Four-pipe Buck-Boost PFC converter control method and control circuit
Technical Field
The invention belongs to the technical field of power converters, and particularly relates to a four-pipe Buck-Boost PFC converter control method and a control circuit.
Background
In the daily life and industrial fields, electric energy is usually obtained from an alternating current power grid, and many electric equipment needs to be supplied with direct current, so that the AC-DC converter is widely applied to occasions such as LED illumination power supplies, communication power supplies, storage battery chargers and direct current motor power supplies. The traditional AC-DC conversion device generally adopts a circuit structure of a rectifier bridge and a filter capacitor, and the circuit structure has the advantages of simple structure and lower cost, but the input current distortion is serious, and a larger phase difference exists between the input current distortion and the input voltage, so that the power factor is lower. The power factor is too low to cause adverse effects on the power grid, and the power factor is specifically characterized in that 1) the utilization rate of a generator and a transformer is reduced, the power supply cost is increased, 2) the effective value of the power grid current is increased, the transmission loss of a line is correspondingly increased, and 3) the input current harmonic wave generates voltage drop on the impedance of the line, so that the power grid voltage is distorted, namely a secondary effect.
In order to increase the power factor of powered devices, power Factor Correction (PFC) techniques are required. PFC technology can be classified into passive PFC and active PFC depending on whether or not active components such as switching transistors are used. The passive PFC circuit adopts elements such as an inductor, a capacitor, a diode and the like to form a passive network so as to correct an input current waveform, has simple structure, high reliability and lower cost, but has limited improvement on a power factor, cannot adjust an output voltage, has larger fluctuation along with the change of the input voltage and a load, and has poor power supply quality. In an active PFC converter, the input current of the Buck PFC converter has a dead zone and thus a low power factor. The input current of the Boost PFC converter has no dead zone, can realize the unit power factor, but can only be applied to occasions of high-voltage output. Compared with the two, the Buck-Boost PFC converter has no input current dead zone, and can flexibly select output voltage, however, the polarity of the output voltage is negative, the voltage stress of the power tube is higher, and the voltage stress is the sum of the peak value of the input voltage and the output voltage. A pair of switching tubes and diodes are added in the Buck-Boost PFC converter, so that the double-tube Buck-Boost PFC converter can be obtained, and the voltage stress of the power tube is reduced while the advantages of the Buck-Boost PFC converter are maintained. However, due to unidirectional conductivity of the diode, the inductor current in the double-tube Buck-Boost PFC converter can only flow unidirectionally, and Zero Voltage Switching (ZVS) of the switching tube cannot be realized. Two diodes in the double-tube Buck-Boost PFC converter are replaced by synchronous rectifying tubes, so that the four-tube Buck-Boost PFC converter can be obtained. In the four-tube Buck-Boost PFC converter, inductive current can flow in two directions, so that ZVS of all switching tubes can be realized, and a PWM (pulse width modulation) plus phase shift control mode can be adopted for the four-tube Buck-Boost converter, so that ZVS of all switching tubes and minimum pulse of inductive current can be realized.
When the four-tube Buck-Boost converter is applied to the PFC converter, the input voltage and the input current of the four-tube Buck-Boost converter are both rectified sine waves, the variation range is wide, and the four-tube Buck-Boost converter is different from the working mode and the design method of the DC-DC converter. Therefore, aiming at the characteristics of the four-tube Buck-Boost PFC converter based on the wide range change of the input voltage and the input current, the problem to be solved by a researcher in the field is to find a simple and feasible control scheme by combining the control thought of the four-tube Buck-Boost converter.
Disclosure of Invention
Aiming at the defects of the prior art, the invention provides a four-tube Buck-Boost PFC converter control method and a control circuit, which fully consider the characteristic of wide-range change of the input voltage and the input current of the converter, can realize power factor correction and realize the optimal working modes of PCRM and PDCM.
