CN103107686B - Switch converter two-edge pulse frequency modulation C-type control method and device thereof - Google Patents

Abstract

The invention discloses a switching converter double-edge pulse frequency modulation C-type control method and its device, according to the relationship between the control voltage _Vc generated after the reference voltage _Vref and the output voltage _Vos pass through the error compensator and the inductor current _Is , combined with the preset constant on-time or constant off-time, generate three periods of time t ₁ , t ₂ and t ₃ , each cycle adopts the control sequence composed of t ₁ , t ₂ and t ₃ to control the switching converter Switching on and off. The present invention can be used to control switching converters with various topological structures such as Buck converters, Boost converters, Buck-Boost converters, Cuk converters, SEPIC converters, and Zeta converters. Its advantages are: fast transient response speed, High precision of voltage regulation, good stability, low electromagnetic noise, strong anti-interference ability, wide application range, and current limiting function.

Description

Double edge pulse frequency modulation C-type control method and device for switching converter

technical field

The invention relates to power electronic equipment, in particular to a control method and device for a switching converter.

Background technique

With the continuous development of power electronic devices and the continuous updating of power electronic converter technology, switching power supply technology, as an important field of power electronics, has received more and more attention and research. The switching power supply is mainly composed of two parts: a switching converter and a control circuit. The switching converter is also called the power main circuit, and mainly has various topologies such as buck, boost, buck-boost, forward, flyback, half-bridge, and full-bridge. The control circuit is used to monitor the working state of the switching converter, and generate a control pulse signal to control the switching tube of the switching converter, and adjust the energy supplied to the load to stabilize the output. For the same switching converter, converters using different control methods have different transient performance, steady-state performance, voltage regulation accuracy, protection functions (overvoltage, undervoltage, overcurrent, etc.), stability and other indicators.

The traditional pulse width modulation (PWM) voltage-type control is one of the common switching converter control methods. Its control idea is: the error signal obtained by comparing the converter output voltage with the reference voltage is compensated by the error amplifier to generate a control voltage. The control voltage is compared with the fixed-frequency sawtooth wave to obtain high-level and low-level pulse control signals, and then the drive circuit controls the switching on and off of the switching tube to realize the adjustment of the output voltage of the switching converter. The traditional PWM modulation voltage control method is simple to implement, but because it uses a fixed-frequency sawtooth wave as the modulation wave, it has the disadvantages of slow input transient response and slow load transient response, so it is difficult to apply to applications that require fast transient response speed. occasions. Compared with PWM modulation voltage-type control, current-mode control has faster load and input transient response speed, improves the accuracy of output voltage regulation, and because of its own current limiting function, it is easy to realize the overcurrent of the converter Protection, when multiple power supplies are connected in parallel, it is easier to achieve current sharing. However, the traditional current-mode control method (peak current control) will generate sub-harmonic oscillation when the duty cycle is greater than 0.5, which seriously affects the stability of the converter. Constant on-time modulation current mode control is one of the pulse frequency modulation (PFM) current mode control methods of switching converters. After the on-time, the switch tube is turned off, and the inductor current drops. When it drops to the control signal, the switch tube is turned on again to start a new switching cycle. Compared with the peak current control method, the switching converter adopting the PFM modulation current mode control method has good stability performance, and there will be no sub-harmonic oscillation problem when the duty cycle is greater than 0.5.

Contents of the invention

The object of the present invention is to provide a control method for a switching converter, which has good transient performance and steady-state performance at the same time, and is suitable for switching converters with various topological structures.

The technical solution adopted by the present invention to realize its object of the invention is: the switching converter dual-edge pulse frequency modulation C-type control method detects the inductance current and the output voltage at the beginning moment of a sampling pulse signal CLK, and the output voltage value V _os of the detection is and the voltage reference value V _ref are sent to the error compensator to generate the control voltage V _c , and the detected inductor current I _s and the control voltage V _c are simultaneously sent to the time operation unit, combined with the preset constant on-time or constant off-time, The operation generates three periods of time t ₁ , t ₂ and t ₃ , and each cycle adopts the control sequence composed of t ₁ , t ₂ and t ₃ in turn to control the switching on and off of the switching tube of the switching converter.

