JP2017034869A - Ac-dc conversion circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact AC-DC power conversion circuit which can securely suppress a rush current.SOLUTION: An AC-DC power conversion circuit includes: a series circuit composed of a reactor 6, to which a rectification voltage of an AC power supply 1 or an AC power voltage is applied, and a semiconductor switching element 7; and a series circuit composed of a reverse blocking rectifier cell 14 and a capacitor 9 and connected in parallel to the switching element 7. By the operation of the switching element 7, the AC-DC power conversion circuit converts the AC power voltage into a DC voltage which is higher than the peak value of the AC power voltage, to supply to a load 10 which is connected to both end of the capacitor 9. As a reverse blocking rectifier cell 14, there is used a reverse blocking IGBT in which conduction to a forward direction can be controlled by a control signal and which has a function to block a current in a reverse direction, with the reduction of a reverse recovery loss, which is generated at a shift from the conduction state in the forward direction to a state in which a reverse current is blocked, to be smaller than and including the switching loss of the switching element 7.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technique that enables downsizing of an AC-DC conversion circuit and suppression of inrush current.

  FIG. 9 shows a conventional AC-DC conversion circuit, which is well known as a so-called PFC (Power Factor Correction) circuit. In FIG. 9, 1 is an AC power source, 2 to 5 are diodes constituting a rectifier circuit, 6 is a reactor, 7 is a semiconductor switching element, 8 is a diode, 9 is a capacitor, 10 is a load, 11 is a capacitor for absorbing ripples, Reference numeral 12 is a current limiting resistor, and 13 is a relay (relay contact).

Here, the circuit composed of the reactor 6, the switching element 7, the diode 8, and the capacitor 9 is also known as a so-called step-up chopper that converts a DC input voltage into a higher DC voltage and outputs it. In FIG. 9, an IGBT (insulated gate bipolar junction transistor) is used as the switching element 7, but a MOSFET (field effect transistor) or BJT (bipolar junction transistor) may be used.
Note that an AC-DC conversion circuit configured almost in the same manner as in FIG. 9 is described in Patent Document 1 described later.

The function of this prior art is as follows.
(1) The AC input voltage is converted into a DC voltage of a desired magnitude and output, and the DC output voltage is kept constant regardless of fluctuations in the AC input voltage and load current.
(2) The AC input current is a sine wave having a power factor of about 1.

An operation for realizing the above function will be described with reference to FIG.
As shown in FIG. 10, the AC input voltage V _in is the sinusoidal waveform, the output voltage V _r of the rectifier circuit is a full-wave rectified waveform as shown. Here, if the voltage V _in the positive polarity, when turning on the switching element 7, the AC power source 1 → diode 2 → reactor 6 → the switching element 7 → the diode 5 → current flows through a path of the AC power source 1 (Here, ignore current limiting resistor 12 and the relay contacts 13 will be described later these functions), the voltage V _r current I _L increases applied to the opposite ends of the reactor 6.

When the switching element 7 is turned off, a current flows through the path of the AC power source 1 → the diode 2 → the reactor 6 → the diode 8 → the capacitor 9 → the diode 5 → the AC power source 1. At this time, a differential voltage between the voltage E and the voltage _Vr is applied to the reactor 6. As described below, the voltage E by the operation of the step-up chopper is kept higher than the peak value of V _in or V _r, the current I _L decreases.

Thus current I _L increases, by repeating the reduction, the waveform of the current I _L becomes sawtooth waveform as shown, on the switching element 7, by controlling the ratio when off, current I _L It is possible to arbitrarily control the waveform and size of the.
If the current I _L and the voltage V _r and the full-wave rectified waveform similarity, input current I _in, after excluding the switching ripple component by the capacitor 11 becomes a sinusoidal waveform. In FIG. 10, a demand has been represented at 18 times the frequency of the voltage V _in considering the ripple frequency visibility of the current I _L, practically, to reduce the size of the reactor 6, the switching element the switching frequency of 7, high often set to several hundreds thousands times the frequency of the voltage _{V in.}

In the prior art shown in FIG. 9, during normal operation after starting the circuit, it is possible to keep the output voltage E to the desired constant value by controlling the amplitude of the current I _L in accordance with the load power. This constant value, so that the operation described above is satisfied, a value higher than the peak value of the input voltage V _in and rectified voltage V _r.
On the other hand, since the capacitor 9 is not yet charged at the start of the circuit, the voltage E is 0 [V] or an extremely low value. When the voltage V _in from the AC power supply 1 via a switch or the like (not shown) is turned on, the order at the time is V _r> E, current I _L is not reduced even switching element 7 is turned off. Therefore, a so-called inrush current flows into the capacitor 9, and there is a danger that the current _IL becomes excessive and damages the circuit and the power supply.