In order to achieve the technical purpose, the invention adopts the following technical scheme:
A four-tube Buck-Boost PFC converter control method comprises four switching tubes Q 1、Q2、Q3、Q4, a filter inductor L c, an output filter capacitor C o, a rectifier bridge capacitor C g and a diode rectifier bridge connected with an input voltage source v in, wherein Q 1 and Q 2 are complementarily conducted to form a bridge arm unit, Q 3 and Q 4 are complementarily conducted to form a bridge arm unit, two ends of L c are respectively connected with the midpoint of the bridge arm unit of Q 1、Q2 and the midpoint of the bridge arm unit of Q 3、Q4, C o is connected with the bridge arm unit of Q 3、Q4 in parallel, the diode rectifier bridge is, c g is connected with the bridge arm unit of Q 1、Q2 in parallel, and the voltages at two ends of C o、Cg are respectively output voltage v o and input voltage v g, and the control method comprises the following steps:
Step 1, sampling V o and V g, obtaining an error of an output voltage sampling signal V o_s, an input voltage sampling signal V g_s,vo_s and a reference signal V o_ref, amplifying the error by an output voltage regulator to obtain a signal V c, and multiplying the signal V c by V g_s to obtain an input current reference signal i g_ref;
Step 2, sampling input current i g to obtain an input current sampling signal i g_s,ig_s and i g_ref, comparing the input current sampling signal i g_s,ig_s with the input current sampling signal i g_ref, performing closed-loop adjustment through an input current regulator to enable the input current to follow a reference to obtain a duty ratio D y1 of Q 1 so as to control the switching action of a switching tube Q 1, wherein an inverted signal of the duty ratio D y1 is used for controlling the switching action of the switching tube Q 2;
Step 3, sampling the inductance current I Lc of the L c, comparing with the negative current reference-I ZVS required by the soft switch, and turning off the switching tube Q 3 when the I Lc linearly drops to-I ZVS to obtain the duty ratio 1-D y2 of the Q 3 so as to control the switching action of the switching tube Q 3, wherein the inverse signal is used for controlling the switching action of the switching tube Q 4;
Step 4, under PDCM, approximately calculating a phase shift angle D θ_PCRM of the phase difference between the two switching-on moments of the Q 1、Q3 according to v g、ig_ref, approximately calculating a phase shift angle D θ_PDCM of the phase difference between the two switching-on moments of the switching tube Q 1、Q3 according to v o and v g、Dy1, and sending D θ_PCRM and D θ_PDCM into a diode gating circuit to obtain larger values of the two values as a phase shift duty ratio D θ so as to control the phase difference between the switching tube Q 1 and the switching-on moment of the switching tube Q 3.
In order to optimize the technical scheme, the specific measures adopted further comprise:
The step 4 mentioned above, the D θ_PCRM is:
Dθ_PCRM=Kvgvg+Kigig_ref+Dθ_PCRM_dc
Wherein, K vg、Kig and D θ_PCRM_dc are both constants.
The step 4 mentioned above, the D θ_PDCM is:
wherein, the expression of D c_max is:
Dc_max=2LcIZVS/(VoTs)
Wherein, L c is the inductance value of the filter inductance L c;
t s is the switching period duration of the switching tube;
I ZVS is the minimum current value to achieve soft switching;
D c_max is the maximum value of the duty cycle corresponding to the time the inductor current rises from-I ZVS to I ZVS or falls from I ZVS to-I ZVS.
I ZVS is the magnitude of positive current required to realize the soft switching of the switching tubes Q 2 and Q 3, ensuring that the inductor current is positive before the switching tube is turned on, discharging the junction capacitance of the switching tube to zero to reverse the junction capacitance and naturally conducting the diode.
