Resonant converter and control method and modulation method thereof

Abstract

The application discloses a resonant converter and a control method and a modulation method thereof. The resonant converter comprises a transformer, a primary winding of which receives an input voltage through a primary circuit, and a secondary winding of which outputs an output voltage through a secondary circuit. The secondary circuit comprises two parallel secondary half-bridge arms, each of which comprises upper and lower arm switches connected in series, and the midpoints of the two secondary half-bridge arms are connected to the secondary winding. The upper arm switch of the first secondary half-bridge arm is a first controllable switch, and the lower arm switch of the second secondary half-bridge arm is a second controllable switch. The control method comprises: controlling the duty ratio of the first of the first and second controllable switches in a first switching period to exist a first period, and the secondary current flows through a first short-circuit loop in the first period; and controlling the duty ratio of the second of the first and second controllable switches in a second switching period to exist a second period, and the secondary current flows through a second short-circuit loop in the second period.

Description

Technical Field

[0001] This invention relates to a power conversion technology, and more particularly to a resonant converter and its control and modulation methods. Background Technology

[0002] Isolated resonant converters, applied to solid-state transformers (SSTs), have broad application prospects in DC power consumption or generation fields such as data centers, electric vehicle charging and swapping stations, photovoltaics, and energy storage. An SST can consist of a front-end AC-DC converter and a back-end DC-DC converter, with the input sides of each phase cascaded and the output sides connected in parallel.

[0003] In data center and electric vehicle charging / battery swapping station applications, SSTs require high reliability, high efficiency, and a wide output voltage range. For example, when SSTs are used in data centers, the required voltage range is 200V to 900V; while electric vehicle charging / battery swapping stations require a voltage range of 200V to 1000V. The wide output voltage range of the SST is achieved through downstream control. When a resonant converter is used in the downstream stage, its circuit topology mainly includes a transformer. The primary winding of the transformer receives an input voltage through a primary circuit, and the secondary winding outputs an output voltage through a secondary circuit. However, frequency modulation control alone is insufficient to achieve a wide-range voltage boost in a resonant converter. Therefore, wide-range, efficient control of the resonant converter is crucial for improving the reliability and efficient operation of the SST.

[0004] Existing technology (I) discloses a method for boosting voltage using secondary-side phase shift control, which mainly involves controlling the phase shift angle between the secondary-side switch and the primary-side switch. A short-circuit loop is formed on the secondary side to achieve boost control. However, this method has a limitation: as the boost ratio increases, the phase shift angle on the secondary side also increases. As the voltage gain increases, the turn-off current of the secondary-side controllable switch also increases, leading to higher turn-off losses. This is especially true at high gain levels (voltage gain of 2 times or higher), where the turn-off losses of the secondary-side controllable switch are significant.

[0005] Existing technology (II) discloses a method for boosting voltage using secondary-side PWM control, which mainly achieves output voltage boosting by adjusting the duty cycle of two controllable switches on the secondary side, with a short-circuit loop on the secondary side. However, this method has limitations: one of the two controllable switches on the secondary side has a fixed duty cycle while the other has an adjustable duty cycle. The operating states of the two switches are asymmetrical, resulting in uneven losses, which will affect the device's lifespan and reliability. Summary of the Invention

[0006] The purpose of this invention is to provide a resonant converter and its control and modulation methods, which can effectively solve at least one defect of the prior art and realize a wide range of voltage boost for the resonant converter output.

[0007] To achieve the above objectives, the present invention provides a control method for a resonant converter. The resonant converter includes a transformer. The primary winding of the transformer receives an input voltage through a primary circuit, and the secondary winding of the transformer outputs an output voltage through a secondary circuit. The secondary circuit includes two parallel secondary half-bridge arms, namely a first secondary half-bridge arm and a second secondary half-bridge arm. Each secondary half-bridge arm includes an upper bridge arm switch and a lower bridge arm switch connected in series. The midpoint of the two secondary half-bridge arms is connected to the secondary winding. The upper arm switch of one side half-bridge arm corresponds to a first controllable switch, and the lower arm switch of the second side half-bridge arm corresponds to a second controllable switch. The control method includes: controlling the duty cycle of the first controllable switch and the second controllable switch during a first switching cycle to create a first time period during which the secondary side current flows through a first short-circuit loop; and controlling the duty cycle of the second controllable switch during a second switching cycle to create a second time period during which the secondary side current flows through a second short-circuit loop.

[0008] In one embodiment of the present invention, the first switching cycle and the second switching cycle are adjacent switching cycles; or, the first switching cycle and the second switching cycle are spaced apart by an integer number of switching cycles.

[0009] In one embodiment of the present invention, the control method further includes: acquiring the output voltage and obtaining an adjustment signal based on the output voltage; during the first switching cycle, configuring the duty cycle of the first of the first controllable switch and the second controllable switch as the adjustment signal to modulate the first of the first controllable switch and the second controllable switch according to the adjustment signal, and configuring the duty cycle of the second of the first controllable switch and the second controllable switch as a fixed value; during the second switching cycle, configuring the duty cycle of the first of the first controllable switch and the second controllable switch as the fixed value, and configuring the duty cycle of the second of the first controllable switch and the second controllable switch as the adjustment signal to modulate the second of the first controllable switch and the second controllable switch according to the adjustment signal.

[0010] In one embodiment of the present invention, when 1≤Gain≤2, where Gain is the voltage gain, during the first switching cycle, the duty cycle of the first controllable switch and the second controllable switch is controlled to be greater than or equal to 0.5 and less than or equal to 1 according to the output voltage, and the duty cycle of the second controllable switch is modulated to be equal to 0.5; during the second switching cycle, the duty cycle of the first controllable switch and the second controllable switch is modulated to be equal to 0.5, and the duty cycle of the second controllable switch is controlled to be greater than or equal to 0.5 and less than or equal to 1 according to the output voltage.

[0011] In one embodiment of the present invention, when 1≤Gain≤2, where Gain is the voltage gain; within the first switching cycle, the first time period begins at the turn-off time of the second of the first and second controllable switches and ends at the turn-off time of the first of the first and second controllable switches; within the second switching cycle, the second time period begins at the turn-off time of the first of the first and second controllable switches and ends at the turn-off time of the second of the first and second controllable switches.

[0012] In one embodiment of the present invention, when 1≤Gain≤2, where Gain is the voltage gain; the first short-circuit loop corresponds to the loop formed by the secondary winding, the first controllable switch and the second controllable switch, and the upper or lower bridge arm switch connected in series with the first or second controllable switch; the second short-circuit loop corresponds to the loop formed by the secondary winding, the second controllable switch and the first controllable switch, and the upper or lower bridge arm switch connected in series with the first or second controllable switch.

[0013] In one embodiment of the present invention, when Gain > 2, where Gain is the voltage gain, during the first switching cycle, the duty cycle of the first controllable switch and the second controllable switch is controlled to be greater than 0.5 and less than 1 according to the output voltage, and the duty cycle of the second controllable switch is modulated to be equal to 1; during the second switching cycle, the duty cycle of the first controllable switch and the second controllable switch is modulated to be equal to 1, and the duty cycle of the second controllable switch is controlled to be greater than 0.5 and less than 1 according to the output voltage.

[0014] In one embodiment of the present invention, when Gain > 2 and the secondary current is continuous, where Gain is the voltage gain, within the first switching cycle, the first time period begins at the turn-off time of the first of the first controllable switches and the second controllable switch, and ends at the turn-off time of the second of the first controllable switches and the second controllable switch; within the second switching cycle, the second time period begins at the turn-off time of the second of the first controllable switches and the second controllable switch, and ends at the turn-off time of the first of the first controllable switches and the second controllable switch.

