JP5776287B2 - Induction heating power supply - Google Patents

Description

  The present invention relates to an induction heating power supply apparatus in which a plurality of power converters are connected to a plurality of heating coils, and the respective heating coils are magnetically coupled to each other.

FIG. 2 is a circuit diagram for explaining the background art, and FIGS. 3 and 4 are vector diagrams for explaining the operation. First, the circuit diagram shown in FIG. 2 will be described.
In this configuration, two full-bridge power converters 17a and 17b having a DC power supply 11 as an input are used, and resonance capacitors (12a and 12b) and heating coils (14a and 14b) are connected to the AC output, respectively. Here, the mutual inductances 15a and 15b indicate that the heating coils 14a and 14b are magnetically coupled to each other.

  The first induction heating power source 19a (No. 1 power source) includes a DC power source 11 constituted by a diode rectifier or the like at the DC input of the power converter 17a, and a resonance capacitor 12a and a heating coil at the AC output of the power converter 17a. A series circuit with 14a is connected to each other. The power converter 17a is a single-phase output voltage type full bridge inverter circuit composed of a capacitor 17e1 and semiconductor elements (IGBTs) 17a1, 17a2, 17a3, 17a4 in which diodes are connected in antiparallel.

  Here, 13a represents the DC resistance of the heating coil 14a, and 15a represents the mutual inductance of the magnetically coupled heating coil. The output frequency of the power converter 17a is several tens of kHz, and the output voltage is one pulse per half cycle. A control circuit 18a detects the AC output current I1 of the power converter 17a with the current detector 16a, and controls the pulse width so that this current becomes a command value. That is, control is performed to widen the voltage pulse width when the detected value is small compared to the command value, and to narrow the voltage pulse width when the detected value is large compared to the command value.

Since the second induction heating power source 19b (NO. 2 power source) has the same configuration and operation, the description thereof is omitted.
Further, the control circuits (18a, 18b) exchange signals in order to match the phases of the AC output current I1 of the power converter 17a and the AC output current I2 of the power converter 17b.

  Next, the vector diagrams of FIGS. 3 and 4 will be described. In this example, the mutual inductance component (M) / (mutual inductance component (M) + self-inductance component (L)) is about 20%. For simplicity, the circuit constants of the two units are the same, and the AC output currents I1 and I2 of the power converters 17a and 17b are in phase.

FIG. 3 shows a case where I1 = I2 = rated current.
Assuming that the maximum voltage that can be output by the power converter is 1.0, no. The delay invalid component voltage of one power supply is large at jωL × I1 = 8.0 and jωM × I2 = 2.0, but the advance invalid component voltage is −j / ωC × I1 = 9.25. The reactive voltage divided by the delay and advance of one power supply is canceled out to 0.75. At this time, the effective divided voltage is R × I1 = 0.5, and the total load voltage V1 = √ (0.75 ^ 2 + 0.5 ^ 2) = 0.9 is less than the maximum voltage that can be output by the power converter. It becomes.

No. Since two power supplies are I1 = I2, the vector diagram is the same.
FIG. 4 shows a case where I1 = rated current and I2 = rated current × 0.88.
No. The delay ineffective voltage of one power supply is jωL × I1 = 8.0 and jωM × I2 = 2.0 × 0.88 = 1.76, and the advanced ineffective voltage is changed by −j / ωC × I1 = 9.25. Since there is no delay, the reactive partial voltage including the delay and the advance is 0.51. The effective divided voltage also does not change at R × I1 = 0.5, and the total load voltage V1 = √ (0.51 ^ 2 + 0.5 ^ 2) = 0.71.

  On the other hand, no. The delayed invalid voltage of the two power sources is jωL × I2 = 8.0 × 0.88 = 7.04 and jωM × I1 = 2.0, and the advanced invalid voltage is −j / ωC × I2 = 9.25 × 0. Since .88 = 8.14, the ineffective divided voltage including delay and advance is 0.9. The effective voltage division is R × I1 = 0.5 × 0.88 = 0.44, and the total load voltage V2 = √ (0.9 ^ 2 + 0.44 ^ 2) = 1.0.

