JP2686689B2 - Inverter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an inverter used for induction heating a material to be heated.

[0002]

2. Description of the Related Art An induction heating device is used to heat a rolled material being conveyed in a hot rolling line. This induction heating device uses a control rectifying element to change the heating output by the load current whose phase is controlled according to the heating position of the rolled material, that is, the load, in order to uniformly heat the rolled material being conveyed over the entire length. Equipped with an inverter.

Conventional inverters of this type operate without changing the phase control angle for controlling the phase of the load current even when the output current changes. Therefore, in an inverter with a large output, no load and 10% of the specified output are used. When the load is extremely low, which is less than the level, operation becomes impossible. This is because the commutation between the controlled rectifying elements cannot be performed stably. That is, this is because the load current is used to turn off the control rectifying element that is on, and when the load current is small, the control rectifying element cannot be turned off.

Therefore, in order to stably turn off the controlled rectifying element that is turned on when the load is low, it is considered to use a self-extinguishing type GTO, for example, as the controlled rectifying element, or connect a dummy load that flows a load current. Is being considered. However, in order to adopt the former method, an extremely expensive GTO with large capacity and high speed switching must be used, and it has not been put to practical use. On the other hand, if the latter method is adopted,
Since the dummy load consumes unnecessary power and reduces efficiency, this has not been put into practical use either.

On the other hand, as another induction heating method, for example, Japanese Patent Publication No. 55-10958 proposes a method of controlling the heating temperature of a material to be heated by induction heating. This induction heating method
By intermittently controlling the operation of the inverter, the average output is reduced, and the lower limit value of the output of the inverter is further reduced.

[0006]

By the way, as described above, the conventional inverter cannot operate at an extremely low load, so that the heating output range is limited. Therefore, a single inverter cannot output a proper heating output according to the heating position of the rolled material. There is also a problem that the GTO or dummy load cannot be put to practical use in terms of cost or efficiency.

On the other hand, in the method of controlling the inverter on / off to reduce the average output, the on-state cannot be stably maintained at an extremely low load, and the heating output is intermittent so that the rolling material is not heated. There is a problem that it becomes uniform. In view of such a problem, it is an object of the present invention to provide an inverter capable of uniformly inductively heating a material to be heated that is being conveyed over its entire length.

[0008]

An inverter according to the present invention includes a current detection circuit for detecting its output current, a plurality of comparison circuits for comparing the detected output current with a predetermined value, and a comparison result of the comparison circuits. , A state transition determination circuit that determines and outputs the transition of the load configuration based on the combination of the comparison results retained by the retention circuit, and the phase of the control rectifying element based on the output of the state transition determination circuit. A phase control angle generation circuit for determining a control angle is provided, and the output current is adjusted according to the determined phase control angle.

[0009]

The output current is detected and the detected output current is compared with a predetermined value. Determine the phase control angle that should decrease (increase) the output current when the output current exceeds the specified value (below).
Conducting phase control of the controlled rectifying element is performed at the determined phase control angle.
As a result, when the load changes and the output current changes, the phase control angle changes, the load change is absorbed, and the output current change is suppressed. Therefore, even when the load is small, it is possible to secure a load current sufficient to turn off the controlled rectifying element.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings showing the embodiments. FIG. 1 (a) is a schematic plan view showing a state of induction heating a rolled material conveyed on a rolling line, and FIG. 1 (b) is a schematic side view thereof. Heating coils B ₁ and B ₁ are arranged above the side edges of the rolled material A to be conveyed,
Heating coil B _1, B ₁ below the respective heating coils B _2,
B ₂ (only one shown) is provided. Heating coil B
₁ , B ₁ , B ₂ , B ₂ are connected to the inverter C, and the heating coils B ₁ , B ₁ , B ₂ , B are connected from the inverter C.
AC current is supplied to ₂ and heating coils B ₁ , B ₁ , B
_A heating output is obtained at ₂ and B ₂ according to the alternating current, and the rolled material A is heated by the heating output.

Above the rolled material A being conveyed,
The carry-in side and the carry-out side of the strip A to the heating coil B _1, B ₁ is rolled material sensor PH0 for detecting the rolled material A, PH1
Is arranged.

