TW201838307A - Power converter and control method thereof - Google Patents

Abstract

A power converter includes a primary-side switching circuit, a resonant circuit, a transformer, a secondary-side rectifying circuit, and a processing circuit. The primary-side switching circuit includes switches and configured to switch the switches to be on or off based on a switching frequency to convert a dc input voltage to an AC signal. The resonant circuit is coupled to the primary-side switching circuit and configured to receive the AC signal to provide a resonant current. The primary winding of the transformer is coupled to the resonant circuit. The secondary-side rectifying circuit is coupled to the secondary winding of the transformer and configured to rectify the secondary ac signal output by the secondary winding and output an output voltage. The processing circuit receives a cut-off current detecting signal via a current-detecting circuit when the corresponding switch is turned off, and adjusts the switching frequency accordingly.

Description

Power converter and control method thereof

The present disclosure is directed to a power converter, and more particularly to a resonant power converter.

The LLC resonant converter achieves a stable output voltage through frequency modulation. Recently, the LLC resonant converter is widely used in renewable energy power supply systems such as solar photovoltaic power generation because it is suitable for a wide range of input voltages and high power output.

However, when the operating frequency of the LLC resonant converter is too high or too low, it is easy to increase the switching loss or conduction loss on the circuit, which leads to an increase in the overall loss of the system and a reduction in conversion efficiency. Therefore, how to control the frequency of the LLC resonant converter to control the operating frequency near the ideal operating point is an important research topic in the current related field.

One aspect of the present disclosure is a power converter. The power converter comprises: a primary switching circuit, comprising a plurality of switches, wherein the primary switching circuit switches the switching of the switches according to a switching frequency to convert the DC input voltage into an AC signal; a resonant circuit Electrically connected to the primary switching circuit for receiving the alternating current signal to provide a resonant current; a transformer, wherein a primary winding of the transformer is electrically connected to the resonant circuit; a secondary rectifier circuit, electrical a secondary winding connected to the transformer for rectifying a secondary AC signal outputted by the secondary winding and outputting an output voltage; and a processing circuit for detecting a current from the corresponding switch when the switch is turned off The measuring circuit receives a turn-off current detecting signal and adjusts the switching frequency according to the turn-off current detecting signal.

In some embodiments, when the shutdown current detection signal is greater than a first threshold, the processing circuit decreases the switching frequency, wherein when the shutdown current detection signal is equal to or less than a second threshold, the The processing circuit increases the switching frequency.

In some embodiments, the processing circuit is further configured to detect the change of the resonant current before the corresponding switch is turned off through the current detecting circuit, and adjust the switching frequency according to the change of the resonant current.

In some embodiments, the processing circuit receives a first current detecting signal from the current detecting circuit at a first moment before the corresponding switch is turned off, and the current is generated at a second moment after the first moment. The detecting circuit receives a second current detecting signal to selectively increase or decrease the switching frequency according to the first current detecting signal and the second current detecting signal.

In some embodiments, when the second current detecting signal is greater than the first current detecting signal, and the difference between the second current detecting signal and the first current detecting signal is greater than a threshold, the processing circuit Increase the switching frequency.

In some embodiments, when the first current detection signal is greater than the second current detection signal, and the difference between the first current detection signal and the second current detection signal is less than a threshold value, the processing circuit Reduce the switching frequency.

In some embodiments, the power converter further includes a driving circuit electrically connected to the processing circuit and the switches in the primary switching circuit, and the processing circuit calculates the signal according to the shutdown current detection signal. A pulse frequency modulation signal is output, and the driving circuit outputs a plurality of driving signals to the switches according to the pulse frequency modulation signal to switch the opening and closing of the switches according to the switching frequency.

Another aspect of the present disclosure is a power converter. The power converter comprises: a primary switching circuit, comprising a plurality of switches, wherein the switches are respectively selectively turned on or off according to the plurality of driving signals to convert the DC input voltage into an AC signal; a resonant circuit Receiving the alternating current signal to provide a resonant current; a current detecting circuit for detecting the resonant current and outputting a current detecting signal according to the resonant current; and a transformer comprising: a primary winding for Receiving a primary side AC signal from the resonant circuit; a side winding for outputting a side alternating current signal corresponding to the primary side alternating current signal; and a secondary side rectifying circuit for rectifying the secondary side alternating current signal And outputting an output voltage; and a processing circuit, configured to control a switching frequency of the driving signals according to the current detecting signal when one of the switching signals turns off the corresponding switch.

In some embodiments, the processing circuit receives a turn-off current detection signal from the current detecting circuit when the corresponding switch is turned off, and when the turn-off current detecting signal is greater than a first threshold, the processing circuit The switching frequency is lowered, and the processing circuit increases the switching frequency when the shutdown current detection signal is equal to or less than a second threshold.

In some embodiments, the processing circuit is further configured to receive a first current detecting signal from the current detecting circuit at a first moment before the corresponding switch is turned off, at a second moment after the first moment. Receiving a second current detecting signal from the current detecting circuit to selectively increase or decrease the switching frequency according to the first current detecting signal and the second current detecting signal.

In some embodiments, when the second current detecting signal is greater than the first current detecting signal, and the difference between the second current detecting signal and the first current detecting signal is greater than a first threshold, the The processing circuit increases the switching frequency. When the first current detecting signal is greater than the second current detecting signal, and the difference between the first current detecting signal and the second current detecting signal is less than a second threshold value, The processing circuit reduces the switching frequency.

In some embodiments, the processing circuit is further configured to determine, according to the current detection signal, whether the switching frequency is adjusted to a resonant frequency of the resonant circuit when the corresponding switch is turned off.

In some embodiments, the power converter further includes: a driving circuit electrically connected to the processing circuit and the switches in the primary switching circuit; wherein the processing circuit calculates and outputs a current according to the current detecting signal The pulse frequency modulation signal, the driving circuit respectively outputs the driving signals to the switches according to the pulse frequency modulation signal.

