DE10113123C2 - Device for inductive heating and method for reducing the sound level in the case of inductive heating - Google Patents

Description

The invention relates to a device for inductive Heating materials and a process for reducing the Sound level with such warming.

Inductive heating of materials occurs in the different fields of application for use, whereby the power required for heating by an inductor is induced in the workpiece. One area of application is for example the heating of pipes for the Heating through the center of the winding of an inductor be performed. For the energy supply of the used Different generators can be used for inductors become. The use of parallel resonant circuit Inverters in which the inductor is in the Parallel resonant circuit is integrated.

There is a problem with inductive heating due to the Lorentz force = × that in induction occurs. Because through the Lorentz force they become heating materials stimulated to vibrate, causing too lead to impermissibly high sound levels at the workplaces can.

In practice, it is therefore common to use devices for inductive heating in the area of induction heating with rebuild sound absorbing casings to prevent the spread of the  to obstruct the resulting sound. Such conversions are however, it is often time-consuming and the sound can usually escape cannot be prevented to a satisfactory extent.

From other fields of technology it is known that Sound waves are extinguished at a given location if the sound waves are 180 ° out of phase, equal frequency sound waves are superimposed, so that on Location of the desired extinction the sound levels are the same, but the phases are inverted. Such an approach would be but disproportionate for inductive heating complicated.

DE 100 17 76 A1 is also an induction hotplate known to be powered by generators Induction heating elements is operated. The well-known Device has a first AC-powered Inductor and at least a second AC-powered Inductor on. In addition, a control device for Setting the angular frequency of the current through the first Inductor provided over which the angular frequency of the current through the second inductor to the same value as that Angular frequency of the current through the first inductor and a Phase shift angle between the current through the first inductor and the current through the second inductor can be adjusted. With one Induction cooktops are used for cooking food in the normal domestic environment and noises Difficulty controlling multiple at the same time operated induction devices reduced. Become suitably equipped induction heating devices  but operated in large-scale use, it shows that it is due to inevitable tolerances and not predictable changes in operating conditions how there is considerable noise.

The invention has for its object a device for inductive heating of materials with reduced To provide noise development, as well as a Process for reducing the sound level in the inductive Heating of a material.

This object is achieved on the one hand by a device for inductive heating of materials, the first AC powered inductor and at least one second AC inductor comprises, and a control device for adjusting the Angular frequency of the current through the first inductor to Setting the angular frequency of the current through the at least second inductor to the same value as that Angular frequency of the current through the first inductor and to Setting a phase shift angle between the Current through the first inductor and the current through the second inductor, wherein a sensor for detecting the at heating of a material generated sound level and a controller to which the value of that sensed by the sensor Sound level is supplied to change the through the Control device set phase shift angle between the current through the first inductor and the current through the at least second inductor into a predetermined one Direction as long as the detected sound level is a given  Sound level exceeds and has not reached a minimum, are provided.

On the other hand, the object is achieved by a method for reducing the sound level during inductive heating of a material, the inductive heating being carried out by at least two AC-fed inductors, which has the following steps:

• - Setting the same angular frequency for the currents through the two inductors and
• - Setting a phase shift angle between the Current through the first inductor and the current through the second inductor by increasing the sound level when heating of the material is recorded,
• - The detected sound level with a predetermined sound level is compared, and
• - The phase shift angle between the current through the first inductor and the current through the second The inductor is changed in a predetermined direction, as long as the recorded sound level is the specified one Sound level exceeds and has not reached a minimum.

So far, the power required for heating exclusively through a single inductor in that Workpiece was induced, which is the Lorentz force allowed to take effect without restriction, the Induction of performance according to the invention by at least two inductors. The at least two inductors with an alternating current of the same angular frequency but with fed a phase shift angle to each other. With  the device according to the invention and the inventive This makes it possible to use a force Inductor field due to the force of at least one overlay the second inductor field in such a way that the resulting force effect tends towards zero. This ensures that the level of the resulting Sound waves minimized and accordingly one Noise pollution to a large extent at the processing location of the material is suppressed. The noise abatement according to the invention continues thus already at the cause of the sound waves on. In addition, they are very easy to implement is.

Advantageous embodiments of the invention The device and the method according to the invention go out the subclaims.

Basically, it is possible to change the phase shift angle between the current through the first inductor and the current through the second inductor to a fixed value set. In many cases, this can be simple Adequate sound level reduction already implemented can be achieved. An advantageous constant phase The displacement angle is π / 2.