[0015] In one embodiment of the present invention, when Gain > 2 and the secondary-side current is discontinuous, where Gain is the voltage gain, during the first switching cycle, the first time period begins at the turn-off time of the first controllable switch and the second controllable switch and ends at the time when the secondary-side current decreases to zero; during the second switching cycle, the second time period begins at the turn-off time of the second controllable switch and the second controllable switch and ends at the time when the secondary-side current decreases to zero.

[0016] In one embodiment of the present invention, the first short-circuit circuit corresponds to a circuit formed by the secondary winding, the second of the first and second controllable switches, and an upper or lower bridge arm switch connected in series with the first of the first and second controllable switches; the second short-circuit circuit corresponds to a circuit formed by the secondary winding, the first of the first and second controllable switches, and an upper or lower bridge arm switch connected in series with the second of the first and second controllable switches.

[0017] In one embodiment of the present invention, the control method includes: comparing the output voltage with a reference value to obtain an error signal; adjusting the error signal to obtain a first intermediate signal; superimposing a constant on the first intermediate signal to obtain a second intermediate signal; and limiting the second intermediate signal to obtain the adjustment signal.

[0018] In one embodiment of the present invention, when the primary-side circuit is the full-bridge circuit, the control method further includes: when a first primary-side switch in the primary-side circuit has an open-circuit fault, keeping the second primary-side switch in the primary-side circuit located in the same primary-side bridge arm as the first primary-side switch constantly conducting, and keeping the third and fourth primary-side switches in the primary-side circuit located in another primary-side bridge arm conducting complementaryly with a 50% duty cycle.

[0019] To achieve the above objectives, the present invention further provides a resonant converter, comprising a transformer. The primary winding of the transformer receives an input voltage through a primary circuit, and the secondary winding of the transformer outputs an output voltage through a secondary circuit. The secondary circuit includes two parallel secondary half-bridge arms, namely a first secondary half-bridge arm and a second secondary half-bridge arm. Each secondary half-bridge arm includes an upper bridge arm switch and a lower bridge arm switch connected in series, and the midpoint of the two secondary half-bridge arms is connected to the secondary winding. The upper bridge arm switch of the first secondary half-bridge arm... The switch corresponding to the first controllable switch is the lower arm switch of the second secondary half-bridge arm, which corresponds to the second controllable switch. The resonant converter also includes a control unit configured to perform: controlling the duty cycle of the first of the first and second controllable switches during a first switching cycle to allow a first time period in which the secondary current flows through a first short-circuit loop; and controlling the duty cycle of the second of the first and second controllable switches during a second switching cycle to allow a second time period in which the secondary current flows through a second short-circuit loop.

[0020] In another embodiment of the present invention, the first switching cycle and the second switching cycle are adjacent switching cycles; or, the first switching cycle and the second switching cycle are spaced apart by an integer number of switching cycles.

[0021] In another embodiment of the invention, the control unit is configured to perform: acquiring the output voltage and obtaining an adjustment signal based on the output voltage; during a first switching cycle, configuring the duty cycle of the first of the first and second controllable switches as the adjustment signal to modulate the first of the first and second controllable switches according to the adjustment signal, and configuring the duty cycle of the second of the first and second controllable switches as a fixed value; during a second switching cycle, configuring the duty cycle of the first of the first and second controllable switches as the fixed value, and configuring the duty cycle of the second of the first and second controllable switches as the adjustment signal to modulate the second of the first and second controllable switches according to the adjustment signal.

[0022] In another embodiment of the invention, when 1 ≤ Gain ≤ 2, where Gain is the voltage gain, the control unit is configured to perform: during the first switching cycle, controlling the duty cycle of the first controllable switch and the second controllable switch to be greater than or equal to 0.5 and less than or equal to 1 according to the output voltage, and modulating the duty cycle of the second controllable switch and the first controllable switch to be equal to 0.5; during the second switching cycle, modulating the duty cycle of the first controllable switch and the second controllable switch to be equal to 0.5, and controlling the duty cycle of the second controllable switch and the first controllable switch to be greater than or equal to 0.5 and less than or equal to 1 according to the output voltage.

[0023] In another embodiment of the present invention, when 1≤Gain≤2, where Gain is the voltage gain; within the first switching cycle, the first time period begins at the turn-off time of the second of the first and second controllable switches and ends at the turn-off time of the first of the first and second controllable switches; within the second switching cycle, the second time period begins at the turn-off time of the first of the first and second controllable switches and ends at the turn-off time of the second of the first and second controllable switches.

[0024] In another embodiment of the present invention, when 1≤Gain≤2, where Gain is the voltage gain; the first short-circuit loop corresponds to the loop formed by the secondary winding, the first controllable switch and the second controllable switch, and the upper or lower bridge arm switch connected in series with the first or second controllable switch; the second short-circuit loop corresponds to the loop formed by the secondary winding, the second controllable switch and the first or second controllable switch, and the upper or lower bridge arm switch connected in series with the first or second controllable switch.

[0025] In another embodiment of the invention, when Gain > 2, where Gain is the voltage gain, the control unit is configured to perform: during the first switching cycle, controlling the duty cycle of the first controllable switch and the second controllable switch to be greater than 0.5 and less than 1 according to the output voltage, and modulating the duty cycle of the second controllable switch to be equal to 1; during the second switching cycle, modulating the duty cycle of the first controllable switch and the second controllable switch to be equal to 1, and controlling the duty cycle of the second controllable switch to be greater than 0.5 and less than 1 according to the output voltage.

[0026] In another embodiment of the present invention, when Gain > 2 and the secondary side current is continuous, where Gain is the voltage gain; within the first switching cycle, the first time period begins at the turn-off time of the first of the first controllable switches and the second controllable switches, and ends at the turn-off time of the second of the first controllable switches and the second controllable switches; within the second switching cycle, the second time period begins at the turn-off time of the second of the first controllable switches and the second controllable switches, and ends at the turn-off time of the first of the first controllable switches and the second controllable switches.

[0027] In another embodiment of the present invention, when Gain > 2 and the secondary-side current is discontinuous, where Gain is the voltage gain; within the first switching cycle, the first time period begins at the turn-off time of the first of the first controllable switch and the second controllable switch, and ends at the time when the secondary-side current decreases to zero; within the second switching cycle, the second time period begins at the turn-off time of the second of the first controllable switch and the second controllable switch, and ends at the time when the secondary-side current decreases to zero.

[0028] In another embodiment of the present invention, the first short-circuit circuit corresponds to a circuit formed by the secondary winding, the second of the first and second controllable switches, and an upper or lower bridge arm switch connected in series with the first of the first and second controllable switches; the second short-circuit circuit corresponds to a circuit formed by the secondary winding, the first of the first and second controllable switches, and an upper or lower bridge arm switch connected in series with the second of the first and second controllable switches.

[0029] In another embodiment of the present invention, the control unit includes: a subtractor for comparing the output voltage with a reference value to obtain an error signal; a regulator for adjusting the error signal to obtain a first intermediate signal; an adder for superimposing a constant on the first intermediate signal to obtain a second intermediate signal; and a limiter for limiting the second intermediate signal to obtain the adjusted signal.

