CN201839200U - Power factor correction circuit with variable duty cycle control - Google Patents

Abstract

The utility model provides a power factor correction circuit controlled by a variable duty ratio. The circuit topology of the Boost converter in the circuit and the control circuit for realizing the variable duty ratio sequence together constitute the PFC stage of a commonly used LED drive power supply. , the front stage of the PFC stage is connected to the output terminal of the single-phase diode uncontrolled rectifier bridge through the input filter capacitor, and the rear stage of the PFC stage is connected to the DC/DC stage of the common LED drive power supply through the output filter inductor and output filter capacitor. The utility model controls the on-off of the switch tube according to the principle of equal impulse area, so that the impulse area of the input inductive current and the sinusoidal half-wave current in each switching cycle is equal to achieve high power factor (PF), and the higher the switching frequency, the higher the PF The closer the value is to 1. The utility model can not only realize high input power factor, but also reduce output voltage ripple, and the control circuit is simple and easy to realize by analog circuit, which is beneficial to large-scale integration.

Description

A Power Factor Correction Circuit Controlled by Variable Duty Ratio

technical field

The utility model relates to a single-phase power factor correction circuit in the field of switching power supplies, in particular to a power factor correction circuit controlled by variable duty ratio.

Background technique

When the traditional AC-DC conversion circuit is running, the power factor of the grid side is generally around 0.6~0.7, and a large amount of harmonic current will be generated, which will cause serious harm to the grid. In order to meet the requirements of high power factor and suppression of harmonic generation, a PFC stage with power factor correction function is usually added. The PFC stage is a DC/DC switching converter added between the rectifier and the load. The voltage and current feedback technology is applied to make the waveform of the input current close to a sine wave to improve the power factor. According to the different requirements of different loads on the voltage, it is usually necessary to add a DC/DC stage between the PFC stage and the load to adjust the voltage.

The DCM Boost PFC converter has the advantages of zero-current turn-on of the switch tube and no reverse recovery of the boost diode, and the switching frequency is constant. However, the inductor current varies with the input voltage when the switch tube is turned on, and the average value is sinusoidal, but the average value of the inductor current is non-sinusoidal when the switch tube is turned off, so the average value of the inductor current in one switching cycle is also non-sinusoidal. In sinusoidal form, its PF value is relatively low, especially at high voltage input.

The traditional control method is based on constant duty cycle control. The common control method applied to DCM Boost PFC converter is peak current control. Since the input current waveform increases with the increase of U _m /U _o , the THD increases. Add harmonic compensation to the comparator input. Another new control method for injecting third harmonics requires online adjustment of the amount of injected harmonics because the injected third harmonic content is related to the input voltage, and the implementation method is too complicated.

The traditional control strategy circuit is obtained by comparing the duty ratio signal with the sawtooth signal. When the duty ratio expression is more complicated, it needs complex operation circuits or digital fitting simplification to obtain it, which will inevitably increase the complexity of the analog circuit. The degree of load may reduce the control accuracy.

Utility model content

The purpose of this utility model is to provide a power factor correction circuit with variable duty cycle control, which adopts the principle of equal impulse area to obtain a variable duty cycle control sequence that can achieve high power factor, and solves the problem of complex and inaccurate traditional PFC control methods. High problem, while improving the power factor, it also obtains smaller output voltage ripple and higher efficiency. The utility model is realized through the following technical solutions:

），乘法器的输出端接比较器的另一个输入端，比较器的输出端与脉冲调节驱动的输入端连接。A power factor correction circuit controlled by a variable duty ratio, including a circuit topology of a Boost converter and a control circuit for realizing a variable duty ratio sequence, the control circuit for realizing a variable duty ratio sequence includes an input voltage detection circuit, an output Voltage detection circuit, analog operation circuit and pulse adjustment driver; the input voltage sampling resistor of the input voltage detection circuit is connected to the input filter capacitor C _in two ends, and the input voltage sampling resistor of the input voltage detection circuit is the first resistor and the second resistor connected in series Two resistors, between the first resistor and the second resistor is the first sampling point, the first sampling point is connected to an input end of the subtractor in the analog operation circuit; the output voltage sampling resistor of the output voltage detection circuit is connected to In the circuit topology of the boost converter, between the cathode of the diode and the ground, the output voltage sampling resistor of the output voltage detection circuit is a third resistor and a fourth resistor connected in series, and between the third resistor and the fourth resistor is The second sampling point, the second sampling point is connected with another input end of the subtractor and an input end of the divider in the analog computing circuit; the analog computing circuit includes a subtractor, a divider, a multiplier, a sawtooth wave signal generator and comparator, where the output of the subtractor is connected to the other input of the divider, and the output of the divider is connected to one input of the comparator; the sawtooth signal is connected to both inputs of the multiplier to calculate the square value (the constant term K of the multiplier is

), the output terminal of the multiplier is connected to the other input terminal of the comparator, and the output terminal of the comparator is connected to the input terminal of the pulse regulation drive.

