KR20200103697A - 3-phase AC switching power supply - Google Patents

Abstract

As a switching power supply for three-phase AC, it adopts a forward method that enables high output to be achieved and makes the power factor good. A three-phase transformer having a primary coil and a secondary coil on three legs and one end of each primary coil connected to the input terminal of each phase of a three-phase AC, switching elements of each phase connected in series to the primary coil of each phase, and In a three-phase AC switching power supply having a rectifying unit each connected to the secondary coil of the phase, and a smoothing unit including at least one reactor and a smoothing capacitor connected to the rectifying unit of each phase, the switching elements of each phase are connected to the primary coil of each phase On/off control is performed only when the applied phase voltage is a positive voltage, whereas in the case of a negative voltage, it is maintained in an off state, and the switching elements of each phase are controlled on/off by the same PWM signal, and from the switching element to the primary coil It includes a reverse flow prevention diode to block the flowing current.

Description

3-phase AC switching power supply

The present invention relates to a switching power supply, and in particular, to a three-phase AC switching power supply having excellent power factor.

It is known to use the power factor improvement circuit of Patent Documents 1 to 3 at the input terminal of a switching power supply that converts AC to DC power. The power factor correction circuit is, for example, a circuit for inputting a sinusoidal current in phase with the sinusoidal input voltage as much as possible. The power factor correction circuit is usually composed of a non-isolated boost converter. Therefore, it is common to configure one isolated type switching power supply in a two-converter method in which an isolated DC/DC converter is disposed at the rear end of the power factor improvement circuit. Representative methods of the isolated DC/DC converter include a forward method and a flyback method. The forward method is suitable for high output power.

Meanwhile, as in Patent Documents 4 and 5, a one-converter method, which is an isolated DC/DC converter having a power factor improvement function, is also known. The one-converter type isolated DC/DC converter is constructed in a flyback type that performs substantially the same operation as a boost converter. The flyback method has a power factor improvement function, but is not suitable for high output power.

Prior art literature

Patent Literature

Patent Document 1: Japanese Unexamined Patent Publication No. Hei 5-111246

Patent Document 2: Japanese Unexamined Patent Publication No. 2007-37297

Patent Document 3: Unexamined Patent Publication No. 2015-23722

Patent Document 4: Unexamined Patent Publication No. Hei 5-236749

Patent Document 5: Japanese Unexamined Patent Publication No. 2002-300780

When an AC full wave rectified voltage is input, a switching power supply having an excellent power factor is employed as an insulated type, a flyback type, and a non-insulated type, a boost converter. On the other hand, in order to realize high output of the switching power supply, a forward method capable of outputting a current in both an ON period and an OFF period of switching is suitable. However, in the forward switching power supply, the load current can be output only when the electromotive force generated in the secondary coil during the ON period exceeds the voltage of the smoothing capacitor C connected in parallel to the output terminal. Therefore, when an AC full-wave rectified voltage is input, the load current does not flow to the secondary side in the low input voltage range, and thus the input current of the primary side paired with the load current does not flow. As a result, the power factor deteriorates.

From the above phenomena, the present invention aims to achieve high output in a three-phase AC switching power supply and at the same time improve power factor.

In order to achieve the above object, the present invention provides the following configuration.

The first aspect of the present invention has a primary coil and a secondary coil wound on each of three legs, each overlapping, and one end of each primary coil is connected to the input terminals of each phase of three-phase AC. A three-phase transformer,

A switching element of each phase connected in series to the primary coil of each phase,

Rectification and smoothing parts of each phase connected to the secondary coil of each phase

In the three-phase AC switching power supply having,

The switching element of each phase is controlled on/off by the same PWM signal when the input voltage applied to the primary coil of each phase is a positive voltage, whereas when the input voltage is negative, it is maintained in an off state,

And a reverse flow prevention diode for each phase for preventing current from flowing in a direction opposite to the current flowing in the on-period in the primary coil of each phase.

In the first aspect, in the on period of the on/off control,

An input current flows through the primary coil connected in series to the switching elements of each phase controlled on/off, and a forward current flows through the secondary coil wound thereon,

The input current does not flow to the primary coil connected in series to the switching element of each phase maintained in the off state, and the input current flows in the secondary coil superimposed thereon due to magnetic flux from the primary coil of the other phase. It is preferable that the forward current is configured to flow by electromotive force.

In the first aspect, in the off period of the on/off control,

A current does not flow in the primary coil connected in series to the switching element of each phase controlled on/off due to the reverse flow prevention diode, and a flyback current flows in the secondary coil wound thereon,

It is preferable that a current does not flow in the primary coil connected in series to the switching element of each phase maintained in an off state, and a flyback current flows through the secondary coil superimposed thereon. Do.

