TWI680636B - Power conversion circuit and control method of power conversion circuit - Google Patents

Abstract

A power conversion circuit includes a switching circuit, a resonance circuit, a transformer, a rectifier circuit, and a controller. The resonance circuit is electrically connected to the switching circuit. The transformer includes a primary winding and a secondary winding. The primary winding is electrically connected to the resonance circuit. The rectifier circuit is electrically connected to the secondary winding of the transformer. The controller is electrically coupled to the switching circuit and the rectifying circuit, and is used to selectively output one of the frequency modulation signal and the pulse width modulation signal as the second control signal according to the working frequency of the first control signal to control the switching. Circuit.

Description

Power conversion circuit and method for controlling power conversion circuit

The present disclosure relates to a circuit and a control method, and more particularly, to a power conversion circuit and a control method of a power conversion circuit.

Recently, LLC resonant converters are widely used in various applications because they are suitable for a wide range of input voltages and high power outputs.

When the load is light, the DC gain curve at high frequencies is distorted due to the parasitic capacitance in the LLC resonant conversion circuit, which makes the output voltage of the LLC resonant converter unstable and the conversion efficiency reduced.

One aspect of the present disclosure relates to a power conversion circuit including a switching circuit, a resonance circuit, a transformer, a rectifier circuit, and a controller. The resonance circuit is electrically connected to the switching circuit. The transformer includes a primary winding and a secondary winding. The primary winding is electrically connected to the resonance circuit. The rectifier circuit is electrically connected to the secondary winding of the transformer. The controller is electrically coupled to the switching circuit and the rectifying circuit, and is used to selectively output one of the frequency modulation signal and the pulse width modulation signal as the second control signal according to the working frequency of the first control signal to control the switching. Circuit.

Another aspect of the present disclosure relates to a method for controlling a power conversion circuit, including: a controller selectively outputting one of a frequency modulation signal and a pulse width modulation signal as a working frequency of a first control signal as A second control signal; the switching circuit converts the DC input voltage into a switching signal according to the second control signal.

The following is a detailed description with examples and the accompanying drawings to better understand the aspect of the case, but the examples provided are not intended to limit the scope covered by this disclosure, and the description of structural operations is not intended to limit The order of execution, any structure with recombination of components, and a device with equal efficacy are the scope covered by this disclosure. In addition, according to industry standards and common practices, the drawings are only for the purpose of assisting the description, and are not drawn according to the original dimensions. In fact, the dimensions of various features can be arbitrarily increased or decreased for ease of explanation. In the following description, the same elements will be described with the same symbols to facilitate understanding.

The terms used throughout the specification and the scope of patent applications, unless otherwise specified, usually have the ordinary meaning of each term used in this field, in the content disclosed here, and in special content. Certain terms used to describe this disclosure are discussed below or elsewhere in this specification to provide additional guidance to those skilled in the art on the description of this disclosure.

In addition, the terms "including", "including", "having", "containing" and the like used in this article are all open-ended terms, meaning "including but not limited to." In addition, "and / or" as used herein includes any one or more of the related listed items and all combinations thereof.

In this article, when a component is called "connected" or "coupled", it can mean "electrically connected" or "electrically coupled". "Connected" or "coupled" can also be used to indicate that two or more components operate together or interact with each other. In addition, although the terms "first", "second", ... are used herein to describe different elements, this term is only used to distinguish elements or operations described in the same technical term. Unless the context clearly indicates otherwise, the term is not specifically referring to or implying order or order, nor is it intended to limit the invention.

Please refer to Figure 1. FIG. 1 is a schematic diagram of a power conversion circuit 100 according to some embodiments. As shown in FIG. 1, in some embodiments, the power conversion circuit 100 includes a switching circuit 110, a resonance circuit 120, a transformer 130, a rectifier circuit 140, an output capacitor Co, and a controller 150. The transformer 130 includes a primary winding Np and a secondary circuit. The secondary windings Ns1 and Ns2. In other embodiments, the power conversion circuit 100 further includes an isolated driver 160.