The circuit topology of the Boost converter includes an inductor, a switch tube and a diode, one end of the inductor is connected to the positive output terminal of the single-phase diode uncontrolled rectifier bridge, and the other end of the inductor is connected to the drain of the switch tube, The source of the switching tube is connected to the negative output terminal of the single-phase diode uncontrolled rectifier bridge, the gate of the switching tube is connected to the output terminal of the pulse width adjustment driver; at the same time, the other end of the inductor is connected to the anode of the diode, and the cathode of the diode is output The filter inductor is connected to the DC/DC stage.

The control principle of the above-mentioned PFC circuit with high input power factor: adopt the circuit topology of Boost converter, according to the principle of equal impulse area, use the variable duty ratio control sequence to control the on-off of the power electronic switch, and perform high-frequency active Power factor correction makes the input inductor current equal to the impulse area of the sinusoidal half-wave current in each switching cycle, thereby realizing the sinusoidalization of the input current and making the input power factor close to 1. the

等于标准正弦半波在该时间段的积分面积

，即，其中The variable duty ratio control sequence is obtained according to the principle of equal impulse area, specifically including: dividing each half of the AC side input current cycle into n small time periods, and the width of each time period is the switching period , for each switching cycle period, the integral area of the inductor current waveform

Equal to the integral area of the standard half-sine wave in this time period

,Right now ,in

              (1)

(1)

(2)

是电感电流峰值，

是电感电流断续模式（DCM）下各开关周期的导通占空比，

是断续模式下各开关周期中电感电流下降时间占空比，

是单相二极管不控整流桥（B）的输出电压，

是PFC级的输出电压，

是Boost升压变换器的电路拓扑结构（1）中电感（L）的感抗值，

是输入电压峰值，是输入电压角频率，

是理想输入正弦输入电流幅值，

是标准正弦半波在各开关周期时间段的中间弧度值，

是输出功率，由（1）、（2）式相等得

is the peak inductor current,

is the on-duty cycle of each switching cycle in the inductor current discontinuous mode (DCM),

is the duty cycle of inductor current falling time in each switching cycle in discontinuous mode,

is the output voltage of the single-phase diode uncontrolled rectifier bridge (B),

is the output voltage of the PFC stage,

is the inductance value of the inductor (L) in the circuit topology (1) of the Boost converter,

is the peak input voltage, is the input voltage angular frequency,

is the ideal input sinusoidal input current amplitude,

is the middle radian value of the standard sine half wave in each switching period,

is the output power, obtained by equalizing (1) and (2)

                       (3)

(3)

The formula (3) is the expression about the square of the duty ratio sequence obtained according to the principle of equal impulse.

The above PFC control method can be transformed according to (3) to get

                (4)

(4)

In each switching cycle, time t is counted until the formula (4) is established at a certain moment, which is the moment when the switching tube is turned off.

。The sawtooth signal in the analog operation circuit is a clock signal that can be periodically cleared, and the slope of the sawtooth is numerically equal to , the cycle is

.

The control circuit of the utility model and the circuit topology of the Boost converter together constitute the PFC stage of the commonly used LED drive power supply, and the front stage of the PFC stage is connected to the output end of the single-phase diode uncontrolled rectifier bridge through the input filter capacitor C _in , the latter stage of the PFC stage is connected to the DC/DC stage of the commonly used LED drive power supply through the output filter inductor and output filter capacitor.

Compared with the prior art, the utility model has the following advantages: it solves the problem of large current ripple and low power factor in the traditional DCM Boost PFC converter, and can increase the power factor to close to 1 within the entire input voltage range; the control circuit It is easy to implement, abandoning the original method of comparing the duty cycle with the time sawtooth wave, and using the self-multiplication of the time sawtooth wave signal instead of the original open circuit or fitting simplification to make the control circuit simpler and the control strategy more accurate , only using some basic analog computing circuits, which is conducive to large-scale integration; compared with constant duty ratio control, it can not only make the input power factor close to 1, but also reduce the output voltage ripple, making the output voltage close to stable .

