JP6472051B2 - Switching power supply device and electromagnet power supply system - Google Patents

Description

  The present invention relates to a switching power supply device and an electromagnet power supply system including the switching power supply device.

  As a switching power supply device for an electromagnet, for example, the one described in Patent Document 1 is known. The switching power supply device described in Patent Document 1 includes a first current source including a switch circuit and a capacitor made of a bridge-connected IGBT, and a second current source similarly including a switch circuit and a capacitor. According to this switching power supply device, the first current source and the second current source can be controlled to suppress a change at the top of the pulsed current supplied to the electromagnet.

  FIG. 4 shows an electromagnet power supply system 100B including another switching power supply apparatus 1B. The electromagnet power supply system 100B includes a transformer 11, a voltage conversion circuit 12, and a switching power supply device 1B.

  The voltage conversion circuit 12 converts the AC voltage input from the transformer 11 into a DC voltage and outputs the DC voltage. The voltage conversion circuit 12 includes a rectifying unit composed of a diode and a smoothing unit composed of a coil and a capacitor C1.

  The switching power supply device 1B includes a switch circuit 2 in which IGBTs are bridge-connected, a filter circuit 3 including an LC high frequency filter, and a control circuit (not shown) that performs PWM control of the IGBTs of the switch circuit 2. The control circuit of the switching power supply device 1B can control the output current supplied to the electromagnet 10 by controlling the on-time (duty ratio) of the IGBT.

JP 2012-243503 A

  By the way, if the ON time of the IGBT is made smaller than a predetermined lower limit value (minimum ON gate width), the IGBT may not be turned on due to characteristics. For example, when the control circuit performs PWM control of the IGBT at a switching frequency of 20 [kHz] (switching cycle of 50 [μs]), if the IGBT on-time is attempted to be smaller than 1 [μs], the IGBT is not turned on. There is.

  If the IGBT is not turned on, the switching operation of the IGBT by PWM control becomes intermittent, and the switching frequency of the IGBT is lowered. Here, since the filter circuit 3 is designed according to the switching frequency of the IGBT at the time of PWM control so as to attenuate the current ripple due to the switching of the IGBT, if the switching frequency is lowered, the attenuation factor of the current ripple due to the switching Becomes smaller.

  For this reason, when the low current output control is performed by making the on-time of the IGBT smaller than the predetermined lower limit value, in the conventional switching power supply device 1B, the attenuation factor of the current ripple due to the switching in the filter circuit 3 becomes small. As a result, there is a problem that the output current ripple output from the filter circuit 3 becomes large.

  The present invention has been made in view of the above circumstances, and it is an object of the present invention to provide a switching power supply device capable of performing low current output control without increasing output current ripple and an electromagnet including the switching power supply device. To provide a power supply system.

In order to solve the above problems, a switching power supply device according to the present invention provides:
A first switch circuit including at least one first switch means;
A filter circuit connected to an output terminal of the first switch circuit;
A control circuit for PWM controlling the first switch means;
A switching power supply device comprising:
A second switch circuit including at least one second switch means connected in parallel to the first switch circuit;
The control circuit includes:
The second switch so that the ON time of the second switch means is shorter than the ON time of the first switch means, and the first switch circuit and the second switch circuit output voltages having different polarities. PWM control means with the same switching frequency as the first switch means ,
The first switch circuit is a bridge circuit in which a plurality of the first switch means are bridge-connected,
The second switch circuit is a bridge circuit in which a plurality of the second switch means are bridge-connected .

  According to this configuration, since the excessive output voltage of the first switch circuit can be absorbed by the second switch circuit, it is not necessary to extremely reduce the ON time of the first switch means during the low current output control. As a result, according to this configuration, it is possible to prevent the output current ripple from becoming large during the low current output control.

In the above switching power supply device,
The control circuit includes:
In the range where the switching frequency of the first switch means does not change, the lower limit value of the ON time of the first switch means is set,
Preferably, the second switch means is PWM-controlled so that the minimum ON time of the second switch means becomes smaller than the lower limit value.