Structurally, the input terminal of the switching circuit 110 is electrically coupled to a DC voltage source for receiving a DC input voltage Vin. The output terminal of the switching circuit 110 is electrically coupled to the input terminal of the resonance circuit 120 for outputting the switching signal Sig1 converted from the DC input voltage Vin by the switching circuit 110 to the resonance circuit 120. The output terminal of the resonance circuit 120 is electrically coupled to the primary side of the transformer 130. The input terminal of the rectifier circuit 140 is electrically coupled to the secondary side of the transformer 130. The output terminal of the rectifier circuit 140 is electrically coupled to the output capacitor Co to provide a DC output voltage Vo to the subsequent circuit. The input terminal of the controller 150 is electrically coupled to the output capacitor Co to detect the output voltage Vo and the output current Io. The output terminal of the controller 150 is electrically coupled to the isolated driver 160 to output a second control signal CS2 to the isolated driver 160. The output terminal of the isolated driver 160 is electrically coupled to the switching circuit 110 to output the driving signals DS1 and DS2 to the switching circuit 110 according to the second control signal CS2. In this way, the controller 150 can control the LLC resonance conversion circuit structure formed by the switching circuit 110, the resonance circuit 120, the transformer 130, and the rectifier circuit 140 through the isolation driver 160 through the second control signal CS2.

Specifically, in some embodiments, the controller 150 may be located on the primary side, and in other embodiments, the controller 150 may be located on the secondary side. For example, the controller 150 may include various processing circuits, digital signal processors (DSPs), complex programmable logic devices (Complex Programmable Logic Devices, CPLDs), and field-programmable gate arrays (Field-programmable gates). array, FPGA).

In some embodiments, the primary side of the transformer 130 includes a set of primary windings Np. The secondary side of the transformer 130 includes two sets of secondary windings Ns1 and Ns2. The starting end of the secondary winding Ns2 is electrically coupled to the ending end of the secondary winding Ns1 and is electrically coupled to the negative terminal of the output capacitor Co together. . For example, in some embodiments, the transformer 130 may be a transformer with a center tap on the secondary side to divide the secondary side of the transformer 130 into a secondary winding Ns1 and a secondary winding Ns2 that are coupled to each other. In some embodiments, the transformer 130 can also be a transformer with only one set of secondary windings on the secondary side, and is equipped with a full-bridge rectifier circuit. The secondary side and its rectifier circuit can be completed according to any form known to those skilled in the art.

In some embodiments, the switching circuit 110 in the power conversion circuit 100 may adopt a half-bridge architecture to implement a half-bridge resonance conversion circuit, but this case is not limited thereto. As shown in FIG. 1, in some embodiments, the switching circuit 110 includes a switch S1 and a switch S2. Structurally, the first terminal of the switch S1 is electrically coupled to the positive terminal of the DC input voltage Vin, and the second terminal of the switch S1 is electrically coupled to the resonance circuit 120. The first terminal of the switch S2 is electrically coupled to the second terminal of the switch S1, and the second terminal of the switch S2 is electrically coupled to the negative terminal of the DC input voltage Vin. The control terminals of the switches S1 and S2 are respectively used to receive the driving signals DS1 and DS2, so that the switches S1 and S2 are selectively turned on or off according to the driving signals DS1 and DS2.

Thereby, the switching circuit 110 can selectively turn on one of the switches S1 and S2 to output a switching signal Sig1 with a high level (eg, a DC input voltage Vin) when the switch S1 is turned on, and switch the switch S2. When turned on, a switching signal Sig1 with a low level (such as zero potential) is output. In other words, the switching frequency and duty cycle of the switching signal Sig1 will be equal to the switching frequency and duty cycle of the driving signals DS1 and DS2. For example, in a complete switching cycle, the driving signals DS1 and DS2 can be Pulse Width Modulation (PWM) signals. The switches S1 and S2 can be turned on for half a cycle respectively to output a duty cycle of 50%. Switching signal Sig1. In addition, in other embodiments, the switching circuit 110 may also adopt a full-bridge architecture to implement a full-bridge resonant conversion circuit. For example, the switching circuit 110 may also include four groups of two pairs of switches, which are selectively turned on or off by receiving corresponding driving signals.

