Adaptive voltage positioning constant on-time control method for quasi-parallel converter

Abstract

This invention proposes an adaptive voltage positioning constant on-time control method for a quasi-parallel converter. The method obtains the average output current of BUCK and LLC, i.e., the load current output by Sigma, through current sampling; the output voltage V... o With reference voltage V RFE The voltage loop compensation output V is obtained through a differential amplifier circuit. c The difference between this signal and the current signal is used to obtain the charging current I through the transconductance gm. RAMP Charging capacitor C T Charging generates harmonic signals V RAMP When V RAMP Rise to V TH The system enters the conduction phase, and simultaneously V RAMP Zeroing; Fixed conduction T on Time, and T on Automatic adjustment is performed according to different operating conditions to ensure that the switching frequency remains approximately constant under different conditions; after conduction ends, the switch is turned off, and it waits for V again. RAMP equals V TH Entering the next conduction cycle; taking the Sigma converter as a typical application, there is no need to sample the inductor current, and under certain design conditions, AVP control can be implemented simply and reliably.

Description

TECHNICAL FIELD

[0001] The present application relates to a switching power supply, in particular to a constant on-time control (COT) control method with adaptive voltage positioning (AVP) function applied to a quasi-parallel converter. TECHNICAL BACKGROUND

[0002] Switching power supplies generate a regulated output voltage based on an input voltage to power a load. With the rapid development of Internet technology, central processing units (CPUs), field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), and even peripheral devices are becoming more and more complex, and their power supply requirements are also becoming more and more complex. In order to meet higher requirements, switching power supplies are becoming more and more common in many computing fields, including notebook computers, tablet computers, servers, etc. In recent years, data centers have replaced 12VDC server rack power supply solutions with 48VDC server rack power supply solutions, thereby significantly improving the overall system efficiency. However, the 48V rack architecture poses a major challenge to the voltage regulator module (VRM) required to power the processor. The 48V VRM near the central processing unit (CPU) and the graphics processing unit (GPU) requires high efficiency, high power density, high light load efficiency, and must meet all the transient requirements of the CPU and GPU.

[0003] A quasi-parallel converter has two converters in series at the input side and two converters in parallel at the output side. One of the converters is responsible for delivering high power to the load and often adopts a resonant topology; the other is responsible for regulating the output voltage. The present application uses a Sigma converter as a typical application, which is a combination of LLC and BUCK in series at the input and in parallel at the output. Compared with a two-stage structure with 48V input, the output power of the Sigma converter is equal to the sum of the output powers of the LLC and BUCK structures, and the Sigma structure fully combines the advantages of the LLC and BUCK structures, i.e. the LLC works at resonant frequency to efficiently transmit most of the power, and the BUCK samples the output voltage to perform system voltage regulation and adjustment. In the design, the LLC works at resonant frequency, and the LLC can be regarded as a direct current transformer, whose input voltage is proportional to the output voltage with a proportionality coefficient of the number of turns N. The input voltage of the BUCK is equal to the total input voltage minus the input voltage of the LLC. Therefore, reasonable design of the output power ratio of the two structures will make the efficiency of the system theoretically higher than that of the two-stage structure.

[0004] Constant on-time control is a kind of nonlinear control, which provides a switch setting signal after processing the feedback signal, and turns off after a constant time T on on. COT control includes current-mode constant on-time (CMCOT) control, V 2Control and reverse charging constant on-time control, etc. Compared with the traditional PID linear control, the COT control omits the inertia link and only retains the proportional link before the nonlinear link, thereby accelerating the response speed during the transient state.

[0005] The system cannot achieve instantaneous response at the load switching moment, so the output voltage is necessarily reduced during the light-to-heavy process, and the output voltage is necessarily increased during the heavy-to-light process. The AVP control design utilizes an effective output voltage accuracy window, and the stable output voltage is high under light load conditions and low under heavy load conditions, thereby reducing the response time of all loads returning to the same output voltage operating point, and allowing the output voltage over-undershoot window to be enlarged by one time. There are mainly two kinds of traditional AVP design schemes, namely, a peak current mode and an active droop control mode. The traditional AVP design needs to sample the current, superimposes the current information on the output voltage or the reference through a sampling resistor, and designs a compensator to make the closed-loop output impedance as constant as possible in the full frequency range. This method needs a current sampling circuit and a high-speed high-precision ADC converter in digital control, and the compensation design is too complex and is greatly affected by peripheral parameters. SUMMARY