[0030] In another embodiment of the present invention, when the primary-side circuit is the full-bridge circuit, the control unit is further configured to perform: when a first primary-side switch in the primary-side circuit has an open-circuit fault, to keep the second primary-side switch in the primary-side circuit located in the same primary-side bridge arm as the first primary-side switch constantly conducting, and to keep the third and fourth primary-side switches in the primary-side circuit located in another primary-side bridge arm conducting complementaryly with a 50% duty cycle.

[0031] In another embodiment of the present invention, the secondary circuit further includes: a DC blocking capacitor, which is connected in series with the secondary winding of the transformer and then connected to the midpoint of the two secondary half-bridge arms.

[0032] To achieve the above objectives, the present invention provides a modulation method for a resonant converter. The resonant converter includes a transformer. The primary winding of the transformer receives an input voltage through a primary circuit, and the secondary winding of the transformer outputs an output voltage through a secondary circuit. The secondary circuit includes two parallel secondary half-bridge arms, namely a first secondary half-bridge arm and a second secondary half-bridge arm. Each secondary half-bridge arm includes an upper bridge arm switch and a lower bridge arm switch connected in series. The midpoint of the two secondary half-bridge arms is connected to the secondary winding. The upper bridge arm switch in the first secondary half-bridge arm corresponds to a first controllable switch, and the lower bridge arm switch in the second secondary half-bridge arm corresponds to a second controllable switch. The modulation method includes modulating the first controllable switch and the second controllable switch respectively, so that a short-circuit loop exists in the secondary circuit of the transformer to achieve a midpoint voltage of 0 between the midpoints of the two secondary half-bridge arms.

[0033] This invention achieves wide-range output boost of the resonant converter by controlling the alternating modulation of the first and second controllable switches, which are diagonally arranged in the two secondary half-bridge arms of the resonant converter, and by using the output voltage closed-loop control to control the duty cycle of the first and second controllable switches in the secondary circuit, thereby reducing the switching losses of the secondary circuit and improving the reliability of the SST.

[0034] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. Attached Figure Description

[0035] The above and other features and advantages of the present invention will become more apparent from a detailed description of exemplary embodiments thereof with reference to the accompanying drawings.

[0036] Figure 1 This is a schematic diagram of the circuit topology of the resonant converter of the present invention, wherein the secondary circuit can be the circuit structure shown in part (A) or part (B);

[0037] Figure 2 This is a flowchart illustrating the control method of the resonant converter of the present invention;

[0038] Figure 3 This is a schematic diagram of the alternating half-bridge control method for the resonant converter of the present invention, wherein the secondary circuit of the resonant converter is based on... Figure 1 Take the circuit structure shown in section (A) as an example;

[0039] Figure 4 The typical operating waveforms of a circuit with a primary-side topology of SHB are shown when 1 ≤ Gain < 2.

[0040] Figure 5 The typical operating waveforms of a circuit with a primary-side topology of SHB are shown when Gain > 2.

[0041] Figure 6A The closed-loop control block diagram is shown when 1≤Gain≤2;

[0042] Figure 6B The closed-loop control block diagram for Gain > 2 is shown.

[0043] Figure 7A The simulation circuit topology is shown when Gain = 2 and the primary-side circuit is a series half-bridge topology;

[0044] Figure 7B The control effect of the simulation circuit of the present invention compared with that of the prior art (II) is shown when Gain=2;

[0045] Figure 8 The control effect of the control method of the present invention during load increase and decrease is shown;

[0046] Figure 9 The control effect of the control method of the present invention when the output voltage reference increases is shown;

[0047] Figure 10 The circuit structure of the resonant converter of the present invention is shown when the primary side circuit is a full-bridge topology;

[0048] Figure 11 This demonstrates the control effect of the control method of the present invention when the primary-side circuit is a full-bridge topology;

[0049] Figure 12 This is a circuit diagram of the resonant converter of the present invention operating with fault tolerance when an open-circuit fault occurs in one of the primary-side switches in the primary-side circuit (taking an open-circuit fault in primary-side switch S1 as an example).

[0050] Figure 13 The control effect is shown when an open-circuit fault occurs in a primary-side switch in the primary-side circuit (taking an open-circuit fault in primary-side switch S1 as an example).

[0051] Figure 14 This is a schematic diagram of the modulation method of the resonant converter of the present invention. Detailed Implementation

[0052] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that the invention will be thorough and complete, and the concept of the exemplary embodiments will be fully conveyed to those skilled in the art. The same reference numerals in the drawings denote the same or similar structures, and therefore their detailed description will be omitted.

[0053] In describing the elements / components / etc. described and / or illustrated herein, the terms “a,” “an,” “the,” “the,” and “at least one” are used to indicate the presence of one or more elements / components / etc. The terms “comprising,” “including,” and “having” are used to indicate an open-ended inclusion and to mean that additional elements / components / etc. may exist in addition to those listed. Furthermore, the terms “first,” “second,” etc., in the claims are used only as designations and are not intended to limit the number of objects to which they pertain.

[0054] like Figure 1 The diagram illustrates a circuit topology for a resonant converter 100 according to the present invention, which can be used for wide-range output boost. The resonant converter 100 includes a transformer 10. The primary winding of the transformer 10 receives an input voltage V through a primary circuit 20. in The secondary winding of transformer 10 outputs an output voltage V through a primary circuit 30. o In this embodiment, the resonant converter 100 is an LLC resonant converter, wherein the transformer 10 has a turns ratio of n:1, v p The voltage of the primary bridge arm, v s For the secondary arm voltage, C r L r L m These are the resonant capacitor, resonant inductor, and magnetizing inductor, respectively. C s For DC blocking capacitor, C o This is the output capacitor. The DC blocking capacitor C... s It is connected in series with the secondary winding and then connected to the midpoint of the two secondary half-bridge arms. Of course, it is understood that in other embodiments, the resonant converter 100 may also be other types of converters, which are not intended to limit the invention.

[0055] In this invention, the secondary circuit 20 may include two parallel secondary half-bridge arms, namely a first secondary half-bridge arm 31 and a second secondary half-bridge arm 32. Each secondary half-bridge arm includes an upper bridge arm switch and a lower bridge arm switch connected in series, and the midpoint of the two secondary half-bridge arms (31, 32) is connected to the secondary winding. Specifically, the upper bridge arm switch of the first secondary half-bridge arm 31 corresponds to a first controllable switch 311, and the lower bridge arm switch of the second secondary half-bridge arm 32 corresponds to a second controllable switch 321. Figure 1 In the embodiment shown, the secondary circuit 20 of the present invention may be... Figure 1 In the circuit structure of either part (A) or part (B), the controllable switches (311, 321) in the two secondary half-bridge arms (31, 32) are located diagonally. For example, in the secondary circuit of part (A), the upper bridge arm switch S5 of the first secondary half-bridge arm 31 (corresponding to the first controllable switch) and the lower bridge arm switch S8 of the second secondary half-bridge arm 32 (corresponding to the second controllable switch) are located diagonally in the circuit. The other two switches can be diodes D1 and D2, or synchronous rectifiers. In the secondary circuit of part (B), the upper bridge arm switch S7 of the first secondary half-bridge arm 31 (corresponding to the first controllable switch) and the lower bridge arm switch S6 of the second secondary half-bridge arm 32 (corresponding to the second controllable switch) are located diagonally in the circuit. The other two switches can be diodes D3 and D4, or synchronous rectifiers.

[0056] like Figure 2 As shown, in this invention, the control method 200 for the resonant converter may include:

[0057] Step S201: During the first switching cycle, control the duty cycle of the first controllable switch and the second controllable switch to create a first time period, during which the secondary current flows through the first short-circuit loop.

