A control method of a three-level converter and related components

Abstract

The application discloses a control method of a three-level converter and related components, and relates to the field of circuits. When the first controllable switch and the third controllable switch are turned on, the voltage source between the bridge arms charges the flying capacitor; when the first controllable switch and the second controllable switch are turned on, the flying capacitor voltage between the flying capacitor remains unchanged; when the second controllable switch and the fourth controllable switch are turned on, the flying capacitor is discharged; when the third controllable switch and the fourth controllable switch are turned on, the flying capacitor voltage remains unchanged; and when the current flows into the bridge arm midpoint, the on duration of the first controllable switch is longer than that of the second controllable switch, and when the current flows out of the bridge arm midpoint, the on duration of the first controllable switch is shorter than that of the second controllable switch, so that the flying capacitor voltage can drop to half of the voltage of the voltage source between the bridge arms. The clamping diode can maintain the flying capacitor voltage stable when the flying capacitor voltage drops to half of the voltage of the voltage source between the bridge arms, so that the flying capacitor voltage can be automatically balanced without real-time detection of the flying capacitor voltage.

Description

Technical Field

[0001] This invention relates to the field of circuits, and in particular to a control method and related components for a three-level converter. Background Technology

[0002] Three-level converters, as the most commonly used multilevel converters, have the advantages of low voltage stress on switching devices and low output voltage harmonics. The most commonly used three-level converters in current technology are flying capacitor type three-level converters. To ensure the normal operation of the flying capacitor type three-level converter, the voltage across the flying capacitor needs to be kept stable within a preset range. Current technology involves real-time acquisition of the flying capacitor voltage, followed by closed-loop control of the controllable switch based on the flying capacitor voltage value to maintain voltage stability. Therefore, current technology requires real-time acquisition of the flying capacitor voltage and closed-loop control, making the control strategy relatively complex. Summary of the Invention

[0003] The purpose of this invention is to provide a control method and related components for a three-level converter, which can maintain the stability of the flying capacitor voltage across the flying capacitor without requiring real-time detection of the flying capacitor voltage, and the control strategy is relatively simple.

[0004] To solve the above technical problems, the present invention provides a control method for a three-level converter. The three-level converter includes voltage sources at both ends of a bridge arm, a current source at the midpoint of the bridge arm, a first controllable switch to a fourth controllable switch, a flying capacitor, a first clamping diode, a second clamping diode, a first voltage dividing capacitor, and a second voltage dividing capacitor. The two ends of the circuit formed by the first controllable switch to the fourth controllable switch in series are connected to the two ends of the circuit formed by the first voltage dividing capacitor and the second voltage dividing capacitor in series, as well as the two ends of the voltage sources at both ends of the bridge arm. The two ends of the circuit formed by the first clamping diode and the second clamping diode in series are connected to the two ends of the flying capacitor and the two ends of the circuit formed by the second controllable switch and the third controllable switch in series. The midpoint of the connection between the second controllable switch and the third controllable switch is connected to the current source at the midpoint of the bridge arm.

[0005] The control method for the three-level bridge arm includes:

[0006] The first controllable switch and the fourth controllable switch are controlled to conduct in a complementary manner, and the conduction period of the first controllable switch to the fourth controllable switch is a preset period.

[0007] Halfway through the preset period after the first controllable switch begins to conduct, the second controllable switch and the third controllable switch are controlled to conduct complementaryly.

[0008] Furthermore, when current flows into the midpoint of the bridge arm connecting the second controllable switch and the third controllable switch, the first controllable switch is on for a preset duration longer than the second controllable switch is on; when current flows out of the midpoint of the bridge arm, the first controllable switch is on for a preset duration shorter than the second controllable switch is on.

[0009] To solve the above-mentioned technical problems, the present invention also provides a control device for a three-level converter, comprising:

[0010] Memory, used to store computer programs;

[0011] A processor is used to implement the steps of the control method for the three-level converter described above when executing the computer program.

[0012] To solve the above-mentioned technical problems, the present invention also provides a three-level converter, including the control device of the above-mentioned three-level converter, and further including voltage sources at both ends of the bridge arm, current source at the midpoint of the bridge arm, a first controllable switch to a fourth controllable switch, a flying capacitor, a first clamping diode, a second clamping diode, a first voltage divider capacitor and a second voltage divider capacitor;

[0013] The two ends of the circuit formed by the first controllable switch and the fourth controllable switch in series are connected to the two ends of the circuit formed by the first voltage divider capacitor and the second voltage divider capacitor in series, as well as the two ends of the voltage source at both ends of the bridge arm. The two ends of the circuit formed by the first clamping diode and the second clamping diode in series are connected to the two ends of the flying capacitor and the two ends of the circuit formed by the second controllable switch and the third controllable switch in series. The midpoint of the connection between the second controllable switch and the third controllable switch is connected to the midpoint current source of the bridge arm.