In the first aspect, the rectification unit has two pairs of series-connected positive-side diodes and negative-side diodes, and the connection points of each pair of series-connected diodes are connected to each end of the secondary coil, respectively,

One end of each of the two reactors is connected to the cathode of each of the two positive-side diodes, and the other ends of the two reactors are connected to the positive electrode end of the smoothing capacitor,

It is preferable that the anode of each of the two negative-side diodes is connected to the negative electrode terminal of the smoothing capacitor.

In the first aspect, the rectification unit has two pairs of series-connected positive-side diodes and negative-side diodes, and the connection points of each pair of series-connected diodes are connected to each end of the secondary coil, respectively,

One end of each of the two reactors is connected to the anode of each of the two negative-side diodes, and the other ends of the two reactors are connected to the negative electrode end of the smoothing capacitor,

It is preferable that the cathode of each of the two positive-side diodes is connected to the positive electrode terminal of the smoothing capacitor.

The second aspect of the present invention is a three-phase reactor having a reactor wound on each of three legs, and one end of each reactor connected to an input terminal of each phase of three-phase AC, respectively,

A switching element of each phase connected in series to the reactor of each phase,

A rectifier diode of each phase connected to the other end of the reactor of each phase,

Smoothing capacitor connected to the rectifier diode of each phase

In the three-phase AC switching power supply having,

The switching elements of each phase are controlled on/off by the same PWM signal when the input voltage applied to the reactor of each phase is a positive voltage, whereas when the input voltage is a negative voltage, the switching element is maintained in an off state,

And a reverse flow prevention diode for preventing a current from flowing in a direction opposite to a current flowing to the reactor in each phase during the ON period.

In the second aspect, in the on period of the on/off control,

While the current passing through the switching element flows through the reactor connected in series to the switching element of each phase controlled on/off,

It is preferable that it is configured so that no current flows through the reactor connected in series to the switching elements of each phase maintained in an off state.

In the second aspect, in the off period of the on/off control,

Current flows in the reactor connected in series to the switching elements of each phase controlled on/off and is output through the rectifier diode,

It is preferable that the reactor is connected in series to the switching elements of each phase maintained in an off state, and is configured such that no current flows due to the reverse flow prevention diode.

In any of the above aspects, it is preferable that the reverse flow prevention diode is connected between the primary coil or the reactor and the switching element.

In the three-phase AC switching power supply according to the present invention, a reverse flow prevention diode is provided for the switching element while performing predetermined on/off control on the switching element, thereby preventing reflux on the input side, It accumulates magnetic energy in a three-phase transformer or three-phase reactor as much as possible and can output the accumulated magnetic energy. In addition, excellent power factor can be realized by outputting magnetic energy accumulated in a three-phase transformer or three-phase reactor by a flyback current.

1 is a diagram schematically showing a circuit example of a first embodiment of an insulated three-phase AC switching power supply of the present invention.
[Fig. 1A] A circuit example showing parts omitted from the circuit example of Fig. 1.
Fig. 1B is a diagram showing another example of a circuit on the secondary side in the circuit example of Fig. 1.
[Fig. 2] Fig. 2 shows the current in the ON period of two phases of the positive voltage in the circuit example of Fig. 1.
3 is a diagram schematically showing a state of a three-phase transformer during the ON period shown in FIG. 2.
[Fig. 4] Fig. 4 shows the current in the off period of two phases of the positive voltage in the circuit example of Fig. 1.
[Fig. 5] Fig. 5 is a schematic timing diagram in the circuit example of Fig. 1.
6 is a diagram schematically showing a circuit example of the second embodiment of the non-insulated three-phase AC switching power supply of the present invention.
[Fig. 7] Fig. 7 shows the current in the ON period of two phases of the positive voltage in the circuit example of Fig. 6.
[Fig. 8] Fig. 8 is a diagram schematically showing the state of the three-phase reactor during the ON period shown in Fig. 6.
[Fig. 9] Fig. 9 shows the current in the off period of two phases of the positive voltage in the circuit example of Fig. 6.
[FIG. 10] FIG. 10 is a schematic timing diagram in the circuit example of FIG. 6.

Hereinafter, an embodiment of a three-phase AC switching power supply according to the present invention will be described with reference to the drawings shown as examples.

(1) Embodiment 1 (insulation type)

(1-1) Configuration of circuit example of the first embodiment

1 is a diagram schematically showing a circuit example of an insulated three-phase AC switching power supply according to a first embodiment of the present invention. 1A is a circuit example showing in detail an example of a portion surrounded by a dotted line omitted from the circuit example of FIG. 1.

<Configuration of the primary side of the three-phase transformer (T)>

In the switching power supply for three-phase AC of Fig. 1, a three-phase AC voltage is input to the input terminals R, S, and T. Here, the three-phase AC voltage is, for example, a sine wave having a frequency of 50 Hz or 60 Hz of a system power supply or a frequency of several Hz to several kHz generated by various power generation devices.

