Soft-switching common-ground three-level inverter

Abstract

The invention belongs to the technical field of power converters, and discloses a soft switching common-ground type three-level inverter. The circuit comprises a resonance unit and an output unit. The resonance unit comprises a direct-current voltage input end, a power switch tube, a resonance inductor, a switch capacitor and a diode; the output unit comprises a power switch tube and a load; the capacitance values of the stray capacitors are equal, and the stray capacitors and the stray capacitors jointly form a resonant network to realize soft switching; and the on-off of each power switch tube is controlled by adopting a sine pulse width modulation mode. Through a resonant structure, ZVS switching is realized at the level switching moment, switching loss and electromagnetic interference are reduced, power density is improved, equipment size is reduced, leakage current in a photovoltaic application system can be eliminated, and safe operation of the system is guaranteed.

Description

Technical Field

[0001] This invention belongs to the field of power converter technology, specifically relating to a soft-switching common-ground type three-level inverter. Background Technology

[0002] Currently, the demand for miniaturized, high-power-density, high-energy-conversion-efficiency, and high-reliability power converters is continuously increasing in fields such as new energy power generation and electric vehicles. However, existing multilevel inverters generally adopt a hard-switching working mode, which has problems such as large switching losses, difficulty in increasing the switching frequency, and electromagnetic interference (EMI) caused by waveform abrupt changes during hard switching.

[0003] Meanwhile, multilevel inverters with a common ground structure have significant advantages in photovoltaic power generation systems: by sharing a common ground between the input and output sides, leakage current caused by stray capacitance between photovoltaic modules and inverters can be eliminated. This not only avoids system efficiency loss caused by leakage current, but also avoids the risk of electric shock and device damage caused by leakage current, ensuring the safe and stable operation of the system.

[0004] Conventional ground-based multilevel inverters rely on large-capacitance capacitors (mostly millifarad-level electrolytic capacitors) to suppress capacitor ripple and ensure output voltage quality. However, the large size and short lifespan of these large-capacitance electrolytic capacitors directly limit the power density improvement of the inverter. Therefore, combining soft-switching technology with ground-based multilevel topologies with small capacitance values ​​has become a key direction for improving the performance of such inverters. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by providing a soft-switching common-ground three-level inverter that can solve the leakage current problem in photovoltaic systems, shorten capacitor discharge time, reduce inverter size, and has high power density and reliability.

[0006] Specifically, the present invention is implemented using the following technical solutions:

[0007] This invention provides a soft-switching common-ground three-level inverter, including a resonant unit and an output unit;

[0008] The resonant unit includes a DC voltage input terminal and a power switch transistor. Power switching transistors Resonant inductor Switched capacitors ,diode The output unit includes a power switching transistor. Power switching transistors ,load ;

[0009] The positive terminal of the DC voltage input is connected to the power switch transistor. The first terminal is connected; the negative terminal of the DC voltage input terminal and the power switch are connected. The second end, diode The second terminal of the circuit is connected to the second terminal of the load, and the negative terminal of the DC voltage input is grounded; power switching transistor The second terminal and the power switch First end, resonant inductor The first end is connected; resonant inductor The second terminal and the switched capacitor The first end constitutes port 1 of the resonant unit; switched capacitor The second end and the diode The first end constitutes port 2 of the resonant unit; diode The first end is the anode, diode The second end is the cathode; power switch transistor There is a parasitic capacitance between the first and second terminals. Power switching transistor There is a parasitic capacitance between the first and second terminals. , The capacitance values ​​are all equal, both being Cr; the parasitic capacitance With resonant inductor Together they form a resonant network, used to generate resonance so that the power switching transistors... To achieve soft switching; the power switching transistor The body diode is Power switching transistors The body diode is ;

[0010] The power switch The first end is connected to port 1 of the resonant unit; power switch transistor The second end and the load The first terminal, power switching transistor The first terminal is connected; power switching transistor The second end is connected to port 2 of the resonant unit;

[0011] The on / off state of each power switch is controlled by a sinusoidal pulse width modulation method.