[0006] TECHNICAL PROBLEM: In order to overcome the limitations and deficiencies of the prior art, the application provides an adaptive voltage positioning constant on-time control method for a quasi-parallel converter, takes the Sigma converter as a typical application, adopts a reverse charging COT control mode, obtains current information with BUCK alternating current and overall output current direct current as an AVP window design by means of the estimated current of the BUCK and the proportion relationship between the BUCK and the LLC output current in the Sigma structure, does not need to sample the inductor current, and can simply and reliably realize the AVP control under certain design conditions.

[0007] TECHNICAL SCHEME: In order to achieve the above purpose, the application adopts an adaptive voltage positioning constant on-time control method for a quasi-parallel converter, and the following technical scheme is applied in a Sigma converter:

[0008] The reverse charging COT control mode adopted by the application can fundamentally solve the above problems. The current output by the transconductance gm is directly proportional to V c and I L *R ses When V c is less than I L *R ses , in order to ensure fast response of the control, the minimum charging current is set to 0. If the phenomenon of V c <I L *R ses occurs under normal steady-state conditions in the design, the output voltage can be obtained according to the charge and discharge of the electric charge.

[0009] The adaptive voltage positioning constant on-time control method for the quasi-parallel converter of this invention obtains the average output current of BUCK and LLC through current sampling, i.e., the load current output by Sigma; the output voltage V o With reference voltage V RFE The voltage loop compensation output V is obtained through a differential amplifier circuit. c The difference between this signal and the current signal is used to obtain the charging current I through the transconductance gm. RAMP Charging capacitor C T Charging generates harmonic signals V RAMP When V RAMP Rise to V TH The system enters the conduction phase, and simultaneously V RAMP Zeroing; Fixed conduction T on Time, and T on Automatic adjustment is performed according to different operating conditions to ensure that the switching frequency remains approximately constant under different conditions; after conduction ends, the switch is turned off, and it waits for V again. RAMP equals V TH Enter the next conduction cycle; during the light-to-heavy switching process, if the system switching cycle is less than the conduction time, the system will be in a long conduction phase until the loop self-adjusts and the switching cycle is greater than the conduction time before turning off; this method is beneficial to improve the response speed of light-to-heavy switching, but it should be noted that the inductor current during long conduction in actual operation should not exceed the current limit of the power transistor.

[0010] The quasi-parallel converter employs a Sigma converter, which includes an LLC resonant converter for delivering high power to the load and a Buck converter for regulating the output voltage; the control system employed in the control method includes a set pulse V TR Signal generation module and start time T on Generate modules;

[0011] Set pulse V TR Signal generation module: This module is an integral module for constant on-time (COT) control, generating an error signal V. c It is the output voltage V o and reference voltage V REF The difference is amplified by the op-amp's gain H. v Magnified, V c and inductor current I L × Equivalent sampling resistance R ses The difference between the two values ​​is converted into current by a transconductance gm amplifier, and this current is then used to charge the capacitor, resulting in the voltage V across the capacitor. RAMP Ramp signal, set pulse V TR Compare voltage V based on thresholdTH and V RAMP The voltage comparison generates a decision of the on-time of the switch tube;

[0012] T on The generating module: T on The signal is generated by the capacitor voltage V CAP and the reference voltage V REF The comparison generates V CAP The controlled current source controlled by the input voltage V in charges the capacitor to generate V CAP The reset signal of the voltage is completed by the reset signal V T , V T The signal is V TR The signal and the inverse duty cycle signal (D_B) together constitute a function.

[0013] The control method has an effective output voltage precision window, the stable output voltage is high under light load conditions, and the stable output voltage is low under heavy load conditions; the output voltage and the load current output by the BUCK converter are linearly related under the condition of meeting V c >I L *R ses The output voltage is not only related to the load current, but also related to the switching frequency, and the switching frequency of the system changes under different load currents in the reverse charging COT control, and the heavier the load, the higher the corresponding switching frequency.

