CN1124675C - Active Peak Current Controlled Filter with Fixed Frequency and High Power Factor - Google Patents

Abstract

The invention relates to an active peak current control filter with a fixed frequency and high power factor, which comprises a boost conversion unit and an active power factor corrector, wherein the boost conversion unit trims input current into a sine wave waveform by a change-over switch, the active power factor corrector consists of a current loop unit and a voltage loop unit, the current loop unit provides a detection current induced by the input current to a pulse width modulator in the unit, the voltage loop unit provides a current command with the same phase as the input voltage to the pulse width modulator, and the pulse width modulator is controlled to enable the input voltage and the input current to have the same phase so as to achieve higher power factor to reduce power loss.

Description

Active Peak Current Controlled Filter with Fixed Frequency and High Power Factor

The invention relates to an active peak current control filter with constant frequency and high power factor.

Generally, power factor correction technologies can be broadly classified into two types: active and passive. The passive type mainly uses passive components such as inductors, capacitors and other filter elements to improve the waveform and phase of the input current; the active type uses a power factor corrector after the diode rectifier to modify the input current into a sine wave by means of the action of the active switch waveform, while improving the power factor.

Generally, an active filter adds a boost converter between the bridge rectifier and the filter capacitor to control the switching of the converter to obtain a sine wave input current. This method can indeed obtain high power factor when applied to a single-phase rectifier circuit. with low total harmonic distortion. Generally, converters generally adopt the control method of voltage follower method or error multiplication method, and the switching frequency varies with the input voltage, and the switching frequency of each voltage level is different, so it is difficult to comply with the EMI filter design. Require.

Due to the need to meet the requirements of low harmonic distortion and high power factor, active power factor correction circuits are usually used to achieve the purpose of improvement. The active power factor correction strategy mainly adopts the current mode, that is, directly feeds back the input current and follows the waveform of a current command.

In the past, active power factor correctors were realized by analog control, but because of the complex circuit structure and lack of flexibility, once the resistance and capacitance values were fixed, the best efficiency could only be achieved for a limited number of conditions, while It is impossible to quickly improve the harmonic distortion for several orders, and every time a change is made, the resistors and capacitors must be replaced, so the power factor and total harmonic distortion cannot be improved immediately and effectively.

From the above, it can be seen that the existing active filters still have deficiencies in improving the power factor and reducing the total harmonic distortion, and further improvement is needed.

Therefore, the object of the present invention is to provide an active peak current control filter with constant frequency and high power factor, which can be adjusted according to different circuit conditions, thus having great flexibility and greatly reducing power loss.

In order to achieve the aforementioned purpose, the active peak current control filter with fixed frequency and high power factor provided by the present invention is characterized in that it includes a boost conversion unit and an active power factor corrector; The voltage conversion unit includes: a power supply, a boost inductor connected to the power supply, a first and a second diode, an output load capacitor, a bridge rectifier and a switching switch; the input end of the bridge rectifier is connected to the boost inductor and the first The positive terminal of the diode; the load capacitance is connected in series between the negative terminal of the first diode and the positive terminal of the second diode; the input current is trimmed into a sinusoidal waveform by switching the switch; the active power factor The rectifier is composed of a current loop unit connected to the step-up conversion unit and a voltage loop unit connected to the aforementioned current loop unit; the current loop unit includes a pulse width modulator, and the output terminal of the pulse width modulator connected to an optocoupler, the optocoupler is connected to the base of the switch, and; the voltage loop unit includes a microprocessor to provide a current command in phase with the input voltage to the pulse width modulation Inverter, the current command has the effect of adding harmonic compensation; the pulse width modulator controls the switching switch through an optocoupler to obtain a detection current, which is compared with the current command to control the input voltage and current .

By adopting the above scheme, the input voltage and current can be adjusted according to different circuit conditions to achieve the same phase of the input voltage and current, thereby improving the power factor and having great flexibility.

In order to further understand the purpose, features and advantages of the present invention, a preferred embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

Fig. 1 is the structure circuit diagram that has fixed frequency high power factor active type peak current control type filter of the present invention;

Fig. 2 (A) and Fig. 2 (B) are the output waveform diagrams of the boost conversion unit of a preferred embodiment of the present invention;

Fig. 3 is the oscillogram of electric current order I _C of the present invention;

FIG. 4 is a waveform diagram of the detection current I _CT of the present invention.

The active peak current control type filter with constant frequency and high power factor of the present invention is shown in Figure 1, and it comprises:

A step-up conversion unit 10, a voltage loop unit 20 and a current loop unit 30; the step-up conversion unit 10 is connected to a boost inductor 12 by a power supply 11, and is connected to the aforementioned booster with the input end of a bridge rectifier 18. The positive terminal of piezoelectric inductance 12 and a diode 13, the negative terminal of described diode 13 connects two output load capacitors 14,15 in series, and described load capacitor 15 is connected to the positive terminal of another diode 16, and the negative terminal of described diode 16 is connected To the positive end of the aforementioned boost inductor 12 and diode 13, a switch 17 is provided to trim the input current Is into a sinusoidal waveform. The working principle of the circuit is as follows:

When the switch 17 is turned on, the input current _IS flows through the switch 17, at this time, the power supply 11 charges the boost inductor 12, and the waveform of the input current Is is shown in the t ₀ -t ₁ section in FIG. 2(A) .