[0012] Furthermore, the power switch transistor , , , The same fully controlled power switching device is used.

[0013] Furthermore, the power switch transistor , , , Gallium nitride power switches are used, and in the power switch... , Silicon carbide Schottky diodes are connected in anti-parallel to replace the power switching transistors. body diode Power switching transistors body diode .

[0014] Furthermore, the switched capacitor It is obtained by combining several identical surface-mount ceramic capacitors in series and parallel.

[0015] Furthermore, the power switch in the resonant unit , High-frequency switching is performed, and the power switching transistor in the output unit... , Only power frequency switching is performed.

[0016] Furthermore, the soft-switching common-ground three-level inverter has three output voltage levels: zero level, positive level 1, and negative level 1.

[0017] Where zero level is 0V, positive level is The negative level is , The voltage at the DC voltage input terminal;

[0018] When the output voltage switches from a positive level to a zero level or from a zero level to a negative level, the power switch transistor... Achieving ZVS activation; when the output voltage switches from negative one level to zero level, the power switch transistor... Enable ZVS.

[0019] Furthermore, the zero level has two operating modes, which are switched during the positive and negative cycle transition of each power frequency sinusoidal pulse;

[0020] In the first operating mode, the power switch transistor , On, power switching transistor , and diodes Disconnect, switch capacitor Suspended;

[0021] In the second operating mode, the power switch transistor , and diodes On, power switching transistor , Disconnect, switch capacitor Charge.

[0022] Furthermore, when the output voltage is at a positive level, the power switch transistor... , and diodes On, power switching transistor , Disconnect, switch capacitor Charge to ;

[0023] When the output voltage is at a negative level, the power switch transistor , On, power switching transistor , and diodes Disconnect, switch capacitor Discharge.

[0024] Furthermore, the power switching transistor , Eight time points are divided within one switching cycle at resonance. This corresponds to 8 intermediate working modes, including:

[0025] The first intermediate operating mode of the time period, this time period is the power switching transistor Turn off, while power switching transistor The intermediate process before the circuit is connected. Power switching transistor Shut down, at this moment , Parasitic capacitance during this period Resonant inductor Provides a freewheeling path, parasitic capacitance , With resonant inductor Resonance occurs. It started to descend. Decline, at the same time Charge, The resonant inductor The current; For the power switching transistor parasitic capacitance voltage, For the power switching transistor parasitic capacitance The voltage; in order to ensure the inductance during this process Sufficient energy for regulation The voltage needs to meet the following requirements:

[0026] ;

[0027] in, For the inductor current in Initial value at time, resonant angular frequency This state continues until ;

[0028] The second intermediate operating mode during this time period is when the power switching transistor... Turn off, while power switching transistor The intermediate process before the circuit is connected. time Drop to 0, at the same time Charge to , The body diode has not yet dropped to 0 during this period. The natural conduction continues as a resonant inductor. Provide a continuation path, and at the same time Clamped to 0, this state persists until time;

[0029] The third intermediate operating mode of the time period, during which the power switch transistor... On, power switching transistor Turn off, Power switching transistor The power switch is triggered by the conduction control signal. Achieving ZVS turn-on creates a new inductor freewheeling path, increasing the inductor current. It continued to decline, and this state persisted until... time;

[0030] The fourth intermediate working mode in the time period, Inductor current at all times When the voltage drops to 0, diode D naturally turns off, and the output voltage gradually decreases from 0 to... The inductor current increases in the reverse direction until it reaches the output voltage. The steady state, which lasts until time;

[0031] The fifth intermediate operating mode of the time period, this time period is the power switching transistor Turn off, while power switching transistor The intermediate process before the circuit is connected. Power switching transistor The shutdown control signal is triggered, and the initial voltage value at this moment is... , Parasitic capacitance during this period Resonant inductor Providing a freewheeling path, unlike the second intermediate operating mode, the parasitic capacitance is [not specified]. , Resonant inductor and load Resonance occurs, inductor current make Decline, at the same time When charging, the output voltage will decrease from - It begins to rise to 0, and this state continues until... time;

