An ANPC three-level converter hybrid modulation method

Abstract

The application discloses an ANPC three-level converter hybrid modulation method, when the ANPC three-level converter is in a first working state, the ANPC three-level converter hybrid modulation is carried out by using modulation method one, short commutation path commutation is realized, the switch tube turn-off voltage peak is reduced, the switch tube is prevented from being damaged due to overvoltage, when the ANPC three-level converter is in a second working state, the ANPC three-level converter hybrid modulation is carried out by using modulation method two, the loss of each switch tube is balanced, the switch tube temperature rise is reduced, the service life of the switch tube is prolonged through the hybrid modulation, and the safe working of the ANPC three-level converter is ensured.

Description

Technical Field

[0001] This invention relates to a hybrid modulation method for an ANPC three-level converter, belonging to the field of power electronics technology. Background Technology

[0002] In wind, solar, and energy storage systems, converters typically use a three-level topology. Active clamped type (ANPC) three-level topology is widely used due to its redundant switching states, which offer more flexible control. An ANPC three-level converter topology is shown below. Figure 1 As shown, the circuit includes DC bus capacitors C1 to C2, six switching transistors T1 to T6 and their anti-parallel diodes D1 to D6. The on / off states of the switching transistors under different switching conditions are shown in Table 1.

[0003] Table 1 On / Off Table of Switching Transistors under Different Switching States

[0004]

[0005] Among them, V dc This refers to the input voltage value of the ANPC three-level converter.

[0006] Currently, the ANPC three-level converter uses either modulation method one or modulation method two, where:

[0007] Modulation method 1: During the positive half-cycle (modulation voltage command is greater than 0), switch T2 remains on, switches T3 and T4 remain off, switches T1 and T5 are complementary in conduction, and switch T6 is in the same state as T1; During the negative half-cycle (modulation voltage command is less than 0), switch T3 remains on, switches T1 and T2 remain off, switches T4 and T6 are complementary in conduction, and switch T5 is in the same state as T4.

[0008] Modulation method 2: During the positive half-cycle, switches T1 and T6 remain on, switches T4 and T5 remain off, and switches T2 and T3 are complementary in conduction; during the negative half-cycle, switches T4 and T5 remain on, switches T1 and T6 remain off, and switches T2 and T3 are complementary in conduction.

[0009] In modulation method one, switches T1, T4, T5, and T6 operate at the switching frequency, while switches T2 and T3 operate at the power frequency. The higher the operating frequency of the switches, the greater the losses; therefore, switches T1, T4, T5, and T6 have higher losses. In modulation method two, switches T1, T4, T5, and T6 operate at the power frequency, while switches T2 and T3 operate at the switching frequency. Therefore, switches T2 and T3 have higher losses, and a long commutation path is used during switching. Higher losses in the switches lead to greater temperature rise. If the operating temperature of the switches is too high, it will shorten their lifespan. If it exceeds the maximum withstand temperature, the switches will explode. A longer commutation path results in greater stray inductance and a higher turn-off peak voltage. Furthermore, the turn-off peak voltage is linearly related to the current flowing through the switch. If the sum of the turn-off peak voltages exceeds the switch's withstand voltage, it will also cause the switches to explode.

[0010] Therefore, using either modulation method one or modulation method two alone carries the risk of damage to the switching transistor, affecting the safe operation of the ANPC three-level converter. Summary of the Invention

[0011] This invention provides a hybrid modulation method for an ANPC three-level converter, which solves the problems disclosed in the background art.

[0012] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows:

[0013] A hybrid modulation method for an ANPC three-level converter includes:

[0014] If the ANPC three-level converter is in the first operating state, the existing modulation method 1 is used to perform hybrid modulation of the ANPC three-level converter; wherein, the first operating state is when the instantaneous value of the AC output current of the ANPC three-level converter is greater than the current threshold I1 or less than the current threshold I2;

[0015] If the ANPC three-level converter is in the second operating state, the existing modulation method 2 is used to perform hybrid modulation of the ANPC three-level converter; wherein, the second operating state is that the instantaneous value of the AC output current of the ANPC three-level converter is less than the current threshold I1 and greater than the current threshold I2;

[0016] Among them, the current threshold I1 is greater than 0, the current threshold I2 is less than 0, and the absolute values ​​of the current threshold I1 and the current threshold I2 are equal but opposite in sign.

