JPH0226466B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a high frequency inverter circuit used for high frequency heating, etc., and in particular to a high frequency inverter circuit that reduces power loss, cost, etc. by effectively using a saturable reactor. Regarding.

First, the operating principle of this type of high frequency inverter circuit will be explained based on FIG. In the high frequency inverter circuit shown in FIG. 1, 1 is terminal 2,
This is a power supply circuit that converts the three-phase AC power supplies U, V, and W supplied to terminals 3 and 4 into DC power supplies of two arbitrary voltages, and a rectifier circuit 1a in which six thyristors whose conduction angles are controlled are bridge-connected. It also has a smoothing circuit 1b consisting of a chiyoke coil 5 and two capacitors 6 and 7 connected in series. 8 is the first and second thyristors 9a and 9b connected in series, and the third thyristor 8 is also connected in series.
The fourth thyristors 9c and 9d are connected in parallel with the same current direction, and the thyristors 9a and 9d are connected in parallel.
This is a bridge circuit in which a commutation capacitor 10 (capacitance C) is inserted between the connection point of thyristors 9c and 9d, and 11 is a commutation capacitor 10 that forms a resonance circuit with the capacitor 10. coil (inductance L), and 12 is a load such as an induction heating coil. 13 is a commutation coil (inductance L) that is paired with the coil 11;
4 is a bridge circuit paired with the bridge circuit 8, and the bridge circuit 14 connects thyristors 15a and 15b connected in series and thyristors 15c and 15d connected in series in parallel with the same current direction. Thyristor 15a, 15
A commutation capacitor 16 (capacitance C) is inserted between the connection point of thyristors 15c and 15d.

In this configuration, thyristors 9a, 9d, thyristors 15a, 15d, thyristors 9b, 9c,
The thyristors 15b and 15c correspond to A, B and B in FIG.
Due to the gate current shown in c and d, time t ₁ ,
When t ₂ , t ₃ , t ₄ . . . are fired in this order, the load 12
As shown in E of the figure, a smoothing capacitor 6,
A sine half-wave current _i1 generated by resonance between the capacitance C of the capacitor 10 and the inductance L of the coil 11 in a resonant circuit consisting of the capacitor 10, the coil 11, and the load 12, and the smoothing capacitor 7, the load 12, the coil 13, and the capacitor Capacitance C of capacitor 16 and coil 1 in a resonant circuit consisting of 16
The sine half-wave current i ₂ (i ₁ and i ₂ have symmetrical waveforms) generated by resonance with the inductance L of 3 is,
It is alternately supplied at each of the ignition timings t ₁ , t ₂ , t ₃ , t ₄ . Also in this case, capacitor 1
0 voltage V _c1 and capacitor 16
The voltage V _c2 generated across the terminal changes as shown at the bottom of FIG. In this way, according to the circuit configuration shown in FIG. 1, the output currents are composed of half-sine wave output currents i ₁ and i ₂ and have periods of time t ₁ to t ₃ , time t ₃ to _{t 5} , etc. High frequency output current can be obtained.

In a high-frequency inverter circuit based on the operating principle as described above, when trying to obtain a high-frequency output current with a frequency of 10 KHz or higher, for example, each thyristor in the bridge circuit corresponding to bridge circuits 8 and 14 shown in FIG. Since there is a risk that the reverse bias time may be insufficient, in order to ensure sufficient reverse bias time for each of these thyristors, the third
As shown in the figure, the bridge circuit 8 is replaced with n bridge circuits 8 _-1 to _{8 -o} , and the bridge circuit 14 is replaced with n bridge circuits 14 _-1 to 14 _-o ,
These bridge circuits 8 _-1 to 8 _-o and bridge circuits 14 _-1 to 14 _-o may be operated in a time-division manner, respectively.

