LLC resonant converter with variable resonant frequency

Abstract

A resonant converter includes a high-side switch and a low-side switch both coupled to a common node and driven by complementary input signals. The common node drives a coupled inductor connected in parallel with a variable impedance. The coupling inductor may be coupled in series with a capacitor and a transformer. The variable impedance may be adjusted to modify a resonant frequency of the resonant converter.

Description

[0001] priority

[0002] This application claims priority to commonly owned U.S. Patent Application No. 63 / 437,191 filed on January 5, 2023, the entire contents of which are hereby incorporated by reference for all purposes. Technical Field

[0003] The present disclosure relates to resonant converters, and more particularly to the control of LLC resonant converters. Background Art

[0004] The resonant converter may convert an input signal into a DC voltage. The resonant converter may include: a switch in a half-bridge configuration or a full-bridge configuration; and a resonant circuit. The resonant circuit may be used to control the resonant frequency in the resonant converter. The output of the resonant circuit may be input to a first winding of a transformer, and a load may be coupled across a second winding of the transformer.

[0005] As one of the various examples, the resonant circuit may include a tank circuit connected in series with a load. When used in a resonant converter, the resonant circuit may act as a voltage divider between the impedance of the resonant circuit and the impedance of the load. Under light load conditions, the impedance of the load is very large compared to the impedance of the tank circuit, and thus it becomes difficult to adjust the output because this requires the frequency to approach infinity as the load approaches zero. Even at nominal load, a wide frequency variation is required to adjust the output.

[0006] As one example among various examples, the resonant circuit may include a tank circuit coupled in parallel with the load. When used in a resonant converter, the resonant circuit may shunt current or voltage from the load through the parallel tank circuit. The parallel resonator requires a large amount of circulating current. This makes it difficult to apply the parallel resonant topology in applications with high power density or large load variations.

[0007] The LLC resonant converter includes a resonant circuit or tank circuit consisting of two inductors and a capacitor. The first inductor may be a resonant inductor, and the second inductor may be one winding of a transformer. The LLC resonant circuit resonates at a specific frequency called the resonant frequency. An LLC resonant converter including an LLC tank circuit may achieve higher switching frequencies and lower switching losses than a configuration with fewer components.

[0008] The LLC resonant converter can adjust the output across output load changes with relatively small changes in switching frequency while maintaining excellent efficiency. It can also achieve zero voltage switching (ZVS) over the entire operating range.

[0009] Due to the fixed resonant frequency of the resonant circuit, an LLC resonant converter may have a limited input voltage range. There is a need for an LLC resonant converter with an adjustable resonant circuit. Summary of the invention

[0010] According to one aspect, an LLC resonant converter with adjustable impedance can achieve an adjustable resonant frequency and can achieve voltage regulation across a wide range of input voltages.

[0011] According to one aspect, a resonant converter is provided, comprising: a first power switch having a first node coupled to a first phase of a complementary input signal and a second node coupled to a common node; a second power switch having a first node coupled to a second phase of the complementary input signal and a second node coupled to the common node, wherein the common node is coupled to a resonant circuit, the resonant circuit comprising: a resonant inductor having a first coupled inductor winding and a second coupled inductor winding, the first coupled inductor winding being coupled between the common node and a first plate of a capacitor, and the second coupled inductor winding being coupled in parallel with a variable impedance circuit, the variable impedance circuit adjusting a resonant frequency of the resonant circuit; and a transformer having a first transformer winding and a second transformer winding, the first transformer winding being coupled between the second plate of the capacitor and a loop, and the second transformer winding being coupled to a load.

[0012] According to one aspect, a method is provided, the method comprising: driving a first node of a first power switch and a first node of a second power switch using complementary periodic signals, wherein the second node of the first power switch and the second node of the second power switch are coupled to a common node; coupling a resonant circuit to the common node; and adjusting a resonant frequency of the resonant circuit by changing an impedance of a variable impedance circuit. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings illustrate example apparatus and methods for controlling an LLC resonant converter.

[0014] Figure 1 An LLC resonant converter according to various examples is shown.

