THREE-PHASE RESONANT CONVERTER AND METHOD OF CONTROLLING THE SAME

Abstract

A three-phase resonant converter includes a three-phase transformer, an input bridge arm assembly, an output bridge arm assembly, and a control unit. The input bridge arm assembly has three input switch arms, and each input switch arm has an upper switch and a lower switch. The output bridge arm assembly has three output synchronous rectification switch arms respectively coupled to the three secondary-side windings. Each output synchronous rectification switch arm has an upper rectification switch and a lower rectification switch. The control of each output synchronous rectification switch arm is corresponding to the control of each input switch arm. The control unit controls the upper rectification switch or the lower rectification switch to be turned on with a leading phase angle to the corresponding upper switch or the lower switch so as to maintain an output voltage of the resonant converter to be higher than a voltage threshold.

Description

BACKGROUND

Technical Field

The present disclosure relates to a resonant converter and a method of controlling the same, and more particularly to a three-phase resonant converter and a method of controlling the same.

Description of Related Art

The statements in this section merely provide background information related to the present disclosure and do not necessarily constitute prior art.

Due to soft-switching characteristics, the resonant converter has better conversion efficiency than the traditional DC-to-DC converter, and therefore the resonant converter has been widely used in various power supply products in recent years, among which the LLC structure is more common. However, the resonant converter has the characteristic that high gain and high efficiency cannot be satisfied at the same time: if the characteristic curve is optimized for high efficiency, the gain capability will be sacrificed, resulting in the inability to meet the current market requirement that the output voltage of the power converter needs to be maintained at a certain output level (referred to as the voltage threshold in the following) for a hold-up time when the input power is lost. Conversely, if optimized for a high gain curve, the efficiency will be sacrificed for increased energy consumption.

Existing control strategies have been successfully applied to single-phase resonant converters. However, with the gradual development of power supply products to higher output power, the application of single-phase resonant converters began to appear inadequate. In order to achieve three-phase current balance in three-phase resonant converters, a common method used in the past was to independently adjust the duty cycle of the three phases. However, this method cannot make the duty cycle of the three phases operate at the optimum point, thereby affecting efficiency. Another common method is to adjust the relative angles of the three-phase duty cycle so that the three phases are not fixed at 120 degrees from each other so as to achieve current balance, but the control difficulty of this method is relatively high.

Therefore, how to design a three-phase resonant converter and a method of controlling the same to solve the problems and technical bottlenecks in the existing technology has become a critical topic in this field.

SUMMARY

An objective of the preset disclosure is to provide a three-phase resonant converter. The three-phase resonant converter includes a three-phase transformer, an input bridge arm assembly, an output bridge arm assembly, and a control unit. The three-phase transformer includes three primary-side windings and three secondary-side windings. The input bridge arm assembly includes three input switch arms respectively coupled to the three primary-side windings, wherein each input switch arm includes an upper switch and a lower switch. The output bridge arm assembly includes three output synchronous rectification switch arms respectively coupled to the three secondary-side windings, wherein each output synchronous rectification switch arm includes an upper rectification switch and a lower rectification switch, and the control of each output synchronous rectification switch arm is corresponding to the control of each input switch arm. The control unit controls the upper rectification switch or the lower rectification switch to be correspondingly turned on with a phase angle leading to the upper switch or the lower switch so as to maintain an output voltage of the resonant converter to be higher than a voltage threshold.

Accordingly, the three-phase resonant converter has the following characteristics and advantages: 1. the three-phase resonant converter and the method of controlling the same can provide both high-gain and high-efficiency characteristics, and can be applied to higher output power design; 2. the unbalanced input currents can be controlled to adjust the phase angle differences for the first phase angle, the second phase angle, and the third phase angle so as to achieve the optimum control of leading phase angle and the balance of the three-phase current; 3. three primary-side windings and three secondary-side windings of the three-phase transformer can be implemented in a star connection (Y connection) or a delta connection (A connection), thereby increasing the flexibility and convenience of circuit design.

Another objective of the preset disclosure is to provide a method of controlling a three-phase resonant converter. The method includes steps of: providing a three-phase resonant converter having a three-phase transformer, an input bridge arm, and an output bridge arm; wherein the input bridge arm assembly includes three input switch arms, and each input switch arm includes an upper switch and a lower; wherein the output bridge arm assembly includes three output synchronous rectification switch arms, and each output synchronous rectification switch arm includes an upper rectification switch and a lower rectification switch, controlling each output synchronous rectification switch arm and each input switch arm correspondingly, and control the upper rectification switch or the lower rectification switch to be correspondingly turned on with a phase angle leading to the upper switch or the lower switch so as to maintain an output voltage of the resonant converter to be higher than a voltage threshold.

