WO2019183880A1

WO2019183880A1 - Llc resonant converter as well as control circuit and resonant current sampling circuit thereof

Info

Publication number: WO2019183880A1
Application number: PCT/CN2018/081086
Authority: WO
Inventors: 戴国峰; 程中原
Original assignee: 深圳驿普乐氏科技有限公司
Priority date: 2018-03-29
Filing date: 2018-03-29
Publication date: 2019-10-03

Abstract

An LLC resonant converter as well as a control circuit and a resonant current sampling circuit thereof. An inductor is connected to a resonant cavity (30) of the LLC resonant converter, so as to induce a resonant current of the resonant cavity and convert the resonant current into an alternating current induced voltage; a voltage conversion sub-circuit further converts the alternating current induced voltage into a direct current voltage and outputs same to a controller (610). Therefore, the resonant current is sampled in real time, thereby providing a basis for further control of the controller, and the control to a turnoff current of a switch tube facilitates reducing switch loss of a bridge arm switch and improving the control accuracy of the controller.

Description

LLC resonant converter and its control circuit and resonant current sampling circuit

Technical field

The invention relates to the field of LLC resonant converters, and in particular to an LLC resonant converter, a control circuit thereof and a resonant current sampling circuit.

Background technique

With the development of the new energy industry, the demand for the charging pile industry is increasing, and the power level requirements for charging piles are increasing. The 10KW-20KW DC charging module has begun to spread. In the current AC/DC DC module, DC/ The DC adopts a three-level LLC resonant DC converter. The three-level LLC resonant DC converter can reduce the voltage stress of the switching transistor to half of the input DC bus (DC700V-850V), and select the low-voltage device under the high-voltage input. The LLC resonant DC converter can realize the ZVS of the switching tube and the ZCS of the rectifier diode, improve the conversion efficiency and reduce the electromagnetic interference.

A common three-level LLC topology is shown in Figure 1. Figure 2 shows the operating waveforms of the individual switching tubes when the resonant frequency is greater than the operating frequency. The resonant frequency is greater than the operating frequency. In this state, the switching transistor operates in the ZVS state and the rectifier diode operates in the ZCS state. When the resonant frequency is equal to the operating frequency, iLr (the current of Lr) is a complete sine wave, the output current of the secondary rectifier is critically continuous, and the conduction loss of the converter is minimized, resulting in higher efficiency. When the resonant frequency is less than the operating frequency, when iLr and iLm are not equal, the switching transistor has been forcibly turned off, iLr is decreased, and the secondary diode current is also rapidly reduced. At this time, the switching current of the switching transistor is lower than the first two. The situation is much larger, so the loss is larger; in this case, the switching transistor Vs1 is taken as an example for description. When Vs1 is turned off, the current iLr flowing through Vs1 is greater than iLm, and the loss is large; at this time, iLr is soft at the same time. The switch charges C1 (the equivalent output capacitor corresponding to Vs1), and C4 (the equivalent output capacitor corresponding to Vs4) discharges. In actual design, if iLr is large, the turn-off loss is relatively large. If iLr is small, then turn off. When C1 is charged, the C4 discharge is not completed, resulting in an unsatisfactory ZVS implementation.

It can be seen that there is a relatively large loss at the time t2-t4 when the switch is turned off. Because the switch tube realizes the hard switch when the switch is turned off, since the controller of the LLC resonant DC converter cannot obtain the resonant current, the corresponding control of the bridge arm switch cannot be performed to realize the ZVS of the switch tube, and the converter efficiency is low.

Summary of the invention

The invention mainly provides an LLC resonant converter, a control circuit thereof and a resonant current sampling circuit, which are intended to sample the resonant current and provide a basis for the control of the controller.

According to a first aspect, an embodiment provides a resonant current sampling circuit of an LLC resonant converter, including:

An inductor for sensing a resonant current of the LLC resonant converter and converting the resonant current into an alternating current induced voltage;

a voltage conversion sub-circuit for converting an alternating induction voltage into a direct current voltage;

The input end of the inductor is connected to the resonant cavity of the LLC resonant converter, and the output of the inductor is connected to the controller AD port of the LLC resonant converter through a voltage conversion sub-circuit.