In some embodiments, the resonant circuit includes a resonant capacitor unit, a resonant inductor unit, and a field inductor unit connected in series with each other, wherein the field inductor unit and the primary winding are connected in parallel with each other.

In some embodiments, the switch includes: a first switch, a first end of the first switch is electrically connected to a positive end of an input voltage source, and a second end of the first switch is electrically connected a first end of the resonant circuit; a second switch, a first end of the second switch is electrically connected to the first end of the resonant circuit, and a second end of the second switch is electrically connected to a negative terminal of the input voltage source; a third switch, a first end of the third switch is electrically connected to the positive end of the input voltage source, and a second end of the third switch is electrically connected to the a second end of the resonant circuit; and a fourth switch, a first end of the fourth switch is electrically connected to the second end of the resonant circuit, and a second end of the fourth switch is electrically connected to the Input the negative terminal of the voltage source.

In some embodiments, the secondary rectifier circuit includes: a first diode, an anode end of the first diode is electrically connected to a first end of the secondary winding, and the first diode a cathode end is electrically connected to a first end of an output capacitor; a second diode body, an anode end of the second diode body is electrically connected to a second end of the output capacitor, the second diode a cathode end of the body is electrically connected to the anode end of the first diode; a third diode, an anode end of the third diode is electrically connected to a second end of the secondary winding, a cathode end of the third diode is electrically connected to the first end of the output capacitor; and a fourth diode, an anode end of the fourth diode is electrically connected to the output capacitor The cathode end of the fourth diode is electrically connected to the anode end of the third diode.

Yet another aspect of the present disclosure is a method of controlling a power converter. The control method includes: driving a driving signal to control a corresponding switch in a primary switching circuit of the power converter through a driving circuit in a power converter to switch an alternating current received by a resonant circuit in the power converter a current detecting circuit in the power converter detects a resonant current flowing through the resonant circuit in the power converter to obtain a turn-off current detecting signal when the corresponding switch is turned off; And determining, by the processing circuit of the power converter, whether a switching frequency of the driving signal is adjusted to a resonant frequency of the resonant circuit according to the shutdown current detecting signal, and selectively adjusting the switching frequency.

In some embodiments, the switching frequency of the driving signal is: when the shutdown current detection signal is greater than a first threshold, the switching frequency is reduced by the processing circuit; and when the current detection signal is turned off When the value is equal to or less than a second threshold, the switching frequency is increased by the processing circuit.

In some embodiments, the power converter control method further includes: detecting, by a current detecting circuit in a power converter, a current flowing through the power converter at a first moment before the corresponding switch is turned off. a resonant current of the resonant circuit to obtain a first current detecting signal; after the first moment, a second moment before the corresponding switch is turned off, detecting the current flowing through the resonant circuit through the current detecting circuit The resonant current is used to obtain a second current detecting signal; and the processing circuit is configured to selectively adjust the switching frequency of the driving signal according to the first current detecting signal and the second current detecting signal.

In some embodiments, the switching frequency of the driving signal is: when the second current detecting signal is greater than the first current detecting signal, and the second current detecting signal and the first current detecting signal are When the difference is greater than a third threshold, the switching frequency is increased by the processing circuit; and when the first current detection signal is greater than the second current detection signal, and the first current detection signal and the second current detection When the difference between the test signals is less than a fourth threshold, the switching frequency is reduced by the processing circuit.

The embodiments are described in detail below to better understand the aspects of the disclosure, but the embodiments are not intended to limit the scope of the disclosure, and the description of the structural operation is not used. In order to limit the order in which they are performed, any device that has been re-combined by the components, resulting in equal functionality, is covered by this disclosure. In addition, according to industry standards and practices, the drawings are only for the purpose of assisting the description, and are not drawn according to the original size. In fact, the dimensions of the various features may be arbitrarily increased or decreased for convenience of explanation. In the following description, the same elements will be denoted by the same reference numerals for explanation.

The terms used in the entire specification and the scope of the patent application, unless otherwise specified, generally have the ordinary meaning of each term used in the field, the content disclosed herein, and the particular content. Certain terms used to describe the disclosure are discussed below or elsewhere in this specification to provide additional guidance to those skilled in the art in the description of the disclosure.

In addition, the terms "including", "including", "having", "containing", and the like, as used herein, are all open terms, meaning "including but not limited to". Further, "and/or" as used herein includes any one or combination of one or more of the associated listed items.

As used herein, when an element is referred to as "connected" or "coupled", it may mean "electrically connected" or "electrically coupled". "Connected" or "coupled" can also be used to indicate that two or more components operate or interact with each other. In addition, although the terms "first", "second", and the like are used herein to describe different elements, the terms are used only to distinguish the elements or operations described in the same technical terms. The use of the term is not intended to be a limitation or a

Please refer to Figure 1. FIG. 1 is a schematic diagram of a power converter 100 in accordance with some embodiments of the present disclosure. As shown in FIG. 1 , in some embodiments, the power converter 100 includes a primary switching circuit 120 , a resonant circuit 140 , a transformer 160 , a secondary rectifier circuit 180 , a current detecting circuit 130 , a processing circuit 150 , and a driving circuit 170 . . In some embodiments, the power converter 100 can be applied to a DC-to-DC conversion device in a solar photovoltaic system to convert the DC voltage output by the solar panel to an appropriate voltage level. In this way, the inverter of the latter stage can convert the DC power into AC power in phase with the same frequency of the power grid, and realize the grid connection of the renewable energy and the commercial power.