[0014] Preferably, the voltage source at both ends of the bridge arm is a first input capacitor, and the current source at the midpoint of the bridge arm includes a first output capacitor and a first inductor;

[0015] The negative terminals of the first input capacitor and the first output capacitor are both connected to the output terminal of the fourth controllable switch. The positive terminal of the first input capacitor is connected to the input terminal of the first controllable switch. The positive terminal of the first output capacitor is connected to the first terminal of the first inductor. The other terminal of the first inductor is connected to the midpoint of the bridge arm connecting the second controllable switch and the third controllable switch.

[0016] The two ends of the first output capacitor serve as the output terminals of the three-level converter, and the two ends of the first input capacitor serve as the input terminals of the three-level converter.

[0017] Preferably, the voltage source at both ends of the bridge arm is the second output capacitor, and the current source at the midpoint of the bridge arm includes the second input capacitor and the second inductor;

[0018] The negative terminals of the second input capacitor and the second output capacitor are both connected to the output terminal of the fourth controllable switch. The positive terminal of the second input capacitor is connected to the first terminal of the second inductor. The second terminal of the second inductor is connected to the midpoint of the bridge arm connecting the second controllable switch and the third controllable switch. The positive terminal of the second output capacitor is connected to the input terminal of the first controllable switch.

[0019] The two ends of the second output capacitor serve as the output terminals of the three-level converter, and the two ends of the second input capacitor serve as the input terminals of the three-level converter.

[0020] Preferably, the voltage sources at both ends of the bridge arm are the third input capacitor and the third output capacitor, and the current source at the midpoint of the bridge arm is the third inductor;

[0021] The positive terminal of the third input capacitor is connected to the input terminal of the first controllable switch, the negative terminal of the third input capacitor is connected to the positive terminal of the third output capacitor, and the common terminal of the connection is connected to the first terminal of the third inductor. The second terminal of the third inductor is connected to the midpoint of the bridge arm connecting the second controllable switch and the third controllable switch. The negative terminal of the third output capacitor is connected to the output terminal of the fourth controllable switch.

[0022] The two ends of the third input capacitor serve as the input terminals of the three-level converter, and the two ends of the third output capacitor serve as the output terminals of the three-level converter.

[0023] Preferably, it also includes a first power supply, a transformer, a fifth controllable switch, and a sixth controllable switch;

[0024] The output terminal of the first power supply is connected to the primary side of the transformer, and the two ends of the circuit formed by the series connection of the fifth controllable switch and the sixth controllable switch are connected to the two ends of the circuit formed by the series connection of the first voltage divider capacitor and the second voltage divider capacitor.

[0025] The common terminal of the fifth controllable switch and the sixth controllable switch is connected to the first terminal of the secondary side of the transformer, and the second terminal of the secondary side of the transformer is connected to the common terminal of the first voltage dividing capacitor and the second voltage dividing capacitor.

[0026] Preferably, it also includes a second capacitor, a third capacitor, a second power supply, and a third power supply;

[0027] The second capacitor is connected in series with the third capacitor, the second power supply is connected in parallel across the two ends of the second capacitor, the third power supply is connected in parallel across the two ends of the third capacitor, and the output voltage of the second power supply is equal to the output voltage of the third power supply.

[0028] To solve the above-mentioned technical problems, the present invention also provides a control system for a three-level converter. The three-level converter includes voltage sources at both ends of a bridge arm, a current source at the midpoint of the bridge arm, a first controllable switch to a fourth controllable switch, a flying capacitor, a first clamping diode, a second clamping diode, a first voltage dividing capacitor, and a second voltage dividing capacitor. The two ends of the circuit formed by the first controllable switch to the fourth controllable switch in series are connected to the two ends of the circuit formed by the first voltage dividing capacitor and the second voltage dividing capacitor in series, as well as the two ends of the voltage sources at both ends of the bridge arm. The two ends of the circuit formed by the first clamping diode and the second clamping diode in series are connected to the two ends of the flying capacitor and the two ends of the circuit formed by the second controllable switch and the third controllable switch in series. The midpoint of the connection between the second controllable switch and the third controllable switch is connected to the current source at the midpoint of the bridge arm.

[0029] The control system of the three-level bridge arm includes:

[0030] The first control unit is used to control the first controllable switch and the fourth controllable switch to conduct in a complementary manner, wherein the conduction period of the first controllable switch to the fourth controllable switch is a preset period.

[0031] The second control unit is configured to control the second controllable switch and the third controllable switch to conduct complementaryly after half of the preset cycle following the start of conduction of the first controllable switch;

[0032] Furthermore, when current flows into the midpoint of the bridge arm connecting the second controllable switch and the third controllable switch, the first controllable switch is on for a preset duration longer than the second controllable switch is on; when current flows out of the midpoint of the bridge arm, the first controllable switch is on for a preset duration shorter than the second controllable switch is on.

