JPH0315434B2 - - Google Patents

Description

[Detailed description of the invention] The present invention relates to an inverter device.

FIG. 1 shows a conventional example of this type of inverter device. This conventional inverter device is composed of a push-pull type transistor inverter circuit A, etc.
A rectifier bridge 1 and a smoothing capacitor 3 are connected from the commercial power supply Vs via a switch S to form a DC power supply, and the center tap of the primary winding N1 of the oscillation transformer 7 is connected from the side terminal shown in the figure via a choke coil ₂ . connected to. One end of the primary winding _N1 is connected to the collector of the transistor 4, and the other end to the collector of the transistor 5, and the emitters of each of the transistors 4 and 5 are collectively connected to the side terminal of the DC power supply. Also transistors 4 and 5
A feedback winding N _B of an oscillation transformer 7 is connected to the base of the oscillation transformer 7, and further connected to a side terminal of a DC power source via resistors 8 and 9. Primary winding of oscillation transformer 7
A resonance capacitor 6 is connected between both ends of N ₁ , that is, between the collectors of transistors 4 and 5, and a load 10 and a chiyoke coil 11 for variable output are connected between both ends of the secondary winding N ₂ of the oscillation transformer 7. A series circuit is connected.

In this conventional example, a resistor 8,
When a drive current is applied to the base of each transistor 4 and 5 through the transistor 9, the transistor 4 or 5
Either one of them is turned on. Now, if transistor 4 is turned on, the primary winding of oscillation transformer 7
A current flows through N ₁ and induces a back electromotive force in the secondary winding N ₂ and the feedback winding N _B. Afterwards, this electromotive force turns on and off transistors 4 and 5 alternately. The current flowing through the primary winding N ₁ is alternately reversed,
Due to the resonance operation with the capacitor 6, the secondary winding N ₂
A high frequency sine wave output is obtained. This output is applied to a load 10 via a chiyoke coil 11 for variable output.
supplied to

Figure 2a shows the above transistor inverter circuit A.
This figure shows an equivalent circuit of the resonant system under load. [B in the same figure is an equivalent circuit in which a is rewritten. ]. In Figure 2a, C is the capacitance of the capacitor 6, L ₁ is the excitation inductance of the oscillation transformer 7, and L ₂
represents the inductance of the choke coil 11, and R represents the resistance of the load 10. Furthermore, L' ₂ in Figure 2b has the relationship L' ₂ = R ² + ω ² L ² / ₂ / ω ² L ₂ , and R' in Figure 2 b has the relationship R' = R ² + ω ₂ L There is a relationship of ² / ₂ /R.

Now, when the impedance seen from the input terminals A and A' of this equivalent circuit is expressed with frequency plotted on the horizontal axis, it becomes as shown in Fig. 2c. That is, the point P is the parallel resonance point (anti-resonance point), and the self-excited inverter stably maintains oscillation at this point. If the capacitance value of the capacitor 6 shown in FIG. 1 is changed in this state, the parallel resonant circuit impedance changes, and the anti-resonance point P in FIG. 2c changes as shown in FIG. 2d. That is, when the capacitor capacitance C is increased, the anti-resonance frequency is lowered, and the impedance of the choke coil 11 is therefore reduced, and the output to the load 10 is increased, and when the capacitor capacitance C is decreased, the opposite is true. Furthermore, if the excitation inductance _L1 of the oscillation transformer 7 is changed instead of changing the capacitance C of the capacitor 6, the anti-resonance point changes as shown in FIG. 2e. That is, when the inductance L ₁ is increased, the anti-resonance frequency is lowered, and the impedance of the choke coil 11 is therefore reduced, and the output to the load 10 is increased, and the opposite is true when the excitation inductance L ₁ is decreased.

Furthermore, the inductance L ₂ of the chiyoke coil 11
Even if the value is changed, the impedance of the parallel resonant circuit changes, and the anti-resonance point P in FIG. 2c changes as shown in FIG. 2e. That is, when the inductance L ₂ is increased, the anti-resonance frequency is lowered, and in this case, even if the frequency is lowered because the inductance L ₂ of the choke coil 11 is increased, the output to the load 10 is decreased. Of course, the opposite is true if the inductance L ₂ is reduced. Note that the case where a capacitor is used instead of the Chi-Yoke coil 11 to vary the output can be explained in the same manner as the Chi-Yoke coil 11, but in that case, as the anti-resonance point frequency becomes higher, the capacitor impedance becomes smaller, so the output increases. However, using a capacitor in place of the choke coil 11 causes a phase-advanced current to flow through switching elements such as transistors, which may destroy these elements, increase the loss of the transistor inverter circuit A, or cause noise due to increased waveform distortion. Since it causes disadvantages such as increased generation, it is not used much other than for special purposes.

