JP6168809B2 - Switching power supply circuit - Google Patents

Description

  The present invention relates to a switching power supply circuit, and more particularly to a switching power supply circuit that can improve the generation of ripple that is a pulsation component contained in a direct current.

  As a circuit used for a voltage booster of a power supply circuit, an interleaved switching power supply circuit including two or more switching circuits is known (for example, Patent Document 1).

  Patent Document 1 discloses a switching power supply circuit in which at least one of the characteristics of a reactor, a switching element, and a diode belonging to each of two switching circuits is different from each other. According to Patent Document 1, since this switching power supply circuit can select three electrical characteristics as appropriate, the power factor, efficiency, and harmonics can be adjusted.

Japanese Patent No. 4844696 (FIGS. 9 to 11)

In Patent Document 1, FIGS. 9 to 11 show examples of waveforms of currents I1 and I2 flowing through the respective reactors and a current I which is the sum of the currents when various switching methods are employed. In this switching power supply circuit, the inductance of one reactor is twice that of the other reactor. Note that I1, I2, and I are used only to distinguish each current, and so on.
However, as long as the current waveforms shown in FIGS. 9 to 11 of Patent Document 1 are referred to, the ripple rate of the current I becomes large and a stable output cannot be obtained.
An object of the present invention is to obtain a stable output current by reducing a ripple rate in a switching power supply circuit including at least two switching circuits including a reactor, a switching element, and a diode.

For this purpose, the switching power supply circuit of the present invention includes a first switching circuit, a second switching circuit, and a control unit.
The first switching circuit is connected in series to the first reactor, the first reactor, the first diode disposed with the anode facing the first reactor, the first reactor, and the first reactor And a first switching element provided between the diodes.
The second switching circuit includes a second reactor having an inductance smaller than that of the first reactor,
A second diode connected in series with the second reactor and having the anode facing the second reactor, and a second switching element provided between the second reactor and the second diode; Have
The control unit controls the switching operation of the first switching element and the second switching element,
When the switching frequency of the first switching element is f1 and the switching frequency of the second switching element is f2, the switching operation is controlled so that the switching frequency f2 is higher than the switching frequency f1.
According to the switching power supply circuit of the present invention, since the second reactor has an inductance smaller than that of the first reactor, the number of turns of the coil constituting the second reactor can be made smaller than that of the first reactor. Therefore, in addition to realizing the downsizing of the second reactor, the manufacturing cost can be suppressed.
In the switching power supply circuit of the present invention, the switching frequency f2 is larger than the switching frequency f1, so that the current I2 flowing through the second reactor is similar to the current I1 flowing through the first reactor, and 180 A degree of phase difference can be provided. Therefore, the ripple rate of the current I, which is the sum of the currents I1 and I2, can be reduced.

In the switching power supply circuit of the present invention, the first switching element is constituted by a silicon semiconductor, the second switching element is Ru is constituted by a silicon carbide semiconductor or gallium nitride semiconductor.
In the present invention, since the second switching element switches at a higher frequency than the first switching element, the loss due to switching is larger than that of the first switching element. Therefore, a SiC (silicon carbide) semiconductor or a GaN (gallium nitride) semiconductor that can significantly reduce the loss is used as the second switching element. On the other hand, the manufacturing cost can be reduced by forming the first switching element by a low-cost Si (silicon) semiconductor.

In the switching power supply circuit of the present invention, the control unit has a predetermined current with respect to a reference waveform in which the current flowing through the second reactor is similar to the waveform of the current flowing through the first reactor and has a phase difference of 180 degrees. The switching operation can be controlled so as to be within the ripple current width.
This control is based on hysteresis control, and since the ripple width can be controlled to be constant, it is suitable for applications in which high-precision current output with stable ripple is important.

In the switching power supply circuit of the present invention, the control unit controls the switching operation so that the switching frequency of the second switching element is an integer multiple of 2 or more of the switching frequency of the first switching element. Can do.
In this control, PWM (Pulse Width Modulation) control is suitable for applications where low cost is important.

  According to the present invention, it is possible to reduce the ripple rate of the current I, which is the sum of the current I1 and the current I2, in addition to the reduction in size and cost of the second reactor.