[0015] Figure 2 The LLC resonant circuit gain response in a first configuration is shown.

[0016] Figure 3 The LLC resonant circuit gain response in a first configuration and a second configuration is shown.

[0017] Figure 4 A method for controlling the resonant frequency of a resonant converter is shown. DETAILED DESCRIPTION

[0018] Figure 1 An example of various examples of LLC resonant converter 100 is shown. Signal source 110 can generate an input signal. Signal source 110 is shown as a sinusoidal source, but this is not intended to be limiting. Signal source 110 can generate a square wave input signal, a pulse width modulated input signal, a triangle wave input signal, or any other periodic input signal. The output of signal source 110 can be input to phase shift circuit 122. Phase shift circuit 122 can shift the phase of the output of signal source 110. In one example of various examples, phase shift circuit 122 can shift the phase of the output of signal source 110 by 180 degrees.

[0019] The output of the signal source 110 may provide an input to the gate of the high-side power switch 120. The output of the phase shift circuit 122 may provide an input to the gate of the low-side power switch 121. In this manner, the high-side power switch 120 and the low-side power switch 121 may be driven with complementary input signals. The high-voltage power switch 120 may be driven with a first phase of the complementary input signal 112, and the low-voltage power switch 121 may be driven with a second phase of the complementary input signal 113. The complementary input signals may be square wave input signals, pulse width modulated input signals, triangle wave input signals, or any other periodic input signals. Figure 1 In the example shown in , the phase shift circuit 122 is shown as a discrete component, but in other examples, the complementary inputs to the high-side power switch 120 and the low-side power switch 121 can be provided directly by the signal source 120 with appropriate phase shifts, and thus the phase shift circuit 122 may not be required, or may be considered to be incorporated into the signal source 110. The high-side power switch 120 may be a metal oxide field effect transistor (MOSFET), or a bipolar transistor or another type of transistor. The low-side power switch 121 may be a metal oxide field effect transistor (MOSFET), or a bipolar transistor or another type of transistor. The high-side power switch 120 may be coupled to a high-side power supply 190. The low-side power switch 121 may be coupled to a loop, including but not limited to a ground node 160. The high-side power switch 120 and the low-side power switch 121 may be coupled to a common node 125. The high-side power switch 120 and the low-side power switch 121 are shown as n-channel transistors, but this is not intended to be limiting. The high-side power switch 120 may be a p-channel transistor. The low-side power switch 121 may be a p-channel transistor. The high-side power switch 120 and the low-side power switch 121 are shown as field effect devices, but this is not intended to be limiting. The high-side power switch 120 may be a bipolar device. The low-side power switch 121 may be a bipolar device.

[0020] The high-side power switch 120 and the low-side power switch 121 may be coupled to a resonant inductor 130. The resonant inductor 130 may be the first inductor in the LLC resonant converter. The resonant inductor 130 may be coupled to a variable impedance circuit 135 in parallel.

[0021] In operation, the impedance value of the variable impedance circuit 135 can be modified to change the resonant frequency of the resonant converter 100. Figure 1 130 is shown as a variable resistor, but this is not intended to be limiting. The variable impedance circuit 135 can be a variable resistor. The variable impedance circuit 135 can be a variable amplitude direct current (DC) current source that can saturate the core of the resonant inductor 130 and change the impedance of the resonant inductor 130. The variable impedance circuit 135 can be a variable amplitude alternating current (AC) current source. The variable impedance circuit 135 can be a switch in series with a resistor, including but not limited to a MOSFET switch.

[0022] The resonant inductor 130 may be coupled to a first plate of the resonant capacitor 140. The transformer 150 may be coupled to a second plate of the resonant capacitor 140. The first winding of the transformer 150 may be a second inductor in the LLC resonant converter. The first winding of the transformer 150 may be coupled between the second plate of the resonant capacitor 140 and a loop including, but not limited to, a ground node 160. The second winding of the transformer 150 may be coupled to a load 170. The signal transmitted to the load may also be referred to as an output of the LLC resonant converter 100.