  According to this configuration, since the on-time of the first switch means is not made smaller than the lower limit value during the low current output control, the output current is reduced by the filter circuit designed according to the switching frequency without lowering the switching frequency. Ripple can be reliably suppressed.

In the above switching power supply device,
The control circuit can be configured to PWM control the second switch means only when the minimum on-time of the first switch means becomes the lower limit value.

In the switching power supply device, for example,
Before SL filter circuit is a LC filter circuit comprising a coil and a capacitor.

In the switching power supply device, for example,
The first switch means is an IGBT;
The second switch means is an FET.

In order to solve the above problems, an electromagnet power supply system according to the present invention includes:
A transformer,
A voltage conversion circuit that converts the alternating voltage output from the transformer into a direct voltage; and
One of the above-described switching power supplies that generates an output current to be supplied to the electromagnet based on the DC voltage output from the voltage conversion circuit.

  ADVANTAGE OF THE INVENTION According to this invention, the switching power supply device and electromagnet power supply system which can perform low current output control, without increasing output current ripple can be provided.

1 is a block diagram of a switching power supply device according to the present invention. (A) is a timing chart of the first switch means S1 to S4. (B) is a timing chart of the second switch means S5 to S8. (C) is a timing chart which shows the state of terminal voltage V1-V3. It is a figure which shows the relationship between time Ta-Tc shown in FIG. 2, and an output current. It is a block diagram which shows the conventional electromagnet power supply system.

  Embodiments of a switching power supply apparatus and an electromagnet power supply system according to the present invention will be described below with reference to the accompanying drawings.

  The electromagnet power supply system according to an embodiment of the present invention is obtained by replacing the switching power supply 1B with the switching power supply 1A shown in FIG. 1 in the conventional electromagnet power supply system 100B shown in FIG.

  As shown in FIG. 1, the switching power supply device 1 </ b> A includes a first switch circuit 2, a filter circuit 3, a control circuit 4, and a second switch circuit 5. Note that, among the components shown in FIG. 1, the components given the same reference numerals as those in FIG. 4 are the same as those described in the related art, and thus the description thereof is partially omitted here.

  The first switch circuit 2 is a bridge circuit in which four first switch means S1 to S4 are bridge-connected. The four first switch means S1 to S4 are each composed of an IGBT, and each of the diodes D1 to D4 is connected in reverse parallel to the IGBT. The first switch circuit 2 has an input terminal connected to the capacitor C1 of the voltage conversion circuit 12, and output terminals T1 and T1 ′ connected to the input terminals T3 and T3 ′ of the filter circuit 3 via the coils L1 and L2. .

  The filter circuit 3 is an LC high frequency filter including a coil L3 and a capacitor C2. The filter circuit 3 is designed according to the switching frequency of the first switch means S1 to S4 during PWM control so as to attenuate the current ripple due to the switching of the first switch means S1 to S4.

  The second switch circuit 5 is connected in parallel to the first switch circuit 2. Specifically, the input terminal of the second switch circuit 5 is connected to the input terminal of the first switch circuit 2, and the output terminals T2 and T2 ′ are connected to the first switch circuit via the coils L4 and L5 and the coils L1 and L2. 2 are connected to the output terminals T1 and T1 ′. The second switch circuit 5 is a bridge circuit in which four second switch means S5 to S8 are bridge-connected. The four second switch means S5 to S8 are each composed of an FET, and each of the diodes D5 to D8 is connected in reverse parallel to the FET.

  The control circuit 4 performs PWM control and on / off control for the first switch means S1 to S4 and the second switch means S5 to S8. The PWM control is control for switching the switch means at a constant switching frequency, and the on / off control is control for continuously turning the switch means on or off. In the case of FIG. 2, the control circuit 4 performs PWM control on the first switch means S1, S2 and the second switch means S6, S7, and on the first switch means S3, S4 and the second switch means S5, S8. On / off control.