By in the invention, the phase shift over a Control loop is set to its optimal value however, component tolerances etc. are also taken into account. For this purpose, a sensor is provided which detects the currently generated one Sound level recorded. The sensor delivers the recorded value a controller, the measured value with a predetermined  Limit value for the sound level is compared. At high This limit value is required for noise reduction set to zero. As long as there is a difference between the detected and the predetermined sound level is determined or as long as no minimum of this difference has been reached, the controller causes the control device to Change displacement angle in a certain direction d. H. to raise or lower it. The change can take place, for example, in uniform steps or depending on the currently recorded sound level. It is also conceivable to make a change while hiring the particular direction when the sound level with the change of the phase shift angle in the specified direction increases instead of decreases. It makes the most sense it, at the start with a phase shift angle of 0 too start and then slowly increase it. A minimum can then be considered reached, for example, as soon as an increase in the phase shift angle none Reduction or even a new increase in the sound level entails.

Advantageously takes place throughout A repeated or constant adjustment of the phase shift angle to a permanent To ensure compliance with a sound level minimum. For a repetitive or constant adjustment should be a Change of certain direction of change of phase  Displacement angle may be possible in any case, because Adjustments in both directions may be required.

In principle, the two inductors should be designed in this way be that in absolute terms they have the same force effect train so that the force effects of the generated Can compensate inductor fields exactly. Are suitable for this z. B. inductors of identical design. Possibly leaves the sound level with the adjustment of the phase Displacement angle due to location-dependent damping the tube's natural vibration is still not complete to reduce. Advantageously, therefore, the next An additional reduction in the remaining sound level Control loop used. This includes a discriminator which is also the input variable that is detected by the sensor Sound level is supplied. The tension over one of the Inductors are also powered by a voltage regulator set, the next to one detected on this inductor Actual voltage, a target voltage is supplied, which with the the signal output by the discriminator is varied. By the variation of the target voltage across the inductor becomes the Strength of the induced in the material to be heated Lorentz force varies, causing location-dependent damping of the Natural tube vibrations can be compensated.

The at least two inductors used are preferably arranged close to each other, since larger ones Distances between the inductors may still be Runtimes and changes in inductor currents at Sound minimization must be taken into account.  

In the method according to the invention is preferably carried out first setting the frequency of the current through the first inductor to a value at which the phase Angle of displacement between the current through the and the Voltage across the first inductor zero or another predetermined value. Then the same frequency for the one impressed in the at least second inductor Current specified. Only then does the Setting the optimal phase shift angle between the current through the first and the current through the at least second inductor. In the end, eventually another variation of the voltage across one of the inductors to further reduce the sound level if the sound level only with a change in the phase Angle of displacement between the current through the inductors was not satisfactorily adjustable.

The device according to the invention and the invention Methods can be used with any type of generator Power supply to the inductors are used independent control variables for power, frequency and Have phase angles.

Particularly suitable for the device and the method according to the invention are parallel resonant circuit Inverters, each with one inverter Parallel resonant circuit with one of the inductors AC powered. With such parallel resonant circuit Inverters can have one rectifier and one with them connected intermediate circuit to supply the individual Inverters with smoothed direct current can be used.  

Alternatively, the inverters can also be used in parallel switched and shared by a single one DC link connected rectifiers are supplied. In In this case, the rectifier and DC link must Compared to the single supply to double the power to be brought. The latter arrangement only comes in Consider if on the additional regulation by variation the setpoint voltage over one of the inductors should, since the voltage regulation in one Parallel resonant circuit converter by controlling the Rectifier and a separate voltage control is therefore not possible.

The invention is based on Exemplary embodiments with reference to drawings explained. It shows:

Fig. 1 is a schematic circuit diagram of a first device without the sensor according to the invention for detecting the sound level

Fig. 2 is a schematic circuit diagram of an embodiment of a device according to the invention.

In Fig. 1, a parallel resonant circuit converter is shown for heating pipes R.

The parallel resonant circuit converter comprises a rectifier GR1, which is connected to a three-phase voltage source, not shown. A control angle controller 1 has controlling access to the thyristors from which the rectifier GR1 is constructed. The rectifier GR1 is connected to two inverters WR1 and WR2 connected in parallel via an intermediate circuit ZK1, which has coupled smoothing chokes.

Each of the inverters WR1 and WR2 has four transistors, the transistors of the first inverter WR1 being controlled via a first and the transistors of the second inverter WR2 via a second control circuit 2 and 3, respectively. The output of the first control circuit 2 is additionally fed to an input of the second control circuit 3 . Both control circuits 2 , 3 together form the control device used according to the invention.

The output of the first inverter WR1 is with a Parallel resonant circuit connected, which consists of a first Capacitance C1 and a first inductor W1. The The output of the second inverter WR2 is with a Parallel resonant circuit connected, which consists of a second Capacitance C2 and a second inductor W2 is composed. The two inductors W1, W2 are identical and the turns of the inductors W1 and W2 are parallel aligned to each other so that the pipes to be heated R can be passed in the direction of the arrow.