Accordingly, the method of controlling the three-phase resonant converter has the following characteristics and advantages: 1. the three-phase resonant converter and the method of controlling the same can provide both high-gain and high-efficiency characteristics, and can be applied to higher output power design; 2. the unbalanced input currents can be controlled to adjust the phase angle differences for the first phase angle, the second phase angle, and the third phase angle so as to achieve the optimum control of leading phase angle and the balance of the three-phase current; 3. three primary-side windings and three secondary-side windings of the three-phase transformer can be implemented in a star connection (Y connection) or a delta connection (Δ connection), thereby increasing the flexibility and convenience of circuit design.

It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the present disclosure as claimed. Other advantages and features of the present disclosure will be apparent from the following description, drawings, and claims.

BRIEF DESCRIPTION OF DRAWINGS

The present disclosure can be more fully understood by reading the following detailed description of the embodiment, with reference made to the accompanying drawing as follows:

FIG. 1 is a block circuit diagram of a three-phase resonant converter according to the present disclosure.

FIG. 2A is a schematic waveform of switch signals of operating a conventional three-phase resonant converter at a frequency being less than a frequency threshold.

FIG. 2B is a schematic waveform of switch signals of operating the conventional three-phase resonant converter at a frequency being greater than the frequency threshold.

FIG. 3A is a schematic waveform of switch signals of operating the three-phase resonant converter at a frequency being less than the frequency threshold according to the present disclosure.

FIG. 3B is a schematic waveform of switch signals of operating the three-phase resonant converter at a frequency being greater than the frequency threshold according to the present disclosure.

FIG. 4 is a block diagram of a current balance controller according to the present disclosure.

FIG. 5A is a schematic waveform of an unbalanced input current of the three-phase resonant converter of the present disclosure.

FIG. 5B is a schematic waveform of a balanced input current of the three-phase resonant converter of the present disclosure.

FIG. 6A to FIG. 6H are circuit diagrams of three primary-side windings of a three-phase transformer according to different embodiments of the present disclosure.

FIG. 7A and FIG. 7B are circuit diagrams of three secondary-side windings of the three-phase transformer according to different embodiments of the present disclosure.

FIG. 8 is a flowchart of a method of controlling the three-phase resonant converter according to the present disclosure.

DETAILED DESCRIPTION

Reference will now be made to the drawing figures to describe the present disclosure in detail. It will be understood that the drawing figures and exemplified embodiments of present disclosure are not limited to the details thereof.

Please refer to FIG. 1, which shows a block circuit diagram of a three-phase resonant converter according to the present disclosure. The three-phase resonant converter includes a three-phase transformer 11, an input bridge arm assembly 12, an output bridge arm assembly 13, and a control unit 10. The three-phase transformer 11 includes a resonant circuit (having resonant capacitors Cr1-Cr3 and resonant inductors Lr1-Lr3), and three primary-side windings and three secondary-side windings. The control strategy proposed in the present disclosure may be applied to various three-phase resonant converter structures, and as shown in FIG. 6A to FIG. 6H, the three primary-side windings of the three-phase transformer 11 are star-connected (wye-connected) or delta-connected (triangle-connected), and as shown in FIG. 7A and FIG. 7B, the three secondary-side windings of the three-phase transformer 11 are star-connected or delta-connected.

The input bridge arm assembly 12 includes three input switch bridge arms 121, 122, 123, i.e., a first input switch bridge arm 121, a second input switch bridge arm 122, and a three input switch bride arm 123, respectively coupled to the three primary-side windings. Each input switch bridge arm 121, 122, 123 includes an upper switch Q₁, Q₃, Q₅ and a lower switch Q₂, Q₄, Q₆, that is, the first input switch bridge arm 121 includes a first upper switch Q₁ and a first lower switch Q₂, and the first upper switch Q₁ and the first lower switch Q₂ are commonly connected at a first node N_A. The second input switch bridge arm 122 includes a second upper switch Q₃ and a second lower switch Q₄, and the second upper switch Q₃ and the second lower switch Q₄ are commonly connected at a second node NB. The third input switch bridge arm 123 includes a third upper switch Q₅ and a third lower switch Q₆, and the third upper switch Q₅ and the third lower switch Q₆ are commonly connected at a third node N_C.

The output bridge arm assembly includes three output synchronous rectification switch arms 131, 132, 133, i.e., a first output synchronous rectification switch arm 131, a second output synchronous rectification switch arm 132, and a three output synchronous rectification switch arm 133, respectively coupled to the three secondary-side windings. Each output synchronous rectification switch arm 131, 132, 133 includes an upper rectification switch SR₁, SR₃, SR₅ and a lower rectification switch SR₂, SR₄, SR₆, that is, the first output synchronous rectification switch arm 131 includes a first upper rectification switch SR₁ and a first lower rectification switch SR₂. The second output synchronous rectification switch arm 132 includes a second upper rectification switch SR₃ and a second lower rectification switch SR₄. The third output synchronous rectification switch arm 133 includes a third upper rectification switch SR₅ and a third lower rectification switch SR₆.