[0017] During the switching process of modulation method one and modulation method two, the switch tube that is turned on after a preset dead time is delayed before being turned on again. The start time of the delay is the turn-off time of the online turn-off switch tube.

[0018] The ANPC three-level converter includes switching transistors T1 to T6;

[0019] If the ANPC three-level converter is in its first operating state:

[0020] When the modulation voltage is in the positive half-cycle, when the switching state of the ANPC three-level converter switches from P to OU1, switching transistors T1 and T6 are turned off simultaneously. Switching transistor T5 is turned on after a preset dead time following the turn-off of switching transistors T1 and T6. When the switching state of the ANPC three-level converter switches from OU1 to P, switching transistor T5 is turned off first. Switching transistors T1 and T6 are turned on after a preset dead time following the turn-off of switching transistor T5.

[0021] During the negative half-cycle of the modulation voltage, when the switching state of the ANPC three-level converter switches from N to OL1, switching transistors T4 and T5 are turned off simultaneously. Switch T6 is turned on after a preset dead time following the turn-off of switching transistors T4 and T5. When the switching state of the ANPC three-level converter switches from OL1 to N, switching transistor T6 is turned off first. Switches T4 and T5 are turned on after a preset dead time following the turn-off of switching transistor T6.

[0022] The ANPC three-level converter includes switching transistors T1 to T6;

[0023] If the ANPC three-level converter is in the second operating state:

[0024] When the modulation voltage is in the positive half-cycle, when the switching state of the ANPC three-level converter switches from P to OL2, switch T2 is turned off first, and switch T3 is turned on after a preset dead time after switch T2 is turned off; when the switching state of the ANPC three-level converter switches from OL2 to P, switch T3 is turned off first, and switch T2 is turned on after a preset dead time after switch T3 is turned off.

[0025] During the negative half-cycle of the modulation voltage, when the switching state of the ANPC three-level converter switches from N to OU2, switch T3 is turned off first, and switch T2 is turned on after a preset dead time following the turn-off of switch T3; when the switching state of the ANPC three-level converter switches from OU2 to N, switch T2 is turned off first, and switch T3 is turned on after a preset dead time following the turn-off of switch T2.

[0026] When the instantaneous value of the AC output current of the ANPC three-level converter is equal to the current threshold I1 or the current threshold I2, the ANPC three-level converter switches from the first operating state to the second operating state, or from the second operating state to the first operating state.

[0027] The switching process of the operating state during the positive half-cycle of the modulation voltage is as follows:

[0028] When switching from the first working state to the second working state, if the switching state of the ANPC three-level converter is P, the switching state switching sequence is P, OL2; if the switching state of the ANPC three-level converter is OU1, the switching state switching sequence is OU1, P, OL2.

[0029] When switching from the second operating state to the first operating state, if the switching state of the ANPC three-level converter is P, the switching state switching sequence is P, OU1. If the switching state of the ANPC three-level converter is OL2, the switching state switching sequence is OL2, P, OU1.

[0030] The switching process of the operating state during the negative half-cycle of the modulation voltage is as follows:

[0031] When switching from the first working state to the second working state, if the switching state of the ANPC three-level converter is N at this time, the switching state switching sequence is N, OU2; if the switching state of the ANPC three-level converter is OL1 at this time, the switching state switching sequence is OL1, N, OU2.

[0032] When switching from the second operating state to the first operating state, if the switching state of the ANPC three-level converter is N, the switching state switching sequence is N, OL1; if the switching state of the ANPC three-level converter is OU2, the switching state switching sequence is OU2, P, OL1.

