JPS59153473A - High frequency induction heating transistor inverter - Google Patents

Abstract

PURPOSE:To prevent a shortcircuit phenomenon in a bridge circuit without narrowing the drive waveform of a switching element from 180 deg. by forming a tank circuit in the bridge circuit in a parallel resonance circuit. CONSTITUTION:To lead DC power to a transistor bridge circuit 2 from a DC power source, an inductive energization is applied thereto by a choke coil CH. A tank circuit in the bridge circuit 2 is formed in a parallel resonance circuit made of a parallel capacitor CP, and a series resonance circuit of a series capacitor CS and a load LS.

Description

[Detailed Description of the Invention] The present invention is a transistor for high frequency induction heating, which has been put into practical use for induction heating in a medium frequency region, and in recent years, transistor inverters are being used for induction heating in a high frequency region. However, the following points are important when converting an induction heating device in the nuclear high frequency region into a solid stay.

(a) The FE resistance of the half-quad elements (inverter switching elements) is low.

(b): Since the IF dropout is relatively small, it is necessary to operate several to several dozen elements in parallel.

(C) Since a large output is required, when the output voltage is low, a large current is generated, the load impedance is low, and the inductance (L) becomes extremely small at high frequencies.

(d) The object to be heated is viewed from a single terminal of the work coil or heating furnace.The impedance of this coil is very poor, so a power factor correction capacitor is required, and therefore a resonant circuit is inevitably present. leading to.

In solving the above problems, it is better to use a series resonant circuit as the resonant circuit than to use a parallel resonant circuit.
A large voltage can be easily obtained across the work coil or the heating furnace body, thus increasing the load impedance and increasing flexibility in the design of the work coil including the furnace body or outlet transformer. In addition, routing the furnace body or outlet transformer to a remote location is advantageous as it reduces power transmission iA loss.
A prior art technology of an inverter having a series resonant circuit has been proposed in Japanese Patent No. 7-23989.

On the other hand, in a transistor inverter having only a self-effective resonant circuit, a power source l-i supplying power to the inverter VC7 must be connected to a capacitor. In the nuclear diagram, capacitor (Oo) is much larger than capacitor (os), and (Ls)
('Os) and must present a low impedance to the resonant current. Therefore, such a capacitive store [a capacitively energized In other words, it is not possible to connect a parallel resonant power factor correction circuit to the transistor bridge circuit (1), which is a type of constant voltage power supply with inertia that keeps the voltage constant. Regarding the impedance of the resonant circuit, as shown in Figure 2, the absolute value of the impedance IZ+ shows the maximum value for the resonance frequency C, but it is extremely small for the high frequencies fs, fb, etc. This is because the high frequency components included will be short-circuited, making it impossible to operate.On the other hand, in the case where the series resonant circuit (Ls) (as) is connected as shown in Figure 1, the 1 As the in-begence force of series resonance to the conductor is small, the impedance for odd high frequencies of fs, fS, etc. becomes large.
Unlike the case of parallel resonant circuits, the square wave voltage of the bridge circuit is not short-circuited and operates normally.

However, on the other hand, h transistors have a delay time associated with switching such as turn-on and turn-on, so when switching is performed with a square wave with a duty of 50, the switching element (transistor spanning pnT) (8 people) is shown in Figure 1. (SB), (SC) and (S7)) overlap in on time (overlap time)
occurs, and during this period (00) → (SA) → (8B) → (
oo) or (00) → (Sc) → (SD) → (
aO) [A short circuit is formed.

Fig. 4 is a signal waveform diagram of the circuit shown in Fig. 1, showing that such a gap love occurs.
D) is the drive waveform of the base or gate, C) is the same drive waveform of the element (SB), (SC), (, -3 is the conduction waveform of the element (SA), (SD), and) is the same element (8B). ).

(Sc) is a positive waveform. To avoid this short circuit,
The driving waveform of the switching element must be made narrower than the XSO degree and the occurrence of overlap must be suppressed, which is also disclosed in the above-mentioned Japanese Patent Publication No. 57-23989. However, narrowing the driving waveform of the switching element also complicates and delicately sets and designs the pulse width of the driving waveform.

The present invention aims to eliminate these difficulties and provide a transistor inverter that is stable, easy to design and maintain.

That is, when direct current power is led from a direct current power source to a transistor bridge circuit, the present invention applies inductance bias (inertia so that the flowing current is constant) to the transistor bridge circuit using a choke coil. is made into a parallel resonant circuit consisting of a parallel capacitor, a series capacitor, and a series resonant circuit of a load, thereby suppressing the short circuit phenomenon in the bridge circuit without making the drive waveform of the switching element narrower than 180 degrees, and achieving the above purpose. The goal is to reach tj7.

Hereinafter, details of the present invention will be explained using the drawings from FIG. 5 onwards.

