JP2011172372A - Pfc converter - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To structure a PFC converter that reduces a ripple current and decreases a peak level of EMI noise. <P>SOLUTION: A diode bridge B1 is connected to input terminals P11, P12. At the output side of the diode bridge B1, two PFC circuits PFC1, PFC2 are structured with inductors L11, L12, switching elements Q11, Q12, and diodes D11, D12. Output terminals P21, P22 are connected to both ends of a smoothing capacitor Co. A switching control circuit 30 PWM-modulates a gate control voltage signal to the switching elements Q11, Q12 so that average currents flowing in the inductors L11, L12 become similar in shape to an input voltage waveform (full-wave rectified waveform) and an output voltage becomes constant. In that case, the switching elements Q1, Q2 are switched by a plurality of switching frequencies different from each other. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a PFC converter, and more particularly to a PFC converter using a multiphase PFC circuit.

  In general, a PFC converter (power factor correction circuit) used for an AC-DC converter in order to clear the harmonic current regulation is configured as a boost chopper circuit using one switch element. In the case of high power applications, a multi-phase PFC converter that shares power conversion is configured by connecting a plurality of PFC circuits in parallel as shown in Patent Document 1.

FIG. 1A is a circuit diagram showing a configuration of a main part of the multiphase PFC converter, and FIG. 1B is a waveform diagram of a current flowing through the inductor.
A voltage obtained by full-wave rectifying an AC input voltage of a commercial AC power supply is applied to terminals P31 and P32. Between the terminals P31 and P32, a series circuit including an inductor L11 and a switching element Q11, and an inductor L12 and a switching element Q12 are provided. Another series circuit consisting of is connected in parallel. A diode D11 is connected between the connection point between the switching element Q11 and the inductor L11 and the smoothing capacitor Co, and a diode D12 is connected between the connection point between the switching element Q12 and the inductor L12 and the smoothing capacitor Co. Both ends of the smoothing capacitor Co are connected to output terminals P21 and P22.

  The PFC control IC (not shown) receives a detection signal of the current flowing through the inductors L11 and L12, sends a control signal to the switching elements Q11 and Q12, and alternately switches the switching elements Q11 and Q12 with a phase difference 180 (in an interleaved manner). ) Turn on / off.

  As shown in FIG. 1B, the input current i (L11 + L12) for the PFC converter is the sum of the current i (L11) flowing through the inductor L11 and the current i (L12) flowing through the inductor L12. As described above, in the multi-phase PFC converter, the ripple of the input current from the commercial AC power supply is reduced, and the components such as the inductor can be reduced in size, and the PFC converter can be reduced in size and height.

JP 2006-187140 A

  The switching power supply device disclosed in Patent Document 1 has four PFC circuits connected in parallel, and the four switching elements operate at the same frequency and at different phases (ie, four phases) every 90 °. . When the number of phases is increased in this way, the ripple current is reduced accordingly.

  However, since the switching frequency of the four switching elements is the same, the switching frequency and the higher-order EMI noise are generated with the same strength as a single-phase PFC using a single inductor and a single switching element. There was a problem that it would.

  Here, FIG. 2 shows an example of the spectrum of the generated EMI noise for the single-phase PFC and the two-phase PFC. 2A shows the spectrum of EMI noise when a single-phase PFC switching element is driven at 100 kHz, and FIG. 2B shows the EMI noise when the two-phase PFC switching element is driven at 100 kHz with a phase difference of 180 degrees. Is the spectrum.

  In the case of a single phase PFC, as shown in FIG. 2A, EMI noise is also generated at a frequency that is an integral multiple of 100 kHz in addition to 100 kHz. The level of these higher-order noises gradually decreases as the order increases.

  In the case of the two-phase PFC, as shown in FIG. 2B, EMI noise is also generated at a frequency that is an integral multiple of 100 kHz in addition to 100 kHz. At a frequency that is an even multiple of the fundamental frequency of 100 kHz, such as 200 kHz or 400 kHz, noise components generated by the two PFC circuits overlap, and high-level noise still occurs.

  Thus, since the frequency components of the noise generated by switching of each switching element are the same and are superimposed, the peak level of EMI noise is equivalent to that of the single phase PFC.

  An object of the present invention is to provide a PFC converter in which the peak level of EMI noise is reduced.

