Resonant converter and control method thereof

Abstract

The invention relates to a resonant converter and a control method thereof, the resonant converter is provided with a control unit, the control unit is provided with a preset full-bridge state track and a preset half-bridge state track, the full-bridge state track corresponds to a state moving track when the resonant converter operates in a full-bridge mode, and the half-bridge state track corresponds to a state moving track when the resonant converter operates in a half-bridge mode. The half-bridge state track corresponds to a state operation track when the resonant converter operates in a half-bridge mode, and the control unit controls the primary side circuit and / or the secondary side circuit to be switched from the full-bridge mode to the half-bridge mode according to the full-bridge state track when the voltage gain of the resonant converter is determined to be larger than or equal to a gain threshold value. And / or the control unit controls the primary side circuit and / or the secondary side circuit to be switched from the half-bridge mode to the full-bridge mode according to the half-bridge state track when confirming that the voltage gain of the resonant converter is smaller than the gain threshold value.

Description

Technical Field

[0001] This case relates to the field of power electronic converters, and particularly to a resonant converter and its control method. Background Art

[0002] With the continuous development of electric vehicles, the requirements for on-vehicle converters in electric vehicles have increased accordingly. With the gradual popularization of 800V power batteries, the on-vehicle power supply in electric vehicles includes an on-board charger (On Board Charger) and an on-vehicle low-voltage DC converter (Low Voltage DC Converter). Among them, the input and output gain ranges of the on-board charger and the on-vehicle low-voltage DC converter are continuously widening. Currently, the series resonant converter in the on-vehicle power supply is controlled by two modes, namely the buck mode and the boost mode. The buck mode uses frequency conversion control, and the boost mode uses phase-shift control. The gain of the series resonant converter is between 0.7 and 1.3, resulting in an overly wide gain range, which causes problems such as reduced efficiency and increased frequency variation range of the series resonant converter, making it difficult to improve the power density and at the same time increasing the equipment cost. Therefore, traditional series resonant converters are difficult to meet the dual-platform output requirements of compatible two voltages (such as 400V and 800V).

[0003] The front-end input side and the rear-end output side of the series resonant converter work in the full-bridge mode or the half-bridge mode respectively. By reasonably setting the switching working point, the gain range of the series resonant converter can be significantly broadened and the working efficiency of the overall circuit can be improved. However, during the switching process of traditional series resonant converters, the gains of the full-bridge circuit and the half-bridge circuit are different, resulting in obvious overshoot or undershoot of the output voltage during the switching process. In addition, since the DC voltages of the resonant capacitors in the resonant converter are zero and half of the DC voltage in the full-bridge circuit and the half-bridge circuit respectively, the charging and discharging processes of the resonant capacitors will cause high current stress and oscillation, which are likely to damage the power semiconductor devices and resonant capacitors in the resonant converter.

[0004] Therefore, it is necessary to develop a resonant converter and its control method to solve the problems faced by the prior art. Summary of the Invention

[0005] The object of this case is to provide a resonant converter and its control method. The resonant converter has a control unit. When the control unit confirms that the voltage gain of the resonant converter is greater than or equal to the gain threshold, it controls the primary circuit and / or the secondary circuit to switch from the full-bridge mode to the half-bridge mode according to the full-bridge state trajectory, and / or when the control unit confirms that the voltage gain of the resonant converter is less than the gain threshold, it controls the primary circuit and / or the secondary circuit to switch from the half-bridge mode to the full-bridge mode according to the half-bridge state trajectory. Therefore, the resonant converter of this case changes the gain of the primary circuit and the secondary circuit by switching between the full-bridge mode and the half-bridge mode, enabling the input voltage of the resonant converter of this case to cover a wider gain range and optimizing the overall efficiency of the resonant converter. In addition, the fluctuation of the output voltage of the resonant converter during state switching is reduced, and both the overshoot and the undershoot are significantly reduced. Moreover, during state switching, the capacitor voltage of the resonant capacitor and the inductor current flowing through the resonant inductor hardly oscillate, significantly shortening the switching time between the full-bridge mode and the half-bridge mode, thereby improving the reliability of the overall resonant converter. In addition, since the fluctuation of the output voltage of the resonant converter of this case during state switching is reduced, the capacitance value or the number of output capacitors can be reduced.

[0006] To achieve the above object, this case provides a resonant converter, which includes an input side, an output side, a primary circuit, a secondary circuit, a transformer and a control unit. The input side has an input voltage, and the output side has an output voltage. The primary circuit is connected to the input side and includes a plurality of primary switches, a resonant capacitor and a resonant inductor. The secondary circuit is connected to the output side and includes a plurality of secondary switches, where the number of the plurality of primary switches and / or the number of the plurality of secondary switches is at least four. The transformer is connected between the primary circuit and the secondary circuit. The control unit has a preset full-bridge state trajectory and a half-bridge state trajectory. The full-bridge state trajectory corresponds to the state operation trajectory when the resonant converter operates in the full-bridge mode, and the half-bridge state trajectory corresponds to the state operation trajectory when the resonant converter operates in the half-bridge mode. When the control unit confirms that the voltage gain of the resonant converter is greater than or equal to the gain threshold, it controls the primary circuit and / or the secondary circuit to switch from the full-bridge mode to the half-bridge mode according to the full-bridge state trajectory, and / or when the control unit confirms that the voltage gain of the resonant converter is less than the gain threshold, it controls the primary circuit and / or the secondary circuit to switch from the half-bridge mode to the full-bridge mode according to the half-bridge state trajectory.

