CN116365890B - Three-phase staggered T-shaped three-level LLC converter and wide voltage transformation control method thereof - Google Patents

Abstract

The invention discloses a three-phase staggered T-shaped three-level LLC converter and a wide voltage transformation control method thereof, comprising a capacitor: the three-phase three-level inverter bridge is formed by two capacitors Cdc1 and Cdc2 which equally divide input direct-current voltage and three T-shaped half-bridges; three T-shaped half-bridges are connected into three groups of resonance capacitors, resonance inductors and transformers which are connected in series, and the output end of each transformer is connected to a load after passing through a three-phase rectifier bridge and a direct-current capacitor Co; the converter can correspondingly perform flexible switching by a T-shaped three-phase topology, a T-shaped full bridge and a T-shaped half bridge according to the change of power and input voltage, and frequency conversion and duty ratio change control are combined, so that the gain range of the converter is widened; the resonant network input is clamped to zero by a T-half bridge or switch S, thereby creating a zero level and reducing the circulating current loss. The invention can widen the voltage regulating range of the high-power LLC converter, reduce zero level circulation loss, and realize high efficiency and wide voltage transformation of the LLC converter by utilizing the soft switching characteristic.

Description

A three-phase interleaved T-shaped three-level LLC converter and its wide voltage transformation control method

Technical field

The invention belongs to the technical fields of power electronics and DC converters, and in particular relates to a three-phase interleaved T-type three-level LLC converter and a wide voltage control method thereof.

Background technique

The LLC converter has high efficiency and low electromagnetic noise because it can realize zero-voltage turn-on of the primary switch and zero-current turn-off of the secondary switch, which makes it widely used. In DC converters, reducing the voltage and current stress of power switching devices is the key to improving system reliability. Reducing the size of the inductor is the key to improving the dynamic performance of the converter. Reducing the current ripple is conducive to reducing the size of the filter capacitor and thus Reduce the size of the converter.

Three-level technology and interleaved parallel technology are two widely used technologies. The former can be used to reduce the voltage stress of switching devices and adjust the duty cycle to adjust the voltage by generating zero level. The latter can be used to reduce the voltage stress of switching devices. current stress, reducing inductor size and ripple current.

Some applications require the converter to have the function of wide input and wide output voltage regulation. However, in the traditional LLC converter solution, the input voltage of the suspended resonant network is used to adjust the output voltage, which will lead to an increase in circulating current losses; in some new energy systems, full load and light load operation The power levels vary greatly, making it difficult to take into account the high efficiency requirements of the converter within the entire operating range. In the traditional variable topology scheme, there are large voltage and current pulses during topology switching, which will produce large losses and electromagnetic noise. , and the control of these topologies is very complex; that is, the single use of three-level technology or interleaved parallel technology can no longer meet the performance requirements of DC converters in new energy systems.

Contents of the invention

In order to solve the above problems, the present invention proposes a three-phase interleaved T-type three-level LLC converter and its wide voltage transformation control method. The converter can adopt T-type three-phase topology, T-type according to changes in power and input voltage. Flexible switching between full bridge and T-shaped half bridge, combined with variable frequency and variable duty cycle control, thereby broadening the gain range of the converter; clamping the input end of the resonant network to zero through the T-shaped half bridge or switch S, thereby generating zero power level and reduce circulation losses.

In order to achieve the above object, the technical solution adopted by the present invention is: a three-phase interleaved T-type three-level LLC converter, including:

Capacitor Cdc1 and capacitor Cdc2 are connected in series to equally share the input DC voltage;

Three T-shaped half bridges form a three-phase three-level inverter; the first phase T-shaped half bridge: switches Sa1 and Sa2 form a half bridge, switches Sa3 and Sa4 are connected in reverse series and connected to the midpoint of the input DC capacitor; the second phase Phase T-shaped half bridge: switches Sb1 and Sb2 form a half bridge, switches Sb3 and Sb4 are connected in reverse series and connected to the midpoint of the input DC capacitor; third phase T-shaped half bridge: switches Sc1 and Sc2 form a half bridge, switches Sc3 and Sc4 Connect in reverse series and connect to the midpoint of the input DC capacitor;