[0014] The switching frequency changes, which means that the switching frequency changes less than 2 times in the full load range, and the amplitude change is A V *H f Reduced, the output voltage change caused by the frequency in the full load range is within 5mV-10mV; by compensating a fixed offset voltage to the reference, the influence of the frequency is offset; at the same time, the current information with BUCK alternating current and overall output current direct current is obtained as the AVP window by means of the estimated current of BUCK and the relationship between BUCK and LLC output current in the Sigma structure.

[0015] The AVP window is designed to ensure that the output voltage V o and the inductor current meet V c >I L *R ses ; if V c <I L *R ses phenomenon occurs under normal steady state conditions in the design, the relationship between the output voltage and the frequency can be obtained according to the charge and discharge of the charge, such as formula (1)

[0016]

[0017] Equation (1) shows that the output voltage Vo is not linearly proportional to the load current, making it impossible to achieve controllable AVP control. Therefore, it is necessary to maintain V c >I L *R ses .

[0018] The output currents of BUCK and LLC are obtained by current sampling, which yields the average output current of BUCK and LLC, i.e., the load current output by Sigma; the output voltage V o With reference voltage V RFE The voltage loop compensation output V is obtained through a differential amplifier circuit. c The difference between this signal and the current signal is used to obtain the charging current I through the transconductance gm. RAM P charges the capacitor C T Charging generates harmonic signals V RAMP When V RAMP Rise to V TH The system enters the conduction phase, and simultaneously V RAMP Zeroing; Fixed conduction T on Time, and T on Automatic adjustment is performed according to different operating conditions to ensure that the switching frequency remains approximately constant under different conditions; after conduction ends, the switch is turned off, and it waits for V again. RAMP equals V TH Enter the next conduction cycle; during the light-to-heavy switching process, if the system switching cycle is less than the conduction time, the system will be in a long conduction phase until the loop adjusts itself and the switching cycle is greater than the conduction time before turning off; this design is beneficial to improve the response speed of light-to-heavy switching, but it should be noted that the inductor current during long conduction in actual operation should not exceed the current limit of the power transistor.

[0019] Beneficial effects:

[0020] 1. The constant on-time control method with adaptive voltage positioning function used in this invention for quasi-parallel structure converters is typically applied to the reverse charging COT control of Sigma converters. The Sigma converter includes an LLC resonant converter for delivering high power to the load and a Buck converter for regulating the output voltage. Compared with the traditional AVP control design with current sampling, it does not require a high-speed ADC with a frequency much higher than the switching frequency, which can reduce costs, reduce circuit size, and has high versatility.

[0021] 2. This invention employs a reverse charging COT control method, utilizing the full switching cycle (T) ON +T OFF The concept of integration can enable the inductor current i LRise faster, significantly reduce undershoot at the output end, with good transient performance.

[0022] 3. The constant conduction time control method with adaptive voltage positioning function applied to the quasi-parallel converter is not only suitable for Sigma converter, but also for other converters, and has high flexibility. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is the system structure block diagram of the application of the constant conduction time control method with adaptive voltage positioning function in Sigma converter.

[0024] Figure 2 is the corresponding transient response waveform when the Buck output current is used as the AVP window in the application.

[0025] Figure 3 is the corresponding transient response waveform when the total output current is used as the AVP window in the application. DETAILED DESCRIPTION

[0026] In order to more clearly illustrate the application, the technical solutions of the application will be further explained below in combination with the drawings.

[0027] Figure 1 is the system structure block diagram of the application of the constant conduction time control method with adaptive voltage positioning function in Sigma converter, Sigma converter includes LLC resonant converter for delivering high power to load and Buck converter for regulating output voltage. The system structure mainly includes power stage module, current and voltage sampling module, V TR signal generation module and T on generation module. The synchronous rectification Buck converter controls the output voltage by controlling the on and off time of the two MOS1 and MOS2 switch tubes, L is the filter inductance of the Buck converter, C o is the ideal filter capacitor, and ESR is the series equivalent resistance of the filter capacitor. The error signal V c is the difference between the output voltage V o and the reference voltage V REF amplified by the coefficient H v , V c and the difference between I L *R i is converted into current by using a transconductance (g m ) amplifier, and then this current is used to charge the capacitor. The voltage (V RAMP ) of this capacitor is compared with a fixed threshold voltage (V TH ) to generate V TRPulse, through T on Generator trigger T on Pulse. In reverse charge COT control, the current output by transconductance gm is proportional to Vc and I L *R ses But when V c is less than I L *R ses , in order to ensure the control fast response, set the minimum charging current to 0. If the design in the normal steady state condition, V c <I L *R ses phenomenon, according to the charge and discharge can get the output voltage and frequency relationship, such as formula (1).