Structurally, the input side of the primary side switching circuit 120 is electrically coupled to the input voltage source for receiving the DC input voltage Vin. The output side of the primary side switching circuit 120 is electrically coupled to the input side of the resonant circuit 140 for outputting an alternating current signal to the resonant circuit 140. The output side of the resonant circuit 140 is electrically connected to the primary winding Np of the transformer 160. The secondary winding Ns of the transformer 160 is electrically connected to the input side of the secondary rectifier circuit 180. The output side of the secondary side rectifier circuit 180 is electrically coupled to the output capacitor Co to provide a DC output voltage Vo to the subsequent stage circuit. In this way, the primary side switching circuit 120, the resonant circuit 140, the transformer 160, and the secondary side rectifier circuit 180 can form the circuit architecture of the LLC resonant converter.

In addition, as shown in FIG. 1, the current detecting circuit 130 is disposed on the line of the resonant circuit 140 to detect the resonant current Ir flowing through the resonant circuit 140. For example, the current detecting circuit 130 can include a current detecting unit 132 and a rectifying unit 134. In some embodiments, the current detecting unit 132 can be implemented by a Hall element, but the disclosure is not limited thereto. The rectifying unit 134 is electrically coupled to the current detecting unit 132 for rectifying the detecting signal obtained by the current detecting unit 132 to output a current detecting signal Sig_I for representing the resonant current Ir. the size of.

Structurally, the processing circuit 150 is electrically connected to the current detecting circuit 130. The driving circuit 170 is electrically connected between the processing circuit 150 and the primary switching circuit 120. In some embodiments, the processing circuit 150 may include a Voltage-To-Frequency Converter for outputting a Pulse Frequency Modulation (PFM) signal PFM to the driving circuit 170 according to the current detecting signal Sig_I. . After receiving the pulse frequency modulation signal PFM from the processing circuit 150, the driving circuit 170 can output a plurality of driving signals CS1 CS CS4 to the switches S1 S S4 in the primary switching circuit 120 according to the pulse frequency modulation signal PFM. The switching frequency switching switches S1 to S4 of the signals CS1 to CS4 are turned on and off. Thereby, the processing circuit 150 can change the switching frequency of the AC signal output by the primary switching circuit 120 through the pulse frequency modulation signal PFM. In some embodiments, the voltage to frequency converter in processing circuit 150 can be implemented by various circuits, such as an integrator and a comparator, the details of which are not described herein.

Thereby, as the switching frequency of the alternating current signal output by the primary side switching circuit 120 changes, the impedance of the resonant circuit 140 also changes with the switching frequency. As a result, the magnitude of the electromotive force induced by the primary winding Np of the transformer 160 changes with the change of the switching frequency, and the corresponding DC output voltage Vo is outputted via the secondary winding Ns of the secondary side and the secondary rectifier circuit 180. In other words, the DC output voltage Vo can be controlled by the switching frequency of the driving signals CS1 to CS4.

In particular, in various embodiments, primary switching circuit 120 can be implemented through a half bridge, full bridge, or other type of switching circuit. For example, in the embodiment shown in FIG. 1, the primary side switching circuit 120 can be implemented by a full bridge circuit. The primary side switching circuit 120 includes switches S1, S2, S3, and S4. As shown, the first end of the switch S1 is electrically connected to the positive terminal of the input voltage source. The second end of the switch S1 is electrically connected to the first end of the resonant circuit 140. The first end of the switch S2 is electrically connected to the first end of the resonant circuit 140. The second end of the switch S2 is electrically connected to the negative terminal of the input voltage source. The first end of the switch S3 is electrically connected to the positive terminal of the input voltage source. The second end of the switch S3 is electrically connected to the second end of the resonant circuit 140. The first end of the switch S4 is electrically connected to the second end of the resonant circuit 140. The second end of the switch S4 is electrically connected to the negative terminal of the input voltage source.

Therefore, when the switches S1 and S4 are turned on according to the corresponding driving signals CS1 and CS4, and the switches S2 and S3 are turned off according to the corresponding driving signals CS2 and CS3, the first end of the resonant circuit 140 is electrically connected to the positive input source. Extremely, the second end of the resonant circuit 140 is electrically coupled to the negative terminal of the input voltage source. In contrast, when the switches S1 and S4 are turned off according to the corresponding driving signals CS1 and CS4, and the switches S2 and S3 are turned on according to the corresponding driving signals CS2 and CS3, the first end of the resonant circuit 140 is electrically connected to the negative of the input voltage source. Extremely, the second end of the resonant circuit 140 is electrically coupled to the positive terminal of the input voltage source. In this way, the primary side switching circuit 120 can switch the opening and closing of the switches S1 to S4 according to the switching frequency, and convert the DC input voltage Vin into an AC signal with a duty cycle of 50% to be transmitted to the resonant circuit 140.

In some embodiments, the resonant circuit 140 includes a resonant capacitor unit Cr, a resonant inductor unit Lr, and a magnetizing inductance unit Lm. Structurally, the resonant capacitor unit Cr, the resonant inductor unit Lr, and the exciting inductor unit Lm are connected in series with each other, and the exciting inductor unit Lm and the primary winding Np of the transformer 160 are connected in parallel with each other. For example, as shown in FIG. 1, the first end of the resonant capacitor unit Cr is electrically connected to the first end of the resonant circuit 140 to be electrically connected to the switches S1 and S2. The second end of the resonant capacitor unit Cr is electrically connected to the first end of the resonant inductor unit Lr. The second end of the resonant inductor unit Lr is electrically connected to the first end of the magnetizing inductance unit Lm. The second end of the magnetizing inductance unit Lm is electrically connected to the second end of the resonant circuit 140 to be electrically connected to the switches S3 and S4, but the disclosure is not limited thereto. In some embodiments, the resonant inductor unit Lr and the magnetizing inductor unit Lm may be formed by the leakage inductance and the magnetizing inductance of the transformer 160, respectively. In other embodiments, the resonant capacitor unit Cr, the resonant inductor unit Lr, and the magnetizing inductor unit Lm may also be electrically connected in different manners to implement an LLC resonant circuit.