Three sets of series-connected resonant capacitors Cr, resonant inductors Lr and isolation transformers are connected to the three T-shaped half-bridges. The midpoint of the Y-shaped connection on the primary side of the isolation transformer is connected to the midpoint of the input DC capacitor through the switch S;

and a diode rectifier bridge set on the secondary side of the isolation transformer, and then connected to the load through the output DC capacitor Co.

Further, the isolation transformer adopts Y-Y type or Y-Δ type.

Further, the diode rectifier bridge includes six diodes D1, D2, D3, D4, D5 and D6, which are connected in series and then in parallel.

Furthermore, a three-phase three-level inverter is formed by three T-shaped half bridges to convert DC into AC with adjustable frequency and variable duty cycle, and the energy is transferred to the load through the resonant network, transformer and diode rectifier bridge; The output voltage or current is adjusted by changing the frequency and effective value of the fundamental wave component in the resonant network; the input voltage of the resonant network is clamped to zero through the midpoint of the T-shaped half-bridge or the switch S, and the input voltage of the resonant network is adjusted. The air ratio is adjusted to adjust the effective value of the equivalent input voltage to adjust the transformer range and at the same time reduce the zero-level circulating current loss.

On the other hand, the present invention also proposes a wide voltage transformation control method for a three-phase interleaved T-type three-level LLC converter. Based on the proposed three-phase interleaved T-type three-level LLC converter, the input voltage and load power are Determine the form of the required working topology. Switching between topology forms is realized through flexible topology. The topology forms include three-level T-type three-phase interleaved LLC conversion form, three-level T-type full-bridge LLC conversion form and three-level Flat T-shaped half-bridge LLC transformation form;

According to changes in power and input voltage, the converter performs flexible switching in T-type three-phase topology, T-type full bridge and T-type half bridge, combined with variable frequency and variable duty cycle control, thereby broadening the gain range of the converter; through T-type The half-bridge or switch S clamps the input end of the resonant network to zero voltage, thereby equivalently regulating the input voltage of the resonant network.

Further, a wide voltage transformation control method for a three-phase interleaved T-type three-level LLC converter includes the steps:

S1, when the load power is greater than 70% of the rated power: the converter works in a three-level T-type three-phase interleaved LLC conversion form;

S2, when the load power is between 30% and 70% of the rated power: the converter operates as a three-level T-type full-bridge LLC converter; when the input voltage is lower than 0.5 times the rated input voltage, the T-type full bridge operates with Vdc /2, 0, -Vdc/2 operates at three levels; when the input voltage is higher than 0.5 times the rated input voltage, the T-type full bridge operates at three levels: Vdc, 0, -Vdc;

S3, when the load power is less than 30% of the rated power: the converter operates in a three-level T-type half-bridge LLC conversion form.

Further, in step S1, when the converter operates in a three-level T-type three-phase interleaved LLC conversion mode:

The T-type three-phase topology works with three levels: Vdc/2, 0 and -Vdc/2. The switches Sa1 and Sa4 are complementary to each other to generate the first phase level: Vdc/2 and -Vdc/2; switches Sa2 and Sa3 The conduction of switches Sb1 and Sb4 produces the first phase level: 0; the complementary conduction of switches Sb1 and Sb4 produces the second phase level: Vdc/2, -Vdc/2; the conduction of switches Sb2, Sb3 and S produces the second phase level. : 0; switches Sc1 and Sc4 are turned on complementaryly to produce the third phase level: Vdc/2, -Vdc/2; switches Sc2, Sc3 and S are turned on to produce a third phase level: 0; the three phases are at 120° Staggered runs.