The PFC converter of this invention is
An AC voltage input unit to which a commercial AC power supply is connected;
A DC voltage output unit to which a load is connected;
An inductor, a switching element for energizing the inductor during the on period with a current input from the AC voltage input unit, and a diode for energizing a current (generated voltage) flowing through the inductor during the off period of the switching element, respectively Including a plurality of PFC circuits connected in parallel;
A smoothing capacitor that smoothes the voltage output from the PFC circuit and outputs it to the DC voltage output unit at a stage after the PFC circuit;
A switching control circuit for controlling the switching element,
The switching control circuit switches the plurality of switching elements at a plurality of switching frequencies having different frequencies.

  For example, there are three or more PFC circuits and three or more switching frequencies, and these switching frequencies have the same frequency difference between adjacent frequencies. That is, it is determined at equal intervals.

The switching control circuit varies the plurality of switching frequencies in accordance with a change in time while keeping the frequency difference between them substantially equal. That is, frequency jitter is included.
The switching frequency fluctuates so as to periodically increase and decrease, and the time when the switching frequency changes from rising to falling or from falling to rising is a time when the current input from the AC voltage input unit becomes substantially zero. And

  According to the present invention, the superposition of EMI noise at the same frequency is eliminated, and the peak level of EMI noise is suppressed.

FIG. 1A is a circuit diagram showing a configuration of a main part of a multi-phase PFC converter, and FIG. 1B is a waveform diagram of a current flowing through the inductor. FIG. 2A shows the spectrum of EMI noise when a single-phase PFC switching element is driven at 100 kHz, and FIG. 2B shows the EMI when the two-phase PFC switching element is driven at 100 kHz with a phase difference of 180 degrees. It is a spectrum of noise. 1 is a circuit diagram of a switching power supply device according to a first embodiment. FIG. 4A shows the spectrum of EMI noise when two switching elements of a two-phase PFC are driven at 100 kHz. FIG. 4B shows the driving of one switching element of the two-phase PFC at 95 kHz, and the other. It is the spectrum of EMI noise when it drives by switching element 105kHz. 3 is a block diagram illustrating a configuration of a switching control circuit 30. FIG. 6 (A) and 6 (B) are diagrams showing the change of the switching frequency of the two switching elements Q1, Q2 with time. FIG. 7A shows the spectrum of EMI noise in the PFC converter shown in the first embodiment. FIG. 7B shows an EMI noise spectrum when jitter is included in the switching frequency of the switching elements Q1 and Q2 as shown in FIG. 6A or 6B.

<< First Embodiment >>
The PFC converter according to the first embodiment will be described with reference to FIGS.
FIG. 3 is a circuit diagram of the PFC converter 101 according to the first embodiment. In FIG. 3, a commercial AC power supply AC is connected to input terminals P11 and P12. Further, the load 20 is connected to the output terminals P21 and P22, and a predetermined DC voltage is output to the load 20. The input terminals P11 and P12 correspond to an “AC voltage input unit” according to the present invention. The output terminals P21 and P22 correspond to the “DC voltage output unit” according to the present invention.

  The load 20 is, for example, a DC-DC converter and a circuit of an electronic device that is supplied with power by the DC-DC converter.

  A diode bridge B1 is connected to the input terminals P11 and P12, and a series circuit composed of an inductor L11 and a switching element Q11 and another series circuit composed of an inductor L12 and a switching element Q12 are connected to the output of the diode bridge B1. It is connected. A diode D11 is connected between the connection point between the switching element Q11 and the inductor L11 and the smoothing capacitor Co, and a diode D12 is connected between the connection point between the switching element Q12 and the inductor L12 and the smoothing capacitor Co. Output terminals P21 and P22 are connected to both ends of the smoothing capacitor Co.

  The switching element Q11 supplies current that is input from the input terminals P11 and P12 to the inductor L11 during the ON period. The diode D11 energizes a current (generated voltage) flowing through the inductor L11 during the OFF period of the switching element Q11. Similarly, the switching element Q12 supplies the current input from the input terminals P11 and P12 to the inductor L12 during the ON period. The diode D12 energizes the current flowing through the inductor L12 during the OFF period of the switching element Q12.

  The inductor L11, the diode D11, and the switching element Q11 constitute a first PFC circuit PFC1. Similarly, a second PFC circuit PFC1 is configured by the inductor L12, the diode D12, and the switching element Q12.

An input voltage detection circuit 11 is provided between the input terminals P11 and P12. An output voltage detection circuit 12 is provided between the output terminals P21 and P22.
The switching control circuit 30 receives the input voltage detection signal detected by the input voltage detection circuit 11, the output voltage detection signal detected by the output voltage detection circuit 12, and the detection signal of the current flowing through the inductors L11 and L12, respectively, and the switching element Q11. , Q12 output a gate control voltage.