The current limiting resistor 12 in FIG. 9 is for limiting the inrush current. That is, the capacitor 9 is charged while limiting the current via the current limiting resistor 12 at the time of starting the circuit, and the limit is established by turning on the relay 13 when the voltage E is sufficiently increased and the above-described control becomes possible. The current resistor 12 is short-circuited and switched to normal operation. The current limiting resistor 12 and the relay contact 13 are collectively referred to as an initial charging circuit.
Here, it is assumed that the load 10 can control the power consumption by a control means (not shown), and the power consumption is set to 0 while the capacitor 9 is being charged. This is because the voltage E cannot be raised to a predetermined value even if the capacitor 9 is charged while the load 10 is consuming power.

FIG. 11 is a waveform diagram showing an operation when a voltage drop of a period of several [ms] to several cycles, that is, a so-called instantaneous voltage drop (hereinafter referred to as a momentary drop) occurs in the AC power supply 1.
In this case, since it is necessary to supply predetermined power to the load 10 using the energy remaining in the capacitor 9, the voltage E gradually decreases. In this state, when the AC power supply 1 is restored and then V _r > E, the capacitor 9 is rapidly charged in the same manner as when the circuit is started, and an inrush current is generated. .

JP 2013-172632 A (paragraphs [0011] to [0022], FIG. 1 and the like)

In the prior art described in FIG. 9 and Patent Document 1, the initial charging circuit including the current limiting resistor 12 and the relay 13 does not contribute to the performance and function during normal operation, but occupies the circuit configuration. The volume was large and hindered miniaturization. In addition, when an instantaneous drop occurs in the AC power supply 1, suppression of inrush current at the time of subsequent power recovery has also been a problem.
SUMMARY OF THE INVENTION An object of the present invention is to provide an AC-DC power conversion circuit that can reduce the size of a circuit and can reliably suppress an inrush current.

In order to solve the above-mentioned problem, an invention according to claim 1 is directed to a series circuit of a reactor and a semiconductor switching element to which a rectified voltage of an AC power supply or an AC power supply voltage is applied, and a reverse circuit connected in parallel to the semiconductor switching element. A series circuit of a blocking rectifier and a capacitor,
In an AC-DC conversion circuit that converts an AC power supply voltage into a DC voltage higher than its peak value by a switching operation of the semiconductor switching element and supplies the voltage to a load connected to both ends of the capacitor.
The reverse-blocking rectifier element is capable of controlling forward conduction by a control signal and has a function of blocking reverse current, and is in a state of blocking reverse current from the forward conduction state. The reverse recovery loss that occurs during the transition is less than or equal to the switching loss of the semiconductor switching element.

  According to a second aspect of the present invention, in the AC-DC converter circuit according to the first aspect, the reverse blocking rectifier element is a reverse blocking insulated gate bipolar junction transistor.

  According to a third aspect of the present invention, in the AC-DC conversion circuit according to the first or second aspect, when the AC-DC conversion circuit is activated, the voltage of the capacitor is equal to or higher than the instantaneous value of the AC power supply voltage. The reverse blocking rectifier element is electrically connected in a forward direction.

  According to a fourth aspect of the present invention, in the AC-DC converter circuit according to the third aspect, the timing at which the reverse blocking rectifier starts to conduct in the forward direction is gradually advanced from the zero cross point of the AC power supply voltage as a starting point. It is characterized by going.

  The invention according to claim 5 is the AC-DC converter circuit according to any one of claims 1 to 4, further comprising a current detection unit that detects a current flowing through the reactor, and a current detection value by the current detection unit. Is less than a specified value, the forward current of the reverse blocking rectifier is cut off.