Furthermore, in step S2, when the converter operates in a three-level T-type full-bridge LLC conversion mode:

Switch S is normally open; switches Sc1, Sc2, Sc3 and Sc4 are normally open; at this time, the equivalent quality factor of the resonant network is 2 times that in the three-phase interleaved working mode;

Using a T-shaped full-bridge topology composed of Sa1-Sa4 and Sb1-Sb4, switches S, Sc1, Sc2, Sc3 and Sc4 remain open, and switches Sa1-Sa4 and Sb1-Sb4 serve as PWM high-frequency switches;

Or use a T-shaped full-bridge topology composed of Sb1-Sb4 and Sc1-Sc4. Switch S, switches Sa1, Sa2, Sa3 and Sa4 remain disconnected, and switches Sb1-Sb4 and Sc1-Sc4 serve as PWM high-frequency switches;

Or use a T-shaped full-bridge topology composed of Sc1-Sc4 and Sa1-Sa4, with switch S, switches Sb1, Sb2, Sb3 and Sb4 kept open; switches Sc1-Sc4 and Sa1-Sa4 serve as PWM high-frequency switches;

At this time, the equivalent quality factor of the resonant network is 2 times that in the three-phase interleaved operating mode; when the input voltage is lower than 0.5 times the rated input voltage, the T-type full bridge operates at three levels: Vdc, 0, and -Vdc. : When the input voltage is higher than 0.5 times the rated input voltage, the T-type full bridge operates at three levels: Vdc/2, 0, and -Vdc/2.

Further, in step S3, the converter operates as a three-level T-type half-bridge LLC converter, including the following steps:

Six switches participate in the work to form a half-bridge topology: a T-shaped half-bridge topology composed of Sa1-Sa4 and Sb2-Sb3. Switch S, switches Sb1, Sb4, and Sc1-Sc4 remain open, and switches Sa1-Sa4 and Sb2, Sb3 serves as a PWM high-frequency switch;

Or use a T-shaped half-bridge topology composed of Sb1-Sb4 and Sa2-Sa3. Switch S, switches Sa1, Sa4, and Sc1-Sc4 remain disconnected, and switches Sb1-Sb4 and Sa2-Sa3 serve as PWM high-frequency switches;

Or use a T-shaped half-bridge topology composed of Sc1-Sc4 and Sb2-Sb3. Switch S, switches Sb1, Sb4, and Sa1-Sa4 remain disconnected, and switches Sc1-Sc4 and Sb2-Sb3 serve as PWM high-frequency switches.

Further, in step S3, the converter operates as a three-level T-type half-bridge LLC converter, including the following steps:

A half-bridge topology is formed by the participation of four switch tubes and S switches: a T-shaped half-bridge topology composed of Sa1-Sa4 and switch S. The switches Sb1-Sb4 and Sc1-Sc4 remain disconnected, and the switches Sa1-Sa4 serve as PWM high-frequency switch, switch S remains on;

Or a T-shaped half-bridge topology composed of Sb1-Sb4 and switch S. The switches Sa1-Sa4 and Sc1-Sc4 remain open, the switches Sb1-Sb4 serve as PWM high-frequency switches, and the switch S remains on;

Or a T-shaped half-bridge topology composed of Sc1-Sc4 and switch S. The switches Sa1-Sa4 and Sb1-Sb4 remain open, the switches Sc1-Sc4 serve as PWM high-frequency switches, and the switch S remains on.

Beneficial effects of adopting this technical solution:

The converter of the present invention can perform flexible switching in T-type three-phase topology, T-type full bridge and T-type half bridge according to changes in power and input voltage, combined with variable frequency and variable duty cycle control, thereby broadening the gain range of the converter. It can also match the load power range and improve converter efficiency. The input end of the resonant network is clamped to zero voltage through a T-type half-bridge switch or switch S, thereby realizing variable duty cycle control and variable frequency control of various three-level topologies, thereby equivalently adjusting the input voltage of the resonant network, thereby converting the converter The gain range can be broadened to widen the transformer range of the converter while reducing the circulating current loss.