[0033] To solve the above-mentioned technical problems, the present invention also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the control method for the three-level converter described above.

[0034] In summary, this invention discloses a control method and related components for a three-level converter. When the first and third controllable switches are turned on, the voltage sources at both ends of the bridge arm charge the flying capacitor. When the first and second controllable switches are turned on, the voltage across the flying capacitor remains unchanged. When the second and fourth controllable switches are turned on, the flying capacitor discharges. When the third and fourth controllable switches are turned on, the voltage across the flying capacitor remains unchanged. Furthermore, when current flows into the midpoint of the bridge arm, the conduction time of the first controllable switch is longer than that of the second controllable switch, and when current flows out of the midpoint of the bridge arm, the conduction time of the first controllable switch is shorter than that of the second controllable switch, causing the flying capacitor voltage to drop to half the voltage of the voltage sources at both ends of the bridge arm. Clamping diodes ensure that the flying capacitor voltage stabilizes when it drops to half the voltage of the voltage sources at both ends of the bridge arm, achieving automatic voltage equalization of the flying capacitor voltage without the need for real-time detection of the flying capacitor voltage. Attached Figure Description

[0035] To more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings used in the prior art and embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0036] Figure 1 A flowchart of a control method for a three-level converter provided by the present invention;

[0037] Figure 2 A control mode diagram of a three-level converter provided by the present invention;

[0038] Figure 3 This is a schematic diagram of the structure of a control device for a three-level converter provided by the present invention;

[0039] Figure 4 A circuit diagram of a three-level converter provided by the present invention;

[0040] Figure 5 This invention provides a first circuit diagram of a buck three-level converter;

[0041] Figure 6 A circuit diagram of a boost-type three-level converter provided by the present invention;

[0042] Figure 7 A circuit diagram of a buck-boost three-level converter provided by the present invention;

[0043] Figure 8 This invention provides a second circuit diagram of a buck three-level converter;

[0044] Figure 9This invention provides a third circuit diagram for a buck three-level converter;

[0045] Figure 10 This is a schematic diagram of the control system of a buck three-level converter provided by the present invention. Detailed Implementation

[0046] The core of this invention is to provide a control method and related components for a three-level converter, which can maintain the stability of the flying capacitor voltage across the flying capacitor without requiring real-time detection of the flying capacitor voltage, and the control strategy is relatively simple.

[0047] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] Please refer to Figure 1 , Figure 1 The flowchart of a control method for a three-level converter provided by the present invention includes a voltage source at both ends of a bridge arm, a current source at the midpoint of the bridge arm, a first controllable switch to a fourth controllable switch, a flying capacitor, a first clamping diode, a second clamping diode, a first voltage divider capacitor, and a second voltage divider capacitor.

[0049] The two ends of the circuit after the first controllable switch to the fourth controllable switch are connected to the two ends of the circuit after the first voltage divider capacitor and the second voltage divider capacitor are connected in series, as well as the two ends of the voltage source at both ends of the bridge arm. The two ends of the circuit after the first clamping diode and the second clamping diode are connected to the two ends of the flying capacitor and the two ends of the circuit after the second controllable switch and the third controllable switch are connected. The midpoint of the connection between the second controllable switch and the third controllable switch is connected to the current source at the midpoint of the bridge arm.

[0050] The control method for the three-level bridge arm includes:

[0051] S1: Control the first controllable switch and the fourth controllable switch to conduct in a complementary manner, and the conduction period of the first controllable switch to the fourth controllable switch is a preset period;

[0052] S2: After half a preset cycle after the first controllable switch starts to conduct, control the second and third controllable switches to conduct in a complementary manner;

[0053] Furthermore, when current flows into the midpoint of the bridge arm connecting the second and third controllable switches, the first controllable switch conducts for a preset duration longer than the second controllable switch conducts for a preset duration; when current flows out of the midpoint of the bridge arm, the first controllable switch conducts for a preset duration shorter than the second controllable switch conducts for a preset duration.

[0054] In a typical flying capacitor three-level converter, the flying capacitor requires additional voltage equalization control. This is generally achieved by sampling the voltage across the flying capacitor in real time and controlling the on / off state of various controllable switches in the converter via closed-loop control to regulate the flying capacitor voltage and maintain its stability. However, this control process is relatively complex and inconvenient to use.

[0055] In this application, a first clamping diode and a second clamping diode are first connected in series across the two ends of the flying capacitor, and two clamping modes for clamping the flying capacitor are added based on the three-level voltage of the flying capacitor.

[0056] When the first controllable switch is turned on, if the voltage vf across the flying capacitor is lower than half of the output voltage of the power supply module or tends to be lower, the second clamping switch will be turned on. The power supply module charges the flying capacitor through the first controllable switch and the second clamping switch, so that the voltage of the flying capacitor reaches half of the output voltage of the power supply module. In other words, the voltage of the flying capacitor will be clamped to more than half of the output voltage of the power supply module.