In this way, in one complete cycle, the switching circuit 110 can turn on one pair of switches according to the driving signal in the first half cycle, turn off the other pair of switches to output the switching signal Sig1 with a positive level, and according to the driving signal in the second half cycle The switch is turned on and off to output a switching signal Sig1 having a negative level.

In some embodiments, the resonance circuit 120 includes a resonance capacitor unit C1, a resonance inductance unit L1, and an excitation inductance unit L2, but this case is not limited thereto. Structurally, the resonant capacitor unit C1, the resonant inductor unit L1, and the primary winding Np of the transformer 130 are connected in series with each other. The excitation inductance unit L2 and the primary winding Np of the transformer 130 are connected in parallel with each other. For example, as shown in FIG. 1, the first terminal of the resonance capacitor unit C1 is electrically connected to the first terminal of the resonance circuit 120, and is electrically connected to the second terminal of the switch S1 and the first terminal of the switch S2. The second terminal of the resonance capacitor unit C1 is electrically connected to the first terminal of the resonance inductor unit L1. The second end of the resonant inductance unit L1 is electrically connected to the first end of the excitation inductance unit L2. The second terminal of the excitation inductance unit L2 is electrically connected to the second terminal of the resonance circuit 120 and is electrically connected to the negative terminal of the DC input voltage Vin, but the disclosure is not limited thereto.

In some embodiments, the resonance inductance unit L1 and the excitation inductance unit L2 may include the leakage inductance and the magnetization inductance of the transformer 130, respectively. In other embodiments, the resonant capacitor unit C1, the resonant inductor unit L1, and the excitation inductor unit L2 may be electrically connected in different ways to implement the resonant circuit 120. In addition, in other embodiments, the resonant circuit 120 can also implement an LC resonant circuit, an LCC resonant circuit, and an LLCC resonant circuit by using one or more sets of inductive units and capacitive units. Therefore, the resonant circuit 120 shown in the drawings of this case This is only one of the possible implementations of the case, and is not intended to limit the case. In other words, those with ordinary knowledge in the technical field should understand that the resonant circuit 120 in each embodiment of the present invention can be any combination of one or more sets of inductive units and one or more sets of capacitive units, and is electrically connected in different ways such as serial or parallel Connect for resonance.

As shown in FIG. 1, in some embodiments, the rectifier circuit 140 is electrically connected to the secondary winding Ns1 and the secondary winding Ns2 of the transformer 130, and is configured to sense the primary winding Np to the secondary winding Ns1 and the secondary winding Ns2. The secondary current Is outputted by the signal changes is rectified to provide an output voltage Vo across the output capacitor Co.

In some embodiments, the rectifier circuit 140 includes a diode D1 and a diode D2. Structurally, the anode end of the diode D1 is electrically coupled to the starting end of the secondary winding Ns1. The cathode terminal of the diode D1 is electrically coupled to the positive terminal of the output capacitor Co. The anode terminal of the diode D2 is electrically coupled to the end of the secondary winding Ns2. The cathode terminal of the diode D2 is electrically coupled to the cathode terminal of the diode D1. Thus, the rectified circuit 140 and the output capacitor Co rectify and filter the electrical signals induced by the secondary windings Ns1 and Ns2 to provide a DC output voltage Vo.

In this way, through the operation of the above circuit, the power conversion circuit 100 can convert the DC input voltage Vin into a DC output voltage Vo with an appropriate voltage level and provide it to the subsequent circuit.