In the switching converter double edge pulse frequency modulation C-type control method described in the present invention, there are two ways to generate the three periods t ₁ , t ₂ and t ₃ :

①Preset a constant on-time T _ON , if t ₁ and t ₃ are on-time and satisfy t ₁ +t ₃ =T _ON , then t ₂ is off-time; if t ₂ is on-time and satisfy t ₂ =T _ON , then t ₁ and t ₃ are the turn-off time; the turn-off time is determined by K ₁ (I _s -V _c )+K ₂ T _ON , and K ₁ and K ₂ are two related to the inductor current ripple coefficient.

②Preset a constant off time T _OFF , if t ₁ and t ₃ are the off time and satisfy t ₁ +t ₃ =T _OFF , then t ₂ is the on time; if t ₂ is the off time and satisfy t ₂ =T _OFF , then t ₁ and t ₃ are the conduction time; the conduction time is determined by K ₃ (V _c -I _s )+K ₄ T _OFF , and K ₃ and K ₄ are two related to the inductor current ripple coefficient.

Compared with prior art, the beneficial effect of the present invention is:

1. Compared with the existing PWM-modulated voltage-type control switching converter, the switching converter of the present invention can quickly adjust the length of on or off time of the switching tube of the switching converter when the load and input voltage change, The overshoot of output voltage and inductor current is small, which improves the transient performance of the converter and has a current limiting function.

2. Compared with the existing PFM modulation voltage type control switching converter, the switching converter of the present invention has high voltage stabilization accuracy, good steady-state performance, low electromagnetic noise, strong anti-interference ability, and has a current limiting function.

3. Compared with the existing peak current control switching converter, the switching converter of the present invention does not generate sub-harmonic oscillation when the duty ratio is greater than 0.5, has good system stability, and does not need slope compensation.

4. Compared with the existing PFM modulation current control switching converter, when the switching converter of the present invention changes in a large load range, the transient overshoot of output voltage and inductor current is small, the adjustment time is short, and the transient performance is good .

5. Compared with the existing PWM or PFM modulation ^V2 type control switching converter, the switching converter of the present invention does not depend on the equivalent series resistance of the output capacitor, can work normally when the output voltage is low ripple, and is anti-interference Strong capacity, good stability, and current limiting function.

Another object of the present invention is to provide a device for realizing the above-mentioned double edge pulse frequency modulation C-type control method of the switching converter. Wave generator SG, double edge pulse modulator DPM and drive circuit DR, including: voltage detection circuit VS, error compensator EC, time operation unit TU, variable frequency sawtooth wave generator SG, double edge pulse modulator DPM, drive circuit DR is connected in sequence; the current detection circuit CS, the time operation unit TU, and the double edge pulse modulator DPM are connected in sequence; the frequency conversion sawtooth wave generator SG is connected to the error compensator EC; the frequency conversion sawtooth wave generator SG is connected to the voltage detection circuit VS; The sawtooth generator SG is connected to the current detection circuit CS.

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

Description of drawings

FIG. 1 is a signal flow chart of a method according to Embodiment 1 of the present invention.

FIG. 2 is a block diagram of the circuit structure of Embodiment 1 of the present invention.

3 is a schematic diagram of the relationship among the inductor current, the control voltage V _c , the time t ₁ , the time t ₂ , the time t ₃ , the sampling pulse signal CLK and the driving signal in the first embodiment of the present invention.

FIG. 4 is a time-domain simulation waveform diagram of the output voltage of the switching converter under steady-state conditions according to Embodiment 1 of the present invention and a traditional peak current control switching converter.

FIG. 5 is a time-domain simulation waveform diagram of the inductor current in the steady-state condition of the first embodiment of the present invention and the conventional peak current control switching converter.

6 is a time-domain simulation waveform diagram of the output voltage of the switching converter under the first embodiment of the present invention and the traditional PWM modulation voltage type control when the load changes suddenly.

