CN116191362A

CN116191362A - Control method of power converter and LLC controller

Info

Publication number: CN116191362A
Application number: CN202111419334.9A
Authority: CN
Inventors: 陈耀宗; 周冠贤
Original assignee: Leadtrend Technology Corp
Current assignee: Leadtrend Technology Corp
Priority date: 2021-11-26
Filing date: 2021-11-26
Publication date: 2023-05-30

Abstract

The embodiment of the invention provides a control method suitable for a power converter. The power converter comprises an upper arm switch and a lower arm switch which are electrically connected in series between an input power supply and a grounding wire to drive a resonant circuit. The power converter further comprises a detection circuit for detecting the resonance circuit to provide a detection signal. The control method comprises the following steps: providing an upper arm control signal and a lower arm control signal to control the upper arm switch and the lower arm switch respectively; detecting a working period of one of the upper arm switch and the lower arm switch; providing a threshold according to the working period; and triggering an overcurrent protection according to the detection signal and the threshold. When the overcurrent protection is triggered, the upper arm control signal and the lower arm control signal stop the resonance circuit from oscillating.

Description

Control method of power converter and LLC controller

Technical Field

The present invention relates generally to a control method of a switching mode power converter and a related controller, and more particularly to a control method and a related controller applicable to over-current protection of an LLC resonant power converter.

Background

An LLC resonant power converter is a switching power supply with excellent conversion efficiency. In a switching power supply, a power switch is often one of the main components that consumes power. Theoretically, each switching cycle of the LLC resonant power converter can be zero-voltage switched (zero voltage switching, ZVS) with two most dominant power switches, namely the upper arm switch and the lower arm switch. Therefore, the conduction loss (conduction loss) of the upper arm switch and the lower arm switch can be controlled to a very low level. LLC resonant power converters are mostly suitable for high-power supplies.

A single output LLC resonant power converter typically employs symmetric pulse width modulation (pulse width modulation, PWM). The dual-output LLC resonant power converter may employ Asymmetric Pulse Width Modulation (APWM) to achieve accurate control of the output voltage (tight output voltage regulation). However, how to achieve accurate control of the output current under the control of the APWM to achieve the over-current protection (over current protection) or overload protection (over load protection) necessary for some general power supplies is a goal of continuous efforts in the industry.

Disclosure of Invention

The embodiment of the invention provides an LLC controller which is suitable for an LLC resonant power converter. The LLC resonant power converter comprises a resonant circuit, an upper arm switch, a lower arm switch and a detection circuit. The upper arm switch and the lower arm switch are electrically connected in series between an input power supply and a ground wire to drive the resonant circuit so as to maintain the resonant circuit to oscillate. The detection circuit is electrically connected to the resonance circuit to provide a detection signal. The LLC controller controls the upper arm switch and the lower arm switch. The LLC controller includes a duty cycle detector, a threshold generator, and an over-current protector. The duty cycle detector detects a duty cycle of one of the upper arm switch and the lower arm switch. The threshold generator provides a threshold according to the working period. The over-current protector triggers an over-current protection according to the threshold value and the detection signal. When the overcurrent protection is triggered, the upper arm switch and the lower arm switch are controlled to stop the resonance circuit from oscillating.

Drawings

Fig. 1 shows a dual output LLC resonant power converter 100 in accordance with the invention.

Fig. 2 shows an LLC controller 102 implemented in accordance with the invention.

FIG. 3A shows the working signal DT _H And a critical value V _CSP-OCP Relationship between them.

FIG. 3B shows the working signal DT _H And a critical value V _CSP-OCP Relationship between them.

Fig. 4 shows some of the signal waveforms of fig. 1 and 2 when the duty cycle of the upper arm switch HS and the lower arm switch LS is about 50%.

Fig. 5 shows some of the signal waveforms of fig. 1 and 2 when the duty cycle of the upper arm switch HS is 25%.

Fig. 6 shows a control method M01 used in the LLC resonant power converter 100 in fig. 1.