In the present invention, multiple topologies can be flexibly switched according to changes in input voltage or load, which further broadens the transformer range of the converter while improving the efficiency of the converter within the entire operating range.

The present invention can realize zero-voltage turn-on or zero-current turn-off of the switch without additional hardware and auxiliary circuits, and the switch transitions the switching state in a multi-level manner, greatly reducing the switching loss; while retaining the input and The advantage of output current ripple interleaving and cancellation reduces the size of the converter and improves the dynamic performance of the converter.

The converter of the present invention has a certain self-current balancing capability, which reduces the requirements on device tolerances, thereby making the converter easier to use.

Description of drawings

Figure 1 is a topological schematic diagram of a three-phase interleaved T-type three-level LLC converter in the present invention in which the transformer adopts a Y-Δ structure.

Figure 2 is a topological diagram of a three-phase interleaved T-type three-level LLC converter in which the transformer adopts a Y-Y structure in the present invention.

Figure 3 is a schematic diagram of the three-phase interleaved T-type three-level LLC converter of the present invention and its wide voltage transformation control.

Figure 4 is a schematic diagram of the working waveform of the three-phase interleaved T-type three-level LLC converter based on variable frequency combined with variable duty cycle control in the present invention.

Figure 5 is a schematic topology diagram of a T-type full-bridge three-level converter with flexible switching according to the present invention.

Figure 6 is a schematic topology diagram of a T-type half-bridge three-level converter with flexible switching according to the present invention.

Figure 7 is a topological diagram of a T-type half-bridge three-level converter with the S switch turned on according to the present invention.

Figure 8 is an equivalent simplified topological circuit diagram of the T-type half-bridge three-level converter with the S switch turned on according to the present invention.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention clearer, the present invention will be further described below in conjunction with the accompanying drawings.

In this embodiment, as shown in Figures 1 and 2, the present invention proposes a three-phase interleaved T-type three-level LLC converter, including:

Capacitor Cdc1 and capacitor Cdc2 are connected in series to equally share the input DC voltage;

Three T-shaped half bridges form a three-phase three-level inverter; the first phase T-shaped half bridge: switches Sa1 and Sa2 form a half bridge, switches Sa3 and Sa4 are connected in reverse series and connected to the midpoint of the input DC capacitor; the second phase Phase T-shaped half bridge: switches Sb1 and Sb2 form a half bridge, switches Sb3 and Sb4 are connected in reverse series and connected to the midpoint of the input DC capacitor; third phase T-shaped half bridge: switches Sc1 and Sc2 form a half bridge, switches Sc3 and Sc4 Connect in reverse series and connect to the midpoint of the input DC capacitor;

Three sets of series-connected resonant capacitors Cr, resonant inductors Lr and isolation transformers are connected to the three T-shaped half-bridges. The midpoint of the Y-shaped connection on the primary side of the isolation transformer is connected to the midpoint of the input DC capacitor through the switch S;

and a diode rectifier bridge set on the secondary side of the isolation transformer, and then connected to the load through the output DC capacitor Co.

Preferably, the isolation transformer adopts Y-Δ-type (as shown in Figure 1) or Y-Y type (as shown in Figure 2).

Preferably, the diode rectifier bridge includes six diodes D1, D2, D3, D4, D5 and D6, which are connected in series and then in parallel.

A three-phase three-level inverter is composed of three T-shaped half-bridges to convert DC into AC with adjustable frequency and variable duty cycle. The energy is transferred to the load through the resonant network, transformer and diode rectifier bridge; by changing the resonant network The frequency and effective value of the fundamental wave component realize the regulation of the output voltage or current; the input voltage of the resonant network is clamped to zero through the midpoint of the T-shaped half bridge or the switch S, and the input voltage duty cycle of the resonant network is adjusted, thereby Adjust the effective value of the equivalent input voltage to adjust the transformer range and reduce the zero-level circulating current loss.