[0007] To achieve the above object, the present case provides a control method for a resonant converter. The resonant converter includes an input side, an output side, a primary circuit, a secondary circuit, and a transformer. The primary circuit includes a plurality of primary switches, a resonant capacitor, and a resonant inductor. The secondary circuit includes a plurality of secondary switches. The number of the plurality of primary switches and / or the number of the plurality of secondary switches is at least four. The transformer is connected between the primary circuit and the secondary circuit. The control method includes the following steps. First, a control unit is set. The control unit has a preset full-bridge state trajectory and a half-bridge state trajectory. The full-bridge state trajectory corresponds to the state operation trajectory when the resonant converter operates in the full-bridge mode. The half-bridge state trajectory corresponds to the state operation trajectory when the resonant converter operates in the half-bridge mode. Next, the control unit confirms whether the voltage gain of the resonant converter is greater than or equal to a gain threshold. When the control unit confirms that the voltage gain of the resonant converter is greater than or equal to the gain threshold, the primary circuit and / or the secondary circuit is controlled to switch from the full-bridge mode to the half-bridge mode according to the full-bridge state trajectory. When the control unit confirms that the voltage gain of the resonant converter is less than the gain threshold, the primary circuit and / or the secondary circuit is controlled to switch from the half-bridge mode to the full-bridge mode according to the half-bridge state trajectory. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] Figure 1 is the circuit architecture diagram of the resonant converter of the present case;

[0009] Figure 2A is Figure 1 the preset state trajectory diagram in the control unit of the resonant converter shown;

[0010] Figure 2B is Figure 1 the preset half-bridge state trajectory diagram in the control unit of the resonant converter shown;

[0011] Figure 3A is Figure 1 the state trajectory diagram of the resonant converter shown switching from the full-bridge state trajectory to the half-bridge state trajectory;

[0012] Figure 3B is Figure 3A the timing diagram of the resonant converter shown switching from the full-bridge state trajectory to the half-bridge state trajectory;

[0013] Figure 4A is Figure 1 the state trajectory diagram of the resonant converter shown switching from the half-bridge state trajectory to the full-bridge state trajectory;

[0014] Figure 4B is Figure 4A the timing diagram of the resonant converter shown switching from the half-bridge state trajectory to the full-bridge state trajectory;

[0015] Figure 5 is Figure 1Flowchart of the control method for the resonant converter shown;

[0016] Figure 6A For Figure 3A Voltage and current waveform diagram when the resonant converter shown switches from the full-bridge state trajectory to the half-bridge state trajectory; and

[0017] Figure 6B For Figure 3B Voltage and current waveform diagram when the resonant converter shown switches from the half-bridge state trajectory to the full-bridge state trajectory.

[0018] Among them, the description of the reference numerals is as follows:

[0019] 1: Resonant converter

[0020] 21: Input side

[0021] Vin: Input voltage

[0022] 22: Output side

[0023] Vo: Output voltage

[0024] Io: Output current

[0025] 3: Primary circuit

[0026] Cin: Input capacitor

[0027] 31: First bridge arm

[0028] P1: First primary switch

[0029] P2: Second primary switch

[0030] A1: First connection point

[0031] 32: Second bridge arm

[0032] P3: Third primary switch

[0033] P4: Fourth primary switch

[0034] A2: Second connection point

[0035] C1: Resonant capacitor

[0036] L: Resonant inductor

[0037] 4: Transformer

[0038] 41: Primary winding

[0039] 42: Secondary winding

[0040] 5: Secondary circuit

[0041] 51: Third bridge arm

[0042] S1: The first secondary switch

[0043] S2: The second secondary switch

[0044] A3: The third connection point

[0045] C2: The secondary capacitor

[0046] 52: The fourth leg

[0047] S3: The third secondary switch

[0048] S4: The fourth secondary switch

[0049] A4: The fourth connection point

[0050] Co: The output capacitor

[0051] 6: The control unit

[0052] Z1, Z2, Z3, Z4: The switching points

[0053] t0 - t2: Moments

[0054] T: The first pulse width length

[0055] K1 - K4: Steps

[0056] α: The first mode angle

[0057] β: The second mode angle

[0058] γ: The third mode angle Detailed implementation manners

[0059] Some typical embodiments embodying the features and advantages of this case will be described in detail in the following description. It should be understood that this case can have various variations in different aspects, all of which do not depart from the scope of this case, and the descriptions and diagrams therein are essentially for illustrative purposes and not for limiting this case.

[0060] Please refer to Figure 1 , Figure 2A , Figure 2B , Figure 3A , Figure 3B , Figure 4A and Figure 4B , where Figure 1 is the circuit architecture diagram of the resonant converter of this case, Figure 2A is Figure 1 the preset state trajectory diagram in the control unit of the resonant converter shown in Figure 2B is Figure 1 the preset half - bridge state trajectory diagram in the control unit of the resonant converter shown in Figure 3A isFigure 1 The state trajectory diagram of the resonant converter shown switching from the full-bridge state trajectory to the half-bridge state trajectory Figure 3B is Figure 3A The timing diagram of the resonant converter shown switching from the full-bridge state trajectory to the half-bridge state trajectory Figure 4A is Figure 1 The state trajectory diagram of the resonant converter shown switching from the half-bridge state trajectory to the full-bridge state trajectory Figure 4B is Figure 4A The timing diagram of the resonant converter shown switching from the half-bridge state trajectory to the full-bridge state trajectory

[0061] As shown in the figure, the resonant converter 1 of this case includes an input side 21, an output side 22, a primary circuit 3, a transformer 4, a secondary circuit 5, and a control unit 6. The input side 21 has an input voltage Vin. In this embodiment, the input voltage Vin of the input side 21 is between 230V and 850V. The output side 22 has an output voltage Vo and an output current Io. In this embodiment, the output voltage Vo of the output side 22 is between 40V and 50V.