In Figure 5, (OH) is the DC current 1k I D flowing from the DC power supply to the transistor bridge circuit [2].
A choke coil for an inductance store (an inductance-energized power supply, i.e., a type of constant current power supply with inertia so that the current is constant) that provides inertia to C; (OP) is a parallel capacitor, (O
s) is the series capacitor, (Ls) is the total load, the work coil (which may include an output transformer) or the furnace body. (O8) and (Ls) constitute a series resonant circuit, and this series resonant circuit (03), (LS) and a parallel capacitor (op) constitute a parallel resonant circuit (3), that is, a tank circuit. , transistor bridge circuit (2)
connected to.

The DC power supplied from the DC power source is passed through the choke coil (O
H) provides a certain inertia to the DC current IDc. And this is the transistor PuIJ Tsuji episode #(
When switched in step 2), the bridge output becomes a square wave because the choke coil (OH) provides the precondition that the current is constant. In this case, if we consider that the load (Ls) is connected as a parallel resonant circuit as shown in Figure 6, the absolute value of the load impedance IZ+ with respect to fl will be maximum as explained in Figure 2 in 1-,
At both ends of the parallel resonant circuits (Cp) and (Ls), a component of the fundamental wave f+ of the square wave current appears as a product of the value of impedance + Zl for 11, resulting in a sine wave. However, the amplitude of the high-frequency current t is small, and the IZI c, f
Since the value for s is small, the electric power as a bond is small and can be ignored.

However, in the circuit shown in Figure 5, all 11 town rows are 1 line circuit (Os).
.

Since the parallel capacitor (Op) is connected in parallel to (Ls), two resonance points are obtained, the series resonance frequency /s = = 2πJ〒7viewi and the parallel resonance frequency, and the circuit ( 3) as (fP
), it will resonate! , the flow is (OF) → (O8]
→ Circulate within (L8). And (CP) and (OS)
By choosing an appropriate capacity for VC, pressure is generated at both ends of (r, s) and (O8), making it easy to obtain high pressure. In other words, by selecting a series capacitor (Os) and a parallel capacitor ωaB−Nop, the voltage across the load (Ls) is boosted, and at the same time, the voltage across the series capacitor (O8) is boosted, making the output impedance high impedance.・KVA (high frequency high power) can be easily increased to a large value.

Also, when driving with a square wave with a duty and tee of 50%, current overlap occurs, but with this method, the overlap time (
Even between the overlap angle (or overlap angle), the direct current (IDc) is regulated by the choke coil (OH), so it does not lead to a short circuit, causing strain on the switching element, and is extremely narrow compared to the overlap angle of 11,180 degrees. , there is almost no harm to the operation.

This is shown in the signal waveform diagram in Figure 7. In the figure,
(A) is the gate-spanning base drive waveform of elements (SA) and (SD), and (B) is the same element (8B) - (
8a) drive waveform, (c) is element (SA)-(SD
) is the conduction current waveform of the element (SB), (Sa
), (E) is the voltage waveform at both ends of the element (SA), (8D), and (F) is the element (SB).

(So) is the voltage waveform at both ends, and (G) is the voltage waveform between P and Q in FIG.

In such an inverter, when looking at the tank circuit from the transistor bridge circuit side, it can be seen as a load similar to a parallel resonant circuit, and it functions as an inductance store type inverter that is inductively energized. op
) and (Os) act serially and resonantly on the load (Ls) side, resulting in a high voltage, which is very preferable because the output at both ends of the bridge circuit (2) can be made high voltage and high impedance.

Further, since it is possible to drive the switching element with a square wave with a duty cycle of 50, processing and adjustment of the active signal and circuit design are extremely easy.

Furthermore, when the DC power supply voltage is constant, the output voltage at both ends of the load (Ls) can be freely increased by changing the capacitance of (OF) and (O6), and the output voltage at both ends of the load (Ls) can be freely increased. , several thousand V to 10,000 V can be easily obtained if necessary.

By the way, in induction heating, the load impedance changes suddenly and the resonant frequency also changes. Therefore, as shown in Figure 8, the transformer (T) detects the signal voltage from both ends of the load (LS).
At the same time, in the signal processing circuit (4), two sets of drive signals (square wave drive signals of duty 504) having the same phase and opposite phase as the detection signal are created from the detection signal, and these are used to output the switching element ( 8A) N (8D)
Configure the drive to be applied to the base of the If this is done, switching elements (8A), (8D) and (SB),
A very stable high frequency inverter can be obtained by forming a pair of (sc) and selecting a polarity in which the phase of the drive signal promotes resonance at both ends of the load (Ls). The frequency of this inverter operates like a self-excited oscillator based on the resonant frequency of the tank circuit, so for the load changer #jc, the changed resonant frequency is the oscillation frequency, and is the same as the master oscillator. Then, there are methods to track that frequency to the resonant frequency, and phase-locked
It is much more stable than that by loop IO and the load (Ls
), there is no need to initialize the free-running frequency of the master oscillator, and it can accommodate a wide range of load changes (coil changes).