  The invention according to claim 6 is the AC-DC converter circuit according to any one of claims 1 to 5, wherein either one or both of the switching element and the reverse blocking rectifier element are connected to the element. A voltage limiting means capable of limiting the voltage between both ends to a predetermined value higher than the voltage of the capacitor and lower than the withstand voltage of the element is connected.

  The invention according to claim 7 is the AC-DC conversion circuit according to claim 1 or 2, wherein when the voltage of the capacitor decreases during normal operation of the AC-DC conversion circuit, the voltage of the capacitor is AC. The reverse blocking rectifier is turned off only during a period that is less than the instantaneous value of the power supply voltage.

  The invention according to claim 8 is the AC-DC converter circuit according to claim 7, wherein a series circuit of another rectifier element and a resistor is connected in parallel to the reverse blocking rectifier element. To do.

  According to the present invention, since an inrush current can be prevented without using a conventional initial charging circuit, the number of parts can be reduced and the circuit can be downsized. In addition, the inrush current can be reliably suppressed even at the time of power recovery after a sag during normal operation.

1 is a circuit diagram showing a first embodiment of the present invention. It is a wave form diagram which shows charge operation of the capacitor | condenser in 1st Embodiment of this invention. It is a wave form diagram which shows the other charge operation of the capacitor | condenser in 1st Embodiment of this invention. It is a circuit diagram which shows 2nd Embodiment of this invention. It is a circuit diagram which shows 3rd Embodiment of this invention. It is a circuit diagram which shows 4th Embodiment of this invention. It is a wave form diagram which shows another charge operation of the capacitor | condenser in 1st Embodiment of this invention. It is a circuit diagram which shows 5th Embodiment of this invention. It is a circuit diagram which shows a prior art. It is a wave form diagram which shows operation | movement of the prior art of FIG. In the prior art of FIG. 9, it is a wave form diagram which shows the operation | movement at the time of a sag.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a circuit diagram showing a first embodiment of the present invention and corresponds to the first and second aspects of the present invention. The same parts as those in FIG. 9 are denoted by the same reference numerals, and the description thereof will be omitted. Hereinafter, parts different from those in FIG. 9 will be mainly described.

In FIG. 1, a ripple absorbing capacitor 11 is directly connected to both ends of the AC power supply 1, and the initial charging circuit including the current limiting resistor 12 and the relay 13 shown in FIG. 9 is removed. Further, a reverse blocking rectifier element 14 is connected between the connection point of the reactor 6 and the switching element 7 and one end of the capacitor 9 instead of the diode 8 in FIG. 9.
This reverse-blocking rectifier element 14 is a so-called reverse-blocking IGBT, and can control conduction / cutoff of a forward current by a gate, has a blocking performance against a reverse current, and applies a reverse voltage. Even in such a case, the device has a breakdown voltage equivalent to that at the time of blocking in the forward direction.
In FIG. 1, the control circuit for controlling on / off of the switching element 7 and the reverse blocking rectifier element 14 is not shown.

The charging operation of the capacitor 9 at the start-up of the first embodiment will be described with reference to the waveform diagram of FIG. This operation corresponds to the invention according to claim 3.
First, the voltages V _r and E are detected using appropriate voltage detection means (not shown). When the phase of the voltage _V r _{(V in)} to gate on a reverse blocking rectifier element 14 only just before the 180 ° or 360 °, due to the low instantaneous value of the voltage _{V r,} without generating an inrush current, the current _{I L} The capacitor 9 is slightly charged. Since the period of V _r <E occurs due to the rise of the voltage E, the reverse blocking rectifier element 14 is turned on during this period, and the switching element 7 is switched to perform the boosting operation, while the voltage E reaches the peak value of V _r. The capacitor 9 is charged until it exceeds the value. In FIG. 2, the voltage E is shown as a substantially constant value, but in reality, it gradually increases, and this is the same in FIG. 3 described later.