[0032] The sixth intermediate operating mode of the time period, this time period is the power switching transistor Turn off, while power switching transistor The intermediate process before the circuit is connected. time Charge to ,at the same time Descending to During this period, the body diode Natural conduction continues to provide a freewheeling path for the resonant inductor, while also... Clamp to 0, switch capacitor Resonant inductor and load An RLC series structure is formed, and this state continues until time;

[0033] The seventh intermediate working mode in the time period. Power switching transistor The power switch is triggered by the conduction control signal. Achieving ZVS activation creates a new inductor freewheeling path, and this state continues until... time;

[0034] To the next cycle The eighth intermediate working mode in the time period. Inductor current at all times When the voltage drops to 0, diode D naturally turns off. After this point, the inductor current increases in the reverse direction until a steady state is reached, at which point the output voltage is zero. This state continues until the next cycle. Trigger power switching transistors at all times The shutdown control signal is then received, and the system subsequently re-enters the first intermediate working mode.

[0035] The beneficial effects of the soft-switching common-ground three-level inverter of the present invention are as follows:

[0036] In the soft-switching common-ground three-level inverter of the present invention, a resonant inductor is introduced into the switched capacitor to realize the power switching transistor in the resonant unit. ZVS (zero voltage switching) turn-on, and power switching transistors that perform hard switching in the output unit. , Power switching transistor , The switching frequency is 50Hz, which can reduce switching losses and reduce electromagnetic interference.

[0037] In the soft-switching common-ground three-level inverter of the present invention, the switched capacitor The charging and discharging occur alternately according to the modulated carrier frequency. Due to the soft-switching effect, the power switching transistor can be significantly upgraded as the power output increases. The switching frequency is reduced, thereby lowering the required capacitance value of the switching capacitor. At the same time, multiple identical surface-mount ceramic capacitors are selected and connected in series and parallel, which significantly reduces the inverter size and increases power density compared to electrolytic capacitors of the same capacity.

[0038] The soft-switching common-ground three-level inverter of this invention adopts a common-ground structure. In photovoltaic power generation system applications, the common-ground structure of the input and output sides can eliminate leakage current caused by stray capacitance between photovoltaic modules and inverters, thus solving the efficiency loss and system stability problems caused by it.

[0039] The soft-switching common-ground three-level inverter of the present invention was tested after simulation verification. The experimental results proved that the soft-switching common-ground three-level inverter can work normally and provide stable power supply to the load while possessing soft-switching characteristics. Attached Figure Description

[0040] Figure 1 This is a circuit diagram of an embodiment of the present invention.

[0041] Figure 2 This is a schematic diagram of the output waveform of an embodiment of the present invention under sinusoidal pulse width modulation.

[0042] Figure 3 This is a schematic diagram of the first operating mode in which the output voltage is zero, according to an embodiment of the present invention.

[0043] Figure 4 This is a schematic diagram of the second operating mode in which the output voltage is zero, according to an embodiment of the present invention.

[0044] Figure 5 This is a schematic diagram of the working mode in which the output voltage is positive one level according to an embodiment of the present invention.

[0045] Figure 6 This is a schematic diagram of the working mode where the output voltage is at a negative one level according to an embodiment of the present invention.

[0046] Figure 7 This embodiment of the invention relates to a power switching transistor within a switching cycle. , A schematic diagram of the working conditions.

[0047] Figure 8 This is a schematic diagram of the first intermediate working mode in a switching cycle according to an embodiment of the present invention.

[0048] Figure 9 This is a schematic diagram of the second intermediate working mode in a switching cycle according to an embodiment of the present invention.

[0049] Figure 10 This is a schematic diagram of the third intermediate working mode in a switching cycle according to an embodiment of the present invention.

[0050] Figure 11 This is a schematic diagram of the fourth intermediate working mode in a switching cycle according to an embodiment of the present invention.

[0051] Figure 12 This is a schematic diagram of the fifth intermediate working mode in a switching cycle according to an embodiment of the present invention.

[0052] Figure 13 This is a schematic diagram of the sixth intermediate working mode in a switching cycle according to an embodiment of the present invention.

