A variable inductance-based CLLC resonant converter and a control method thereof

Abstract

This invention discloses a CLLC resonant converter based on variable inductors and its control method, comprising a primary resonant inductor, a primary resonant capacitor, an equivalent magnetizing inductor, a transformer, a secondary resonant capacitor, and a secondary resonant inductor; both the primary and secondary resonant inductors are variable inductors; the primary resonant inductor and the primary resonant capacitor are connected in series on the primary side of the transformer, and the equivalent magnetizing inductor is connected in parallel on the primary side of the transformer; it also includes a DC current source; the primary resonant inductor, the secondary resonant inductor, and the DC current source are connected sequentially to form a complete circuit; the magnitudes of the primary and secondary resonant inductors are controlled by the output current of the DC current source. This invention can expand the voltage gain range, reduce the frequency modulation range, and improve the electromagnetic compatibility of a traditional CLLC resonant converter while maintaining its excellent characteristics.

Description

Technical Field

[0001] This invention relates to the field of power electronic power conversion technology, and in particular to a CLLC resonant converter based on a variable inductor and its control method. Background Technology

[0002] The CLLC resonant converter is positioned between the DC bus and the energy storage device, enabling bidirectional power transmission between the DC bus and the energy storage device. It can also achieve soft switching across the entire load range, greatly improving the power transmission efficiency. Therefore, it is widely used in microgrids and electric vehicles.

[0003] In traditional CLLC resonant converters, in order to obtain a wide voltage gain, the frequency modulation range or phase shift range of the resonant converter is generally increased. This method can easily cause the CLLC resonant converter to lose zero voltage switching (ZVS) or zero current switching (ZCS), increasing power loss. Furthermore, when the phase shift angle is too large, two switches on the same bridge arm may shoot through, damaging the CLLC resonant converter.

[0004] To address these issues, researchers proposed a method combining pulse width modulation (PWM) control with frequency conversion control to extend the output voltage gain range of CLLC resonant converters. However, this method is highly complex for controlling CLLC resonant converters, and the control system has low fault tolerance and is prone to failure.

[0005] In order to expand the voltage gain range, reduce the frequency modulation range, and improve the electromagnetic compatibility of the CLLC resonant converter while ensuring its characteristics, this invention proposes a CLLC resonant converter based on a variable inductor and its control method. Summary of the Invention

[0006] This invention provides a CLLC resonant converter based on a variable inductor and its control method, which can expand the voltage gain range of the CLLC resonant converter, reduce the frequency modulation range of the CLLC resonant converter, and improve the electromagnetic compatibility of the CLLC resonant converter while ensuring the characteristics of the CLLC resonant converter.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a CLLC resonant converter based on a variable inductor, comprising a primary-side full-bridge circuit, a resonant cavity circuit, and a secondary-side full-bridge circuit connected sequentially between a DC bus and an energy storage power source. The resonant cavity circuit comprises: a primary-side resonant inductor, a primary-side resonant capacitor, an equivalent magnetizing inductor, a transformer, a secondary-side resonant capacitor, and a secondary-side resonant inductor; both the primary-side resonant inductor and the secondary-side resonant inductor are variable inductors.

[0009] The primary resonant inductor and the primary resonant capacitor are connected in series in the primary winding of the transformer, and the equivalent magnetizing inductor is connected in parallel in the primary winding of the transformer; the secondary resonant capacitor and the secondary resonant inductor are connected in series in the secondary winding of the transformer.

[0010] It also includes a DC current source; the primary resonant inductor, the secondary resonant inductor, and the DC current source are connected in sequence to form a complete circuit;

[0011] The magnitudes of the primary resonant inductor and the secondary resonant inductor are controlled by the magnitude of the output current of the DC current source.

[0012] In one possible implementation, the primary-side full-bridge circuit includes a primary-side filter capacitor, a first switch, a second switch, a third switch, and a fourth switch.

[0013] The primary-side filter capacitor is connected in parallel across the DC bus.

[0014] The positive terminal of the DC bus is connected to the drain of the first switch and the drain of the third switch, the negative terminal of the DC bus is connected to the source of the second switch and the source of the fourth switch, the source of the first switch is connected to the drain of the second switch, and the source of the third switch is connected to the drain of the fourth switch.

[0015] One end of the primary resonant inductor is connected to the source of the first switching transistor and the drain of the second switching transistor. The other end of the primary resonant inductor is connected to one end of the primary resonant capacitor. The other end of the primary resonant capacitor is connected to one end of the equivalent magnetizing inductor and one end of the primary winding of the transformer. The other end of the equivalent magnetizing inductor is connected to the other end of the primary winding of the transformer, the source of the third switching transistor, and the drain of the fourth switching transistor.

[0016] In one possible implementation, the secondary-side full-bridge circuit includes a secondary-side filter capacitor, a fifth switch, a sixth switch, a seventh switch, and an eighth switch.

[0017] The secondary filter capacitor is connected in parallel across the energy storage power supply.