FIG. 2 is a block diagram showing a main configuration of an inverter according to the present invention. The 3-phase AC power supply 3P is a control rectifier element CR that constitutes the converter unit CNV that performs 6-phase rectification.
₁ (CR ₂ , CR ₃ ) anode and control rectifier CR ₄ (C
R ₅ and CR ₆ ) are connected to each connection to the cathode. The cathodes of the controlled rectifiers CR ₁ , CR ₂ and CR ₃ are connected in common, and the connection part is a controlled rectifier CR ₁₀ , CR ₁₁ , CR ₁₂ , which converts a DC voltage into an AC voltage via a reactor DCL.
Controlled rectifier element of inverter INV consisting of CR ₁₃ CR ₁₀ , CR
Connected with each of the ₁₂ anodes.

The cathode of the controlled rectifier element CR ₁₀ (CR ₁₂ ) is connected to the anode of the controlled rectifier element CR ₁₁ (CR ₁₃ ), and the cathodes of the controlled rectifier elements CR ₁₁ and CR ₁₃ are connected in common to connect the converter CNV. Connected to the anodes of controlled rectifiers CR ₄ , CR ₅ , and CR ₆ . A current detector DA for detecting a load current is arranged in the middle of the circuit connecting the converter unit CNV and the reactor DCL. The connection part of the control rectifiers CR ₁₀ and CR ₁₁ of the inverter INV and the control rectifiers CR ₁₂ and CR ₁₁
A load circuit LC in which a capacitor D is connected in parallel to the series circuit of the heating coils B ₁ and B ₂ is provided between the connection part of the CR ₁₃ and the load circuit LC is in a parallel resonance state at the start of operation of the inverter. The start-up circuit IS is interposed.

First, the principle of the present invention will be described. The inverter of the present invention changes the phase control angle of the inverter according to the output current of the operating inverter in order to perform stable operation over a load range from an extremely low load to a maximum load, and Make sure that the output current does not change significantly due to changes. That is, the impedance of the load circuit LC seen from the inverter INV is Z _L , the inverter
When the output from INV to the load circuit LC is P and the phase control angle of the inverter INV (phase difference between the output voltage and the output current) is γ, the output current I of the inverter INV is

[0015]

(Equation 1)

## EQU1 ## Therefore, if the load impedance Z _L and the phase control angle γ are constant, the output current I is extremely reduced when the load is low, so that the commutation of the controlled rectifying element is disabled and the operation of the inverter is disabled. on the other hand,
If the phase control angle γ is changed according to the output P given to the load circuit LC, that is, the output current of the inverter INV, the output current I
Is not affected by the output P.

When the output P is small, the phase control angle γ
Is increased (and therefore cosγ is decreased), the output current I required for commutation is secured. And output P
Since the output current I increases with increasing, the phase control angle γ is reduced (and therefore cosγ is increased) to suppress the extreme increase of the output current I. Therefore, if such a control operation is repeated according to the change of the output P, it is possible to cope with the large change of the output P without enlarging the output current I and to expand the heating output range.

FIG. 3 is a block diagram showing the configuration of the control circuit of the inverter according to the present invention shown in FIG. The output current I detected by the current detector DA is the comparison circuit COMPR for reset.
1, set comparison circuit COMPS2, reset comparison circuit COMPR
2, input to each one side input terminal of the set comparator circuit COMPS3, and reference values I _R1 , I _S2 , I _R2 , to the other side input terminals respectively.
I _S3 is input. As shown in FIG. 6, I _R2 > I _R1 > I _S3
> I _S2 . Comparison result serving the output signal of the comparator circuit COMPR1 is inputted to the reset terminal R of the flip-flop FF _1,
The set terminal S has a state selection signal for selecting an activation state.
SS ₁ and inverter stop command signal IVS are input.