FIG. 7 is a time-domain simulation waveform diagram of the inductor current when the load changes suddenly in the switching converter of the embodiment 1 of the present invention and the traditional PWM modulation voltage type control.

FIG. 8 is a block diagram of the circuit structure of Embodiment 2 of the present invention.

9 is a schematic diagram of the relationship between the inductor current, the control voltage V _c , the time t ₁ , the time t ₂ , the time t ₃ , the sampling pulse signal CLK and the driving signal in the second embodiment of the present invention.

FIG. 10 is a block diagram of the circuit structure of the third embodiment of the present invention.

In FIG. 4 : a is the output voltage waveform of the traditional peak current control switching converter in the steady state; b is the output voltage waveform in the steady state of Embodiment 1 of the present invention.

In FIG. 5 : a is the inductor current waveform of the traditional peak current control switching converter in the steady state; b is the inductor current waveform in the steady state of Embodiment 1 of the present invention.

In FIG. 6 : a is the output voltage waveform of the traditional PWM modulation voltage-type control switching converter when the load changes suddenly; b is the output voltage waveform when the load changes in Embodiment 1 of the present invention.

In FIG. 7 : a is the inductor current waveform of a traditional PWM modulation voltage-type control switching converter when the load changes suddenly; b is the inductor current waveform when the load changes in Embodiment 1 of the present invention.

Detailed ways

The present invention will be further described in detail through specific examples and in conjunction with the accompanying drawings.

Embodiment one

Figure 1 shows that a specific embodiment of the present invention is: a switching converter double edge pulse frequency modulation C-type control method and its device C-PFM, the C-PFM device is mainly composed of a voltage detection circuit VS, a current detection circuit CS , error compensator EC, time operation unit TU, variable frequency sawtooth wave generator SG, double edge pulse modulator DPM and drive circuit DR. The voltage detection circuit VS is used to obtain the output voltage value V _os , the current detection circuit CS is used to obtain the inductor current value I _s , the error compensator EC is used to generate the control voltage V _c , and the time operation unit TU is used to generate three periods of time t _{1 . _ _ _ _ _} The control pulse signal of the control circuit DR controls the turn-on and turn-off of the switching tube of the switching converter TD.

This example adopts the device in Figure 2, which can realize the above-mentioned control method conveniently and quickly. Fig. 2 shows that the device of the double-edge pulse frequency modulation C-type control method of the switching converter in this example is composed of the converter TD and the control device C-PFM of the switching tube S. 3 is a schematic diagram of the relationship among the inductor current, the control voltage V _c , the time t ₁ , the time t ₂ , the time t ₃ , the sampling pulse signal CLK and the driving signal.

Its work process and principle of the device of this example are:

The working process and principle of the control device C-PFM using double-edge pulse frequency modulation C-type control are as follows: Figure 2 and Figure 3 show that the switch tube is turned on at the beginning of any sampling pulse signal CLK, and the sampling pulse signal CLK is determined by The frequency conversion sawtooth wave generator SG generates; at the same time, the voltage detection circuit VS detects the output voltage of the converter TD to obtain the output voltage value V _os , and the current detection circuit CS detects the inductor current of the converter TD to obtain the inductor current value I _s , and outputs The voltage value V _os is sent to the error compensator EC together with the reference voltage V _ref to generate the control voltage V _c . A constant on-time T _ON is preset, t ₁ and t ₃ are both on-time and satisfy t ₁ +t ₃ =T _ON , then t ₂ is off-time. In the time operation unit TU, t ₂ =K ₁ (I _s -V _c )+K ₂ T _ON can be calculated, where K ₁ and K ₂ are two coefficients related to the inductor current ripple. The frequency of the frequency-variable sawtooth generator SG is controlled according to time t ₁ , t ₂ , and t ₃ to generate a frequency-variable sawtooth wave V _saw . In the variable frequency sawtooth wave generator SG, a small constant is compared with the sawtooth wave V _saw , and the sampling pulse signal CLK is generated according to the comparison result, which is used to determine the switching period, sampling output voltage, sampling inductor current and control error compensator EC. In the double-edge pulse modulator DPM, the sawtooth wave V _saw , time t ₁ , and time t ₂ are compared, and according to the comparison results, turn-on (t ₁ ), turn-off (t ₂ ), and turn-on (t ₃ ) are generated. The control pulse signal controls the turn-on and turn-off of the switch tube S of the converter TD via the drive circuit DR.