[0053] Figure 14 This is a schematic diagram of the seventh intermediate working mode in a switching cycle according to an embodiment of the present invention.

[0054] Figure 15 This is a schematic diagram of the eighth intermediate working mode in a switching cycle according to an embodiment of the present invention.

[0055] Figure 16 This is a simulation waveform diagram of the output voltage and capacitor voltage in an embodiment of the present invention.

[0056] Figure 17 This is a power switch transistor in one switching cycle of an embodiment of the present invention. , Waveform diagram for implementing soft switching.

[0057] Figure 18 The waveforms of the output voltage and capacitor voltage obtained from the experiment in the embodiment of the present invention are shown.

[0058] Figure 19 The power switch transistor in one switching cycle obtained from the experiment of the embodiment of the present invention. , Waveform diagram for implementing soft switching. Detailed Implementation

[0059] The present invention will now be described in further detail with reference to the embodiments and the accompanying drawings.

[0060] Example 1:

[0061] One embodiment of the present invention is a soft-switching common-ground three-level inverter, such as... Figure 1 As shown, it includes a resonant unit and an output unit. The resonant unit includes a DC voltage input terminal and a power switch transistor. Power switching transistors Resonant inductor Switched capacitors ,diode The output unit includes power switching transistors. Power switching transistors ,load .

[0062] The positive terminal of the DC voltage input is connected to the power switch transistor. The first terminal is connected; the negative terminal of the DC voltage input terminal and the power switch are connected. The second end, diode The second terminal of the circuit is connected to the second terminal of the load, and the negative terminal of the DC voltage input is grounded; power switching transistor The second terminal and the power switch First end, resonant inductor The first end is connected; resonant inductor The second terminal and the switched capacitor The first end constitutes port 1 of the resonant unit; switched capacitor The second end and the diode The first end constitutes port 2 of the resonant unit; diode The first end is the anode, diode The second end is the cathode. Power switching transistor. There is a parasitic capacitance between the first and second terminals. Power switching transistor There is a parasitic capacitance between the first and second terminals. , All capacitance values ​​are equal and are Cr. Parasitic capacitance. With resonant inductor Together they form a resonant network, used to generate resonance so that the power switching transistors... To achieve soft switching, use power switching transistors. The body diode is Power switching transistors The body diode is .

[0063] power switching transistors The first end is connected to port 1 of the resonant unit; power switch transistor The second end and the load The first terminal, power switching transistor The first terminal is connected; power switching transistor The second end is connected to port 2 of the resonant unit.

[0064] Preferably, in another embodiment, the power switch transistor , , , The same fully controllable power switching device is used; for example, the device model EPC2050 is selected. Because this model is an enhancement-mode HEMT (High Electron Mobility Transistor) structure, its operating principle differs from that of a traditional MOSFET. When the power switching transistor... , , , When using gallium nitride (GaN) power switches, higher switching frequencies can be achieved while maintaining lower switching and conduction losses; however, GaN power switches do not have parasitic body diodes. Preferably, in another embodiment, when using GaN power switches... , Silicon carbide Schottky diodes (such as the KS06065-F silicon carbide Schottky diode) are connected in anti-parallel to replace the power switching transistors. body diode Power switching transistors body diode It can completely replace the freewheeling function of traditional body diodes.

[0065] Preferably, the resonant inductor The selected component is model IHLP4040DZERR56M01, and its inductance value is... This device adopts a one-piece molded structure, which achieves compact miniaturization to save circuit board space, while having extremely low DC resistance, excellent saturation current and temperature rise current characteristics. It can avoid magnetic saturation and reduce heat loss under high current and high frequency conditions, and ensure the stability of circuit operation.

[0066] Preferably, the switched capacitor in a soft-switching common-ground three-level inverter This is achieved by combining several identical small surface-mount ceramic capacitors in series and parallel, such as multiple FS32X106K101EGG surface-mount ceramic capacitors in series and parallel. Compared to using electrolytic capacitors, this approach reduces the inverter size and increases the inverter power density.