Transformer (T) is a three-phase transformer with three legs. On each of the three legs, the primary coil N1 and the secondary coil N2, the primary coil N3 and the secondary coil N4, and the primary coil N5 and the secondary coil N6 are wound with the same polarity overlapping each other. Is indicated by a black circle). One end of the primary coils N1, N2, and N3 of each phase is connected to the input terminals of each phase, respectively.

Reverse flow prevention diodes D1, D2, D3 and switching elements Q1, Q2, and Q3 connected in series are connected to the other ends of the primary coils N1, N2, and N3 of each phase, respectively. Switching elements (Q1, Q2, Q3) of each phase are turned on/off by inputting a PWM signal to each control terminal in order to conduct or cut off the current flowing through the primary coils (N1, N2, N3) of each phase. Is controlled. The switching elements Q1, Q2, Q3 are n-channel MOSFETs (hereinafter referred to as'FET') here, and the control terminal is a gate. The frequency of the PWM signal is several tens of kH to several hundreds of kH, which is higher than that of three-phase AC.

In addition, the switching element may be an IGBT or a bipolar transistor instead of a MOSFET (the same applies in the following embodiments).

The polarity of the reverse flow prevention diodes D1, D2, and D3 is opposite to the polarity of the body diode of the FETs Q1, Q2, and Q3. That is, in the illustrated example, the anode is connected to the other end of the primary coils N1, N2, and N3 of each phase, and the cathode is connected to the drains of the FETs Q1, Q2, and Q3. The reverse flow prevention diodes D1, D2, D3 of each phase, as well as the positions shown, current paths from the input terminals R, S, T of each phase to the ground terminal through the primary coils N1, N3, N5 Can be inserted on top.

Further, freewheeling diodes D16, D17, and D18 are connected between the input terminal and the ground terminal of each phase, respectively. In these freewheeling diodes D16, D17, D18, the anode is connected to the common ground terminal of each phase and the cathode is connected to the input terminal of each phase. Accordingly, the input voltage of each phase to the primary coils N1, N2, and N3 of the transformer T is clamped on the negative voltage side by the freewheeling diodes D16, D17, and D18.

<Switching element ON/OFF control circuit configuration>

1A is a circuit diagram showing in detail examples of portions 10, 20, and 30 in the circuit of FIG. 1. Since these parts have the same configuration, a circuit on R-phase will be described, for example. A PWM signal Vg is generated by a control unit (not shown). The PWM signal Vg is one voltage signal common to each phase, and has a predetermined frequency and duty ratio. The input terminal of the PWM signal Vg is connected to an emitter of the p-type transistor Q11. The collector of transistor Q11 is connected to the gate of FET Q1. Meanwhile, the divided voltage of the input voltage of the R-phase is applied to the base of the n-type transistor Q12. The collector of transistor Q12 is connected to the base of transistor Q11 through a resistor, and the emitter is grounded.

When the input voltage on R- is a negative voltage, transistor Q11 is in an off state, and thus transistor Q12 is also in an off state. At this time, the PWM signal Vg is blocked and is not applied to the gate of the FET Q1. Thus, when the input voltage on R- is a negative voltage, the FET Q1 is kept off.

When the input voltage on the R-phase is a positive voltage, the transistors Q11 and Q12 are turned on, so that the PWM signal Vg is applied to the gate of the FET Q1. Accordingly, when the input voltage on the R-phase is a positive voltage, the FET Q1 is controlled on/off by the PWM signal Vg.

In this way, in this circuit, switching elements of each phase are ON/OFF controlled only when the input voltage of each phase of 3-phase AC is a positive voltage, and when the input voltage of each phase is a negative voltage, the switching elements of each phase are kept in an off state. do.

<Configuration of the secondary side of a three-phase transformer>

On the secondary side of the three-phase transformer T, a rectifying portion and a smoothing portion at a rear stage thereof are arranged for each phase. Since the circuit configuration of each phase is the same, the circuit configuration of the secondary side will be described taking the R-phase as an example. The rectifier is a type based on a bridge rectifier circuit consisting of four diodes (D4, D5, D6, D7). A first pair of positive-side diodes D4 and negative-side diodes D6 are connected in series, and a second pair of positive-side diodes D5 and negative-side diodes D7 are connected in series. The connection point of the series-connected first pair of diodes D4 and D6 is connected to one end of the secondary coil N2, and the connection point of the series-connected second pair of diodes D5 and D7 is the secondary coil N2 It is connected to the other end of ).

Unlike a typical bridge rectification circuit, in the configuration of Fig. 1, the cathodes of the positive side diodes D4 and D5 are not connected to each other. The cathode of one positive-side diode D4 is connected to one end of the first reactor L1, and the cathode of the other positive-side diode D5 is connected to one end of the second reactor L2. The inductance of each of the first reactor L1 and the second reactor L2 has substantially the same value.