A four-pipe Buck-Boost PFC converter control circuit comprises an input current reference signal generating circuit, Q 1 and Q 2 driving signal generating circuits, Q 3 and Q 4 driving signal generating circuits and a phase-shifting signal generating circuit;
an input current reference signal generating circuit for generating input current reference signals i g_ref;Q1 and Q 2 using an output voltage regulator, a multiplier, for generating drive signals of Q 1 and Q 2 using an input current regulator, a comparator, a clock signal CLK1, a 1# rs flip-flop, a Q 3 and Q 4 drive signal generating circuit for generating drive signals of Q 3 and Q 4 using a hysteresis comparator, an or gate, CLK1, a clock signal CLK2, a 2# rs flip-flop, and a phase shift signal generating circuit for generating a clock signal CLK2 using a subtractor, a multiplier Mult2, an adder, a diode gating circuit, a comparator, and a monostable circuit, which phase-shift duty ratio D θ corresponds to a phase difference of CLK 1.
The output voltage regulator includes an operational amplifier EA1 and its peripheral circuits, and is configured to amplify an error between the output voltage sampling signal V o_s and the reference signal V o_ref, and after the output signal V c of EA1 and the input voltage sampling signal V g_s are multiplied by a multiplier, waveforms of the input current reference signals i g_ref,ig_ref and V g are the same.
The input current regulator includes an operational amplifier EA2 and its peripheral circuit, amplifies the error between the input current sampling signal i g_s and the reference signal i g_ref, and after the output signal V error of EA2 and the sawtooth wave V saw are compared by a comparator, they are sent to a 1#rs trigger together with CLK1 to generate driving signals of Q 1 and Q 2, the sawtooth wave V saw is synchronous with CLK1, the amplitude of V saw is denoted as V M, and the duty ratio D y1 of Q 1 is:
In the above-mentioned Q 3 and Q 4 driving signal generating circuits, I Lc and-I ZVS are sent to the hysteresis comparator Comp2, or the gate performs an or operation on the output signals v comp and CLK1 of the hysteresis comparator, when I Lc falls to-I ZVS, v comp is high, Q 3off generated by the or gate is also high, Q 3off is sent to the reset terminal of the 2#rs flip-flop, so that Q 3 is turned off, if I Lc fails to fall to-I ZVS at the end of the switching period, when CLK1 is high, Q 2 and Q 3 are turned off simultaneously, and the turn-on time of Q 3 is determined by CLK 2.
In the above phase-shift signal generating circuit, the subtracter includes EA3 and its peripheral circuit, the adder includes EA4 and its peripheral circuit, under PDCM, the sampled signals v g_s and v o_s are sent to the subtracter, and then the y input signal y Mult2,yMult2 of Mult2 is generated after diode clamping, multiplied by v error and divided by v o_s, and then added with D c_maxVM by the adder, to obtain the modulated signal v θ_PDCM of D θ_PDCM, which is:
The proportional adder comprises an operational amplifier EA5 and a peripheral circuit thereof, and under PCRM, an input voltage sampling signal V g_s is sent to an inverting input end of the EA5, an input current reference signal i g_ref and a direct current signal V M are sent to a non-inverting input end of the EA5, and finally a modulation signal V θ_PCRM of D θ_PCRM is generated;
v θ_PCRM and v θ_PDCM are compared with a sawtooth wave v saw by a comparator to obtain v θ through a diode gating circuit, and then phase-shifting PWM signal Q θ is generated, the rising edge of the phase-shifting PWM signal corresponds to CLK1, and the duty ratio is D θ, wherein v θ is:
vθ=min[max(vθ_PCRM,vθ_PDCM),verror]
q θ is fed to a monostable whose falling edge produces CLK2, which lags CLK1 by a time D θTs.
The invention has the following beneficial effects:
The invention can realize the control of the four-tube Buck-Boost PFC converter power factor correction and the ZVS of all switching tubes and the minimization of the effective value of the inductance current. Compared with a Boost PFC converter, the invention can realize flexible selection of output voltage by adjusting the duty ratio of the switching tube Q 1. Compared with a double-tube Buck-Boost PFC converter, the invention realizes ZVS of all switching tubes by replacing diodes with switching tubes so that inductive current can flow reversely. The invention uses PWM plus phase shift control mode to realize the minimum of inductance current pulsation and effective value.