The output signal of the comparison circuit COMPS2 and the state selection signal SS ₂ are input to the set terminal S of the flip-flop FF ₂ , and the output signal of the comparison circuit COMPR2 is input to the reset terminal R thereof. Output signal and the state selection signal SS ₃ of the comparator circuit COMPS3 is inputted to the set terminal S of the flip-flop FF _3, the inverter stop signal is in its reset terminal R
IVS is input. Flip-flops FF ₁ , FF ₂ , FF ₃
Latch data S ₁ , S ₂ , S ₃ of the state transition judging circuit X
Is input to The output signal S, which is the determination result of the state transition determination circuit X, is input to the phase control angle generation circuit Y. The signal of the phase control angle γ generated by the phase control angle generation circuit Y is given to the gates of the controlled rectifying elements CR ₁₀ , CR ₁₁ , CR ₁₂ and CR ₁₃ of the inverter unit INV to ignite them.

By the way, since the load circuit LC of the inverter thus constructed forms a parallel resonance circuit by the heating coils B ₁ and B ₂ and the capacitor D, the oscillation is started by the initial discharge by the starting circuit IS. The waveforms of the output voltage V and the output current I of the inverter INV at that time change as shown in FIG.

It is assumed that the phase control angle γ is changed in, for example, three stages (n = 3 when the number of switching stages of the phase control angle γ is n), the state at the time of starting the inverter is set to 1 and then the load increases. State 2 as the output current I increases
From the state to the state 3, and the phase control angles γ ₁ , γ ₂ , and γ ₃ are selected so that cos γ ₁ <cos γ ₂ <cos γ ₃ according to the state change. Furthermore, when the inverter is started, the state selection signal to select the phase control angle γ ₁
Make sure that SS ₁ and SS ₂ are output.

The state transition judging circuit X is a flip-flop.
FF _1, FF _2, signals S ₁ from the FF _3, S _2, S ₃ is (H,
H, L) (L, H, H) or (H, L, L), the phase control angle is γ ₁ , (L, H, L) or (L, L, H)
When the phase control angle is γ ₂ and (L, L, L), the signal S for setting the phase control angle to γ ₃ is output to the phase control angle generating circuit Y.

Next, the operation of the thus constructed inverter will be described with reference to the flowchart of FIG. 5 showing the control contents, FIG. 6 showing the output current change with respect to the phase control angle, and FIG. 7 showing the rolled material conveyance state. For convenience of explanation, FIG. 3 shows a case where the phase control angle γ is switched in three stages. In FIG. 6, the vertical axis represents the output current I and the phase control angle γ, and the horizontal axis represents the time t. Now, as shown in FIG. 7A, when the rolled material A is located on the loading side of the heating coils B ₁ and B ₂ , the rolled material sensor PHO detects the rolled material A. When the inverter is activated, the activation state selection signals SS ₁ and SS ₂ are set to the set terminals S of the flip-flops FF ₁ and FF _2.
Is input to

As a result, the flip-flops FF ₁ and FF ₂
Is set. The flip-flop FF ₂ is in a reset state by a stop operation as described later. Therefore, S ₁ ,
A signal in which S ₂ and S ₃ are H, H, and L, respectively, is input to the state control determination circuit X, and a corresponding signal S is given to the phase control angle generation circuit Y. The phase control angle generation circuit Y generates the phase angle γ ₁ of state 1. The output current I _{1 at} this time is

[0025]

(Equation 2)

## EQU2 ## The phase control angle γ ₁ is the output current I ₁ even when the lower limit value P _min of the target output range is being output.
Determines to secure a commutation limit current I _com or more. That is, cosγ ₁ is The phase control angle γ ₁ is determined so that As a result, the controlled rectifiers CR ₁₀ , CR ₁₁ , C of the inverter INV are
The phase control angle γ that controls the phase of R ₁₂ and CR ₁₃ is set to γ ₁ (L1). Then, the output current I starts to flow from the inverter INV to the load circuit LC, and the rolled material A is induction-heated.

Subsequently, it is determined whether or not the inverter stop signal IVS is input to determine whether or not to stop heating (L2), and when it is determined to stop heating, the control operation is ended. Even during heating, the tip of the rolled material A from the carry-in side of the heating coil B _1, B _2, as shown in FIG. 7 (b), when a state began enters between the heating coil B _1, B ₂ The load increases and the output P increases. When the output P increases, the output current I ₁ increases according to the equation (2) and as shown in FIG. The output current I ₁ is detected by the current detector DA, and the detected output current I ₁ is input to the comparison circuits COMPR1, COMPS2, COMPR2, COMPS3.