In this way, the primary side winding Np connected in parallel with the exciting inductance unit Lm can receive the primary side alternating current signal from the resonant circuit 140. The secondary winding Ns can output the secondary side alternating current signal to the secondary side rectifying circuit 180 corresponding to the primary side alternating current signal, so that the transformer 160 realizes energy transfer between the primary side and the secondary side.

In various embodiments, secondary rectifier circuit 180 can be implemented through a half bridge, full bridge, or other type of rectifier circuit. For example, in the embodiment shown in FIG. 1, the secondary side rectifier circuit 180 can be implemented by a full bridge rectifier circuit. The secondary side rectifier circuit 180 includes diodes D1, D2, D3, and D4. As shown, the anode end of the diode D1 is electrically connected to the first end of the secondary winding Ns, and the cathode end of the diode D1 is electrically connected to the first end of the output capacitor Co. The anode end of the diode D2 is electrically connected to the second end of the output capacitor Co, and the cathode end of the diode D2 is electrically connected to the anode end of the diode D1. The anode end of the diode D3 is electrically connected to the second end of the secondary winding Ns. The cathode end of the diode D3 is electrically connected to the first end of the output capacitor Co. The anode end of the diode D4 is electrically connected to the second end of the output capacitor Co, and the cathode end of the diode D4 is electrically connected to the anode end of the diode D3.

Thereby, the secondary side alternating current signal Vo is outputted by the secondary side rectifying circuit 180 and the output capacitor Co rectifying and filtering the secondary side alternating current signal induced and output by the secondary side winding Ns.

In this way, through the operation of the above circuit, the power converter 100 can convert the DC input voltage Vin into a DC output voltage Vo having an appropriate voltage level to be supplied to the subsequent stage circuit. It should be noted that, in some embodiments, when the load variation causes the power converter 100 to be under light load or heavy load, if the switching frequency of the switches S1 S S4 is too different from the resonant frequency of the resonant circuit 140, the power component may be caused. The additional loss causes the conversion efficiency of the power converter 100 to decrease. Therefore, the processing circuit 150 can pass the current detecting circuit 130 to detect the resonant current Ir when the corresponding switches S1 S S4 are turned off or before being turned off. The size and the change thereof are adjusted, and the switching frequency of the switches S1 to S4 is adjusted according to the magnitude of the resonant current Ir at the time of turning off or the change of the detecting resonant current Ir before turning off. The following paragraphs will be described in detail with respect to the specific operation of the processing circuit 150 to adjust the switching frequency of the switches S1 to S4 in conjunction with the related drawings.

Please refer to Figure 2 and Figure 3A and Figure 3B together. FIG. 2 is a schematic diagram of waveforms when the power converter 100 is operated in an over-resonant mode according to some embodiments of the present disclosure. 3A and 3B are schematic diagrams showing the operation of the power converter 100 according to some embodiments of the present disclosure.

As shown in Fig. 3A, in the upper half cycle, the switches S1, S4 are turned on. The difference between the resonant current Ir and the exciting current Im flows into the primary winding Np, and the energy is transmitted to the secondary winding Ns through the transformer 160, and finally the current Id1 is output via the turned-on diodes D1, D4.

As shown in Fig. 3B, in the second half cycle, switches S2, S3 are turned on. The flow direction of the resonant current Ir is opposite to that of the upper half cycle, and the polarity of the exciting inductance unit Lm is reversed. The difference between the resonant current Ir and the exciting current Im flows into the primary winding Np, and the energy is transmitted to the secondary winding Ns through the transformer 160, and finally the current Id3 is output via the turned-on diodes D2 and D3.

When the power converter 100 is operated in the over-resonant mode, the waveform of each signal changes as shown in FIG. Since the switching frequency of the switches S1 to S4 is greater than the resonant frequency of the resonant circuit 140 at this time, when the upper half cycle of the resonant current Ir is not completed, the control signals CS1 and CS4 are switched from the enable level (eg, high level). To the disable level (eg, low level), the switches S1 and S4 are turned off first, so that the resonant current Ir changes from a sinusoidal waveform to a linear decrease. After a short dead time, the control signals CS2, CS3 are switched from the disable level to the enable level, and then the switches S2, S3 are turned on and enter the second half cycle. Therefore, the resonant current Ir is not a complete sinusoidal waveform, and the currents Id1, Id3 flowing through the secondary side rectifying circuit 180 in the upper half cycle and the lower half cycle are also incomplete sinusoidal waveforms.

In this mode, the diodes D1 to D4 in the secondary side rectifier circuit 180 are hard switches. When the switching frequency of the switches S1 to S4 is too large, the switches S1 to S4 also have a large loss when they are turned off.

As shown in Fig. 2, since the sinusoidal waveform of the resonant current Ir is interrupted before either of the corresponding switches S1 to S4 is turned off. Therefore, when the corresponding switches S1 to S4 are turned off, the magnitude of the resonant current Ir is larger than the magnitude of the exciting current Im. Thereby, the processing circuit 150 can estimate the magnitude of the exciting current Im under the current circuit operation according to the formula, and add an appropriate tolerance value as the first threshold value. If the shutdown current detection signal Sig_I of the magnitude of the representative resonant current Ir measured at time T3 is greater than the first threshold, the switching frequency of the switches S1 to S4 is too high, so that the sinusoidal waveform of the resonant current Ir is beaten earlier. Broken. At this time, the processing circuit 150 can determine that the current switching frequency is too high, and adjust the pulse frequency modulation signal PFM outputted to the driving circuit 170 to lower the switching frequency.