Applying this control circuit to the PFC stage of the LED drive power supply, not only high power factor can realize high-efficiency lighting power supply, but also the reduction of output voltage ripple can reduce the requirement for output capacitor capacity, so that the service life can be longer Advanced ceramic capacitors or film capacitors replace large electrolytic capacitors with large volume and short life, which improves the life of LED drive power as a whole.

Description of drawings

Figure 1 is a LED drive circuit with variable duty cycle control at the PFC level.

Figure 2 is a waveform diagram of the input current at low voltage input.

Figure 3 is a waveform diagram of the inductor current at low voltage input.

Figure 4 is a waveform diagram of the input current at high voltage input.

Figure 5 is a waveform diagram of the inductor current at high voltage input.

Figure 6 is a power factor diagram at low voltage input.

Figure 7 is a power factor diagram at high voltage input.

Figure 8 is a waveform diagram of the output voltage at low voltage input.

Figure 9 is a waveform diagram of the output voltage at high voltage input.

Figure 10 is an enlarged view of the steady-state ripple of the output voltage when the input voltage is low.

Figure 11 is an enlarged view of the steady-state ripple of the output voltage at high voltage input.

Detailed ways

The following is an LED drive circuit with variable duty cycle control combined with PFC level, as shown in Figure 1, the specific implementation of the technical solution of the utility model is described in further detail, but the implementation and protection scope of the utility model are not limited thereto.

The basic structure of the LED drive circuit is composed of input power supply, uncontrolled rectifier bridge, input filter, PFC stage, output filter, DC/DC stage, and LED lamp load.

，那么经不控整流桥的输出电压为

。Let the input voltage be

, then the output voltage of the uncontrolled rectifier bridge is

.

During one switching cycle, the peak value of the inductor current is:

                   （5）

(5)

表示开关导通占空比。in

Indicates the switch conduction duty cycle.

From the equalization of volt-seconds across the inductor during each switching cycle:

                        （6）

(6)

表示开关周期中电感电流下降时间的占空比。in

Indicates the duty cycle of the inductor current fall time during the switching cycle.

From (6) can get:

                    （7）

(7)

According to (5) and (6) formula can get

(8)

Then the input current is:

                    （9）

(9)

，故Will Per unitization, the base value is

, so

                     (10)

(10)

越小，输入电流波形越接近正弦函数，PF值越高。反之，输入电压幅值越接近输出电压幅值，PF值越低，这就限制了输入电压的幅值，不利于功率因数调节。It can be seen that the waveform of the input current is only related to the transformation ratio of the Boost converter,

The smaller it is, the closer the input current waveform is to a sinusoidal function, the higher the PF value. Conversely, the closer the input voltage amplitude is to the output voltage amplitude, the lower the PF value, which limits the input voltage amplitude and is not conducive to power factor adjustment.

The circuit topology 1 of the Boost converter includes an inductance L, a switch tube Q and a diode D, one end of the inductance L is connected to the positive output terminal of the single-phase diode uncontrolled rectifier bridge B, and the other end of the inductance L is connected to The drain of the switching tube Q is connected, the source of the switching tube Q is connected to the negative output terminal of the single-phase diode uncontrolled rectifier bridge B, and the gate of the switching tube Q is connected to the output terminal of the pulse width adjustment driver 5; meanwhile, the inductor L The other end of the diode is connected to the anode of the diode D, and the cathode of the diode D is connected to the DC/DC stage through the output filter inductor L _o .