[0062] The primary circuit 3 includes an input capacitor Cin, a first bridge arm 31, a second bridge arm 32, a resonant capacitor C1, and a resonant inductor L. The input capacitor Cin is connected to the input side 21. The first bridge arm 31 is connected in parallel to the input capacitor Cin and includes a first primary switch P1 and a second primary switch P2. The first primary switch P1 and the second primary switch P2 are connected in series, and the connection point between the first primary switch P1 and the second primary switch P2 forms a first connection point A1. The second bridge arm 32 is connected in parallel to the first bridge arm 31 and includes a third primary switch P3 and a fourth primary switch P4. The third primary switch P3 and the fourth primary switch P4 are connected in series, and the connection point between the third primary switch P3 and the fourth primary switch P4 forms a second connection point A2. One end of the resonant capacitor C1 is connected to the first connection point A1, and the other end of the resonant capacitor C1 is connected to the resonant inductor L. When the first primary switch P1, the second primary switch P2 of the first bridge arm 31, the third primary switch P3, and the fourth primary switch P4 of the second bridge arm 32 of the primary circuit 3 are all turned on, the primary circuit 3 operates in the full-bridge mode; when the third primary switch P3 of the second bridge arm 32 of the primary circuit 3 remains off and the fourth primary switch P4 of the second bridge arm 32 remains on, the primary circuit 3 operates in the half-bridge mode.

[0063] The transformer 4 is connected between the primary circuit 3 and the secondary circuit 5 and includes a primary winding 41 and a secondary winding 42. The first end of the primary winding 41 is connected to the resonant inductor L, and the second end of the primary winding 41 is connected to the second connection point A2, where the first end of the primary winding 41 and the first end of the secondary winding 42 are the same-named ends.

[0064] The secondary circuit 5 includes a third bridge arm 51, a secondary capacitor C2, a fourth bridge arm 52, and an output capacitor Co. The third bridge arm 51 includes a first secondary switch S1 and a second secondary switch S2. The first secondary switch S1 and the second secondary switch S2 are connected in series. The first secondary switch S1 is located on the upper bridge arm of the third bridge arm 51, and the second secondary switch S2 is located on the lower bridge arm of the third bridge arm 51. The connection point between the first secondary switch S1 and the second secondary switch S2 forms a third connection point A3. The secondary capacitor C2 is connected between the third connection point A3 and the first end of the secondary winding 42 of the transformer 4. The fourth bridge arm 52 is connected in parallel with the third bridge arm 51 and includes a third secondary switch S3 and a fourth secondary switch S4. The third secondary switch S3 and the fourth secondary switch S4 are connected in series. The third secondary switch S3 is located on the upper bridge arm of the fourth bridge arm 52, and the fourth secondary switch S4 is located on the lower bridge arm of the fourth bridge arm 52. The connection point between the third secondary switch S3 and the fourth secondary switch S4 forms a fourth connection point A4, and the fourth connection point A4 is connected to the second end of the secondary winding 42. The output capacitor Co is connected in parallel with the fourth bridge arm 52 and is connected to the output side 22. When the first secondary switch S1, the second secondary switch S2 of the third bridge arm 51, the third secondary switch S3, and the fourth secondary switch S4 of the fourth bridge arm 52 of the secondary circuit 5 are all turned on, the secondary circuit 5 operates in the full-bridge mode; when the third secondary switch S3 of the fourth bridge arm 52 of the secondary circuit 5 remains off and the fourth secondary switch S4 of the fourth bridge arm 52 remains on, the secondary circuit 5 operates in the half-bridge mode.

[0065] In this embodiment, the number of primary switches of the primary circuit 3 is four, and the number of secondary switches of the secondary circuit 5 is four. In an embodiment, the number of primary switches of the primary circuit 3 is four, and the number of secondary switches of the secondary circuit 5 is two; or the number of primary switches of the primary circuit 3 is two, and the number of secondary switches of the secondary circuit 5 is four. It should be noted that in other embodiments, the number of primary switches and the number of secondary switches may not be four, as long as at least four primary switches or at least four secondary switches are ensured, a full-bridge structure can be formed and switched to a half-bridge structure.

[0066] The control unit 6 has a preset full-bridge state trajectory and a half-bridge state trajectory, as Figure 2A shown. The full-bridge state trajectory corresponds to the state operation trajectory when the resonant converter 1 operates in the full-bridge mode, and the half-bridge state trajectory corresponds to the state operation trajectory when the resonant converter 1 operates in the half-bridge mode. The full-bridge state trajectory and the half-bridge state trajectory are respectively correlated with the inductor current on the resonant inductor L and the capacitor voltage on the secondary capacitor C2. For example Figure 2AThe X-axis of the medium-state operation trajectory diagram is the capacitance voltage on the secondary-side capacitor C2, and the Y-axis is the inductor current on the resonant inductor L. The full-bridge state trajectory and the half-bridge state trajectory within each switching period are composed of multiple circular trajectories, and each circular trajectory is determined by the state trajectory equation in the corresponding mode. The representation methods of the full-bridge state trajectory and the half-bridge state trajectory will be further described later.

