Double-voltage three-level inverter circuit and control method and control system thereof

Abstract

The embodiment of the invention provides a double-voltage three-level inverter circuit and a control method and a control system of the double-voltage three-level inverter circuit. The circuit comprises a direct-current power supply, a voltage-multiplying module and a three-level inverter which are connected in sequence, the voltage-multiplying module comprises two driving loops, and each driving loop comprises a power switch, a diode, a direct current link capacitor and a resonant inductor which are connected in sequence. According to the embodiment of the invention, the voltage-multiplying module is added to be combined with a traditional diode clamping type three-level inverter, and the power switches are alternately conducted in the voltage-multiplying module to carry out complementary half-wave resonant charging control on the two direct-current link capacitors, so that time-sharing multiplexing of the direct-current power supply is realized; the two capacitor voltages are charged to be the same as the direct-current power supply voltage, so that the inverter obtains double voltage gain on the direct-current side, and the voltage utilization rate is improved; meanwhile, the neutral point of the inverter is connected between the two direct-current link capacitors with the same voltage, the voltage of the neutral point of the inverter is automatically balanced, and the control difficulty of the inverter is reduced.

Description

Technical Field

[0001] The embodiments of the present disclosure belong to the field of power electronics technology, and specifically relate to a double-voltage three-level inverter circuit and a control method and control system thereof. Background Art

[0002] Compared with the traditional two-level inverter, the output waveform of the three-level converter has better harmonics, and each switch device is subjected to less voltage stress, which is particularly suitable for high-voltage and high-power occasions, such as high-voltage AC speed regulation, power system static VAR generator, power active filter, AC flexible transmission and distribution, and new DC transmission. There are three basic structures of three-level inverters: diode clamped, flying capacitor, and cascade. Among them, the diode clamped type has a wider application field.

[0003] There are two problems with the diode-clamped three-level inverter: first, the inverter does not have the ability to boost voltage, and when the DC voltage is low, it cannot obtain a higher AC voltage; second, there is a problem of neutral point voltage imbalance. The neutral point voltage imbalance not only reduces the quality of the voltage waveform, but in severe cases it may even damage the power tube and cause the system to crash.

[0004] Currently, the voltage balance about the neutral point is mainly achieved through modulation algorithm, but this increases the complexity of the three-level inverter control method. Summary of the invention

[0005] The embodiments of the present disclosure aim to solve at least one of the technical problems existing in the prior art, and provide a double voltage three-level inverter circuit and a control method and control system thereof.

[0006] One aspect of the present disclosure provides a double voltage three-level inverter circuit, the circuit comprising a DC power supply, a voltage doubler module and a three-level inverter connected in sequence;

[0007] The voltage doubling module includes a first driving circuit and a second driving circuit;

[0008] The first driving circuit includes a first power switch, a first diode, a first DC link capacitor and a resonant inductor connected in sequence; wherein the collector of the first power switch is connected to the anode of the first diode;

[0009] The second driving circuit comprises a second power switch, the resonant inductor, a second DC link capacitor and a second diode connected in sequence; wherein the emitter of the second power switch is connected to the cathode of the second diode;

[0010] The positive electrode of the DC power supply is connected between the first power switch and the first diode, and the negative electrode of the DC power supply is connected between the second power switch and the second diode;

[0011] The positive electrode of the three-level inverter is connected between the first diode and the first DC link capacitor, and the negative electrode of the three-level inverter is connected between the second diode and the second DC link capacitor.

[0012] Furthermore, the capacitance of the first DC link capacitor is equal to that of the second DC link capacitor.

[0013] Furthermore, a neutral point of the three-level inverter is connected between the first DC link capacitor and the second DC link capacitor.

[0014] Further, when the first power switch and the second power switch are alternately turned on at a preset frequency, the second power switch, the DC power supply, the first diode, the first DC link capacitor and the resonant inductor form a first second-order resonant circuit, and the first power switch, the DC power supply, the resonant inductor, the second DC link capacitor and the second diode form a second second-order resonant circuit;

[0015] The first second-order resonant circuit and the second second-order resonant circuit are complementary.

[0016] Another aspect of the present disclosure provides a control method for a double voltage three-level inverter circuit. Based on the double voltage three-level inverter circuit described above, the method includes:

[0017] A driving signal is sent alternately to the base of the first power switch and the base of the second power switch at a preset frequency, so that the voltage on the DC side of the three-level inverter is twice that of the DC power supply.

[0018] Furthermore, the frequency of the driving signal is the resonant frequency of the second-order resonant circuit.

[0019] Furthermore, the inductance of the resonant inductor is selected by the following formula:

[0020]

[0021] In the formula, ω s is the angular frequency of the power switch driving signal, L is the inductance of the resonant inductor, C is the capacitance of the DC link capacitor, and ω is the angular frequency of the inverter output voltage.