Please refer to Figure 2. FIG. 2 is a schematic diagram illustrating an operation mode switching according to some embodiments of the present disclosure. As shown in FIG. 2, the controller 150 selectively outputs one of the frequency modulation signal and the pulse width modulation signal as the second control signal CS2 according to the operating frequency F of the first control signal CS1 to control the switching circuit. 110. Specifically, when the operating frequency F is less than the set frequency Fth, the controller 150 outputs a frequency modulation signal as the second control signal CS2 to control the switching circuit 110. In other words, the controller 150 adjusts the switching frequency of the second control signal CS2. To control the switching circuit 110. When the operating frequency F is greater than the set frequency Fth, the controller 150 outputs a pulse width modulation signal as the second control signal to control the switching circuit 110. In other words, the controller 150 adjusts the duty cycle of the second control signal CS2 to control the switching circuit. 110.

In some embodiments, the set frequency Fth is the operating frequency F corresponding to the lowest point in the DC gain curve. For example, as shown in FIG. 2, the lowest point of the DC gain curve is at a position where the operating frequency F is about 140 kHz, so the set frequency Fth is about 140 kHz. When the operating frequency F is less than 140 kHz, the controller 150 outputs a frequency modulation signal as the second control signal CS2. When the operating frequency F is greater than 140 kHz, the controller 150 outputs a pulse width modulation signal as the second control signal CS2. It should be noted that the above-mentioned value of the set frequency Fth is only an example for convenience of explanation, and is not intended to limit the case. Those with ordinary knowledge in the field can set it according to actual needs.

In this way, when the power converter is lightly loaded, the DC gain curve at high frequencies is distorted due to the parasitic capacitance in the LLC resonant conversion circuit, and the output voltage of the LLC resonant conversion circuit is unstable and converted. Reduced efficiency.

Please refer to Figure 3A. FIG. 3A is a functional block diagram of a controller 150A according to some embodiments of the present disclosure. In some embodiments, the controller 150A is configured to detect the output voltage Vo of the rectifier circuit 140 and obtain a frequency command f * according to the output voltage Vo and the reference voltage Vref, so as to generate a first control signal CS1 according to the frequency command f *. Specifically, as shown in FIG. 3A, the controller 150A calculates the difference between the output voltage Vo and the reference voltage Vref, and obtains the frequency command f * through the voltage proportional gain Gv (z), and then the frequency command f * serves as the first control signal CS1.

Then, the first control signal CS1 is adjusted by setting the upper limit value and the lower limit value to obtain the second control signal CS2, and the driving signals DS1 and DS2 are generated through the isolated driver 160 according to the second control signal CS2. In some embodiments, the highest upper limit value is about 250 kHz, and the lowest lower limit value is about 36 kHz. It is worth noting that the above values are only examples for convenience of explanation, and are not intended to limit the case. Those with ordinary knowledge in the field can set it according to actual needs.

Next, please refer to Figure 3B. FIG. 3B is a functional block diagram of a controller 150B according to other embodiments of the present disclosure. In the embodiment shown in FIG. 3B, components similar to those in the embodiment shown in FIG. 3A are represented by the same component symbols, and their operations have been described in the previous paragraphs, and will not be repeated here. Compared with the embodiment shown in FIG. 3A, in this embodiment, the controller 150B is further configured to detect the output current Io of the rectifier circuit 140, and adjust the frequency command f * at a frequency compensation value f 'according to the output current Io. Specifically, as shown in FIG. 3B, after the output current Io is obtained by the controller 150B, the analog digital sampling (ADC sampling) is performed, and the frequency compensation value f 'is obtained through the current proportional gain Gi (z). Next, the frequency command f * is subtracted from the frequency compensation value f 'as the first control signal CS1. The analog to digital signal sampling frequency can be about 200kHz.

In this way, by increasing the sampling frequency and increasing the current loop feedback signal, it can improve the situation that the output voltage changes too much as the output load changes, reduce voltage overshoot, and shorten the LLC resonance. Settling time required for switching circuits.