[0067] In this embodiment, the full-bridge state trajectory can be shown by Expressions (1) and (2),

[0068]

[0069] where, in the above Expressions (1) and (2), V o is the output voltage of the output side 22, V in is the input voltage of the input side 21, N is the turns ratio between the primary winding 41 and the secondary winding 42 of the transformer 4, v cr is the capacitance voltage on the resonant capacitor C1, i lr is the inductor current flowing through the resonant inductor L, V cr0_N is the initial value of the voltage of the resonant capacitor C1, I lr0_N is the initial value of the current of the resonant inductor L, C r is the capacitance value of the resonant capacitor C1, L r is the inductance of the resonant inductor L.

[0070] Please refer to Figure 2B , in this embodiment, the half-bridge state trajectory can be shown by Expressions (3) and (4),

[0071]

[0072] where, in the above Expressions (3) and (4), V o is the output voltage, V in is the input voltage, N is the turns ratio between the primary winding 41 and the secondary winding 42 of the transformer 4, v cr is the capacitance voltage on the resonant capacitor C1, i lr is the inductor current flowing through the resonant inductor L, V ce0_N is the initial value of the voltage of the resonant capacitor C1, I lr0_N is the initial value of the current of the resonant inductor L, C r is the capacitance value of the resonant capacitor C1, L ris the inductance of the resonant inductor L. The six state trajectory equations in the above expression (3) respectively correspond to six modes of the resonant converter 1 in a working cycle in the half-bridge mode, and are sequentially defined as the first mode, the second mode, the third mode, the fourth mode, the fifth mode, and the sixth mode starting from the current zero-crossing point. Taking the positive half-cycle of the current, and defining the mode angles of the first mode, the second mode, and the third mode as the first mode angle α, the second mode angle β, and the third mode angle γ respectively, as Figure 2B shown.

[0073] Please continue to refer to Figure 1 , the control unit 6 is connected to the input side 21, the primary circuit 3, and the secondary circuit 5, and has a preset gain threshold, for example, 0.64. Wherein the control unit 6 confirms whether the voltage gain of the resonant converter 1 is greater than or equal to the gain threshold, and when the control unit 6 confirms that the voltage gain of the resonant converter 1 is greater than or equal to the gain threshold, it controls the primary circuit 3 and / or the secondary circuit 5 of the resonant converter 1 to switch from the full-bridge mode to the half-bridge mode according to the full-bridge state trajectory, that is, from Figure 3A the full-bridge state trajectory of switches to the half-bridge state trajectory along the dotted line. The control unit 6 calculates the full-bridge switching frequency (the working frequency in the current full-bridge mode) and the full-bridge voltage peak value of the resonant capacitor C1 according to the input voltage Vin, output voltage Vo, and output current Io of the resonant converter 1 at the time of switching, and then calculates the first pulse width length according to the full-bridge voltage peak value of the resonant capacitor C1, and the primary circuit 3 increases the first pulse width length during the conduction time of the first switch pulse signal received after switching from the full-bridge mode to the half-bridge mode.

[0074] In this embodiment, the full-bridge voltage peak value can be shown by expression (5),

[0075]

[0076] wherein, in the above expression (5), I o is the output current, and V cr_pk is the full-bridge voltage peak value of the resonant capacitor C1.

[0077] In this embodiment, the first pulse width length can be shown by expression (6),

[0078]

[0079] wherein, in the above expression (6), t1 is the first pulse width length, and f0 is the resonant frequency of the resonant converter 1.

[0080] Please continue to refer to Figure 3A , the full-bridge state trajectory starts to switch when the inductor current flowing through the resonant inductor L is positively zero-crossing, that is, Figure 3AAt the Z1 point, the full-bridge switching frequency is increased during the switching, making the radius of the full-bridge state trajectory smaller, and switching via the dotted-line trajectory, ultimately making the coincidence occur when switching from the full-bridge mode to the half-bridge mode at the positive zero-crossing of the inductor current flowing through the resonant inductor L, that is Figure 3A at the Z2 point, to complete the switching of the full-bridge state trajectory to the half-bridge state trajectory and correct the frequency duty cycle, as Figure 3B shown, thereby reducing the fluctuations of the inductor current of the resonant inductor L, the capacitor voltage on the resonant capacitor C1, and the output voltage Vo. Please refer to Figure 1 、 3A and 3B. In this embodiment, the driving signal of the switch (i.e., the second secondary switch S2) located at the lower arm of the third bridge arm 51 is delayed by a phase shift angle compared with the driving signal of the switch (i.e., the first secondary switch S1) located at the upper arm of the third bridge arm 51. In some embodiments, the driving signal of the switch (i.e., the fourth secondary switch S4) located at the lower arm of the fourth bridge arm 52 is delayed by a phase shift angle compared with the driving signal of the switch (i.e., the third secondary switch S3) located at the upper arm of the fourth bridge arm 52, where the phase shift angle is determined according to the input voltage Vin and the output voltage Vo of the resonant converter 1.