[0058] Step S202: During the second switching cycle, control the duty cycle of the second of the first and second controllable switches to create a second time period, during which the secondary current flows through the second short-circuit loop.

[0059] In this embodiment, the first switching cycle and the second switching cycle can be adjacent switching cycles. In other embodiments, the first switching cycle and the second switching cycle can also be spaced apart by an integer number of switching cycles.

[0060] Figure 3 This invention illustrates an alternating half-bridge control method for a resonant converter, wherein the secondary circuit of the resonant converter is... Figure 1 Taking the circuit structure shown in section (A) as an example, switches S5 and S8 are controlled switches. Here, Gain represents the voltage gain, and its calculation formula is, for example, Gain = nV.o / V in Where n is the transformer turns ratio, V o V is the output voltage. in The input voltage is the voltage across a capacitor when it is a Series Half Bridge (SHB). s The switching cycle. PWM S5 PWM S8 These are the drive signals for switches S5 and S8, respectively. S5 D S8 D represents the duty cycle of switches S5 and S8 during one switching cycle. S5 and D S8 Equivalent. The circuit operates at the resonant frequency. The two controllable switches (S5 and S8) in the secondary circuit are controlled by duty cycle. One controllable switch has a fixed duty cycle, while the other has an adjustable duty cycle to meet the output voltage requirements. Furthermore, the two controllable switches alternately modulate the duty cycle, causing the two short-circuit loops on the secondary side to operate alternately.

[0061] Figure 3 The example uses two alternating switching cycles T1 and T2. Specifically, when 1 ≤ Gain < 2, during the first switching cycle T1, D... S5 =0.5, 0.5≤D S8 <1, based on the output voltage V o The closed-loop modulation switch S8 exists in a first time period. During the first time period, the secondary winding is short-circuited, and the secondary current flows through the short-circuit loop of the lower half-bridge arm. For example, the secondary current flows in reverse. Figure 1 The voltage boost is achieved by the first short-circuit loop L1 formed by the secondary winding, switch S8 in part A of the secondary circuit, and diode D1. During the second switching cycle T2, the duty cycles of switches S5 and S8 are switched, i.e., D... S8 =0.5, 0.5≤D S5 <1, based on the output voltage V o The closed-loop modulation switch S5 exists in a second time period. During this second time period, the secondary winding is short-circuited, and the secondary current flows through the short-circuit loop of the upper half-bridge arm. For example... Figure 1 After the secondary current reverses, it flows through the secondary winding, switch S5 in part of the secondary circuit (A), and the second short-circuit loop L2 formed by diode D2, thus achieving voltage boost. When Gain = 2, switch S8 remains closed during the first switching cycle T1, i.e., D... S8 =1, at this time D S5 =0.5; During the second switching cycle T2, switch S5 remains closed, i.e., D S5 =1, at this time D S8=0.5. When Gain = 2, it is equivalent to the switching frequency of switches S5 and S8 being half the switching frequency of the primary-side switches, and the secondary-side circuit operates as an alternating half-bridge to achieve voltage multiplication. When Gain > 2, during the first switching cycle T1, switch S8 remains closed, modulating switch S5; during the second switching cycle T2, switch S5 remains closed, modulating switch S8 to control the output voltage V. o Therefore, the present invention can reduce secondary-side switching losses over a wide range of voltage boosting, and the operating modes of the two controllable switches (e.g., S5 and S8) are symmetrical over two switching cycles, thus achieving loss balance and improving reliability.

[0062] The primary side topology is a series half bridge (SHB), and the secondary side circuit is... Figure 1 Taking the circuit structure shown in Part (A) as an example, the typical operating waveform of the circuit is as follows: Figure 4 As shown, g5 and g8 are the switching signals for switches S5 and S8. Preferably, the explanation will be based on the example of exchanging the duty cycles of the two controllable switches (e.g., S5 and S8) after each switching cycle. Figure 4 In this case, 1 ≤ Gain < 2, and one switching cycle contains four switching modes. Taking the switching cycle T1 as an example, t0~t1 is the positive half-cycle, during which switches S5 and S8 are simultaneously turned on, and power is transferred from the primary circuit to the secondary circuit. At t=t1, after half a switching cycle, the resonant current i Lr Equal to excitation current i Lm At this time, the secondary current i s When the current equals 0, switch S5 is turned off with zero current. During the period from t1 to t2 (i.e., the first time period), switch S8 remains on, the secondary current of the transformer increases in the reverse direction, and the secondary current flows through the first short-circuit loop L1, short-circuiting the secondary winding. The circuit operates in boost mode, the resonant inductor stores energy, and the resonant current increases rapidly. At t = t2, switch S8 is turned off. During the period from t2 to t3, the secondary current flows through diode D2, the output terminal, and diode D1, and the secondary bridge arm voltage v... s Approximately equal to the output voltage V o The secondary current decreases in the reverse direction, and the primary circuit transfers power to the output side, resulting in the resonant current i. Lr Gradually decrease until it matches the excitation current i Lm Equal. During the period t3 to t4, the secondary current i s When the voltage is reduced to 0, the secondary side operates in discontinuous mode, the magnetizing inductance participates in resonance, and the secondary arm voltage v s This is the excitation inductance voltage induced on the secondary side of the transformer.

[0063] Please refer to Figure 4During the switching cycle T1 (t0~t4), switch S5 is turned off for half a cycle with a duty cycle of 0.5; switch S8 remains on after half a cycle with a duty cycle greater than 0.5 and less than 1. In the next switching cycle T2, the duty cycles of switches S5 and S8 are swapped, and the primary-side bridge arm voltage v... p Secondary bridge arm voltage v s Resonant inductor current i Lr Magnetizing inductor current i Lm Secondary current i s The waveform is the same as within the switching cycle T1. Within the switching cycle T2, after half a switching cycle, the resonant current equals the excitation current, and at this time the secondary current i s When the current decreases to 0, switch S8 turns off with zero current, while switch S5 remains on. At this point, the second time period begins, and the secondary current of the transformer increases in the reverse direction. This secondary current flows through the second short-circuit loop L2, causing a short circuit in the secondary winding, and the circuit operates in boost mode. Within the switching cycle T2, switch S8 turns off for half a cycle, with a duty cycle of 0.5; switch S5 remains on after half a cycle, with a duty cycle greater than 0.5 and less than 1.

[0064] When 1 ≤ Gain ≤ 2, within a switching cycle, there exists a first time period (e.g., between t1 and t2) or a second time period, corresponding to the boosting period of the switching cycle. When the load is constant, the longer the boosting period within each switching cycle, the greater the voltage gain achieved. By controlling the switching duty cycle to adjust the boosting period of each switching cycle, i.e., adjusting the first or second time period, the desired voltage gain can be obtained.

[0065] When 1 ≤ Gain ≤ 2, within the first switching period T1, the first time period begins, for example, at the turn-off time of switch S5 and ends, at the turn-off time of switch S8. Within the second switching period T2, the second time period begins, for example, at the turn-off time of switch S8 and ends, for example, at the turn-off time of switch S5.