[0033] The beneficial effects achieved by this invention are as follows: When the ANPC three-level converter is in its first operating state, modulation method one is used to perform hybrid modulation of the ANPC three-level converter, which realizes short commutation path commutation, reduces the turn-off voltage spike of the switching transistor, and prevents overvoltage damage to the switching transistor. When the ANPC three-level converter is in its second operating state, modulation method two is used to perform hybrid modulation of the ANPC three-level converter, which balances the losses of each switching transistor, reduces the temperature rise of the switching transistor, and improves the service life of the switching transistor through hybrid modulation, thus ensuring the safe operation of the ANPC three-level converter. Attached Figure Description

[0034] Figure 1 This is the main circuit topology diagram of the ANPC three-level converter;

[0035] Figure 2 This is a schematic diagram of the hybrid modulation method for the ANPC three-level converter.

[0036] Figure 3 A schematic diagram illustrating the two operating states of the modulation method;

[0037] Figure 4A schematic diagram of the switching state transition process of each switching transistor during the positive half-cycle of the first working state;

[0038] Figure 5 A schematic diagram of the switching state transition process of each switching transistor during the negative half-cycle of the first operating state;

[0039] Figure 6 A schematic diagram of the switching state transition process of each switching transistor during the positive half-cycle of the second working state;

[0040] Figure 7 A schematic diagram of the switching state transition process of each switching transistor during the negative half-cycle of the second operating state;

[0041] Figure 8(a) is a schematic diagram of the process of switching from the second working state to the first working state during the positive half-cycle P and then to OU1;

[0042] Figure 8(b) is a schematic diagram of the process of switching from the second working state to the positive half-cycle of the first working state, OL2, and then to OU1.

[0043] Figure 9(a) is a schematic diagram of the process of switching from the first working state to the second working state during the positive half-cycle P, which then switches to OL2.

[0044] Figure 9(b) is a schematic diagram of the process of switching from the first working state to the second working state during the positive half-cycle OU1 to OL2;

[0045] Figure 10(a) is a schematic diagram of the process of switching from the second working state to the negative half-cycle N of the first working state and then switching to OL1;

[0046] Figure 10(b) is a schematic diagram of the process of switching from the second working state to the negative half-cycle of the first working state, OU2, and then switching to OL1.

[0047] Figure 11(a) is a schematic diagram of the process of switching from the first working state to the second working state, switching from the negative half-cycle N to OU2;

[0048] Figure 11(b) is a schematic diagram of the process of switching from the first working state to the second working state during the negative half-cycle, OL1 switches to OU2. Detailed Implementation

[0049] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0050] like Figure 2 As shown, a hybrid modulation method for an ANPC three-level converter includes the following steps:

[0051] 1) If the ANPC three-level converter is in the first operating state, the existing modulation method 1 is used to perform hybrid modulation of the ANPC three-level converter; wherein, the first operating state is when the instantaneous value of the AC output current of the ANPC three-level converter is greater than the current threshold I1 or less than the current threshold I2;

[0052] 2) If the ANPC three-level converter is in the second operating state, the existing modulation method 2 is used to perform hybrid modulation of the ANPC three-level converter; wherein, the second operating state is when the instantaneous value of the AC output current of the ANPC three-level converter is less than the current threshold I1 and greater than the current threshold I2;

[0053] Among them, the current threshold I1 is greater than 0, the current threshold I2 is less than 0, and the absolute values ​​of the current threshold I1 and the current threshold I2 are equal but opposite in sign.

[0054] The above method employs modulation method one for hybrid modulation of the ANPC three-level converter when the ANPC three-level converter is in its first operating state. This achieves short-path commutation, reduces the turn-off voltage spike of the switching transistors, and prevents overvoltage damage to the switching transistors. When the ANPC three-level converter is in its second operating state, modulation method two is employed for hybrid modulation of the ANPC three-level converter. This balances the losses of each switching transistor and prevents overvoltage damage to the switching transistors. Hybrid modulation improves the service life of the switching transistors and ensures the safe operation of the ANPC three-level converter.