[0022] Another aspect of the present disclosure provides a double voltage three-level inverter circuit control system. Based on the double voltage three-level inverter circuit described above, the system includes:

[0023] A driving module is used to alternately send driving signals to the bases of the first power switch and the second power switch at a preset frequency, so that the voltage on the DC side of the three-level inverter is twice that of the DC power supply.

[0024] Furthermore, the frequency of the driving signal is the resonant frequency of the second-order resonant circuit.

[0025] Furthermore, the inductance of the resonant inductor is selected by the following formula:

[0026]

[0027] In the formula, ω s is the angular frequency of the power switch driving signal, L is the inductance of the resonant inductor, C is the capacitance of the DC link capacitor, and ω is the angular frequency of the inverter output voltage.

[0028] A double voltage three-level inverter circuit and its control method and control system of the embodiment of the present disclosure, by adding a voltage doubling module and combining it with a traditional diode clamped three-level inverter, can realize time-sharing multiplexing of the DC power supply after complementary half-wave resonant charging control, so that the inverter obtains double voltage gain, improves voltage utilization, and automatically balances the neutral point voltage of the inverter without taking additional balancing measures, thereby reducing the control difficulty of the inverter. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 A circuit diagram of an existing diode-clamped three-level inverter;

[0030] Figure 2 It is a structural schematic diagram of a double voltage three-level inverter circuit according to an embodiment of the present disclosure;

[0031] Figure 3 FIG. 4 is a schematic diagram of the voltage gain implementation principle of another embodiment of the present disclosure. DETAILED DESCRIPTION

[0032] like Figure 1 The figure shows a common topology of a diode clamped three-level inverter. The existing diode clamped three-level inverter does not have the ability to boost voltage. When the voltage of the DC power supply is low, the AC voltage after inversion is also low, which cannot meet the power supply demand of the load. In addition, the neutral point voltage of the existing diode clamped three-level inverter is easily unbalanced, thereby affecting the quality of the inverter output power and even causing damage to internal components. At present, the balance of the neutral point voltage of the existing diode clamped three-level inverter is achieved through modulation algorithm, which increases the complexity of controlling the power switch in the inverter.

[0033] To overcome the above problems, embodiments of the present disclosure provide a double voltage three-level inverter circuit and a control method and control system thereof.

[0034] The following will be combined with the drawings in the embodiments of the present disclosure to clearly and completely describe the technical solutions in the embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, not all of the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present disclosure.

[0035] In addition, the described features, structures or characteristics may be combined in one or more embodiments in any suitable manner. In the following description, many specific details are provided to provide a full understanding of the embodiments of the present disclosure. However, those skilled in the art will appreciate that the technical solutions of the present disclosure may be practiced without one or more of the specific details, or other methods, components, devices, steps, etc. may be adopted. In other cases, known methods, devices, implementations or operations are not shown or described in detail to avoid blurring the various aspects of the present disclosure.

[0036] The flowcharts shown in the accompanying drawings are only exemplary and do not necessarily include all the contents and operations / steps, nor must they be executed in the order described. For example, some operations / steps can be decomposed, and some operations / steps can be combined or partially combined, so the actual execution order may change according to actual conditions.

[0037] It should be understood that although the terms first, second, third, etc. may be used in this disclosure to describe various components, these components should not be limited by these terms. These terms are used to distinguish one component from another component. Therefore, the first component discussed below can be referred to as the second component without departing from the teachings of the concepts of the present disclosure. As used in this disclosure, the term "and / or" includes any one of the associated listed items and all combinations of one or more.

[0038] Those skilled in the art will appreciate that the drawings are merely schematic diagrams of example embodiments, and the modules or processes in the drawings are not necessarily necessary for implementing the present disclosure, and therefore cannot be used to limit the protection scope of the present disclosure.

[0039] like Figure 2As shown, an embodiment of the present disclosure provides a double voltage three-level inverter circuit, the circuit includes a DC power supply 100, a voltage doubling module 200 and a three-level inverter 300 connected in sequence. The voltage doubling module 200 includes a first drive circuit 210 and a second drive circuit 220. The first drive circuit 210 includes a first power switch S1, a first diode D1, a first DC link capacitor C1 and a resonant inductor L connected in sequence. The collector of the first power switch S1 is connected to the positive electrode of the first diode D1. The second drive circuit 220 includes a second power switch S2, the resonant inductor L, a second DC link capacitor C2 and a second diode D2 connected in sequence. The emitter of the second power switch S2 is connected to the negative electrode of the second diode D2. The positive electrode of the DC power supply 100 is connected between the first power switch S1 and the first diode D1, and the negative electrode of the DC power supply 100 is connected between the second power switch S2 and the second diode D2. The positive electrode of the three-level inverter 300 is connected between the first diode D1 and the first DC link capacitor C1 , and the negative electrode of the three-level inverter 300 is connected between the second diode D2 and the second DC link capacitor C2 .