In this example, the control pulses of the switching tube S with the time sequence of t ₁ , t ₂ , and t ₃ are generated in the double-edge pulse modulator DPM. The specific generation method is: at the beginning of each cycle, the switching tube S is turned on, and the diode When D is turned off, the inductor current starts to rise from the initial value; the switch tube S is turned off after the on-time t ₁ , and the diode D is turned on at the same time, and the inductor current starts to drop immediately. After the turn-off time _t2 , the double-edge pulse modulator DPM changes the control pulse from low level to high level, the switch tube S is turned on again, and the diode D is turned off again. After the switch tube S is turned on for _t3 , the current The cycle ends.

The converter TD in this example is a Buck converter.

Use Matlab/Simulink software to carry out time domain simulation analysis on the method of this example, the results are as follows.

Fig. 4 is a time-domain simulation waveform diagram of the output voltage of the switching converter adopting the traditional peak current control and the present invention under steady state conditions, sub-graphs a and b respectively correspond to the traditional peak current control and the present invention. Fig. 5 is a time-domain simulation waveform diagram of the inductor current under steady-state conditions for a switching converter adopting traditional peak current control and the present invention, and sub-graphs a and b respectively correspond to the traditional peak current control and the present invention. It can be seen from Figure 4 and Figure 5 that the output voltage of the switching converter using traditional peak current control (switching frequency is 50KHz) fluctuates at 3V, the inductor current fluctuates at 1.5A, and the converter has sub-harmonic oscillation. Both the output voltage and the inductance are unstable, while the average output voltage and the average inductance current of the present invention are stable at 3V and 1.5A. It can be seen that adopting the present invention has better stability performance. The simulation conditions of Figure 4 and Figure 5: input voltage V _in =5V, voltage reference value V _ref =3V, inductance L=20μH, capacitance C=1420μF (its equivalent series resistance is 30mΩ), load current I _o =1.5A ; Constant on-time T _ON =12 μs, t ₁ =t ₃ =6 μs; coefficient K ₁ =6.67*10 ⁻⁶ , coefficient K ₂ =2/3.

Fig. 6 is a time-domain simulation waveform diagram of the output voltage of the switching converter adopting the traditional PWM modulation voltage control and the present invention when the load changes suddenly, and sub-graphs a and b respectively correspond to the traditional PWM modulation voltage control and the present invention. Fig. 7 is a time-domain simulation waveform diagram of the inductor current when the load changes suddenly using the traditional PWM modulation voltage type control and the switching converter of the present invention, sub-graphs a and b respectively correspond to the traditional PWM modulation voltage type control and the present invention. In Fig. 6 and Fig. 7, the load changes step by step from 1A to 10A in 6ms, adopts traditional PWM modulation voltage control (switching frequency is 50KHz), enters a new steady state after about 1.82ms, and the peak-to-peak output voltage fluctuates 654mV, The peak-to-peak value fluctuation of the inductor current is 15.53A; while the adjustment time for the switching converter of the present invention to enter a new steady state is 1.76ms, the peak-to-peak value fluctuation of the output voltage is 421mV, and the peak-to-peak value of the inductor current is 11.07A. It can be seen that the output voltage and inductor current transient overshoot of the switching converter of the present invention is small, the adjustment time is short, and the load transient performance is good. Simulation conditions of Fig. 6 and Fig. 7: voltage reference value V _ref =1.5V, coefficient K ₁ =1.33*10 ^-5 , coefficient K ₂ =7/3, constant on-time T _ON =6μs, t ₁ =t ₃ =3μs, other parameters are consistent with those shown in Figure 4 and Figure 5.