However, when turning off the reverse blocking rectifier element 14 when the current I _L of the reactor 6 is flowing, since the overvoltage at both ends of the reverse blocking rectifier element 14 by stored energy of the reactor 6 is in danger of occurring, practical period of 0 ° to 90 °, and, 180 ° to 270 the switching element 7 is turned off before the _{V r} ≒ E in period °, reverse blocking rectifier after current _{I L} becomes 0 [a] The element 14 is turned off to avoid the occurrence of overvoltage.

As another charging operation of the capacitor 9, an example corresponding to claim 4 is shown in FIG.
In this example, the reverse blocking rectifier 14 is turned on starting from the zero-cross point of the voltage V _r during the period in which the phase of the voltage V _r (V _in ) is 90 ° to 180 ° and 270 ° to 360 °. The timing to do is gradually advanced. For example, the reverse blocking rectifier element 14 is turned on when V _r ≈E, and the timing at which the reverse blocking rectifier element 14 is turned on as the voltage E rises due to charging of the capacitor 9 is increased, so-called phase control. I do. When the turn-on timing of the reverse blocking rectifier element 14 reaches 90 ° or 270 ° and the voltage E becomes approximately equal to the peak value of the voltage V _r , the reverse blocking rectifier element 14 is always turned on to shift to normal operation. .

  In FIG. 1, during the normal operation, the gate of the reverse blocking rectifier 14 is always turned on, thereby playing the same role as the diode 8 of FIG. Further, every time the switching element 7 is turned on, a reverse voltage is applied to the reverse blocking rectifier element 14 to cut off the current so-called reverse recovery operation.

  Since the switching element 7 performs high-frequency switching, the reverse blocking rectifier element 14 has a small reverse recovery loss, specifically, less than or equal to the switching loss of the switching element 7 (similar to the switching loss of the switching element 7 or Or less), and there are commercially available reverse blocking IGBTs that satisfy such performance. Although it is possible to obtain the same function by connecting an IGBT having no general reverse blocking capability and a high-frequency diode in series, the conduction loss of this part is approximately doubled by connecting both elements in series. There are disadvantages to become. Further, since the reverse recovery loss is large in a thyristor or the like, it cannot be applied to the high-frequency switching circuit as in this embodiment.

  In addition to the circuit configuration as shown in FIG. 1, it is possible to replace the diodes 2 to 5 with a thyristor to form a rectifier circuit and perform the above-described control by this rectifier circuit. The forward voltage step-down is larger than the conventional diodes 2 to 5, and there is a drawback that the conduction loss increases as in the case where the IGBT and the high frequency diode not having the reverse blocking capability are connected in series. Since the reverse blocking IGBT has a larger forward voltage drop than the thyristor, it is impractical to replace a part of the rectifier circuit with the reverse blocking IGBT.

By the way, the overvoltage generated by cutting off the current of the reactor 6 can be generated when the capacitor 9 is not charged, for example, when the operation of the circuit is stopped.
FIG. 4 is a second embodiment corresponding to claim 5 for suppressing an overvoltage when the operation of the circuit is stopped. The same parts as those in FIG. 1 are denoted by the same reference numerals, and the description thereof will be omitted. Hereinafter, parts different from those in FIG. 1 will be mainly described.

4, 100 is a current detector for detecting a current I _L of the reactor 6, 101 is a control circuit for controlling the on and off of the switching element 7 and the reverse blocking rectifier element 14.
When stopping the operation of the circuit, the control circuit 101, first off the switching element 7 to turn off the reverse blocking rectifier element 14 after the current I _L is detected by the current detector 100 falls below a specified value . Here, the specified value is a value that does not reach an overvoltage even if the current _IL is cut off from the inductance value of the reactor 6 and the turn-off loss and other circuit loss elements of the reverse blocking rectifier element 14. .
According to the present embodiment, when the reverse blocking rectifier element 14 is turned off, the current _IL has a sufficiently small value, so that the occurrence of overvoltage can be prevented.

Further, FIG. 5 shows a third embodiment corresponding to claim 6 and includes a component that absorbs stored energy of the reactor 6 and suppresses overvoltage when the reverse blocking rectifying element 14 is turned off. The same parts as those in FIGS. 1 and 4 are denoted by the same reference numerals, and the description thereof will be omitted. Hereinafter, parts different from those in FIGS. 1 and 4 will be mainly described.
In the following embodiments including the third embodiment, a control circuit for controlling on / off of the switching element and the reverse blocking rectifier element is not shown.

