CN102710117B - High-efficiency passive power factor correction circuit - Google Patents

Abstract

The invention relates to a high-efficiency passive power factor correction circuit, which includes a rectifier bridge circuit, a passive power factor correction circuit and a flyback circuit. The passive power factor correction circuit is cascaded between the rectifier bridge circuit and the bridge arm of the flyback circuit; the rectifier bridge circuit includes a first diode (D1), a second diode (D2), a first Three diodes (D3) and a fourth diode (D4); the passive power factor correction circuit includes a first inductor (L1), a secondary inductor (L2) of a transformer (T1), a fifth diode (D5), the first capacitor (C1), the second capacitor (C2); the flyback circuit includes a MOS tube (Q), the primary inductance (L3) of the transformer (T1), another secondary of the transformer (T1) Inductor (L4), sixth diode (D6), third capacitor (C3). The passive power factor correction circuit proposed by the invention has low cost, small volume, simple structure and high efficiency.

Description

A High Efficiency Passive Power Factor Correction Circuit

technical field

The invention relates to the technical field of power correction in the AC-DC conversion process, in particular to a passive power factor correction circuit.

Background technique

Power factor (PF) is defined as the ratio of active power to apparent power, as shown in formula (1), where V _in represents the input voltage, I represents the effective value of the pulse current, and _In represents the effective value of the nth harmonic , I ₁ represents the effective value of the fundamental current, and θ is the phase difference between the fundamental current I ₁ and the input voltage _Vin .

in The total harmonic distortion factor (Total Harmonics Distortion, THD) is defined as the ratio of the total effective value of the high-order harmonic current component to the effective value of the fundamental current, as shown in (2).

$\mathrm{<span\; class="notranslate">\; THD</span>}<span\; class="notranslate">\; =</span>\sqrt{\underset{\mathrm{<span\; class="notranslate">\; no</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2</span>}}{\overset{<span\; class="notranslate">\; \&infin;</span>}{\mathrm{<span\; class="notranslate">\; \&Sigma;</span>}}}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; no</span>}}}<span\; class="notranslate">\; /</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$

The relationship between power factor and total harmonic distortion factor can be expressed by (3) formula. When the phase difference θ is 0 and THD<5%, the power factor can be controlled above 0.99. Therefore, the improvement of power factor is mainly carried out from two aspects: reducing the harmonic current component and reducing the difference between the input fundamental current and the input voltage.

$\mathrm{<span\; class="notranslate">\; PF</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; cos</span>}\mathrm{<span\; class="notranslate">\; \&theta;</span>}<span\; class="notranslate">\; /</span>\sqrt{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; THD</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$

In power electronic equipment, electronic instruments and home appliances, rectifying the 220V AC grid power supply to obtain DC power is a very widely used and most basic AC-DC (AC-DC) conversion scheme. Under normal circumstances, this kind of AC-DC conversion is realized by a full-bridge rectifier circuit, followed by a large filter capacitor to obtain a DC voltage source with a relatively flat waveform. When the potential of the input AC voltage is low, the energy required by the load is provided by the energy storage capacitor, and the AC voltage source itself does not provide current; when the potential of the input AC voltage is high, the AC voltage source directly charges the energy storage capacitor. Therefore, although the input AC voltage is a sine wave, the input AC current is pulse-like, and the waveform distortion is serious. These pulse-shaped input currents contain a large number of harmonics. If a large number of current harmonic components flow back into the power grid, on the one hand, the level of harmonic noise in the power grid will increase, resulting in harmonic "pollution" of the power grid. On the other hand, There will be a "secondary effect", that is, the current flows through the line impedance to form a harmonic voltage drop, which in turn distorts the grid voltage (original sine wave). When these effects are serious, it will cause circuit failure and damage the substation equipment.

If there is no parallel energy storage capacitor behind the rectifier bridge, but a purely resistive load is directly connected, then obviously, the phase difference between the voltage and current is zero and there is no harmonic current, and the power factor is 1. Therefore, the essence of power factor correction (PFC) technology is to use the input terminal of the electrical equipment to present a "pure resistance" to the input grid, that is, to make the input current and input voltage proportional. On the other hand, from the perspective of energy transmission, PFC technology uses the input end of electrical equipment to draw energy from the input grid, rather than feeding energy back to the input grid.