[0081] When the control unit 6 controls the resonant converter 1 to switch from the full-bridge mode to the half-bridge mode, the control unit 6 controls the four primary switches P1, P2, P3, P4 of the primary circuit 3 to operate according to the full-bridge switching frequency, the first pulse width length, and the phase shift angle, so that the four primary switches P1, P2, P3, P4 of the primary circuit 3 are connected to the transformer 4 in a half-bridge manner. In other words, the control unit 6 controls the third primary switch P3 of the second bridge arm 32 of the primary circuit 3 to remain off, and the fourth primary switch P4 of the second bridge arm 32 to remain on. As Figure 3B shown, between time t0 and t1, the primary circuit 3 operates in the full-bridge mode. At this time, the first primary switch P1, the second primary switch P2, the third primary switch P3, and the fourth primary switch P4 of the first bridge arm 31 of the primary circuit 3 are on; between time t1 and t2, the primary circuit 3 switches to operate in the half-bridge mode. At this time, the third primary switch P3 of the second bridge arm 32 of the primary circuit 3 remains off, and the fourth primary switch P4 of the second bridge arm 32 remains on. In Figure 3B , T is the first pulse width length increased within the conduction time of the first switch pulse signal received after the primary circuit 3 switches from the full-bridge mode to the half-bridge mode.

[0082] In some other embodiments, the control unit 6 can also control the four secondary switches S1, S2, S3, and S4 of the secondary circuit 5 to operate according to the full-bridge switching frequency, the first pulse width length T, and the phase shift angle, so that the four secondary switches S1, S2, S3, and S4 of the secondary circuit 5 are connected to the transformer in a half-bridge manner. In other words, the control unit 6 controls the third secondary switch S3 of the fourth bridge arm 52 of the secondary circuit 5 to remain off, and the fourth secondary switch S4 of the fourth bridge arm 52 to remain on. The control method is similar to that of the primary circuit 3, so it will not be elaborated here.

[0083] When the control unit 6 confirms that the voltage gain of the resonant converter 1 is less than the gain threshold, it controls the primary circuit 3 and / or the secondary circuit 5 of the resonant converter 1 to switch from the half-bridge mode to the full-bridge mode according to the half-bridge state trajectory, that is, from Figure 4A the half-bridge state trajectory switches along the dotted line to the full-bridge state trajectory. The control unit 6 calculates the half-bridge switching frequency and the half-bridge voltage peak according to the first modal angle α, the second modal angle β, the third modal angle γ, and the resonant frequency at the time of switching. And the primary circuit 3 reduces the first pulse width length T within the conduction time of the first switching pulse signal received after the switching.

[0084] In this embodiment, the half-bridge operating frequency and the half-bridge voltage peak can be shown by Expression (7),

[0085]

[0086] wherein, in the above Expression (7), f s_hb is the half-bridge operating frequency, I o is the output current, V cr_pk_hb_neg is the half-bridge voltage peak of the resonant capacitor C1 in the half-bridge mode, α is the first modal angle, β is the second modal angle, γ is the third modal angle, R1, R2, R3, a2, and h2 are intermediate variables respectively. The first modal angle α, the second modal angle β, and the third modal angle γ can be derived from the above Expression (7).

[0087] Please continue to refer to Figure 4A , the half-bridge state trajectory starts to switch when the inductor current flowing through the resonant inductor L is positively zero-crossing, that is, Figure 4A at the Z3 point of Figure 4A , so that the radius of the half-bridge state trajectory becomes smaller, and it switches through the dotted line trajectory. Finally, the switching from the half-bridge mode to the full-bridge mode coincides when the inductor current flowing through the resonant inductor L is positively zero-crossing, that is, Figure 4B at the Z4 point of Figure 1 , to complete the switching of the half-bridge state trajectory to the full-bridge state trajectory within one switching period and correct the frequency duty ratio, as shown in Figure 4B , so as to reduce the fluctuations of the inductor current of the resonant inductor L, the capacitor voltage on the resonant capacitor C1, and the output voltage Vo. Please refer to Figure 1 ,Figure 4A and Figure 4B , in this embodiment, the driving signal of the switch (i.e., the second secondary switch S2) on the lower arm of the third bridge arm 51 is phase-shifted with a delay compared to the driving signal of the switch (i.e., the first secondary switch S1) on the upper arm of the third bridge arm 51. In some embodiments, the driving signal of the switch (i.e., the fourth secondary switch S4) on the lower arm of the fourth bridge arm 52 is phase-shifted with a delay compared to the driving signal of the switch (i.e., the third secondary switch S3) on the upper arm of the fourth bridge arm 52, where the phase-shift angle is determined according to the input voltage Vin and the output voltage Vo of the resonant converter 1.

[0088] When the control unit 6 controls the resonant converter 1 to switch from the half-bridge mode to the full-bridge mode, the control unit 6 controls the four primary switches P1, P2, P3, P4 of the primary circuit 3 to operate according to the half-bridge switching frequency, the first pulse width length, and the phase-shift angle, so that the four primary switches P1, P2, P3, P4 of the primary circuit 3 are connected to the transformer 4 in a full-bridge manner. In other words, the control unit 6 controls the first primary switch P1, the second primary switch P2 of the first bridge arm 31 of the primary circuit 3, the third primary switch P3, and the fourth primary switch P4 of the second bridge arm 32 to be all turned on. As Figure 4B shown, between time t0 and t1, the primary circuit 3 operates in the half-bridge mode. At this time, the third primary switch P3 of the second bridge arm 32 of the primary circuit 3 remains off, and the fourth primary switch P4 of the second bridge arm 32 remains on; between time t1 and t2, the primary circuit 3 switches to operate in the full-bridge mode. At this time, the first primary switch P1, the second primary switch P2 of the first bridge arm 31 of the primary circuit 3, the third primary switch P3, and the fourth primary switch P4 of the second bridge arm 32 are turned on.