[0028]

[0029] Where L is the BUCK inductance, △I p is the peak-peak value of BUCK inductance current, T sw is the BUCK cycle, T on is the fixed on time. Formula (2) shows that the output voltage V o is not linearly proportional to the load current, and cannot realize controllable AVP control. When the design is guaranteed to meet V c >I L *R ses always, the expression of the output voltage and the load current is as formula (2).

[0030]

[0031] Under the condition of meeting V c >I L *R ses , the output voltage and the load current of BUCK output are linearly related. Although the output voltage in this expression is not only related to the load current, but also related to the switching frequency, and in the reverse charge COT control, the switching frequency of the system changes under different load currents, and the heavier the load, the higher the corresponding switching frequency. But the switching frequency changes less than 2 times in the full load range, and the amplitude of the change is reduced by A V *H f , so the output voltage change caused by the frequency is within 5mV-10mV in the full load range. The influence of frequency can be offset by compensating a fixed offset voltage to the reference. At the same time, the current information with BUCK AC and overall output current DC is obtained as the AVP window design by means of the estimated current of BUCK and the relationship between BUCK and LLC output current in Sigma structure, and the corresponding expression is as formula (3)

[0032]

[0033] output voltage V o and reference voltage V RFE The voltage loop compensation output V c , the signal is subtracted from the current signal through the transconductance gm to obtain the charging current I RAMP The charging capacitor C T The charging harmonic signal V RAMP , when V RAMP rises to V TH , the system enters the conduction phase, and V RAMP is cleared. The fixed conduction T on time, while T on According to different working conditions, automatic adjustment is carried out to realize that the switching frequency is approximately unchanged under different working conditions. After the conduction ends, the switch tube is turned off, and V RAMP is equal to V TH , the next conduction period is entered. In the light cutting process, if the system switching period is less than the conduction time, the system will be in a long conduction stage until the loop itself adjusts the switching period to be greater than the conduction time. This design is beneficial to improve the response speed of light cutting, but attention should be paid to the fact that the inductance current in the long conduction process cannot exceed the current limiting value of the power tube.

[0034] Figure 2 and Figure 3 is the SIMPLIS simulation output voltage waveform of the constant conduction time control method with adaptive voltage positioning function of the Sigma converter of the application. The simulation conditions of the system are V in = 48V, V o = 1.8V, F LLC = F buck = 840kHz, L r = 0.243uH, C r = 148nF, N = 20, C in1 = C in2 = 58.8uF, C o = 5.93mF, R esr = 0.1mΩ, R llc = 0.465mΩ, R buck = 3mΩ. Figure 2 is the load transient response waveform of the Buck output current under the condition of 0-100A-0, Figure 3is the load transient response waveform diagram under the condition of 0-100A-0 using total output current. The sampling resistance of the two controls is 8.8mΩ, and the total output current is used as the control under the AVP input. Compared with the control under the input of BUCK, in the light-to-heavy process, the undershoot voltage is reduced from 30mV to 0, and the corresponding response time is reduced from 41us to 20us; in the heavy-to-light process, the overshoot voltage is reduced from 33mV to 6.5mV, and the corresponding response time is reduced from 42us to 22us. Therefore, compared with the control of the total output current as the AVP window, the control of the BUCK output current as the AVP window has obvious improvement in dynamic response performance.

[0035] The above is a further detailed description of the present application in combination with the drawings, and it cannot be considered that the specific implementation of the present application is limited to these descriptions. The above is only a preferred embodiment of the present application. Any modification, equivalent replacement, improvement, etc. made by those skilled in the art without departing from the principles of the present application shall be included in the protection scope of the present application.