In order to cooperate with the implementation of the above-mentioned device of the present invention, based on the same inventive concept, the present invention also provides a wide transformer control method for a three-phase interleaved T-type three-level LLC converter. Based on the proposed three-phase interleaved T-type three-level For LLC converters, the required operating topology is determined by the input voltage and load power. Switching between topology forms is achieved through flexible changing topology. The topology forms include three-level T-type three-phase interleaved LLC conversion forms, three-level T-type full-bridge LLC conversion form and three-level T-type half-bridge LLC conversion form;

According to changes in power and input voltage, the converter performs flexible switching in T-type three-phase topology, T-type full bridge and T-type half bridge, combined with variable frequency and variable duty cycle control, thereby broadening the gain range of the converter; through T-type The half-bridge or switch S clamps the input end of the resonant network to zero voltage, thereby equivalently regulating the input voltage of the resonant network.

Specifically, the wide transformer control method of the three-phase interleaved T-type three-level LLC converter is shown in Figure 3, including the steps:

S1, when the load power is greater than 70% of the rated power: the converter works in a three-level T-type three-phase interleaved LLC conversion form, with the circuit topology shown in Figure 1 or Figure 2;

S2, when the load power is between 30% and 70% of the rated power: the converter works as a three-level T-type full-bridge LLC converter, as shown in the circuit topology in Figure 5; when the input voltage is lower than 0.5 times the rated input When the input voltage is high, the T-type full bridge operates at three levels: Vdc/2, 0, and -Vdc/2; when the input voltage is higher than 0.5 times the rated input voltage, the T-type full bridge operates at three levels: Vdc, 0, and -Vdc. level to work;

S3, when the load power is less than 30% of the rated power: the converter works in the form of three-level T-type half-bridge LLC conversion, as shown in Figure 6-Figure 8 of the circuit topology, that is, Vdc/2, 0, -Vdc/ 2Three levels.

As an optimization solution of the above embodiment, in step S1, when the converter operates in a three-level T-type three-phase interleaved LLC conversion form:

The T-type three-phase topology works with three levels: Vdc/2, 0 and -Vdc/2. The switches Sa1 and Sa4 are complementary to each other to generate the first phase level: Vdc/2 and -Vdc/2; switches Sa2 and Sa3 The conduction of switches Sb1 and Sb4 produces the first phase level: 0; the complementary conduction of switches Sb1 and Sb4 produces the second phase level: Vdc/2, -Vdc/2; the conduction of switches Sb2, Sb3 and S produces the second phase level. : 0; switches Sc1 and Sc4 are turned on complementaryly to produce the third phase level: Vdc/2, -Vdc/2; switches Sc2, Sc3 and S are turned on to produce a third phase level: 0; the three phases are at 120° Interleaved operation, the corresponding working waveform at this time is shown in Figure 4.

As an optimization solution of the above embodiment, in step S2, when the converter operates in the three-level T-type full-bridge LLC conversion form:

Switch S is normally open; switches Sc1, Sc2, Sc3 and Sc4 are normally open; at this time, the equivalent quality factor of the resonant network is 2 times that in the three-phase interleaved working mode;

Using a T-shaped full-bridge topology composed of Sa1-Sa4 and Sb1-Sb4, switches S, Sc1, Sc2, Sc3 and Sc4 remain open, and switches Sa1-Sa4 and Sb1-Sb4 serve as PWM high-frequency switches, as shown in Figure 5;

Or use a T-shaped full-bridge topology composed of Sb1-Sb4 and Sc1-Sc4. Switch S, switches Sa1, Sa2, Sa3 and Sa4 remain disconnected, and switches Sb1-Sb4 and Sc1-Sc4 serve as PWM high-frequency switches;

Or use a T-shaped full-bridge topology composed of Sc1-Sc4 and Sa1-Sa4, with switch S, switches Sb1, Sb2, Sb3 and Sb4 kept open; switches Sc1-Sc4 and Sa1-Sa4 serve as PWM high-frequency switches;

At this time, the equivalent quality factor of the resonant network is 2 times that in the three-phase interleaved operating mode; when the input voltage is lower than 0.5 times the rated input voltage, the T-type full bridge operates at three levels: Vdc, 0, and -Vdc. : When the input voltage is higher than 0.5 times the rated input voltage, the T-type full bridge operates at three levels: Vdc/2, 0, and -Vdc/2.