[0089] In some other embodiments, the control unit 6 can also control the four secondary switches S1, S2, S3, S4 of the secondary circuit 5 to operate according to the half-bridge switching frequency, the first pulse width length T, and the phase-shift angle, so that the four secondary switches S1, S2, S3, S4 of the secondary circuit 5 are connected to the transformer 4 in a full-bridge manner. In other words, the control unit 6 controls the first secondary switch S1, the second secondary switch S2 of the third bridge arm 51 of the secondary circuit 5, the third secondary switch S3, and the fourth secondary switch S4 of the fourth bridge arm 52 to be all turned on. Its control method is similar to that of the primary circuit 3, so it will not be elaborated here.

[0090] Please refer to Figure 5 , which is Figure 1Flowchart of the control method for the resonant converter shown. As shown in the figure, first, step K1 is executed to set the control unit 6, which has a preset full-bridge state trajectory and a half-bridge state trajectory. The full-bridge state trajectory corresponds to the state operation trajectory when the resonant converter operates in the full-bridge mode, and the half-bridge state trajectory corresponds to the state operation trajectory when the resonant converter operates in the half-bridge mode. Next, step K2 is executed, and the control unit 6 confirms whether the voltage gain of the resonant converter 1 is greater than or equal to the gain threshold. When the confirmation result of step K2 is yes, that is, when the control unit 6 confirms that the voltage gain of the resonant converter 1 is greater than or equal to the gain threshold, step K3 is executed to control the primary circuit 3 and / or the secondary circuit 5 to switch from the full-bridge mode to the half-bridge mode according to the full-bridge state trajectory. When the confirmation result of step K2 is no, that is, when the voltage gain of the resonant converter 1 is less than the gain threshold, step K4 is executed to control the primary circuit 3 and / or the secondary circuit 5 to switch from the half-bridge mode to the full-bridge mode according to the half-bridge state trajectory.

[0091] Please refer to Figure 6A and Figure 6B , where Figure 6A is Figure 3A the voltage-current waveform diagram when the resonant converter shown switches from the full-bridge state trajectory to the half-bridge state trajectory, Figure 6B and Figure 3B is Figure 6A the voltage-current waveform diagram when the resonant converter shown switches from the half-bridge state trajectory to the full-bridge state trajectory. 6B In and , from top to bottom are the voltage waveform diagram of the output voltage Vo, the capacitor voltage waveform diagram of the resonant capacitor C1, and the inductor current waveform diagram flowing through the resonant inductor L. It can be seen from the figure that the fluctuation of the output voltage Vo of the resonant converter 1 in this case is reduced during the state switch, and both the overshoot and the undershoot are significantly reduced. Moreover, during the state switch, the capacitor voltage of the resonant capacitor C1 and the inductor current flowing through the resonant inductor L hardly oscillate, significantly shortening the switching time between the full-bridge mode and the half-bridge mode, thereby improving the reliability of the overall resonant converter 1. In addition, since the fluctuation of the output voltage Vo of the resonant converter 1 in this case is reduced during the state switch, the capacitance value or the number of the output capacitor Co can be reduced. In addition, due to the switching time between the full-bridge mode and the half-bridge mode, and the symmetry of the arms of the primary circuit 3 and the arms of the secondary circuit 5 when switching between the full-bridge mode and the half-bridge mode, the resonant inductor L and the transformer 4 will not generate magnetic saturation.

[0092] In summary, the resonant converter in this case has a control unit. When the control unit confirms that the voltage gain of the resonant converter is greater than or equal to the gain threshold, it controls the primary circuit and / or the secondary circuit to switch from the full-bridge mode to the half-bridge mode according to the full-bridge state trajectory. And / or when the control unit confirms that the voltage gain of the resonant converter is less than the gain threshold, it controls the primary circuit and / or the secondary circuit to switch from the half-bridge mode to the full-bridge mode according to the half-bridge state trajectory. Therefore, the resonant converter in this case changes the gain of the primary circuit and the secondary circuit by switching between the full-bridge mode and the half-bridge mode, enabling the input voltage of the resonant converter in this case to cover a wide gain range and optimizing the overall efficiency of the resonant converter. In addition, the fluctuation of the output voltage of the resonant converter during state switching is reduced, and both the overshoot and the undershoot are significantly reduced. Moreover, during state switching, the capacitor voltage of the resonant capacitor and the inductor current flowing through the resonant inductor hardly oscillate, significantly shortening the switching time between the full-bridge mode and the half-bridge mode, thereby improving the reliability of the overall resonant converter. In addition, since the fluctuation of the output voltage of the resonant converter in this case during state switching is reduced, the capacitance value or the number of output capacitors can be reduced. In addition, due to the switching time between the full-bridge mode and the half-bridge mode, and the symmetry of the bridge arms of the primary circuit and the bridge arms of the secondary circuit during the mutual switching between the full-bridge mode and the half-bridge mode, the resonant inductor and the transformer will not be magnetically saturated.