From the current point of view, there are two ways to solve the harmonic pollution of the power grid: one is to compensate the generated harmonic current on the grid side; the other is to set a passive or active PFC circuit inside the power electronic device to achieve PFC the goal of. Among them, the latter is a more fundamental solution.

Contents of the invention

The object of the present invention is to provide a high-efficiency passive power factor correction circuit, which is located between a rectifier bridge and a DC-DC converter, and is used to improve the power factor of the circuit. The specific technical solution is as follows.

The invention is suitable for a passive high-frequency power factor correction circuit and includes three parts: a rectifier bridge circuit, a passive power factor correction circuit and a flyback circuit. The passive power factor correction circuit is cascaded between the rectifier bridge circuit and the bridge arm of the flyback circuit.

Preferably, the rectifier bridge circuit includes a first diode, a second diode, a third diode and a fourth diode; the passive power factor correction circuit includes a first inductor, a secondary of a transformer An inductor, a fifth diode, a first capacitor, and a second capacitor; the flyback circuit includes a MOS tube, a primary inductance of a transformer, another secondary inductance of the transformer, a sixth diode, and a third capacitor.

Preferably, the connection relationship of the components in the rectifier bridge circuit is as follows: the cathode of the first diode is connected to the cathode of the second diode, the anode of the third diode is connected to the anode of the fourth diode, and the cathode of the second diode is connected to the anode of the fourth diode. The cathodes of the three diodes are connected to the anode of the first diode, and the cathodes of the fourth diode are connected to the anode of the second diode; the input terminal of the rectifier bridge circuit is connected to an AC voltage, and one input terminal is connected to the first diode. The anode of one diode is connected to the cathode of the third diode, and the other input terminal is connected to the anode of the second diode and the cathode of the fourth diode; the cathode of the second diode is the positive output terminal, The anode of the fourth diode is the output negative terminal, wherein the output negative terminal is grounded.

Preferably, the connection relationship of the components in the passive power factor correction circuit is as follows: one end of the first inductance is connected to the cathodes of the second diode and the fourth diode, and the other end of the first inductance is connected to the fifth diode The anode of the tube is connected, the same-named end of the secondary inductance of the transformer is connected with the anode of the fifth diode, the non-identical end of the secondary inductance of the transformer is connected with one end of the first capacitor, and the other end of the first capacitor is grounded. The cathode of the fifth diode is connected to one end of the second capacitor, and the other end of the second capacitor is grounded.

Preferably, the connection relationship of each component in the flyback circuit is as follows: the terminal with the same name of the initial inductance of the transformer is connected to the drain of the MOS transistor, the source of the MOS transistor is grounded, and the non-identical terminal of the initial inductance of the transformer is connected to the drain of the MOS transistor. The cathodes of the five diodes are connected, the same-named end of the other secondary inductance of the transformer is connected to the anode of the sixth diode, the non-identical end of the other secondary inductance of the transformer is connected to the output negative end, and the sixth diode The cathode of the third capacitor is connected to the output positive terminal, and the two ends of the third capacitor are the output positive terminal and the negative terminal respectively.

Preferably, the first diode, the second diode, the third diode and the fourth diode are all rectifier diodes, the sixth diode is an ultra-fast recovery diode, and the fifth diode is fast recovery diode.

Compared with the prior art, the present invention has the following advantages: the passive power factor correction circuit proposed by the present invention is low in cost, small in size, simple in structure and high in efficiency, and complies with the C-class standard in EU EN61000-3-2. The circuit can increase the power factor to 0.995 under the optimal condition, which overcomes the shortcoming of low power factor of common passive power factor correction circuit.

Description of drawings

Figure 1 is a schematic diagram of a passive power factor correction circuit.

Detailed ways

The specific implementation of the present invention will be further described below in conjunction with the accompanying drawings and examples, but the implementation and protection of the present invention are not limited thereto.

As shown in Figure 1, the composition and components of the high-efficiency passive power factor correction circuit are as follows:

The power factor correction circuit suitable for passive high frequency includes three parts: rectifier bridge circuit, power factor correction circuit and flyback circuit. The power factor correction circuit is cascaded between the rectifier bridge circuit and the bridge arm of the flyback circuit.