[0023] exist Figure 1 In one example of the various examples, changing the impedance of the resonant inductor 130 can change the resonant frequency of the resonant converter 100. In one example of the various examples, the variable impedance circuit 135 can be a variable resistor. Adjusting the value of the variable resistor can change the resonant point of the resonant converter 100. The increase in the variable resistor can increase the inductance. In one example of the various examples, the variable impedance circuit 135 can be a variable amplitude DC current source. Adjusting the amplitude of the variable amplitude DC current source can change the resonant point of the converter because the amplitude of the variable amplitude DC current source can magnetize the inductor core of the resonant inductor 130. In one example of the various examples, the variable impedance circuit 135 can be a variable amplitude AC current source. Adjusting the amplitude of the variable amplitude AC current source can magnetize the core of the resonant inductor 130. The magnetization of the core can indirectly reduce the inductance of the resonant inductor 130.

[0024] Figure 2One example of a variety of examples of multiple frequency response graphs 200 for an LLC resonant converter in a first configuration is shown. In the first configuration, the inductance value of the resonant inductor can be selected to achieve a specific output response. The y-axis can represent the gain from the input to the output of the resonant circuit, shown by the label Vout / V. Frequency response graphs for multiple load values ​​are shown on the graph. Each trace represents a different load value. An output at a specific voltage can only be achieved by operating the resonant circuit below its resonant frequency. The resonant frequency is located at the peak of the trace, at Figure 2 210. When the high-side power switch 120 and the low-side power switch 121 are switched when there is zero volt voltage across the respective switches, the zero voltage switching (ZVS) mode occurs. When the high-side power switch 120 and the low-side power switch 121 are switched when zero current flows through the respective switches, the zero current switching (ZCS) mode occurs. When operating below the resonant frequency, the high-side power switch and the low-side power switch may not operate in the ZVS mode and may introduce high current. This may lead to catastrophic failure of the converter.

[0025] Figure 3 1 shows one example of various examples of multiple frequency response graphs 300 for an LLC resonant converter in a first configuration and a second configuration. The group of traces (indicated by reference numeral 320) that form a peak at a frequency closest to 100 kHz shows that Figure 2 1. The resonant circuit in the first configuration shown. The group of traces peaking at frequencies closest to 70 kHz (indicated by reference numeral 310) shows the resonant circuit in the second configuration. In the second configuration, the inductance value of the resonant inductor may be selected to achieve a particular output response. The y-axis may represent the gain from input to output of the resonant circuit, indicated by reference numeral Vout / V. Frequency response plots for multiple load values ​​are shown on the graph. Each trace represents a different load value. Figure 3 In the example of FIG. 1 , the impedance of the variable impedance circuit 135 can be modified to change the resonant circuit from a first configuration to a second configuration to produce a ratio Figure 2 The inductance of the resonant inductor can be increased by increasing the impedance of the variable impedance circuit 135. The inductance of the resonant inductor can be decreased by decreasing the impedance of the variable impedance circuit 135. By increasing the inductance of the resonant inductor 130, the resonant frequency can be decreased and the circuit can continue to operate above the resonant frequency in the ZVS mode.

[0026] Figure 4 One example of various examples of methods for controlling the resonant frequency of a resonant converter is shown. The resonant converter may be as previously described with reference to Figure 1 An LLC resonant converter is described.

[0027] At operation 410, the first power switch and the second power switch may be driven with a complementary input signal. The complementary input signal may be a square wave input signal, a pulse width modulated input signal, a triangle wave input signal, or any other periodic input signal. The first power switch and the second power switch may be coupled to a common node.

[0028] At operation 420, a resonant circuit may be coupled to a common node of the first power switch and the second power switch. The resonant circuit may include a resonant inductor connected in parallel with a variable impedance circuit. In one of the various examples, the variable impedance circuit may be a variable resistor. In one of the various examples, the variable impedance circuit may be a variable amplitude direct current source. In one of the various examples, the variable impedance circuit may be a variable amplitude alternating current source. Adjusting the amplitude of the variable amplitude alternating current source may magnetize the core of the resonant inductor. The magnetization of the core may indirectly reduce the inductance of the resonant inductor.