[0057] When the fourth controllable switch is turned on, if the flying capacitor voltage vf across the flying capacitor is lower than half of the output voltage of the voltage source at both ends of the bridge arm or has such a tendency, the first clamping diode will be turned on. The voltage source at both ends of the bridge arm charges the flying capacitor through the fourth controllable switch and the first clamping diode, so that the flying capacitor voltage reaches half of the output voltage of the voltage source at both ends of the bridge arm. That is, the flying capacitor voltage will be clamped to more than half of the output voltage of the voltage source at both ends of the bridge arm.

[0058] However, the first and second clamping diodes only function when the voltage across the flying capacitor is less than half the output voltage of the voltage sources at both ends of the bridge arm. This means they can only guarantee that the clamping voltage is greater than half the output voltage of the voltage sources at both ends of the bridge arm, but they cannot control the upper limit of the clamping voltage. Therefore, in this application, the first and fourth controllable switches are first controlled to conduct complementaryly. If the conduction periods of the first to fourth controllable switches are all preset periods, then half a preset period after the first controllable switch begins to conduct, the second and third controllable switches are controlled to conduct complementaryly. Furthermore, different asynchronous duty cycle control strategies are selected for the direction of current inflow. Specifically, when current flows into the midpoint of the bridge arm connected to the second and third controllable switches, the conduction time of the first controllable switch is longer than the conduction time of the second controllable switch by a preset duration; when current flows out of the midpoint of the bridge arm, the conduction time of the first controllable switch is shorter than the conduction time of the second controllable switch by a preset duration.

[0059] Specifically, taking the case where the first controllable switch conducts for a time that is less than the second controllable switch conducts for a preset duration when the voltage gain is greater than 1 / 2 and the current flows out of the midpoint of the bridge arm as an example, the three-level converter in this application divides the state within one preset cycle into five different modes. Please refer to... Figure 2 , Figure 2 This invention provides a control mode diagram for a three-level converter. Figure 2 S11 corresponds to the on state of the first controllable switch, S22 corresponds to the on state of the fourth controllable switch, S12 corresponds to the on state of the second controllable switch, S21 corresponds to the on state of the third controllable switch, iL is the inductor current in the LC filter module, iC is the current of the flying capacitor, and vf is the voltage across the flying capacitor.

[0060] At time t0-t1, the three-level converter is in the first mode. At this time, the first and third controllable switches are turned on. Since the inductor current in the midpoint current source of the bridge arm is continuous, the flying capacitor is charged.

[0061] At time t1-t2, the three-level converter is in the second mode, at which time the first and second controllable switches are turned on, and the voltage across the flying capacitor remains unchanged.

[0062] At times t2-t3, the three-level converter is in the third mode. At this time, the second and fourth controllable switches are turned on. Due to the freewheeling effect of the inductor in the midpoint current source of the bridge arm, the flying capacitor will be discharged, and the voltage of the flying capacitor will continue to decrease. When the third and fourth controllable switches are turned on, the voltage of the flying capacitor remains unchanged. Since the second controllable switch is turned on for a preset time longer than the first controllable switch, the discharge time is greater than the charging time. Therefore, the voltage of the flying capacitor will definitely drop to half of the output voltage of the voltage source at both ends of the bridge arm at a certain moment. At this time, the first clamping diode is turned on.

[0063] At times t3-t4, the three-level converter is in the fourth mode. At this time, the second and fourth controllable switches are still on. Since the first clamping diode is on, the flying capacitor voltage will be clamped to more than half of the output voltage of the voltage source at both ends of the bridge arm. However, in reality, due to the existence of line impedance, the flying capacitor voltage may be slightly lower than half of the output voltage of the voltage source at both ends of the bridge arm. At time t4, the first controllable switch is on, which causes the second clamping switch to be on, and the flying capacitor voltage is clamped to half of the output voltage of the voltage source at both ends of the bridge arm.

[0064] At time t4-t5, the three-level converter is in the fifth mode. At this time, the first and second controllable switches are turned on, and the voltage of the flying capacitor remains unchanged.

[0065] In summary, this invention discloses a control method and related components for a three-level converter. When the first and third controllable switches are turned on, the voltage sources at both ends of the bridge arm charge the flying capacitor. When the first and second controllable switches are turned on, the voltage across the flying capacitor remains unchanged. When the second and fourth controllable switches are turned on, the flying capacitor discharges, and when current flows into the midpoint of the bridge arm, the conduction time of the first controllable switch is longer than that of the second controllable switch. When current flows out of the midpoint of the bridge arm, the conduction time of the first controllable switch is shorter than that of the second controllable switch, causing the flying capacitor voltage to drop to half the voltage of the voltage sources at both ends of the bridge arm. A clamping diode ensures that the flying capacitor voltage stabilizes when it drops to half the output voltage of the voltage sources at both ends of the bridge arm. When the first and second controllable switches are turned on, the flying capacitor voltage is always maintained at half the voltage of the voltage sources at both ends of the bridge arm, thus maintaining the stability of the flying capacitor voltage without the need for real-time monitoring.