  Specifically, the switching control circuit 30 applies current to the switching elements Q11 and Q12 so that the current flowing through the inductors L11 and L12 is similar to the input voltage waveform (full-wave rectification waveform) and the output voltage is constant. PWM modulates the gate control voltage signal. That is, the on-duty (on period) of the gate control voltage signal is controlled.

  FIG. 5 is a block diagram showing the configuration of the switching control circuit 30. In FIG. 5, the addition element 31 obtains an error ev of the output voltage detection value Vo with respect to the output voltage target value Vref. The output voltage error amplifier 32 obtains the current reference amplitude value Vm by multiplying the error ev by a predetermined proportional coefficient. The multiplier 33 multiplies the current reference amplitude value Vm by the input voltage detection value Vi to obtain a sinusoidal current reference value iref.

  The inductor current average value detector 37A generates a voltage corresponding to the average value of the inductor current from the voltage Vrs1 of the current detection signal. Similarly, the inductor current average value detector 37B generates a voltage corresponding to the average value of the inductor current from the voltage Vrs2 of the current detection signal.

  The adding element 34A obtains an input current error value ei1 which is a difference between the inductor current average value V (iL) 1 with respect to the current reference value iref. The input current error amplifier 35A amplifies the input current error value ei1 and generates a modulation signal D1 for the pulse generator. Similarly, the adding element 34B obtains an input current error value ei2 which is a difference between the average value V (iL) 2 of the inductor current with respect to the current reference value iref. The input current error amplifier 35B amplifies the input current error value ei2 and generates a modulation signal D2 for the pulse generator.

  The oscillator 38A generates a triangular wave signal having a frequency corresponding to the oscillation frequency control voltage Fc1 supplied from a control circuit provided in the switching control circuit 30. Similarly, the voltage controlled oscillator 38B generates a triangular wave signal having a frequency corresponding to the oscillation frequency control voltage Fc2 supplied from the control circuit provided in the switching control circuit 30.

  The pulse generator 36A compares the modulation signal D1 with the triangular wave signal and outputs a PWM-modulated gate control voltage Qg1. Similarly, the pulse generator 36B compares the modulation signal D2 with the triangular wave signal and outputs a PWM-modulated gate control voltage Qg2.

The pulse generator 36B outputs the gate control voltage Qg2 of the switching element Q2 based on the modulation signal D2.

  The switching control circuit 30 shown in FIG. 5 outputs the oscillation frequency control voltages Fc1 and Fc2 so that the switching elements Q1 and Q2 have different switching frequencies.

For example, if the frequency of the gate control voltage signal of the switching element Q11 is f1, and the frequency of the gate control voltage signal of the switching element Q12 is f2, then f1 = 95 kHz and f2 = 105 kHz.

  FIG. 4A shows the spectrum of EMI noise when two switching elements of a two-phase PFC are driven at 100 kHz. FIG. 4B shows the driving of one switching element of the two-phase PFC at 95 kHz, and the other. It is a spectrum of EMI noise when the switching element is driven at 105 kHz.

  Noise peaks occur at a frequency of 190 kHz, which is twice 95 kHz, and at a frequency of 210 kHz, which is twice that of 105 kHz. Similarly, high-order noise of 3rd harmonic or higher has peaks at frequencies that are integral multiples of 95 kHz and 105 kHz.

  As described above, since the frequency components of the noises generated in the first PFC circuit PFC1 and the second PFC circuit PFC2 are shifted in peak frequency, respectively, EMI noise at a high frequency of 200 kHz or more, particularly noise reduction of the second harmonic wave. It turns out that an effect is high.

<< Second Embodiment >>
A PFC converter according to a second embodiment will be described with reference to FIGS.
The circuit diagram of the PFC converter 102 according to the second embodiment and the switching control circuit 30 are the same as those of the PFC converter 101 according to the first embodiment. The first embodiment is different from the PFC converter 101 shown in FIG. 3 in that an oscillator having a jitter function is provided in the switching control circuit 30.

  In the second embodiment, the switching control circuit 30 shown in FIG. 5 controls the oscillation frequency so that the switching frequency of the switching elements Q1 and Q2 varies according to the time change while keeping the frequency difference between them substantially equal. The voltages Fc1 and Fc2 are output.

6 (A) and 6 (B) are diagrams showing the change of the switching frequency of the two switching elements Q1, Q2 with time.
In the example of FIG. 6A, the switching frequencies F1 and F2 of the switching elements Q1 and Q2 repeat rising and falling while keeping the frequency difference equal to each other. In this example, the switching frequency F1 of the switching element Q1 changes in the range from the frequency fL to fc around the frequency fo1, and the switching frequency F2 of the switching element Q2 changes in the range from the frequency fc to fH around the frequency fo2.