In addition, in some embodiments, the processing circuit 150 can further detect the change of the resonant current Ir before the switch S1 to S4 is turned off by the current detecting circuit 130, thereby determining whether the switching frequency of the switches S1 to S4 exceeds the preset. The operating frequency range is output, and the corresponding pulse frequency modulation signal PFM is output to reduce the switching frequency of the switches S1 to S4.

For example, the processing circuit 150 can receive the first current detecting signal Sig_I from the current detecting circuit 130 at the first time T1 before the corresponding switches S1 S S4 are turned off, at the second time T2 after the first time T1. The current detecting circuit 130 receives the second current detecting signal Sig_I. As shown in Fig. 2, the slope of the sinusoidal waveform of the resonant current Ir decreases from the maximum value to zero. If the difference of the current detection signals Sig_I measured at the times T1 and T2 is small, the switching frequency of the switches S1 to S4 is too high, so that the sinusoidal waveform of the resonant current Ir is interrupted earlier. In other words, when the first current detection signal Sig_I is greater than the second current detection signal Sig_I, and the difference between the first current detection signal Sig_I and the second current detection signal Sig_I is less than a third threshold, the processing circuit 150 can determine At present, the switching frequency is too high, and the pulse frequency modulation signal PFM outputted to the driving circuit 170 is adjusted to lower the switching frequency.

Please refer to Figure 4 and Figure 5A and Figure 5B together. FIG. 4 is a schematic diagram of waveforms when the power converter 100 is operated in an under-resonant mode according to some embodiments of the present disclosure. 5A and 5B are schematic diagrams showing the operation of the power converter 100 according to some embodiments of the present disclosure.

When the power converter 100 operates in the under-resonant mode, the operation of the power converter 100 when the resonant half-cycle has not been completed is as shown in FIGS. 3A and 3B, the details of which are described in the previous paragraphs, and thus will not be described herein. .

On the other hand, as shown in Fig. 5A, in the upper half period, when the resonance half period is completed, the resonance current Ir coincides with the excitation current Im, and at this time, no current flows through the primary winding Np. At this time, the diodes D1 to D4 in the secondary side rectifier circuit 180 do not provide a current path, and the energy required for the subsequent stage circuit is supplied from the output capacitor Co.

Similarly. As shown in Fig. 5B, in the second half cycle, when the resonance half cycle is completed, the resonance current Ir coincides with the excitation current Im, and at this time, no current flows through the primary winding Np. At this time, the diodes D1 to D4 in the secondary side rectifier circuit 180 also do not provide a current path, and the energy required for the subsequent stage circuit is also supplied by the output capacitor Co.

When the power converter 100 operates in the under-resonant mode, the waveform of each signal changes as shown in FIG. Since the switching frequency of the switches S1 to S4 is lower than the resonant frequency of the resonant circuit 140 at this time, when the first half of the resonant current Ir is completed, the control signals CS1 and CS4 are maintained at the enable level (eg, high level). Has not been switched to the disable level (eg low level). As a result, the resonant current Ir will be combined with the waveform of the exciting current Im to gradually rise. Until the control signals CS1 and CS4 are switched to the disable level, and after a short dead time, the control signals CS2 and CS3 are switched from the disable level to the enable level, thereby turning on the switches S2 and S3 and entering the lower half. cycle. Therefore, the currents Id1 and Id3 flowing through the secondary rectifier circuit 180 include a half sine wave and a cutoff time in the upper half cycle and the second half cycle, respectively, and the resonant current Ir continues to rise before the switches S1 to S4 are turned off. . In this mode, during the period in which the secondary side rectifying circuit 180 is turned off, the primary side circuit causes a large conduction loss due to the presence of a circulating current.

Therefore, when the corresponding switches S1 to S4 are turned off, the magnitude of the resonant current Ir is approximately equal to or smaller than the value of the exciting current Im. Thereby, the processing circuit 150 can estimate the magnitude of the exciting current Im under the current circuit operation according to the formula as the second threshold value. If the shutdown current detection signal Sig_I representing the magnitude of the resonance current Ir measured at the time T3 is equal to or smaller than the second threshold value, the switching frequency of the switches S1 to S4 is too low, so that the power converter 100 operates in the under resonance. mode. At this time, the processing circuit 150 can judge that the current switching frequency is too low, and adjust the pulse frequency modulation signal PFM outputted to the driving circuit 170 to increase the switching frequency.

In other words, as shown in FIG. 2 to FIG. 5A and FIG. 5B, the processing circuit 150 can be used to transmit the current detecting circuit 130, and when the corresponding switches S1 to S4 are turned off (for example, the third time T3), the current detecting is performed. The measuring circuit 130 receives the turn-off current detecting signal Sig_I, and determines whether the switching frequency is adjusted to the resonant frequency of the resonant circuit 140 according to the turn-off current detecting signal Sig_I, and adjusts the switching frequency according to the turn-off current detecting signal Sig_I.

Further, as shown in Fig. 4, since the switching of any of the switches S1 to S4 is turned off, the resonance current Ir continues to rise. Therefore, the processing circuit 150 can also pass the current detecting circuit 130 to detect the change of the resonant current Ir before the switches S1 S S4 are turned off, thereby determining whether the switching frequency of the switches S1 S S4 is lower than the preset operating frequency range. And outputting the corresponding pulse frequency modulation signal PFM through the processing circuit 150 to increase the switching frequency of the switches S1 to S4.

Similar to the previous paragraph, the processing circuit 150 can receive the first current detecting signal Sig_I from the current detecting circuit 130 at the first time T1 before the corresponding switches S1 S S4 are turned off, and the second after the first time T1. The second current detecting signal Sig_I is received from the current detecting circuit 130 at time T2. When the second current detecting signal Sig_I is greater than the first current detecting signal Sig_I, and the difference between the second current detecting signal Sig_I and the first current detecting signal Sig_I is greater than a fourth threshold, the processing circuit 150 can determine the resonant current. Ir continues to rise, the power converter 100 operates in the under-resonant mode and the switching frequency is too low, and adjusts the pulse frequency modulation signal PFM outputted to the driving circuit 170 to increase the switching frequency.