The voltage across the first inductor W1 and the current I ₁ through the first inductor W1 are detected by means not shown and made available to the first control circuit 2 as an input variable.

The voltage U ₁ across the first inductor I ₁ is also the actual voltage U _1actual, together with an inverted _target voltage U _1set, input variable of the control _angle regulator 1 .

The parallel resonant circuit converter works as follows:
The inverters WR1 and WR2 are supplied with a smoothed direct current in a known manner via the rectifier GR1 and the intermediate circuit ZK1, the control angle controller 1 for controlling the thyristors of the rectifier G1 being the difference between a voltage _setpoint of U _1set for the voltage U ₁ is provided over the first inductor W1 and the _actual voltage _value U _{1 is} over the first inductor W1.

The control circuit 2 determines the frequency f1 or the angular frequency ω1 at which the phase shift angle between the voltage U ₁ across the first inductor W1 and the current I ₁ through the first inductor W1 becomes zero and sets this angular frequency ω1 for the control of the Transistors of the first inverter WR1.

The angular frequency ω1 is also transmitted to the second control circuit 3 . The second control circuit 3 in turn controls the transistors of the second inverter with the same frequency f2 = f1 or angular frequency ω2 = ω1, but shifted by a fixed phase shift angle of π / 2.

The power required for heating is achieved by the Inductors W1 and W2 induced in the tubes R through the  Windings of the inductors W1, W2 are transported. The Lorentz force caused by the first inductor W1 thereby caused by the second inductor W2 Lorentz force superimposed so that the resulting The effect of the force is reduced or ideally extinguished. At the same time, the Vibrations in the pipes and the resulting Sound waves reduced.

In Fig. 2 of the invention are illustrated two parallel resonant circuit converters for heating of pipes as a second embodiment.

Like the exemplary embodiment in FIG. 1, the exemplary embodiment in FIG. 2 also has two parallel resonant circuits, each of a capacitor C1, C2 and an inductor W1, W2, wherein pipes R to be heated can be transported through the turns of the inductors W1, W2 of the same design , The parallel resonant circuits are each supplied with energy via a first or second inverter WR1, WR2.

In contrast to the exemplary embodiment in FIG. 1, the inverters WR1, WR2 are not connected in parallel here. Rather, the first inverter WR1 is connected to its own first rectifier GR1 via a first intermediate circuit ZK1 and the second inverter WR2 is connected to its own second rectifier GR2 via a second intermediate circuit ZK2.

A first control angle controller 1 has control access to the thyristors of the first rectifier GR1 and a second control angle controller 7 has control access to the thyristors of the second rectifier GR2. The difference between the _actual voltage _value U _1actual or U _2actual via the associated inductor W1 or W2 and a voltage _{setpoint value} U _1setpoint or U _2setpoint is available as an input variable for control _angle controllers 1 and 7 .

As in FIG. 1, the transistors of the two inverters WR1, WR2 are each controlled by a control circuit 2 , 3 . The control circuit 2 for the first inverter WR1 has the voltage U ₁ across the first inductor W1 and the current I ₁ through the first inductor W1 available as an input variable. The control circuit 3 for the second inverter WR2 receives as input the output of the first control circuit. 2

A sound level sensor 4 is connected via a controller 4 to a further input of the second control circuit 3 , whereby a first control loop is formed. The sound level sensor 4 is also connected to the input of the control angle controller 7 via a discriminator 6 to form a second control loop. Control angle controller 7 is thus also a voltage controller for the second control loop.

The second embodiment works as follows:
The power supply of the two inductors W1, W2 by the rectifiers GR1, GR2, the intermediate circuits ZK1, ZK2 and the inverters WR1, WR2 takes place in a known manner, the rectifiers GR1, GR2 and the intermediate circuits ZK1, ZK2 compared to the circuit from FIG must be brought. 1 only to half the power. In the case of inductors W1, W2 of the same design, both parallel resonant circuit converters each contribute half to the heating power required for heating.

Both parallel resonant _circuit inverters are started by specifying the same voltage _setpoints U _1set and U _2set .

As in the first exemplary embodiment, the first control circuit 2 determines the frequency f1 or the angular frequency ω1 at which the phase shift angle between the voltage U ₁ across the first inductor W1 and the current I ₁ through the first inductor W1 becomes zero. The control circuit 2 then bases this angular frequency ω1 on for driving the transistors of the first inverter WR1.

The same angular frequency ω1 is used by the second control circuit 3 as the angular frequency ω2 to control the second inverter WR2.