[0067] Preferably, the soft-switching common-ground three-level inverter uses sinusoidal pulse width modulation (SPWM) to control the switching of each power switch. Under this modulation method, the output waveform of the soft-switching common-ground three-level inverter is as follows: Figure 2 As shown, the power switch in the resonant unit , High-frequency switching is performed using the power switching transistors in the output unit. , Only power frequency switching is performed. Power switching transistor. , The power switching transistor switches only once during the positive and negative half-cycle transition in each output cycle. , The switching frequency is the power frequency of 50Hz, which can reduce power consumption.

[0068] When performing circuit analysis, the power switching transistor is set. , For an ideal switch (ignoring parasitic parameters), its body diode... , With diode All are ideal devices, meaning they have instantaneous response and zero on-state voltage drop.

[0069] The soft-switching common-ground three-level inverter in this embodiment has three output voltage levels: zero level, positive 1 level, and negative 1 level. The zero-level output voltage is... The output voltage at positive level is The output voltage at the negative level is , The voltage at the DC voltage input terminal is [value].

[0070] When the output voltage is at zero level, it has two operating modes, which are switched during the positive and negative cycle transition of each power frequency sine pulse;

[0071] In the first working mode, such as Figure 3 As shown, power switching transistor , On, power switching transistor , and diodes Disconnect, switch capacitor It is suspended in the air, neither charging nor discharging;

[0072] In the second working mode, such as Figure 4 As shown, power switching transistor , and diodes On, power switching transistor , Disconnect, switch capacitor Charge.

[0073] When the output voltage is positive level, such as Figure 5 As shown, power switching transistor , and diodes On, power switching transistor , Disconnect, switch capacitor Charge to ;

[0074] When the output voltage is at a negative level, such as Figure 6 As shown, power switching transistor , On, power switching transistor , and diodes Disconnect, switch capacitor Discharge.

[0075] Table 1 shows Figure 1 The switching states of power transistors and diodes, and the charging and discharging states of the switched capacitors in a soft-switching common-ground three-level inverter at different operating levels. During the negative half-cycle of the output power frequency, it alternates between charging and discharging at a sinusoidal pulse width modulation frequency, and will not discharge continuously for a long time.

[0076] Table 1. Operating conditions of various devices in a soft-switching common-ground three-level inverter at different operating levels.

[0077] Output voltage level ( ) value Conductivity disconnect Positive level 、 、 、 Charge Zero level (first operating mode) 0 、 、 、 Suspended Zero level (second operating mode) 0 、 、 、 Charge negative one level 、 、 、 Discharge

[0078] As a specific implementation, when the output voltage switches from a positive level to a zero level or from a zero level to a negative level, the power switch transistor... Achieving ZVS (zero voltage switching); when the output voltage switches from negative one level to zero level, the power switch transistor... Enable ZVS.

[0079] As a specific implementation method, power switching transistors , Eight time points are divided within one switching cycle at resonance. This corresponds to 8 intermediate working modes, such as Figure 7 As shown. Figure 7 middle These represent power switching transistors. , The control signal (off or on). The time indicates the corresponding power switch ( ) Conduction, The time indicates the corresponding power switch ( Turn off; Represents resonant inductance The current; Power switching transistor parasitic capacitance voltage, Power switching transistor parasitic capacitance The voltage. The eight intermediate operating modes include:

[0080] The first intermediate working mode of the time period, such as Figure 7 and Figure 8 As shown, this time period is for the power switching transistor. Turn off, while power switching transistor The intermediate process before the circuit is connected. Power switching transistor When the power switch is turned off, the voltage of its parasitic capacitance is... , Parasitic capacitance during this period Resonant inductor Provides a freewheeling path, parasitic capacitance , With resonant inductor Resonance occurs, resonant inductor current It begins to decline, parasitic capacitance voltage Decrease, while parasitic capacitance voltage During charging, in order to ensure the resonant inductance Sufficient energy to regulate parasitic capacitance The voltage needs to meet the following requirements:

[0081]

[0082] in, For the inductor current in The initial value at time , This is the inductance of the resonant inductor. Power switching transistor The parasitic capacitance value of S2 and the resonant angular frequency. This state continues until time.