According to a second aspect, an embodiment of the present invention provides a control circuit for an LLC resonant converter, comprising:

a resonant current sampling circuit as described above;

The controller is configured to convert the DC voltage outputted by the resonant current sampling circuit into a resonant current; according to the magnitude of the resonant current, increase or decrease the dead time to reduce the current when the bridge switch is turned off.

According to a third aspect, an embodiment provides an LLC resonant converter including: a DC output circuit, a switching bridge arm, a resonant cavity, a power conversion circuit, a rectifier circuit, and the above control circuit; and an output of the DC output circuit The terminal is connected to the resonant cavity through the switch bridge arm, and the resonant cavity is connected to the rectifier circuit through a power conversion circuit; the controller is connected to the control end of each bridge arm switch.

According to the LLC resonant converter of the above embodiment and its control circuit and resonant current sampling circuit, the inductor is connected to the resonant cavity of the LLC resonant converter to sense the resonant current of the resonant cavity and convert the resonant current into an AC induced voltage. The voltage conversion sub-circuit converts the AC induced voltage into a DC voltage and outputs it to the controller; thereby realizing the real-time sampling of the resonant current, providing a basis for further control of the controller, by controlling the off current of the switch tube, It is beneficial to reduce the switching loss of the bridge arm switch and improve the accuracy of the controller control.

DRAWINGS

Figure 1 is a conventional three-level LLC topology diagram;

2 is a diagram showing the operation waveforms of the respective switching tubes when the resonant frequency is greater than the operating frequency in FIG. 1;

3 is a circuit diagram of an embodiment of an LLC resonant converter provided by the present invention.

detailed description

The present invention will be further described in detail below with reference to the accompanying drawings. Similar elements in different embodiments employ associated similar component numbers. In the following embodiments, many of the details are described in order to provide a better understanding of the application. However, those skilled in the art can easily realize that some of the features may be omitted in different situations, or may be replaced by other components, materials, and methods. In some cases, some operations related to the present application have not been shown or described in the specification, in order to avoid that the core portion of the present application is overwhelmed by excessive description, and those skilled in the art will describe these in detail. Related operations are not necessary, they can fully understand the relevant operations according to the description in the manual and the general technical knowledge in the field.

In addition, the features, operations, or characteristics described in the specification may be combined in any suitable manner to form various embodiments. At the same time, the steps or actions in the method description can also be sequentially changed or adjusted in a manner that can be apparent to those skilled in the art. Therefore, the various sequences in the specification and the drawings are only for the purpose of describing a particular embodiment, and are not intended to

The serial numbers themselves for the components herein, such as "first", "second", etc., are only used to distinguish the described objects, and do not have any order or technical meaning. As used herein, "connected" or "coupled", unless otherwise specified, includes both direct and indirect connections (joining).

Please refer to FIG. 3 , the LLC resonant converter provided by the present invention includes: a DC output circuit 10 , a switch bridge arm 20 , a resonant cavity 30 , a power conversion circuit 40 , a rectifier circuit 50 , and a control circuit 60 . The DC output circuit 10 The output terminal is connected to the resonant cavity 30 through the switch bridge arm 20, and the resonant cavity 30 is connected to the rectifier circuit 50 through the power conversion circuit 40; the controller 610 is connected to the control terminals of the respective bridge arm switches (Vs1-Vs4).

The control circuit 60 is a total control of the input and output states of the entire converter, and controls the entire power transmission by controlling the respective bridge arm switches.

Further, the control circuit 60 includes a resonant current sampling circuit and a controller 610.

The resonant current sampling circuit is configured to sample the resonant current in real time, and can monitor the resonant current change at a time to facilitate the controller 610 to perform control.

The resonant current sampling circuit includes an inductor and a voltage conversion sub-circuit; an input end of the inductor is connected to a resonant cavity 30 of an LLC resonant converter, and an output end of the inductor is connected to an input end of the voltage conversion sub-circuit, The output of the voltage conversion sub-circuit is connected to the AD port of the controller 610 of the LLC resonant converter. The AD (Analog-to-Digital Conversion) port of the controller is used to sample the DC voltage outputted by the voltage conversion sub-circuit to obtain sampled data, which is a digital signal. The sampled data serves as a basis for the controller to adjust the magnitude of the off current of the control bridge arm switch.

The inductor is for sensing a resonant current of the resonant cavity 30 and converting the resonant current into an alternating current induced voltage.