[0055] like Figure 1 The diagram shows the structure of an ANPC three-level converter, specifically including DC bus capacitors C1-C2, six switching transistors T1-T6, and their anti-parallel diodes D1-D6. Switches T1, T2, T3, and T4 are connected in series between the positive and negative terminals of the power supply. Switches T5 and T6 are connected in parallel between switches T2 and T3. DC bus capacitors C1 and C2 are also connected in series between the positive and negative terminals of the power supply. The common point between DC bus capacitors C1 and C2 is connected to the common point between switches T5 and T6. Diodes D1-D6 are connected in anti-parallel to each of the switching transistors T1-T6.

[0056] To implement the above method, two current thresholds are preset, namely current threshold I1 and current threshold I2. In order to ensure that the losses of the upper and lower bridge arm switching tubes in the ANPC three-level converter are uniform and symmetrical, the absolute values ​​of the two current thresholds are equal and opposite in sign. The specific size of the two current thresholds can be set according to the actual converter operating parameters. In the following description of the present invention, it is specified that current threshold I1 is greater than 0 and current threshold I2 is less than 0.

[0057] Based on the two set current thresholds, and according to the instantaneous value of the AC output current of the ANPC three-level converter, it can be divided into two operating states, such as... Figure 3 As shown, when the instantaneous value of the AC output current of the ANPC three-level converter is greater than the current threshold I1 or less than the current threshold I2, the ANPC three-level converter is defined as being in the first operating state; when the instantaneous value of the AC output current of the ANPC three-level converter is less than the current threshold I1 but greater than the current threshold I2, the ANPC three-level converter is defined as being in the second operating state.

[0058] If the ANPC three-level converter is in its first operating state, the existing modulation method one is used for hybrid modulation of the ANPC three-level converter, as follows:

[0059] A1) During the positive half-cycle of the modulation voltage, the switching state of the ANPC three-level converter switches between P and OU1. Switch T2 remains on, switch T3 and switch T4 remain off, switch T1 and switch T5 are complementary on, and switch T6 and switch T1 are in the same state.

[0060] To prevent device damage due to overvoltage, a preset dead time is used during the switching process (the dead time here is the same as the subsequent dead time). The switch that is turned on later is delayed by the preset dead time before turning on again. The start time of the delay is the turn-off time of the online turn-off switch.

[0061] When the switching state of the ANPC three-level converter changes from P to OU1, switching transistors T1 and T6 are turned off simultaneously. Switch T5 is turned on after a preset dead time following the turn-off of switching transistors T1 and T6. When the switching state of the ANPC three-level converter changes from OU1 to P, switching transistor T5 is turned off first. Switches T1 and T6 are turned on after a preset dead time following the turn-off of switching transistor T5.

[0062] See details Figure 4 At time t1, the switch state begins to switch from P to OU1. Switches T1 and T6 are turned off simultaneously, while T2 remains on. At time t2, switch T5 turns on, completing the switch state switch from P to OU1. At time t3, the switch state begins to switch from OU1 to P. Switch T5 is turned off first, while T2 remains on. At time t4, switches T1 and T6 turn on simultaneously, completing the switch state switch from OU1 to P. Here, t1~t2 and t3~t4 are dead time.

[0063] A2) During the negative half-cycle of the modulation voltage, the switching state of the ANPC three-level converter switches between N and OL1. Switch T3 remains on, switch T1 and switch T2 remain off, switch T4 and switch T6 are complementary on, and switch T5 and switch T4 are in the same state.

[0064] To prevent device damage due to overvoltage, a dead time is preset during the switching process. The switch that is turned on later is delayed by the preset dead time before being turned on again. The start time of the delay is the turn-off time of the online turn-off switch.

[0065] When the switching state of the ANPC three-level converter changes from N to OL1, switching transistors T4 and T5 are turned off simultaneously. Switch T6 is turned on after a preset dead time following the turn-off of switching transistors T4 and T5. When the switching state of the ANPC three-level converter changes from OL1 to N, switching transistor T6 is turned off first. Switches T4 and T5 are turned on after a preset dead time following the turn-off of switching transistor T6.