The rectifier bridge circuit includes a first diode D1, a second diode D2, a third diode D3 and a fourth diode D4; the passive power factor correction circuit includes a first inductor L1, a transformer T1 The secondary inductance L2 of the transformer T1, the fifth diode D5, the first capacitor C1, and the second capacitor C2; the flyback circuit includes a MOS transistor Q, the primary inductance L3 of the transformer T1, another secondary inductance L4 of the transformer T1, The sixth diode D6 and the third capacitor C3.

The first diode D1 is connected to the cathode of the second diode D2, and the anode of the third diode D3 is connected to the anode of the fourth diode D4. The cathode of the first diode D1 is connected to the cathode of the second diode D2, the cathode of the third diode D3 is connected to the anode of the first diode D1, and the cathode of the fourth diode D4 is connected to the second and second diodes D2. The anode of the pole tube D2 is connected; the input terminal of the rectifier bridge circuit is connected to the AC voltage, the input terminal AC_L is connected to the anode of the first diode D1 and the cathode of the third diode D3, and AC_N is connected to the second diode D2 The anode of the second diode D4 is connected to the cathode of the fourth diode D4; the cathode of the second diode D2 is the positive output terminal, and the anode of the fourth diode D4 is the negative output terminal, wherein the negative output terminal is grounded.

One end of the first inductance L1 is connected to the cathodes of the second diode D2 and the fourth diode D4, the other end of the first inductance L1 is connected to the anode of the fifth diode D5, and the secondary inductance L2 of the transformer T1 The terminal with the same name is connected to the anode of the fifth diode D5, the terminal with the same name of the secondary inductance L2 of the transformer T1 is connected to one terminal of the first capacitor C1, and the other terminal of the first capacitor C1 is grounded. The cathode of the fifth diode D5 is connected to one end of the second capacitor C2, and the other end of the second capacitor C2 is grounded.

The same-named end of the initial inductance L3 of the transformer T1 is connected to one end of the MOS transistor Q, the other end of the MOS transistor Q is grounded, the non-identical end of the initial-end inductance L3 of the transformer T1 is connected to the cathode of the fifth diode D5, and the transformer T1 The same-named end of the other secondary inductance L4 of the transformer T1 is connected to the anode of the sixth diode D6, the non-identical end of the other secondary inductance L4 of the transformer T1 is connected to the output negative terminal DC-, and the cathode of the sixth diode D6 It is connected to the positive output terminal DC+, and the two ends of the third capacitor C3 are the positive and negative output terminals DC+ and DC- respectively.

This circuit is a passive power factor correction circuit, and the devices used are passive devices, so that the cost of the whole circuit is greatly reduced, and the structure is much simpler than that of an active power factor correction circuit; High power factor, so the volume of the circuit is also greatly reduced.

During the working process, the circuit uses the energy storage inductor L1 and capacitor C2 to boost the DC voltage and fill in the valley of the DC ripple to make the DC voltage more stable, and uses another secondary inductor L2 and capacitor C1 of the transformer for feedback to start To fill the bottom of the DC ripple, through the above two functions, the conduction pin of the rectifier diode is expanded, so that the waveform of the input current is close to the waveform of the input voltage, which greatly reduces the harmonic distortion of the input current. Thereby improving the power factor of the circuit.

The parameters of the main components in this circuit can be determined by the following formula.

When the switch is turned on, the first inductor L1 satisfies:

${\mathrm{<span\; class="notranslate">\; i</span>}}_{\mathrm{<span\; class="notranslate">\; L</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; in</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; C</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}}{\mathrm{<span\; class="notranslate">\; L</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$

Where V _in is the input voltage, V _C1 is the voltage across the first capacitor, V _C2 is the voltage across the second capacitor, t ₀ -t ₁ is the switch on time, and i _L1 is the current flowing through the first inductor.