[0066] Furthermore, the first to fourth controllable switches in this application can all be MOSFETs or GaN transistors; this application does not impose any particular limitation on this. Among these, MOSFETs, as controllable switches, have a series of advantages such as fast switching speed, high-frequency performance, high input impedance, low noise, low drive power, large dynamic range, and wide safe operating area, further ensuring the stability of the flying capacitor voltage and the stability of the three-level converter; this application does not impose any particular limitation on this either.

[0067] Please refer to Figure 3 , Figure 3 This is a schematic diagram of a control device for a three-level converter provided by the present invention. The control device for the three-level converter includes:

[0068] Memory 11 is used to store computer programs;

[0069] The processor 12 is used to implement the control method of the above-described three-level converter when executing a computer program.

[0070] For a detailed description of the control device for a three-level converter provided by this invention, please refer to the embodiments of the control method for the three-level converter described above; further details will not be repeated here.

[0071] Please refer to Figure 4 , Figure 4 The present invention provides a circuit diagram of a three-level converter, which includes the control device of the above-mentioned three-level converter, and further includes voltage sources at both ends of the bridge arm, current source at the midpoint of the bridge arm, a first controllable switch to a fourth controllable switch, a flying capacitor, a first clamping diode, a second clamping diode, a first voltage divider capacitor and a second voltage divider capacitor;

[0072] The two ends of the circuit after the first to fourth controllable switches are connected to the two ends of the circuit after the first and second voltage divider capacitors are connected in series, as well as the two ends of the voltage source at both ends of the bridge arm. The two ends of the circuit after the first and second clamping diodes are connected to the two ends of the flying capacitor and the two ends of the circuit after the second and third controllable switches are connected in series. The midpoint of the connection between the second and third controllable switches is connected to the current source at the midpoint of the bridge arm.

[0073] Figure 4 In the diagram, Is represents the midpoint current source of the bridge arm, S1, S2, S3 and S4 represent the first controllable switch, the second controllable switch, the third controllable switch and the fourth controllable switch, respectively, vf is the flying capacitor, and Vm represents the first voltage divider capacitor and the second voltage divider capacitor, respectively.

[0074] For a detailed description of the three-level converter provided by this invention, please refer to the embodiments of the control method of the three-level converter described above; further details will not be repeated here.

[0075] Based on the above embodiments:

[0076] In a preferred embodiment, the voltage source at both ends of the bridge arm is the first input capacitor, and the current source at the midpoint of the bridge arm includes the first output capacitor and the first inductor;

[0077] The negative terminals of the first input capacitor and the first output capacitor are both connected to the output terminal of the fourth controllable switch. The positive terminal of the first input capacitor is connected to the input terminal of the first controllable switch. The positive terminal of the first output capacitor is connected to the first terminal of the first inductor. The other terminal of the first inductor is connected to the midpoint of the bridge arm connecting the second and third controllable switches.

[0078] The two ends of the first output capacitor serve as the output terminals of the three-level converter, and the two ends of the first input capacitor serve as the input terminals of the three-level converter.

[0079] Please refer to Figure 5 , Figure 5 The present invention provides a first circuit diagram of a buck three-level converter, where iL represents the first inductor, V0 represents the first output capacitor, Vin represents the first input capacitor, S1, S2, S3 and S4 represent the first controllable switch, the second controllable switch, the third controllable switch and the fourth controllable switch respectively, vf is the flying capacitor, and Vm represents the first voltage divider capacitor and the second voltage divider capacitor respectively.

[0080] In this embodiment, by setting the voltage sources at both ends of the bridge arm as the first input capacitor and using the two ends of the first input capacitor as the input terminals of the three-level converter, and setting the current source at the midpoint of the bridge arm as the first output capacitor and the first inductor and using the two ends of the first output capacitor as the output terminals of the three-level converter, the three-level converter in this embodiment is specifically a buck three-level converter. Furthermore, when controlling the voltage across the flying capacitor in the buck three-level converter, it is not necessary to detect the flying capacitor voltage, making the control method simple.

[0081] In a preferred embodiment, the voltage source at both ends of the bridge arm is the second output capacitor, and the current source at the midpoint of the bridge arm includes the second input capacitor and the second inductor;

[0082] The negative terminals of the second input capacitor and the second output capacitor are both connected to the output terminal of the fourth controllable switch. The positive terminal of the second input capacitor is connected to the first terminal of the second inductor. The second terminal of the second inductor is connected to the midpoint of the bridge arm connecting the second controllable switch and the third controllable switch. The positive terminal of the second output capacitor is connected to the input terminal of the first controllable switch.