In particular, the control of each output synchronous rectification switch arm 131, 132, 133 is corresponding to the control of each input switch arm 121, 122, 123. Specifically, the control of the first upper rectification switch SR₁ and the first lower rectification switch SR₂ of the first output synchronous rectification switch arm 131 is corresponding to the first upper switch Q₁ and the first lower switch Q₂ of the first input switch bridge arm 121. The control of the second upper rectification switch SR₃ and the second lower rectification switch SR₄ of the second output synchronous rectification switch arm 132 is corresponding to the second upper switch Q₃ and the second lower switch Q₄ of the second input switch bridge arm 122. The control of the third upper rectification switch SR₅ and the third lower rectification switch SR₆ of the third output synchronous rectification switch arm 133 is corresponding to the third upper switch Q₅ and the third lower switch Q₆ of the third input switch bridge arm 123.

In different embodiments, the controller unit 10 may receive an input voltage Vdc or the output voltage Vout of the three-phase resonant converter, that is, as long as the state of the output voltage Vout can be directly or indirectly acquired, it can be a source of voltage information. Taking the embodiment of receiving the output voltage Vout in FIG. 1 as an example, the control unit 10 provides input bridge arm switch signals S_Q1-S_Q6 to respectively control the upper switches Q₁, Q₃, Q₅ and the lower switches Q₂, Q₄, Q₆ and provides output bridge arm switch signals S_SR1-S_SR6 to respectively control the upper rectification switches SR₁, SR₃, SR₅ and the lower rectification switches SR₂, SR₄, SR₆ according to the output voltage Vout so that the upper rectification switch SR₁, SR₃, SR₅ or the lower rectification switch SR₂, SR₄, SR₆ to be correspondingly turned on with a phase angle leading to the upper switch Q₁, Q₃, Q₅ or the lower switch Q₂, Q₄, Q₆ so as to maintain the output voltage Vout of the resonant converter to be higher than a voltage threshold. Accordingly, when the three-phase resonant converter is shut down or the input power source does not supply power, the hold-tup time for the output voltage Vout to be kept at the output level can be extended. The detailed operation and principle will be explained later.

Please refer to FIG. 2A and FIG. 2B, which respectively show schematic waveforms of switch signals of operating a conventional three-phase resonant converter at a frequency being less than a frequency threshold and at the frequency being greater than the frequency threshold. As shown in FIG. 2A, when the resonant converter operates at the frequency being less than the frequency threshold, such as but not limited to, a resonant frequency of the resonant converter, and the resonant frequency will be described later as examples, in order to avoid the hard switching of the synchronous rectification switch on the output side, resulting in increased switching loss, the turned-on time period is reduced. For example, a time period of turning on the third lower rectification switch SR₆ shown in the figures is the resonant period 1/f_R. However, it will reduce the hold-up time that the power supply can maintain the output voltage at a certain/specific output level when the power supply is turned off or the input power source does not supply power. The resonant converter operating above the resonant frequency (as shown in FIG. 2B) is less likely to have this situation than the resonant converter operating below the resonant frequency.

Therefore, in order to solve the situation that the switching mode and the hold-up time of the switches cannot be considered in the previous disclosure, the present disclosure provides a three-phase resonant converter and a method of controlling the same to solve the existing problems and technical bottlenecks in the related art.

Please refer to FIG. 3A, which shows a schematic waveform of switch signals of operating the three-phase resonant converter at a frequency being less than the frequency threshold according to the present disclosure. The control unit 10 acquires a working frequency command according to the output voltage Vout of the three-phase resonant converter. Based on the working frequency command being less than the frequency threshold (for example, the resonant frequency f_R) of the resonant converter, the upper rectification switch SR₁, SR₃, SR₅ or the lower rectification switch SR₂, SR₄, SR₆ is correspondingly turned on with a phase angle leading to the upper switch Q₁, Q₃, Q₅ or the lower switch Q₂, Q₄, Q₆. That is, the first upper rectification switch SR₁ is turned on with a first phase angle ΦL1 leading to the first upper switch Q₁, or the first lower rectification switch SR₂ is turned on with the first phase angle ΦL1 leading to the first lower switch Q₂. Similarly, the second upper rectification switch SR₃ is turned on with a second phase angle ΦL2 leading to the second upper switch Q₃, or the second lower rectification switch SR₄ is turned on with the second phase angle ΦL2 leading to the second lower switch Q₄. Similarly, the third upper rectification switch SR₅ is turned on with a third phase angle ΦL3 leading to the third upper switch Q₅, or the third lower rectification switch SR₆ is turned on with the third phase angle ΦL3 leading to the third lower switch Q₆.