  In FIG. 5, reference numeral 15 denotes a Zener diode as voltage limiting means connected in parallel to the switching element 7. The Zener diode 15 has a characteristic that the voltage at both ends is substantially constant regardless of the current value when conducting in the reverse direction. This voltage, that is, the Zener voltage, is higher than the voltage generated in the normal operation of this circuit, that is, the voltage obtained by adding the surge voltage due to the wiring inductance (not shown) to the voltage E, and is equal to or lower than the withstand voltage of the switching element 7. . The reason is that the energy generated by the high-frequency switching operation of the switching element 7 is not processed by the Zener diode 15 to prevent an increase in loss and an increase in size of the Zener diode 15.

  In FIG. 5, the Zener diode 15 is connected in parallel to the switching element 7, but the Zener diode 15 may be connected in parallel to the reverse blocking rectifier element 14. However, in that case, it is necessary to connect a backflow prevention diode in series to the Zener diode 15 so that the Zener diode 15 does not turn on in the forward direction when the switching element 7 is turned on. In this case, the voltage across the switching element 7 is an added value of the voltage E and the Zener voltage. Therefore, it is necessary to select the Zener voltage and the breakdown voltage of the switching element 7 in consideration of this.

The voltage limiting means in the third embodiment is not limited to the Zener diode 15, but is a so-called charge / discharge type C (capacitor) snubber circuit, RC (resistance, capacitor) snubber circuit, RCD (resistance, capacitor, diode). It is also possible to use what is known as a snubber circuit.
However, for the purpose of this circuit, since it is assumed that the current is interrupted in a state where the voltage E is not established, a voltage limiting means of the type using the voltage E as a clamp voltage cannot be used.

Here, the circuits of FIGS. 4 and 5 can be used together. That is, by adding the current detector 100 in FIG. 4 to the circuit of FIG. 5, may be configured to control the reverse blocking rectifier element 14 in accordance with the current I _L of the reactor 6. In this case, the trade-off relationship between the energy capacity of current I _L and the Zener diode 15 of the reactor 6 to be cut off, may be set to a specified value or the like for turning off the reverse blocking rectifier element 14.

Next, FIG. 6 shows a fourth embodiment in which the present invention is applied to a so-called bridgeless type PFC circuit.
In FIG. 6, 20 and 21 are semiconductor switching elements, and 22 and 23 are reverse blocking rectifiers. Both ends of the series circuit of the capacitor 11 and the reactor 6 are connected in series between the reverse blocking rectifier 22 and the switching element 20. The capacitor 9 and the load 10 are connected to the connection point and the series connection point of the reverse blocking rectifying element 23 and the switching element 21 respectively, and to both ends of the series circuit of the reverse blocking rectifying element 23 and the switching element 21. Has been.
In this embodiment, the connection relationship between the reactor 6, the switching element 20, the reverse blocking rectifying element 22 and the capacitor 9, and the connection relationship between the reactor 6, the switching element 21, the reverse blocking rectifying element 23 and the capacitor 9 are as shown in FIG. Is substantially the same as the connection relationship of the reactor 6, the switching element 7, the reverse blocking rectifier element 14 and the capacitor 9, and the operation is the same as that of the first embodiment.

Next, FIG. 7 is a waveform diagram showing another operation of the first embodiment described above, and corresponds to claim 7.
In the first embodiment, during normal operation, when the voltage V _r becomes 0 and the voltage E of the capacitor 9 decreases due to the instantaneous drop, as shown in FIG. 7, the reverse blocking type is performed only during the period of V _r > E. After the rectifier element 14 is turned off and the voltage _Vr is restored, the same operation as in claims 1 to 3 may be performed.
According to this embodiment, as is apparent from a comparison between FIG. 7 and FIG. 11, it is possible to prevent an inrush current from occurring during a period of V _r > E.