As an optimization solution of the above embodiment, in step S3, the converter operates as a three-level T-type half-bridge LLC converter, including the following steps:

Six switches participate in the work to form a half-bridge topology: a T-shaped half-bridge topology composed of Sa1-Sa4 and Sb2-Sb3. Switch S, switches Sb1, Sb4, and Sc1-Sc4 remain open, and switches Sa1-Sa4 and Sb2, Sb3 serves as a PWM high-frequency switch; as shown in Figure 6;

Or use a T-shaped half-bridge topology composed of Sb1-Sb4 and Sa2-Sa3. Switch S, switches Sa1, Sa4, and Sc1-Sc4 remain disconnected, and switches Sb1-Sb4 and Sa2-Sa3 serve as PWM high-frequency switches;

Or use a T-shaped half-bridge topology composed of Sc1-Sc4 and Sb2-Sb3. Switch S, switches Sb1, Sb4, and Sa1-Sa4 remain disconnected, and switches Sc1-Sc4 and Sb2-Sb3 serve as PWM high-frequency switches.

As an optimization solution of the above embodiment, in step S3, the converter operates as a three-level T-type half-bridge LLC converter, including the following steps:

A half-bridge topology is formed by the participation of four switch tubes and S switches: a T-shaped half-bridge topology composed of Sa1-Sa4 and switch S. The switches Sb1-Sb4 and Sc1-Sc4 remain disconnected, and the switches Sa1-Sa4 serve as PWM high-frequency switch, switch S remains on; as shown in Figure 7;

Or a T-shaped half-bridge topology composed of Sb1-Sb4 and switch S. The switches Sa1-Sa4 and Sc1-Sc4 remain open, the switches Sb1-Sb4 serve as PWM high-frequency switches, and the switch S remains on;

Or a T-shaped half-bridge topology composed of Sc1-Sc4 and switch S. The switches Sa1-Sa4 and Sb1-Sb4 remain open, the switches Sc1-Sc4 serve as PWM high-frequency switches, and the switch S remains on.

That is to say, by arbitrarily enabling one group of three groups of half-bridge switches Sa1-Sa4, Sb1-Sb4 and Sc1-Sc4, a T-type half-bridge LLC converter topology can be formed, as shown in Figure 8.

The converter can perform flexible switching in T-type three-phase topology, T-type full bridge and T-type half bridge according to changes in power and input voltage, combined with variable frequency and variable duty cycle control, thereby broadening the gain range of the converter and also enabling Match the load power range and improve converter efficiency. The input end of the resonant network is clamped to zero voltage through a T-shaped half-bridge switch or switch S, thereby equivalently adjusting the input voltage of the resonant network and thus broadening the gain range of the converter.

The basic principles and main features of the present invention and the advantages of the present invention have been shown and described above. Those skilled in the industry should understand that the present invention is not limited by the above embodiments. The above embodiments and descriptions only illustrate the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention will also have other aspects. Various changes and modifications are possible, which fall within the scope of the claimed invention. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims (7)