  Further, the control circuit 4 sets a lower limit value of the ON time of the first switch means S1 to S4 within a range where the switching frequency of the first switch means S1 to S4 does not change, and turns on the first switch means under PWM control. Make sure that time does not fall below the lower limit. For example, when the switching frequency is 20 [kHz] (when the switching period is 50 [μs]), the control circuit 4 sets the lower limit value of the ON time of the first switch means S1 to S4 to 1 [μs], The ON time of the first switch means under PWM control is made not to be less than 1 [μs]. The reason why the lower limit value is set in this way is that the IGBTs that are the first switch means S1 to S4 may not turn on when the on-time is reduced, and in that case, the switching frequency changes. On the other hand, for the second switch means S5 to S8, the control circuit 4 does not set the lower limit value of the on time. This is because the FETs that are the second switch means S5 to S8 operate normally (turn on) even if the ON time is reduced.

  Further, the control circuit 4 is configured so that the minimum ON time of the second switch means S5 to S8 is smaller than the above lower limit value, and the first switch circuit 2 and the second switch circuit 5 output voltages having different polarities. The second switch means S5 to S8 are PWM-controlled. Here, the minimum on-time is the smallest of the on-times of the switch means under PWM control. For example, in the case of FIG. 2A, the minimum on time is the on time of the first switch means S1, and in the case of FIG. 2B, the minimum on time is the on time of the second switch means S6 and S7.

  As described above, when the first switch circuit 2 and the second switch circuit 5 output voltages having different polarities, an excessive output voltage of the first switch circuit 2 can be absorbed by the second switch circuit 5. . For this reason, in the switching power supply device 1A, the low current output control can be performed without making the ON time of the first switch means S1 to S4 smaller than the lower limit value.

  Next, a specific example of low current output control will be described with reference to FIGS. Hereinafter, a case where the output current is supplied in the positive direction (the terminal voltage V3 shown in FIG. 2C is a positive voltage) will be described. It is assumed that the lower limit value of the ON time of the first switch means S1 to S4 is set to 1 [μs].

  As shown in FIG. 2A, the control circuit 4 performs PWM control of the first switch means S1 and S2 with a switching period T (switching frequency is 20 [kHz]). On the other hand, the control circuit 4 performs on / off control of the first switch means S3 and S4, the first switch means S3 is maintained in the off state, and the first switch means S4 is maintained in the on state.

  As shown in FIG. 2B, the control circuit 4 performs PWM control of the second switch means S6 and S7 with a switching period T (switching frequency is 20 [kHz]). On the other hand, the control circuit 4 performs on / off control of the second switch means S5 and S8, and the second switch means S5 and S8 are maintained in the off state.

Focusing on one switching cycle T from time t _{1 to} t ₄ , the first switch means S1 and S4 and the second switch means S6 and S7 are turned on during the time t _{1 to} t ₂ , and the first switch means S2, S3 and the second switch means S5 and S8 are turned off. At this time, the first path (capacitor C1 → first switch means S1 → coil L1 → coil L4 → second switch means S6) and the second path (capacitor C1 → second switch means S7 → coil L5 → coil L2 → first A current flows through the switch means S4).

  Therefore, if the voltage across the capacitor C1 is X (X> 0) [V], a positive voltage (X [V] voltage) is output from the first switch circuit 2, as shown in FIG. As described above, the terminal voltage V1 of the output terminals T1 and T1 ′ of the first switch circuit 2 is X [V]. On the other hand, a negative voltage (−X [V] voltage) is output from the second switch circuit 5, and the terminal voltage V2 at the output terminals T2 and T2 ′ of the second switch circuit 5 becomes −X [V]. As a result, the voltage input to the filter circuit 3 becomes 0 [V], and the terminal voltage V3 at the input terminals T3 and T3 'of the filter circuit 3 becomes 0 [V].

