CN108599564B - Capacitor voltage discontinuous mode capacitor series connection type staggered parallel Bcuk PFC converter - Google Patents

Abstract

The invention discloses a capacitor-voltage discontinuous mode capacitor series-connected interleaved parallel Bcuk PFC converter and its control idea. Mainly used in applications requiring ultra-low voltage output and high power factor correction, especially in the LED field. The intermediate energy storage capacitor of the converter works in the voltage discontinuous mode and realizes the function of automatic power factor correction. In addition, the voltage peak value of the intermediate storage capacitor of the converter is clamped to the input voltage. In addition, by effectively adjusting the charging and discharging time of the voltage of the intermediate energy storage capacitor, the energy transferred to the load in one switching cycle is effectively controlled, and the ultra-high step-down ratio of the converter is realized, and the step-down ratio is independent of the duty cycle. . The control strategy of the converter adopts the idea of variable frequency interleaving control. When the load changes, the frequency of the interleaving pulse is automatically adjusted to maintain the output voltage stability. The circuit provided by the present invention has the characteristics of capacitor voltage clamping (low voltage stress), ultra-low voltage output, high power factor and the like.

Description

A Capacitor Voltage Discontinuous Mode Capacitor Series Interleaved Parallel Bcuk PFC Converter

technical field

The invention belongs to the field of electronic circuits, in particular to the application of medium and small power, which requires high power factor and ultra-low voltage output, especially the technical field of LED power supply.

Background technique

LED lighting technology is a new, clean and efficient modern lighting technology with significant advantages such as energy saving, environmental protection and long service life. In order to make the harmonic pollution of the LED drive circuit to the power grid reach the IEC61000-3-2C regulatory standard, active power factor correction technology is usually required. The single-stage active power factor correction converter has the advantages of simple control and low cost, and is widely used in small and medium power applications. Its topology is usually divided into two categories: isolated topology and non-isolated topology. The isolated topology usually adopts the critical conduction mode or discontinuous mode Flyback power factor correction converter with simple circuit structure and simple control strategy. However, the Flyback power factor correction converter has problems such as serious voltage spikes caused by leakage inductance, large input current peak value and rms value in inductor current discontinuous mode, and large output voltage double power frequency ripple. On the other hand, non-isolated topologies usually use inductor current discontinuous mode Boost power factor correction units to cascade DC/DC units, however, it will make the intermediate bus voltage higher and reduce the efficiency of lower-level DC/DC step-down units. Therefore, some researchers use Buck, Buck-Boost, such as step-down power factor correction units, to cascade DC/DC converters to solve the problem of high intermediate bus voltage caused by the use of inductor current discontinuous mode Boost power factor correction units. However, the above non-isolated single-stage active power factor correction converters all make the power factor correction unit work in the input current discontinuous mode to obtain the function of automatic power factor correction. The working mode of the input current discontinuous mode will increase the current stress of the power device in the main circuit of the converter, and increase the conduction loss of the power device.

In order to solve the influence of the input current discontinuous mode on the converter, related researchers proposed the dual operation mode of the input current discontinuous mode, the capacitor voltage discontinuous mode. Cuk and Buck converters work in capacitor voltage discontinuous mode, and both can realize automatic power factor correction. The capacitor-voltage discontinuous mode solves the shortcomings of large current stress and low efficiency of the input current discontinuous mode converter. However, converters operating in capacitor-voltage discontinuous mode,

Figures 1 and 2 show the traditional capacitor voltage discontinuous mode Buck PFC and Cuk PFC converters, respectively. Figures 3 and 4 show the capacitor voltage waveforms of the traditional capacitor voltage discontinuous mode Buck PFC and Cuk PFC converters, respectively. It can be seen from Figures 3 and 4 that the voltage peak value on the energy storage capacitor is determined by the switch off time, input current, and energy storage capacitor value. power devices, increasing the circuit cost.

SUMMARY OF THE INVENTION

The circuit topology and its working mode provided by the present invention overcome the two shortcomings of the existing input current discontinuous mode power factor correction converter with large input current peak value and the capacitor voltage discontinuous mode power factor correction converter with high intermediate energy storage capacitor voltage . In addition, the topology provided by the present invention has the characteristics of an ultra-high step-down ratio, that is, an ultra-low voltage output, and the step-down ratio has nothing to do with the duty cycle.

