JPH0216114B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention reduces the power loss during turn-on of the current control element used, and shortens the fall time of the current of the current control element to increase the output frequency, that is, increase the speed. This article relates to an advanced high frequency inverter circuit.

First, the operating principle of this type of high frequency inverter circuit will be explained based on the basic circuit shown in FIG.
In the high-frequency inverter circuit shown in FIG. 1, 1 is a DC power supply that generates two DC voltages E ₁ and E ₂ (E ₁ = E ₂ ), and includes a variable voltage source 2, a chiyoke coil 3, and smoothing capacitors 4 and 5. It is made up of. 6 are thyristors 6a and 6b connected in series.
and thyristors 6c and 6d, which are also connected in series.
and are connected in parallel with each other in the same current direction, and the connection point of thyristors 6a and 6b in this switch circuit 6 and the thyristor 6
A first resonant capacitor 7 (a commutation capacitor with a capacitance of C) is inserted between the connection points c and 6d. Further, 8 is a first resonant coil (an induction coil for commutation, and has an inductance of L). Next, 9 is a second switch circuit having the same configuration as the switch circuit 6, 10 is a second resonant capacitor (capacitance C), and 11 is a second resonant coil (inductance L). And smoothing capacitor 4
(DC power supply with voltage E ₁ ), a first series resonant circuit 12 consisting of a switch circuit 6, a resonant capacitor 7 and a resonant coil 8, and a smoothing capacitor 5 (with a voltage E ₂
A load 16 (equivalent resistance R ₀ ) is inserted between terminals 14 and 15 at both ends of the second series resonant circuit 13 consisting of a DC power source), a switch circuit 9, a resonant capacitor 10, and a resonant coil 11. .

In this configuration, the thyristors 6a, 6d, thyristors 9c, 9b, thyristors 6c, 6b, and thyristors 9a, 9d are operated at times t ₁ and t ₂ by gate currents as shown in A, B, C, and D of FIG. ,t ₃ ,
t ₄ ..., the first series resonant circuit 12 has L, C, R ₀ , as shown in E of the figure.
The approximately sinusoidal half-wave resonant current I ₁ determined by
Similarly, a substantially sinusoidal half-wave resonant current I ₂ flows through the series resonant circuit 13, and as a result, the load 16 receives a high-frequency current I _l which is a combination of both resonant currents I ₁ and I ₂ .
flows. In this case, the resonance capacitors 7, 1
The voltages V _c1 and V _c2 between both ends of 0 change as shown in F and G of FIG.

By the way, in such a high frequency inverter circuit, when the output frequency is set high, the current change rate di/dt of each thyristor 6a to 6d, 9a to 9d becomes extremely large, and accordingly, the turn-on speed of each of these thyristors increases. The power loss during this time becomes extremely large. Figure 3 is a characteristic diagram showing the power loss during turn-on of this thyristor.As shown in A of this figure, the thyristor fired at time _t1 has a resonant current _I1 (or
I ₂ ) flows, and at this time, the voltage between the anode and cathode of this thyristor changes as shown by the solid line b, and as a result, the power loss of this thyristor becomes as shown by the solid line c in FIG. As is clear from the waveform shown in Fig. 3, when the output frequency is increased in this type of high-frequency inverter circuit, the power loss when each thyristor is turned on becomes extremely large, so each thyristor is connected in parallel. There is a problem in that the power loss must be distributed by replacing each thyristor with a plurality of thyristors, resulting in extremely high costs.

As a solution to this problem, as shown in FIG. Saturable reactors 17, 18 whose turn-on time is slightly longer than the turn-on time of each of these thyristors 6a-6d, 9a-9d.
There is a method of inserting each reactor in series (assuming the reactor when unsaturated is L ₁ ). FIG. 5 is a characteristic diagram showing the power loss during turn-on of each thyristor 6a to 6b, 9a to 9d in the high frequency inverter circuit shown in FIG. 4, and as shown in this diagram,
The current of the thyristor fired at time _t1 (solid line a) is the period _Tsf until the magnetic flux of the corresponding saturable reactor 17 or saturable reactor 18 transitions from an unsaturated state to a saturated state at time _t2 .
Since (L ₁ +
The impedance increases gradually at the resonant frequency determined by L) and C, and then increases sharply at the resonant frequency determined by L and C since the impedance becomes low when the impedance reaches the saturated state at time _t2 . Further, the current of this thyristor once reaches its maximum value at time _t3 , and then rapidly decreases until time _t4 , when the saturable reactor 17 (or 18) continues to maintain the saturated state, and at time _t4 . During the period T _sr from when the saturable reactor 17 (or 18) transitions from the saturated state to the unsaturated state until time t ₅ when the current becomes zero, the thyristor operates again at the resonant frequency determined by (L ₁ +L) and C. The current decreases slowly until it reaches zero. According to this method, each thyristor 6a to 6b, 9 is connected as shown by the solid line c in FIG.
The power loss during turn-on of a to 9d can be effectively reduced.