It is a figure which shows schematic structure of the switching power supply circuit in this embodiment. The waveform of the electric current of the 2nd reactor by this embodiment obtained by performing hysteresis control is shown. It is a graph which shows the relationship between the switching frequency ratio (f2 / f1) measured in this embodiment, and a ripple rate. The waveform of the electric current of the 2nd reactor by this embodiment obtained by performing PWM control is shown. It is a figure which shows the example of the current waveform by interleave control.

Hereinafter, the switching power supply circuit of the present invention for reducing the ripple rate will be described based on the embodiment shown in FIGS.
[Configuration of switching power supply circuit]
First, the configuration of the switching power supply circuit 10 will be described.
As shown in FIG. 1, the switching power supply circuit 10 includes a plurality of (here, two) first switching circuits 3a and second switching circuits 3b. Each of the switching circuits 3a and 3b is connected to the input terminals 11 and 12 and the output terminals 13 and 14, and boosts the DC voltage applied between the input terminals 11 and 12, and from the output terminals 13 and 14, respectively. Is output.
The switching power supply circuit 10 includes an AC power supply 1 and a rectifier circuit 2, rectifies the AC voltage supplied from the AC power supply 1 by the rectifier circuit 2, and applies the rectified DC voltage between the input terminals 11 and 12.
In the switching power supply circuit 10, the DC voltage boosted by the switching circuits 3 a and 3 b is input to the inverter 4 via the output terminals 13 and 14. Further, the switching power supply circuit 10 includes a control unit 5 that controls the operation of the switching elements S1 and S2 of the switching circuits 3a and 3b.

  The switching circuit 3a includes a first reactor L1, a first diode D1, and a first switching element S1. The reactor L1 and the diode D1 are arranged on a conductive line 15 connecting the input end 11 and the output end 13 such that the reactor L1 is on the input end 11 side and the diode D1 is on the output end 13 side. Connected to. The anode of the diode D1 is arranged toward the reactor L1.

  Switching element S1 is connected to conductive line 15 between reactor L1 and diode D1. The operation of the switching element S1, that is, conduction and non-conduction is controlled by the control unit 5.

  The switching circuit 3b includes a second reactor L2, a second diode D2, and a second switching element S2. The reactor L2 and the diode D2 are arranged on the conductive line 16 connecting the input terminal 12 and the output terminal 14 such that the reactor L2 is on the input terminal 12 side and the diode D2 is on the output terminal 14 side. Connected to. The anode of the diode D2 is provided toward the reactor L2.

  In the present embodiment, the inductance value of the reactor L2 of the switching circuit 3b can be set smaller than the inductance value of the reactor L1 of the switching circuit 3a, for example, 1/2. By doing so, the number of turns of the coil constituting reactor L2 can be made half of reactor L1. Therefore, the reactor L2 can be reduced in size, and the manufacturing cost can be reduced. However, 1/2 is an example and does not limit the present invention.

  In order to reduce noise of currents input to the switching circuits 3a and 3b, a capacitor is provided between the input terminals 11 and 12, and an output terminal is used to smooth the DC voltage boosted by the switching circuits 3a and 3b. Other elements can be added to the switching power supply circuit 10, such as providing a capacitor between 13 and 14.

The control unit 5 includes an arithmetic processing device 5a and a storage device 5b. The arithmetic processing unit 5a executes a procedure for controlling the operation of the switching power supply circuit 10 including the operations of the switching elements S1 and S2 according to the program stored in the storage device 5b.
The arithmetic processing unit 5a is composed of, for example, a microcomputer, and the storage unit 5b is a single or plural storage units such as a ROM (Read-Only-Memory), a RAM (Random-Access-Memory), and a hard disk unit. Composed.

  The switching power supply circuit 10 is used for various applications. For example, when used in an air conditioner, the inverter 4 applies an AC voltage toward a compressor or a motor that drives a fan of the air conditioner.