Claims

1. A resonant converter, comprising: An input side and an output side; A primary circuit, connected to the input side, and including a plurality of primary switches, a resonant capacitor and a resonant inductor; A secondary circuit, connected to the output side, and including a plurality of secondary switches, wherein the number of the plurality of primary switches and / or the number of the plurality of secondary switches is at least four; A transformer, connected between the primary circuit and the secondary circuit; and A control unit, having a preset full-bridge state trajectory and a half-bridge state trajectory, the full-bridge state trajectory corresponding to the state operation trajectory when the resonant converter operates in a full-bridge mode, the half-bridge state trajectory corresponding to the state operation trajectory when the resonant converter operates in a half-bridge mode, wherein when the control unit confirms that a voltage gain of the resonant converter is greater than or equal to a gain threshold, the control unit controls the primary circuit and / or the secondary circuit to switch from the full-bridge mode to the half-bridge mode according to the full-bridge state trajectory, and / or when the control unit confirms that the voltage gain of the resonant converter is less than the gain threshold, the control unit controls the primary circuit and / or the secondary circuit to switch from the half-bridge mode to the full-bridge mode according to the half-bridge state trajectory.

2. The resonant converter according to claim 1, wherein at least two of the secondary switches in the secondary circuit form a first bridge arm, and at least two other secondary switches in the secondary circuit form a second bridge arm, the transformer includes a secondary winding, two ends of the secondary winding are respectively connected to the midpoint of the first bridge arm and the midpoint of the second bridge arm, and a driving signal of a switch located at a lower bridge arm of the first bridge arm is delayed by a phase shift angle compared with a driving signal of a switch located at an upper bridge arm of the first bridge arm, and / or a driving signal of a switch located at a lower bridge arm of the second bridge arm is delayed by the phase shift angle compared with a driving signal of a switch located at an upper bridge arm of the second bridge arm, wherein the phase shift angle is determined according to an input voltage and an output voltage of the resonant converter.

3. The resonant converter according to claim 2, wherein the control unit controls the secondary circuit and / or the primary circuit to switch from the full-bridge mode to the half-bridge mode according to the full-bridge state trajectory, and further includes: Calculate a full-bridge switching frequency and a full-bridge voltage peak value of the resonant capacitor according to the input voltage, the output voltage and an output current of the resonant converter at the time of switching, and then calculate a first pulse width length according to the full-bridge voltage peak value, and the primary circuit increases the first pulse width length during the conduction time of the first switch pulse signal received after the switching.

4. The resonant converter according to claim 3, wherein the expression of the full-bridge state trajectory is: Among them, V o is the output voltage, V in is the input voltage, N is the turns ratio of the primary and secondary sides of the transformer, v cr is a capacitor voltage across the resonant capacitor, i lr is an inductor current flowing through the resonant inductor, V cr0_N is an initial value of the voltage of the resonant capacitor, I lr0_N is an initial value of the current of the resonant inductor, C r is the capacitance value of the resonant capacitor, L r is the inductance of the resonant inductor.

5. The resonant converter according to claim 3, wherein the full-bridge voltage peak value is obtained according to the following expression, Among them, I o is the output current, V cr_pk is the peak value of the full-bridge voltage of the resonant capacitor.

6. The resonant converter according to claim 3, wherein the first pulse width length is obtained according to the following expression, Among them, t1 is the first pulse width length, and f0 is a resonant frequency.

7. The resonant converter according to claim 3, wherein the switching is started when an inductor current flowing through the resonant inductor is positively zero-crossing when switching from the full-bridge mode to the half-bridge mode or from the half-bridge mode to the full-bridge mode.

8. The resonant converter according to claim 3, wherein the expression of the half-bridge state trajectory is: Among them, V o is the output voltage, V in is the input voltage, N is the turns ratio of the primary and secondary sides of the transformer, v cr is the capacitor voltage of the resonant capacitor, i lr is the inductor current of the resonant inductor, V cr0_N is the initial value of the voltage of the resonant capacitor, I lr0_N is the initial value of the current of the resonant inductor, C r is the capacitance value of the resonant capacitor, L r is the inductance of the resonant inductor. Among them, the six state trajectory equations in the half-bridge state trajectory respectively correspond to six modes of the resonant converter in one working cycle in the half-bridge mode. Starting from the current zero-crossing point, they are respectively defined as a first mode, a second mode, a third mode, a fourth mode, a fifth mode, and a sixth mode. And the mode angles of the first mode, the second mode, and the third mode are respectively defined as a first mode angle, a second mode angle, and a third mode angle.

9. The resonant converter as claimed in claim 8, wherein controlling the secondary circuit and / or the primary circuit to switch from the half-bridge mode to the full-bridge mode according to the half-bridge state trajectory further comprises: Calculate a half-bridge switching frequency and a peak half-bridge voltage based on the first modal angle, the second modal angle, the third modal angle, and a resonant frequency, and reduce the first pulse width duration within the conduction time of the first switching pulse signal received by the primary circuit after switching.

10. The resonant converter according to claim 9, wherein the half-bridge switching frequency and the peak half-bridge voltage are obtained according to the following expressions Among them, f s_hb is the half-bridge switching frequency, I o is an output current, V cr_pk_hb_neg is the peak value of the half-bridge voltage of the resonant capacitor in the half-bridge mode, α is the first modal angle, β is the second modal angle, γ is the third modal angle, and R1, R2, R3, a2, h2 are intermediate variables respectively.