The inductor outputs an AC induced voltage, and the voltage conversion sub-circuit is used to convert the AC induced voltage into a DC voltage; to facilitate reception by the AD port of the controller. It can be seen that the utility model realizes sampling of the resonant current, and provides a basis for further control of the controller 610. By controlling the off current of the switch tube, it is beneficial to reduce the switching loss of the bridge arm switch.

The controller 610 is configured to convert the DC voltage outputted by the resonant current sampling circuit into a resonant current, thereby obtaining a resonant current at each moment, in particular, a turn-off current of the bridge switch; according to the magnitude of the resonant current, Increase or decrease the dead time to reduce the current when the bridge switch is turned off, thereby reducing switching losses. The invention reduces the switching loss of the bridge arm switch by adjusting the dead time, and improves the overall efficiency of the LLC resonant DC converter. The controller 610 can employ a DSP. The control effect of the controller is largely related to the signal it inputs, such as the DC voltage output from the resonant current sampling circuit. In the present invention, since the resonant current sampling circuit outputs a DC voltage, the controller 610 can obtain the resonant current at each moment in real time, has good timeliness, and improves the accuracy of controlling the LLC resonant DC converter.

The inductor is a coupling winding Ls, which is coupled to a resonant inductor Lr of an LLC resonant converter, the coupling winding Ls being connected to the voltage converting subcircuit. The number of turns of the coupling winding Ls can adjust the voltage of the first capacitor C1, and the specific number of turns can be determined according to the magnitude of the voltage that the controller 610 can receive. The coupling winding Ls is coupled to the resonant inductor Lr in the form of a transformer winding. For example, the resonant inductor Lr may be the primary winding of the transformer, and the coupled winding Ls may be the secondary winding of the transformer.

The voltage conversion sub-circuit includes a first resistor R1 and a first capacitor C1, one end of the coupling winding Ls is connected to one end of the first capacitor C1 through a first resistor R1; one end of the first capacitor C1 is a voltage conversion sub-circuit The output terminal is connected to the AD port of the controller 610; the other end of the first capacitor C1 is connected to the other end of the coupling winding Ls and the boost voltage supply terminal VREF. The boost voltage provided by the boost voltage supply terminal VREF is used to raise the lowest voltage of the first capacitor C1 to greater than 0V to convert the voltage of the first capacitor into a DC voltage. In other words, if the voltage is not raised, the voltage of the first capacitor C1 changes according to the change of the resonant current iLr, but is an alternating current; by setting the boosting voltage, the voltage of the first capacitor C1 becomes the following resonant current iLr. The change of DC power changes, easy to DSP, AD port processing.

In this embodiment, the resonant resonant inductance of the LLC resonant converter 30 is N; the number of turns of the coupled winding Ls is 1, the resonant current passes through Lr, passes through the transformer T1, generates an AC induced voltage on Ls, and is composed of R1, C1. The RC circuit generates a voltage on C1. At this time, the voltage on C1 is an AC signal, and a certain value is raised by VREF, so that the voltage is superimposed DC, so that the controller 610 samples. The controller 610 reflects the magnitude of the resonant cavity current by detecting the voltage on C1. Its gain is G. The gain G represents the voltage V1 generated at C1 when the current flowing through Lr is 1, G = V1/I. The invention detects the induced voltage on the first capacitor C1, and the obtained voltage is a direct current whose voltage value is constantly changing. The controller 610 can acquire in real time, so that the resonant current can be sampled in real time, so that the LLC resonance can be real-time and accurate. The converter performs control.

The DC output circuit 10 is configured to receive external DC power, and after filtering, output to the switch bridge arm 20 to provide power for the LLC resonant converter.

The switch bridge arm 20 includes a plurality of bridge arm switches. Each of the bridge arm switches may be composed of a single or a plurality of MOS tubes, a single or a plurality of IGBTs (Insulated Gate Bipolar Transistors), or a combination of MOS tubes and IGBTs. The switch bridge arm 20 functions as a high frequency square wave generator for generating a high frequency square wave to change the direct current voltage into a high frequency square wave voltage.

The power conversion circuit 40 includes a power transformer T.