[0018] The positive terminal of the energy storage power supply is connected to the drain of the fifth switch and the drain of the seventh switch, the negative terminal of the energy storage power supply is connected to the source of the sixth switch and the source of the eighth switch, the source of the fifth switch is connected to the drain of the sixth switch, and the source of the seventh switch is connected to the drain of the eighth switch.

[0019] One end of the secondary resonant inductor is connected to the source of the fifth switch and the drain of the sixth switch. The other end of the secondary resonant inductor is connected to one end of the secondary resonant capacitor. The other end of the secondary resonant capacitor is connected to one end of the secondary winding of the transformer. The other end of the secondary winding of the transformer is connected to the source of the seventh switch and the drain of the eighth switch.

[0020] In one possible implementation, the resonant converter includes a forward operating state and a reverse operating state; the forward operating state is the state in which electrical energy is transmitted from the DC power supply sequentially through the primary-side full-bridge circuit, the resonant cavity circuit, and the secondary-side full-bridge circuit to the energy storage power supply; the reverse operating state is the state in which electrical energy is transmitted from the energy storage power supply sequentially through the secondary-side full-bridge circuit, the resonant cavity circuit, and the primary-side full-bridge circuit to the DC power supply.

[0021] In the forward operating state, the drive signals of the first and second switches are complementary, the drive signals of the third and fourth switches are complementary, the drive signals of the first and fourth switches are the same, and the drive signals of the second and third switches are the same; the fifth, sixth, seventh, and eighth switches have no drive signals, the primary-side full-bridge circuit operates in inverter mode, and the secondary-side full-bridge circuit operates in rectification mode.

[0022] In the reverse operation state, the drive signals of the fifth and sixth switches are complementary, and the drive signals of the seventh and eighth switches are complementary; the drive signals of the fifth and eighth switches are the same, and the drive signals of the sixth and seventh switches are the same; the first, second, third, and fourth switches have no drive signals, the primary-side full-bridge circuit operates in rectification mode, and the secondary-side full-bridge circuit operates in inverter mode.

[0023] Secondly, the present invention provides a control method for a CLLC resonant converter based on a variable inductor, comprising: acquiring the voltage fluctuation value of the DC bus within a preset time period;

[0024] The first scheme or the second scheme is determined based on the magnitude of the voltage fluctuation value and the preset threshold as the scheme for adjusting the output of the resonant converter; the first scheme is to adjust only the output current of the DC current source, and the second scheme is to adjust both the output current of the DC current source and the switching frequency of the resonant converter.

[0025] In one possible implementation, determining either the first or second scheme as the method for adjusting the output of the resonant converter based on the magnitude of the voltage fluctuation value and a preset threshold specifically includes:

[0026] When the voltage fluctuation value of the DC bus is less than the preset threshold, the first scheme is used as the scheme for adjusting the output of the resonant converter;

[0027] When the voltage fluctuation value of the DC bus is greater than the preset threshold, the second scheme will be used as the scheme for adjusting the output of the resonant converter.

[0028] In one possible implementation, adjusting only the output current of the DC current source specifically includes:

[0029] Obtain the output voltage of the resonant converter;

[0030] When the output voltage is greater than the target voltage, the output current of the DC current source is reduced, thereby lowering the output voltage.

[0031] When the output voltage is less than the target voltage, the output current of the DC current source is increased to raise the output voltage.

[0032] In one possible implementation, simultaneously adjusting the output current of the DC current source and the switching frequency of the resonant converter specifically includes:

[0033] Obtain the output voltage and switching frequency of the resonant converter;

[0034] When the output voltage is greater than the target voltage, the output current of the DC current source is reduced to a minimum value, and then the switching frequency is increased to reduce the output voltage.

[0035] When the output voltage is less than the target voltage, the output current of the DC current source is increased to its maximum value, and then the switching frequency is reduced to increase the output voltage.

[0036] The CLLC resonant converter based on variable inductance provided in this invention achieves electrical isolation between the primary and secondary sides through a transformer. Furthermore, this invention replaces the fixed primary and secondary resonant inductors in the prior art with variable inductors, allowing adjustment of the output voltage gain of the CLLC resonant converter by adjusting the inductance values ​​of the primary and secondary resonant inductors. Since the primary and secondary resonant inductors and the DC current source are sequentially connected to form a complete circuit, the control method of the CLLC resonant converter is changed from the traditional frequency modulation or phase-shift frequency modulation method to an inductance-adjusted method. That is, only the output current of the DC current source needs to be adjusted to adjust the inductance values ​​of the primary and secondary resonant inductors, thus simplifying the control method. After the inductance values ​​of the primary and secondary resonant inductors are adjusted to their limit values, the switching frequency of the resonant converter can be adjusted to further achieve bidirectional wide voltage gain adjustment, thereby improving the compatibility of the resonant converter. In other words, this invention can guarantee the characteristics of the CLLC resonant converter while expanding the voltage gain range of the CLLC resonant converter, reducing the frequency modulation range of the CLLC resonant converter, and improving the electromagnetic compatibility of the CLLC resonant converter. Attached Figure Description

[0037] Figure 1 A topology diagram of a CLLC resonant converter based on a variable inductor provided in an embodiment of the present invention;

[0038] Figure 2 The control winding diagrams for the primary-side resonant inductor and the secondary-side resonant inductor are provided for embodiments of the present invention.