In this operation, since the upper rectification switch SR₁, SR₃, SR₅ or the lower rectification switch SR₂, SR₄, SR₆ is correspondingly turned on with the phase angle leading to the upper switch Q₁, Q₃, Q₅ or the lower switch Q₂, Q₄, Q₆, compared to the FIG. 2A (the time period of turning on the rectification switch SR₆ is the resonant period 1/f_R), the turned-on time period is greater than the resonant period 1/f_R, wherein the resonant period 1/f_R is the reciprocal of the resonant frequency f_R.

Moreover, as shown in FIG. 3A, a time point of turning on the upper rectification switch SR₁, SR₃, SR₅ or turning on the lower rectification switch SR₂, SR₄, SR₆ is earlier than a time point of turning on the corresponding upper switch Q₁, Q₃, Q₅ or lower switch Q₂, Q₄, Q₆; a time point of turning off the upper rectification switch SR₁, SR₃, SR₅ or turning off the lower rectification switch SR₂, SR₄, SR₆ is earlier than a time point of turning off the corresponding upper switch Q₁, Q₃, Q₅ or lower switch Q₂, Q₄, Q₆, and the time period of turning on the upper rectification switch SR₁, SR₃, SR₅ or turning on the lower rectification switch SR₂, SR₄, SR₆ at different switching cycles gradually increases with time. Specifically, taking the third lower rectification switch SR₆ and the third lower switch Q₆ as an example. A time point (time t0″) of turning on the third lower rectification switch SR₆ is earlier than a time point (time t0) of turning on the three lower switch Q₆, and a time point (time t0′) of turning off the third lower rectification switch SR₆ is earlier than a time point (time t2) of turning off the third lower switch Q₆. The same is true for other upper and lower rectification switches and the corresponding upper and lower switches.

Please refer to FIG. 3B, which shows a schematic waveform of switch signals of operating the three-phase resonant converter at a frequency being greater than the frequency threshold according to the present disclosure. The control unit 10 acquires the working frequency command according to the output voltage Vout of the three-phase resonant converter. Based on the working frequency command being greater than the frequency threshold (for example, the resonant frequency f_R) of the resonant converter, the upper rectification switch SR₁, SR₃, SR₅ or the lower rectification switch SR₂, SR₄, SR₆ is correspondingly turned on with a phase angle leading to the upper switch Q₁, Q₃, Q₅ or the lower switch Q₂, Q₄, Q₆. That is, the first upper rectification switch SR₁ is turned on with a first phase angle ΦL1 leading to the first upper switch Q₁, or the first lower rectification switch SR₂ is turned on with the first phase angle ΦL1 leading to the first lower switch Q₂. The same is true for other upper and lower rectification switches and the corresponding upper and lower switches.

Moreover, as shown in FIG. 3B, a time point of turning on the upper rectification switch SR₁, SR₃, SR₅ or turning on the lower rectification switch SR₂, SR₄, SR₆ is earlier than a time point of turning on the corresponding upper switch Q₁, Q₃, Q₅ or lower switch Q₂, Q₄, Q₆, and a time period of turning on the upper rectification switch SR₁, SR₃, SR₅ or turning on the lower rectification switch SR₂, SR₄, SR₆ is equal to a time period of turning on the corresponding upper switch Q₁, Q₃, Q₅ or lower switch Q₂, Q₄, Q₆. Specifically, taking the third lower rectification switch SR₆ and the third lower switch Q₆ as an example. A time point (time t0″) of turning on the third lower rectification switch SR₆ is earlier than a time point (time t0) of turning on the three lower switch Q₆, and a time period of turning on the third lower rectification switch SR₆ (from time t0″ to time t0′″) is equal to a time period of turning on the third lower switch Q₆ (from time t0 to time t2). The same is true for other upper and lower rectification switches and the corresponding upper and lower switches.

In one operation situation, based on three input currents flowing into the three primary-side windings being the same, that is, the input currents of the three-phase resonant converter are balanced (refer to FIG. 5B), the three phase angles which the three upper rectification switches SR₁, SR₃, SR₅ or the three lower rectification switches SR₂, SR₄, SR₆ are correspondingly turned on leading to the three upper switches Q₁, Q₃, Q₅ or the three lower switches Q₂, Q₄, Q₆ are the same. In another operation situation, based on three input currents flowing into the three primary-side windings being not the same, that is, the input currents of the three-phase resonant converter are not balanced (refer to FIG. 5A), the three phase angles which the three upper rectification switches SR₁, SR₃, SR₅ or the three lower rectification switches SR₂, SR₄, SR₆ are correspondingly turned on leading to the three upper switches Q₁, Q₃, Q₅ or the three lower switches Q₂, Q₄, Q₆ are not the same. The specific description of the above two operation situations is as follows.