[0083] The second intermediate working mode during the time period, such as Figure 7 and Figure 9As shown, this time period is for the power switching transistor. Turn off, while power switching transistor The intermediate process before the circuit is connected. Parasitic capacitance at all times voltage Drops to 0, while parasitic capacitance voltage Output voltage when charged to positive level Inductor current The body diode has not yet dropped to 0 during this period. The natural conduction continues as a resonant inductor. Provides a freewheeling path while also mitigating parasitic capacitance. voltage When clamped to 0, the inductor current expression is:

[0084]

[0085] in, For capacitor Voltage at The initial value at time , For switched capacitors The capacitance value, this state continues until time.

[0086] The third intermediate working mode of the time period, such as Figure 7 and Figure 10 As shown, the power switching transistor during this time period On, power switching transistor Turn off. Trigger power switching transistors at all times The conduction control signal, due to parasitic capacitance voltage The voltage has dropped to 0, power switching transistor Achieving ZVS turn-on and forming a new resonant inductor Freewheeling path, inductor current It will continue to drop to 0. The equivalent circuit for this process is the same as that for the second intermediate operating mode. The expression for the inductor current is:

[0087]

[0088] This state continues until time.

[0089] The fourth intermediate working mode of the time period, such as Figure 7 and Figure 11 As shown, Inductor current at all times When the voltage drops to 0, diode D naturally turns off, and the output voltage will gradually decrease from 0 to negative one level after this moment. ), inductor current It will increase in the opposite direction until the output voltage reaches a negative one level. The steady state of ) lasts until time;

[0090] The fifth intermediate working mode of the time period, such as Figure 7 and Figure 12 As shown, this time period is for the power switching transistor. Turn off, while power switching transistor The intermediate process before the circuit is connected. Trigger power switching transistors at all times The shutdown control signal, power switching transistor Turn off, initial voltage value at this moment , Parasitic capacitance during this period Resonant inductor Providing a freewheeling path, unlike the second intermediate operating mode, the parasitic capacitance is [not specified]. , Resonant inductor and load Resonance occurs, inductor current This will cause parasitic capacitance voltage Decrease, while parasitic capacitance voltage When charging, the output voltage will change from a negative one level ( The inductor current begins to rise to 0, and the expression for this process is:

[0091]

[0092] Among them, the damping coefficient resonant angular frequency , For the inductor current in The initial value at time t, this state lasts until time.

[0093] The sixth intermediate working mode of the time period, such as Figure 7 and Figure 13 As shown, this time period is for the power switching transistor. Turn off, while power switching transistor The intermediate process before the circuit is connected. Parasitic capacitance at all times voltage Charge to Meanwhile, parasitic capacitance voltage Descending to During this period, the body diode Natural conduction continues to provide a freewheeling path for the inductor, while also... Clamp to 0, switch capacitor Resonant inductor and load The inductor current expression for an RLC series structure is as follows:

[0094]

[0095] in, for Voltage at The initial value at time , , This state continues until time.

[0096] The seventh intermediate working mode of the time period, such as Figure 7 and Figure 14 As shown, Trigger power switching transistors at all times The conduction control signal, due to The voltage has dropped to 0, power switching transistor Achieving ZVS turn-on creates a new inductor freewheeling path; the equivalent circuit of this process is the same as that of the sixth intermediate operating mode; this state continues until... time.

[0097] To the next cycle The eighth intermediate working mode of the time period, such as Figure 7 and Figure 15 As shown, Inductor current at all times When the voltage drops to 0, diode D naturally turns off. After this point, the inductor current will increase in the reverse direction until a steady state is reached, at which point the output voltage is zero. This state continues until the next cycle. Trigger power switching transistors at all times The shutdown control signal is then received, and the system subsequently re-enters the first operating mode.