[0039] Figure 3 A flowchart illustrating the steps of a control method for a CLLC resonant converter based on a variable inductor, provided in an embodiment of the present invention.

[0040] Figure 4 The resonant cavity current waveform of a CLLC resonant converter based on a variable inductor in an under-resonant state, provided for an embodiment of the present invention;

[0041] Figure 5 The resonant cavity current waveform of a CLLC resonant converter based on a variable inductor in a quasi-resonant state, provided for an embodiment of the present invention;

[0042] Figure 6 The resonant cavity current waveform of a CLLC resonant converter based on a variable inductor in an over-resonance state, provided for an embodiment of the present invention;

[0043] Figure 7 shows the operating mode diagram of the CLLC resonant converter based on variable inductor in the under-resonance state during half a cycle provided in the embodiment of the present invention; wherein Figure 7(a) shows the resonant converter in the under-resonance state t0~t 0′The operating mode diagram, Figure 7(b) shows the resonant converter in the underresonant state t. 0′ Figure 7(c) shows the operating mode diagram of the resonant converter in the under-resonance state t1~t2, Figure 7(d) shows the operating mode diagram of the resonant converter in the under-resonance state t2~t3, and Figure 7(e) shows the operating mode diagram of the resonant converter in the under-resonance state t3~t4.

[0044] Figure labels and descriptions:

[0045] 1. DC bus; 2. Energy storage power supply; 3. Primary-side full-bridge circuit; 4. Resonant cavity circuit; 5. Secondary-side full-bridge circuit. Detailed Implementation

[0046] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0047] Hereinafter, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of embodiments of this disclosure, unless otherwise stated, "a plurality of" means two or more. Furthermore, the use of "based on" or "according to" implies openness and inclusiveness, because processes, steps, calculations, or other actions "based on" or "according to" one or more of the stated conditions or values ​​may in practice be based on additional conditions or beyond the stated values.

[0048] like Figure 1 As shown, this embodiment of the invention provides a CLLC resonant converter based on a variable inductor, including a primary-side full-bridge circuit 3, a resonant cavity circuit 4, and a secondary-side full-bridge circuit 5, which are sequentially connected and disposed between the DC bus 1 and the energy storage power supply 2.

[0049] Specifically, in this embodiment, DC bus 1 carries the rectification in the converter to convert AC to DC, and in the inverter it converts DC to AC. The voltage across DC bus 1 is V1; energy storage power supply 2 is a battery, and the voltage across energy storage power supply 2 is V2.

[0050] The resonant cavity circuit 4 includes: primary resonant inductor L vi1 Primary resonant capacitor C r1 Equivalent magnetizing inductance L m Transformer T, secondary resonant capacitor C r2and secondary resonant inductor L vi2 Primary resonant inductance L vi1 and secondary resonant inductor L vi2 All are variable inductors.

[0051] Primary resonant inductance L vi1 With the primary resonant capacitor C r1 The equivalent magnetizing inductance L is connected in series on the primary side of transformer T. m Parallel connection to the primary side of transformer T; secondary resonant capacitor C r2 With secondary resonant inductor L vi2 It is connected in series on the secondary side of transformer T.

[0052] like Figure 2 As shown, the CLLC resonant converter based on variable inductor also includes a DC current source.

[0053] Primary resonant inductance L vi1 Secondary resonant inductor L vi2 And a DC current source is connected in sequence to form a complete circuit.

[0054] Primary resonant inductance L vi1 and secondary resonant inductor L vi2 The magnitude is determined by the output current I of the DC current source. c Size control.

[0055] Specifically, a variable inductor is a variable inductor with a saturable magnetic core. This core has three core pillars: a central core pillar and two outer core pillars. A control coil is wound on the central core pillar, and two parallel outer coils are wound on the outer core pillars. The inductance of the outer coils on the outer core pillars varies with the current flowing through the control coil. Therefore, when the primary and secondary resonant inductors are connected in series, the magnitudes of the primary and secondary resonant inductors can be adjusted by changing the output current of the DC current source connected in series with them.

[0056] In other words, the primary resonant inductance L vi1 and secondary resonant inductor L vi2 The inductance value can be changed by altering the output current I of the DC current source. c And change, when the output current I c When the value increases, the primary resonant inductance L vi1 and secondary resonant inductor L vi2 When the inductance value decreases, the output current I c When the value decreases, the primary resonant inductance L vi1 and secondary resonant inductor L vi2 The inductance value increases.

[0057] When the output current I is changed c When the size is small, the primary resonant inductance Lvi1 and secondary resonant inductor L vi2 Simultaneous increases or decreases have a unidirectional enhancing effect on the voltage gain of the resonant converter of the present invention.