Drawings
Fig. 1 is a circuit configuration diagram of a four-tube Buck-Boost PFC converter.
Fig. 2 is an overall block diagram of a four-pipe Buck-Boost PFC converter control circuit according to an embodiment of the present invention.
Fig. 3 is an operational waveform of the inverter of the present invention.
FIG. 4a is a diagram showing experimental waveforms of PCRM mode under 220V full load of the effective input voltage according to the present invention.
FIG. 4b is a diagram showing experimental waveforms of PDCM mode under 220V full load of the effective input voltage according to the present invention.
Fig. 5a is a graph of experimental waveforms for the full load transition of the effective value of the input voltage between 176V and 264V in the present invention.
Fig. 5b is a graph of experimental waveforms for a load jump between 10% and 90% for an effective value of 220V input voltage in the present invention.
Detailed Description
Embodiments of the present invention are described in further detail below with reference to the accompanying drawings.
The invention provides a control method of a four-tube Buck-Boost PFC converter, and fig. 1 is a circuit structure diagram of the four-tube Buck-Boost PFC converter, which mainly comprises four switching tubes Q 1、Q2、Q3、Q4, a filter inductor L c, an output filter capacitor C o, a rectifier bridge capacitor C g and a diode rectifier bridge connected with an input voltage source v in. The switching tube Q 1 and the switching tube Q 2 are complementarily conducted to form a bridge arm unit, and the switching tube Q 3 and the switching tube Q 4 are complementarily conducted to form a bridge arm unit. two ends of the inductor L c are respectively connected with the middle point of the bridge arm of the switching tube Q 1、Q2 and the middle point of the bridge arm of the switching tube Q 3、Q4, and two ends of the output filter capacitor C o are respectively connected with the drain electrode of the switching tube Q 3 and the source electrode of the switching tube Q 4 so as to filter ripple waves of switching frequency. the two ends of the rectifier bridge capacitor C g are respectively connected with the drain electrode of the switching tube Q 1 and the source electrode of the switching tube Q 2, so as to absorb the short-time negative current of i g and ensure that v g is basically unchanged in T s.
The control method comprises three control amounts, namely the duty ratio D y1 of the switch tube Q 1, the duty ratio D y2 of the switch tube Q 4, And a phase shift duty ratio D θ corresponding to the phase difference between the Q 1 and Q 3 on times. The control degree of freedom D y1 is used for controlling the switching action of the switching tube Q 1, the inverse signal of the control degree of freedom D y1 is used for controlling the switching action of the switching tube Q 2, the control degree of freedom D y2 is used for controlling the switching action of the switching tube Q 4, the inverse signal of the control degree of freedom D y1 is used for controlling the switching action of the switching tube Q 3, and the control degree of freedom D θ is used for controlling the phase difference between the switching tube Q 1 and the switching tube Q 3 at the switching-on time. the soft switching of the switching tubes Q 1 and Q 4 is realized, the inductor current needs to be ensured to be over negative before the switching tube is turned on, the junction capacitance of the switching tube is discharged to zero to enable the junction capacitance to be reversely conducted by the diode to be naturally conducted, and the magnitude of negative current needed to be realized is defined as-I ZVS. The soft switching of the switching tubes Q 2 and Q 3 is realized, the inductor current is required to be ensured to be positive before the switching tube is turned on, the junction capacitance of the switching tube is discharged to zero to enable the junction capacitance to be inverted, the diode is naturally conducted, and the size of positive current required to be realized is defined as I ZVS.