[0098] The results obtained using PSIM simulation are as follows: Figure 16 The output voltage waveform and the switched capacitor are shown. Voltage (Vc) waveform, output voltage The root mean square value is (Peak 150V), with an output frequency of 50Hz (power frequency), it was verified that the soft-switching common-ground three-level inverter of the present invention can work normally, while the voltage ripple ratio of the switched capacitor is maintained within 5%. Figure 17 Demonstrates the power switching transistors that achieve soft switching within one switching cycle. control signals (Off or On), Power Switch control signals (Switch-off or switch-on) and voltage stress From the waveform, it can be observed that the power switch transistor... When turned on, its voltage stress It will first drop to 0, then the control signal will... The arrival of power switching transistors Achieving ZVS turn-on; power switching transistor When turned on, its voltage stress It will first drop to 0, then the control signal will... arrival, ZVS activation was achieved; all results are consistent with theoretical analysis, verifying the feasibility of the present invention.

[0099] Table 2 Parameters of the Experimental Prototype

[0100] parameter numerical values DC input voltage 150V Output voltage Root Mean Square 110V Output power 200W Capacity 50 F Switching frequency 40kHz Output frequency 50Hz

[0101] In this embodiment, an experimental prototype was designed and manufactured according to the parameters in Table 2, and the experimental results are as follows. Figure 18 The output voltage was shown. Waveform and switched capacitor Voltage Waveform, Figure 19 Demonstrates a power switch transistor during a switching cycle. control signals Power switching transistors control signals With voltage stress , The waveform verified that the soft-switching common-ground three-level inverter of the present invention can normally supply power to the load while the power switching transistors... , It has the feature of ZVS activation.

Claims

1. A soft-switching common-ground type three-level inverter, characterized in that, Includes a resonant unit and an output unit; The resonant unit includes a DC voltage input terminal and a power switch transistor. Power switching transistors Resonant inductor Switched capacitors ,diode The output unit includes a power switch transistor. Power switching transistors ,load ; The positive terminal of the DC voltage input is connected to the power switch transistor. The first terminal is connected; the negative terminal of the DC voltage input terminal and the power switch are connected. The second end, diode The second terminal of the circuit is connected to the second terminal of the load, and the negative terminal of the DC voltage input is grounded; power switching transistor The second terminal and the power switch First end, resonant inductor The first end is connected; resonant inductor The second terminal and the switched capacitor The first end constitutes port 1 of the resonant unit; switched capacitor The second end and the diode The first end constitutes port 2 of the resonant unit; diode The first end is the anode, diode The second end is the cathode; power switch transistor There is a parasitic capacitance between the first and second terminals. Power switching transistor There is a parasitic capacitance between the first and second terminals. , The capacitance values ​​are all equal, both being Cr; the parasitic capacitance With resonant inductor Together they form a resonant network, used to generate resonance so that the power switching transistors... To achieve soft switching; the power switching transistor The body diode is Power switching transistors The body diode is ; The power switch The first end is connected to port 1 of the resonant unit; power switch transistor The second end and the load The first terminal, power switching transistor The first terminal is connected; power switching transistor The second end is connected to port 2 of the resonant unit; The on / off state of each power switch is controlled by a sinusoidal pulse width modulation method.

2. The soft-switching common-ground three-level inverter according to claim 1, characterized in that, The power switch , , , The same fully controlled power switching device is used.

3. The soft-switching common-ground three-level inverter according to claim 2, characterized in that, The power switch , , , Gallium nitride power switches are used, and in the power switch... , Silicon carbide Schottky diodes are connected in anti-parallel to replace the power switching transistors. body diode Power switching transistors body diode .

4. The soft-switching common-ground three-level inverter according to claim 1, characterized in that, The switched capacitor It is obtained by combining several identical surface-mount ceramic capacitors in series and parallel.

5. The soft-switching common-ground three-level inverter according to claim 1, characterized in that, The power switch in the resonant unit , High-frequency switching is performed, and the power switching transistor in the output unit... , Only power frequency switching is performed.

6. The soft-switching common-ground three-level inverter according to claim 5, characterized in that, Its output voltage has three voltage levels: zero level, positive level 1, and negative level 1. Where zero level is 0V, positive level is The negative level is , The voltage at the DC voltage input terminal; When the output voltage switches from a positive level to a zero level or from a zero level to a negative level, the power switch transistor... Achieving ZVS activation; when the output voltage switches from negative one level to zero level, the power switch transistor... Enable ZVS.