The invention clamps the voltage peak value of the intermediate energy storage capacitor to the input voltage, and effectively controls the energy transferred to the load in one switching cycle by effectively adjusting the charging and discharging time of the intermediate energy storage capacitor voltage, thereby realizing the ultra-high voltage of the converter. Step-down ratio, that is, ultra-low voltage output, and the step-down ratio is independent of the duty cycle. Therefore, the technical solution of the present invention is: a series-connected capacitor voltage clamping type interleaved parallel Buck PFC converter, the converter comprises: an input rectifier circuit, an LC filter circuit, a main circuit, and a control circuit in series; the main circuit includes: : A-phase switch S _a , A-phase diode, A-phase inductor, B-phase switch S _b , B-phase diode, B-phase inductor, energy storage capacitor C _t , output filter capacitor C _o ; among which A-phase switch S _a The drain is connected to the output end of the LC filter circuit, and then the source of the A-phase switch S _a is connected in series with the energy storage capacitor C _t and the A-phase inductor, and the output end of the A-phase inductor is connected to the output filter capacitor C _o The positive pole is used as the output of the main circuit , the negative electrode of the output filter capacitor C _o is grounded, the cathode of the A-phase diode is connected to the common contact of the energy storage capacitor C _t and the A-phase inductance, and the anode of the A-phase diode is grounded; the B-phase switch tube S _b is connected in series with the B-phase inductance, and the B-phase switch tube S The drain of _b is connected to the common junction of the A-phase switch S _a and the energy storage capacitor C _t , the B-phase inductor is connected to the output terminal of the A-phase inductor, and the B-phase diode cathode is connected to the common junction of the B-phase switch S _b and the B-phase inductor , B-phase diode anode is grounded.

Further, the input rectifier circuit includes: a first rectifier diode, a second rectifier diode, a third rectifier diode, and a fourth rectifier diode, the first rectifier diode is connected in series with the fourth rectifier diode, and the second rectifier diode is connected with the third rectifier diode in series. The rectifier diodes are connected in series, the anode of the fourth rectifier diode and the third rectifier diode are connected together and then grounded, and the cathode of the first rectifier diode and the second rectifier diode are connected together as the output of the input rectifier circuit; The common node, the common node of the second rectifier diode and the third rectifier diode are used as the input of the input rectifier circuit.

Further, the LC filter circuit includes: a filter inductor and a filter capacitor; the input end of the filter inductor is connected to the output end of the input rectifier circuit, and the output end is connected to the input end of the main circuit; one end of the filter capacitor is connected to the output end of the filter inductor terminal, and the other terminal is grounded.

Further, the sampling circuit includes an output filter capacitor and a load, the sampling capacitor is connected in parallel with the load, one end of the parallel connection is connected to the output end of the main circuit, and the other end is grounded.

In the present invention, when the A-phase switch tube S _a is turned on, the intermediate energy storage capacitor C _t is charged by a constant current, and when the voltage of the intermediate energy storage capacitor C _t rises to the input voltage, the voltage across the A-phase freewheeling diode is zero, and the conduction Through freewheeling, the negative electrode of the intermediate storage capacitor C _t is grounded, so the voltage of the intermediate storage capacitor C _t is clamped to the value of the input voltage. Since the switches _Sa and _Sb of the next working mode are both turned off, the intermediate energy storage capacitor C _t has no discharge loop, so its voltage remains unchanged at the value of the input voltage. When the _B -phase switch tube Sb is turned on, the intermediate energy storage capacitor _Ct is discharged at this time, and its discharge loop is the A-phase diode Da, _Ct , the B-phase switch tube Sb, the _B -phase inductance _Lb , and the load. When the voltage of the intermediate storage capacitor C _t drops to zero, the B-phase freewheeling diode D _b is turned on. At this time, since the A and B-phase diodes are both turned on, the voltage of the intermediate storage capacitor C _t is clamped to zero. In the next switching mode, the switches _Sa and _Sb are both turned off, and the intermediate energy storage capacitor C _t has no charging loop, so its voltage remains zero. In this way, it is realized that the intermediate storage capacitor C _t operates in the capacitor voltage discontinuous mode and the voltage peak is clamped to the input voltage. In addition, by effectively adjusting the charging and discharging time of the voltage of the intermediate energy storage capacitor, the energy transferred to the load in one switching cycle is effectively controlled, and the ultra-high step-down ratio of the converter is realized, that is, the ultra-low voltage output, and the step-down The ratio has nothing to do with the duty cycle. The controller adopts the variable frequency interleaving control technology with constant duty cycle, forms a closed loop by sampling the output voltage, adjusts the switching frequency correspondingly according to the output voltage change, outputs the interleaving control pulse, and controls the main circuit switch tube through the driving circuit to maintain the output. Voltage is stable.