Therefore, the utility model proposes a variable duty cycle control method based on the principle of equal impulse area to achieve high input power factor within a wide input voltage range. The specific implementation method is as follows:

，对每个开关周期时间段，使电感电流波形的积分面积

等于标准正弦半波在该时间段的积分面积

，即

，其中Divide each half of the input current cycle of the AC side into n small intervals, and the width of each interval is the switching cycle

, for each switching cycle period, the integral area of the inductor current waveform

Equal to the integral area of the standard half-sine wave in this time period

,Right now

,in

              (1)

(1)

          (2)

(2)

是电感电流峰值，

是电感电流断续模式下各开关周期的导通占空比，

是断续模式下各开关周期中电感电流下降时间占空比，

是单相二极管不控整流桥B的输出电压，

是PFC级的输出电压，

是Boost升压变换器的电路拓扑结构1中电感L的感抗值，

是输入电压峰值，

是输入电压角频率，

是理想输入正弦输入电流幅值，

是标准正弦半波在各开关周期时间段的中间弧度值，

是输出功率，由（1）、（2）式相等得

is the peak inductor current,

is the conduction duty cycle of each switching cycle in the inductor current discontinuous mode,

is the duty cycle of inductor current falling time in each switching cycle in discontinuous mode,

is the output voltage of single-phase diode uncontrolled rectifier bridge B,

is the output voltage of the PFC stage,

is the inductance value of the inductor L in the circuit topology 1 of the Boost converter,

is the peak input voltage,

is the input voltage angular frequency,

is the ideal input sinusoidal input current amplitude,

is the middle radian value of the standard sine half wave in each switching period,

is the output power, obtained by equalizing (1) and (2)

                       (3)

(3)

The formula (3) is the expression about the square of the duty ratio sequence obtained according to the principle of equal impulse.

The control circuit for realizing the variable duty ratio sequence is obtained according to (3) transformation, that is,

                (4)

(4)

In each switching cycle, time t is counted until the formula (4) is established at a certain moment, which is the moment when the switching tube is turned off.

的序列，使每个开关周期内的输入电流波形为正弦波，从而实现PF=1。By solving it can be obtained a duty cycle

The sequence, so that the input current waveform in each switching cycle is a sine wave, so as to achieve PF=1.

The formula (3) calculated by the principle of equal impulse area is the expression about the square of the duty cycle sequence. The traditional control circuit implementation is to construct the duty ratio circuit of the expression (3), and then compare it with the sawtooth wave to obtain the duty ratio signal, which will make the control circuit very complicated because the expression has radicals, and if you want to eliminate the radicals It is necessary to fit and simplify through Taylor expansion, which will reduce the accuracy of the control. Therefore, the realization of the control circuit in the utility model obtains the formula (4) by simplifying the formula (3), and obtains the required control signal by comparing the signal quantities at both ends of the formula (4).

；乘法器的输出端接比较器的另一个输入端，比较器的输出端与脉冲调节驱动器5的输入端连接。模拟运算电路4中的锯齿波信号为能周期清零的时钟信号，时钟信号斜率在数值上等于

，周期为

，使得锯齿波信号发生器产生的信号表达式为

，并且每个周期清零一次。As shown in Figure 1, the control circuit that realizes the variable duty cycle sequence includes an input voltage detection circuit 2, an output voltage detection circuit 3, an analog operation circuit 4 and a pulse adjustment driver 5; the input voltage sampling resistor of the input voltage detection circuit 2 is connected to At both ends of the input filter capacitor C _in , the input voltage sampling resistor of the input voltage detection circuit 2 is a first resistor R ₁ and a second resistor R ₂ connected in series, and the first resistor R ₁ and the second resistor R ₂ are connected between the first resistor R 1 and the second resistor R 2 A sampling point a, the first sampling point a is connected to an input end of the subtractor in the analog operation circuit 4; the output voltage sampling resistance of the output voltage detection circuit 3 is connected to the diode in the circuit topology 1 of the Boost boost converter Between the cathode of D and the ground, the output voltage sampling resistor of the output voltage detection circuit 3 is a third resistor R ₃ and a fourth resistor R ₄ connected in series, and the third resistor R 3 and the fourth resistor R 4 are connected between the third resistor R ₃ and the fourth resistor R ₄ . Two sampling points b, the second sampling point b is connected with another input end of the subtractor in the analog operation circuit 4 and an input end of the divider; The analog operation circuit 4 includes a subtractor, a divider, a multiplier, a sawtooth wave A signal generator and a comparator, wherein the output of the subtractor is connected to the other input of the divider, and the output of the divider is connected to one input of the comparator; the sawtooth signal generator is connected to the two inputs of the multiplier terminal connection to calculate the square value, the constant term K of the multiplier is

; The output terminal of the multiplier is connected to the other input terminal of the comparator, and the output terminal of the comparator is connected to the input terminal of the pulse adjustment driver 5 . The sawtooth wave signal in the analog operation circuit 4 is a clock signal that can be periodically cleared, and the slope of the clock signal is numerically equal to

, the cycle is

, so that the signal expression generated by the sawtooth signal generator is

, and is cleared every cycle.