In summary, the processing circuit 150 can detect the change of the primary side resonance current Ir before the respective switches S1 to S4 are turned off, and the processing circuit 150 can be based on the first current detection signal Sig_I and the second current detection signal Sig_I. The switching frequency is selectively increased or decreased, so that the switches S1 S S4 of the primary switching circuit operate near the resonant frequency, avoiding excessive or excessive switching frequency, resulting in an increase in overall system loss and reducing conversion efficiency of the power converter 100.

Please refer to Figure 6. FIG. 6 is a schematic diagram of waveforms when the power converter 100 is operated in a full resonance mode according to some embodiments of the present disclosure. As shown in Fig. 6, when the switching frequency is close to or exactly equal to the resonant frequency, each of the upper half cycle and the second half cycle completely includes one resonant half cycle. When the switches S1 to S4 are switched, the resonance current Ir is approximately equal to the excitation current Im, and the currents Id1 and Id3 output from the secondary rectifier circuit 180 are reduced to approximately zero. At this time, the power converter 100 has the highest conversion efficiency.

In some embodiments, the processing circuit 150 is further configured to pass the current detecting circuit 130, and receive the off current detecting signal from the current detecting circuit 130 when the corresponding switches S1 to S4 are turned off (eg, the third time T3). Sig_I, and according to the shutdown current detection signal Sig_I, it is judged whether the switching frequency is adjusted to the resonance frequency of the resonance circuit 140.

As shown in Fig. 6, when the power converter 100 is operated in the full resonance mode, the switches S1 to S4 are switched, and the resonant current Ir is approximately equal to the exciting current Im. In this way, the processing circuit 150 can calculate the target value of the excitation current Im according to the component parameters, and compare with the detected shutdown current detection signal Sig_I. When the two are close, the processing circuit 150 can determine that the switching frequency of the primary switching circuit 120 has been adjusted to be close to the resonant frequency of the resonant circuit 140, and stop continuously adjusting the output pulse frequency modulation signal PFM. Thereby, the power converter 100 can complete the frequency control.

In summary, by detecting the magnitude of the resonant current Ir when the switches S1 S S4 are turned off during each switching cycle, or the change of the resonant current Ir before the switches S1 S S4 are turned off, the switches S1 to S4 can be gradually increased or decreased. The switching frequency is until the processing circuit 150 determines that the switching frequency is within the operating range of the target based on the detected resonant current Ir, which is close to or exactly equal to the resonant frequency.

In addition, since in this frequency control operation, only the resonant current Ir of the primary side needs to be detected, there is no need to feedback the detection signal from the secondary side, and no additional isolation circuit is required to be performed between the primary and secondary sides. Signal transmission, which simplifies control circuit design and reduces cost.

Please refer to Figure 7 and Figure 8. 7 and 8 are flowcharts of control methods 700, 800 of power converter 100, respectively, according to some embodiments of the present disclosure. For convenience and clarity of description, the following control methods 700 and 800 are described in conjunction with the embodiments shown in FIGS. 1 to 6 , but are not limited thereto, and those skilled in the art will not deviate from the disclosure. Within the spirit and scope, when you can make a variety of changes and retouching. As shown in FIG. 7, the control method 700 includes steps S710, S720, and S730.

First, in step S710, the power converter 100 transmits the drive signals 170 in the power converter 100, and outputs the drive signals CS1 CS CS4 to control the corresponding switches S1 S S4 in the primary side switching circuit 120 to switch the received by the resonant circuit 140. Exchange signal.

Next, in step S720, when the corresponding switches S1 to S4 are turned off, the power converter 100 detects the resonant current Ir flowing through the resonant circuit 140 through the current detecting circuit 130 to obtain the turn-off current detecting signal Sig_I.

Next, in step S730, the power converter 100 passes through the processing circuit 150 in the power converter 100 to determine whether the switching frequency of the driving signals CS1 CS CS4 is adjusted to the resonant frequency of the resonant circuit 140 according to the turn-off current detecting signal Sig_I. Selectively adjust the switching frequency.

Specifically, in some embodiments, when the shutdown current detection signal Sig_I is greater than a first threshold, the power converter 100 reduces the switching frequency through the processing circuit 150. When the turn-off current detecting signal Sig_I is equal to or smaller than the second threshold value, the power converter 100 increases the switching frequency through the processing circuit 150.

In some embodiments, the power converter 100 can adjust the switching frequency by detecting a change in the resonant current Ir before the switch is turned off. As shown in FIG. 8, the control method 800 includes steps S810, S820, S830, S840, S850, and S860.

First, in step S810, the power converter 100 detects the resonant current Ir flowing through the resonant circuit 140 through the current detecting circuit 130 to obtain the first current at the first time T1 before the corresponding switches S1 to S4 are turned off. Detection signal Sig_I.

Next, in step S820, after the first time T1, the power converter 100 detects the second current time T2 before the corresponding switches S1 to S4 are turned off, and the current detecting circuit 130 detects the resonant current Ir flowing through the resonant circuit 140. To obtain the second current detecting signal Sig_I.

Next, in step S830, the power converter 100 transmits the drive signals 170 through the drive circuit 170 of the power converter 100 at the third time T3, and outputs the drive signals CS1 to CS4 to control the corresponding switches S1 to S4 in the primary side switching circuit 120 to switch. The AC signal received by the resonant circuit 140.

Next, in step S840, the power converter 100 transmits the switching frequency of the driving signals CS1 CS CS4 according to the first current detecting signal Sig_I and the second current detecting signal Sig_I through the processing circuit 150.