[0066] The primary side topology remains a series half-bridge (SHB), and the secondary side circuit is... Figure 1 Taking the circuit structure shown in Part (A) as an example, the typical operating waveform of the circuit is as follows: Figure 5 As shown. Preferably, the explanation will be based on the example of exchanging the duty cycles of two controllable switches (e.g., S5 and S8) after each switching cycle. Figure 5 In this circuit, the voltage gain Gain > 2, and four switching modes are contained within one switching cycle. Taking the switching cycle T1 as an example, t0 to t1 is the positive half-cycle, during which switches S5 and S8 are simultaneously turned on, and power is transferred from the primary circuit to the secondary circuit. At t = t1, after half a switching cycle, the resonant current i Lr Equal to excitation current i Lm At this time, the secondary current is The value is equal to 0. During the period from t1 to t2, switches S5 and S8 remain in the on state, and the secondary current i s The reverse current flows through switch S8, the output capacitor, and switch S5, therefore the secondary bridge arm voltage v s Equal to output voltage V o At this time, the output capacitor outputs power to the load, the resonant cavity and secondary currents reverse, the resonant inductor stores energy, and the resonant current i Lr The reverse current increases rapidly, and the circuit operates in boost mode. At t = t2, switch S5 is off, and its duty cycle is greater than 0.5 and less than 1, while switch S8 remains on. During the period from t2 to t3 (i.e., the first time period), the secondary current decreases in the reverse direction, flowing through the first short-circuit loop L1 on the secondary side until the resonant current i... Lr Equal to excitation current i Lm During the period from t3 to t4, the secondary current i s When the voltage is reduced to 0, the secondary side operates in discontinuous mode, the magnetizing inductance participates in resonance, and the secondary arm voltage v s This is the excitation inductance voltage induced on the secondary side of the transformer. At t = t4, switch S8 is turned off, and the switching cycle T1 ends.

[0067] Please refer to Figure 4 During the switching cycle T1 (t0~t4), the duty cycle of switch S5 is greater than 0.5 and less than 1; the duty cycle of switch S8 is equal to 1. It should be noted that when the secondary side operates in discontinuous mode, switch S8 can be turned off at any time after the secondary side current drops to zero, i.e., switch S8 can be turned off at any time during the period t3~t4. Early turn-off of switch S8 helps reduce turn-on losses. To simplify duty cycle control, in this embodiment, switch S8 is always on during the switching cycle T1. In the next switching cycle T2, the duty cycles of switches S5 and S8 are swapped, and the primary side bridge arm voltage v... p Secondary bridge arm voltage v s Resonant inductor current i Lr Magnetizing inductor current i Lm Secondary current i s The waveform is the same as within the switching cycle T1. Within the switching cycle T2, after half a switching cycle, the resonant current equals the excitation current, and at this time the secondary current i s The duty cycle decreases to 0. After half a switching cycle, switches S5 and S8 continue to conduct. After a period of time, switch S8 turns off, and the second time period begins. The secondary current flows through the second short-circuit loop L2, and the secondary current of the transformer decreases in the reverse direction. When the secondary current of the transformer decreases to zero in the reverse direction, the second time period ends. Switch S5 continues to conduct until the end of switching cycle T2, and the duty cycle of switch S5 is equal to 1.

[0068] When Gain > 2, switch S5 or S8 remains on throughout a switching cycle, and the secondary circuit operates in alternating half-bridge mode, achieving voltage multiplication. Each switching cycle includes a boosting period (e.g., between t1 and t2), further boosting the voltage on top of the doubled output, rapidly increasing the voltage gain to greater than 2. When the load is constant, the longer the boosting period within each switching cycle, the greater the achieved voltage gain. The desired voltage gain can be obtained by adjusting the boosting period in each switching cycle by controlling the switch duty cycle.

[0069] When Gain > 2 and the secondary current is continuous, within the first switching period T1, the first time period begins, for example, at the turn-off time of switch S5 and ends at the turn-off time of switch S8. Within the second switching period T2, the second time period begins, for example, at the turn-off time of switch S8 and ends at the turn-off time of switch S5. When the secondary current is discontinuous, within the first switching period T1, the first time period begins, for example, at the turn-off time of switch S5 and ends when the secondary current equals 0 and becomes discontinuous. Within the second switching period T2, the second time period begins, for example, at the turn-off time of switch S8 and ends when the secondary current equals 0 and becomes discontinuous.

[0070] In the present invention, for example Figures 3-5 In some of the embodiments shown, the control method for the resonant converter may include:

[0071] Obtain the output voltage and obtain an adjustment signal based on the output voltage;

[0072] During the first switching cycle (e.g., switching cycle T1), the duty cycle of the first of the first and second controllable switches (e.g., switch S8) is configured as the adjustment signal to modulate the first switch according to the adjustment signal, and the duty cycle of the second of the first and second controllable switches (e.g., switch S5) is configured as a fixed value.

[0073] During the second switching cycle (e.g., switching cycle T1), the duty cycle of the first controllable switch (e.g., switch S8) is configured to the fixed value, and the duty cycle of the second controllable switch (e.g., switch S5) is configured as the adjustment signal to modulate the second switch according to the adjustment signal. The first and second switching cycles can be continuous.

[0074] In other words, this invention proposes an alternating half-bridge control method for a resonant converter. It utilizes a closed-loop output voltage adjustment mechanism to regulate the duty cycle of two diagonally arranged controllable switches in the two secondary half-bridge arms of the secondary circuit. By alternately modulating the duty cycles of the two controllable switches, a wide-range output voltage boost is achieved. Furthermore, by controlling the two short-circuit loops in the secondary circuit to operate alternately, the switching losses in the secondary circuit are balanced, improving system reliability.

[0075] In practice, the present invention is not limited to the above embodiments. When there are at least two switching cycles, one of which is the first switching cycle and the other of which is the second switching cycle, these are all different embodiments of the present invention.

[0076] In this invention, the resonant converter may further include a control unit for executing the above control method, wherein the control unit may be a digital processing chip, such as a DSP or FPGA; the control unit may also be an analog circuit.

[0077] In this invention, the duty cycle under different boost ratios can be controlled in a closed loop, as shown in the control block diagram below. Figure 6A and Figure 6B As shown, the control unit may include, for example, a subtractor 61, a regulator 62, an adder 63, and a limiter 64. The subtractor 61 is used to compare the output voltage v. o With a reference value v oref An error signal Δv is obtained. Regulator 62 adjusts the error signal Δv to obtain a first intermediate signal MS1. Adder 63 adds a constant (e.g., 0.5, but this invention is not limited thereto) to the first intermediate signal MS1 to obtain a second intermediate signal MS2. Limiter 64 limits the second intermediate signal MS2 to obtain an adjustment signal RS. This adjustment signal RS can be used to control, for example, the duty cycle of switches S8 and S5. Figure 6A As shown, when the voltage gain 1 ≤ Gain ≤ 2, D S5 =0.5, D S8 The initial value is 0.5, based on the output voltage v. o Closed-loop regulation D S8The duty cycle of switch S5 is 0.5 in the first switching cycle. The duty cycle of switch S8 is controlled by the adjustment signal RS, varying within the range of [0.5, 1] ​​to obtain the desired output voltage. In the second switching cycle, the duty cycle of switch S8 is 0.5, and the duty cycle of switch S5 is controlled by the adjustment signal RS, varying within the range of [0.5, 1] ​​to obtain the desired output voltage. Specifically, when the load is constant, in the first switching cycle, a larger duty cycle of switch S8 results in a longer first time period, a longer boost time for the secondary circuit, and ultimately a greater voltage gain. Similarly, in the second switching cycle, a larger duty cycle of switch S5 results in a longer second time period, a longer boost time for the secondary circuit, and ultimately a greater voltage gain.