In this case, the voltage V _c1 across the resonant capacitor 7 or the voltage V _c2 across the resonant capacitor 10 is determined at the time t ₃ when the current flowing through the thyristor reaches its maximum value, as shown by the solid line d shown in FIG. During the period when the polarity is reversed after , and the thyristor is completely off, their absolute values become equal. In addition, the voltage V _l1 across the saturable reactor 17 (or the voltage V _l2 across the saturable reactor 18) is determined at time t, which is the current increasing process of the thyristor, as shown by the solid line e in Figure 6 (b). ₁ ~ _t2
(period T _sf ), this saturable reactor has high impedance, so approximately V _c1 +E ₁ (or
V _c2 + E ₂ ), and at time t ₂ to _{t 4} ,
The saturable reactor has extremely low impedance (for example, 1/200 of the impedance in the unsaturated state)
(This is extremely small compared to the inductance L), so it decreases by that amount, and from time t ₄ to
At t ₅ (period T _sr ), approximately V _c1 −E ₁ (or V _c2 −
_E2 ). As mentioned above, since the absolute values of V _c1 (or V _c2 ) when the thyristor is in the off state are equal, the voltage V _l1 (or V _l2 ) during the period T _sf and the voltage V _l1 during the period T _sr (or
There is a voltage difference of 2E ₁ (or 2E ₂ ) between the absolute value and V _l2 ). Therefore, the period T _sr is longer than the period T _sf (normally, the ratio of the voltage V _c1 +E ₁ to the voltage V _c1 −E ₁ is 2:1 to 3.5:1.5, so the period T _sr and the period T sf are The ratio of T _sf is about 1:2 to 1:2.5.

If the period T _sr is long in this way, the time from when the thyristor used becomes conductive to when it becomes non-conductive becomes longer, so in order to perform the commutation operation accurately, it is necessary to carry out the commutation operation next time. It is necessary to delay the firing timing of the thyristor by that amount. Therefore, in order to increase the speed of this type of high-frequency inverter while reducing power loss during turn-on of the thyristor, it is necessary to shorten this period T _sr by some means.

This invention was made in view of the above circumstances, and its purpose is to provide a high-frequency inverter circuit that achieves both reduction in power loss during turn-on of the current control element used and increased speed. It's about doing.

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 7 is a circuit diagram showing the configuration of an embodiment of the present invention, and in this figure, parts corresponding to those in FIG. 4 are given the same reference numerals. In FIG. 7, between both ends 19 and 20 of a saturable reactor 17 (inductance when unsaturated is L ₁ ), a first energy source is formed by connecting a diode 21 and a resistor 22 (resistance value R) in series. Absorption circuit 2
3 is inserted so that the forward direction of the diode 21 is opposite to the direction of the resonant current _I1 . Further, between both ends 24 and 25 of the saturable reactor 18 (inductance when unsaturated is L ₁ ), a second energy absorbing circuit 28 is provided, which includes a diode 26 and a resistor 27 (resistance value R) connected in series. , are inserted so that the forward direction of the diode 26 is opposite to the direction of the resonant current _I2 .

In the above configuration, thyristors 6a, 6d or thyristors 6c, 6b (or thyristors 9
c, 9b or thyristor 9a, 9d) is fired at time _t1 in FIG. 8, the voltage across the saturable reactor 17 (or 18) V _l1
(or V _l2 ) is positive from time t ₁ to around time t ₃ as shown in FIG. 6B, so the diode 21 (or 26) is reverse biased. Further, this voltage V _l1 (or V _l2 ) becomes negative from near time t ₃ to time t ₄ , but its value is small, so the voltage between diode 21 and resistor 22 (or diode 26 and resistor 27 ) can be ignored. Therefore, time
The resonant current I ₁ (or I ₂ ) between t ₁ and _{t 4} is the 8th
As shown in the figure, the waveform is the same as that shown in A of FIG. On the other hand, after time _t4 , the voltage V _l1 (or V _l2 ) tends to take an extremely large value in the negative direction, as shown in FIG. 6B. This is because the saturable reactor 17 (or 18) is in an unsaturated state, so that the voltage (V _c1 - E ₁ ) or the voltage (V _c2 -
This is because almost all of E ₂ ) will be applied to the saturable reactor 17 (or 18). Therefore, the diode 21 (or 26) becomes conductive,
The energy of the saturable reactor 17 (or 18) is released via the energy absorption circuit 23 (or 28), and during this time the resonant current I ₁ (or I ₂ )
is reduced by the resistance value R (R≫R ₀ ) through this energy absorption circuit 23 (or 28), as shown by the solid line a in A of FIG. 8, and becomes zero at time t ₅ '. Become. In this case, the resonant current at time t ₄
If the value of I ₁ (or I ₂ ) is I ₀ , the current flowing through the saturable reactor 17 (or 18) hardly decreases as indicated by the broken line a′ due to its high inductance, so the resonant current I ₁ (or When I ₂ ) suddenly decreases from time t ₄ to _{t 5} ', as shown by the solid line g in B of this figure, the saturable reactor 17 (or 18)
A current corresponding to the difference between the current and the resonant current I ₁ (or I ₂ ) will flow through the energy absorption circuit 23 (or 28). Then, when the resonant current I ₁ (or I ₂ ) becomes zero at time t ₅ ′, the current I ₀ ′ still flowing through the saturable reactor 17 (or 18) at this time t ₅ ′ becomes (See the solid line g in FIG. 2). Since this attenuation characteristic is extremely gentle, the power loss of the absorbers (not shown) added to the thyristors 6a to 6d and 9a to 9d can be suppressed, and it is not necessary to provide absorbers to the diodes 21 and 26. It disappears.