Please refer to FIG. 3A and FIG. 3B, the first upper rectification switch SR₁ and the first lower rectification switch SR₂ are correspondingly turned on with a first phase angle ΦL1 leading to the first upper switch Q₁ and the first lower switch Q₂. The second upper rectification switch SR₃ and the second lower rectification switch SR₄ are correspondingly turned on with a second phase angle ΦL2 leading to the second upper switch Q₃ and the second lower switch Q₄. The third upper rectification switch SR₅ and the third lower rectification switch SR₆ are correspondingly turned on with a third phase angle ΦL3 leading to the third upper switch Q₅ and the third lower switch Q₆. In particular, the relationships between the first phase angle ΦL1, the second phase angle ΦL2, and the third phase angle ΦL3 are:

• • the second phase angle ΦL2 is equal to the first phase angle ΦL1 plus a first phase angle difference ΔΦL12, that is, ΦL2=ΦL1+ΔΦL12;
  • the third phase angle ΦL3 is equal to the first phase angle ΦL1 plus a second phase angle difference ΔΦL13, that is, ΦL3=ΦL1+ΔΦL13.

For the balanced-current operation situation of the three-phase resonant converter, since the first phase angle difference ΔΦL12 and the second phase angle difference ΔΦL13 are zero, the first phase angle ΦL1, the second phase angle ΦL2, and the third phase angle ΦL3 are the same.

For the unbalanced-current operation situation of the three-phase resonant converter, since the first phase angle difference ΔΦL12 and the second phase angle difference ΔΦL13 are not zero, the first phase angle ΦL1, the second phase angle ΦL2, and the third phase angle ΦL3 are not the same.

Moreover, the first phase angle difference ΔΦL12 is determined by a first current Ir1 and a second current Ir2, and the second phase angle difference ΔΦL13 is determined by the first current Ir1 and a third current Ir3. In particular, the first current Ir1 is a current flowing from a command node, i.e., a first node N_A between the first upper switch Q₁ and the first lower switch Q₂ to the three-phase transformer 11, the second current Ir2 is a current flowing from a command node, i.e., a second node NB between the second upper switch Q₃ and the second lower switch Q₄ to the three-phase transformer 11, and the third current Ir3 is a current flowing from a command node, i.e., a third node N_C between the third upper switch Q₅ and the third lower switch Q₆ to the three-phase transformer 11.

When the second current Ir2 is greater than the first current Ir1, the first phase angle difference ΔΦL12 is negative, and when the second current Ir2 is less than the first current Ir1, the first phase angle difference ΔΦL12 is positive. Moreover, an absolute value of a current difference between the second current Ir2 and the first current Ir1 is greater, an absolute value of the first phase angle difference ΔΦL12 is greater. That is, when the second current Ir2 is increasingly greater than the first current Ir1, the first phase angle difference ΔΦL12 is a decreasingly negative value, and when the second current Ir2 is decreasingly less than the first current Ir1, the first phase angle difference ΔΦL12 is an increasingly positive value.

Similarly, when the third current Ir3 is greater than the first current Ir1, the second phase angle difference ΔΦL13 is negative, and when the third current Ir3 is less than the first current Ir1, the second phase angle difference ΔΦL13 is positive. Moreover, an absolute value of a current difference between the third current Ir3 and the first current Ir1 is greater, an absolute value of the second phase angle difference ΔΦL13 is greater. That is, when the third current Ir3 is increasingly greater than the first current Ir1, the second phase angle difference ΔΦL13 is a decreasingly negative value, and when the third current Ir3 is decreasingly less than the first current Ir1, the second phase angle difference ΔΦL13 is an increasingly positive value.

Please refer to FIG. 4, which shows a block diagram of a current balance controller according to the present disclosure. The three-phase resonant converter further includes a current balance controller 101. The current balance controller 101 receives the first current Ir1, the second current Ir2, and the third current Ir3, and calculates the first phase angle difference ΔΦL12 and the second phase angle difference ΔΦL13 according to peak values, average values, or root-mean-square values of the first current Ir1, the second current Ir2, and the third current Ir3.

Therefore, the unbalanced input currents are controlled by the current balance controller 101, and the phase angle differences are adjusted for the first phase angle ΦL1, the second phase angle ΦL2, and the third phase angle ΦL3 so as to achieve the optimum control of leading phase angle.