Note that the turns of the primary inductance L3, one secondary inductance L4 and the other secondary inductance L2 of the transformer T1 are N1, N2 and N3 respectively, and the relationship between N1, N2 and N3 satisfies:

N1i ₁ +N2i ₂ -N3i _C1 = 0 and i ₂ = 0 (2);

Wherein, i ₁ represents the current flowing through the third inductor L3, i ₂ represents the current flowing through the fourth inductor L4, and i _C1 represents the current flowing through the second inductor L2. Between the second inductance L2 and the third inductance L3 satisfies:

N1>N3 (3);

The first capacitor C1 and the second capacitor C2 satisfy:

C2>C1 (4);

Between the second inductance L2 and the third inductance L3 satisfies:

$\frac{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; N</span>}\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; \&Greater\; Equal;</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; ;</span>$

It is best to use an ultra-fast recovery diode for the sixth diode D6, and a fast recovery diode for the fifth diode D5, and the rated current value of the diode should meet the circuit requirements.

Claims (4)

1. A high-efficiency passive power factor correction circuit, comprising a rectifier bridge circuit and a flyback circuit, is characterized in that it also includes a passive power factor correction circuit, and the passive power factor correction circuit is cascaded between the rectifier bridge circuit and the between the bridge arms of the flyback circuit; the rectifier bridge circuit includes a first diode (D1), a second diode (D2), a third diode (D3) and a fourth diode (D4 ); the passive power factor correction circuit includes a first inductor (L1), a secondary inductor (L2) of a transformer (T1), a fifth diode (D5), a first capacitor (C1) and a second capacitor ( C2); the cathode of the first diode (D1) is connected to the cathode of the second diode (D2), and the anode of the third diode (D3) is connected to the anode of the fourth diode (D4); The cathode of the three diodes (D3) is connected to the anode of the first diode (D1), and the cathode of the fourth diode (D4) is connected to the anode of the second diode (D2); the rectifier bridge circuit The two input terminals of the AC voltage are connected to the AC voltage, one of the input terminals (AC_L) is connected to the anode of the first diode (D1) and the cathode of the third diode (D3), and the other input terminal (AC_N) is connected to the second The anode of the diode (D2) is connected to the cathode of the fourth diode (D4); the cathode of the second diode (D2) is the positive output terminal, and the anode of the fourth diode (D4) is the negative output terminal , wherein the negative output terminal is grounded; in the passive power factor correction circuit, one end of the first inductor (L1) is connected to the cathode of the second diode (D2) and the fourth diode (D4), and the first inductor The other end of (L1) is connected to the anode of the fifth diode (D5), the same name end of the secondary inductance (L2) of the transformer (T1) is connected to the anode of the fifth diode (D5), and the transformer (T1) The non-identical end of the secondary inductor (L2) is connected to one end of the first capacitor (C1), and the other end of the first capacitor (C1) is grounded; the cathode of the fifth diode (D5) is connected to the second capacitor (C2) One end of the second capacitor (C2) is connected to the ground. 2. The high-efficiency passive power factor correction circuit according to claim 1, characterized in that: the flyback circuit includes a MOS transistor (Q), a primary inductance (L3) of a transformer (T1), a transformer (T1) Another secondary inductance (L4), the sixth diode (D6) and the third capacitor (C3); in the flyback circuit, the end of the initial inductance (L3) of the transformer (T1) with the same name as the MOS tube The drain of (Q) is connected, the source of the MOS transistor (Q) is grounded, the non-identical end of the initial inductance (L3) of the transformer (T1) is connected to the cathode of the fifth diode (D5), and the transformer (T1) The same-named end of the other secondary inductance (L4) of the transformer (T1) is connected to the anode of the sixth diode (D6), and the non-identical end of the other secondary inductance (L4) of the transformer (T1) is connected to the output negative end (DC-) The cathode of the sixth diode (D6) is connected to the positive output terminal (DC+), and the two ends of the third capacitor (C3) are the positive output terminal (DC+) and the negative output terminal (DC-). 3. The high-efficiency passive power factor correction circuit according to claim 1, characterized in that: the first diode (D1), the second diode (D2), and the third diode of the rectifier bridge circuit Tube (D3) and fourth diode (D4) are rectifier diodes. 4. The high-efficiency passive power factor correction circuit according to claim 2, characterized in that: the sixth diode (D6) is an ultra-fast recovery diode, and the fifth diode (D5) is a fast recovery diode .