[0029] At operation 430, the resonant frequency of the resonant circuit may be adjusted by changing the impedance of the variable impedance circuit. Adjusting the value of the variable impedance may change the resonant point of the resonant converter. Adjusting the amplitude of the variable amplitude DC current source may change the resonant point of the converter because the amplitude of the variable amplitude DC current source may magnetize the inductor core of the resonant inductor. Adjusting the amplitude of the variable amplitude AC current source may magnetize the core of the resonant inductor. The magnetization of the core may indirectly reduce the inductance of the resonant inductor.

Claims

1. A resonant converter, comprising: a first power switch having a first node coupled to a first phase of a complementary input signal and a second node coupled to a common node; a second power switch having a first node coupled to a second phase of the complementary input signal and a second node coupled to the common node; wherein the common node is coupled to a resonant circuit, the resonant circuit comprising: a resonant inductor having a first coupled inductor winding and a second coupled inductor winding, the first coupled inductor winding being coupled between the common node and the first plate of the capacitor, and the second coupled inductor winding being coupled in parallel with a variable impedance circuit, the variable impedance circuit being used to adjust a resonant frequency of the resonant circuit, and A transformer having a first transformer winding coupled between the second plate of the capacitor and the return and a second transformer winding coupled to a load. 2 . The resonant converter of claim 1 , wherein the first power switch comprises a power metal oxide semiconductor field effect device (MOSFET) and the second power switch comprises a power metal oxide semiconductor field effect device (MOSFET).

3. The resonant converter of any one of claims 1 to 2, wherein the first phase and the second phase of the complementary input signal comprise periodic signals.

4. The resonant converter of any one of claims 1 to 2, wherein the first phase and the second phase of the complementary input signal comprise pulse width modulated signals.

5. The resonant converter according to any one of claims 1 to 4, wherein the variable impedance circuit comprises a variable resistor. 6 . The resonant converter of claim 5 , the variable impedance circuit comprising at least one switch coupled to the variable resistor.

7. A resonant converter according to any one of claims 1 to 6, wherein the variable impedance circuit comprises a variable amplitude DC source.

8. A resonant converter according to any one of claims 1 to 6, wherein the variable impedance circuit comprises a variable amplitude AC source.

9. A method comprising: driving a first node of a first power switch and a first node of a second power switch with a complementary periodic signal, wherein a second node of the first power switch and a second node of the second power switch are coupled to a common node; coupling a resonant circuit to the common node; as well as The resonant frequency of the resonant circuit is adjusted by changing the impedance of the variable impedance circuit.

10. The method of claim 9, the first power switch comprising a power metal oxide semiconductor field effect device (MOSFET), and the second power switch comprising a power metal oxide semiconductor field effect device (MOSFET).

11. The method according to any one of claims 9 to 10, wherein the input signal comprises a pulse width modulated signal.

12. The method of any one of claims 9 to 11, wherein the variable impedance circuit comprises a variable resistor.

13. A method according to any one of claims 9 to 12, wherein the variable impedance circuit comprises a variable amplitude DC source.

14. A method according to any one of claims 9 to 13, wherein the variable impedance circuit comprises a variable amplitude AC source.

15. The method of any one of claims 9 to 14, wherein the resonant circuit comprises a coupled inductor, a capacitor and a transformer.

16. The method of claim 13, wherein adjusting the resonant frequency by varying the impedance of a variable impedance circuit comprises varying the impedance of the variable impedance circuit based at least on a current in the variable amplitude DC source.

17. The method of claim 14, wherein adjusting the resonant frequency by varying the impedance of a variable impedance circuit comprises varying the impedance of the variable impedance circuit based at least on a current in the variable amplitude AC source.

18. The method of claim 15, the coupled inductor comprising a first coupled inductor winding coupled between the common node and the first plate of the capacitor and a second coupled inductor winding coupled in parallel with the variable impedance circuit.

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