Compared with the prior art, the beneficial effects of the present invention are:

1. Compared with the existing discontinuous inductor current mode (DICM) PFC converter, the input current of the present invention is continuous, so the peak value and RMS value of the input current are small, the conduction loss of the power device is small, and the converter has a cost Low, high efficiency advantages;

2. Compared with the existing capacitor voltage discontinuous mode (DCVM) PFC converter, the voltage peak value of the intermediate energy storage capacitor of the present invention is clamped to the value of the input voltage, and the voltage stress of the main circuit power device will not be increased, so it can be Choose a power switch tube with a suitable withstand voltage level to reduce costs.

3. Compared with the existing low-voltage output step-down converter, the present invention has a larger duty cycle and lower requirements on the switching speed of the power switch tube, so the cost of the power switch tube and the controller can be saved.

The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

Description of drawings

FIG. 1 is a circuit diagram of a conventional capacitor-voltage discontinuous mode Buck PFC converter.

FIG. 2 is a circuit diagram of a conventional capacitor-voltage discontinuous mode Cuk PFC converter.

Fig. 3 is the energy storage capacitor voltage waveform diagram of the traditional capacitor voltage discontinuous mode Buck PFC converter.

FIG. 4 is a waveform diagram of the energy storage capacitor voltage of the traditional capacitor voltage discontinuous mode Cuk PFC converter.

FIG. 5 is a circuit structure diagram of a series capacitor voltage clamping type interleaved parallel Buck PFC converter and a control method thereof according to the present invention.

Figures 6, 7, 8, 9, 10, and 11 are the working modal circuit diagrams of the intermediate storage capacitors connected in series when the voltage of the intermediate energy storage capacitors is in discontinuous mode, taking the two-phase Buck interleaving as an example, respectively corresponding to working mode 1, working mode Mode 2, Working Mode 3, Working Mode 4, Working Mode 5, Working Mode 6.

Figures 12 and 13 are respectively the main time domain power frequency simulation waveforms and several switching cycle simulation waveforms when the intermediate storage capacitor voltage in series is in discontinuous mode, taking the two-phase Buck interleaving as an example (open loop). .

Detailed ways

The present invention will be described in further detail below with reference to the accompanying drawings through specific examples.

As shown in Figures 6, 7, 8, 9, 10, and 11, the circuit has six modes when the intermediate storage capacitor voltage is in discontinuous mode.

Mode1: Working mode ₁ corresponds to the period t1 in Figure 13. At the beginning of this period, the switch S _a is turned on, D _a is turned off, the input voltages V _i and C provide energy for phase A, and V _C drops. _Ct is charged and u _Ct rises linearly from 0. u _Da decreases linearly from _Vi . When u _Ct =V _i , the A-phase freewheeling diode D _a is turned on, and the mode ends.

Mode2: Working mode 2 corresponds to the period t ₂ in Figure 13. At the beginning of this period, the freewheeling diode D _a of phase A conducts freewheeling. At this stage, C and C _t are connected in parallel. Since C ₁ is much larger than C _t , the current flowing through C _t can be ignored, and it is considered that _IL1 only charges C.