The comparison circuit COMPR1 has a reference value I _R1 and an output current I
_When it is determined that the output current I ₁ has exceeded the reference value I _R1 (L3), the comparison circuit COMPR1 outputs an output signal and supplies it to the reset terminal R of the flip-flop FF ₁ . As a result, the flip-flop FF ₁ is reset, and the state signal S ₁ input from the flip-flop FF ₁ to the state transition determination circuit X becomes “L” (that is, off). As a result, the state transition determination circuit X determines that the state signal S ₁ is inverted from "H" to "L" and thus transitions from the current state 1 to state 2, and outputs the signal S to the phase control angle generation circuit Y. input.
In response to the signal S, the phase control angle generation circuit Y changes to the phase control angle γ ₂ in state 2 (L4).

As a result, the output current I ₂ at the time t ₁ shown in FIG.

[0030]

(Equation 3)

Changes to. Since cos γ ₁ <cos γ ₂ here, the output current I ₂ decreases. In this way, when operating in the state 2, as shown in FIG. 7 (c), the central portion of the rolled material A is conveyed to between the heating coils B ₁ and B ₂ ,
When the load further increases and the output P increases, the output current I ₂ increases according to the equation (4). Comparator circuit COMPR2 since this output current I ₂ is detected by the same way the current detector DA is compared with a reference value I _R2, becomes equal to or larger than the reference value I _R2 (L6), the signal is outputted from the comparison circuit COMPR2 The flip-flop FF ₂ is reset, and the state signal S ₂ becomes “L”.

As a result, the state transition judging circuit X judges that the state has changed from the state 2 to the state 3, and the signal S thereof is inputted to the phase control angle generating circuit Y so that the phase control angle γ ₂ so far is changed to that of the state 3. Change to the phase control angle γ ₃ (L7). As a result, FIG.
The output current I ₂ at time t ₂ shown in

[0033]

(Equation 4)

Changes to. Since cosγ ₂ <cosγ ₃ here, the output current decreases. Further, when operating in state 3, as shown in FIG. 7 (d), when the rear end of the rolled material A is located between the heating coils B ₁ and B ₂ and the load decreases and the output P decreases, The output current I ₃ decreases according to the equation (5). This output current I ₃ is detected in the same manner as described above, and the comparison circuit COMP
When S3 compares the output current I ₃ with the reference value I _S3 and becomes equal to or less than the reference value I _S3 , the flip-flop FF ₃ is set and the state signal S ₃ is held at “H”.

When the status signal S ₃ is "H", the status shift judging circuit X judges that the status 3 has shifted to the status 2 (L
8), the signal S is input to the phase control angle generation circuit Y, and the phase control angle generation circuit Y changes the phase control angle γ ₃ to the phase control angle γ ₂ in state 2 according to the signal S (L4). As a result, the output current I ₂ changes according to the equation (3) at the time point t ₃ shown in FIG. Since cosγ ₂ <cos ₃ here, the output current I ₂
Increases.

As described above, when operating in the state 2,
As shown in Fig. 7 (e), the rolled material A has heating coils B ₁ and B ₂
When the load is reduced by separating from the unloading side, the output current I ₂ decreases according to the equation (4). This output current I ₂ is detected in the same manner as described above, and the comparison circuit COMPS ₂ outputs the output current I ₂ and the reference value I _2.
Compare with _S2 (L5). When the reference value I _S2 or less, the comparison circuit
Flip-flop FF ₂ by a signal from COMPS2 is set, the state signal S ₂ is held at "H". Therefore, the state transition determination circuit X determines that the state 2 has transited to the state 1 and inputs the signal S to the phase control angle generation circuit Y.

The phase control angle generation circuit Y receives the input signal S
Accordingly, the phase control angle γ ₂ is changed to the phase control angle γ ₁ in the state 1 (L1). As a result, the output current I ₂ changes according to the equation (4) at the time point t ₄ shown in FIG. Where cosγ ₁ <cosγ
₂ , the output current I ₂ increases, and the commutation limit current I
More than _com is secured.