1. A wide transformer control method for a three-phase interleaved T-type three-level LLC converter, which is characterized in that, based on a three-phase interleaved T-type three-level LLC converter, it includes: capacitor Cdc1 and capacitor Cdc2 are connected in series for equal input DC voltage; three T-shaped half bridges form a three-phase three-level inverter; the first phase T-shaped half bridge: switches Sa1 and Sa2 form a half bridge, switches Sa3 and Sa4 are connected in reverse series and connected to the midpoint of the input DC capacitor ; Second phase T-shaped half bridge: switches Sb1 and Sb2 form a half bridge, switches Sb3 and Sb4 are connected in reverse series and connected to the midpoint of the input DC capacitor; third phase T-shaped half bridge: switches Sc1 and Sc2 form a half bridge, switches Sc3 and Sc4 are connected in reverse series and connected to the midpoint of the input DC capacitor; three sets of series resonant capacitors Cr, resonant inductor Lr and isolation transformers are connected to the three T-shaped half bridges. The midpoint of the Y-shaped connection on the primary side of the isolation transformer is The switch S is connected to the midpoint of the input DC capacitor; and the diode rectifier bridge set on the secondary side of the isolation transformer, and then connected to the load through the output DC capacitor Co; The required operating topology is determined by the input voltage and load power. Switching between topology forms is achieved through flexible changing topology. The topology forms include three-level T-type three-phase interleaved LLC conversion form, three-level T-type full bridge LLC conversion form and three-level T-type half-bridge LLC conversion form; According to changes in power and input voltage, the converter performs flexible switching in T-type three-phase topology, T-type full bridge and T-type half bridge, combined with variable frequency and variable duty cycle control, thereby broadening the gain range of the converter; through T-type The half-bridge or switch S clamps the input end of the resonant network to zero voltage, thereby equivalently adjusting the input voltage of the resonant network; Includes steps: S1, when the load power is greater than 70% of the rated power: the converter works in a three-level T-type three-phase interleaved LLC conversion form; S2, when the load power is between 30% and 70% of the rated power: the converter operates as a three-level T-type full-bridge LLC converter; when the input voltage is lower than 0.5 times the rated input voltage, the T-type full bridge operates with Vdc /2, 0, -Vdc/2 operates at three levels; when the input voltage is higher than 0.5 times the rated input voltage, the T-type full bridge operates at three levels: Vdc, 0, -Vdc; In the step S2, when the converter operates in the three-level T-type full-bridge LLC conversion mode: Switch S is normally open; switches Sc1, Sc2, Sc3 and Sc4 are normally open; at this time, the equivalent quality factor of the resonant network is 2 times that in the three-phase interleaved working mode; Using a T-shaped full-bridge topology composed of Sa1-Sa4 and Sb1-Sb4, switches S, Sc1, Sc2, Sc3 and Sc4 remain open, and switches Sa1-Sa4 and Sb1-Sb4 serve as PWM high-frequency switches; Or use a T-shaped full-bridge topology composed of Sb1-Sb4 and Sc1-Sc4. Switch S, switches Sa1, Sa2, Sa3 and Sa4 remain disconnected, and switches Sb1-Sb4 and Sc1-Sc4 serve as PWM high-frequency switches; Or use a T-shaped full-bridge topology composed of Sc1-Sc4 and Sa1-Sa4, with switch S, switches Sb1, Sb2, Sb3 and Sb4 kept open; switches Sc1-Sc4 and Sa1-Sa4 serve as PWM high-frequency switches; At this time, the equivalent quality factor of the resonant network is 2 times that in the three-phase interleaved operating mode; when the input voltage is lower than 0.5 times the rated input voltage, the T-type full bridge operates at three levels: Vdc, 0, and -Vdc. : When the input voltage is higher than 0.5 times the rated input voltage, the T-type full bridge operates at three levels: Vdc/2, 0, and -Vdc/2; S3, when the load power is less than 30% of the rated power: the converter operates in a three-level T-type half-bridge LLC conversion mode. 2. A