By the way, in the high frequency inverter circuit as explained above, the load 12 is connected to the induction heating coil 12a and the phase advance capacitor 1 as shown in FIG.
2b is connected in parallel with the resonant load circuit 12c.
In order to effectively inject the output energy of the high frequency inverter circuit into the resonant load circuit _12c , as shown in _FIG . It is necessary to make it shorter than half the period of the resonant frequency of the load circuit 12c (the frequency of the voltage V _L across the resonant load circuit 12c). Therefore, when driving the resonant load circuit 12c having a resonant frequency of 50 KHz, for example, the time width of each half-sine wave output current i ₁ and i ₂ must be 10 μs or less. In this case, for example, the sine half-wave output current i ₁ ,
Assuming that each peak value of i ₂ is 1000 A and the time width is 10 μs, each bridge circuit 8 _-1 to 8 _-o shown in Fig. 3
The current change rate di/dt of each thyristor at _14-1 to 14 _-o is di/dt≒1000/10/2×1.6(A/μs)=320(A/μs)
The voltage loss in each of these thyristors becomes extremely large. FIG. 5 is a waveform diagram showing the above-mentioned power loss from when each of these thyristors is turned on until it is turned off, and the solid line a in A of this figure indicates the voltage between the anode and cathode of each of the thyristors at one point. The dashed line b shows the current flowing through these thyristors,
Further, the solid line c in the lower part of this figure shows the voltage loss in these thyristors. As is clear from FIG. 5, the power loss of the thyristor during turn-on starting from time _t1 and turn-off completing at time _t2 is extremely large. As described above, when driving a resonant load circuit having a high resonant frequency such as 50 KHz, there is a problem in that the power loss during switching in each thyristor becomes extremely large. To solve this problem, replace each thyristor with multiple thyristors connected in parallel,
This is a way to disperse power loss, but
This method is disadvantageous in terms of cost. Therefore, as another method for solving this problem, a method using an annular ferrite core is known. Figure 6 shows each bridge circuit 8 _-1 to 8 _-o when using this method.
The configuration of _14-1 to 14 _-o is shown using bridge circuit _8-1 as an example. As shown in this figure, each anode line of thyristor 9a _-1 , _9c-1 and thyristor _{9b -1} , 9 _d-1 each of the annular ferrite cores 17 _a-1 , 1 having a magnetic flux saturation endurance time T _s slightly longer than the turn-on time of these thyristors.
They are inserted into 7 _c-1 , 17 _b-1 , and 17 _d-1 , respectively.
When configured in this way, each thyristor 9 _a-1 ~
9 The power loss from when _d-1 is turned on until it is turned off is as shown in Figure 7. The solid line a in A of this figure shows the voltage between the anode and cathode of these thyristors, the dashed line b shows the current flowing through these thyristors, and the solid line c in B of the same figure shows the voltage between the anode and cathode of these thyristors.
shows the voltage loss in these thyristors. As is clear from FIG. 7, according to this configuration, during turn-on starting from time t ₁ , the corresponding annular ferrite core suppresses the rapid increase in current until the thyristor becomes completely conductive. Also, during turn-off, which is completed at time _t2 , rapid changes in current are suppressed.
As a result, the power loss of the thyristor can be significantly reduced compared to that shown in FIG. However, even with this method, each of the annular ferrite cores is distributed, so it is difficult to cool or wire these annular ferrite cores, especially in a high-capacity high-frequency inverter circuit with a high operating frequency of, for example, 50 KHz. There is a problem with becoming. Therefore, as a further solution to this problem, as shown in FIG. 8, each bridge circuit 8 _-1 to 8 _-o , 14 _-1
Connect saturable reactors 17 _{-1 to} 17 _-o each having a magnetic core such as a ferrite core in series with ~14 -o (the figure shows bridge circuit 8 _-1 and saturable reactor 1).
However, even in this configuration, the current flowing through the saturable reactors 17 _-1 to 17 _-o only flows in one direction, so the cross-sectional area of these magnetic cores must be increased _. or the thyristors 9 _b-1 and 9 _{d-1 in} this figure are not completely turned off.
There is a problem that the saturable reactor 17 _-1 does not work effectively when 9 _c-1 is turned on.