The control method specifically comprises the following steps:
Step 1, sampling an output voltage V o and an input voltage V g, amplifying an error of an output voltage sampling signal V o_s and a reference signal V o_ref by an output voltage regulator, and multiplying an output signal V c of the output voltage regulator by the input voltage sampling signal V g_s to obtain an input current reference signal i g_ref;
Step 2, sampling an input current i g, comparing an input current sampling signal i g_s with an input current reference signal i g_ref, and performing closed-loop adjustment on the input current to follow a reference through an input current regulator to obtain a duty ratio D y1 of a switching tube Q 1;
Step 3, sampling an inductive current I Lc, comparing the inductive current I Lc with a negative current reference-I ZVS required by soft switching, and turning off a switching tube Q 3 when I Lc linearly drops to-I ZVS to obtain a duty ratio 1-D y2 of the switching tube Q 3;
Step 4, under PRCM, the theoretical calculation value of the phase shift duty ratio D θ is actually a function of the input voltage v g and the input current i g, and a curved surface of the phase shift duty ratio is approximated by a plane, so that the aim of simplifying control is achieved, and the simplified phase shift duty ratio is a linear combination of an input voltage sampling value and an input current reference signal. Sampling input voltage v g, and approximately calculating a phase shift angle D θ_PCRM of a phase difference between the switching tube Q 1、Q3 and the switching time, namely:
Dθ_PCRM=Kvgvg+Kigig_ref+Dθ_PCRM_dc
Wherein, K vg、Kig and D θ_PCRM_dc are both constants.
At PDCM, the input voltage v g and the output voltage v o are sampled, and the phase shift angle D θ_PDCM of the phase difference between the two switching-on moments of the switching tube Q 1、Q3 is approximately calculated, namely:
wherein, the expression of D c_max is:
Dc_max=2LcIZVS/(VoTs)
In order to ensure that i Lc has enough fluctuation to realize ZVS of the switching tube, D θ_PCRM and D θ_PDCM are sent into a diode gating circuit to obtain larger values of the two, namely the phase-shifting duty ratio D θ.
In addition, the invention also provides a four-pipe Buck-Boost PFC converter control circuit, an analog control circuit is adopted as an example in the embodiment of the invention, a schematic diagram of the control circuit is shown in figure 2, and the control circuit mainly comprises four components, namely an input current reference signal generating circuit, Q 1 and Q 2 driving signal generating circuits, Q 3 and Q 4 driving signal generating circuits and a phase-shifting signal generating circuit.
(A) Input current reference signal generating circuit
The input current reference signal generating circuit is used for obtaining an input current reference signal i g_ref. The operational amplifier EA1 and its peripheral circuits constitute an output voltage regulator that amplifies the error of the output voltage sample signal V o_s and the reference signal V o_ref. The output signal v c of EA1 is multiplied by the input voltage sampling signal v g_s to obtain the input current reference signal i g_ref. At steady state, v c remains substantially unchanged, so the waveforms of i g_ref and v g are identical.
(B) Q 1 and Q 2 drive signal generating circuit
The Q 1 and Q 2 drive signal generation circuits are used to derive the drive signals of Q 1 and Q 2. The operational amplifier EA2 and its peripheral circuits constitute an input current regulator that amplifies the error of the input current sample signal i g_s and the reference signal i g_ref. After the output signal v error of EA2 is compared with sawtooth v saw, it is then fed into the 1#RS flip-flop along with CLK1 to generate the drive signals for Q 1 and Q 2. V saw is synchronized with CLK1, and the amplitude of V saw is denoted as V M, the duty cycle D y1 of Q 1 is:
(C) Q 3 and Q 4 drive signal generating circuit
The Q 3 and Q 4 drive signal generation circuits are used to derive the drive signals of Q 3 and Q 4. Q 3 needs to be turned off when I Lc falls to-I ZVS and cannot be turned off later than Q 2 to ensure optimal switching timing. I Lc and-I ZVS are fed into the hysteresis comparator Comp2, and when I Lc falls to-I ZVS, the output signal v comp of the comparator is high, and Q 3off generated by the or gate is also high. Q 3off is fed to the reset terminal of the 2#RS flip-flop, turning Q 3 off. In order to ensure the optimal switching time sequence, CLK1 and v comp are introduced for OR operation. if I Lc fails to fall to-I ZVS at the end of the switching cycle, Q 2 and Q 3 are turned off simultaneously when CLK1 is high. The turn-on time of Q 3 is determined by CLK 2.