[0066] See details Figure 5 At time t5, the switch state begins to switch from N to OL1. Switches T4 and T5 are turned off simultaneously, while T3 remains on. At time t6, switch T6 turns on, completing the switch state switch from N to OL1. At time t7, the switch state begins to switch from OL1 to N. Switch T6 is turned off first, while T3 remains on. At time t8, switches T4 and T5 turn on simultaneously, completing the switch state switch from OL1 to N. Among these, t5~t6 and t7~t8 are dead time intervals.

[0067] If the ANPC three-level converter is in its second operating state, the existing modulation method two is used for hybrid modulation of the ANPC three-level converter, as follows:

[0068] B1) During the positive half-cycle of the modulation voltage, the switching state of the ANPC three-level converter switches between P and OL2. Switches T1 and T6 remain on, while switches T4 and T5 remain off, and switches T2 and T3 are complementary in conduction.

[0069] To prevent device damage due to overvoltage, a dead time is preset during the switching process. The switch that is turned on later is delayed by the preset dead time before being turned on again. The start time of the delay is the turn-off time of the online turn-off switch.

[0070] When the switching state of the ANPC three-level converter is switched from P to OL2, switch T2 is turned off first, and switch T3 is turned on after a preset dead time after switch T2 is turned off; when the switching state of the ANPC three-level converter is switched from OL2 to P, switch T3 is turned off first, and switch T2 is turned on after a preset dead time after switch T3 is turned off.

[0071] See details Figure 6At time t9, the switch state begins to switch from P to OL2. Switch T2 is turned off first, while T1 and T6 remain on. At time t10, switch T3 turns on, completing the switch state switch from P to OL2. At time t11, the switch state begins to switch from OL2 to P. Switch T3 is turned off first, while T1 and T6 remain on. At time t12, switch T2 turns on, completing the switch state switch from OL2 to P. Here, t9~t10 and t11~t12 are dead time intervals.

[0072] B2) During the negative half-cycle of the modulation voltage, the switching state of the ANPC three-level converter switches between N and OU2. Switches T4 and T5 remain on, switches T1 and T6 remain off, and switches T2 and T3 are complementary in conduction.

[0073] To prevent device damage due to overvoltage, a dead time is preset during the switching process. The switch that is turned on later is delayed by the preset dead time before being turned on again. The start time of the delay is the turn-off time of the online turn-off switch.

[0074] When the switching state of the ANPC three-level converter changes from N to OU2, switch T3 is turned off first, and switch T2 is turned on after a preset dead time following the turn-off of switch T3; when the switching state of the ANPC three-level converter changes from OU2 to N, switch T2 is turned off first, and switch T3 is turned on after a preset dead time following the turn-off of switch T2.

[0075] See details Figure 7 At time t13, the switch state begins to switch from N to OU2. Switch T3 is turned off first, while T4 and T5 remain on. At time t14, switch T2 turns on, completing the switch state switch from N to OU2. At time t15, the switch state begins to switch from OU2 to N. Switch T2 is turned off first, while T4 and T5 remain on. At time t16, switch T3 turns on, completing the switch state switch from OU2 to N. Here, t13~t14 and t15~t16 are dead time intervals.

[0076] When the instantaneous value of the AC output current of the ANPC three-level converter is equal to the current threshold I1 or the current threshold I2, the ANPC three-level converter switches from the first operating state to the second operating state, or from the second operating state to the first operating state.

[0077] During the positive half-cycle of the modulation voltage, the process of switching operating states is as follows:

[0078] C1) When switching from the first working state to the second working state, if the switching state of the ANPC three-level converter is P at this time, the switching state switching sequence is P, OL2; if the switching state of the ANPC three-level converter is OU1 at this time, the switching state switching sequence is OU1, P, OL2.

[0079] C2) When switching from the second working state to the first working state, if the switching state of the ANPC three-level converter is P at this time, the switching state switching sequence is P, OU1. If the switching state of the ANPC three-level converter is OL2 at this time, the switching state switching sequence is OL2, P, OU1.

[0080] During the negative half-cycle of the modulation voltage, the process of switching operating states is as follows:

[0081] D1) When switching from the first working state to the second working state, if the switching state of the ANPC three-level converter is N at this time, the switching state switching sequence is N, OU2; if the switching state of the ANPC three-level converter is OL1 at this time, the switching state switching sequence is OL1, N, OU2.