The resonant cavity 30 includes a first inductor Lr, a second inductor Lm and a capacitor Cr, that is, a first inductor Lr, and the second inductor Lm and the capacitor Cr are connected in series to form a resonant circuit, and the resonant frequency thereof is

The resonant cavity 30 causes the current in the resonant cavity 30 to vary in a sinusoidal manner when the power supply is a DC power source. Since the current or voltage changes according to a sinusoidal law, there is a zero crossing. If the switching device (bridge arm switch) is turned on or off at this time, the loss generated is zero and the circuit is energized. In this embodiment, the first inductor Lr is the above-mentioned resonant inductor, and the second inductor Lm is the magnetizing inductance of the primary winding of the power transformer T. In the circuit, iLr is a resonant current, and iLm is an exciting current.

The rectifying circuit 50 is configured to rectify the alternating current outputted by the secondary winding of the power transformer T; and is composed of a common full bridge, full wave, half wave or other rectifying method and a filtering circuit.

The controller 610 is specifically configured to: compare a magnitude of the resonant current with a preset current value; and increase a first dead time and/or a third dead time when the resonant current is greater than a preset current; The first dead time and/or the third dead time is decreased when the resonant current is less than the preset current value. The preset current value is not lower than a minimum current value capable of achieving zero voltage switching of the bridge arm; the first dead time is the first dead time in a working cycle, and the third dead zone Time is the third dead time in a work cycle.

In this embodiment, the LLC resonant converter is a three-level LLC resonant DC converter.

The switch bridge arm 20 includes a first diode D1', a second diode D2', a first bridge arm switch Vs1, a second bridge arm switch Vs2, a third bridge arm switch Vs3, and a fourth bridge arm switch. Vs4; the first bridge arm switch Vs1 and the second bridge arm switch Vs2 are upper arm switches, and in one duty cycle, the second bridge arm switch Vs2 is turned off later than the first bridge arm switch Vs1; the third bridge arm switch Vs3 And the fourth bridge arm switch Vs4 is a lower arm switch, and the third bridge arm switch Vs3 is turned off later than the fourth bridge arm switch Vs4 in one duty cycle. The first pole of the first bridge arm switch Vs1 is connected to the anode of the direct current, and the second pole of the first bridge arm switch Vs1 is connected to the first pole of the second bridge arm switch Vs2 and the cathode of the first diode D1'. The control pole (gate) of the first bridge arm switch Vs1 is connected to the first output end of the controller 610; the anode of the first diode D1' is connected to the cathode of the second diode D2'; the second bridge arm The second pole of the switch Vs2 is connected to one end of the first inductor Lr and the first pole of the third bridge arm Vs3; the other end of the first inductor Lr is connected to one end of the capacitor Cr through the primary winding of the power transformer T, and the other end of the capacitor Cr Connecting the DC output circuit 10, the anode of the first diode D1' and the cathode of the second diode D2'; the control pole (gate) of the second bridge switch Vs2 is connected to the second output of the controller 610; The second pole of the three-legged arm switch Vs3 is connected to the positive pole of the second diode D2' and the first pole of the fourth bridge arm switch Vs4, and the control pole (gate) of the third bridge arm switch Vs3 is connected to the controller 610 a third output terminal; a second pole of the fourth bridge arm switch Vs4 is grounded, and a control pole (gate) of the fourth bridge arm switch Vs4 is connected to the fourth of the controller 610 Output.

In this embodiment, the first bridge arm switch Vs1, the second bridge arm switch Vs2, the third bridge arm switch Vs3, and the fourth bridge arm switch are four identical power MOS tubes. VD1, VD2, VD3, and VD4 are equivalent body diodes of respective corresponding power MOS tubes, and VC1, VC2, VC3, and VC4 are equivalent output capacitors corresponding to the respective power MOS tubes. The first diode D1' and the second diode D2' are three-level clamping diodes.

The controller 610 obtains the real-time current of the LLC resonant cavity, and satisfies the requirement that the power bridge arm switch ZVS current can be turned off at a relatively small current, thereby reducing the loss and improving the efficiency. Simultaneously detecting the resonant current in real time, the state of the DC converter can be monitored in real time, thereby achieving more protection and improving system reliability. In order to reduce the amount of data processing of the controller 610 without affecting the control effect, the controller 610 can acquire the resonant current only at several critical time points. Specifically, the controller 610 acquires the current of the LLC resonant cavity when the second bridge arm is turned off after starting a working cycle; and/or acquires the current of the LLC resonant cavity when the third bridge arm is turned off. Wherein, the second bridge arm switch Vs2 is the upper arm switch that is turned off after the two upper arm switches, and the third bridge arm switch Vs3 is the one of the two lower arm switches that is turned off later Bridge arm switch. In this embodiment, the current of the LLC resonant cavity when the second bridge arm switch is turned off is obtained, and the current of the LLC resonant cavity when the third bridge arm switch is turned off is obtained.