(D) Phase-shift signal generating circuit
The phase-shifted signal generating circuit is used to obtain the clock signal CLK2, which has a phase-shifted duty cycle D θ corresponding to the phase difference of CLK 1. In different modes, D θ has different expressions, and the analysis is performed separately below.
At PCRM, an operational amplifier EA5 and its peripheral circuitry are used to form a proportional adder. Input voltage sample signal V g_s is fed to the inverting input of EA5, input current reference signal i g_ref and dc signal V M are fed to the non-inverting input of EA5, ultimately producing modulated signal V θ_PCRM of D θ_PCRM.
At PDCM, the computation circuit of v θ_PDCM consists of subtractor (EA 3 and its peripheral circuits), multiplier Mult2, and adder (EA 4 and its peripheral circuits). The sampled signals v g_s and v o_s are sent to a subtracter, then are clamped by a diode to generate a y input signal of Mult2, y Mult2 is multiplied by v error and divided by v o_s, and then added with D c_maxVM, so that a modulated signal v θ_PDCM of D θ_PDCM can be obtained, and the modulated signal v θ_PDCM is:
To ensure that i Lc has sufficient amount of pulsation to achieve ZVS of the switching tube, v θ should take a larger value of v θ_PCRM and v θ_PDCM, but not exceed v error to ensure optimal switching timing, namely:
vθ=min[max(vθ_PCRM,vθ_PDCM),verror]
After v θ is obtained by using a diode gating circuit and is compared with the sawtooth wave v saw, a phase-shifting PWM signal Q θ is generated, the rising edge of the phase-shifting PWM signal Q θ corresponds to CLK1, the duty ratio is D θ.Qθ, the falling edge of the phase-shifting PWM signal Q θ is fed into a monostable circuit, and CLK2 is generated, so that the time of the CLK2 lagging behind the CLK1 is D θTs.
By the control circuit described above, the operation waveforms shown in fig. 3 can be realized.
To further illustrate the advantages of the present control method, an experimental example of the present invention is given below.
According to the parameters of the 500W four-tube Buck-Boost PFC converter shown in the table 1, a principle model machine is built in a laboratory. Fig. 4a and fig. 4b show experimental waveforms of the input voltage with an effective value of 220V under full load, wherein fig. 4a is an experimental waveform of PCRM mode, and fig. 4b is an experimental waveform of PDCM mode, and it can be seen that all switching tubes can realize ZVS and the inductor current pulsation is smaller. Fig. 5a and 5b show experimental waveforms of load jump and input voltage jump, wherein fig. 5a shows experimental waveforms of jump between 176V and 264V of the effective value of the input voltage when full load is applied, and fig. 5b shows experimental waveforms of jump between 10% and 90% of the load when the effective value of the input voltage is 220V, and it can be seen that the output voltage can be stabilized at 300V and has a faster dynamic response speed.
TABLE 1 main parameters of four-tube Buck-Boost PFC converter
| Parameters (parameters) |
Sign symbol |
Numerical value |
Parameters (parameters) |
Sign symbol |
Numerical value |
| Effective value of input voltage |
Vin |
220V±20% |
Filtering inductance |
Lc |
16μH |
| Input voltage frequency |
fin |
50Hz |
Output filter capacitor |
Co |
360μF |
| Output voltage |
Vo |
300V |
Input filter inductance |
Lin |
12μH |
| Output power |
Po |
500W |
Input filter capacitor |
Cin |
510nF |
| Switching frequency |
fs |
500kHz |
Rectifier bridge capacitor |
Cg |
270nF |
The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above examples, and all technical solutions belonging to the concept of the present invention belong to the protection scope of the present invention. It should be noted that modifications and adaptations to the invention without departing from the principles thereof are intended to be within the scope of the invention as set forth in the following claims.