[0078] like Figure 6B As shown, when the voltage gain Gain > 2, D S8 =1,D S5 The initial value is 0.5, based on the output voltage v. o Closed-loop regulation D S5 The output voltage is boosted by adjusting the duty cycle of switch S8. In the first switching cycle, the duty cycle of switch S8 is 1. The duty cycle of switch S5 is controlled by the adjustment signal RS, varying within the range of (0.5, 1) to obtain the desired output voltage. In the second switching cycle, the duty cycle of switch S5 is 1. The duty cycle of switch S8 is controlled by the adjustment signal RS, varying within the range of (0.5, 1) to obtain the desired output voltage. Specifically, when the load is constant, in the first switching cycle, a larger duty cycle of switch S5 results in a longer boost time for the secondary circuit, leading to a greater voltage gain. Similarly, in the second switching cycle, a larger duty cycle of switch S8 results in a longer boost time for the secondary circuit, also leading to a greater voltage gain.

[0079] When the voltage gain Gain = 2, the simulation topology of the control method of the present invention is as follows: Figure 7A As shown, the primary circuit is a series half-bridge (SHB) topology, and the transformer turns ratio n is equal to 1. Figure 7B This is a comparison of simulation results between the present invention and prior art 2. It can be seen that during voltage multiplication output, a switch Q in the secondary circuit of prior art 2... SR1 Always on, another switch Q SR2 With 50% duty cycle modulation, its switching frequency is equal to the primary-side switching frequency, and the turn-off loss of the secondary-side switch is concentrated in switch Q. SR2In this invention, the two secondary half-bridge arms containing switches S5 and S8 are modulated alternately, and the two actively controlled switches on the secondary side switch the same number of times, thus achieving balanced losses. Furthermore, the switching frequency on the secondary side is half that of the primary side.

[0080] The control effect of the control method of the present invention during load increase and decrease is as follows: Figure 8 As shown, where V oref The voltage is 600V, the input voltage is 500V, the transformer turns ratio n is equal to 1, and the voltage gain is 1.2. (From...) Figure 8 It can be seen that the control method of the present invention is stable under dynamic conditions of sudden load increase and decrease; the output voltage and the waveform of the resonant cavity remain stable, and the envelope of the resonant cavity follows the load changes. Figure 8 As shown in parts (A) and (B), the resonant current i between 0 and 0.05s Lr The peak value is 50A. For example... Figure 8 As shown in parts (A) and (C), the load decreases at t = 0.05s, and the resonant current i between 0.05 and 0.1s... Lr With a peak value less than 50A, the output voltage and the waveform of the resonant cavity remain stable. Figure 8 The boost period (i.e., the secondary short-circuit time) in part (C) is less than Figure 8 During the boost phase in section (B), when the load decreases, the duty cycle of the control switch decreases, the boost time of the secondary circuit decreases, and the output voltage remains stable. For example... Figure 8 As shown in parts (A) and (D), the load increases at t = 0.1s, and the resonant current i increases between 0.1 and 0.15s. Lr The peak value is close to 50A, and the output voltage and the waveform of the resonant cavity remain stable. Figure 8 The boost period (i.e., the secondary short-circuit time) in part (D) is greater than Figure 8 During the boost phase in section (C), as the load increases, the duty cycle of the control switch increases, the boost time of the secondary circuit increases, and the output voltage remains stable. Figure 8 It can be seen that the short-circuit time on the secondary side follows the load change, which verifies the feasibility of the control method of the present invention when the load changes.

[0081] The control effect of the control method of the present invention when the output voltage reference changes is as follows: Figure 9 As shown, the input voltage is 500V, and the transformer turns ratio n is equal to 1. Figure 9 As shown in parts (A) and (B), the reference value for the output voltage between 0 and 0.05s is 600V. The output voltage equals 600V following the voltage reference value, the waveform of the resonant cavity remains stable, and the voltage gain is equal to 1.2. (As shown in the diagram...) Figure 9As shown in parts (A) and (C), at t = 0.05s, the reference value of the output voltage increases to 800V, and between 0.05 and 0.1s, the output voltage is equal to 800V following the reference voltage value. The waveform of the resonant cavity remains stable, and the voltage gain increases to 1.6. Figure 9 The boost period (i.e., the secondary short-circuit time) in part (C) is greater than Figure 9 During the boost phase in section (B), as the output voltage reference value increases, the voltage gain increases, the duty cycle of the control switch increases, the boost time of the secondary circuit increases, and the output voltage rises to follow the voltage reference value. Figure 9 It is known that as the voltage gain increases, the output voltage increases, and the short-circuit time on the secondary side increases. The control method of this invention can adapt to step changes in the output voltage setpoint and can track V in a timely manner. oref The changes.

[0082] It is understood that the embodiments of the present invention are not limited to the boost control of resonant converters with an SHB topology as the primary side circuit. The alternating half-bridge control method proposed in this invention can be applied in SST applications such as fast charging stations, photovoltaic power plants, data centers, energy storage, and microgrids. The present invention is also not limited to the embodiments listed below.

[0083] Example 1: Wide-range boost control when the primary-side circuit is a full-bridge topology

[0084] like Figure 10 As shown, it illustrates a resonant converter with a full-bridge topology in the primary-side circuit 20, and its control effect is as follows. Figure 11 As shown. When the primary-side circuit 20 is a full-bridge topology, the primary-side bridge arm voltage of the primary-side circuit is at +V. in and -V in The control method of this invention is also applicable when switching between different modes.

[0085] Example 2: Fault-tolerant operation when the primary-side switch experiences an open-circuit fault

[0086] When one primary-side switch in the primary circuit experiences an open-circuit fault, the other primary-side switch in the same primary-side bridge arm is turned on, and the primary-side circuit switches to half-bridge operation. For example... Figure 12 As shown, assuming that the primary-side switch S1 in the primary-side circuit cannot receive the drive signal due to a fault, resulting in an open-circuit fault, the primary-side switch S2 in the same primary-side bridge arm can be kept constantly conducting, and the primary-side switches S3 and S4 in the other primary-side bridge arm can be complementaryly conducted with a 50% duty cycle. The secondary-side circuit can be controlled according to the control method of this invention. The same principle applies when the remaining primary-side switches in the primary-side circuit experience open-circuit faults.

[0087] The control effect when the primary switch S1 experiences an open-circuit fault is as follows: Figure 13 As shown, the output voltage is 500V, the input voltage is 500V, and the transformer turns ratio n is equal to 1. Figure 13 As shown in parts (A) and (B), between 0 and 0.05 s, the primary-side switch did not malfunction, and the primary-side bridge arm voltage was within ±V. in Switching between them, the duty cycle of switches S5 and S8 is 0.5, the output voltage is 500V, the voltage gain is 1, and the resonant cavity remains stable. For example... Figure 13 As shown in parts (A) and (C), at t = 0.05s, a fault is simulated in the primary-side switch S1, and the primary-side switch S2 is turned on. The primary-side bridge arm voltage changes from ±V in Switch between them to +V in Switching between 0 and 0, the primary-side bridge arm voltage is half of the pre-fault voltage, equivalent to the input voltage becoming half of the pre-fault voltage. To ensure the output voltage remains constant, the secondary-side circuit switches to alternating half-bridge operation of switches S5 and S8, achieving voltage doubling output, thereby maintaining output voltage stability and allowing the resonant converter to operate fault-tolerantly. For example... Figure 13 As shown in section (C), the output voltage remains stable, the voltage gain is equal to 2, and the resonant cavity remains stable.