[Operation of Switching Power Supply Circuit (Switching Circuits 3a, 3b)]
Hereinafter, the operation of the switching power supply circuit 10 will be described.
The switching power supply circuit 10 operates the switching circuits 3a and 3b by shifting the switching phases of the switching element S1 and the switching element S2. This control is performed by the control unit 5. Here, when the phases of the switching element S1 and the switching element S2 are shifted, as shown in FIG. 5, the valley part where the value of the current I1 flowing through the reactor L1 is low and the peak part where the value of the current I2 flowing through the reactor L2 is high Are offset, and the peak portion where the value of the current I1 flowing through the reactor L1 is high and the valley portion where the value of the current I2 flowing through the reactor L2 is low are offset. Therefore, the fluctuation component (so-called harmonic component) of the current I that is the sum of the current I1 and the current I2 can be reduced.

  In particular, the upper part of FIG. 5 shows an ideal example. Since the current I1 and the current I2 have the same frequency and amplitude and the phase difference is shifted by 180 degrees, the current I (current I1 + current I2) shows a flat waveform, and the ripple rate is zero. Here, the ripple ratio in the present invention is a value obtained by dividing the fluctuation range of the current I by the average of the current I. The lower example in FIG. 5 shows an example in which the currents I1 and I2 have the same frequency, but the amplitude of the current I2 is twice that of the current I1, and in this example, the ripple ratio is 0.67.

  In the present embodiment, the control unit 5 shifts the switching phases of the switching element S1 and the switching element S2. That is, the switching element S2 is turned on when a predetermined time has elapsed since the switching element S1 was turned on. Here, if the frequency obtained from the period from when the switching element S1 is turned on to when it is turned on again is f1, the frequency f2 of the switching element S2 is made smaller than the frequency f1. Here, the amount of change per hour of the current flowing through the coil constituting the reactor increases as the frequency decreases. Therefore, when switching element S2 is switched at a higher frequency than switching element S1, the average waveform of current I2 flowing through reactor L2 is similar to the waveform of current I1 of reactor L1, and the phase difference between the two waveforms Can be set to 180 degrees (see FIG. 2D).

  While changing the ratio of the frequency of the switching element S2 to the switching element S1 (switching frequency ratio = f2 / f1), the waveform of the current I2 flowing through the reactor L2 is measured, and from the current I which is the sum of the current I1 flowing through the reactor L1 The result of the obtained ripple rate will be described with reference to FIGS. Here, the switching ON / OFF timing is performed based on the hysteresis control so that the current I2 of the reactor L2 becomes the set ripple current width RW with respect to the reference waveform IS. The reference waveform IS is similar to the waveform of the current I1 of the reactor L1 and has a phase difference of 180 degrees. The waveform of the current I2 is similar to the waveform of the current I1, and the phase difference between the two is 180 degrees. To function.

As shown in FIGS. 2 and 3, the ripple of the current I2 can be reduced by increasing the switching frequency f2 of the switching element S2 with respect to the switching frequency f1. When the switching frequency ratio (f2 / f1) is set to 13, it can be seen that the waveform as the average of the current I2 is similar to the waveform of the current I1 and can be provided with a phase difference of 180 degrees. Thus, by setting the switching frequency ratio (f2 / f1) high, the harmonic current regulation is satisfied, and a stable output current can be supplied to the device connected to the output. In general, the power supply circuit is designed so that the output ripple is low. However, if the fluctuation of the output ripple is large, a smoothing filter circuit such as a capacitor or a reactor is separately required to smooth the fluctuation. Therefore, according to the present embodiment that can reduce the ripple rate, the size of the switching power supply circuit 10 can be reduced, and the cost can be reduced.
As the switching frequency ratio (f2 / f1) increases, the ripple ratio decreases and the output current becomes flat. On the other hand, since the frequency of the switching element S2 needs to be increased, the switching loss increases, and the circuit increases. Decreases the efficiency. In order to suppress the switching loss, it is preferable to use a SiC (silicon carbide) semiconductor or a GaN (gallium nitride) semiconductor called a wide gap semiconductor power element for the switching element S2, as described later, but the switching frequency ratio ( If f2 / f1) becomes too large, the loss cannot be ignored. Therefore, in consideration of suppressing the ripple rate and suppressing the increase in switching loss, the switching frequency ratio (f2 / f1) is preferably in the range of 5 to 15, more preferably in the range of 5 to 10.