Claims

1. An adaptive voltage positioning constant conduction time control method for a quasi-parallel converter, characterized in that, The average output current of the BUCK and LLC is obtained by current sampling, that is, the load current of the Sigma output; the voltage loop compensation output Vc is obtained by the differential amplification circuit of the output voltage Vo and the reference voltage VRFE, the voltage loop compensation output Vc is subtracted from the current signal to obtain the charging current IRAMP for charging the capacitor CT to form the harmonic signal VRAMP, when VRAMP rises to VTH, the system enters the conduction stage, and VRAMP is cleared at the same time; the fixed conduction Ton time is automatically adjusted under different working conditions, so that the switching frequency is approximately kept unchanged under different working conditions; after the conduction ends, the switch tube is turned off, and the next conduction period is entered again when VRAMP is equal to VTH; in the light cutting process, if the system switching period is less than the conduction time, the system will be in a long conduction stage until the switching period is greater than the conduction time after the loop is adjusted; this method is beneficial to improving the response speed of light cutting, but attention should be paid to that the inductance current in the long conduction process should not exceed the current limiting value of the power tube; The quasi-parallel converter adopts a Sigma converter, the Sigma converter includes an LLC resonant converter for delivering large power to a load and a Buck converter for adjusting an output voltage; the control method adopts a control system including a set pulse VTR signal generation module and an opening time Ton generation module; The set pulse VTR signal generation module is an integral module of constant on-time control COT, an error signal Vc is obtained by amplifying the difference between an output voltage Vo and a reference voltage VREF by an amplification coefficient Hv of an operational amplifier, the difference between Vc and an inductance current ILx and an equivalent sampling resistor Rses is converted into a current by a transconductance gm amplifier, and then the current is used to charge a capacitor to obtain a capacitor voltage VRAMP ramp signal, a set pulse VTR is generated by comparing a threshold voltage VTH and the VRAMP voltage, and determines the conduction time of a switch tube; The Ton generation module: the Ton signal is generated by comparing a capacitor voltage VCAP and a reference voltage VREF, VCAP is generated by charging a capacitor by a controlled current source controlled by an input voltage Vin, and a reset signal of the VCAP voltage is completed by a reset signal VT, and the VT signal is a function of the VTR signal and the inverse duty cycle signal (D_B).

2. The adaptive voltage positioning constant-frequency-time control method of a quasi-parallel converter according to claim 1, characterized in that, The control method has an effective output voltage precision window, the stable output voltage is high under light load conditions, and the stable output voltage is low under heavy load conditions; the output voltage and the load current output by the BUCK converter are linearly related under the condition of Vc>IL*Rses; under different load currents, the switching frequency of the system changes, and the heavier the load, the higher the corresponding switching frequency.

3. The adaptive voltage positioning constant-frequency-time control method of a quasi-parallel converter according to claim 2, characterized in that, The switch frequency has a change, which means that the switch frequency changes less than 2 times in the full load range, and the output voltage change caused by the frequency is within 5mV-10mV in the full load range; the influence caused by the frequency is offset by compensating a fixed offset voltage to the reference; and the current information with BUCK alternating current and overall output current direct current is obtained as the AVP window by means of the current estimated by the BUCK and the proportion relationship of the BUCK and LLC output currents in the Sigma structure.

4. The adaptive voltage positioning constant-frequency-time control method of a quasi-parallel converter according to claim 3, characterized in that, The BUCK and LLC output currents obtain the average output currents of the BUCK and LLC, i.e. the load currents of the Sigma, through current sampling; the output voltage Vo and the reference voltage VRFE obtain the voltage loop compensation output Vc through a differential amplification circuit, the signal is subtracted from the current signal to obtain the charging current IRAMP of the charging capacitor CT through the transconductance gm to form the harmonic signal VRAMP, when VRAMP rises to VTH, the system enters the conduction stage, and VRAMP is cleared at the same time; the fixed conduction Ton time is automatically adjusted under different working conditions, so that the switch frequency is approximately kept unchanged under different working conditions; after the conduction ends, the switch tube is turned off, and the next conduction period is entered again when VRAMP is equal to VTH; in the light cutting heavy process, if the system switch period is less than the conduction time, the system will be in a long conduction stage until the loop is self-regulated and the switch period is greater than the conduction time; this design is beneficial to improve the response speed of light cutting heavy, but attention should be paid to that the inductance current in the long conduction process in the actual working process should not exceed the current limiting value of the power tube.

Images