[0058] Furthermore, such as Figure 1 As shown, the primary-side full-bridge circuit 3 includes a primary-side filter capacitor C1, a first switch Q1, a second switch Q2, a third switch Q3, and a fourth switch Q4.

[0059] The primary-side filter capacitor C1 is connected in parallel across DC bus 1;

[0060] The positive terminal of DC bus 1 is connected to the drain of the first switch Q1 and the drain of the third switch Q3. The negative terminal of DC bus 1 is connected to the source of the second switch Q2 and the source of the fourth switch Q4. The source of the first switch Q1 is connected to the drain of the second switch Q2, and the source of the third switch Q3 is connected to the drain of the fourth switch Q4.

[0061] Primary resonant inductance L vi1 One end is connected to the source of the first switching transistor Q1 and the drain of the second switching transistor Q2, and the primary resonant inductor L vi1 The other end is connected to the primary resonant capacitor C. r1 At one end, the primary resonant capacitor C r1 The other end is connected to the equivalent magnetizing inductance L m One end is connected to one end of the primary winding of transformer T, and the equivalent magnetizing inductance L m The other end is connected to the other end of the primary winding of transformer T, the source of the third switch Q3, and the drain of the fourth switch Q4.

[0062] Furthermore, the secondary-side full-bridge circuit 5 includes a secondary-side filter capacitor C2, a fifth switch Q5, a sixth switch Q6, a seventh switch Q7, and an eighth switch Q8;

[0063] The secondary-side filter capacitor C2 is connected in parallel across the energy storage power supply 2;

[0064] The positive terminal of the energy storage power supply 2 is connected to the drain of the fifth switch Q5 and the drain of the seventh switch Q7. The negative terminal of the energy storage power supply 2 is connected to the source of the sixth switch Q6 and the source of the eighth switch Q8. The source of the fifth switch Q5 is connected to the drain of the sixth switch Q6, and the source of the seventh switch Q7 is connected to the drain of the eighth switch Q8.

[0065] Secondary resonant inductor L vi2 One end is connected to the source of the fifth switch Q5 and the drain of the sixth switch Q6, and the secondary resonant inductor L vi2 The other end is connected to the secondary resonant capacitor C. r2 One end, secondary resonant capacitor Cr2 The other end is connected to one end of the secondary winding of transformer T, and the other end of the secondary winding of transformer T is connected to the source of the seventh switch Q7 and the drain of the eighth switch Q8.

[0066] Furthermore, the resonant converter includes a forward operating state and a reverse operating state.

[0067] The forward operating state is when electrical energy is transmitted from the DC power supply through the primary-side full-bridge circuit 3, the resonant cavity circuit 4, and the secondary-side full-bridge circuit 5 to the energy storage power supply 2; the reverse operating state is when electrical energy is transmitted from the energy storage power supply 2 through the secondary-side full-bridge circuit 5, the resonant cavity circuit 4, and the primary-side full-bridge circuit 3 to the DC power supply.

[0068] Figure 1 In the diagram, the arrow above the resonant cavity circuit 4 indicates that the resonant converter is operating in the forward direction, and the arrow below the resonant cavity circuit 4 indicates that the resonant converter is operating in the reverse direction.

[0069] In the forward operation state, the drive signals of the first switch Q1 and the second switch Q2 are complementary, and the drive signals of the third switch Q3 and the fourth switch Q4 are complementary; the drive signals of the first switch Q1 and the fourth switch Q4 are the same, and the drive signals of the second switch Q2 and the third switch Q3 are the same; the fifth switch Q5, the sixth switch Q6, the seventh switch Q7 and the eighth switch Q8 have no drive signal, the primary-side full-bridge circuit 3 operates in the inverter state, and the secondary-side full-bridge circuit 5 operates in the rectification state;

[0070] In reverse operation, the drive signals of the fifth switch Q5 and the sixth switch Q6 are complementary, and the drive signals of the seventh switch Q7 and the eighth switch Q8 are complementary; the drive signals of the fifth switch Q5 and the eighth switch Q8 are the same, and the drive signals of the sixth switch Q6 and the seventh switch Q7 are the same; the first switch Q1, the second switch Q2, the third switch Q3 and the fourth switch Q4 have no drive signals, the primary-side full-bridge circuit 3 operates in rectification mode, and the secondary-side full-bridge circuit 5 operates in inverter mode.

[0071] In other words, by combining the switching on and off of each switch in the primary-side full-bridge circuit 3 and the secondary-side full-bridge circuit 5, the input voltage of the resonant cavity circuit 4 can be maintained at two different levels: 0V or V1.

[0072] Specifically, in the forward operation state, the primary resonant inductance L of the resonant converter of the present invention... vi1 The change in inductance value plays a dominant role in the voltage gain, and the secondary resonant inductance L... vi2 The change in inductance plays a supporting role in the voltage gain, that is, when the output current I... c When the primary resonant inductance L changes, vi1The secondary resonant inductor L has a significant impact on the voltage gain of the resonant converter and plays a dominant role. vi2 It has little effect on the voltage gain of the resonant converter and plays an auxiliary role in voltage regulation.