100 LLC resonant power converter

102 LLC controller

108. Detection circuit

202. Duty cycle detector

204P, 204N threshold generator

206. Overcurrent protector

208. Opening time controller

1041. 1042 load

1061. 1062 feedback circuit

CA. CB capacitor

CL capacitor

CO1 and CO2 output capacitor

D1, D2 diode

DT _H 、DT _L Working signal

GND _IN Grounding wire

HS upper arm switch

I _CL Electric current

I _D1 、I _D2 Induced current

Lm, lr inductance

LP main winding

LS lower arm switch

LS1, LS2 secondary winding

M01 control method

ND connection point

RA, RB resistance

RSNT resonant circuit

S10, S12, S14, S16 and S18 steps

S _H Upper arm control signal

S _L Lower arm control signal

S _OCP Protecting signals

TF transformer

V _CS Current detection signal

V _CSN-OCP 、V _CSP-OCP Critical value of

V _CSP-H 、V _CSP-L 、V _CSN-H 、V _CSN-L Fixed constant value

V _FB1 、V _FB2 Feedback signal

V _IN Input power supply

V _O1 、V _O2 Output power supply

Detailed Description

In the description, the same reference numerals are used to designate elements having the same or similar structures, functions, and principles, and those skilled in the art can understand the teachings of the present description. For simplicity of the description, elements with the same symbols will not be repeated.

Although the present invention is exemplified by the APWM dual output LLC resonant power converter, the present invention is not limited thereto. In other embodiments, any other type of resonant power converter may be used with the present invention.

In one embodiment of the present invention, an LLC controller in a dual-output LLC resonant power converter provides two thresholds for determining whether an over-current event occurs at the two outputs, respectively, and the two thresholds can be changed according to a duty cycle of a power switch driving a resonant circuit, so as to prevent over-current protection from being triggered by mistake.

Fig. 1 shows a dual output LLC resonant power converter 100 in accordance with the invention. LLC resonant power converter 100 will input power V _IN Converted into an output power V _O1 And V is equal to _O2 Loads 1041 and 1042 are powered separately.

The upper arm switch HS and the lower arm switch LS are electrically connected in series with the input power V _IN And the ground line GND _IN The driving circuit is used for driving the resonant circuit RSNT to make the resonant circuit RSNT vibrate. The resonant circuit RSNT includes a transformer TF and a capacitor CL. The primary winding LP and the two secondary windings LS1 and LS2 in the transformer TF are inductively coupled to each other. The inductances Lr and Lm in the transformer TF represent the series leakage inductance and the parallel leakage inductance of the main winding LP of the transformer TF. The main winding LP is connected in series with the capacitor CL via a connection point ND. In other embodiments, the resonant circuit RSNT may have a different architecture, and is not limited to the structure of fig. 1.

When the resonant circuit RSNT oscillates, the secondary windings LS1 and LS2 generate an induced current I _D1 And I _D2 By rectifying the diodes D1 and D2, an output power V can be established across the output capacitors CO1 and CO2 _O1 And V is equal to _O2 。

Output power supply V _O1 And V is equal to _O2 The feedback signals V can be generated by feedback circuits 1061 and 1062, respectively _FB1 And V is equal to _FB2 . LLC controller 102 provides upper arm control signal S _H And lower arm control signal S _L The upper arm switch HS and the lower arm switch LS are controlled respectively. According to the feedback signal V _FB1 And V is equal to _FB2 The LLC controller 102 may determine the ON-times (ON times), i.e., the ON-times, of the upper arm switch HS and the lower arm switch LS.

The LLC resonant power converter 100 includes a detection circuit 108 composed of resistors RA, RB and capacitors CA and CB connected to each other as shown in FIG. 1. The detection circuit 108 is connected to the connection point ND for detecting the voltage across the capacitor CL in the resonant circuit RSNT, and generating a current detection signal V _CS . Current detection signal V _CS In other embodiments, the detection circuit 108 may provide a different current detection signal V _CS Is provided.

FIG. 2 shows an LLC controller 102 implemented according to the present invention, including an on-time controller 208, a duty cycle detector 202, threshold generators 204P and 204N, and an over-current protector 206.

The on-time controller 208 is based on the feedback signal V _FB1 And V is equal to _FB2 Generating an upper arm control signal S _H And lower arm control signal S _L The opening time of the upper arm switch HS and the lower arm switch LS is also determined by controlling the upper arm switch HS and the lower arm switch LS, respectively. The on-time controller 208 is also configured to enable zero voltage switching (zero voltage switching, ZVS) of the upper arm switch HS and the lower arm switch LS, i.e., to turn on a switch at about 0V across a channel of the switch, thereby reducing switching losses.