For detailed calculation of the current loop, please refer to Figure 4. FIG. 4 is a detailed functional block diagram of a controller 150 according to other embodiments of the present disclosure. As shown in FIG. 4, the controller 150 is further configured to determine the load to adjust the current gain value according to the change in output current ΔI, and adjust the frequency compensation value f ′ according to the current gain value, where the change in output current ΔI = Current at the moment of sampling)-(Current at the moment of sampling).

Specifically, when the controller 150 determines that the load is drawn (that is, ΔI> 0), the frequency compensation value f ′ is adjusted according to the first current gain value. When the controller 150 determines that the load is released (that is, ΔI <0) ), Adjust the frequency compensation value f ′ according to the second current gain value, where the second current gain value is greater than the first current gain value.

For example, when the output current Io is large (that is, the change in the output current ΔI is greater than zero), the controller 150 adjusts and reduces the frequency compensation value f ′ according to the smaller first current gain value, and uses the frequency compensation value f ′ Reduce frequency command f *. When the output current Io decreases (that is, the change in the output current ΔI is less than zero), the controller 150 adjusts and increases the frequency compensation value f ′ according to the larger second current gain value, and increases the frequency by the frequency compensation value f ′. The command f *. When the output current Io is not changed (that is, the change of the output current ΔI is equal to zero), the controller 150 sets the frequency compensation value f 'to zero, that is, the frequency command f * is not adjusted.

In other words, in a mode where the light load changes instantaneously to the heavy load (that is, when the load is increased), the current gain value in the current loop is reduced to avoid that during heavy load, the current gain value is too large and the operating frequency F is too high, resulting in The voltage collapses. Dynamically adjust the current gain value according to the change of the output current Io. In this way, the frequency compensation value f 'can be appropriately adjusted to improve efficiency and prevent the circuit from supplying power within the specification to the load, causing a crash (for example: the output voltage is too low , Trigger to under voltage protection, etc.).

In addition, when the output current Io decreases, the controller 150 is further configured to determine whether the change Δf 'of the frequency compensation value in the current loop is greater than the change threshold value fth. When the change Δf 'of the frequency compensation value is less than or equal to the change threshold value fth, the frequency compensation value f' is determined based on a characteristic curve based on the operating frequency F. When the change Δf 'of the frequency compensation value is greater than the change threshold value fth, the frequency compensation value f' is set to zero.

For example, when the output current Io decreases (that is, the load becomes lighter), the controller 150 adjusts the frequency compensation value f 'according to a larger second current gain value to increase the frequency command f *. If the frequency compensation value f' When the increased change width is less than or equal to the change threshold value fth, the controller 150 increases the frequency compensation value f ′ based on the characteristic curve shown in FIG. 5 in a table lookup manner according to the operating frequency F to avoid voltage overshoot. .

For another example, when the output current Io decreases (that is, the load becomes lighter), the controller 150 adjusts the frequency compensation value f 'according to a larger second current gain value to increase the frequency command f *. If the frequency compensation value f When the increased variation range is greater than the variation threshold fth, the controller 150 sets the frequency compensation value f 'to zero. In other words, when the current gain value is emphasized to increase the frequency compensation value f ', by judging whether the change Δf' of the frequency compensation value exceeds the change threshold value fth, it is avoided that the operating frequency F is easily increased but difficult to decrease, causing voltage collapse. In this way, the magnitude of the change in the frequency compensation value f 'can be adjusted appropriately to avoid crashes.

Please refer to Figure 6. FIG. 6 is a flowchart illustrating a power conversion circuit control method 600 according to some embodiments of the present disclosure. For the sake of convenience and clear description, the following power conversion circuit control method 600 is described in conjunction with the embodiments shown in FIG. 1 to FIG. 6, but is not limited thereto. Any person skilled in the art will not depart from this case. Within the spirit and scope, you can make various changes and retouching. As shown in FIG. 6, the power conversion circuit control method 600 includes operations S620, S641, S642, S660, and S680.