If the force effects of the inductors W1, W2 are rectified after the inverters have been started due to in-phase currents through the inductors W1, W2, high noise levels of the tube's own resonance frequency must be expected. The sound level ps is detected by the sound level sensor 4 designed as a microphone and fed to the controller 5 . Controller 5 , by accessing the second control circuit 3, increases the phase shift angle -k between the current I ₁ through the first inductor W1 and the current I ₂ through the second inductor W2 until a predetermined sound level, for example of zero, is reached ,

If the sound level ps cannot be reduced to the specified sound level, but only to a minimum, which can be caused by the locally different damping of the natural tube vibration, the second control loop is used. The locally different damping of the natural tube vibration can be compensated for by varying the power introduced into the second parallel resonant circuit C2, W2. Depending on how high the remaining sound level ps is after setting the phase shift angle, it is therefore decided in the discriminator 6 whether the _target voltage U ₂ should be changed at the input of the second control _{angle regulator} 7 , so that the voltage U ₂ over the second To influence inductor W2 and thus the strength of the Lorentz force induced in the tubes by the second inductor W2. After setting the optimum phase shift angle between the current I ₁ through the first inductor W1 and the current I ₂ through the second inductor W2, a further reduction in the remaining sound level is thus made possible.

Claims (7)

1. Device for inductive heating of materials (R), which comprises a first AC-fed inductor (W1) and at least a second AC-fed inductor (W2), and a control device ( 2 , 3 ) for adjusting the angular frequency (ω1) of the current (I ₁ ) by the first inductor (W1), for setting the angular frequency (ω2) of the current (I ₂ ) by the at least second inductor (W2) to the same value as the angular frequency (ω1) of the current (I ₁ ) by the first Inductor (W1) and for setting a phase shift angle (ϕk) between the current (I ₁ ) through the first inductor (W1) and the current (I ₂ ) through the second inductor (W2), wherein a sensor ( 4 ) for Detection of the sound level (ps) generated when a material (R) is heated and a controller ( 5 ), to which the value of the sound level (ps) detected by the sensor ( 4 ) is fed, for changing the one set by the control device ( 3 ) Phase shift angle ( ϕk) between the current (I ₁ ) through the first inductor (W1) and the current (I ₂ ) through the at least second inductor (W2) in a given direction, as long as the detected sound level (ps) exceeds a given sound level and no minimum has reached, are provided. 2. Device according to one of the preceding claims, characterized in that the at least two inductors (W1, W2) are identical are executed. 3. Device according to one of the preceding claims, characterized in that the first inductor (W1) and the at least second Inductor (W2) each by an inverter (WR1, WR2) are supplied with current, the Inverters (WR1, WR2) each have one Rectifiers (GR1, GR2) and an intermediate circuit (ZK1, ZK2) with rectified, smoothed current be supplied. 4. Device according to one of the preceding claims characterized by at a voltage regulator (7) to which a reference voltage (U _2soll) and the actual voltage (U _{2 is)} supplied through one of the inductors (W2), the voltage regulator (7) is adapted to the _target voltage (U _2soll ) taking into account the actual voltage (U _2actual ) via this inductor (W2), and a discriminator ( 6 ) to which the detected sound level (ps) is fed by the sound level sensor ( 4 ) and which is suitable determine that a minimum sound level has been reached by changing the phase shift _{angle and} to vary the _target voltage (U _2soll ) applied to the voltage regulator ( 7 ) in accordance with the remaining sound level. 5. Device according to one of the preceding claims, characterized in that the first inductor (W1) and the at least second Inductor (W2) each by an inverter (WR1, WR2) are supplied with current, the Inverters (WR1, WR2) in turn connected in parallel are and via a single rectifier (GR1) and a single intermediate circuit (ZK1) together with rectified, smoothed power are supplied. 6. A method for reducing the sound level (ps) during the inductive heating of a material (R), the inductive heating being carried out by at least two AC-fed inductors (W1, W2), which comprises the following steps:

• - Setting the same angular frequency (ω1, ω2) for the currents (I ₁ , I ₂ ) by the two inductors (W1, W2) and
• - Setting a phase shift angle (ϕk) between the current (I ₁ ) through the first inductor (W1) and the current (I ₂ ) through the second inductor (W2) by the sound level (ps) detected when the material is heated becomes,
• - the detected sound level (ps) is compared with a predetermined sound level, and
• - The phase shift angle (ϕk) between the current (I ₁ ) through the first inductor (W1) and the current (I ₂ ) through the second inductor (W2) is changed in a predetermined direction, as long as the detected sound level (ps) exceeds the specified sound level and has not reached a minimum.

7. The method according to claim 6, characterized in that when an adjustable by changing the phase shift angle (ϕk) minimum of the sound level (ps) is above the predetermined sound level, the voltage (U ₂ ) across one of the inductors (W2) is varied to further reduce the sound level.