In fig. 2, the duty cycle detector 202 is based on the upper arm control signal S _H Providing an operating signal DT _H Representing the duty cycle of the upper arm switch HS. Working signal DT _H May represent a value from 0% to 100%. Working signal DT _L Representing the duty cycle of the lower arm switch LS, can be controlled by the operating signal DT _H Analogize that because of the working signal DT _L And an operating signal DT _H Complementary to each other, add about 1. For example, when working letterNumber DT _H At 35% (representing 35% duty cycle of upper arm switch HS), the complementary operating signal DT _L (representing the duty cycle of the upper arm switch HS) is 65%. In another embodiment, the duty cycle detector 202 may be based on the lower arm control signal S _L To generate and provide an operating signal DT _L And working signal DT _H Can be analogically known.

In FIG. 2, threshold generators 204P and 204N are based on the working signal DT _H Respectively providing critical value V _CSP-OCP And a critical value V _CSN-OCP . In some states, the operating signal DT _H Is changed to result in a threshold value V _CSP-OCP Or critical value V _CSN-OCP Is a change in (c). FIG. 3A shows the working signal DT _H And a critical value V _CSP-OCP Relationship between them. When working signal DT _H Above 35%, critical value V _CSP-OCP About not dependent on the operating signal DT _H Changed fixed constant value V _CSP-L The method comprises the steps of carrying out a first treatment on the surface of the When working signal DT _H At less than 15%, critical value V _CSP-OCP About not dependent on the operating signal DT _H Changed fixed constant value V _CSP-H The method comprises the steps of carrying out a first treatment on the surface of the When working signal DT _H Between 15% and 35%, the threshold value V _CSP-OCP With the working signal DT _H And linearly changes. Similarly, FIG. 3B shows the operating signal DT _H And a critical value V _CSN-OCP Relationship between them. When working signal DT _H Between 65% and 85%, the threshold value V _CSN-OCP With the working signal DT _H And linearly changes. At the working signal DT _H Less than 65% or greater than 85%, critical value V _CSN-OCP Respectively not following the working signal DT _H Changed fixed constant value V _CSN-L And a fixed constant value V _CSN-H As shown in fig. 3B. In one embodiment, four fixed constant values V _CSP-H 、V _CSP-L 、V _CSN-H 、V _CSN-L Are positive values.

Fig. 4 shows some of the signal waveforms of fig. 1 and 2 when the duty cycle of the upper arm switch HS and the lower arm switch LS is about 50%. The signal waveforms in fig. 4 are upper arm control signals from top to bottom, respectivelyNumber S _H Lower arm control signal S _L Current I flowing through capacitor CL _CL Current detection signal V _CS Induced current I flowing through diodes D1 and D2 respectively on the secondary side _D1 And I _D2 . For example, the signal waveforms of fig. 4 may occur when the loads 1041 and 1042 in fig. 1 are both medium-loaded.

If the dead time (dead time) is ignored when both the upper arm switch HS and the lower arm switch LS are closed, the upper arm control signal S of FIG. 4 _H And lower arm control signal S _L It can be seen that the duty cycle of the upper arm switch HS and the lower arm switch LS in FIG. 4 is about 50%, i.e. the duty signal DT _H 50%. According to FIGS. 3A and 3B, the threshold value V in FIG. 4 _CSP-OCP And V is equal to _CSN-OCP The constant values VCSH-L and VCSL-L are respectively fixed.

Please refer to fig. 2 and fig. 4. The over-current protector 206 in fig. 2 is based on the threshold V _CSP-OCP And a critical value V _CSN-OCP And a current detection signal V supplied from the detection circuit 108 _CS To determine whether to output the power V _O1 And V is equal to _O2 One of which an overcurrent event occurs to trigger an overcurrent protection (over current protection, OCP).