Please refer to FIG. 8, which shows a flowchart of a method of controlling the three-phase resonant converter according to the present disclosure. Cooperating with the complete description and diagrams of the previously disclosed three-phase resonant converter, the method of controlling the resonant converter of the present disclosure includes steps as follows. First, providing a three-phase resonant converter having a three-phase transformer, an input bridge arm, and an output bridge arm (step S10), wherein the input bridge arm assembly includes three input switch arms 121, 122, 123, and each input switch arm 121, 122, 123 includes an upper switch Q₁, Q₃, Q₅ and a lower switch Q₂, Q₄, Q₆; wherein the output bridge arm assembly includes three output synchronous rectification switch arms 131, 132, 133, and each output synchronous rectification switch arm 131, 132, 133 includes an upper rectification switch SR₁, SR₃, SR₅ and a lower rectification switch SR₂, SR₄, SR₆. Afterward, controlling each output synchronous rectification switch arm 131, 132, 133 and each input switch arm 121, 122, 123 correspondingly (step S20). Finally, controlling the upper rectification switch SR₁, SR₃, SR₅ or the lower rectification switch SR₂, SR₄, SR₆ to be correspondingly turned on with a phase angle leading to the upper switch Q₁, Q₃, Q₅ or the lower switch Q₂, Q₄, Q₆ so as to maintain an output voltage of the resonant converter to be higher than a voltage threshold (step S30). As for the more complete circuit structure and control method of the three-phase resonant converter, please refer to the content of the previous disclosure, and the detail description is omitted here for conciseness.

In summary, the present disclosure has the following features and advantages:

1. The three-phase resonant converter and the method of controlling the same can provide both high-gain and high-efficiency characteristics, and can be applied to higher output power design.

2. The unbalanced input currents can be controlled to adjust the phase angle differences for the first phase angle, the second phase angle, and the third phase angle so as to achieve the optimum control of leading phase angle and the balance of the three-phase current.

3. Three primary-side windings and three secondary-side windings of the three-phase transformer can be implemented in a star connection (Y connection) or a delta connection (A connection), thereby increasing the flexibility and convenience of circuit design.

Although the present disclosure has been described with reference to the preferred embodiment thereof, it will be understood that the present disclosure is not limited to the details thereof. Various substitutions and modifications have been suggested in the foregoing description, and others will occur to those of ordinary skill in the art. Therefore, all such substitutions and modifications are intended to be embraced within the scope of the present disclosure as defined in the appended claims.

Claims

1. A three-phase resonant converter, comprising: a three-phase transformer, comprising three primary-side windings and three secondary-side windings,an input bridge arm assembly, comprising three input switch arms respectively coupled to the three primary-side windings, wherein each input switch arm comprises an upper switch and a lower switch,an output bridge arm assembly, comprising three output synchronous rectification switch arms respectively coupled to the three secondary-side windings, wherein each output synchronous rectification switch arm comprises an upper rectification switch and a lower rectification switch, and the control of each output synchronous rectification switch arm is corresponding to the control of each input switch arm, anda control unit, configured to control the upper rectification switch or the lower rectification switch to be correspondingly turned on with a phase angle leading to the upper switch or the lower switch so as to maintain an output voltage of the resonant converter to be higher than a voltage threshold.

2. The three-phase resonant converter as claimed in claim 1, wherein the control unit acquires a working frequency command according to the output voltage, wherein based on the working frequency command being less than a frequency threshold of the resonant converter, the upper rectification switch or the lower rectification switch is correspondingly turned on with the phase angle leading to the upper switch or the lower switch,wherein a time period of turning on the upper rectification switch or turning on the lower rectification switch is longer than a period that is the reciprocal of the frequency threshold.

3. The three-phase resonant converter as claimed in claim 2, wherein a time point of turning on the upper rectification switch or turning on the lower rectification switch is earlier than a time point of turning on the corresponding upper switch or lower switch; a time point of turning off the upper rectification switch or turning off the lower rectification switch is earlier than a time point of turning off the corresponding upper switch or lower switch, and the time period of turning on the upper rectification switch or turning on the lower rectification switch at different switching cycles gradually increases with time.

4. The three-phase resonant converter as claimed in claim 2, wherein the frequency threshold is a resonant frequency of the three-phase resonant converter.

5. The three-phase resonant converter as claimed in claim 1, wherein the control unit acquires a working frequency command according to the output voltage, wherein based on the working frequency command being greater than a frequency threshold of the resonant converter, the upper rectification switch or the lower rectification switch is correspondingly turned on with the phase angle leading to the upper switch or the lower switch,wherein a time point of turning on the upper rectification switch or turning on the lower rectification switch is earlier than a time point of turning on the corresponding upper switch or lower switch; a time period of turning on the upper rectification switch or turning on the lower rectification switch is equal to a time period of turning on the corresponding upper switch or lower switch.