Specifically, in some embodiments, when the second current detection signal Sig_I is greater than the first current detection signal Sig_I, and the difference between the second current detection signal Sig_I and the first current detection signal Sig_I is greater than the third threshold At step S840, the processing circuit 150 increases the switching frequency of the drive signals CS1 to CS4.

On the other hand, when the first current detection signal Sig_I is greater than the second current detection signal Sig_I, and the difference between the first current detection signal Sig_I and the second current detection signal Sig_I is less than the fourth threshold, the processing circuit 150 decreases. The switching frequency of the drive signals CS1 to CS4.

In some embodiments, adjusting the switching frequency of the driving signals CS1 CS CS4 includes: calculating, by the processing circuit 150, the pulse current modulation signal PFM according to the first current detection signal Sig_I and the second current detection signal Sig_I; The circuit 170 receives the pulse frequency modulation signal PFM, and outputs the driving signals CS1 CS CS4 according to the pulse frequency modulation signal PFM to adjust the switching frequency of the driving signals CS1 CS CS4.

Next, in step S850, the power converter 100 detects the resonant current Ir flowing through the resonant circuit 140 at the third time T3 to obtain the turn-off current detecting signal Sig_I.

Finally, in step S860, the power converter 100 passes through the processing circuit 150 to determine whether the switching frequency of the driving signals CS1 CS CS4 is adjusted to the resonant frequency of the resonant circuit 140 according to the off current detecting signal Sig_I.

Those skilled in the art can directly understand how the control methods 700, 800 are based on the power converter 100 in the above various embodiments to perform the operations and functions, and therefore will not be described again.

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

The present disclosure has been disclosed in the above embodiments, and is not intended to limit the disclosure, and the present disclosure may be variously modified and retouched without departing from the spirit and scope of the present disclosure. The scope of protection of the content is subject to the definition of the scope of the patent application.

100‧‧‧Power Converter

120‧‧‧ primary switching circuit

130‧‧‧ Current detection circuit

132‧‧‧current detection unit

134‧‧‧Rectifier unit

140‧‧‧Resonance circuit

150‧‧‧Processing circuit

160‧‧‧Transformers

170‧‧‧ drive circuit

180‧‧‧Sub-side rectifier circuit

700‧‧‧Control method

800‧‧‧Control method

S710 ~ S730, S810 ~ S860‧ ‧ steps

S1～S4‧‧‧ switch

D1～D4‧‧‧ diode

Cr‧‧‧Resonant capacitor unit

Lr‧‧‧Resonant Inductance Unit

Lm‧‧‧excited inductance unit

Np‧‧‧ primary winding

Ns‧‧‧ secondary winding

Co‧‧‧ output capacitor

Vin‧‧‧DC input voltage

Vo‧‧‧DC output voltage

Ir‧‧‧Resonance current

Im‧‧‧Excitation current

Id1, Id3‧‧‧ current

PFM‧‧‧ pulse frequency modulation signal

CS1～CS4‧‧‧ drive signal

Sig_I‧‧‧current detection signal

T1, T2, T3‧‧‧ moments

FIG. 1 is a schematic diagram of a power converter according to some embodiments of the present disclosure. FIG. 2 is a schematic diagram of waveforms when the power converter is operated in an over-resonant mode according to some embodiments of the present disclosure. 3A and 3B are schematic diagrams showing the operation of the power converter according to some embodiments of the present disclosure. FIG. 4 is a schematic diagram of waveforms when the power converter is operated in an under-resonant mode according to some embodiments of the present disclosure. 5A and 5B are schematic diagrams showing the operation of the power converter according to some embodiments of the present disclosure. FIG. 6 is a schematic diagram of waveforms when the power converter is operated in the full resonance mode according to some embodiments of the present disclosure. FIG. 7 is a flow chart of a method of controlling a power converter according to some embodiments of the present disclosure. FIG. 8 is a flow chart of a method of controlling a power converter according to some embodiments of the present disclosure.

Claims (20)