For example, if the overcurrent protector 206 finds the current detection signal V _CS Exceeding the critical value V _CSP-OCP And the number of occurrences is a certain number of consecutive times, the overcurrent protector 206 asserts the output power V _O1 An over-current event occurs, triggering the OCP. Similarly, if the overcurrent protector 206 finds the current detection signal V _CS Below the critical value-V _CSN-OCP And the number of occurrences is a certain number of consecutive times, the overcurrent protector 206 asserts the output power V _O2 An over-current event occurs, triggering the OCP.

FIG. 4 shows the current detection signal V _CS Changing from the critical value V _CSP-OCP and-V _CSN-OCP Within a defined tolerance range. Thus, in the signal waveforms of fig. 4, the over-current protector 206 does not trigger OCP.

When OCP triggers, the over-current protector 206 asserts an over-current eventBy protecting signal S _OCP The overcurrent protector 206 disables the on-time controller 208 and controls the upper arm switch HS and the lower arm switch LS such that the resonant circuit rstt stops oscillating with energy loss. In this way, the resonant power converter 100 stops supplying power to the output power V _O1 And V is equal to _O2 . As long as either the upper arm switch HS or the lower arm switch LS remains off (is not turned on), the oscillation of the resonant circuit rst gradually stops. For example, in one embodiment, when the OCP is triggered, the over-current protector 206 keeps both the upper arm switch HS and the lower arm switch LS continuously closed. In another embodiment, when the OCP is triggered, one of the upper arm switch HS and the lower arm switch LS remains off, while the other remains on.

FIG. 5 shows the operating period (operating signal DT) of the upper arm switch HS _H ) 25% of the time, some of the signal waveforms of fig. 1 and 2. Working signal DT _H 25% and means the duty cycle of the lower arm switch LS (working signal DT _L ) 75%. For example, the signal waveform of fig. 5 may occur when the load 1041 in fig. 1 is a medium load and the load 1042 is a light load. According to the operating signal DT shown in FIG. 3A _H And a critical value V _CSP-OCP The relation between these is that the duty cycle of the upper arm switch HS is 25%, so the threshold value V in FIG. 5 _CSP-OCP About a fixed constant value V _CSP-H And a fixed constant value V _CSP-L Is a median value of (c). In FIG. 5, the current detection signal V _CS Still at the critical value V _CSP-OCP and-V _CSN-OCP Within the defined tolerance range, the over-current protector 206 will not trigger OCP either.

Assume the threshold value V in FIG. 5 _CSP-OCP Also as in fig. 4, or a fixed constant value V _CSP-L . It is apparent that although the load 1041 in fig. 1 is a medium load at this time, no overcurrent event occurs, the power supply V is output _O1 Will be mistaken for an over-current event, the OCP will be triggered because of the current sense signal V _CS The peak value of the peak value does exceed a fixed constant value V _CSP-L As shown in fig. 5. In other words, according to FIG. 3A, when the working signalDT _H When (duty cycle of upper arm switch HS) is less than 35%, the threshold value V is increased _CSP-OCP The error recognition of the output power V can be prevented _O1 An overcurrent event occurs. Similarly, according to FIG. 3B, when the working signal DT _H When the ratio is greater than 65%, the critical value V is increased _CSN-OCP The error recognition of the output power V can be prevented _O2 An overcurrent event occurs.

Briefly, the threshold value V _CSP-OCP and-V _CSN-OCP An allowable range may be defined as two boundaries of the allowable range. The over-current protector 206 is based on the allowable range and the current detection signal V _CS To trigger OCP. As can be seen from fig. 3A and 3B, when the working signal DT _H Between 35% and 65% of the intermediate region, the threshold value V _CSP-OCP and-V _CSN-OCP Are fixed values that do not vary with duty cycle, so the allowable range is a standard range, from a fixed constant value-V _CSN-L To V _CSP-L . When working signal DT _H Less than 35%, outside the middle region, the critical value V _CSP-OCP With the working signal DT _H The decrease and increase, which allows the range to be shifted to a relatively wide range, covering the standard range. When working signal DT _H Greater than 65%, after being located outside the middle region, the critical value V _CSN-OCP With the working signal DT _H The increase increases, which allows the range to be shifted to another relatively wide range, also covering the standard range.