It has been explained above that when the circuit constants of the circuit in Figure 1 are changed, the anti-resonance frequency, that is, the oscillation frequency of the transistor inverter circuit A changes, and the output to the load changes. can be done easily.

By the way, the method of changing the capacitor capacitance C of the capacitor 6 does not have a means of continuously changing the capacitor capacitance C, and the method of switching the capacitor capacitance C generates surge voltage and current when switching.
There is a risk of damaging switching elements such as transistors, and if the output to the load 10 is changed significantly (for example, from 100% to 50%), the capacitance C must be changed even more significantly. This is not a preferable method because there is a risk that the transistor inverter circuit A may cause abnormal oscillation.

Also, the excitation inductance L ₁ of the oscillation transformer 7
An oscillation transformer using a saturable reactor has been considered as a method of changing this, but the structure is quite complex and large-scale, making it unsuitable for anything other than special uses. For this reason, generally, as shown in Fig. 1, the coil 11 is
is often used. However, the fact that the output can be controlled by changing the oscillation frequency of the inverter circuit by changing the circuit constants means that when controlling the output by changing the circuit constants, it is difficult to control the output by changing the circuit constants in a self-excited inverter device using LC resonance. It can be said that the inductance L ₂ of the chiyoke coil 11 shown in FIG.
In the case where the output is controlled by changing the inductance L2, there is a drawback that the frequency will necessarily decrease if the inductance _L2 is increased and the output is reduced.

For example, as load 10 in the circuit shown in Figure 1,
Fluorescent light load for FCL32W and FCL40W (DC connection)
As a result of 100% lighting and 60% lighting by switching the inductance of the chiyoke coil 11 using
The frequency at 100% is 40KHz, the frequency at 60% is
It became 25KHz. As is well known, fluorescent lamps emit near-infrared rays, and if the lighting frequency is half or equal to the carrier frequency of communication equipment that uses infrared rays, it can cause interference and cause malfunction of communication equipment. Are known. Currently, the frequency used in such infrared communication equipment is 30K.
Hz to 50KHz, therefore, using 15 to 24KHz or 30 to 48KHz as the lighting frequency of a fluorescent lamp will result in interference, so in order to remove this band, use 25 to 24KHz.
This creates the need to use frequencies above 29KHz and 49KHz. In order to set the frequency of the above lighting device to such a range, there is no other way than to set both 100% lighting and 60% lighting to 49KHz or higher, and 60% lighting is 49K
When set to Hz, the frequency at 100% lighting is 80KHz
This causes new problems such as an increase in radiation noise and an increase in switching loss, so frequency control becomes necessary in order to effectively use a limited range of frequencies. Due to these demands, separately excited inverter devices are attracting attention, but since the circuit is more complex than that of self-excited inverters, problems such as cost and reliability remain. Therefore, it can be said that there is a great need for a simple method of controlling the frequency when the output of a self-excited inverter is changed.

The present invention has been made in view of the above-mentioned points, and its purpose is to design a self-excited inverter device that can set two or more operating points of the inverter when the output is reduced and that takes into account the oscillation frequency. This allows you to easily avoid interference and malfunctions with equipment such as communication equipment installed nearby, and by adjusting the circuit constants, you can change the oscillation frequency during output reduction over a wide range. An object of the present invention is to provide an inverter device that has a simple configuration and is advantageous in terms of cost and reliability.