[0088] like Figure 14 As shown, the present invention also provides an application in, for example... Figure 1 The modulation method 400 of the resonant converter 100 shown includes:

[0089] Step S301: Modulate the first controllable switch and the second controllable switch respectively, so that there is a short circuit loop in the secondary circuit of the transformer to achieve a midpoint voltage of 0 between the midpoints of the two secondary half-bridge arms.

[0090] This invention achieves a wide-range output voltage boost by alternately modulating the duty cycles of two diagonally arranged controllable switches in the secondary circuit. Furthermore, by having the two short-circuit loops in the secondary circuit operate alternately, the switching losses in the two secondary bridge arms of the secondary circuit can be balanced, improving system reliability.

[0091] This invention is applicable not only to resonant converters with a primary-side circuit of full-bridge or half-bridge series topology, but also to fault-tolerant operation when any primary-side switch in the primary-side circuit experiences an open-circuit fault.

[0092] Exemplary embodiments of the present invention have been specifically illustrated and described above. It should be understood that the present invention is not limited to the disclosed embodiments; rather, the present invention is intended to cover various modifications and equivalent arrangements contained within the spirit and scope of the appended claims.

Claims

1. A control method for a resonant converter, the resonant converter comprising a transformer, wherein the primary winding of the transformer receives an input voltage through a primary circuit, and the secondary winding of the transformer outputs an output voltage through a secondary circuit, characterized in that, The secondary circuit includes two parallel secondary half-bridge arms, namely a first secondary half-bridge arm and a second secondary half-bridge arm. Each secondary half-bridge arm includes an upper bridge arm switch and a lower bridge arm switch connected in series, and the midpoint of the two secondary half-bridge arms is connected to the secondary winding. The upper bridge arm switch of the first secondary half-bridge arm corresponds to a first controllable switch, and the lower bridge arm switch of the second secondary half-bridge arm corresponds to a second controllable switch. The control method includes: The duty cycle of the first controllable switch and the second controllable switch is controlled during the first switching cycle to create a first time period during which the secondary current flows through the first short-circuit loop. During the second switching cycle, the duty cycle of the second of the first and second controllable switches is controlled to create a second time period during which the secondary current flows through the second short-circuit loop.

2. The control method for the resonant converter according to claim 1, characterized in that, The first switching cycle and the second switching cycle are adjacent switching cycles; or, The first switching cycle and the second switching cycle are spaced apart by an integer number of switching cycles.

3. The control method for the resonant converter according to claim 1, characterized in that, The control method further includes: The output voltage is acquired, and an adjustment signal is obtained based on the output voltage; During the first switching cycle, the duty cycle of the first of the first controllable switch and the second controllable switch is configured as the adjustment signal to modulate the first of the first controllable switch and the second controllable switch according to the adjustment signal, and the duty cycle of the second of the first controllable switch and the second controllable switch is configured as a fixed value. During the second switching cycle, the duty cycle of the first controllable switch and the second controllable switch is configured to the fixed value, and the duty cycle of the second controllable switch is configured to the adjustment signal to modulate the second controllable switch according to the adjustment signal.

4. The control method for the resonant converter according to claim 1, characterized in that, When 1 ≤ Gain ≤ 2, where Gain is the voltage gain. During the first switching cycle, the duty cycle of the first controllable switch and the second controllable switch is controlled to be greater than or equal to 0.5 and less than or equal to 1 according to the output voltage, and the duty cycle of the second controllable switch is modulated to be equal to 0.

5. During the second switching cycle, the duty cycle of the first controllable switch and the second controllable switch is modulated to be equal to 0.5, and the duty cycle of the second controllable switch is controlled to be greater than or equal to 0.5 and less than or equal to 1 according to the output voltage.

5. The control method for the resonant converter according to any one of claims 1-4, characterized in that, When 1≤Gain≤2, where Gain is the voltage gain; Within the first switching cycle, the first time period begins at the turn-off time of the second of the first and second controllable switches and ends at the turn-off time of the first of the first and second controllable switches. Within the second switching cycle, the second time period begins at the turn-off time of the first controllable switch and the second controllable switch and ends at the turn-off time of the second controllable switch.

6. The control method for the resonant converter according to any one of claims 1-4, characterized in that, When 1≤Gain≤2, where Gain is the voltage gain; The first short-circuit loop corresponds to the loop formed by the secondary winding, the first controllable switch and the second controllable switch, and the upper or lower bridge arm switch connected in series with the second controllable switch and the first controllable switch. The second short-circuit loop corresponds to the loop formed by the secondary winding, the second of the first and second controllable switches, and the upper or lower bridge arm switch connected in series with the first of the first and second controllable switches.

7. The control method for the resonant converter according to claim 1, characterized in that, When Gain > 2, where Gain is the voltage gain. During the first switching cycle, the duty cycle of the first controllable switch and the second controllable switch is controlled to be greater than 0.5 and less than 1 according to the output voltage, and the duty cycle of the second controllable switch is modulated to be equal to 1. During the second switching cycle, the duty cycle of the first controllable switch and the second controllable switch is modulated to be equal to 1, and the duty cycle of the second controllable switch is controlled to be greater than 0.5 and less than 1 according to the output voltage.

8. The control method for the resonant converter according to any one of claims 1-3 and 7, characterized in that, When Gain > 2 and the secondary current is continuous, where Gain is the voltage gain. Within the first switching cycle, the first time period begins at the turn-off time of the first of the first controllable switches and the second controllable switch, and ends at the turn-off time of the second of the first controllable switches and the second controllable switch. Within the second switching cycle, the second time period begins at the turn-off time of the second of the first and second controllable switches and ends at the turn-off time of the first of the first and second controllable switches.

9. The control method for the resonant converter according to any one of claims 1-3 and 7, characterized in that, When Gain > 2 and the secondary-side current is discontinuous, where Gain is the voltage gain. Within the first switching cycle, the first time period begins at the turn-off time of the first controllable switch and the second controllable switch, and ends at the moment when the secondary current decreases to zero. During the second switching cycle, the second time period begins at the turn-off time of the first controllable switch and the second controllable switch and ends at the moment when the secondary current decreases to zero.

10. The control method for the resonant converter according to any one of claims 1-3 and 7, characterized in that, The first short-circuit loop corresponds to the loop formed by the secondary winding, the second of the first controllable switch and the second controllable switch, and the upper or lower bridge arm switch connected in series with the first of the first and second controllable switches. The second short-circuit loop corresponds to the loop formed by the secondary winding, the first of the first and second controllable switches, and the upper or lower bridge arm switch connected in series with the second of the first and second controllable switches.

11. The control method for the resonant converter according to claim 3, characterized in that, The control method includes: The output voltage is compared with a reference value to obtain an error signal; Adjust the error signal to obtain a first intermediate signal; A constant is superimposed on the first intermediate signal to obtain a second intermediate signal; The second intermediate signal is limited to obtain the adjustment signal.

12. The control method for the resonant converter according to claim 1, characterized in that, When the primary-side circuit is a full-bridge circuit, the control method further includes: When the first primary-side switch in the primary-side circuit has an open-circuit fault, the second primary-side switch in the primary-side circuit, which is located in the same primary-side bridge arm as the first primary-side switch, is kept constantly turned on, and the third and fourth primary-side switches in the primary-side circuit, which are located in another primary-side bridge arm, are turned on complementaryly with a 50% duty cycle.