First, in operation S620, the controller 150 determines whether the operating frequency F of the first control signal CS1 is less than a set frequency Fth.

When the operating frequency F is less than the set frequency Fth, it proceeds to operation S641. In operation S641, the controller 150 outputs a frequency modulation signal as the second control signal CS2, so that the driving signals DS1 and DS2 operate in the frequency modulation mode. In other words, the controller 150 adjusts the switching frequency of the second control signal CS2 according to the operating frequency F of the first control signal CS1.

On the other hand, when the operating frequency F is greater than the set frequency Fth, it proceeds to operation S642. In operation S642, the controller 150 outputs a pulse width modulation signal as the second control signal CS2, so that the driving signals DS1 and DS2 are operated in a pulse width modulation mode. In other words, the controller 150 adjusts the duty cycle of the second control signal CS2 according to the operating frequency F of the first control signal CS1.

Then, in operation S660, the controller 150 outputs the second control signal CS2 to the switching circuit 110.

Finally, in operation S680, the switching circuit 110 converts the DC input voltage Vin into the switching signal Sig1 according to the second control signal CS2.

Please refer to Figure 7. FIG. 7 is a flowchart illustrating a power conversion circuit control method 700 according to other embodiments of the present disclosure. For the sake of convenience and clear description, the following method 700 for power conversion circuit control is described in conjunction with the embodiments shown in FIG. 1 to FIG. 7, but is not limited thereto. Any person skilled in the art will not depart from this case. Within the spirit and scope, you can make various changes and retouching. As shown in FIG. 7, the power conversion circuit control method 700 includes operations S710, S720, S731, S732, S733, S740, S751, and S752.

First, in operation S710, the output current Io of the rectifier circuit 140 is detected by the controller 150.

Next, in operation S720, the controller 150 determines the change in the output current Io and determines the load to adjust the current gain value.

When the change of the output current Io is greater than zero (that is, the load is drawn), operation S731 is performed. In operation S731, the controller 150 adjusts the frequency compensation value f 'according to the first current gain value, and decreases the frequency command f * by the frequency compensation value f'.

On the other hand, when the change in the output current Io is less than zero (ie, the load is unloaded), operation S732 is performed. In operation S732, the controller 150 adjusts the frequency compensation value f 'according to the second current gain value, and raises the frequency command f * by the frequency compensation value f'.

In addition, when the change in the output current Io is equal to zero (that is, there is no change in the load), operation S733 is performed. In operation S733, the frequency compensation value f 'is set to zero by the controller 150, that is, the frequency command f * is not adjusted.

In some embodiments, when the change in the output current Io is less than zero (ie, the load is unloaded), operation S740 is further performed. In operation S740, it is determined by the controller 150 whether the change Δf 'of the frequency compensation value is greater than the change threshold value fth.

When the change Δf 'of the frequency compensation value is larger than the change threshold value fth, operation S751 is performed. In operation S751, the frequency compensation value f 'is set to zero by the controller 150, that is, the frequency command f * is not adjusted.

On the other hand, when the change Δf 'of the frequency compensation value is less than or equal to the change threshold value fth, operation S752 is performed. In operation S752, the frequency compensation value f 'is determined by the controller 150 based on the characteristic frequency based on the operating frequency F.

Although the disclosed methods are shown and described herein as a series of steps or events, it should be understood that the order of the illustrated steps or events should not be construed as limiting. For example, some steps may occur in a different order and / or concurrently with steps or events other than the steps or events shown and / or described herein. In addition, not all steps shown herein are necessary to implement one or more aspects or embodiments described herein. In addition, one or more steps herein may also be performed in one or more separate steps and / or stages.