The present invention will be explained below with reference to Examples. First, the operating principle of the present invention will be explained. Figures 3a to 3c show equivalent circuits of an inverter circuit when the resonant system is loaded to explain the principle of the present invention, and Figure 3a shows an inductance element _L3 connected in series with a load _R1 in the output circuit of the inverter circuit. A capacitor _C2 is also provided in parallel with the load _R1 , and a changeover switch _S0 is used to set the state in which the capacitor _C2 is inserted or the state in which it is removed. In other words, if the switch _S0 is on the NC terminal side, these elements _L3 and _C2 are removed from the circuit, and the inverter circuit oscillates at a frequency determined by the capacitor _C1 and the inductance _L1 of the oscillation transformer. . Switch here S ₀
When set to the NO terminal side, the inductance element L ₃ ,
Since capacitor C ₂ is inserted in the circuit, the inverter circuit consists of capacitor C ₁ and inductance L ₁
In addition to the parallel resonant circuit with , it has a series resonant circuit consisting of capacitance C ₂ and inductance L ₂ .
When such a situation is expressed as a frequency characteristic of circuit impedance, it becomes as shown in FIG. In other words, when switch S ₀ is on the NC terminal side, there is a parallel resonance frequency P ₀ of capacitor C ₁ and inductance L ₁ ,
The circuit impedance at that time is maximum, but at frequencies lower than frequency P ₀ , ωL ₁ < 1/ωC ₁ , indicating inductive impedance, and at frequencies higher than frequency P ₀ , ωL ₁ > 1/ωC _1. Therefore, it becomes a capacitive impedance, and exhibits characteristics as shown in FIG. 4a. Now, if the feedback signal of a self-excited inverter device is obtained from an oscillation transformer, the oscillation frequency is determined by the frequency P ₀ at the parallel resonance point, that is, the anti-resonance point, as is well known, and is unstable at other points. However, when switch S ₀ is set to the NO terminal side,
The next three resonance points are formed as shown in FIG. 4b. In other words, at low frequencies that satisfy ωL ₂ ≪1/ωC ₂ , the capacitance of capacitor C ₂ and capacitor C ₁
The capacitance of L1 is added to form a parallel resonance with the inductance _L1 . The parallel resonance point corresponding to this is P ₁
It is. Further, at a frequency of ωL ₂ ≒1/ωC ₂ , a series resonance is formed between the inductance L ₂ and the capacitor C ₂ .
This resonance point is _P2 . Furthermore, at high frequencies that satisfy ωL ₂ ≫ 1/ωC ₂ , inductance L ₁ and inductance L ₂ become parallel, and the capacitor
Forms parallel resonance with _C1 . The parallel resonance point corresponding to this is _P3 .

Among these three resonance points, P ₂ is a series resonance point, which is an unstable region in a self-commutated inverter device that uses parallel resonance, but P ₁ ,
All P ₃ can maintain stable oscillation at the anti-resonance point,
Furthermore, it can be seen that the frequency can be controlled to either of the two operating points P ₁ or P ₃ in FIG. 4b by switching the switch S ₀ from the operating point P ₀ in FIG. 4a. According to experiments conducted by the inventors, if p ₀ > p ₂ , the result is P ₃ , and if p ₀ < p ₂ , the result is P ₁ .

FIG. 3b shows an additional current-limiting inductance element _L4 . That is, when the switch _S0 is on the NC terminal side, the current limiting inductance element _L4 used as a reactance element is short-circuited, and the capacitor _C2 is not connected. Therefore, the inverter device is driven by a parallel resonant circuit consisting of inductances _L1 and _L3 and capacitor _C1 , and inductance element _L3 serves as a stabilizing element for the output current.The operating point in this case is shown in Fig. 4a. Let P be ₀ point.

Next, when the switch S ₀ is switched to the NO terminal side, the current limiting inductance element L ₄ is inserted in series with the load R to reduce the output current, and at the same time the capacitor
Insert C ₂ in parallel. Therefore, in the inverter device, a parallel circuit of capacitor C ₁ and inductance L ₁ and a series circuit of inductance element L ₃ and capacitor C ₃ are formed, and as mentioned above, three resonance points as shown in Fig. 4b are obtained. It will be done. This means that when adjusting the output by restricting the output current, P ₁ at low frequency
It is shown that the oscillation frequency can be set high or low by selecting the _three points. Third
The equivalent circuit in Figure c can be explained in a similar way by replacing the inductance elements L ₃ and L ₄ in Figure 3B with capacitors C ₃ and C ₄ , and replacing the capacitor C ₂ with inductance element L ₅ . be.

The circuit shown in FIG. 5 was formed based on this principle. That is, in this embodiment, in the transistor inverter circuit A, the load 10 is connected to both ends of the secondary winding _N2 of the oscillation transformer 7 via the first and second coils 11a and 11b, and Connect the common terminal COM of the changeover switch _S1 to the connection point between the load 10 and the second
A changeover switch is connected to the connection point of the yoke coil 11b.
Connect the NC terminal of S ₁ , and then connect the secondary winding N ₂ and load 1.
This circuit differs from the conventional circuit shown in FIG. 1 in that a capacitor 12 is connected between the NO terminal of the changeover switch S1 and the NO terminal of the changeover switch _S1 .