This invention was made in view of the above circumstances, and its purpose is to use the minimum necessary number of saturable reactors with a small cross-sectional area of the magnetic core, thereby improving the thyristor's turn-on and turn-off times. It is an object of the present invention to provide a high frequency inverter circuit that can effectively reduce power loss and thereby operate at extremely high frequencies.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 9 is a circuit diagram showing the configuration of a high frequency inverter circuit which is an embodiment of the present invention.
In this figure, parts corresponding to those in FIG. 3 are given the same reference numerals, and their explanations will be omitted. 9th
In the figure, first thyristors 9 _a-1 , 9 _a-2 ,
..., 9 _ao , 15 _a-1 , 15 _a-2 , ..., 15 _ao and the second thyristor 9 _b-1 , 9 _b-2 , ..., 9 _bo , 15 _b-
1 , 15 _b-2 ,..., 15 Connection point with _bo and commutation capacitor 10 _-1 , 10 _-2 ,..., 10 _-o , 16 _-1 ,
16 _-2 , ..., 16 _-o and saturable reactors 17 _-1 , 17 _-2 , whose magnetic cores are ferrite cores, etc.
..., 17 _-o , 18 _-1 , 18 _-2 , ..., 18 _-o are newly inserted.

Next, the operation of the circuit shown in FIG. 9 will be explained using the bridge circuit _8-1 as an example. Now, when the thyristors 9 _a-1 and 9 _d-1 are fired and a sinusoidal half-wave current i _1a flows, the magnetic flux density B of the magnetic core of the saturable reactor 17 _-1 becomes the magnetization curve 18 shown in FIG. Once it reaches one saturation value B ₁ along the magnetization curve 19, it reaches the magnetic flux density B ₂ and stops along the magnetization curve 19. Next, when the thyristors 9 _b-1 and 9 _c-1 are fired and a sinusoidal half-wave current i _1b flows, the magnetic flux density B changes from the magnetic flux density B ₂ along the magnetization curve 19 once to the other saturation value B ₃ . After reaching
The magnetic flux density reaches B ₄ along the magnetization curve 18 and stops. From then on, each time the thyristors 9 _a-1 and 9 _d-1 and the thyristors 9 _b-1 and 9 _c-1 are fired alternately, the magnetic flux density B changes from B ₄ →B ₁ →B ₂ or B ₂ →B ₃ →B ₄ . Thus, in this embodiment, the amount of change B ₀ in the magnetic flux density B when each thyristor turns on is B ₀ =B ₁ -B ₄ =B ₂ -B ₃ . On the other hand, in the conventional circuit shown in FIG. 8, current flows in the saturable reactor 17 _-1 in only one direction, so the magnetic flux density is, for example, B ₂ →B ₁ in FIG. 10. →B ₂ (or B ₄
→B ₃ →B ₄ ), and the amount of change B ₀ ′ in the magnetic flux density B is only B ₀ ′=B ₁ −B ₂ =B ₄ −B ₃ . Here, if the number of windings N for the magnetic core is the same, the cross-sectional area S of the magnetic core required to obtain the same magnetic flux saturation durability time is the amount applied between both ends of the saturable reactor 17 _-1 If the voltage is v, then the relationship is S=1/N・B ₀ vdt (1) Therefore, according to the embodiment shown in FIG. 9, the conventional circuit shown in FIG. B′/B can be reduced by ₀ times.

Considering this effect by substituting specific numerical values,
Now, each turn-on time of thyristor 9 _a-1 to 9 _d-1 is
3μs, the voltage applied across the saturable reactor _17-1 is 1200V, the amount of change _B0 in magnetic flux density B is 6000
Gauss, and when the number of windings N is 1, the saturable reactor 17 is required to sufficiently reduce the power loss when each thyristor is turned on.
The magnetic flux saturation durability time of the magnetic core _-1 must be set to 3 μs as well, so the cross-sectional area S of the magnetic core is calculated using equation (1): S=1200×3×10 ^-6 /6000×10 ^-4 ( m ² ) = 0.6×10 ^-2 (m ² ) = 60 (cm ² ). Therefore, in this case, when using an ^annular ferrite core 17 as shown in FIG. This means that you only need to use 15 of them.