Further, FIG. 8 is a circuit diagram showing a fifth embodiment of the present invention, and corresponds to claim 8. In this embodiment, a series circuit of a thyristor 302 as another rectifier and a resistor 301 is connected in parallel with the reverse blocking rectifier 14 in the circuit of FIG.
As is apparent from FIGS. 7 and 8, the reverse blocking rectifier 14 is intermittently operated in order to prevent inrush current during the period of V _r > E, so that the power for charging the capacitor 9 is reduced. For this reason, load power> charge power may be satisfied. Under this condition, there is a possibility that the voltage E cannot be restored to the specified value in the operation of FIG.

Therefore, considering that the operation is continued even under the condition of load power> charge power, a series circuit of a resistor 301 and a thyristor 302 is connected in parallel to the reverse blocking rectifier element 14 as shown in FIG. To do.
In the fifth embodiment, the thyristor 302 is turned on after the AC power supply 1 is restored, so that the resistor 301 rushes in even when the reverse blocking rectifier 14 is turned off under the condition of V _r > E in FIG. Capacitor 9 can be charged while limiting the maximum value of current. Note that the thyristor 302 is turned off when the capacitor 9 is initially charged.
Also, if the current flowing through the resistor 301 during the initial charging is within an allowable range, the thyristor 302 in FIG. 8 is replaced with a diode, and the capacitor 9 is initially charged through the resistor 301 and the diode with the rectifier 14 turned off. You may do it.

1: AC power supply 2-5: Diode 6: Reactor 7, 20, 21: Semiconductor switching element 9, 11: Capacitor 10: Load 14, 22, 23: Reverse blocking type rectifier 15: Zener diode 100: Current detector 101 : Control circuit 301: Resistor 302: Thyristor

Claims (8)

A series circuit of a reactor and a semiconductor switching element to which a rectified voltage of an AC power supply or an AC power supply voltage is applied, and a series circuit of a reverse blocking rectifier and a capacitor connected in parallel to the semiconductor switching element,
In an AC-DC conversion circuit that converts an AC power supply voltage into a DC voltage higher than its peak value by a switching operation of the semiconductor switching element and supplies the voltage to a load connected to both ends of the capacitor.
The reverse-blocking rectifier element is capable of controlling forward conduction by a control signal and has a function of blocking reverse current, and is in a state of blocking reverse current from the forward conduction state. An AC-DC conversion circuit characterized in that a reverse recovery loss that occurs during transition is less than or equal to a switching loss of the semiconductor switching element. In the AC-DC conversion circuit according to claim 1,
An AC-DC conversion circuit, wherein the reverse blocking rectifier element is a reverse blocking insulated gate bipolar junction transistor. The AC-DC converter circuit according to claim 1 or 2,
An AC-DC conversion circuit characterized in that, when the AC-DC conversion circuit is activated, the reverse blocking rectifier element is electrically connected in a forward direction when the voltage of the capacitor is equal to or higher than an instantaneous value of an AC power supply voltage. In the AC-DC conversion circuit according to claim 3,
2. An AC-DC conversion circuit characterized in that the timing at which the reverse blocking rectifier starts to conduct in the forward direction is gradually advanced from the zero cross point of the AC power supply voltage as a starting point. In the AC-DC converter circuit described in any one of Claims 1-4,
AC current characterized by comprising current detection means for detecting the current flowing through the reactor, wherein the forward current of the reverse blocking rectifier element is cut off when a current detection value by the current detection means is not more than a specified value. DC conversion circuit. In the AC-DC converter circuit described in any one of Claims 1-5,
Voltage limiting means capable of limiting the voltage across the element to a predetermined value higher than the voltage of the capacitor and lower than the withstand voltage of the element is connected to one or both of the switching element and the reverse blocking rectifier element. AC-DC conversion circuit characterized by the above. The AC-DC converter circuit according to claim 1 or 2,
When the voltage of the capacitor decreases during normal operation of the AC-DC conversion circuit, the reverse blocking rectifier is turned off only during a period in which the voltage of the capacitor falls below the instantaneous value of the AC power supply voltage. AC-DC conversion circuit. In the AC-DC converter circuit according to claim 7,
An AC-DC conversion circuit, wherein a series circuit of another rectifying element and a resistor is connected in parallel to the reverse blocking rectifying element.

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