11. A control method for a resonant converter, wherein the resonant converter includes an input side, an output side, a primary circuit, a secondary circuit, and a transformer. The primary circuit includes a plurality of primary switches, a resonant capacitor, and a resonant inductor. The secondary circuit includes a plurality of secondary switches. The number of the plurality of primary switches and / or the number of the plurality of secondary switches is at least four. The transformer is connected between the primary circuit and the secondary circuit. The control method includes: (a) Set a control unit having a preset full-bridge state trajectory and a half-bridge state trajectory. The full-bridge state trajectory corresponds to the state operation trajectory when the resonant converter operates in a full-bridge mode, and the half-bridge state trajectory corresponds to the state operation trajectory when the resonant converter operates in a half-bridge mode; (b) The control unit determines whether a voltage gain of the resonant converter is greater than or equal to a gain threshold; (c) When the control unit determines that the voltage gain of the resonant converter is greater than or equal to the gain threshold, control the primary circuit and / or the secondary circuit to switch from the full-bridge mode to the half-bridge mode according to the full-bridge state trajectory; and (d) When the control unit determines that the voltage gain of the resonant converter is less than the gain threshold, control the primary circuit and / or the secondary circuit to switch from the half-bridge mode to the full-bridge mode according to the half-bridge state trajectory.

12. The control method according to claim 11, wherein at least two of the secondary switches in the secondary circuit form a first bridge arm, and at least two other secondary switches in the secondary circuit form a second bridge arm. The transformer includes a secondary winding, and two ends of the secondary winding are respectively connected to the midpoint of the first bridge arm and the midpoint of the second bridge arm. The driving signal of the switch in the lower arm of the first bridge arm is delayed by a phase shift angle compared with the driving signal of the switch in the upper arm of the first bridge arm, and / or the driving signal of the switch in the lower arm of the second bridge arm is delayed by the phase shift angle compared with the driving signal of the switch in the upper arm of the second bridge arm. The phase shift angle is determined according to an input voltage and an output voltage of the resonant converter.

13. The control method according to claim 12, wherein step (c) further includes: calculating a full-bridge switching frequency and a peak full-bridge voltage of the resonant capacitor according to the input voltage, the output voltage, and an output current of the resonant converter at the time of switching, and then calculating a first pulse width duration according to the peak full-bridge voltage. The primary circuit increases the first pulse width duration within the conduction time of the first switching pulse signal received after switching.

14. The control method according to claim 13, wherein the expression of the full-bridge state trajectory is: Among them, V o is the output voltage, V in is the input voltage, N is the turns ratio of the primary and secondary sides of the transformer, v cr is the capacitor voltage on a resonant capacitor in the primary circuit, i lr is the inductor current flowing through the resonant inductor, V cr0_N is the initial value of the voltage of the resonant capacitor, i lr0_N is the initial value of the current of the resonant inductor, C r is the capacitance value of the resonant capacitor, L r is the inductance of the resonant inductor.

15. The control method according to claim 13, wherein the full-bridge voltage peak value is obtained according to the following expression: Among them, I o is the output current, V cr_pk is the peak value of the full-bridge voltage of the resonant capacitor.

16. The control method according to claim 13, wherein the first pulse width length is obtained according to the following expression: Among them, t1 is the first pulse width length, and f0 is a resonance frequency.

17. The control method according to claim 13, wherein when switching from the full-bridge mode to the half-bridge mode or from the half-bridge mode to the full-bridge mode, the switching starts when the inductor current flowing through the resonance inductor is positively zero-crossing.

18. The control method according to claim 13, wherein the expression of the half-bridge state trajectory is: Among them, V o is the output voltage, V in is the input voltage, N is the turn ratio of the primary and secondary sides of the transformer, v cr is the capacitor voltage of the resonant capacitor in the primary circuit, i lr is the inductor current of the resonant inductor, V cr0_N is the initial voltage value of the resonant capacitor, i lr0_N is the initial current value of the resonant inductor, C r is the capacitance value of the resonant capacitor, L r is the inductance of the resonant inductor. Among them, the six state trajectory equations in the half-bridge state trajectory respectively correspond to six modes of the resonant converter in one working cycle in the half-bridge mode. Starting from the current zero-crossing point, they are respectively defined as a first mode, a second mode, a third mode, a fourth mode, a fifth mode, and a sixth mode. And the mode angles of the first mode, the second mode, and the third mode are respectively defined as a first mode angle, a second mode angle, and a third mode angle.

19. The control method according to claim 18, wherein step (e) further comprises: calculating a half-bridge switching frequency and a half-bridge voltage peak value according to the first mode angle, the second mode angle, the third mode angle and a resonance frequency, and reducing the first pulse width length within the conduction time of the first switching pulse signal received by the primary circuit after the switching.

20. The control method according to claim 19, wherein the half-bridge switching frequency and the half-bridge voltage peak value are obtained according to the following expressions: Among them, f s_hb is the half-bridge switching frequency, I o is an output current, V cr_pk_nb_neg is the peak value of the half-bridge voltage of the resonant capacitor in the half-bridge mode. α is the first mode angle, β is the second mode angle, γ is the third mode angle, and R1, R2, R3, a2, and h2 are intermediate variables respectively.

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