  In the example of FIG. 6 (B), the switching frequencies F1 and F2 of the switching elements Q1 and Q2 change in the upward direction while maintaining the same frequency difference between them, and the frequency relationship between the switching frequencies F1 and F2 is intermittent. Change. In this example, the switching frequency F1 increases from the lower limit frequency fL to the upper limit frequency fH, and then returns to the lower limit frequency fL again. The same applies to the switching frequency F2, but the phase of the change period is shifted by 180 degrees compared to the switching frequency F1.

  As shown in FIG. 6A and FIG. 6B, when the switching operation of the switching frequency F1, F2 is increased or decreased, or when the relationship between the heights of F1, F2 is switched, A point at which the input voltage Vi or the input current Ii becomes zero, that is, a so-called zero cross point may be set. In other words, the fluctuation cycle of the switching frequencies F1 and F2 may be synchronized with a half cycle of the commercial power supply frequency or a cycle that is an integral multiple of the half cycle.

  Since the input current to the PFC converter does not flow or is extremely small at the zero cross point, even if the switching frequencies F1 and F2 change suddenly at that point, the influence on the operation of the PFC converter can be suppressed.

Note that the switching time of the switching frequency may not be exactly the zero cross point but may be near the zero cross point. Since the input current to the PFC converter is small near the zero cross, the influence on the operation of the PFC converter can be reduced.
In this way, jitter is included in the switching frequency of the switching elements Q1, Q2.

  FIG. 7A shows a case where the switching frequency of the first switching element Q1 shown in FIG. 5 is fixed to 95 kHz and the switching frequency of the second switching element Q2 is fixed to 105 kHz (that is, the first embodiment). It is a spectrum of EMI noise (in the PFC converter shown by). FIG. 7B shows an EMI noise spectrum when jitter is included in the switching frequency of the switching elements Q1 and Q2 as shown in FIG. 6A or 6B.

  As shown in FIG. 7B, by including jitter in the switching frequency of the switching elements Q1 and Q2, the frequency spectrum of noise is further spread. Therefore, the quasi-peak value indicated by a circle in the figure can be reduced by several dB, and the average value indicated by a cross in the figure can be reduced by 10 dB or more.

<< Other embodiments >>
In the examples shown in the above embodiments, a two-phase PFC converter is configured, but the present invention can be similarly applied to a multi-phase PFC having three or more phases. That is, three or more PFC circuits are provided, and each switching element is switched at three or more frequencies having different frequencies.

  These switching frequencies may be equal in frequency difference between adjacent frequencies, that is, at equal intervals. As a result, it is possible to suppress a decrease in power conversion characteristics and efficiency due to driving the switching element at an extremely distant switching frequency.

AC ... commercial AC power supply B1 ... diode bridge Co ... smoothing capacitors P11, P12 ... input terminals P21, P22 ... output terminals PFC1, PFC2 ... switching circuit PFC11, PFC12 ... PFC circuit PFC21, PFC22 ... PFC circuit PFC31, PFC32 ... PFC circuit Q1 , Q2 ... switching elements Q11, Q12 ... switching elements Q21, Q22 ... switching element 11 ... input voltage detection circuit 12 ... output voltage detection circuit 20 ... load 30 ... switching control circuits 101-105 ... PFC converter

Claims (4)

An AC voltage input unit to which a commercial AC power supply is connected;
A DC voltage output unit to which a load is connected;
A plurality of inductors, a switching element that supplies current that is input from the AC voltage input unit to the inductor during an ON period, and a diode that supplies current that flows through the inductor during an OFF period of the switching element. A PFC circuit;
A smoothing capacitor that smoothes the voltage output from the PFC circuit and outputs it to the DC voltage output unit at a stage after the PFC circuit;
In a PFC converter comprising a switching control circuit for controlling the switching element,
The PFC converter, wherein the switching control circuit switches the plurality of switching elements at a plurality of switching frequencies having different frequencies.   The PFC converter according to claim 1, wherein there are three or more PFC circuits, and there are three or more switching frequencies, and these switching frequencies have the same frequency difference between adjacent frequencies.   3. The PFC converter according to claim 1, wherein the switching control circuit varies the plurality of switching frequencies while keeping a frequency difference between them substantially equal to each other according to a time change.   The switching frequency fluctuates so as to periodically increase and decrease, and the time when the switching frequency changes from rising to falling or from falling to rising is a time when the current input from the AC voltage input unit becomes substantially zero. The PFC converter according to claim 3.

Images