[0073] In the reverse operating state, the secondary resonant inductor L of the resonant converter of this invention... vi2 The change in inductance plays a dominant role in the voltage gain, and the primary resonant inductance L... vi1 The change in inductance plays a supporting role in the voltage gain, that is, when the output current I... c When the secondary resonant inductance L changes, vi2 The primary-side resonant inductor L has a significant and dominant effect on the voltage gain of the resonant converter. vi1 It has little effect on the voltage gain of the resonant converter and plays an auxiliary role in voltage regulation.

[0074] Furthermore, in this embodiment, the drive signals of the first switch Q1 and the second switch Q2 are complementary, and the drive signals of the third switch Q3 and the fourth switch Q4 are complementary, specifically:

[0075] The first switch Q1 is turned on, the second switch Q2 is turned off, the third switch Q3 is turned off, and the fourth switch Q4 is turned on.

[0076] The drive signals for the fifth switch Q5 and the sixth switch Q6 are complementary, and the drive signals for the seventh switch Q7 and the eighth switch Q8 are complementary, specifically as follows:

[0077] The fifth switch Q5 is turned on, the sixth switch Q6 is turned off, the seventh switch Q7 is turned off, and the eighth switch Q8 is turned on.

[0078] The CLLC resonant converter based on variable inductance provided in this invention achieves electrical isolation between the primary and secondary sides through a transformer. Furthermore, this invention replaces the fixed primary and secondary resonant inductors in the prior art with variable inductors, allowing adjustment of the output voltage gain of the CLLC resonant converter by adjusting the inductance values ​​of the primary and secondary resonant inductors. Since the primary and secondary resonant inductors and the DC current source are sequentially connected to form a complete circuit, the control method of the CLLC resonant converter is changed from the traditional frequency modulation or phase-shift frequency modulation method to an inductance-adjusted method. That is, only the output current of the DC current source needs to be adjusted to adjust the inductance values ​​of the primary and secondary resonant inductors, thus simplifying the control method. After the inductance values ​​of the primary and secondary resonant inductors are adjusted to their limit values, the switching frequency f of the resonant converter can also be adjusted. sThis invention further enables bidirectional wide voltage gain adjustment of the converter, thereby improving the compatibility of the resonant converter. In other words, while ensuring the characteristics of the CLLC resonant converter, this invention expands the voltage gain range of the CLLC resonant converter, reduces the frequency modulation range of the CLLC resonant converter, and improves the electromagnetic compatibility of the CLLC resonant converter.

[0079] This invention also provides a control method for a CLLC resonant converter based on any of the above-mentioned variable inductors, such as... Figure 3 As shown, the method includes:

[0080] Step 101: Obtain the voltage fluctuation value of the DC bus within a preset time period. That is, obtain the range of change of V1 within the preset time period.

[0081] Step 102: Determine the first or second scheme as the scheme for adjusting the output of the resonant converter based on the magnitude of the voltage fluctuation value and the preset threshold.

[0082] The first option involves adjusting only the output current I of the DC current source. c The second option is to simultaneously adjust the output current I of the DC current source. c The switching frequency f of the size and resonant converter s Size.

[0083] Furthermore, based on the magnitude of the voltage fluctuation value and a preset threshold, a first or second scheme is determined as the method for adjusting the output of the resonant converter, specifically including:

[0084] When the voltage fluctuation of the DC bus is less than the preset threshold, the first scheme will be used as the scheme to adjust the output of the resonant converter.

[0085] When the voltage fluctuation of the DC bus exceeds a preset threshold, the second scheme will be used to adjust the output of the resonant converter.

[0086] Furthermore, only the output current I of the DC current source is adjusted. c Size, specifically including:

[0087] Obtain the output voltage of the resonant converter;

[0088] When the output voltage is greater than the target voltage, reduce the output current I of the DC current source. c This causes the output voltage to decrease.

[0089] Specifically, when the output voltage is greater than the target voltage, the output current I is reduced. c This increases the inductance values ​​of the primary and secondary resonant inductors, thereby increasing the resonant frequency f of the resonant converter of this invention. r The voltage decreases, thus entering an over-resonance state, resulting in a decrease in output voltage.

[0090] The resonant frequency f of the resonant converter r It is determined based on the primary resonant inductance, primary resonant capacitance, equivalent magnetizing inductance, transformer, secondary resonant capacitance, and secondary resonant inductance.

[0091] When the output voltage is less than the target voltage, increase the output current I of the DC current source. c The output voltage increases.

[0092] Specifically, when the output voltage is lower than the target voltage, the output current I is increased. c This reduces the inductance values ​​of the primary and secondary resonant inductors, thereby increasing the resonant frequency f of the resonant converter of this invention. r The voltage increases, thus entering an underresonant state, and the output voltage increases.

