Hanging; In the second working mode, the power switch tube , , , , , , and the diode The power switch tube is turned on; , , , , , and the diode Disconnect; the capacitor Charging capacitor , Hanging.

11. The common-ground type switched capacitor multi-level inverter capable of reducing capacitance according to any one of claims 9 or 10, characterized in that: When the output voltage is at a positive level, the power switch tube , , , , , , , and the diode The power switch is turned on. , , , , and the diode Disconnect; the capacitor Charging; the capacitor Charging; the capacitor Discharge; connect capacitor in series with DC input , to the capacitor , Charge to , while giving the load powered by; When the output voltage is at the positive second level, the power switch tube , , , , , , and the diode The power switch is turned on. , , , , and the diode Disconnect; the capacitor Charging; the capacitor Charging; the capacitor Discharge; the DC input terminal and the capacitor In parallel, give capacitor Charge to ,capacitance With capacitor Connect to load in parallel powered by; When the output voltage is positive three-level, the power switch tube , , , , and the diode The power switch is turned on. , , , , , , , and the diode Disconnect; the capacitor Charging; the capacitor Discharge; the capacitor Discharge; connect capacitor in series with DC input , to the capacitor Charge to , DC input terminal and capacitor Connect in series to the load powered by; When the output voltage is at a negative level, the power switch tube , , , , , , , and the diode The power switch is turned on. , , , , and the diode Disconnect; the capacitor Charging; the capacitor Charging; the capacitor Discharge; Capacitor Connect the DC input terminal in series to the capacitor , Charge to , while giving the load powered by; When the output voltage is at the negative second level, the power switch tube , , , , , , and the diode The power switch is turned on. , , , , , and the diode Disconnect; the capacitor Charging; the capacitor Charging; the capacitor Discharge; DC input terminal and capacitor In parallel, give capacitor Charge to ,capacitance With capacitor Connect to load in parallel powered by; When the output voltage is negative three-level, the power switch tube , , , , and the diode The power switch is turned on. , , , , , , , and the diode Disconnect; the capacitor Charging; the capacitor Discharge; the capacitor Discharge; connect capacitor in series with DC input , to the capacitor Charge to , DC input terminal and capacitor Connect in series to the load powered by.

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