[0083] The two ends of the second output capacitor serve as the output terminals of the three-level converter, and the two ends of the second input capacitor serve as the input terminals of the three-level converter.

[0084] Please refer to Figure 6 , Figure 6 The circuit diagram of a boost-type three-level converter provided by the present invention is shown below. iL represents the second inductor, V0 represents the second output capacitor, Vin represents the second input capacitor, S1, S2, S3 and S4 represent the first controllable switch, the second controllable switch, the third controllable switch and the fourth controllable switch in sequence, vf is the flying capacitor, and Vm represents the first voltage divider capacitor and the second voltage divider capacitor, respectively.

[0085] In this embodiment, by setting the voltage source at both ends of the bridge arm as the second output capacitor and using the two ends of the second output capacitor as the output terminal of the three-level converter, and setting the current source at the midpoint of the bridge arm as the second input capacitor and the second inductor, and using the two ends of the first input capacitor as the input terminal of the three-level converter, the three-level converter in this embodiment is specifically a boost three-level converter. Furthermore, when controlling the voltage across the flying capacitor in the boost three-level converter, it is not necessary to detect the flying capacitor voltage, making the control method simple.

[0086] In a preferred embodiment, the voltage sources at both ends of the bridge arm are the third input capacitor and the third output capacitor, and the current source at the midpoint of the bridge arm is the third inductor;

[0087] The positive terminal of the third input capacitor is connected to the input terminal of the first controllable switch, the negative terminal of the third input capacitor is connected to the positive terminal of the third output capacitor and the common terminal of the connection is connected to the first terminal of the third inductor, the second terminal of the third inductor is connected to the midpoint of the bridge arm connecting the second and third controllable switches, and the negative terminal of the third output capacitor is connected to the output terminal of the fourth controllable switch.

[0088] The two ends of the third input capacitor serve as the input terminals of the three-level converter, and the two ends of the third output capacitor serve as the output terminals of the three-level converter.

[0089] Please refer to Figure 7 , Figure 7 The circuit diagram of a buck-boost three-level converter provided by the present invention is shown below. iL represents the third inductor, V0 represents the third output capacitor, Vin represents the third input capacitor, S1, S2, S3 and S4 represent the first controllable switch, the second controllable switch, the third controllable switch and the fourth controllable switch in sequence, vf is the flying capacitor, and Vm represents the first voltage divider capacitor and the second voltage divider capacitor, respectively.

[0090] In this embodiment, by setting the voltage sources at both ends of the bridge arm as the third input capacitor and the third output capacitor, and using the two ends of the third input capacitor as the input terminals of the three-level converter and the two ends of the third output capacitor as the output terminals of the three-level converter, and setting the current source at the midpoint of the bridge arm as the third inductor, the three-level converter in this embodiment is specifically a boost-buck three-level converter. Furthermore, when controlling the voltage across the flying capacitor in the boost-buck three-level converter, it is not necessary to detect the flying capacitor voltage, making the control method simple.

[0091] In a preferred embodiment, it further includes a first power supply, a transformer, a fifth controllable switch, and a sixth controllable switch;

[0092] The output terminal of the first power supply is connected to the primary side of the transformer, and the two ends of the circuit after the fifth and sixth controllable switches are connected to the two ends of the circuit after the first and second voltage divider capacitors are connected in series.

[0093] The common terminal of the fifth and sixth controllable switches is connected to the first terminal of the secondary side of the transformer, and the second terminal of the secondary side of the transformer is connected to the common terminal of the first and second voltage-dividing capacitors.

[0094] Considering that the three-level converter needs to ensure the stability of the flying capacitor voltage, it is necessary to control the first and second voltage dividing capacitors to stabilize the voltage division. In this embodiment, a first power supply, a transformer, a fifth controllable switch, and a sixth controllable switch are provided. Please refer to [reference needed]. Figure 8 , Figure 8 The second circuit diagram of the buck three-level converter provided by the present invention uses voltage doubler rectification to construct two equal voltage sources, thereby achieving voltage equalization of the first and second voltage divider capacitors of the three-level converter and further ensuring the stability of the three-level converter.

[0095] In a preferred embodiment, it further includes a second capacitor, a third capacitor, a second power supply, and a third power supply;

[0096] The second capacitor is connected in series with the third capacitor, the second power supply is connected in parallel across the two ends of the second capacitor, the third power supply is connected in parallel across the two ends of the third capacitor, and the output voltage of the second power supply is equal to the output voltage of the third power supply.