[0093] Furthermore, the output current I of the DC current source is adjusted simultaneously. c The switching frequency f of the size and resonant converter s The size, specifically including:

[0094] Obtain the output voltage of the resonant converter;

[0095] When the output voltage is greater than the target voltage, reduce the output current I of the DC current source. c To the minimum value, then increase the switching frequency f. s This causes the output voltage to decrease.

[0096] Specifically, when the output voltage is much greater than the target voltage, reduce the output current I. c To reach its minimum value, then increase the switching frequency f. s This further exacerbates the over-resonance state and reduces the output voltage.

[0097] When the output voltage is less than the target voltage, increase the output current I of the DC current source. c Reach the maximum value, then decrease the switching frequency f. s The output voltage increases.

[0098] Specifically, when the output voltage is much lower than the target voltage, increase the output current I. c Reach its maximum value, then reduce the switching frequency f. s This further exacerbates the underresonance state and increases the output voltage.

[0099] When the output voltage equals the target voltage, the resonant converter operates in a quasi-resonant state.

[0100] When a user needs to switch between the underresonance and overresonance states of a resonant converter, in order to prevent current spikes and ensure the safety of the resonant converter, the output current I needs to be controlled.c Reducing it to zero allows both the primary and secondary resonant inductances to reach their maximum values, thereby suppressing current spikes caused by switching operating states.

[0101] In this embodiment, when energy is transferred between the DC bus and the energy storage power source, and the voltage fluctuation of the DC bus is less than a preset threshold, the output voltage of the resonant converter can be adjusted simply by adjusting the inductance values ​​of the primary and secondary resonant inductors. At this time, the drive signals of the first and second switches are complementary, as are the drive signals of the third and fourth switches; the first and fourth switches are simultaneously turned on, maintaining a duty cycle of 0.5; the second and third switches are simultaneously turned on, maintaining a duty cycle of 0.5. The output voltage is adjusted by regulating the inductance value of the variable inductor.

[0102] When the voltage fluctuation of the DC bus exceeds the preset threshold, simply adjusting the inductance value of the variable inductor is no longer sufficient to meet the voltage gain requirements of the resonant converter. In this case, it is necessary to adjust the switching frequency f. s That is, when the output voltage is greater than or less than the target voltage, after adjusting the inductance value of the variable inductor to its maximum or minimum value, the switching frequency f of the CLLC resonant converter is further adjusted. s The output voltage can be increased or decreased by adjusting the frequency within a small range, thus achieving a wide range of voltage adjustment.

[0103] The resonant converter of this invention includes three operating states: underresonance, quasi-resonance, and overresonance. The resonant cavity current waveforms in different regions of the three operating states are as follows: Figure 4 , Figure 5 as well as Figure 6 As shown.

[0104] like Figure 4 As shown, in the underresonant state, one cycle of the resonant converter includes time nodes t0 to t8, where t0 to t4 is the first half-cycle and t4 to t8 is the second half-cycle. The operating principle of the first and second half-cycles is the same, and each half-cycle includes 5 modes. For example, the 5 modes of the first half-cycle are t0 to t0′, t... 0′ ~t1, t1~t2, t2~t3 and t3~t4.

[0105] like Figure 5 , Figure 6 As shown, in the quasi-resonant and over-resonant states, one cycle of the resonant converter includes time nodes t0 to t6, where t0 to t3 is the first half-cycle and t3 to t6 is the second half-cycle. The operating principle of the first and second half-cycles is the same, and each half-cycle includes 4 modes. For example, the 5 modes of the first half-cycle are t0 to t0′, t6, t7′, t8′, t9′, t1′, t2′, t3′, t6′ ... 0′~t1, t1~t2, and t2~t3.

[0106] Therefore, it can be seen that the resonant converter is in either a quasi-resonant state or an over-resonant state for each half-cycle. The over-resonant state is only one mode less than the under-resonant state.

[0107] This embodiment only takes the underresonant state as an example to analyze the working mode. Since the working principle of the first half cycle and the second half cycle is the same in the underresonant state, this embodiment only shows the working principle of the resonant converter in the first half cycle, that is, the t0 to t4 segment.

[0108] like Figure 4 As shown in Figures 7(a) and 7(b), at time t0, the first switch Q1 and the fourth switch Q4 are turned on, and the primary resonant inductor L... vi1 current i Lvi1 The parasitic diode D of the switching transistor Q1 and D Q4 During freewheeling, the drain-source voltages of Q1 and Q4 are zero, creating conditions for their zero-voltage turn-on (ZVS). Figure 1 The voltages at terminals A and B are the input voltages V1 and i. Lvi1 The equivalent magnetizing inductance L increases according to a sinusoidal law. m current i Lm As the current i increases linearly, Lvi1 The rate of increase is greater than that of current i Lm Quickly. The parasitic diode D of the secondary-side switching transistor. Q5 and D Q8 When rectification is turned on, the voltage across C and D is clamped by the output voltage V2. At t 0′ At that moment, i Lvi1 The current drops to zero, then changes direction, passing through the horizontal axis until time t1. At this time, Q1 and Q4 remain conducting, and the resonant current i Lvi1 Equal to excitation current i Lm The working mode from t0 to t1 ends. During the process from t0 to t1, regardless of whether it is t0-t... 0′ Time period or t 0′ -t1 time period is L vi1 C r1 L vi2 C r2 The process of four-element resonance, L m It did not participate in the resonance process.