[0040] Specifically, the voltage of the DC power supply 100 is U dc , after being doubled by the voltage doubling module 200, the voltage gain is converted into 2Udc and input into the three-level inverter 300. The capacitance of the first DC link capacitor C1 and the second DC link capacitor C2 are equal. The above-mentioned DC power supply 100, resonant inductor L, diodes D1, D2 and DC link capacitors C1, C2 respectively form two complementary zero-current switching circuits. When the two power switches S1 and S2 are complementary switched at a higher frequency, the DC power supply 100 is time-division multiplexed. In each half cycle, the two DC link capacitors C1 and C2 are respectively charged to a voltage equal to the DC source voltage U dc , so that a double voltage gain 2U can be obtained on the DC side of the inverter 300 dc The complementary on-off of the two power switches S1 and S2 is achieved by sending alternating complementary square wave drive signals to the two at a preset frequency. The power switches S1 and S2 are turned on alternately at the preset frequency to form two complementary second-order resonant circuits. Figure 3 As shown, the second power switch S2, the DC power supply 100, the first diode D1, the first DC link capacitor C1 and the resonant inductor L form a first second-order resonant circuit; the first power switch S1, the DC power supply 100, the resonant inductor L, the second DC link capacitor C2 and the second diode D2 form a second second-order resonant circuit.

[0041] For example, Figure 2As shown, the neutral point of the three-level inverter 300 is connected to the node O between the first DC link capacitor C1 and the second DC link capacitor C2. The neutral point of the three-level inverter 300 has the same potential as the node O. Since the voltages of the two capacitors C1 and C2 are equal, the neutral point voltage is automatically balanced.

[0042] A double voltage three-level inverter circuit of an embodiment of the present disclosure can realize time-sharing multiplexing of a DC power supply by adding a voltage doubling module and combining it with a traditional diode-clamped three-level inverter through complementary half-wave resonant charging control, so that the inverter obtains double voltage gain, improves voltage utilization, and automatically balances the neutral point voltage of the inverter without taking additional balancing measures, thereby reducing the control difficulty of the inverter.

[0043] Another embodiment of the present disclosure provides a control method for a double voltage three-level inverter circuit, based on the double voltage three-level inverter circuit described in the previous embodiment. The method includes:

[0044] A driving signal is sent alternately to the base of the first power switch and the base of the second power switch at a preset frequency, so that the voltage on the DC side of the three-level inverter is twice that of the DC power supply.

[0045] Specifically, refer to Figure 3 , the driving signals of the power switches S1 and S2 are complementary square wave signals, so that the power switches S1 and S2 will be turned on in turn to form two complementary second-order resonant circuits. When the two power switches S1 and S2 are turned on complementary, the DC power supply 100, the first diode D1, and the first DC link capacitor C1 form a zero current switching circuit, and the DC power supply 100, the second diode D2, and the second DC link capacitor C2 form another zero current switching circuit. These two zero current switching circuits operate in a complementary manner, each working half a cycle, and the DC power supply 100 is time-division multiplexed. In each half cycle, the DC power supply 100 charges the first DC link capacitor C1 and the second DC link capacitor C2 with a resonant current, respectively, so that the voltages of the two DC link capacitors are equal to the voltage U of the DC power supply 100. dc , thereby obtaining a double voltage gain on the DC side of the inverter 300.

[0046] Due to the presence of the diode, the second-order resonant circuit can only be turned on in the positive half cycle of the resonant current. Therefore, the frequency of the drive signal of the power switches S1 and S2 should be set to the resonant frequency of the second-order resonant circuit and should be much larger than the frequency of the inverter output voltage.

[0047] Assume that the capacitance of the two DC link capacitors C1 and C2 is C, the inductance of the resonant inductor L is L, and the output voltage angular frequency of the inverter is ω, then the driving signal angular frequency of the power switches S1 and S2 is ω s for:

[0048]

[0049] And the duty cycle of the driving signal is 50%.

[0050] Usually, the capacitance C of the DC link capacitor needs to be selected according to the load current, while the inductance L of the resonant inductor is determined by the above formula.

[0051] A double voltage three-level inverter circuit control method of an embodiment of the present disclosure, by adding a voltage doubling module and combining it with a traditional diode clamped three-level inverter, can realize time-sharing multiplexing of a DC power supply after complementary half-wave resonant charging control, so that the inverter obtains double voltage gain, improves voltage utilization, and automatically balances the neutral point voltage of the inverter without taking additional balancing measures, thereby reducing the control difficulty of the inverter.