At time _t 2 ~t _3, the first switch means S1 and S4 are turned on, the first switch means S2, S3 and the second switch means S5~S8 is turned off. At this time, a current flows through the third path (capacitor C1 → first switch means S1 → coil L1 → filter circuit 3 → electromagnet 10 → filter circuit 3 → coil L2 → first switch means S4).

  For this reason, the voltage X [V] is output from the first switch circuit 2, and the terminal voltage V1 of the output terminals T1 and T1 'of the first switch circuit 2 is X [V]. On the other hand, the voltage output from the second switch circuit 5 is 0 [V], and the terminal voltage V2 of the output terminals T2 and T2 'of the second switch circuit 5 is 0 [V]. As a result, the voltage input to the filter circuit 3 is X [V], and the terminal voltage V3 at the input terminals T3 and T3 'of the filter circuit 3 is X [V].

At time _t 3 ~t _4, first switching means S2, S4 are turned on, the first switch means S1, S3 and the second switch means S5~S8 is turned off. As described above, the first switch means S4 needs to be turned on in order to recirculate the output current, but there is no problem even if the first switch means S2 is always turned off. Therefore, the voltages output from the first switch circuit 2 and the second switch circuit 5 are both 0 [V], the terminal voltages V1 of the output terminals T1, T1 ′ of the first switch circuit 2, and the second switch circuit 5 Both terminal voltages V2 of the output terminals T2 and T2 ′ are 0 [V]. As a result, the terminal voltage V3 of the input terminals T3 and T3 ′ of the filter circuit 3 is also 0 [V].

  Here, as shown in FIG. 2C, the time when the terminal voltage V1 becomes X [V] in one switching period T is Ta, and the time when the terminal voltage V2 becomes -X [V] is Tb. If the time when the terminal voltage V3 is X [V] is Tc, the relationship between the time Ta to Tc and the output current is as shown in FIG. In FIG. 3, Y [A] does not operate the second switch circuit 5, and the minimum on time of the first switch means S1 to S4 (the on time of the first switch means S1) is a lower limit value of 1 [μs. ], The output current value output from the filter circuit 3 when the first switch circuit 2 is operated so that

  As can be seen from FIG. 3, when the output current value is smaller than Y [A], the time Ta is constant at 1 [μs]. The time Tb approaches 0 as the output current value approaches Y [A], and the time Tc approaches 1 [μs] as the output current value approaches Y [A]. That is, from FIG. 3, when the output current value is smaller than Y [A], the voltage input to the filter circuit 3 is obtained by subtracting the voltage absorbed by the second switch circuit 5 from the output voltage of the first switch circuit 2. It can also be seen that the amount of absorption of the second switch circuit 5 decreases as the output current value approaches Y [A].

  On the other hand, when the output current value is Y [A] or more, the time Ta and the time Tc coincide with each other, and both increase in proportion to the output current value. Time Tb becomes zero. That is, it can be seen from FIG. 3 that when the output current value is Y [A] or more, the voltage input to the filter circuit 3 matches the output voltage of the first switch circuit 2. Note that the voltage drop due to the coils L1, L2 and the wiring is ignored.

  After all, according to the switching power supply device 1A and the electromagnet power supply system according to the present embodiment, the excessive output voltage of the first switch circuit 2 can be absorbed by the second switch circuit 5, so that at the time of low current output control, At the time of control such that the output current value is smaller than Y [A], it is not necessary to make the minimum ON time of the first switch means S1 to S4 (ON time of the first switch means S1) smaller than the lower limit value. As a result, according to the switching power supply device 1A and the electromagnet power supply system according to the present embodiment, it is possible to prevent the output current ripple from becoming large during the low current output control.