When the switch S is turned on now, the commercial power supply Vs is connected, and the transistor inverter circuit A operates in oscillation like the conventional example shown in FIG. 1, and a high frequency output is obtained on the secondary side of the oscillation transformer 7. Now changeover switch S ₁ is
On the NC terminal side, the chiyoke coil 11b, which is an output reducing reactance element, is short-circuited, so the secondary output of the oscillation transformer 7 is supplied to the load 10 via the chiyoke coil 11a. Next, when the changeover switch S ₁ is set to the NO side, the yoke coil 1
1a and a chiyoke coil 11b in series with the load 10.
is inserted to reduce the output current, and at the same time, the capacitor 12 is connected in parallel to the series circuit of the load 10 and the choke coil 11b. The oscillation frequency of the transistor inverter circuit A at this time is shown in Fig. 4b.
As explained above, there are two ways to think about this.If you set the frequency before switching the selector switch _S1 , that is, the frequency when the selector switch _S1 is on the NC terminal side, you can increase the frequency when the output is reduced. As mentioned in the explanation of the principle, it is possible to lower the value. However, in consideration of noise interference to other communication equipment, the frequency before switching of the selector switch _S1 is set to a predetermined frequency so that noise interference to communication equipment is not caused even when the output is reduced. The operating point is selected so that there is no

After switching the selector switch S ₁ to the NO terminal side,
For example, short circuit switch SW _a , open switch
The above-mentioned high and low frequencies can also be switched by providing SW _b as shown in FIG. 6 and momentarily changing the circuit mode by operating these switches. Furthermore, by changing the capacitance value of the capacitor 12, the oscillation frequency can be changed over a wide range, and of course, the inductance value of the chiyoke coil 11a may also be changed.

Furthermore, in the above embodiment, since the oscillation of the transistor inverter circuit A is performed by the LC parallel oscillation circuit, another resonant circuit formed when reducing the output is a series resonant circuit, but an inverter circuit using a series resonant circuit In this case, another resonant circuit formed at the time of output reduction may be a parallel resonant circuit.

The present invention has an inverter circuit that performs self-excited oscillation by an LC resonance circuit of a capacitor and the inductance of an oscillation transformer, and a reactance element that switches the reactance value to set the output reduction state is used as the secondary output of the oscillation transformer. In an inverter device inserted in series between a load, the LC resonant circuit of the inverter circuit and the another resonant circuit are provided with another resonant circuit including the reactance element and a switching means when in an output reduction state. Since two or more operating points of the inverter circuit are formed by , and the inverter circuit is driven at one of the operating points,
This has the effect of increasing the design margin when considering the oscillation frequency so that it does not become a source of interference noise from nearby communication equipment, etc., and as a result, interference with other nearby equipment and malfunctions can be easily avoided. In addition to simplifying the design of noise filters, etc., the oscillation frequency during output reduction can be varied over a wide range by adjusting the circuit constants, and it is also possible to simply switch another resonant circuit. Since it only needs to be formed using a means, it can be realized with a simple structure, and has advantages in terms of cost and reliability.

[Brief explanation of the drawing]

Figure 1 is a circuit diagram of a conventional example, Figure 2 a, b, c,
d and e are diagrams explaining the same operation as above, Figures 3 a, b, and c are circuit diagrams of equivalent circuits for explaining the principle of the present invention, Figures 4 a and b are diagrams explaining the same operation, and Figure 5 is the diagram of the present invention. FIG. 6 is a partially omitted circuit diagram of another embodiment of the present invention, and 7 is an oscillation transformer;
10 is a load, 11a and 11b are chiyoke coils,
12 is a capacitor, A is a transistor inverter, and _S1 is a changeover switch.

Claims (1)

[Claims] 1. It has an inverter circuit that performs self-excited oscillation by an LC resonance circuit of a capacitor and the inductance of the oscillation transformer, and a reactance element that switches the reactance value to set the output reduction state is connected to the secondary output of the oscillation transformer and the load. In the inverter device inserted in series between the inverter circuit and the inverter circuit, the inverter device is provided with another resonant circuit configured including the reactance element and a switching means during the output reduction state, and a switching means.
An inverter device characterized in that two or more operating points of an inverter circuit are formed by an LC resonant circuit and the other resonant circuit, and the inverter circuit is driven at any of the operating points.