6. The three-phase resonant converter as claimed in claim 1, wherein based on three input currents flowing into the three primary-side windings being the same, the three phase angles which the three upper rectification switches or the three lower rectification switches are correspondingly turned on leading to the three upper switches or the three lower switches are the same.

7. The three-phase resonant converter as claimed in claim 6, wherein the three upper switches comprise a first upper switch, a second upper switch, and a third upper switch, the three lower switches comprise a first lower switch, a second lower switch, and a third lower switch; the three upper rectification switches comprise a first upper rectification switch, a second upper rectification switch, and a third upper rectification switch, the three lower rectification switches comprise a first lower rectification switch, a second lower rectification switch, and a third lower rectification switch; wherein the first upper rectification switch and the first lower rectification switch are correspondingly turned on with a first phase angle leading to the first upper switch and the first lower switch; the second upper rectification switch and the second lower rectification switch are correspondingly turned on with a second phase angle leading to the second upper switch and the second lower switch; the third upper rectification switch and the third lower rectification switch are correspondingly turned on with a third phase angle leading to the third upper switch and the third lower switch;wherein the second phase angle is equal to the first phase angle plus a first phase angle difference,wherein the third phase angle is equal to the first phase angle plus a second phase angle difference,wherein the first phase angle difference and the second phase angle difference are zero, and therefore the first phase angle, the second phase angle, and the third phase angle are the same.

8. The three-phase resonant converter as claimed in claim 7, further comprising: a current balance controller, configured to receive a first current, a second current, and a third current, and calculate the first phase angle difference and the second phase angle difference according to peak values, average values, or root-mean-square values of the first current, the second current, and the third current,wherein the first current is a current flowing from a command node between the first upper switch and the first lower switch to the three-phase transformer, the second current is a current flowing from a command node between the second upper switch and the second lower switch to the three-phase transformer, and the third current is a current flowing from a command node between the third upper switch and the third lower switch to the three-phase transformer.

9. The three-phase resonant converter as claimed in claim 1, wherein based on three input currents flowing into the three primary-side windings being not the same, the three phase angles which the three upper rectification switches or the three lower rectification switches are correspondingly turned on leading to the three upper switches or the three lower switches are not the same.

10. The three-phase resonant converter as claimed in claim 9, wherein the three upper switches comprise a first upper switch, a second upper switch, and a third upper switch, the three lower switches comprise a first lower switch, a second lower switch, and a third lower switch; the three upper rectification switches comprise a first upper rectification switch, a second upper rectification switch, and a third upper rectification switch, the three lower rectification switches comprise a first lower rectification switch, a second lower rectification switch, and a third lower rectification switch; wherein the first upper rectification switch and the first lower rectification switch are correspondingly turned on with a first phase angle leading to the first upper switch and the first lower switch; the second upper rectification switch and the second lower rectification switch are correspondingly turned on with a second phase angle leading to the second upper switch and the second lower switch; the third upper rectification switch and the third lower rectification switch are correspondingly turned on with a third phase angle leading to the third upper switch and the third lower switch;wherein the second phase angle is equal to the first phase angle plus a first phase angle difference,wherein the third phase angle is equal to the first phase angle plus a second phase angle difference,wherein the first phase angle difference and the second phase angle difference are not zero, and therefore the first phase angle, the second phase angle, and the third phase angle are not the same.

11. The three-phase resonant converter as claimed in claim 10, wherein the first phase angle difference is determined by a first current and a second current, and the second phase angle difference is determined by the first current and a third current; wherein the first current is a current flowing from a command node between the first upper switch and the first lower switch to the three-phase transformer, the second current is a current flowing from a command node between the second upper switch and the second lower switch to the three-phase transformer, and the third current is a current flowing from a command node between the third upper switch and the third lower switch to the three-phase transformer, wherein when the second current is greater than the first current, the first phase angle difference is negative, and when the second current is less than the first current, the first phase angle difference is positive; wherein an absolute value of a current difference between the second current and the first current is greater, an absolute value of the first phase angle difference is greater;wherein when the third current is greater than the first current, the second phase angle difference is negative, and when the third current is less than the first current, the second phase angle difference is positive; wherein an absolute value of a current difference between the third current and the first current is greater, an absolute value of the second phase angle difference is greater.

12. The three-phase resonant converter as claimed in claim 10, further comprising: a current balance controller, configured to receive a first current, a second current, and a third current, and calculate the first phase angle difference and the second phase angle difference according to peak values, average values, or root-mean-square values of the first current, the second current, and the third current,wherein the first current is a current flowing from a command node between the first upper switch and the first lower switch to the three-phase transformer, the second current is a current flowing from a command node between the second upper switch and the second lower switch to the three-phase transformer, and the third current is a current flowing from a command node between the third upper switch and the third lower switch to the three-phase transformer.