In the present embodiment, the switching timing of the switching element S1 and the switching element S2 can also be performed by PWM (Pulse Width Modulation) control. In this case, as shown in FIG. 4, the switching frequency f2 of the switching element S2 is an integral multiple (however, 2 or more) of the switching frequency f2 of the switching element S1.
Switching by hysteresis control suppresses the current ripple below a set value and switches on / off when the current ripple reaches a threshold value, so the switching frequency does not become constant. On the other hand, when PWM control is applied, the switching frequency can be made constant as shown in FIG. However, the magnitude of the ripple for each switching changes. Therefore, when switching control is performed by a CPU (Central Processing Unit), the cycle can be synchronized by an integer multiple, so the software for switching control is simplified, and processing is performed more than by non-integer multiples (hysteresis control). The amount can be reduced. Further, when PWM control is applied, the sampling at the time of detecting the current of the reactor L1 and the reactor L2 can be performed synchronously, so that software processing is simplified.

  As described above, hysteresis control is suitable for applications where high-precision current output is important because ripple width is constant and ripple is stable, while PWM control is important for low cost. Suitable for use.

Incidentally, since the switching element S2 is switched at a higher frequency than the switching element S1, a loss due to switching is larger than that of the switching element S1. Therefore, the switching element S2 is preferably an element that can greatly reduce the loss during switching. For example, by using a SiC (silicon carbide) semiconductor or a GaN (gallium nitride) semiconductor called a wide gap semiconductor power element for the switching element S2, loss due to switching of the switching element S2 can be greatly reduced. On the other hand, the switching element S1 is preferably formed of a Si (silicon) semiconductor that can be manufactured at a lower cost than a SiC semiconductor or a GaN semiconductor. If it does so, compared with the case where both switching element S1, S2 is formed with a SiC semiconductor or a GaN semiconductor, a manufacturing cost can be reduced.
However, the present invention can use other switching elements such as an insulated gate bipolar transistor and a MOS field effect transistor (Metal-Oxide-Semiconductor, Filed Effect Transistor).

As described above, the present invention has been described based on the embodiment. However, the configuration described in the above embodiment may be selected or changed to another configuration as long as it does not depart from the gist of the present invention.
Although the switching power supply circuit 10 includes two switching circuits, the present invention can also be applied to a switching power supply circuit including three or more switching circuits.
In the above description, the operation when the two switching circuits 3a and 3b are interleaved is described. However, in addition to the interleave control, the two switching circuits 3a and 3b are operated individually. May be.

DESCRIPTION OF SYMBOLS 10 Switching power supply circuit 1 AC power supply 2 Rectifier circuit 3a, 3b Switching circuit 4 Inverter 5 Control part 11,12 Input end 13,14 Output end 15,16 Conductive line L1, L2 Reactor S1, S2 Switching element D1, D2 Diode I, I1, I2 current

Claims (3)

A first reactor;
A first diode connected in series with the first reactor and disposed with an anode directed toward the first reactor;
A first switching circuit having a first switching element provided between the first reactor and the first diode;
A second reactor having an inductance smaller than that of the first reactor;
A second diode connected in series with the second reactor and having an anode facing the second reactor;
A second switching circuit having a second switching element provided between the second reactor and the second diode;
A control unit for controlling a switching operation of the first switching element and the second switching element;
With
The controller is
When the switching frequency of the first switching element is f1, and the switching frequency of the second switching element is f2,
As the switching frequency f2 is greater than the switching frequency f1, to control the switching operation,
The first switching element is formed of a silicon semiconductor;
The second switching element is composed of a silicon carbide semiconductor or a gallium nitride semiconductor;
A switching power supply circuit. The controller is
The current flowing through the second reactor is
With respect to a reference waveform that is similar to the waveform of the current flowing through the first reactor and has a phase difference of 180 degrees, it fits within a predetermined ripple current width,
Controlling the switching operation of said second switching element,
The switching power supply circuit according to claim 1 . The controller is
2. The switching power supply circuit according to claim 1, wherein the switching operation is controlled such that a switching frequency of the second switching element is an integer multiple of 2 or more of a switching frequency of the first switching element.

Images