wide voltage transformation control method for a three-phase interleaved T-type three-level LLC converter according to claim 1, characterized in that, in step S1, the converter adopts a three-level T-type three-phase When working in the interleaved LLC transformation form: The T-type three-phase topology works with three levels: Vdc/2, 0 and -Vdc/2. The switches Sa1 and Sa4 are complementary to each other to generate the first phase level: Vdc/2 and -Vdc/2; switches Sa2 and Sa3 The conduction of switches Sb1 and Sb4 produces the first phase level: 0; the complementary conduction of switches Sb1 and Sb4 produces the second phase level: Vdc/2, -Vdc/2; the conduction of switches Sb2, Sb3 and S produces the second phase level. : 0; switches Sc1 and Sc4 are turned on complementaryly to produce the third phase level: Vdc/2, -Vdc/2; switches Sc2, Sc3 and S are turned on to produce a third phase level: 0; the three phases are at 120° Staggered runs. 3. A wide voltage transformation control method for a three-phase interleaved T-type three-level LLC converter according to claim 1, characterized in that, in the step S3, the converter adopts a three-level T-type half bridge The operation of the LLC converter includes the following steps: Six switches participate in the work to form a half-bridge topology: a T-shaped half-bridge topology composed of Sa1-Sa4 and Sb2-Sb3. Switch S, switches Sb1, Sb4, and Sc1-Sc4 remain open, and switches Sa1-Sa4 and Sb2, Sb3 serves as a PWM high-frequency switch; Or use a T-shaped half-bridge topology composed of Sb1-Sb4 and Sa2-Sa3. Switch S, switches Sa1, Sa4, and Sc1-Sc4 remain disconnected, and switches Sb1-Sb4 and Sa2-Sa3 serve as PWM high-frequency switches; Or use a T-shaped half-bridge topology composed of Sc1-Sc4 and Sb2-Sb3. Switch S, switches Sb1, Sb4, and Sa1-Sa4 remain disconnected, and switches Sc1-Sc4 and Sb2-Sb3 serve as PWM high-frequency switches. 4. A wide voltage transformation control method for a three-phase interleaved T-type three-level LLC converter according to claim 1, characterized in that, in the step S3, the converter adopts a three-level T-type half bridge The operation of the LLC converter includes the following steps: A half-bridge topology is formed by the participation of four switch tubes and S switches: a T-shaped half-bridge topology composed of Sa1-Sa4 and switch S. The switches Sb1-Sb4 and Sc1-Sc4 remain disconnected, and the switches Sa1-Sa4 serve as PWM high-frequency switch, switch S remains on; Or a T-shaped half-bridge topology composed of Sb1-Sb4 and switch S. The switches Sa1-Sa4 and Sc1-Sc4 remain open, the switches Sb1-Sb4 serve as PWM high-frequency switches, and the switch S remains on; Or a T-shaped half-bridge topology composed of Sc1-Sc4 and switch S. The switches Sa1-Sa4 and Sb1-Sb4 remain open, the switches Sc1-Sc4 serve as PWM high-frequency switches, and the switch S remains on. 5. A wide voltage transformation control method for a three-phase interleaved T-type three-level LLC converter according to claim 1, characterized in that the isolation transformer adopts Y-Y type or Y-Δ type. 6. A wide voltage transformation control method for a three-phase interleaved T-type three-level LLC converter according to claim 1, characterized in that the diode rectifier bridge includes six diodes D1, D2, D3, D4, D5 and D6 are connected in series and then in parallel. 7. A wide voltage control method for a three-phase interleaved T-type three-level LLC converter according to claim 1, characterized in that a three-phase three-level inverter is formed by three T-type half bridges. The DC becomes AC with adjustable frequency and variable duty cycle, and the energy is transferred to the load through the resonant network, transformer and diode rectifier bridge; the output voltage or current is adjusted by changing the frequency and effective value of the fundamental wave component in the resonant network; Clamp the input voltage of the resonant network to zero through the midpoint of the T-shaped half-bridge or the switch S, adjust the input voltage duty cycle of the resonant network, thereby adjusting the effective value of the equivalent input voltage to adjust the transformer range while reducing the zero level of circulating current loss.