13. A resonant converter comprising a transformer, wherein the primary winding of the transformer receives an input voltage through a primary circuit, and the secondary winding of the transformer outputs an output voltage through a secondary circuit, characterized in that, The secondary circuit includes two parallel secondary half-bridge arms, namely a first secondary half-bridge arm and a second secondary half-bridge arm. Each secondary half-bridge arm includes an upper bridge arm switch and a lower bridge arm switch connected in series, and the midpoint of the two secondary half-bridge arms is connected to the secondary winding. The upper bridge arm switch of the first secondary half-bridge arm corresponds to a first controllable switch, and the lower bridge arm switch of the second secondary half-bridge arm corresponds to a second controllable switch. The resonant converter also includes a control unit configured to execute: The duty cycle of the first of the first controllable switch and the second controllable switch is controlled during the first switching cycle to create a first time period during which the secondary current flows through the first short-circuit loop. The duty cycle of the second of the first and second controllable switches is controlled during the second switching cycle to create a second time period during which the secondary current flows through the second short-circuit loop.

14. The resonant converter according to claim 13, characterized in that, The first switching cycle and the second switching cycle are adjacent switching cycles; or, The first switching cycle and the second switching cycle are spaced apart by an integer number of switching cycles.

15. The resonant converter according to claim 13, characterized in that, The control unit is configured to perform: The output voltage is acquired, and an adjustment signal is obtained based on the output voltage; During the first switching cycle, the duty cycle of the first of the first controllable switch and the second controllable switch is configured as the adjustment signal to modulate the first of the first controllable switch and the second controllable switch according to the adjustment signal, and the duty cycle of the second of the first controllable switch and the second controllable switch is configured as a fixed value. During the second switching cycle, the duty cycle of the first controllable switch and the second controllable switch is configured to the fixed value, and the duty cycle of the second controllable switch is configured to the adjustment signal to modulate the second controllable switch according to the adjustment signal.

16. The resonant converter according to claim 13, characterized in that, When 1 ≤ Gain ≤ 2, where Gain is the voltage gain, the control unit is configured to perform: During the first switching cycle, the duty cycle of the first controllable switch and the second controllable switch is controlled to be greater than or equal to 0.5 and less than or equal to 1 according to the output voltage, and the duty cycle of the second controllable switch is modulated to be equal to 0.

5. During the second switching cycle, the duty cycle of the first controllable switch and the second controllable switch is modulated to be equal to 0.5, and the duty cycle of the second controllable switch is controlled to be greater than or equal to 0.5 and less than or equal to 1 according to the output voltage.

17. The resonant converter according to any one of claims 13-16, characterized in that, When 1≤Gain≤2, where Gain is the voltage gain; Within the first switching cycle, the first time period begins at the turn-off time of the second of the first and second controllable switches and ends at the turn-off time of the first of the first and second controllable switches. Within the second switching cycle, the second time period begins at the turn-off time of the first controllable switch and the second controllable switch and ends at the turn-off time of the second controllable switch.

18. The resonant converter according to any one of claims 13-16, characterized in that, When 1≤Gain≤2, where Gain is the voltage gain; The first short-circuit loop corresponds to the loop formed by the secondary winding, the first controllable switch and the second controllable switch, and the upper or lower bridge arm switch connected in series with the second controllable switch and the first controllable switch. The second short-circuit loop corresponds to the loop formed by the secondary winding, the second of the first and second controllable switches, and the upper or lower bridge arm switch connected in series with the first of the first and second controllable switches.

19. The resonant converter according to claim 13, characterized in that, When Gain > 2, where Gain is the voltage gain, the control unit is configured to perform: During the first switching cycle, the duty cycle of the first controllable switch and the second controllable switch is controlled to be greater than 0.5 and less than 1 according to the output voltage, and the duty cycle of the second controllable switch is modulated to be equal to 1. During the second switching cycle, the duty cycle of the first controllable switch and the second controllable switch is modulated to be equal to 1, and the duty cycle of the second controllable switch is controlled to be greater than 0.5 and less than 1 according to the output voltage.

20. The resonant converter according to any one of claims 13-15 and 19, characterized in that, When Gain > 2 and the secondary side current is continuous, where Gain is the voltage gain; Within the first switching cycle, the first time period begins at the turn-off time of the first of the first controllable switches and the second controllable switch, and ends at the turn-off time of the second of the first controllable switches. Within the second switching cycle, the second time period begins at the turn-off time of the second of the first and second controllable switches and ends at the turn-off time of the first of the first and second controllable switches.

21. The resonant converter according to any one of claims 13-15 and 19, characterized in that, When Gain > 2 and the secondary side current is discontinuous, where Gain is the voltage gain; Within the first switching cycle, the first time period begins at the turn-off time of the first controllable switch and the second controllable switch, and ends at the moment when the secondary current decreases to zero. During the second switching cycle, the second time period begins at the turn-off time of the first controllable switch and the second controllable switch and ends at the moment when the secondary current decreases to zero.

22. The resonant converter according to any one of claims 13-15 and 19, characterized in that, The first short-circuit loop corresponds to the loop formed by the secondary winding, the second of the first controllable switch and the second controllable switch, and the upper or lower bridge arm switch connected in series with the first of the first and second controllable switches. The second short-circuit loop corresponds to the loop formed by the secondary winding, the first of the first and second controllable switches, and the upper or lower bridge arm switch connected in series with the second of the first and second controllable switches.

23. The resonant converter according to claim 15, characterized in that, The control unit includes: A subtractor is used to compare the output voltage with a reference value to obtain an error signal; A regulator is used to adjust the error signal to obtain a first intermediate signal; An adder is used to superimpose a constant onto the first intermediate signal to obtain a second intermediate signal; A limiter is used to limit the second intermediate signal to obtain the adjustment signal.

24. The resonant converter according to claim 13, characterized in that, When the primary-side circuit is a full-bridge circuit, the control unit is further configured to perform: When the first primary-side switch in the primary-side circuit has an open-circuit fault, the second primary-side switch in the primary-side circuit, which is located in the same primary-side bridge arm as the first primary-side switch, is kept constantly turned on, and the third and fourth primary-side switches in the primary-side circuit, which are located in another primary-side bridge arm, are turned on complementaryly with a 50% duty cycle.

25. The resonant converter according to claim 13, characterized in that, The secondary circuit also includes: A DC blocking capacitor is connected in series with the secondary winding of the transformer and then connected to the midpoint of the two secondary half-bridge arms.

26. A modulation method for a resonant converter, the resonant converter comprising a transformer, wherein the primary winding of the transformer receives an input voltage through a primary circuit, and the secondary winding of the transformer outputs an output voltage through a secondary circuit, characterized in that, The secondary circuit includes two parallel secondary half-bridge arms, namely a first secondary half-bridge arm and a second secondary half-bridge arm. Each secondary half-bridge arm includes an upper bridge arm switch and a lower bridge arm switch connected in series, and the midpoint of the two secondary half-bridge arms is connected to the secondary winding. The upper bridge arm switch in the first secondary half-bridge arm corresponds to a first controllable switch, and the lower bridge arm switch in the second secondary half-bridge arm corresponds to a second controllable switch. The modulation method includes: The first controllable switch and the second controllable switch are modulated respectively, so that a first short-circuit loop and a second short-circuit loop exist in the secondary circuit of the transformer to achieve a midpoint voltage of 0 between the midpoints of the two secondary half-bridge arms; The first short-circuit loop corresponds to the loop formed by the secondary winding, the second of the first controllable switch and the second controllable switch, and the upper or lower bridge arm switch connected in series with the first of the first and second controllable switches. The second short-circuit loop corresponds to the loop formed by the secondary winding, the first of the first and second controllable switches, and the upper or lower bridge arm switch connected in series with the second of the first and second controllable switches.

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