[0052] Another embodiment of the present disclosure provides a double voltage three-level inverter circuit control system, based on the double voltage three-level inverter circuit described in the previous embodiment. The system includes:

[0053] A driving module is used to alternately send driving signals to the bases of the first power switch and the second power switch at a preset frequency, so that the voltage on the DC side of the three-level inverter is twice that of the DC power supply.

[0054] Specifically, the frequency of the driving signal is the resonant frequency of the second-order resonant circuit and should be much greater than the frequency of the inverter output voltage. Assuming that the capacitance of the two DC link capacitors C1 and C2 is C, the inductance of the resonant inductor L is L, and the output voltage angular frequency of the inverter is ω, then the driving signal angular frequency ω of the power switches S1 and S2 is s for:

[0055]

[0056] The duty cycle of the driving signal is 50%.

[0057] Usually, the capacitance C of the DC link capacitor needs to be selected according to the load current, while the inductance L of the resonant inductor is determined by the above formula.

[0058] A double voltage three-level inverter circuit control system of an embodiment of the present disclosure, by adding a voltage doubling module and combining it with a traditional diode clamped three-level inverter, can realize time-sharing multiplexing of a DC power supply after complementary half-wave resonant charging control, so that the inverter obtains double voltage gain, improves voltage utilization, and automatically balances the neutral point voltage of the inverter without taking additional balancing measures, thereby reducing the control difficulty of the inverter.

[0059] It is to be understood that the above embodiments are merely exemplary embodiments used to illustrate the principles of the present disclosure, but the present disclosure is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and substance of the present disclosure, and these modifications and improvements are also considered to be within the scope of protection of the present disclosure.

Claims

1. A double voltage three-level inverter circuit, characterized in that: The circuit comprises a DC power supply, a voltage doubling module and a three-level inverter connected in sequence; The voltage doubling module includes a first driving circuit and a second driving circuit; The first driving circuit includes a first power switch, a first diode, a first DC link capacitor and a resonant inductor connected in sequence; wherein the collector of the first power switch is connected to the anode of the first diode; The second driving circuit comprises a second power switch, the resonant inductor, a second DC link capacitor and a second diode connected in sequence; wherein the emitter of the second power switch is connected to the cathode of the second diode; The positive electrode of the DC power supply is connected between the first power switch and the first diode, and the negative electrode of the DC power supply is connected between the second power switch and the second diode; The positive electrode of the three-level inverter is connected between the first diode and the first DC link capacitor, and the negative electrode of the three-level inverter is connected between the second diode and the second DC link capacitor.

2. The double voltage three-level inverter circuit according to claim 1, characterized in that: The capacitance of the first DC link capacitor is equal to that of the second DC link capacitor.

3. The double voltage three-level inverter circuit according to claim 2, characterized in that: The neutral point of the three-level inverter is connected between the first DC link capacitor and the second DC link capacitor.

4. The double voltage three-level inverter circuit according to claim 1, characterized in that: When the first power switch and the second power switch are alternately turned on at a preset frequency, the second power switch, the DC power supply, the first diode, the first DC link capacitor and the resonant inductor form a first second-order resonant circuit, and the first power switch, the DC power supply, the resonant inductor, the second DC link capacitor and the second diode form a second second-order resonant circuit; The first second-order resonant circuit and the second second-order resonant circuit are complementary.

5. A control method for a double voltage three-level inverter circuit, based on the double voltage three-level inverter circuit according to any one of claims 1 to 4, characterized in that: The method comprises: A driving signal is sent alternately to the base of the first power switch and the base of the second power switch at a preset frequency, so that the voltage on the DC side of the three-level inverter is twice that of the DC power supply.

6. The control method of a double voltage three-level inverter circuit according to claim 5, characterized in that: The frequency of the driving signal is the resonant frequency of the second-order resonant circuit.

7. The control method of a double voltage three-level inverter circuit according to claim 6, characterized in that: The inductance of the resonant inductor is selected by the following formula: In the formula, ω s is the angular frequency of the power switch driving signal, L is the inductance of the resonant inductor, C is the capacitance of the DC link capacitor, and ω is the angular frequency of the inverter output voltage.

8. A double voltage three-level inverter circuit control system, based on the double voltage three-level inverter circuit according to any one of claims 1 to 4, characterized in that: The system comprises: A driving module is used to alternately send driving signals to the bases of the first power switch and the second power switch at a preset frequency, so that the voltage on the DC side of the three-level inverter is twice that of the DC power supply.

9. The double voltage three-level inverter circuit control system according to claim 8, characterized in that: The frequency of the driving signal is the resonant frequency of the second-order resonant circuit.

10. The double voltage three-level inverter circuit control system according to claim 9, characterized in that: The inductance of the resonant inductor is selected by the following formula: In the formula, ω s is the angular frequency of the power switch driving signal, L is the inductance of the resonant inductor, C is the capacitance of the DC link capacitor, and ω is the angular frequency of the inverter output voltage.

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