Mode3: The working mode 3 corresponds to the period t ₃ in FIG. 13 . At the beginning of this period, the switch S _a is turned off. Since the current _{i Sa} flowing through the switch tube Sa in the working mode 2 is 0, the switch tube _Sa is turned off at zero current. At this stage, both phases AB are freewheeled by their respective freewheeling diodes. Since both _Sa and _Sb are disconnected, there is no discharge loop for C _t , u _ct remains unchanged, and its value is still V _i .

Mode4: Working mode: 4 corresponds to the period t ₄ in FIG. 13 . At the beginning of this period, the switch tube S _b is turned on, and the switch tube D _b is turned off. The discharge of C _t provides energy for phase B, and u _Ct decreases linearly until u _Ct drops to 0, the freewheeling diode D _b is turned on, and the mode ends.

Mode5: Working mode 5 corresponds to the period t ₅ in FIG. 13 . At the beginning of this period, the freewheeling diode D _b is turned on. At this stage, both phases A and B are freewheeling, and no current flows through the switch tube S _b . The duration of this mode is the same as the duration of working mode 1.

Mode6: The working mode 6 corresponds to the period t ₆ in FIG. 13 . At the beginning of this period, the switch tube S _b is turned off. Since the current i _Sb flowing through the switch tube S _b in the working mode 5 is 0, the switch tube S _b is turned off at zero current. At this stage, the switches _Sa and Sb are both turned off, the capacitor C _t does not have _a charge and discharge loop, and its voltage u _Ct remains at 0. _At time t=t6, the switch tube _Sa is turned on, and the next switching cycle begins.

Simulation analysis results:

Fig. 5 for this invention takes two-phase Buck series capacitors connected in staggered parallel as an example, and the voltage of the energy storage capacitors connected in series in the middle is in a discontinuous mode, and an embodiment of staggered open-loop control is adopted. Figures 12 and 13 are respectively the simulation waveform of the power frequency cycle and the simulation waveform of the switching cycle in the embodiment of Figure 5. The simulation parameters are: input voltage V _in =220Vac, load resistance R _L =1.67Ω, intermediate storage capacitor C _t =24.4 nF, inductor L _a =L _b =226uH, input filter inductor L=800uH, input filter capacitor C=220nF, output capacitor C _o =1mF. It can be seen from Figure 12 that the input current tracks the change of the input voltage, which realizes the automatic power factor correction function in the continuous mode of the input current. It can be seen from Figures 12 and 13 that the intermediate energy storage capacitor works in discontinuous mode, and its voltage peak is clamped to the value of the input voltage V _in , which does not increase the voltage stress of the power device.

To sum up, the converter proposed by the present invention can make the voltage of the intermediate energy storage capacitor intermittent and its voltage peak is clamped to the value of the input voltage, without adding additional devices, that is, without increasing the cost, it can well solve the traditional DCVM The disadvantage of the higher voltage peak value of the PFC intermediate storage capacitor. Moreover, the automatic power factor correction function is realized in the input current continuous mode. Compared with the traditional DICM PFC, the peak value and rms value of the input current are reduced, thus reducing the conduction loss of the power device and improving the circuit efficiency. In addition, compared with the traditional high step-down converter, the circuit provided by the present invention can select a larger duty cycle to achieve an ultra-high step-down ratio, which reduces the switching performance requirements for the power switch tube and the controller, and saves the circuit cost.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included in the protection scope of the present invention. within.

Claims (3)