[0082] D2) When switching from the second working state to the first working state, if the switching state of the ANPC three-level converter is N at this time, the switching state switching sequence is N, OL1; if the switching state of the ANPC three-level converter is OU2 at this time, the switching state switching sequence is OU2, P, OL1.

[0083] Specifically Figure 8(a) to Figure 11(b) When the instantaneous value of the AC output current is equal to the current threshold I1 or equal to the current threshold I2, that is, at the four times ta, tb, tc, and td, the two operating states switch as follows:

[0084] At time ta, the second working state switches to the first working state. If the switch state is P at this time, the switching state switching sequence should be P→OU1, as shown in Figure 8(a). Switches T1 and T6 are turned off simultaneously, while T2 remains on. At time ta1, switch T5 begins to conduct, completing the working state switching. If the switch state is OL2 at this time, the switching state switching sequence should be OL2→P→OU1, as shown in Figure 8(b). Switch T3 is turned off first, while T1 and T6 remain on. At time ta1', switch T2 is on. At time ta2', switches T1 and T6 are turned off simultaneously, while T2 remains on. At time ta3', switch T5 begins to conduct, completing the working state switching. Among these, ta~ta1, ta~ta1', and ta2'~ta3' are dead time intervals.

[0085] At time tb, the first working state switches to the second working state. If the switch state is P at this time, the switching state switching sequence should be P→OL2, as shown in Figure 9(a). Switch T2 is turned off first, while T1 and T6 remain on. At time tb1, switch T3 starts to conduct, completing the working state switching. If the switch state is OU1 at this time, the switching state switching sequence should be OU1→P→OL2, as shown in Figure 9(b). Switch T5 is turned off first, while T2 remains on. At time tb1', switches T1 and T6 are on simultaneously. At time tb2', switch T2 is turned off first, while T1 and T6 remain on. At time tb3', switch T3 starts to conduct, completing the working state switching. Among these, tb~tb1, tb~tb1', and tb2'~tb3' are dead time intervals.

[0086] At time tc, the second working state switches to the first working state. If the switch state is N at this time, the switching state switching sequence should be N→OL1, as shown in Figure 10(a). Switches T4 and T5 are turned off simultaneously, while T3 remains on. At time tc1, switch T6 begins to conduct, completing the working state switching. If the switch state is OU2 at this time, the switching state switching sequence should be OU2→N→OL1, as shown in Figure 10(b). Switch T2 is turned off first, while T4 and T5 remain on. At time tc1', switch T3 is on. At time tc2', switches T4 and T5 are turned off simultaneously, while T3 remains on. At time tc3', switch T6 begins to conduct, completing the working state switching. Among these, tc~tc1, tc~tc1', and tc2'~tc3' are dead time intervals.

[0087] At time td, the first working state switches to the second working state. If the switch state is N at this time, the switching state switching sequence should be N→OU2, as shown in Figure 11(a). Switch T3 is turned off first, while T4 and T5 remain on. At time td1, switch T2 starts to conduct, completing the working state switching. If the switch state is OL1 at this time, the switching state switching sequence should be OL1→N→OU2, as shown in Figure 11(b). Switch T6 is turned off first, while T3 remains on. At time td1', switches T4 and T5 are on simultaneously. At time td2', switch T3 is turned off first, while T4 and T5 remain on. At time td3', switch T2 starts to conduct, completing the working state switching. Among these, td~td1, td~td1', and td2'~td3' are dead time intervals.

[0088] The above method selects different control logics based on the instantaneous value of the AC output current, reduces the temperature rise of the switching transistor and the turn-off peak voltage, extends the service life of the switching transistor, and ensures the safe operation of the ANPC three-level converter.