The other end of each of the first reactor L1 and the second reactor L2 is connected to the positive electrode end of the smoothing capacitor C, and this point is also the positive output terminal p.

In addition, the anode of each of the two negative-side diodes D6 and D7 is connected to the negative electrode terminal of the smoothing capacitor C, and this point is also a negative output terminal n.

<Another embodiment of the secondary side of a three-phase transformer>

1B is another configuration example of a rectifying unit and a smoothing unit on the secondary side in the circuit of Fig. 1. It is shown only for the portion of the R-phase, but the configuration is the same for the other two phases. In the configuration of FIG. 1B, the rectifier is also of a form based on a bridge rectifier circuit composed of four diodes D4 to D7 as shown in FIG. 1. A first pair of positive-side diodes D4 and negative-side diodes D6 are connected in series, and a second pair of positive-side diodes D5 and negative-side diodes D7 are connected in series. The connection point of the series-connected first pair of diodes D4 and D6 is connected to one end of the secondary coil N2, and the connection point of the series-connected second pair of diodes D4 and D6 is the secondary coil N2 It is connected to the other end of ).

In the configuration of Fig. 1B, the anodes of the negative-side diodes D6 and D7 are not connected to each other, unlike a normal bridge rectification circuit. An anode of one negative-side diode D6 is connected to one end of the first reactor L1, and an anode of the other negative-side diode D7 is connected to one end of a second reactor L2. The inductance of each of the first reactor L1 and the second reactor L2 has substantially the same value.

The other end of each of the first reactor L1 and the second reactor L2 is connected to the negative electrode end of the smoothing capacitor C, and this point is also a negative output terminal n.

Further, the cathode of each of the two positive side diodes D4 and D5 is connected to the positive electrode terminal of the smoothing capacitor C, and this point is also the positive output terminal p.

The secondary side circuit of the first embodiment of the three-phase AC switching power supply can be configured in various ways in addition to the circuits shown in Figs. 1 and 1B. It is desirable that the secondary circuit is basically configured in a forward type. In the ON period, forward current flows, and in the OFF period, the reactor current that discharges the magnetic energy of the external reactor flows and the flyback current is generated by the back electromotive force generated in the secondary coil. You just need to have a flowable configuration. The operation of the flyback current flowing through the secondary coil will be described below.

(1-2) Operation of the first embodiment

The operation of the circuit example of the first embodiment will be described with reference to FIGS. 2 to 5. Fig. 5A shows the input voltage waveform of three-phase AC to the three-phase transformer T. As shown in FIG. 5A, there is a period in which two of the three phases are a positive voltage and one of the three phases is a negative voltage, and a period in which one of the three phases is a positive voltage and two phases are a negative voltage. Since there is no essential difference in the operation of these two periods, when one of these periods is described, the operation of the other period can be understood.

Hereinafter, an operation in the range indicated by a dotted line in FIG. 5A will be described by taking a period in which two of the three phases are a positive voltage and one of the three phases is a negative voltage. That is, when the R-phase and S-phase are positive voltages and the T-phase is negative voltage. 5(b) to (m) are timing charts schematically showing this range expanded. In this range, the R-phase and S-phase switching elements are controlled on/off by the same PWM signal, while the T-phase switching elements are kept in an off state. Hereinafter, the operation of the on/off period of the R-phase and S-phase on/off control will be described.

<R-phase, S-phase: operation during the ON period (T-phase remains off)>

FIG. 2 shows the current flowing in the circuit of FIG. 1 during the ON period of the R-phase and S-phase FETs Q1 and Q2 by a solid line with an arrow. 3 is a diagram schematically showing the state of the three-phase transformer T during the ion period.

As shown in Fig. 2, when the FET Q1 is turned on, a current i1 flows through the R-phase primary coil N1 (see Fig. 5C). This current i1 flows in the forward direction of the reverse flow prevention diode D1, and flows back to the input terminal T through the freewheeling diode D18. As a result of the current i1 flowing through the primary coil N1, an electromotive force (meaning voltage) is generated in the secondary coil N2 due to mutual induction, and the current i2 flows. The current i2 flows through the path of the diode D7 → secondary coil N2 → diode D4 → reactor L1 and is output from the output terminal p and supplied to the load (Fig. 5(d)). , (e)). The current i2 is a forward current due to mutual induction of the transformer T. The first reactor L1 is excited (勵磁) by the current i2 and magnetic energy is accumulated. Since diodes D5 and D6 are biased in the reverse direction, no current flows.

Here, the smoothing capacitor C in the steady state is charged with a substantially constant voltage except for ripple fluctuations. Accordingly, the current i2 can flow only when the electromotive force of the secondary coil N2 exceeds the voltage of the smoothing capacitor C. In the range where the input voltage of the R-phase is small, the electromotive force of the secondary coil N2 is also small, so the forward current i2 is not output to the output terminal. This is a feature of the forward operation, and it lowers the power factor.