It should be noted that, in the case of no conflict, the features and circuits in the various drawings, embodiments, and embodiments of the present disclosure may be combined with each other. The circuits shown in the drawings are for example purposes only, and are simplified to make the description concise and easy to understand, and are not intended to limit the case. In addition, each device, unit, and component in each of the above embodiments may be implemented by various types of digital or analog circuits, may also be implemented by different integrated circuit chips, or integrated into a single chip. The foregoing is merely an example, and the present disclosure is not limited thereto.

In summary, the present application can improve the power conversion circuit 100 by applying one of the above embodiments to switch between one of the frequency modulation mode and the pulse width modulation mode based on whether the operating frequency F is greater than the set frequency Fth. Poor efficiency at different loads. In addition, by increasing the current loop feedback signal, the situation where the voltage loop responds slowly can be improved, the occurrence of current and voltage overshoot can be reduced, and the settling time required for the power conversion circuit 100 can be shortened.

Although the present disclosure has been disclosed as above by way of implementation, it is not intended to limit the present disclosure. Persons with ordinary knowledge in the technical field can make various changes and decorations without departing from the spirit and scope of the present disclosure. The scope of protection of the disclosure shall be determined by the scope of the attached patent application.

100: power conversion circuit 110: switching circuit 120: resonance circuit 130: transformer 140: rectifier circuit 150, 150A, 150B: controller 160: isolation driver Vin: DC input voltage S1, S2: switch C1: resonance capacitor unit L1: resonance Inductance unit L2: Excitation inductance unit Np: Primary winding Ns1, Ns2: Secondary winding D1, D2: Diode Co: Output capacitor Vo: Output voltage Io: Output current Sig1: Switching signal CS1, CS2: Control signal DS1, DS2: Driving signal F: Operating frequency Fth: Set frequency Vref: Reference voltage f *: Frequency command f ': Frequency compensation value sample: Sampling Gi (z): Current proportional gain Gv (z): Voltage proportional gain ΔI: Output Current change Δf ': Change in frequency compensation value fth: Change threshold Gdown (z), Gup (z): Current gain 600, 700: Power conversion circuit control method S620, S641, S642, S660, S680, S710, S720, S731, S732, S733, S740, S751, S752: Operation

FIG. 1 is a schematic diagram of a power conversion circuit according to some embodiments of the present disclosure. FIG. 2 is a schematic diagram illustrating an operation mode switching according to some embodiments of the present disclosure. 3A and 3B are functional block diagrams of a controller according to some embodiments of the present disclosure. FIG. 4 is a detailed functional block diagram of a controller according to other embodiments of the present disclosure. FIG. 5 is a schematic diagram illustrating a characteristic curve for adjusting frequency according to other embodiments of the present disclosure. FIG. 6 is a flowchart illustrating a method for controlling a power conversion circuit according to some embodiments of the present disclosure. FIG. 7 is a flowchart illustrating a method for controlling a power conversion circuit according to other embodiments of the present disclosure.

Claims (20)