[0089] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A hybrid modulation method for an ANPC three-level converter, characterized in that, include: If the ANPC three-level converter is in the first operating state, the ANPC three-level converter is mixed-modulated using modulation method one; wherein, the first operating state is when the instantaneous value of the AC output current of the ANPC three-level converter is greater than the current threshold I1 or less than the current threshold I2; the ANPC three-level converter includes switching transistors T1 to T6; If the ANPC three-level converter is in the second operating state, the ANPC three-level converter is hybrid modulated using modulation method two; wherein, the second operating state is when the instantaneous value of the AC output current of the ANPC three-level converter is less than the current threshold I1 and greater than the current threshold I2; Among them, the current threshold I1 is greater than 0, the current threshold I2 is less than 0, and the absolute values ​​of the current threshold I1 and the current threshold I2 are equal but opposite in sign; During the switching process of modulation method one and modulation method two, the switch tube that is turned on after a preset dead time is delayed before being turned on again. The start time of the delay is the turn-off time of the online turn-off switch tube. Modulation Method 1: During the positive half-cycle of the modulation voltage, when the switching state of the ANPC three-level converter switches from P to OU1, switches T1 and T6 are turned off simultaneously. Switch T5 is turned on after a preset dead time following the turn-off of switches T1 and T6. When the switching state of the ANPC three-level converter switches from OU1 to P, switch T5 is turned off first. Switches T1 and T6 are turned on after a preset dead time following the turn-off of switch T5. During the negative half-cycle of the modulation voltage, when the switching state of the ANPC three-level converter switches from N to OL1, switches T4 and T5 are turned off simultaneously. Switch T6 is turned on after a preset dead time following the turn-off of switches T4 and T5. When the switching state of the ANPC three-level converter switches from OL1 to N, switch T6 is turned off first. Switches T4 and T5 are turned on after a preset dead time following the turn-off of switch T6. Modulation Method 2: During the positive half-cycle of the modulation voltage, when the switching state of the ANPC three-level converter switches from P to OL2, switch T2 is turned off simultaneously, and switch T3 is turned on after a preset dead time following the turn-off of switch T2; when the switching state of the ANPC three-level converter switches from OL2 to P, switch T3 is turned off simultaneously, and switch T2 is turned on after a preset dead time following the turn-off of switch T3; during the negative half-cycle of the modulation voltage, when the switching state of the ANPC three-level converter switches from N to OU2, switch T3 is turned off simultaneously, and switch T2 is turned on after a preset dead time following the turn-off of switch T3; when the switching state of the ANPC three-level converter switches from OU2 to N, switch T2 is turned off simultaneously, and switch T3 is turned on after a preset dead time following the turn-off of switch T2.

2. The hybrid modulation method for an ANPC three-level converter according to claim 1, characterized in that, When the instantaneous value of the AC output current of the ANPC three-level converter is equal to the current threshold I1 or the current threshold I2, the ANPC three-level converter switches from the first operating state to the second operating state, or from the second operating state to the first operating state.

3. The hybrid modulation method for an ANPC three-level converter according to claim 2, characterized in that, The switching process of the operating state during the positive half-cycle of the modulation voltage is as follows: When switching from the first working state to the second working state, if the switching state of the ANPC three-level converter is P, the switching state switching sequence is P, OL2; if the switching state of the ANPC three-level converter is OU1, the switching state switching sequence is OU1, P, OL2. When switching from the second operating state to the first operating state, if the switching state of the ANPC three-level converter is P, the switching state switching sequence is P, OU1. If the switching state of the ANPC three-level converter is OL2, the switching state switching sequence is OL2, P, OU1.

4. The hybrid modulation method for an ANPC three-level converter according to claim 2, characterized in that, The switching process of the operating state during the negative half-cycle of the modulation voltage is as follows: When switching from the first working state to the second working state, if the switching state of the ANPC three-level converter is N at this time, the switching state switching sequence is N, OU2; if the switching state of the ANPC three-level converter is OL1 at this time, the switching state switching sequence is OL1, N, OU2. When switching from the second operating state to the first operating state, if the switching state of the ANPC three-level converter is N, the switching state switching sequence is N, OL1; if the switching state of the ANPC three-level converter is OU2, the switching state switching sequence is OU2, P, OL1.

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