In addition, in Figure 8, the detection signal is taken out from both ends of the load (Ls), or there is series resonance between (Ls) and (OB').
Since they are in opposite phases (Os), they may be detected from both ends. This is because the wood of this inverter is a current square wave type inverter with inductance biasing (that is, inductive tape store), and therefore a parallel capacitor (O
F) This is because the voltage at both ends is close to a sine wave. Therefore (O
8), (Ls) The series resonant voltage across both ends is also sinusoidal (simply due to the capacitive energization of only the series resonant circuit,
In other words, the voltage across the inductance in a capacitive store type inverter contains many 3rd harmonics and 5th harmonics.
Although a detection signal can be obtained from the difference between (08) and (08), it is natural that the polarity must be selected so that it is normal.

There is also a method of detecting the current by inserting a peeping current transformer into the series resonant circuit of (Ls) and (O8), but in this case, the current in the series resonant circuit and (LS) i Taha (
Since there is a phase difference of 90 degrees between the voltages of OS), 9
The signal must be phase shifted by 0 degrees before being input to the signal processing circuit (4).

The advantage of this transistor inverter over a silice inverter is that the final rTIJ can freely control the on/off of the main circuit current with a dirt signal, so a parallel resonant circuit (3) is used to turn off the current. The signal processing circuit (4) is simplified in that there is no need for a method of reverse biasing during the turn-off time by allowing the current to advance with respect to the voltage, and the signal processing circuit (4) can be simplified as compared to the Cyrisk inverter. This simplifies the measurement and adjustment, and makes maintenance easier, and this can be expected to have various effects such as making it easier to train maintenance personnel. (static induction transistor), etc., the turn-off time is as short as several tens to hundreds of nanoseconds, so the frequency of the inverter generated by the thyristor is approximately 200 nanoseconds.
KHz, 300KHz ~ 400KHz
This inverter can be easily manufactured. Therefore, the transistor inverter of the present invention has FBT as its transistor.
It is natural that this includes 8-engine T.

The present invention is further developed and has successfully achieved its original purpose.

[Brief explanation of drawings]

Figures 1 to 5 are used to explain the technical problems of the present invention. Figure 1 shows a transistor inverter circuit 1ffi having only a series resonant circuit, and Figures 2 and 3 show a frequency relationship. Impedance characteristic glass, Figure 4 is a signal waveform diagram of Figure @1. Fig. 5 is a circuit diagram of an embodiment of the present invention, Fig. 6 is a circuit diagram of a transistor inverter having only a parallel resonant circuit for comparison with Fig. 5, and Fig. 7 is a signal waveform diagram of Fig. 5, 8
The figure is a circuit diagram showing an application example. (Explanation of symbols) (2) - Transistor bridge circuit, (3) -
Parallel resonant circuit, (4)...signal processing circuit, (OH
)...-Choke coil, (8A) ~ (SD)...
・Switching element (transistor), (Op)・-Parallel capacitor, (O6)...-Series capacitor, (L
s) - Load, (1 unit...transformer. Figure 1 Figure 2 Figure 3 f - Pass f Figure 4 Dark Figure 5 Figure 6 S Figure 7 Figure 8

Claims (1)

[Scope of Claims] 1. A choke coil that provides an inductance bias between the DC power source and the transistor bridge circuit (2) so that the lXm current supplied to the bridge circuit (2) is constant. (OH) and this bridge circuit (
2) Connect a parallel capacitor [O
A transistor inverter for high frequency induction heating, characterized in that a parallel resonant circuit (3) consisting of a series resonant circuit of a series capacitor (O8) and a load (Ls) is connected to the transistor inverter P). 2. The transistor inverter according to claim 1, comprising a series capacitor with the parallel capacitor (OP). 3. Means for detecting a signal from the series resonant circuit of the load (Ls) and the series capacitor (Os), and creating a square wave drive signal of the resonant frequency of the parallel resonant circuit (3) based on this detection signal. In addition, two pairs of switching elements (8 members) on the diagonal of the bridge circuit (2) and (8D),
A patent claim that includes a signal processing circuit (4) that alternately turns on and off (SB) and (8C) using the square wave drive signal that is in phase with the detection signal and has a polarity that enables sustained oscillation. Transistor inverter with range @1 term. 4. The detection means includes a load (Ls) and a series capacitor (
4. The transistor Φ inverter according to claim 3, wherein the transistor Φ inverter is a transformer (T) that extracts the voltage across either of the terminals of the transistor O8). 5. The detection means is a laminar flow transformer that takes out the current of the series resonant circuit, and the phase of the B current signal is shifted by 90 degrees to create a square wave drive signal. The transistor inverter according to item 3.