The S-phase also works the same as the R-phase. A current i3 flows through the primary coil N3 (refer to FIG. 5(g)), and flows back to the input terminal T through the freewheeling diode D18. The forward current i4 flows through the secondary coil N4 and is output to the output terminal p through the first reactor L3 (refer to (h) and (i) in Figs. 5).

Here, referring to FIG. 3, magnetic fluxes (Ø1, Ø2) are generated by the flow of currents (i1, i3) to the primary coils (N1, N3) in the three-phase transformer (T), and the T-phase primary The coil N5 and the secondary coil N6 flow to the wound bridge. As a result, electromotive force is generated in the primary coil N5 by which the reverse flow prevention diode D3 is forward biased, but since the FET Q3 is off, no current flows through the primary coil N5 (Fig. k)). On the other hand, the current i5 shown in Fig. 2 flows by the electromotive force generated in the secondary coil N6. Current i5 flows through the path of diode D14 → secondary coil N6 → diode D13 → reactor L6 and is output from the output terminal p and supplied to the load (Fig. 5(l), (m ) Reference). Current i5 is the forward current.

<R-phase, S-phase: operation of the off period (T-phase remains off)>

Next, FIG. 4 shows the current flowing through the circuit of FIG. 1 during the off period of the R-phase and S-phase FETs Q1 and Q2 by dotted lines with arrows.

Regarding the R-phase, when the FET Q1 is turned off, the current i1 of the primary coil N1 is cut off, and a counter electromotive force is generated in the primary coil N1 and the secondary coil N2, respectively. The back EMF of the primary coil N1 is forward biased with respect to the body diode of the FET Q1, but since the reverse flow prevention diode D1 is inserted in the current path, no current flows (see Fig. 5(c)). That is, the reflux to the input side is prevented. As a result, if there is no reverse flow prevention diode D1, the energy returned to the input side stays in the three-phase transformer T.

On the other hand, by the back electromotive force of the secondary coil N2, the winding start end becomes low potential and the winding end becomes high potential. Since the first reactor (L1) tries to maintain the current in the same direction as the ON period, the current (i6) flows through the path of the diode (D6) → diode (D4) → reactor (L1) and is output to the output terminal (p). And supplied to the load (see Fig. 5(e)). Accordingly, magnetic energy accumulated in the first reactor L1 during the ON period is released. Diode D7 is reverse biased.

In addition, diode D6 is biased in the forward direction by the back electromotive force of the secondary coil N2, and the current (ifb) through the path of the diode (D6) → the secondary coil (N2) → the diode (D5) → the reactor (L2) It flows and is output to the output terminal p and supplied to the load (see Fig. 5(d) and (f)). The current ifb is not due to mutual induction of the three-phase transformer (T), but due to the release of magnetic energy held in the three-phase transformer (T) as the reflux is blocked by the reverse flow prevention diode (D1) on the primary side. By So the current ifb is the flyback current.

Unlike the forward current i2, the flyback current ifb is output to the output terminal p in a size according to the magnitude of the back electromotive force even when the input voltage is small and the back electromotive force generated in the secondary coil N2 is small. Therefore, in the input voltage of a sine wave, the power factor is improved by the flyback current ifb flowing even in a range where the input voltage is small. This circuit is basically a forward type, but has a power factor improvement function because the flyback current (ifb) can also flow. This is realized by providing a reverse flow prevention diode D1 on the primary side.

In addition, in this circuit, there is no reflux to the input side, but a flyback current ifb flows through the secondary coil N2, thereby performing a magnetic reset of the three-phase transformer T. Therefore, also in this circuit, magnetic saturation of the three-phase transformer T can be avoided.

The S-phase also works the same as the R-phase. When the current of the primary coil N3 is cut off, back electromotive force is generated in the primary coil N3, but reflux is prevented by the reverse flow prevention diode D2 (Fig. 5(g)). On the other hand, on the secondary side, while the current i7 emitting magnetic energy of the first reactor L3 flows (refer to Fig. 5(i)), the flyback current is caused by the back electromotive force generated in the secondary coil N4 ( ifb) flows and is output to the output terminal p through the second reactor L4 (see FIGS. 5(h) and (j)).

Regarding the T-phase, the magnetic fluxes Ø1 and Ø2 flowing from the legs of the other phases are lost during the ON period shown in FIG. 3, thereby generating back electromotive force in the primary coil N5 and the secondary coil N6. . Since the back electromotive force generated in the primary coil N5 is a reverse bias of the reverse flow prevention diode D3, no current flows (see Fig. 5(k)). On the other hand, the flyback current ifb flows due to the back electromotive force generated in the secondary coil N6 and is output to the output terminal p through the first reactor L5 (see (l) and (n) in Figs. 5). .