A power conversion circuit includes: a switching circuit; a resonance circuit electrically connected to the switching circuit; a transformer including: a primary winding electrically connected to the resonance circuit; and a primary winding; Is connected to the secondary winding of the transformer; and a controller is electrically coupled to the switching circuit and the rectifying circuit for selectively selecting a frequency modulation signal and a frequency modulation signal according to an operating frequency of a first control signal. One of the pulse width modulation signals is output as a second control signal to control the switching circuit. When the operating frequency is greater than the set frequency, the controller is used to control a duty cycle of the second control signal. The power conversion circuit according to claim 1, wherein when the operating frequency is less than a set frequency, the controller is used to control a switching frequency of the second control signal. The power conversion circuit according to claim 1, wherein the controller is further configured to detect an output voltage of the rectifier circuit, and obtain a frequency command according to a difference between the output voltage and a reference voltage, so as to follow the frequency command. The first control signal is output. The power conversion circuit according to claim 3, wherein the controller is further configured to detect an output current of the rectifier circuit and adjust the frequency command with a frequency compensation value according to the output current. The power conversion circuit according to claim 4, wherein the controller is further configured to judge a load according to a change in the output current to adjust a current gain value, and adjust the frequency compensation value according to the current gain value. The power conversion circuit according to claim 4, wherein when the controller determines that the load is a load, the frequency compensation value is adjusted according to a first current gain value, and when the controller determines that the load is a load shedding according to A second current gain value adjusts the frequency compensation value, wherein the second current gain value is greater than the first current gain value. The power conversion circuit according to claim 4, wherein when the output current changes greater than zero, the controller reduces the frequency command according to the frequency compensation value. The power conversion circuit according to claim 4, wherein when the change of the output current is less than zero, the controller is further configured to determine whether the change of the frequency compensation value is greater than a change threshold and the change of the frequency compensation value is greater than When changing the threshold, set the frequency compensation value to zero. The power conversion circuit according to claim 4, wherein when the change of the output current is less than zero, the controller is further configured to determine whether the change of the frequency compensation value is greater than a change threshold, and the change of the frequency compensation value is less than or When it is equal to the change threshold, the frequency compensation value is determined based on a characteristic curve according to the operating frequency. The power conversion circuit according to claim 1, further comprising: an isolated driver electrically coupled between the controller and the switching circuit for driving the switching circuit by feedback. A method for controlling a power conversion circuit includes: a controller selectively outputting one of a frequency modulation signal and a pulse width modulation signal as a second control signal according to an operating frequency of a first control signal; A switching circuit converts the DC input voltage into a switching signal according to the second control signal; and when the operating frequency is greater than the set frequency, the controller controls a duty cycle of the second control signal. The method for controlling a power conversion circuit according to claim 11, further comprising: when the operating frequency is less than a set frequency, the controller controls a switching frequency of the second control signal. The method for controlling a power conversion circuit according to claim 11, further comprising: detecting, by the controller, an output voltage of a rectifier circuit; and obtaining, by the controller, a frequency command according to a difference between the output voltage and a reference voltage; And the controller outputs the first control signal according to the frequency command. The method for controlling a power conversion circuit according to claim 13, further comprising: detecting an output current of the rectifier circuit by the controller; and adjusting the frequency command by a frequency compensation value according to the output current by the controller. The method for controlling a power conversion circuit according to claim 14, further comprising: determining, by the controller, a load according to a change in the output current to adjust a current gain value; and adjusting the frequency command by the controller according to the current gain value. The method for controlling a power conversion circuit according to claim 15, wherein determining the load to adjust the current gain value according to a change in the output current includes: when the controller determines that the load is a load, the controller according to a first The current gain value adjusts the frequency compensation value; and when the controller determines that the load is a load shedding, the controller adjusts the frequency compensation value according to a second current gain value, wherein the second current gain value is greater than the first Current gain value. The method for controlling a power conversion circuit according to claim 15, wherein determining a load to adjust the current gain value according to a change in the output current includes: when the output current change is greater than zero, the controller reduces the frequency according to the frequency compensation value command. The method for controlling a power conversion circuit according to claim 15, wherein determining the load to adjust the current gain value according to a change in the output current includes: when the change in the output current is less than zero, the controller determines whether the change in the frequency compensation value is Greater than a change threshold; when the change in the frequency compensation value is greater than the change threshold, the controller sets the frequency compensation value to zero. The method for controlling a power conversion circuit according to claim 15, wherein determining the load to adjust the current gain value according to a change in the output current includes: when the change in the output current is less than zero, the controller determines whether the change in the frequency compensation value is Greater than a change threshold; when the change in the frequency compensation value is less than or equal to the change threshold, the controller determines the frequency compensation value based on a characteristic curve based on the operating frequency. The method for controlling a power conversion circuit according to claim 11, further comprising: receiving, by an isolated driver, the second control signal of the controller and driving the switching circuit with a driving signal feedback.