When the switch 17 is turned off, the diode 13 is turned on at this time, and the input current Is flows through the diode 13 to charge the load capacitor 14. At this time, the boost inductor 12 is in a discharging state, and the waveform of the input current Is is shown as t in Fig. 2 (A). ₁ -t ₂ paragraphs.

If the control command of the switching switch 17 is set as a pulse mode, so that the boost inductor 12 is continuously charged and discharged, a whole cycle of sine wave input current I _S can be obtained, and its waveform is shown in FIG. 2B .

Still please refer to Fig. 1, described voltage loop unit 20 comprises a microprocessor 21, a buffer 22 connected to the output end of microprocessor 21; , C2 is composed of a filter circuit, the output end of the filter circuit is connected to the input end comp of the pulse width modulator 40 through two diodes D1, D2.

The microprocessor 21 first detects the output load voltage (V _BUS ) of the boost conversion unit 10 and compares it with an output load voltage preset value (V _BUS ') to obtain an error voltage ( _VE ); then detects the input voltage V phase of _S , and compare it with the preset voltage reference table to obtain a voltage reference value V _REF . A current command I _C can be obtained by multiplying the voltage reference V _REF by the error voltage V _E , and the current command I _C is in phase with the input voltage V _S . This current command _IC is output by the microprocessor 21, and its output capability is improved through the above-mentioned buffer 22. The current command _IC has the effect of adding harmonic compensation, and becomes a non-standard sine wave. Its waveform is shown in Figure 3 , which can reduce the total harmonic distortion and improve the power factor.

The current loop unit 30 includes a pulse width modulator 40, the output of which is connected to an optocoupler 31 for isolation, and the optocoupler 31 is connected to a base electrode of a transistor used as a switching switch 17. The changeover switch 17 is connected to the output of the bridge rectifier 18 via the primary side of a transformer 32 . The secondary side of the transformer 32 is connected to a current detection resistor 34 through a diode 33, and a detection current is output from the current detection resistor 34 to the C/S terminal of the pulse width modulator 40, and the aforementioned voltage loop unit 20 The current command _IC is input to the input terminal comp of the pulse width modulator 40 .

When the entire current loop unit 30 is working, the pulse width modulator 40 sends a pulse signal to the optocoupler 31, and the optocoupler 31 controls the switching switch 17 to be turned on or off. When the switching switch 17 is turned on, the input current Is After the bridge rectifier 18, and then through the primary side of the transformer 32, a detection current I _CT is induced from the secondary side of the transformer 32 and input to the C/S end of the pulse width modulator 40 through the diode 33, and the detection current I The waveform of _CT is shown in Fig. 4. Here, the Comp terminal of the pulse width modulator 40 receives a current command I _C from the voltage loop unit 20, and the current command I _C is in phase with the input voltage, and the C/S terminal receives a detection current I _CT , and is determined by The pulse width modulator 40 compares the two sets of current values. If the current command I _C is greater than the detection current I _CT , the output of the pulse width modulator 40 is a high level, so that the switch 17 is turned on. If the current command I _C is less than the detection current I _CT , the output of the pulse width modulator 40 is at a low level, so that the switch 17 is turned off. By switching the switch 17, the input current Is follows the detection current I _CT , so that the input current Is can be in phase with the input voltage And it is a sine wave waveform, so that the purpose of improving the power factor can be achieved.

To sum up, the design of the present invention can effectively adjust the input voltage and input current to be in the same phase, and further increase the power factor to approach 1, so that the power loss is greatly reduced.

Claims (3)

1. an active peak current control type filter with constant frequency high power factor is characterized in that it comprises a step-up conversion unit and an active power factor corrector; the step-up conversion unit comprises: power supply, A boost inductor connected to the power supply, a first and second diode (D3, D4), output load capacitors (C3, C4), a bridge rectifier, and a switch; the input of the bridge rectifier is connected to the boost inductor and the positive terminal of the first diode (D3); the load capacitance (C3, C4) is connected in series between the negative terminal of the first diode (D3) and the positive terminal of the second diode (D4); through The switching switch modifies the input current into a sine wave waveform; the active power factor corrector is composed of a current loop unit connected to the boost conversion unit and a voltage loop unit connected to the aforementioned current loop unit; the current loop unit It includes a pulse width modulator, the output end of the pulse width modulator is connected with an optocoupler, and the optocoupler is connected with the base of the switching switch, and; the voltage loop unit includes a microprocessor to provide a current command in phase with the input voltage to the pulse width modulator, the current command has the effect of adding harmonic compensation; the pulse width modulator controls the switching switch through an optocoupler to obtain a Current is sensed to control input voltage and current compared to the current command. 2. The active peak current control filter with constant frequency and high power factor as claimed in claim 1, wherein the switch is connected to the output terminal of the bridge rectifier by the primary side of a transformer, The secondary side of the transformer is connected to a current detection resistor through a diode; Among them, the pulse output by the pulse width modulator controls the optocoupler, so that the switch is turned on or off. When it is turned on, the input current induces a detection current on the secondary side of the transformer through the bridge rectifier to input the pulse width modulator. , the pulse width modulator compares the detected current with the current command to control its pulse output. 3. The active peak current control filter with constant frequency and high power factor as claimed in claim 1 or 2, wherein the output terminal of the microprocessor is connected with a buffer, and the buffer is connected with a A filter circuit connected via a diode to the input (comp) of the pulse width modulator.

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