In the operation of the circuit of Fig. 1 above, the flyback currents ifb flowing through the secondary coils N2, N4, and N6 of each phase in the off period, respectively, cause the reverse flow prevention diodes D1, D2, and D3 on the primary side. This is due to the release of magnetic energy held in the three-phase transformer (T). Accordingly, the efficiency of power transfer to the secondary side is improved. Further, since the flyback current ifb is output irrespective of the magnitude of the back electromotive force of the secondary coils N2, N4, and N6, the power factor is improved.

In addition, during a period in which one of the three phases is a positive voltage and two phases are a negative voltage, for example, during a period in which the R-phase is a positive voltage and the S-phase and T-phase are negative voltages, the S-phase operation is described above. Same as the T-phase operation of negative voltage. The R-phase operation and the T-phase operation are as described above, respectively.

(2) Second embodiment (non-insulated type)

(2-1) Configuration of Circuit Example of Second Embodiment

6 is a diagram schematically showing a circuit example of a non-isolated three-phase AC switching power supply according to a second embodiment of the present invention. Although omitted in FIG. 6, portions indicated by reference numerals 10, 20, and 30 surrounded by dotted lines have the same configuration as the circuit shown in FIG. 1A.

In the switching power supply for three-phase AC of Fig. 6, a three-phase AC voltage is input to the input terminals R, S, and T. The three-phase reactor (3ØR) has three legs. Reactors L11, L12, L13 are wound around each of the three legs. One end of each phase reactor (L11, L12, L13) is connected to the input terminals (R, S, T) of each phase, respectively. Reverse flow prevention diodes D21, D22, D23 and switching elements Q21, Q22, and Q23 connected in series are connected to the other ends of the reactors L11, L12, and L13 of each phase, respectively.

The switching elements Q21, Q22, and Q23 of each phase are controlled on/off by inputting a PWM signal to each control terminal in order to conduct or cut off the current flowing through the reactors L11, L12, and L13 of each phase. The switching elements Q21, Q22, and Q23 are n-channel MOSFETs (hereinafter referred to as'FETs') here, and the control terminals are gates.

The polarity of the reverse flow prevention diodes D21, D22, and D23 is opposite to that of the body diodes of the FETs Q21, Q22, and Q23. That is, in the illustrated example, the anode is connected to the other end of the reactors L11, L12, and L13 of each phase, and the cathode is connected to the drain of the FETs Q21, Q22, and Q23 of each phase.

Further, freewheeling diodes D27, D28, and D29 are connected between the input terminal and the ground terminal of each phase, respectively. In these freewheeling diodes D27, D28, and D29, an anode is connected to a common ground terminal of each phase, and a cathode is connected to an input terminal of each phase. Accordingly, the input voltage of each phase to the reactors L11, L12, and L13 is clamped on the negative voltage side by the freewheeling diodes D27, D28, and D29.

Further, anodes of the rectifying diodes D24, D25, and D26 of each phase are connected to the other ends of the reactors L11, L12, and L13 of each phase, respectively. The cathode of each phase rectifier diode D24, D25, D26 is connected to the positive electrode terminal of the smoothing capacitor C, and this point is also the positive output terminal p. The source of each phase FET (Q21, Q22, Q23) is connected to the negative electrode terminal of the smoothing capacitor (C), and this point is both a ground terminal and a negative output terminal (n).

(2-2) Operation of the second embodiment

The operation of the circuit example of the second embodiment will be described with reference to FIGS. 7 to 10. Fig. 10A shows the input voltage waveform of the three-phase AC to the three-phase reactor 3ØR, as in Fig. 5A. There is a period in which two of the three phases are a positive voltage and one phase is a negative voltage and a period in which one of the three phases is a positive voltage and two phases are a negative voltage, and there is no substantial difference in the operation of these periods.

Hereinafter, as an example, the operation in the range indicated by the dotted line in Fig. 10A will be described. That is, when the R-phase and S-phase are positive voltages and the T-phase is negative voltage. 10B to 10E are timing diagrams schematically showing this range expanded. In this range, the R-phase and S-phase switching elements are controlled on/off by the same PWM signal, while the T-phase switching elements are kept in an off state. Hereinafter, the operation of the on period and the off period in the on/off control of the R-phase and S-phase will be described.

<R-phase, S-phase: operation during the ON period (T-phase remains off)>

7 shows the current flowing in the circuit of FIG. 6 during the ON period of the R-phase and S-phase FETs Q21 and Q22 by a solid line with an arrow. Fig. 8 is a schematic configuration diagram showing the state of the three-phase reactor 3ØR during the ion period.

As shown in Fig. 7, when the FET Q21 is turned on, a current i1 flows through the R-phase reactor L11 (see Fig. 10C). This current i1 flows in the forward direction of the reverse flow prevention diode D21, and flows back to the input terminal T through the freewheeling diode D29. Reactor (L11) is excited (勵磁) to accumulate magnetic energy.