13. The three-phase resonant converter as claimed in claim 1, wherein the three primary-side windings of the three-phase transformer are star-connected or delta-connected, and the three secondary-side windings of the three-phase transformer are star-connected or delta-connected.

14. A method of controlling a three-phase resonant converter, comprising steps of: providing a three-phase resonant converter having a three-phase transformer, an input bridge arm, and an output bridge arm; wherein the input bridge arm assembly comprises three input switch arms, and each input switch arm comprises an upper switch and a lower switch; wherein the output bridge arm assembly comprises three output synchronous rectification switch arms, and each output synchronous rectification switch arm comprises an upper rectification switch and a lower rectification switch,controlling each output synchronous rectification switch arm and each input switch arm correspondingly, andcontrolling the upper rectification switch or the lower rectification switch to be correspondingly turned on with a phase angle leading to the upper switch or the lower switch so as to maintain an output voltage of the resonant converter to be higher than a voltage threshold.

15. The method of controlling a three-phase resonant converter as claimed in claim 14, wherein a working frequency command is acquired according to the output voltage, wherein based on the working frequency command being less than a frequency threshold of the resonant converter, the upper rectification switch or the lower rectification switch is correspondingly turned on with the phase angle leading to the upper switch or the lower switch,wherein a time period of turning on the upper rectification switch or turning on the lower rectification switch is longer than a period that is the reciprocal of the frequency threshold.

16. The method of controlling a three-phase resonant converter as claimed in claim 15, a time point of turning on the upper rectification switch or turning on the lower rectification switch is earlier than a time point of turning on the corresponding upper switch or lower switch, and the time period of turning on the upper rectification switch or turning on the lower rectification switch at different switching cycles gradually increases with time.

17. The method of controlling a three-phase resonant converter as claimed in claim 14, wherein a working frequency command is acquired according to the output voltage, wherein based on the working frequency command being greater than a frequency threshold of the resonant converter, a time point of turning on the upper rectification switch or turning on the lower rectification switch is earlier than a time point of turning on the corresponding upper switch or lower switch; a time period of turning on the upper rectification switch or turning on the lower rectification switch is equal to a time period of turning on the corresponding upper switch or lower switch.

18. The method of controlling a three-phase resonant converter as claimed in claim 14, wherein based on three input currents flowing into the three primary-side windings of the three-phase transformer being not the same, the three phase angles which the three upper rectification switches or the three lower rectification switches are correspondingly turned on leading to the three upper switches or the three lower switches are not the same.

19. The method of controlling a three-phase resonant converter as claimed in claim 18, wherein the three upper switches comprise a first upper switch, a second upper switch, and a third upper switch, the three lower switches comprise a first lower switch, a second lower switch, and a third lower switch; the three upper rectification switches comprise a first upper rectification switch, a second upper rectification switch, and a third upper rectification switch, the three lower rectification switches comprise a first lower rectification switch, a second lower rectification switch, and a third lower rectification switch; wherein the first upper rectification switch and the first lower rectification switch are correspondingly turned on with a first phase angle leading to the first upper switch and the first lower switch; the second upper rectification switch and the second lower rectification switch are correspondingly turned on with a second phase angle leading to the second upper switch and the second lower switch; the third upper rectification switch and the third lower rectification switch are correspondingly turned on with a third phase angle leading to the third upper switch and the third lower switch;wherein the second phase angle is equal to the first phase angle plus a first phase angle difference,wherein the third phase angle is equal to the first phase angle plus a second phase angle difference,wherein the first phase angle difference and the second phase angle difference are not zero, and therefore the first phase angle, the second phase angle, and the third phase angle are not the same.

20. The method of controlling a three-phase resonant converter as claimed in claim 19, wherein the first phase angle difference is determined by a first current and a second current, and the second phase angle difference is determined by the first current and a third current; wherein the first current is a current flowing from a command node between the first upper switch and the first lower switch to the three-phase transformer, the second current is a current flowing from a command node between the second upper switch and the second lower switch to the three-phase transformer, and the third current is a current flowing from a command node between the third upper switch and the third lower switch to the three-phase transformer, wherein when the second current is greater than the first current, the first phase angle difference is negative, and when the second current is less than the first current, the first phase angle difference is positive; wherein an absolute value of a current difference between the second current and the first current is greater, an absolute value of the first phase angle difference is greater;wherein when the third current is greater than the first current, the second phase angle difference is negative, and when the third current is less than the first current, the second phase angle difference is positive; wherein an absolute value of a current difference between the third current and the first current is greater, an absolute value of the second phase angle difference is greater.