Embodiment two

Fig. 8 shows that the converter TD controlled in this example is a Boost converter, and the control device of the switching tube S adopts C-PFM. 9 is a schematic diagram of the relationship between the inductor current, the control voltage V _c , the time t ₁ , the time t ₂ , the time t ₃ , the sampling pulse signal CLK and the driving signal in the second embodiment of the present invention.

The specific working process and principle are as follows: Fig. 8 and Fig. 9 show that the switching tube is turned off at the beginning of any sampling pulse signal CLK, and at the same time, the voltage detection circuit VS detects the output voltage of the converter TD to obtain the output voltage value V _os , the current detection circuit CS detects the inductor current of the converter TD to obtain the inductor current value I _s , and sends the output voltage value V _os and the reference voltage V _ref to the error compensator EC to generate the control voltage V _c . A constant off time T _OFF is preset, t ₁ and t ₃ are both off time and satisfy t ₁ +t ₃ =T _OFF , then t ₂ is on time. In the time operation unit TU, t ₂ =K ₃ (V _c -I _s )+K ₄ T _OFF can be calculated, where K ₃ and K ₄ are two coefficients related to the inductor current ripple. The frequency of the frequency-variable sawtooth generator SG is controlled according to time t ₁ , t ₂ , and t ₃ to generate a frequency-variable sawtooth wave V _saw . In the variable frequency sawtooth wave generator SG, a small constant is compared with the sawtooth wave V _saw , and the sampling pulse signal CLK is generated according to the comparison result, which is used to determine the switching period, sample the output voltage, sample the inductor current, and control the error compensator EC. In the double-edge pulse modulator DPM, the sawtooth wave V _saw , time t ₁ , and time t ₂ are compared, and according to the comparison results, turn-off (t ₁ ), turn-on (t ₂ ), and turn-off (t ₃ ) are generated. The control pulse signal, through the driving circuit DR, controls the switching off and on of the switching tube S of the converter TD.

It is also proved by simulation that the Boost converter of the present invention has stable output voltage, high steady-state precision and good load transient performance.

Embodiment three

As shown in FIG. 10 , this example is basically the same as the first example, except that the converter TD controlled in this example is a Buck-Boost converter.

The inventive method can also be used for Cuk converter, SEPIC converter, Zeta converter, forward converter, flyback converter, push-pull converter, half-bridge converter except being applicable to the switching converter in the above embodiment. , full-bridge converter and other circuit topologies.

Claims (1)

1. A switching converter double-edge pulse frequency modulation C-type control method is characterized in that: detect inductor current and output voltage at the beginning moment of a sampling pulse signal CLK, output voltage value V _os and voltage reference value V of detection _ref is sent to the error compensator to generate the control voltage _Vc , and the detected inductor current _Is and the control voltage _Vc are sent to the time operation unit at the same time, combined with the preset constant on-time or constant off-time, the operation generates three periods of time t ₁ , t ₂ and t ₃ , each cycle adopts the control sequence composed of t ₁ , t ₂ and t ₃ in turn to control the switching on and off of the switching tube of the switching converter; the three periods t ₁ , t ₂ and t ₃ is generated in one of two ways: A): Preset a constant on-time T _ON , if t ₁ and t ₃ are on-time and satisfy t ₁ +t ₃ = T _ON , then t ₂ is off-time; if t ₂ is on-time and Satisfy t ₂ ＝T _ON , then t ₁ and t ₃ are the off time; the off time is determined by K ₁ (I _s -V _c )+K ₂ T _ON , K ₁ and K ₂ are two and the inductor current ripple coefficient of wave correlation; B): preset a constant off time T _OFF , if t ₁ and t ₃ are off time and satisfy t ₁ +t ₃ = T _OFF , then t ₂ is on time; if t ₂ is off time and Satisfy t ₂ ＝ T _OFF , then t ₁ and t ₃ are the conduction time; the conduction time is determined by K ₃ (V _c -I _s )+K ₄ T _OFF , K ₃ and K ₄ are two and the inductor current ripple Coefficient of wave correlation.