The S-phase also works the same as the R-phase. A current i2 flows through the reactor L12 (refer to FIG. 10(d)), and reflux to the input terminal T through the freewheeling diode D29. Reactor (L12) is excited (勵磁) to accumulate magnetic energy.

Here, referring to FIG. 8, in the three-phase reactor (3ØR), magnetic fluxes (Ø1, Ø2) are generated by the flow of currents (i1, i2) to the reactors (L11, L12) during the ON period, and the T-phase is generated through the core. It flows through the wound leg of the reactor (L13). As a result, an electromotive force is generated in the reactor L13 in which the reverse flow prevention diode D23 is biased in the forward direction, but since the FET Q23 is off, no current flows through the FET Q23 (see Fig. 10(e)). . Instead, the current i5 shown in Fig. 7 flows by the electromotive force generated in the reactor L13 (the current i5 is not shown in Fig. 8). Current i5 flows through the path of diode D29 → reactor L13 → diode D26 → and is output from the output terminal p and supplied to the load (see Fig. 10(e)). Current i5 is the forward current. Accordingly, magnetic flux is accumulated in the reactor L13.

<R phase, S phase: operation of the off period (T-phase remains off)>

Next, FIG. 9 shows the current flowing in the circuit of FIG. 1 during the off period of the R-phase and S-phase FETs Q21 and Q22 by dotted lines with arrows.

Regarding the R-phase, when the FET Q21 is turned off, the current i1 of the reactor L11 is cut off, thereby generating back electromotive force. The flyback current ifb flows through the diode D24 due to the back electromotive force of the reactor L11 and is output. (See Fig. 10(c)). Accordingly, magnetic energy accumulated in the reactor L11 during the ON period is released. In addition, although the second embodiment is a non-insulated type, a current corresponding to the flyback current in the insulated type will be referred to as a "flyback current" for convenience.

The flyback current ifb is output to the output terminal p in a size corresponding to the magnitude of the back electromotive force even when the input voltage is small and the back electromotive force generated in the reactor L11 is small. Therefore, in the case of the sinusoidal input voltage, the power factor is good because the flyback current ifb flows even in the range where the input voltage is small.

The S-phase also works the same as the R-phase. When the current i2 of the reactor L12 is cut off, a counter electromotive force is generated in the reactor L12, and a flyback current ifb flows through the diode D25 to be output. (See Fig. 10(d)). Accordingly, magnetic energy accumulated in the reactor L12 during the ON period is released.

Regarding the T-phase, the magnetic fluxes Ø1 and Ø2 flowing from the legs of the other phases are lost during the ON period shown in FIG. 8, thereby generating a back electromotive force in the reactor L13. Since the back electromotive force generated in the reactor L13 is a reverse bias of the reverse flow prevention diode D3, no current flows (see Fig. 10(e)). Accordingly, magnetic energy is held in the reactor L13.

In addition, the magnetic energy accumulated in the T-phase reactor L13 in the on period and the magnetic energy held in the T-phase reactor L13 in the off period are the R-phase and S-phase reactors L11 and L12 in the off period. It is emitted by outputting the flyback current (ifb) from ).

If there is no reverse flow prevention diode D3, since reflux flows into the reactor L13 when it is turned off, the magnetic flux of the three-phase reactor 3ØR becomes difficult to decrease, and it becomes difficult to release the accumulated magnetic energy. The presence of the reverse flow prevention diode D3 makes it easy to discharge energy accumulated in the three-phase reactor 3ØR by the flyback current ifb.

(5) summary

The three-phase AC switching power supply of the present invention can be applied to high output by basically having a forward-type operation in the case of an insulated type. In addition, a predetermined current is blocked by installing a reverse flow prevention diode connected in series with the switching element while the switching element of the phase whose input voltage is a negative voltage is kept off, and accordingly, the magnetic energy accumulated in the transformer is prevented by the flyback current. Is released. The power factor is improved as the flyback current flows. Therefore, it is suitable as a high-output one-converter type isolated switching power supply. It provides a power factor improvement function and simplifies the circuit configuration, and at the same time, safety is ensured because it is an isolated type.

In addition, as shown in the circuits of Figs. 1 and 1B, by dividing the conventional forward type reactor into two parallel circuits on the secondary side of the transformer, the current supply capacity is increased and the driving burden on the primary side is increased. This is alleviated.

In addition, in the case of the three-phase AC switching power supply of the present invention, in the case of a non-isolated type, a predetermined current is prevented by installing a reverse flow prevention diode connected in series with the switching element while the switching element of the phase whose input voltage is a negative voltage is kept off. Thus, the magnetic energy accumulated in the three-phase reactor is released by the flyback current. Excellent power factor is obtained by flow of flyback current.