  In the above description, the case where the output current is supplied in the positive direction has been described. However, the same effect can be achieved even when the output current is supplied in the negative direction (the terminal voltage V3 shown in FIG. 2C is a negative voltage). That is, when the output current flows in the minus direction, the first switch means S2 is always turned on instead of the first switch means S4 being always turned on, and the first switch means S1 and the second switch The first switch means S3 and the second switch means S5 and S8 are turned on / off instead of turning the means S6 and S7 on / off. In this case, the first switch means S1 to S4 There is no need to make the minimum ON time (ON time of the first switch means S3) smaller than the lower limit value.

  As mentioned above, although embodiment of the switching power supply device and electromagnet power supply system concerning this invention was described, this invention is not limited to the said embodiment.

The switching patterns of the first switch means S1 to S4 and the second switch means S5 to S8 are at least the minimum on-time of the second switch means S5 to S8 during the low current output control (in the above specific example, the second switch means S6). , S7 ON time) is smaller than the lower limit value of the ON time of the first switch means S1 to S4, and the first switch circuit 2 and the second switch circuit 5 can output voltages having different polarities. Can be changed as appropriate. For example, at time _t 1 ~t ₂ rather than time _t 2 ~t _3, second switching means S6, S7 may be turned on to.

  In the above embodiment, the first switch means S1 to S4 are IGBTs and the second switch means S5 to S8 are FETs. However, the second switch means S5 to S8 are turned on rather than the on time of the first switch means S1 to S4. If the time becomes smaller, any switch means can be used as the first switch means S1 to S4 and the second switch means S5 to S8. For example, the first switch means S1 to S4 may be general (relatively inexpensive) IGBTs, and the second switch means S5 to S8 may be high performance (relatively expensive) IGBTs. Of the first switch means S1 to S4 and the second switch means S5 to S8, the switch means that does not perform PWM control can be omitted or replaced with a rectifying element such as a diode.

  If the structure of the filter circuit 3 is designed according to the switching frequency of 1st switch means S1-S4 under PWM control, it can change suitably.

  In the electromagnet power supply system of the present invention, the output voltage of the voltage conversion circuit 12 (the DC link voltage on the plus side of the capacitor C1) may be reduced during low current output control. In this case, it is preferable that the rectifying means of the voltage conversion circuit 12 is constituted by an AC / DC converter.

1A switching power supply device 2 first switch circuit 3 filter circuit 4 control circuit 5 second switch circuit 10 electromagnet 11 transformer 12 voltage conversion circuit

Claims (6)

A first switch circuit including at least one first switch means;
A filter circuit connected to an output terminal of the first switch circuit;
A control circuit for PWM controlling the first switch means;
A switching power supply device comprising:
A second switch circuit including at least one second switch means connected in parallel to the first switch circuit;
The control circuit includes:
The second switch so that the ON time of the second switch means is shorter than the ON time of the first switch means, and the first switch circuit and the second switch circuit output voltages having different polarities. PWM control means with the same switching frequency as the first switch means ,
The first switch circuit is a bridge circuit in which a plurality of the first switch means are bridge-connected,
The switching power supply device, wherein the second switch circuit is a bridge circuit in which a plurality of the second switch means are bridge-connected . The control circuit includes:
In the range where the switching frequency of the first switch means does not change, the lower limit value of the ON time of the first switch means is set,
2. The switching power supply device according to claim 1, wherein the second switch means is PWM-controlled so that the minimum ON time of the second switch means becomes smaller than the lower limit value. 3. The switching power supply device according to claim 2, wherein the control circuit performs PWM control on the second switch unit only when the minimum ON time of the first switch unit becomes the lower limit value. Before SL filter circuit, the switching power supply device according to claim 1, characterized in that an LC filter circuit comprising a coil and a capacitor. The first switch means is an IGBT;
The switching power supply according to any one of claims 1 to 4, wherein the second switch means is an FET. A transformer,
A voltage conversion circuit that converts the alternating voltage output from the transformer into a direct voltage; and
An electromagnet power source comprising: the switching power source device according to any one of claims 1 to 5 that generates an output current to be supplied to an electromagnet based on a DC voltage output from the voltage conversion circuit. system.

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