The controller 610 increases or decreases the first dead time, specifically by adjusting the PWM duty ratio of Vs1 and/or Vs2; similarly, increasing or decreasing the third dead time, specifically by adjusting The PWM duty cycle of Vs 3 and / or Vs 4 is implemented. In addition, in the LLC resonant DC converter, each of the bridge arm switches in the switch bridge arm 20 operates periodically, so that the first dead time and the third dead time are increased or decreased, and the next time can be increased or decreased. The first dead time and the third dead time may also increase or decrease the first dead time and the third dead time in one or more subsequent work cycles.

The resonant current sampling circuit provided by the invention can output the real-time current of the LLC resonant cavity, so that the controller satisfies the ability to realize the power bridge arm switch ZVS current, and turns off when the current is relatively small, thereby reducing the loss and improving the efficiency. . At the same time, the controller can detect the resonant current in real time, and can monitor the state of the DC converter in real time, thereby achieving more protection and improving system reliability.

The preset current value is not lower than the minimum current value capable of realizing the zero voltage switch of the second bridge arm switch Vs2 or the third bridge arm switch Vs3, thereby ensuring the ZVS of the bridge arm switch while reducing the switching loss. The first dead time is the first dead time in one working cycle, in other words, the first dead time is from the first bridge switch off to the second bridge switch off time. The third dead time is the third dead time in one working cycle. In other words, the third dead time is from the fourth bridge switch to the third bridge in one working cycle. The time the arm switch is turned off.

The invention has been described above with reference to specific examples, which are merely intended to aid the understanding of the invention and are not intended to limit the invention. Variations to the above-described embodiments may be made in accordance with the teachings of the present invention.

Claims

A resonant current sampling circuit for an LLC resonant converter, comprising:

An inductor for sensing a resonant current of the LLC resonant converter and converting the resonant current into an alternating current induced voltage;

a voltage conversion sub-circuit for converting an alternating induction voltage into a direct current voltage;

The input end of the inductor is connected to the resonant cavity of the LLC resonant converter, and the output of the inductor is connected to the controller AD port of the LLC resonant converter through a voltage conversion sub-circuit.
The resonant current sampling circuit according to claim 1, wherein the AD port of the controller is configured to sample the DC voltage outputted by the voltage conversion sub-circuit to obtain sampling data; and the sampling data is used as a controller to adjust the control bridge. The basis for the amount of off current of the arm switch.
A resonant current sampling circuit according to claim 1, wherein said inductor is a coupled winding, said coupled winding is coupled to a resonant inductance of an LLC resonant converter, said coupled winding being coupled to said voltage converting subcircuit.
The resonant current sampling circuit according to claim 3, wherein said voltage conversion sub-circuit comprises a first resistor and a first capacitor, and one end of said coupling winding is connected to one end of said first capacitor through a first resistor; One end of the first capacitor is an output end of the voltage conversion sub-circuit, and is connected to the controller AD port; the other end of the first capacitor is connected to the other end of the coupling winding and the boost voltage supply end.
The resonant current sampling circuit according to claim 4, wherein the boost voltage provided by the boost voltage supply terminal is used to raise the lowest voltage of the first capacitor to greater than 0V to convert the voltage of the first capacitor into DC voltage.
A control circuit for an LLC resonant converter, comprising:

A resonant current sampling circuit according to any of claims 1-5;

The controller is configured to convert the DC voltage outputted by the resonant current sampling circuit into a resonant current; according to the magnitude of the resonant current, increase or decrease the dead time to reduce the current when the bridge switch is turned off.
An LLC resonant converter, comprising: a DC output circuit, a switching bridge arm, a resonant cavity, a power conversion circuit, a rectifier circuit, and the control circuit according to claim 6; the output end of the DC output circuit passes The switch bridge arm is connected to the resonant cavity, and the resonant cavity is connected to the rectifier circuit through a power conversion circuit; the controller is connected to the control end of each bridge arm switch.