1. A capacitor voltage discontinuous mode capacitor series interleaved parallel Bcuk PFC converter is formed by sequentially connecting in series: the input rectification circuit, the LC filter circuit, the main circuit and the sampling circuit; the LC filter circuit includes: a filter inductor L and a filter capacitor C; the input end of the filter inductor L is connected with the output end of the input rectifying circuit, and the output end of the filter inductor L is connected with the input end of the main circuit; one end of the filter capacitor C is connected with the output end of the filter inductor L, and the other end of the filter capacitor C is grounded; the main circuit comprises: a-phase switch tube S_aA-phase continuous current diode Da, A-phase inductor and B-phase switching tube S_bB phase continuous flow diode D_bPhase B inductor and energy storage capacitor C_tAn output filter capacitor C_o(ii) a Wherein, A phase switch tube S_aThe drain electrode is connected with the output end of the LC filter circuit, and then the A-phase switch tube S_aThe source electrodes are sequentially connected in series with an energy storage capacitor C_tAn output end of the A-phase inductor is connected with an output filter capacitor C_oThe positive electrode is used as the output of the main circuit and outputs a filter capacitor C_oThe negative electrode is grounded, the negative electrode of the A phase continuous current diode Da is connected with the energy storage capacitor C_tAnd the common junction of the A phase inductor, the anode of the A phase continuous current diode Da is grounded; b-phase switch tube S_bA B-phase switch tube S connected in series with the B-phase inductor_bThe drain electrode of the switch is connected with an A-phase switch tube S_aAnd an energy storage capacitor C_tThe B-phase inductor is connected with the output end of the A-phase inductor, and the B-phase inductorFreewheeling diode D_bCathode is connected with a B-phase switch tube S_bCommon junction of B-phase inductor and B-phase continuous current diode D_bThe anode is grounded;

the 6 modes of operation of the Bcuk PFC converter are as follows:

mode 1: at the beginning of this period, the switching tube S_aOn, A phase continuous current diode Da is turned off, input voltage V_iAnd C provides energy to phase A, V_CDescending; c_tIs charged u_CtStarts to rise linearly from 0; u. of_DaFrom V_iBeginning a linear decrease; when u is_Ct＝V_iWhen the current is in the mode, the A continuous current diode Da is conducted, and the mode is ended;

mode 2: at the beginning of the period, the A-phase continuous current diode Da conducts continuous current; the stages C and C_tIn parallel, since C is much larger than C_tSo that the flow through C can be ignored_tThe current through inductor L is considered to charge only C;

mode 3: at the beginning of this period, the switching tube S_aDisconnecting; due to the working mode2 flowing through the switch tube S_aCurrent i of_Sa0, so the switch tube S_aZero current is turned off; in the stage, two phases AB are both freewheeling by respective freewheeling diodes; due to S_a、S_bAre all open, therefore C_tAbsence of discharge circuit, u_ctRemains unchanged and has a value of V_i；

Mode 4: at the beginning of this period, the switching tube S_bConducting, B-phase continuous flow diode D_bTurning off; c_tDischarge provides energy to phase B, u_CtLinearly decreases until u_CtDescending to 0, B continuous flow diode D_bConducting, and ending the mode;

mode 5: at the beginning of this period, the B-phase continuous flow diode D_bConducting; the A, B phase flows current with two phases and no current flows through the switch tube S_b(ii) a The duration of this mode is the same as the duration of operating mode 1;

mode 6: at the beginning of this period, the switching tube S_bTurning off; due to the working mode5, the current flows through the switch tube S_bCurrent i of_Sb0, so the switch tube S_bZero current is turned off; the switch tube S at this stage_a、S_bAll turn off, capacitance C_tWithout charging-discharging circuit, its voltage u_CtRemains at 0; at the end of this period, the switching tube switches the tube S_aOn and the next switching cycle begins.

2. The series interleaved parallel Bcuk PFC converter with capacitor voltage discontinuous mode capacitors as claimed in claim 1 wherein said input rectification circuitry comprises: the first rectifier diode is connected with the fourth rectifier diode in series, the second rectifier diode is connected with the third rectifier diode in series, the anodes of the fourth rectifier diode and the third rectifier diode are connected in common and then grounded, and the cathodes of the first rectifier diode and the second rectifier diode are connected in common and then used as the output of the input rectifier circuit; the common joint of the first rectifying diode and the fourth rectifying diode and the common joint of the second rectifying diode and the third rectifying diode are used as the input of the input rectifying circuit.

3. The series-connection type interleaved parallel Buk PFC converter according to claim 1, wherein the sampling circuit comprises an output sampling capacitor and a load, the sampling capacitor is connected with the load in parallel, one end of the sampling capacitor is connected with the output end of the main circuit after the sampling capacitor is connected with the load in parallel, and the other end of the sampling capacitor is grounded.

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