On the other hand, in the conventional circuit shown in Fig. 8, the amount of change B ₀ ' in the magnetic flux density B is 3000 Gauss, so if the other values are set to the same values as in the above case, the magnetic core The cross-sectional area S is doubled, as S=1200×3×10 ⁻⁶ /3000×10 ⁻⁴ (m ² )=120 (cm ² ). Therefore, in this case, the 11th
As shown in the figure, 30 annular ferrite cores with a cross-sectional area of 4 cm ² are required, and when these are connected to form a cylindrical shape, the length becomes 60 cm.

In this way, according to this embodiment, as is clear from the above-mentioned specific values, the size of the saturable reactor used can be significantly reduced compared to the conventional one.

As explained above, according to the high frequency inverter circuit according to the present invention, the first and second current control elements are sequentially connected in series, and the third and fourth current control elements are sequentially connected in series, 1st, 2nd
In each bridge circuit comprising a capacitor inserted between the connection point of the current control element and the connection point of the third and fourth current control elements, a saturable reactor is connected in series with each of the capacitors. This makes it possible to reduce the power loss during switching of the current control element by using the minimum number of saturable reactors required, and also to reduce wiring and cooling for these saturable reactors. Furthermore, since alternating current flows through these saturable reactors, the number of magnetic cores can be halved compared to conventional ones, thereby reducing installation space and cost.

[Brief explanation of drawings]

Figure 1 is a circuit diagram for explaining the operating principle of a high frequency inverter circuit, Figure 2 is a time chart showing the operation timing of the circuit, Figure 3 is a circuit diagram of a time division type high frequency inverter circuit, and Figure 4 is a circuit diagram for explaining the operating principle of the high frequency inverter circuit. The figure is a waveform diagram showing the output current of the high frequency inverter circuit to be supplied to the resonant load circuit, Figure 5 is the waveform diagram showing the power loss during thyristor switching, and Figure 6 is the waveform diagram of the bridge circuit in the conventional high frequency inverter circuit. 7 is a waveform diagram showing power loss during switching of the thyristor in the same example; FIG. 8 is a circuit diagram showing a second example of a bridge circuit in a conventional high frequency inverter circuit;
Fig. 9 is a circuit diagram showing the configuration of a high frequency inverter circuit which is an embodiment of the present invention, Fig. 10 is a magnetization curve diagram of a magnetic core of a saturable reactor for explaining the embodiment, and Fig. 11 is a diagram of annular ferrite. It is a perspective view of an example of a core. 1... Power supply circuit, 6, 7... Smoothing capacitor,
8 _-1 ~ 8 _-o , 14 _-1 ~ 14 _-o ...Bridge circuit,
9 _a-1 ~ 9 _do , 15 _a-1 ~ 15 _do ...thyristor,
10 _-1 ~ 10 _-o , 16 _-1 ~ 16 _-o ... Capacitor, 11, 13 ... Coil, 12 ... Load, 17
_-1 to 17 _-o , 18 _-1 to 18 _-o ...Saturable reactor.

Claims (1)

[Claims] 1. The first and second current control elements are connected in series in sequence, and the third and fourth current control elements are connected in series in sequence.
are connected in parallel in the same current direction, and a saturable reactor and an inverter are connected between the connection point of the first and second current control elements and the connection point of the third and fourth current control elements. At least one bridge circuit formed by inserting a diversion capacitor in series, a commutation coil, and a DC power source are connected in series to form a resonant circuit, and the first and fourth current controls are performed. A high frequency inverter circuit characterized in that the element and the second and third current control elements are alternately made conductive to supply current to a load inserted in series with the resonant circuit.