In this way, a large change in the output P from the extremely low load to the maximum load is absorbed by the phase control angle γ, the change in the output current is suppressed, and the output current of the inverter is stabilized in a wide range. Can be made. As a result, the rolled material A can be heated without causing uneven heating.

When stopping the inverter, the inverter stop command signal IVS is sent to the flip-flops FF ₁ and FF _3.
give. This gives (H, H, L) or (H, L,
L) and the phase control angle is γ ₁ . However, the drive of the inverter is stopped separately from this. Therefore, the phase control angle γ ₁ itself has no special meaning.

FIG. 8 is a waveform diagram showing the phase control angle γ, the output current I and the output P of the inverter according to the present invention by the solid line, and the phase control angle γ and the output current I of the conventional inverter by the broken line. The output P of the inverter is shown by the same curve as the output P of the inverter of the present invention. The vertical axis represents output P, output current I, and phase control angle γ, and the horizontal axis represents time.

As is clear from this figure, in the conventional inverter, the phase control angle γ is, for example, γ ₃ even if the output current I changes.
Since it is constant at, the output current I is proportional to the change of the output P.
Changes. Further, during the period when the output current I is reduced to the commutation limit current I _com or less, the controlled rectifying element of the inverter section does not commutate, and the operation of the inverter becomes impossible.

On the other hand, in the inverter of the present invention, since the phase control angle γ is changed by the change of the output current I, when the load increases and the output current I increases, the load is quickly followed, while the output current I increases. Is gradually reduced, the change width of the output current I is reduced. Further, since the output current I is ensured to be _{equal to} or more than the commutation limit current I _com , the operation of the inverter will not be disabled.

In this embodiment, the comparison circuits COMPR1 and COMP
The case where the phase control angle γ is switched to three stages using S2, COMPR2, and COMPS3 has been described, but this is merely an example, and in practice, a larger number of comparator circuits are used to increase the phase control angle γ. It goes without saying that the steps are switched, and the present invention is not limited to the embodiment.

[0044]

As described in detail above, according to the present invention, when the output changes, the phase control angle for controlling the phase of the inverter is changed. Therefore, even when the load is extremely low, the control rectifying element of the inverter section is switched. The output range of the inverter can be greatly expanded without interrupting the flow. Therefore, when the inverter of the present invention is applied to induction heating, a good heating state can be obtained without heating unevenness in the material to be heated, and operation from before entering to after passing through the material to be heated becomes possible. As a result, there is an excellent effect that uniform heating from the front end to the rear end of the heated material can be realized and the temperature rise of the heated material can be guaranteed.

[Brief description of the drawings]

FIG. 1 is a schematic plan view and a schematic side view showing a state of induction-heating a rolled material conveyed on a rolling line.

FIG. 2 is a block diagram showing a main configuration of an inverter according to the present invention.

FIG. 3 is a block diagram showing a configuration of a starting circuit.

FIG. 4 is a waveform diagram showing the relationship between output voltage and output current.

FIG. 5 is a flowchart showing the control contents of the starting circuit.

FIG. 6 is a waveform diagram showing a relationship between an output current and a phase control angle.

FIG. 7 is an explanatory diagram of a state where a rolled material is conveyed.

FIG. 8 is a waveform diagram showing a relationship among an output, an output current, and a phase control angle.

[Explanation of symbols]

3P 3-phase AC power supply DA Current detector DCL Reactor CR ₁₀ , CR ₁₁ , CR ₁₂ , CR ₁₃ Control rectifier IS Start circuit INV Inverter B ₁ , B ₂ Heating coil D Capacitor

Front page continued (72) Inventor Kiyokazu Nakamura 5520 Minamitamagaki-cho, Suzuka-shi, Mie Fuji Electric Co., Ltd. Suzuka factory (56) References

Claims (1)

(57) [Claims] 1. A current detection circuit for detecting the output current, a plurality of comparison circuits for comparing the detected output current with a predetermined value, a plurality of holding circuits for holding the comparison results of the comparison circuits, and the holding circuit. A state transition determination circuit that determines and outputs a transition of the load configuration based on a combination of comparison results held by the circuit; and a phase control angle generation circuit that determines the phase control angle of the control rectifying element based on the output of the state transition determination circuit. And an inverter for adjusting the output current according to the determined phase control angle.