The above control circuit and the circuit topology of the Boost converter together constitute the PFC stage of the commonly used LED drive power supply. The front stage of the PFC stage is connected to the output end of the single-phase diode uncontrolled rectifier bridge through the input filter capacitor C _in . The latter stage of the stage is connected to the DC/DC stage of the commonly used LED drive power supply through the output filter inductor and output filter capacitor.

Apply this PFC stage that can realize variable duty ratio control to the LED drive power supply. When the input voltage is low, the input current waveform is shown in Figure 2, and the current waveform on the inductor after rectification is shown in Figure 3. , it can be seen intuitively from the waveform that the sinusoidal effect is very good. When a high voltage is input, the input current waveform is shown in Figure 4. Compared with Figure 2, there is a little distortion at the zero crossing of the current. After rectification, the current waveform on the inductor is shown in Figure 5, and its sinusoidal Compared with Figure 3, the effect is slightly distorted on the peak of the sine wave. Judging from the PF value diagrams at low and high voltage input, the power factor is above 0.99, as shown in Figure 6 and Figure 7. The output voltage waveforms at low-voltage input and high-voltage input are shown in Figure 8 and Figure 9. It can be seen that the output voltage stabilizes and responds quickly, and it can be seen from the output voltage steady-state fluctuation that the output ripple value is stable. to 4.5V, and the input voltage increases, the output voltage ripple value does not increase significantly, as shown in Figure 10 and Figure 11.

After the above analysis, applying this variable duty cycle control method based on the principle of equal impulse to the PFC stage of the LED drive power supply not only has a high power factor, but also is suitable for a wide input voltage, and the output voltage ripple is small, reducing the impact on the output capacitance. Capacity requirements, ceramic capacitors or film capacitors with long life can be used instead of large electrolytic capacitors with large volume and short life, so as to improve the life of LED drive power as a whole.

Claims (2)

1. the circuit of power factor correction of variable duty cycle control, the control circuit that it is characterized in that comprising the circuit topological structure of Boost booster converter and realize the variable duty cycle sequence realizes that the control circuit of variable duty cycle sequence comprises input voltage detection circuit (2), output voltage detecting circuit (3), analog operational circuit (4) and pulse regulation driver (5); The input voltage sample resistance of described input voltage detection circuit (2) is connected input filter capacitor C _InTwo ends, the input voltage sample resistance of input voltage detection circuit (2) is the first resistance (R of series connection ₁) and the second resistance (R ₂), the described first resistance (R ₁) and the second resistance (R ₂) between be first sampling point (a), an input of subtracter is connected in first sampling point (a) and the analog operational circuit (4); The output voltage sample resistance of described output voltage detecting circuit (3) is connected between the negative electrode and ground of diode (D) in the circuit topological structure (1) of Boost booster converter, and the output voltage sample resistance of output voltage detecting circuit (3) is the 3rd resistance (R of series connection ₃) and the 4th resistance (R ₄), described the 3rd resistance (R ₃) and the 4th resistance (R ₄) between be second sampling point (b), another input of subtracter and an input of divider are connected in second sampling point (b) and the analog operational circuit (4); Described analog operational circuit (4) comprises subtracter, divider, multiplier, sawtooth signal generator and comparator, wherein, the output of subtracter is connected with another input of divider, and the output of divider is connected with an input of comparator; The sawtooth signal generator is connected with two inputs of multiplier; Another input of the output termination comparator of multiplier, the output of comparator is connected with the input of pulse regulation driver (5).

2. the circuit of power factor correction of a kind of variable duty cycle control according to claim 1, the circuit topological structure (1) that it is characterized in that described Boost booster converter comprises inductance (L), switching tube (Q) and diode (D), one end of described inductance (L) is connected with the positive output end that single-phase diode is not controlled rectifier bridge (B), the other end of inductance (L) is connected with the drain electrode of switching tube (Q), the source electrode of switching tube (Q) is connected with the negative output terminal that single-phase diode is not controlled rectifier bridge (B), and the gate pole of switching tube (Q) is connected with the output of pulse-width regulated driver (5); Simultaneously, the other end of inductance (L) is connected with diode (D) anode, and the negative electrode of diode (D) is through output inductor (L _o) be connected with the DC/DC level.

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