7. The soft-switching common-ground three-level inverter according to claim 6, characterized in that, The zero level has two operating modes, which are switched during the positive and negative cycle transition of each power frequency sine pulse; In the first operating mode, the power switch transistor , On, power switching transistor , and diodes Disconnect, switch capacitor Suspended; In the second operating mode, the power switch transistor , and diodes On, power switching transistor , Disconnect, switch capacitor Charge.

8. The soft-switching common-ground three-level inverter according to claim 6, characterized in that, When the output voltage is at a positive level, the power switch transistor , and diodes On, power switching transistor , Disconnect, switch capacitor Charge to ; When the output voltage is at a negative level, the power switch transistor , On, power switching transistor , and diodes Disconnect, switch capacitor Discharge.

9. The soft-switching common-ground three-level inverter according to claim 8, characterized in that, The power switching transistor , Eight time points are divided within one switching cycle at resonance. This corresponds to 8 intermediate working modes, including: The first intermediate operating mode of the time period, this time period is the power switching transistor Turn off, while power switching transistor The intermediate process before the circuit is connected. Power switching transistor Shut down, at this moment , Parasitic capacitance during this period For resonant inductors Provides a freewheeling path, parasitic capacitance , With resonant inductor Resonance occurs. It started to descend. Decline, at the same time Charge, For the resonant inductor The current; For the power switching transistor parasitic capacitance voltage, For the power switching transistor parasitic capacitance The voltage; in order to ensure the inductance during this process Sufficient energy for regulation The voltage needs to meet the following requirements: ； in, For the inductor current in Initial value at time, resonant angular frequency This state continues until ; The second intermediate operating mode during this time period is when the power switching transistor... Turn off, while power switching transistor The intermediate process before the circuit is connected. time Drop to 0, at the same time Charge to , The body diode has not yet dropped to 0 during this period. The natural conduction continues as a resonant inductor. Provide a continuation path, and at the same time Clamped to 0, this state persists until time; The third intermediate operating mode of the time period, during which the power switch transistor... On, power switching transistor Turn off, Power switching transistor The power switch is triggered by the conduction control signal. Achieving ZVS turn-on creates a new inductor freewheeling path, increasing the inductor current. The decline continued, and this state persisted until... time; The fourth intermediate working mode in the time period, Inductor current at all times When the voltage drops to 0, diode D naturally turns off, and the output voltage gradually decreases from 0 to... The inductor current increases in the reverse direction until it reaches the output voltage. The steady state, which lasts until time; The fifth intermediate operating mode of the time period, this time period is the power switching transistor Turn off, while power switching transistor The intermediate process before the circuit is connected. Power switching transistor The shutdown control signal is triggered, and the initial voltage value at this moment is... , Parasitic capacitance during this period For resonant inductors Providing a freewheeling path, unlike the second intermediate operating mode, the parasitic capacitance is [not specified]. , Resonant inductor and load Resonance occurs, inductor current make Decline, at the same time When charging, the output voltage will decrease from - It begins to rise to 0, and this state continues until... time; The sixth intermediate operating mode of the time period, this time period is the power switching transistor Turn off, while power switching transistor The intermediate process before the circuit is connected. time Charge to ,at the same time Descending to During this period, the body diode Natural conduction continues to provide a freewheeling path for the resonant inductor, while also... Clamp to 0, switch capacitor Resonant inductor and load An RLC series structure is formed, and this state continues until time; The seventh intermediate working mode in the time period. Power switching transistor The power switch is triggered by the conduction control signal. Achieving ZVS activation creates a new inductor freewheeling path, and this state continues until... time; To the next cycle The eighth intermediate working mode in the time period. Inductor current at all times When the voltage drops to 0, diode D naturally turns off. After this point, the inductor current increases in the reverse direction until a steady state is reached, at which point the output voltage is zero. This state continues until the next cycle. Trigger power switching transistors at all times The shutdown control signal is then received, and the system subsequently re-enters the first intermediate working mode.

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