[0097] Considering that the three-level converter needs to ensure the stability of the flying capacitor voltage, it is necessary to control the first and second voltage divider capacitors to stabilize the voltage division. In this embodiment, a second and third power supply with equal output voltages are selected. Please refer to [reference needed]. Figure 9 , Figure 9The present invention provides a third circuit diagram of a buck three-level converter, wherein a second power supply is connected in parallel across the second capacitor to provide a stable voltage to the first voltage divider capacitor, and a third power supply is connected in parallel across the third capacitor to provide a stable voltage to the second voltage divider capacitor, thereby further ensuring the stability of the three-level converter.

[0098] Please refer to Figure 10 , Figure 10 This invention provides a schematic diagram of the control system of a buck three-level converter. The three-level converter includes voltage sources at both ends of the bridge arm, a current source at the midpoint of the bridge arm, a first controllable switch to a fourth controllable switch, a flying capacitor, a first clamping diode, a second clamping diode, a first voltage divider capacitor, and a second voltage divider capacitor. The two ends of the circuit formed by the first to fourth controllable switches in series are connected to the two ends of the circuit formed by the first and second voltage divider capacitors in series, as well as the two ends of the voltage sources at both ends of the bridge arm. The two ends of the circuit formed by the first and second clamping diodes in series are connected to the two ends of the flying capacitor and the two ends of the circuit formed by the second and third controllable switches in series. The midpoint of the connection between the second and third controllable switches is connected to the current source at the midpoint of the bridge arm.

[0099] The control system for the three-level bridge arm includes:

[0100] The first control unit 21 is used to control the first controllable switch and the fourth controllable switch to conduct in a complementary manner, and the conduction period of the first controllable switch to the fourth controllable switch is a preset period.

[0101] The second control unit 22 is used to control the second controllable switch and the third controllable switch to be complementary and turned on after half a preset period after the first controllable switch starts to conduct;

[0102] Furthermore, when current flows into the midpoint of the bridge arm connecting the second and third controllable switches, the first controllable switch conducts for a preset duration longer than the second controllable switch conducts for a preset duration; when current flows out of the midpoint of the bridge arm, the first controllable switch conducts for a preset duration shorter than the second controllable switch conducts for a preset duration.

[0103] For a detailed description of the control system for a three-level converter provided by this invention, please refer to the embodiments of the control method for the three-level converter described above; further details will not be repeated here.

[0104] The present invention also provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the steps of the control method for the three-level converter described above.

[0105] For a detailed description of the computer-readable storage medium provided by this invention, please refer to the embodiments of the control method for the three-level converter described above; further details will not be repeated here.

[0106] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0107] It should also be noted that, in this specification, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

Claims

1. A control method of a three-level converter, characterized by, The three-level converter comprises a bridge arm two-end voltage source, a bridge arm midpoint current source, a first controllable switch to a fourth controllable switch, a flying capacitor, a first clamping diode, a second clamping diode, a first voltage dividing capacitor and a second voltage dividing capacitor; the two ends of the circuit after the first controllable switch to the fourth controllable switch are connected with the two ends of the circuit after the first voltage dividing capacitor and the second voltage dividing capacitor are connected in series, and the two ends of the bridge arm two-end voltage source; the two ends of the circuit after the first clamping diode and the second clamping diode are connected in series are connected with the two ends of the flying capacitor and the circuit after the second controllable switch and the third controllable switch are connected in series, and the midpoint of the connection between the second controllable switch and the third controllable switch is connected with the bridge arm midpoint current source; The control method of the three-level bridge arm comprises: controlling the first controllable switch and the fourth controllable switch to be complementary on, and the on period of the first controllable switch to the fourth controllable switch is a preset period; controlling the second controllable switch and the third controllable switch to be complementary on after one half of the preset period after the first controllable switch starts to be on; and when the current flows into the bridge arm midpoint connected with the second controllable switch and the third controllable switch, the time of the first controllable switch being on is more than the time of the second controllable switch being on by a preset time length; when the current flows out of the bridge arm midpoint, the time of the first controllable switch being on is less than the time of the second controllable switch being on by the preset time length.

2. A control device for a three-level converter, characterized by comprise: a memory for storing a computer program; a processor for executing the computer program to realize the steps of the control method of the three-level converter of claim 1.

3. A three-level converter, characterized by The control device of the three-level converter of claim 2 further comprises a bridge arm two-end voltage source, a bridge arm midpoint current source, a first controllable switch to a fourth controllable switch, a flying capacitor, a first clamping diode, a second clamping diode, a first voltage dividing capacitor and a second voltage dividing capacitor; the two ends of the circuit after the first controllable switch to the fourth controllable switch are connected with the two ends of the circuit after the first voltage dividing capacitor and the second voltage dividing capacitor are connected in series, and the two ends of the bridge arm two-end voltage source; the two ends of the circuit after the first clamping diode and the second clamping diode are connected in series are connected with the two ends of the flying capacitor and the circuit after the second controllable switch and the third controllable switch are connected in series, and the midpoint of the connection between the second controllable switch and the third controllable switch is connected with the bridge arm midpoint current source.