A power converter includes: a primary switching circuit, comprising a plurality of switches, wherein the primary switching circuit is configured to switch the switching of the switches according to a switching frequency to convert the DC input voltage into an AC signal; a resonant circuit electrically connected to the primary switching circuit for receiving the alternating current signal to provide a resonant current; a transformer, wherein a primary winding of the transformer is electrically connected to the resonant circuit; and a secondary side rectifier circuit Electrically connected to a secondary winding of the transformer for rectifying a secondary AC signal outputted by the secondary winding and outputting an output voltage; and a processing circuit for self-closing when the corresponding switch is turned off The current detecting circuit receives a turn-off current detecting signal, and adjusts the switching frequency according to the turn-off current detecting signal. The power converter of claim 1, wherein the processing circuit reduces the switching frequency when the shutdown current detection signal is greater than a first threshold, wherein the shutdown current detection signal is equal to or less than a first The processing circuit increases the switching frequency when the two thresholds are depreciated. The power converter of claim 1, wherein the processing circuit is further configured to: through the current detecting circuit, detect a change of the resonant current before the corresponding switch is turned off, and adjust the switching according to the change of the resonant current. frequency. The power converter of claim 3, wherein the processing circuit receives a first current detecting signal from the current detecting circuit at a first moment before the corresponding switch is turned off, and the first time after the first moment The second current detecting signal is received from the current detecting circuit to selectively increase or decrease the switching frequency according to the first current detecting signal and the second current detecting signal. The power converter of claim 4, wherein the second current detecting signal is greater than the first current detecting signal, and the difference between the second current detecting signal and the first current detecting signal is greater than a threshold At the time of the value, the processing circuit increases the switching frequency. The power converter of claim 4, wherein the first current detection signal is greater than the second current detection signal, and the difference between the first current detection signal and the second current detection signal is less than a threshold The value of the processing circuit reduces the switching frequency. The power converter of claim 1, further comprising a driving circuit electrically connected to the processing circuit and the switches in the primary switching circuit, the processing circuit detecting the signal according to the shutdown current Calculating and outputting a pulse frequency modulation signal, the driving circuit respectively outputs a plurality of driving signals to the switches according to the pulse frequency modulation signal to switch the opening and closing of the switches according to the switching frequency. A power converter comprising: a primary switching circuit comprising a plurality of switches respectively for selectively turning on or off according to a plurality of driving signals to convert a DC input voltage into an AC signal; a resonant circuit for receiving the alternating current signal to provide a resonant current; a current detecting circuit for detecting the resonant current and outputting a current detecting signal according to the resonant current; a transformer comprising: a primary winding, The first side alternating current signal is received from the resonant circuit; the secondary side winding is configured to output a side alternating current signal corresponding to the primary side alternating current signal; and the secondary side rectifying circuit is configured to rectify the secondary side alternating current signal And outputting an output voltage; and a processing circuit, configured to control a switching frequency of the driving signals according to the current detecting signal when one of the switching signals turns off the corresponding switch. The power converter of claim 8, wherein the processing circuit receives a shutdown current detection signal from the current detection circuit when the corresponding switch is turned off, when the shutdown current detection signal is greater than a first threshold The value of the switching circuit reduces the switching frequency. When the shutdown current detecting signal is equal to or less than a second threshold, the processing circuit increases the switching frequency. The power converter of claim 8, wherein the processing circuit is further configured to receive a first current detecting signal from the current detecting circuit at a first moment before the corresponding switch is turned off, at the first moment The second current detecting signal is received by the current detecting circuit to selectively increase or decrease the switching frequency according to the first current detecting signal and the second current detecting signal. The power converter of claim 10, wherein the second current detecting signal is greater than the first current detecting signal, and the difference between the second current detecting signal and the first current detecting signal is greater than one The processing circuit increases the switching frequency when the first current detecting signal is greater than the second current detecting signal, and the difference between the first current detecting signal and the second current detecting signal is less than one The processing circuit reduces the switching frequency when the second threshold is depreciated. The power converter of claim 8, wherein the processing circuit is further configured to determine, according to the current detection signal, whether the switching frequency is adjusted to a resonant frequency of the resonant circuit when the corresponding switch is turned off. The power converter of claim 8, further comprising: a driving circuit electrically connected to the processing circuit and the switches in the primary switching circuit; wherein the processing circuit calculates and outputs according to the current detecting signal a pulse frequency modulation signal, the driving circuit respectively outputs the driving signals to the switches according to the pulse frequency modulation signal. The power converter of claim 8, wherein the resonant circuit comprises a resonant capacitor unit, a resonant inductor unit and a field inductor unit connected in series with each other, wherein the field inductor unit and the primary winding are connected in parallel with each other. The power converter of claim 8, wherein the switches comprise: a first switch, a first end of the first switch is electrically connected to a positive terminal of an input voltage source, and the first switch The second end is electrically connected to a first end of the resonant circuit; a second switch, a first end of the second switch is electrically connected to the first end of the resonant circuit, and a second end of the second switch The second end is electrically connected to a negative end of the input voltage source; a third switch, a first end of the third switch is electrically connected to the positive end of the input voltage source, and a second end of the third switch The first end of the fourth switch is electrically connected to the second end of the resonant circuit, and the second end of the fourth switch is electrically connected to a second end of the resonant circuit, and a fourth switch The terminal is electrically connected to the negative terminal of the input voltage source. The power converter of claim 8, wherein the secondary rectifier circuit comprises: a first diode, an anode end of the first diode is electrically connected to a first end of the secondary winding, a cathode end of the first diode is electrically connected to a first end of an output capacitor; a second diode, an anode end of the second diode is electrically connected to a second end of the output capacitor a cathode end of the second diode is electrically connected to the anode end of the first diode; a third diode, an anode end of the third diode is electrically connected to the secondary winding a second end of the third diode is electrically connected to the first end of the output capacitor; and a fourth diode, an anode end of the fourth diode is electrically connected to The second end of the output capacitor is electrically connected to the anode end of the third diode. A control method for a power converter, comprising: driving a driving signal to control a corresponding switch in a primary switching circuit of the power converter through a driving circuit in a power converter to switch a resonance in the power converter An AC signal received by the circuit; a current detecting circuit in the power converter detects a resonant current flowing through the resonant circuit in the power converter to obtain a level when the corresponding switch is turned off And interrupting the current detection signal; and determining, by the processing circuit of the power converter, whether a switching frequency of the driving signal is adjusted to a resonant frequency of the resonant circuit according to the shutdown current detecting signal, and selectively adjusting the Switch frequency. The control method of the power converter of claim 17, wherein the switching frequency of the driving signal comprises: when the shutdown current detection signal is greater than a first threshold, the switching frequency is reduced by the processing circuit; And when the shutdown current detection signal is equal to or less than a second threshold, the switching frequency is increased by the processing circuit. The control method of the power converter according to claim 17, further comprising: detecting the resonant current through the current detecting circuit at a first moment before the corresponding switch is turned off to obtain a first current detecting After the first time, a second time before the corresponding switch is turned off, the current detecting circuit detects the resonant current to obtain a second current detecting signal; and through the processing circuit, according to The first current detecting signal and the second current detecting signal selectively adjust the switching frequency of the driving signal. The control method of the power converter of claim 19, wherein the switching frequency of the driving signal comprises: when the second current detecting signal is greater than the first current detecting signal, and the second current detecting signal When the difference between the first current detecting signal and the first current detecting signal is greater than a third threshold, the switching frequency is increased by the processing circuit; and when the first current detecting signal is greater than the second current detecting signal, and the first current is When the difference between the detection signal and the second current detection signal is less than a fourth threshold, the switching frequency is reduced by the processing circuit.