Fig. 6 shows a control method M01 used in the LLC resonant power converter 100 in fig. 1. Please refer to fig. 1, fig. 2 and fig. 6. In step S10, upper arm control signal S _H And lower arm control signal S _L The upper arm switch HS and the lower arm switch LS are controlled respectively. In step S12, the duty cycle detector 202 generates a control signal S according to the upper arm _H Providing an operating signal DT _H Representing the duty cycle of the upper arm switch HS. In step S14, the threshold generators 204P and 204N are operated according to the working signal DT _H Respectively providing critical value V _CSP-OCP And a critical value V _CSN-OCP . In step S16, the detection circuit 108 detects the resonant circuit RSNT to generate a current detection signal V _CS . In the step S18 of the process,the over-current protector 206 is based on the threshold value V _CSP-OCP And a critical value V _CSN-OCP And a current detection signal V supplied from the detection circuit 108 _CS To detect the occurrence of an overcurrent event and trigger overcurrent protection.

The foregoing description is only of the preferred embodiments of the invention, and all changes and modifications that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

Claims

1. The control method for power converter includes an upper arm switch and a lower arm switch electrically connected in series between an input power source and a ground wire to drive a resonant circuit (resonant circuit) to oscillate, and a detection circuit for detecting the resonant circuit to provide a detection signal, the control method includes:

providing an upper arm control signal and a lower arm control signal to control the upper arm switch and the lower arm switch respectively;

detecting a working period of one of the upper arm switch and the lower arm switch;

providing a threshold according to the working period; and

triggering an overcurrent protection according to the detection signal and the threshold value;

when the overcurrent protection is triggered, the upper arm control signal and the lower arm control signal stop the oscillation of the resonant circuit.

2. The control method as set forth in claim 1, comprising:

providing a first threshold and a second threshold according to the working period, wherein the first threshold and the second threshold can be used for defining a tolerance range; and

triggering the over-current protection according to the allowable range and the detection signal.

3. The control method of claim 2, wherein the allowable range is a standard range when the duty cycle is 50%, and a relatively wide range when the duty cycle is a relatively small duty cycle less than 50%, and the relatively wide range includes the standard range.

4. The control method of claim 1, wherein the threshold is approximately constant when the duty cycle is within an intermediate region, the intermediate region comprising 50% as a function of duty cycle, and the threshold is changed as a function of duty cycle when the duty cycle is outside the intermediate region.

5. The control method of claim 1, wherein the resonant circuit comprises a transformer and a capacitor, the transformer having a main winding electrically connected to the capacitor and the detection circuit via a connection terminal.

6. An LLC controller adapted for an LLC resonant power converter (LLC resonant converter), the LLC resonant power converter comprising:

a resonant circuit (resonant circuit);

an upper arm switch and a lower arm switch electrically connected in series between an input power supply and a ground wire to drive the resonant circuit so as to maintain the resonant circuit to oscillate; and

the detection circuit is electrically connected to the resonance circuit to provide a detection signal;

the LLC controller controls the upper arm switch and the lower arm switch, and comprises:

a duty cycle detector for detecting a duty cycle of one of the upper arm switch and the lower arm switch;

a threshold generator for providing a threshold according to the working period; and

an overcurrent protector for triggering an overcurrent protection according to the threshold and the detection signal;

when the overcurrent protection is triggered, the upper arm switch and the lower arm switch are controlled to stop the resonance circuit from oscillating.

7. An LLC controller according to claim 1, wherein the resonant circuit comprises a capacitor and a main winding of a transformer, the detection circuit being electrically connected to the capacitor and the main winding via a connection.

8. The LLC controller of claim 1, wherein the threshold generator provides a first threshold and a second threshold according to the duty cycle, and the over-current protector triggers the over-current protection according to the first threshold, the second threshold and the detection signal.

9. The LLC controller of claim 8, wherein the first threshold and the second threshold define an allowable range, the allowable range being a standard range when the duty cycle is 50%, the allowable range being a relatively wide range when the duty cycle is a relatively small duty cycle less than 50%, and the relatively wide range including the standard range.

10. The LLC controller of claim 6, wherein the threshold is approximately constant when the duty cycle is within an intermediate region, which includes 50% of the duty cycle, and the threshold varies with the duty cycle when the duty cycle is in an outer region outside of the intermediate region.