As described above, according to this embodiment, the power loss when the thyristors 6a to 6d and 9a to 9d are turned on can be extremely effectively reduced by effectively using the saturable reactor. The time it takes for the thyristor to transition to a non-conducting state can be reasonably and effectively shortened, thereby increasing the output frequency, that is, increasing the speed.

As explained above, the high frequency inverter circuit according to the present invention includes a first DC power supply, a first switch circuit using a current control element as a circuit opening/closing means,
A first series resonant circuit in which a first resonant capacitor and a first resonant coil are connected in series, a second DC power supply, and a second series resonant circuit in which a current control element is used as circuit switching means.
a switch circuit, a second series resonant circuit in which a second resonant capacitor and a second resonant coil are connected in series, and a load is placed between each end of the first and second series resonant circuits. are inserted in common, the first series resonant circuit supplies the first resonant current to the load in one direction, and the second series resonant circuit supplies the same load with the first resonant current in the direction. In a high frequency inverter circuit configured to supply a second resonant current in the opposite direction, first and second saturable reactors are inserted in series with these first and second series resonant circuits, respectively, and , a first energy absorption circuit including a first diode and a first resistor connected in series is connected to a first energy absorption circuit such that the forward direction of the first diode is opposite to the direction of the first resonant current. A second energy absorbing circuit is inserted in parallel with the saturation reactor, and the second diode and the second resistor are connected in series, and the forward direction of the second diode is opposite to the direction of the second resonant current. Since the saturable reactor is inserted in parallel with the second saturable reactor, the saturable reactor In addition, the current change in the energy absorbing circuit is made gradual in the time it takes for these current control elements to transition from a conductive state to a non-conductive state. However, it can be shortened very effectively. Therefore, according to the present invention, speeding up can be achieved at an extremely low cost without increasing the power capacity of the power control element.

[Brief explanation of drawings]

Figure 1 is a circuit diagram showing the basic configuration of this type of high-frequency inverter circuit, Figure 2 is a time chart to explain the operation of the circuit, and Figure 3 is a waveform diagram showing the power loss of the thyristor in the circuit. , 4th
The figure is a circuit diagram showing an example of a high-frequency inverter circuit that reduces power loss when the thyristor is turned on. Figure 5 is a waveform diagram showing the power loss of the thyristor in the same example. Figure 6 is a waveform diagram of each part of the same example. , FIG. 7 is a circuit diagram showing the configuration of an embodiment of the present invention,
FIG. 8 is a waveform diagram for explaining the operation of the same embodiment. 1...DC power supply, 4, 5...Smoothing capacitor,
6a to 6d, 9a to 9d... Current control element (thyristor), 7, 10... Resonance capacitor, 8, 1
1... Resonance coil, 12, 13... Series resonant circuit, 16... Load, 17, 18... Saturable reactor, 23, 28... Energy absorption circuit.

Claims (1)

[Scope of Claims] 1 (a) A first DC power source, a first switch circuit using a current control element as circuit switching means, a first resonant capacitor, and a first resonant coil are connected in series. A first series resonant circuit, (b) a second DC power supply, a second switch circuit using a current control element as a circuit opening/closing means, a second resonant capacitor, and a second resonant coil are connected in series. (c) a load is commonly inserted between both ends of the first and second series resonant circuits, and the first series resonant circuit A first resonant current is supplied to the load in one direction, and a second resonant current is supplied to the load in a direction opposite to the direction of the first resonant current by the second series resonant circuit. (d) in the first and second series resonant circuits;
(e) a first energy absorbing circuit including a first diode and a first resistor connected in series;
(f) a second diode and a second resistor are connected in series; (f) a second diode and a second resistor are connected in series; a second energy absorbing circuit made of
A high frequency inverter circuit, characterized in that the diode is inserted in parallel with the second saturable reactor so that the forward direction of the diode is opposite to the direction of the second resonant current.