4. The three-level converter of claim 3, wherein, The bridge arm two-end voltage source is a first input capacitor, and the bridge arm midpoint current source comprises a first output capacitor and a first inductor; the negative pole of the first input capacitor and the negative pole of the first output capacitor are connected with the output end of the fourth controllable switch, the positive pole of the first input capacitor is connected with the input end of the first controllable switch, the positive pole of the first output capacitor is connected with the first end of the first inductor, and the other end of the first inductor is connected with the bridge arm midpoint connected with the second controllable switch and the third controllable switch; The two ends of the first output capacitor are the output terminals of the three-level converter, and the two ends of the first input capacitor are the input terminals of the three-level converter.

5. The three-level converter of claim 3, wherein, The bridge arm two-end voltage source is a second output capacitor, and the bridge arm midpoint current source includes a second input capacitor and a second inductor; The negative electrode of the second input capacitor and the negative electrode of the second output capacitor are connected to the output terminal of the fourth controllable switch, the positive electrode of the second input capacitor is connected to the first end of the second inductor, the second end of the second inductor is connected to the bridge arm midpoint connected with the second controllable switch and the third controllable switch, and the positive electrode of the second output capacitor is connected to the input terminal of the first controllable switch. The two ends of the second output capacitor are the output terminals of the three-level converter, and the two ends of the second input capacitor are the input terminals of the three-level converter.

6. The three-level converter of claim 3, wherein, The bridge arm two-end voltage source is a third input capacitor and a third output capacitor, and the bridge arm midpoint current source is a third inductor; The positive electrode of the third input capacitor is connected to the input terminal of the first controllable switch, the negative electrode of the third input capacitor is connected to the positive electrode of the third output capacitor, and the common end connected thereto is connected to the first end of the third inductor, the second end of the third inductor is connected to the bridge arm midpoint connected with the second controllable switch and the third controllable switch, and the negative electrode of the third output capacitor is connected to the output terminal of the fourth controllable switch. The two ends of the third input capacitor are the input terminals of the three-level converter, and the two ends of the third output capacitor are the output terminals of the three-level converter.

7. A three-level converter according to any one of claims 3 to 6, characterised in that, Further comprising a first power supply, a transformer, a fifth controllable switch and a sixth controllable switch; The output terminal of the first power supply is connected to the primary side of the transformer, and the two ends of the circuit connected in series with the fifth controllable switch and the sixth controllable switch are connected to the two ends of the circuit connected in series with the first voltage dividing capacitor and the second voltage dividing capacitor. The common end of the fifth controllable switch and the sixth controllable switch is connected to the first end of the secondary side of the transformer, and the second end of the secondary side of the transformer is connected to the common end of the first voltage dividing capacitor and the second voltage dividing capacitor.

8. A three-level converter as claimed in any one of claims 3 to 6, characterised in that, Further comprising a second capacitor, a third capacitor, a second power supply and a third power supply; The second capacitor and the third capacitor are connected in series, the second power supply is connected in parallel to the two ends of the second capacitor, the third power supply is connected in parallel to the two ends of the third capacitor, and the output voltage of the second power supply is equal to the output voltage of the third power supply.

9. A control system for a three-level converter, characterized by The three-level converter comprises a bridge arm two-end voltage source, a bridge arm midpoint current source, a first controllable switch to a fourth controllable switch, a flying capacitor, a first clamping diode, a second clamping diode, a first voltage division capacitor and a second voltage division capacitor; the circuit with the first controllable switch to the fourth controllable switch connected in series is connected to the circuit with the first voltage division capacitor and the second voltage division capacitor connected in series and the bridge arm two-end voltage source, the circuit with the first clamping diode and the second clamping diode connected in series is connected to the flying capacitor and the circuit with the second controllable switch and the third controllable switch connected in series, and the midpoint where the second controllable switch and the third controllable switch are connected is connected to the bridge arm midpoint current source; The control system of the three-level bridge arm comprises: A first control unit for controlling the first controllable switch and the fourth controllable switch to be complementary on, and the on period of the first controllable switch to the fourth controllable switch is a preset period; A second control unit for controlling the second controllable switch and the third controllable switch to be complementary on after one half of the preset period after the first controllable switch starts to be on; And when the current flows into the bridge arm midpoint where the second controllable switch and the third controllable switch are connected, the time for the first controllable switch to be on is longer than the time for the second controllable switch to be on by a preset time length; when the current flows out of the bridge arm midpoint, the time for the first controllable switch to be on is shorter than the time for the second controllable switch to be on by the preset time length.

10. A computer-readable storage medium, characterized in that, The computer readable storage medium stores a computer program, and the computer program is executed by the processor to realize the steps of the control method of the three-level converter of claim 1.

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