[0109] As shown in Figure 7(c), Q1 and Q4 remain on, and the resonant current i Lvi1 and excitation current i Lm The two diodes are equal, making the secondary current of the transformer zero, and the parasitic diode D of the secondary switching transistor... Q5 and D Q8It also naturally turns off due to the zero secondary current, achieving zero-current turn-off (ZCS) and avoiding reverse recovery problems; at the same time, it disconnects the primary and secondary sides of the transformer, and the resonant inductor L... vi2 and resonant capacitor C r2 It no longer participates in resonance, but instead becomes the equivalent magnetizing inductance L. m and resonant inductance L vi1 Resonant capacitor C r1 When all three elements resonate together, the resonant period of all three is much longer than the switching period. During this time period, i... Lm and i Lvi1 It can be approximated as constant. At time t2, Q1 and Q4 are turned off, and the working mode process from t1 to t2 ends.

[0110] As shown in Figure 7(d), at time t2, Q1 and Q4 are turned off. At this time, all switches are in the off state, i.e., entering the dead time. The resonant current i Lvi1 Parasitic capacitance C of the switching transistor Q1 and C Q4 As charging progresses, the drain-source voltages of switching transistors Q1 and Q4 rise linearly; the resonant current i Lvi1 At the same time, the parasitic capacitance C is given Q2 and C Q3 During discharge, the drain-source voltages of Q2 and Q3 decrease linearly. At time t3, the drain-source voltages of Q1 and Q4 are equal to V1, and the drain-source voltages of Q2 and Q3 are equal to 0, marking the end of the t2-t3 operating mode.

[0111] As shown in Figure 7(e), at time t3, all the switches are still in the off state. The parasitic capacitance charging process of Q1 and Q4 is completed, and the parasitic capacitance discharging process of Q2 and Q3 is completed. At this time, the resonant current i Lvi1 Only the parasitic diodes D of Q2 and Q3 can pass through Q2 and D Q3 The freewheeling current makes the drain-source voltage of Q2 and Q3 zero, allowing Q2 and Q3 to turn on at zero voltage during this stage. During this stage, the voltage across A and B is -V1, and the voltage across C and D is -V2. At time t4, the first half-cycle ends, and the second half-cycle begins.

[0112] Traditional CLLC resonant converters mostly employ phase-shift frequency modulation control, which is complex and requires a large frequency adjustment range to achieve wide voltage gain, hindering the optimal design of magnetic components. Therefore, simplifying the control method of CLLC resonant converters, widening the voltage gain, and narrowing the frequency modulation range while retaining the advantages of traditional CLLC resonant converters is of practical significance. Thus, this invention proposes a CLLC resonant converter based on a variable inductor and its control method.

[0113] This invention utilizes a variable inductor to replace the fixed resonant inductors on the primary and secondary sides of the resonant cavity in a traditional CLLC resonant converter. By adjusting the inductance value of the variable inductor, the bidirectional voltage regulation function of the resonant converter is achieved. Furthermore, by combining frequency modulation control with the adjustment of the switching frequency of the resonant converter, the gain range of the output voltage is broadened.

[0114] This invention does not change the topology of the CLLC resonant converter. Therefore, while retaining the advantages of soft switching in traditional CLLC resonant converters, it can further broaden the output voltage gain range and reduce the frequency modulation range, thus meeting the operating requirements of CLLC resonant converters under extreme conditions and maintaining high conversion efficiency over a wide voltage gain range.