The isolated switching power supply of the present invention described above is not limited to the illustrated configuration example, and various modifications are possible within a range consistent with the spirit of the present invention.

p positive output stage
n negative output stage
T transformer
N1, N3, N5 primary coil
N2, N4, N6 secondary coil
Q1, Q2, Q3 MOSFET
D1, D2, D3 anti-return diode
D4~D18 diode
L1, L3, L5 first reactor
L2, L4, L6 second reactor
R, S, T 3-phase input terminals
3ØR 3-phase reactor
L11, L12, L13 reactor
Q21, Q22, Q23 MOSFET
D21, D22, D23 anti-return diode
D24~D29 diode
C smoothing capacitor

Claims (9)

A three-phase transformer having a primary coil and a secondary coil wound on each of the three legs, each having a primary coil and a secondary coil wound on each of the three-phase alternating current phases;
A switching element of each phase connected in series to the primary coil of each phase,
Rectification and smoothing parts of each phase connected to the secondary coil of each phase
In the three-phase AC switching power supply having,
The switching element of each phase is controlled on/off by the same PWM signal when the input voltage applied to the primary coil of each phase is a positive voltage, whereas when the input voltage is a negative voltage, it is maintained in an off state,
It characterized in that it comprises a reverse flow prevention diode for each phase for preventing a current from flowing in a direction opposite to the current flowing in the on-period in the primary coil of each phase,
Switching power supply for 3-phase AC. The method of claim 1,
In the on period of on/off control,
An input current flows through the primary coil connected in series to the switching elements of each phase controlled on/off, and a forward current flows through the secondary coil wound thereon,
The input current does not flow to the primary coil connected in series to the switching element of each phase maintained in the off state, and the input current flows in the secondary coil superimposed thereon due to magnetic flux from the primary coil of the other phase. Characterized in that configured to flow forward current by electromotive force,
Switching power supply for 3-phase AC. The method according to claim 1 or 2,
In the off period of the on/off control,
A current does not flow in the primary coil connected in series to the switching element of each phase controlled on/off due to the reverse flow prevention diode, and a flyback current flows in the secondary coil wound thereon,
A current does not flow in the primary coil connected in series to the switching element of each phase maintained in an off state due to the reverse flow prevention diode, and a flyback current flows through the secondary coil superimposed thereon. doing,
Switching power supply for 3-phase AC. The method according to any one of claims 1 to 3,
The rectifying unit has two pairs of series-connected positive-side diodes and negative-side diodes, and the connection points of each pair of series-connected diodes are connected to each end of the secondary coil, respectively,
One end of each of the two reactors is connected to the cathode of each of the two positive-side diodes, and the other ends of each of the two reactors are connected to the positive electrode end of the smoothing capacitor,
Characterized in that the anode of each of the two negative-side diodes is connected to the negative electrode terminal of the smoothing capacitor,
Switching power supply for 3-phase AC. The method according to any one of claims 1 to 3,
The rectifying unit has two pairs of series-connected positive-side diodes and negative-side diodes, and the connection points of each pair of series-connected diodes are connected to each end of the secondary coil, respectively,
One end of each of the two reactors is connected to the anode of each of the two negative side diodes, and the other ends of the two reactors are connected to the negative electrode end of the smoothing capacitor,
Characterized in that the cathode of each of the two positive-side diodes is connected to the positive electrode terminal of the smoothing capacitor,
Switching power supply for 3-phase AC. A three-phase reactor having a reactor wound on each of the three legs, and one end of each reactor connected to an input terminal of each phase of three-phase AC;
A switching element of each phase connected in series to the reactor of each phase,
A rectifier diode of each phase connected to the other end of the reactor of each phase,
Smoothing capacitor connected to the rectifier diode of each phase
In the three-phase AC switching power supply having,
The switching elements of each phase are controlled on/off by the same PWM signal when the input voltage applied to the reactor of each phase is a positive voltage, whereas when the input voltage is a negative voltage, the switching element is maintained in an off state,
It characterized in that it comprises a reverse flow prevention diode for preventing the current flowing in the opposite direction of the current flowing in the on-period to the reactor of each phase,
Switching power supply for 3-phase AC. The method of claim 6,
In the on period of on/off control,
While the current passing through the switching element flows through the reactor connected in series to the switching element of each phase controlled on/off,
It characterized in that it is configured so that no current flows in the reactor connected in series to the switching element of each phase maintained in an off state,
Switching power supply for 3-phase AC. The method according to claim 6 or 7,
In the off period of the on/off control,
Current flows in the reactor connected in series to the switching elements of each phase controlled on/off and is output through the rectifier diode,
In the reactor connected in series to the switching element of each phase maintained in an off state, it is characterized in that it is configured so that no current flows due to the reverse flow prevention diode,
Switching power supply for 3-phase AC. The method according to any one of claims 1 to 8,
Characterized in that the reverse flow prevention diode is connected between the primary coil or the reactor and the switching element,
Switching power supply for 3-phase AC.

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