[0115] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions within the technical scope disclosed in the present invention should be covered within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A control method for a CLLC resonant converter based on a variable inductor, characterized in that, This invention relates to a CLLC resonant converter based on variable inductors. The CLLC resonant converter includes a primary-side full-bridge circuit, a resonant cavity circuit, and a secondary-side full-bridge circuit, sequentially connected and disposed between a DC bus and an energy storage power source. The resonant cavity circuit comprises: a primary-side resonant inductor, a primary-side resonant capacitor, an equivalent magnetizing inductor, a transformer, a secondary-side resonant capacitor, and a secondary-side resonant inductor; both the primary-side and secondary-side resonant inductors are variable inductors. The primary resonant inductor and the primary resonant capacitor are connected in series in the primary winding of the transformer, and the equivalent magnetizing inductor is connected in parallel in the primary winding of the transformer; the secondary resonant capacitor and the secondary resonant inductor are connected in series in the secondary winding of the transformer. It also includes a DC current source; the primary resonant inductor, the secondary resonant inductor, and the DC current source are connected in sequence to form a complete circuit; The magnitudes of the primary resonant inductor and the secondary resonant inductor are controlled by the magnitude of the output current of the DC current source. Control methods for CLLC resonant converters based on variable inductors include: Obtain the voltage fluctuation value of the DC bus within a preset time period; Based on the relationship between the voltage fluctuation value and the preset threshold, a first scheme or a second scheme is determined as the scheme for adjusting the output of the resonant converter; the first scheme is to adjust only the output current of the DC current source, and the second scheme is to adjust both the output current of the DC current source and the switching frequency of the resonant converter simultaneously. The step of determining either the first or second scheme as the method for adjusting the output of the resonant converter based on the relationship between the voltage fluctuation value and a preset threshold specifically includes: When the voltage fluctuation value of the DC bus is less than the preset threshold, the first scheme is used as the scheme for adjusting the output of the resonant converter; When the voltage fluctuation value of the DC bus is greater than the preset threshold, the second scheme will be used as the scheme for adjusting the output of the resonant converter. The adjustment of only the output current of the DC current source specifically includes: Obtain the output voltage of the resonant converter; When the output voltage is greater than the target voltage, the output current of the DC current source is reduced, thereby lowering the output voltage. When the output voltage is less than the target voltage, the output current of the DC current source is increased to raise the output voltage. The simultaneous adjustment of the output current of the DC current source and the switching frequency of the resonant converter specifically includes: Obtain the output voltage and switching frequency of the resonant converter; When the output voltage is greater than the target voltage, the output current of the DC current source is reduced to a minimum value, and then the switching frequency is increased to reduce the output voltage. When the output voltage is less than the target voltage, the output current of the DC current source is increased to its maximum value, and then the switching frequency is reduced to increase the output voltage.

2. The control method for a CLLC resonant converter based on a variable inductor according to claim 1, characterized in that, The primary-side full-bridge circuit includes a primary-side filter capacitor, a first switching transistor, a second switching transistor, a third switching transistor, and a fourth switching transistor. The primary-side filter capacitor is connected in parallel across the DC bus. The positive terminal of the DC bus is connected to the drain of the first switch and the drain of the third switch, the negative terminal of the DC bus is connected to the source of the second switch and the source of the fourth switch, the source of the first switch is connected to the drain of the second switch, and the source of the third switch is connected to the drain of the fourth switch. One end of the primary resonant inductor is connected to the source of the first switching transistor and the drain of the second switching transistor. The other end of the primary resonant inductor is connected to one end of the primary resonant capacitor. The other end of the primary resonant capacitor is connected to one end of the equivalent magnetizing inductor and one end of the primary winding of the transformer. The other end of the equivalent magnetizing inductor is connected to the other end of the primary winding of the transformer, the source of the third switching transistor, and the drain of the fourth switching transistor.

3. The control method for a CLLC resonant converter based on a variable inductor according to claim 2, characterized in that, The secondary-side full-bridge circuit includes a secondary-side filter capacitor, a fifth switch, a sixth switch, a seventh switch, and an eighth switch. The secondary filter capacitor is connected in parallel across the energy storage power supply. The positive terminal of the energy storage power supply is connected to the drain of the fifth switch and the drain of the seventh switch, the negative terminal of the energy storage power supply is connected to the source of the sixth switch and the source of the eighth switch, the source of the fifth switch is connected to the drain of the sixth switch, and the source of the seventh switch is connected to the drain of the eighth switch. One end of the secondary resonant inductor is connected to the source of the fifth switch and the drain of the sixth switch. The other end of the secondary resonant inductor is connected to one end of the secondary resonant capacitor. The other end of the secondary resonant capacitor is connected to one end of the secondary winding of the transformer. The other end of the secondary winding of the transformer is connected to the source of the seventh switch and the drain of the eighth switch.

4. The control method for a CLLC resonant converter based on a variable inductor according to claim 3, characterized in that, The resonant converter includes a forward operating state and a reverse operating state; the forward operating state is the state in which electrical energy is transmitted from the DC bus through the primary-side full-bridge circuit, the resonant cavity circuit, and the secondary-side full-bridge circuit to the energy storage power source. The reverse operation state is the state in which electrical energy is transmitted from the energy storage power source through the secondary full-bridge circuit, the resonant cavity circuit, and the primary full-bridge circuit to the DC bus. In the forward operating state, the drive signals of the first and second switches are complementary, the drive signals of the third and fourth switches are complementary, the drive signals of the first and fourth switches are the same, and the drive signals of the second and third switches are the same; the fifth, sixth, seventh, and eighth switches have no drive signals, and the primary-side full-bridge circuit operates in inverter mode. The secondary-side full-bridge circuit operates in rectification mode; In the reverse operation state, the drive signals of the fifth and sixth switches are complementary, and the drive signals of the seventh and eighth switches are complementary; the drive signals of the fifth and eighth switches are the same, and the drive signals of the sixth and seventh switches are the same; the first, second, third, and fourth switches have no drive signals, the primary-side full-bridge circuit operates in rectification mode, and the secondary-side full-bridge circuit operates in inverter mode.

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