  As can be seen from the above, no. The load voltage V2 of the two power supplies is larger when the current I1> I2 in FIG. 4 is reduced than when I1 = I2 in FIG. Therefore, no. In the operation of the power converter of the two power sources, in order to decrease I2, first, the pulse width is once narrowed by the current regulator and then I2 is further reduced by the load voltage V2. spread. Here, up to the current shown in FIG. 4, the load voltage V2 is equal to or lower than the maximum voltage that can be output from the power converter, and therefore can be controlled and operate without any problem.

  However, when I2 is further decreased, the load voltage V2 exceeds the maximum voltage that can be output from the power converter, I2 becomes uncontrollable, and decreases with the load voltage V2-the maximum voltage that can be output from the power converter.

  As a result, not only the necessary heating is not possible, but also when the current is extremely reduced, erroneous detection of the phase of the current occurs, making it impossible to match the phases of the currents of the plurality of power converters. There is also an adverse effect that the exchange of electric power occurs between them and the input electric power is different from the electric power used for heating, making it impossible to perform the desired heating. The exchange of electric power by the phase difference of current is described in Patent Document 1. Further, in Patent Document 2, the voltage and current generated in the load are examined, but this is a case where the ineffective voltage is smaller than the effective voltage and is different from the operation of the proposal. In addition, complicated arithmetic circuits are also required.

JP 2004-146283 A Japanese Patent No. 4015526

  An object of the present invention relates to an induction heating power supply apparatus in which a plurality of power converters are connected to a plurality of heating coils, respectively, and the respective heating coils are magnetically coupled to each other. If the load voltage of the power source with the smaller value exceeds the maximum voltage that can be output by the power converter and becomes uncontrollable, stable heating cannot be performed. Accordingly, an object of the present invention is to detect this and stop the failure. In addition, the embodiment is simply performed.

In order to solve the above-described problem, in the first invention, a plurality of induction heating power sources in which a common DC power source is input and a series circuit of a heating coil and a resonant capacitor is connected to the output of the power converter are used. In the induction heating power supply apparatus in which the respective heating coils are magnetically coupled to each other, the current detection means for detecting the output current of the power converter, and the deviation between the current detection value from the current detection means and the output current command value are input. A current regulator, a pulse width control unit that varies a pulse width according to an output of the current regulator, and a current synchronization unit that synchronizes the currents of the plurality of induction heating power sources, and an operation period of the power supply device the current detection value is detected the following smaller predetermined value than the output current command value, and detects that the output value of the current regulator exceeds a smaller predetermined value than the value that maximizes the pulse width in Sometimes failure to stop.

  In the present invention, when the difference between the currents of a plurality of power supplies is large and control becomes impossible, it is possible to catch the decrease in current and stop the failure, so that the operation can be resumed and the necessary heating can be performed. . In addition, because it is possible to stop the failure before a control failure due to an extreme decrease in current occurs, a phase difference occurs in the currents of multiple power converters, and power exchange occurs between the power converters, as expected. It will not be impossible to heat.

FIG. 3 is a control circuit diagram showing a first embodiment of the present invention. It is a circuit diagram of the induction heating power supply device which this invention is made symmetrical. FIG. 3 is a first vector diagram for explaining the operation of FIG. 2. FIG. 3 is a second vector diagram for explaining the operation of FIG. 2.

  The main point of the present invention is that in an induction heating power supply apparatus in which a plurality of induction heating power sources in which a series circuit of a heating coil and a resonant capacitor is connected to the output of a power converter are used, and each heating coil is magnetically coupled to each other, the load voltage Is detected when the detected current value becomes smaller than the command value when the voltage becomes higher than the maximum voltage that can be output from the converter, or when the pulse width is maximized, the current cannot be increased and decreased. Is a point to stop the failure.

  FIG. 1 shows a first embodiment of the present invention. It consists of a control circuit for controlling the two induction heating power sources shown in FIG. 2 and a protection circuit for detecting and stopping the failure. Since the two induction heating power supplies 19 a and 19 b are operated in parallel, each induction heating power supply is operated in synchronization with the reference oscillator 9. Since the control circuit and the protection circuit of each induction heating power source 19a, 19b have the same configuration, the induction heating power source 19a (No. 1) will be described.

  The phase of the current detection value a (I1) of the current detector 16a and the reference oscillator 9 is detected by the phase detector 1a, and the frequency is controlled by the frequency control circuits 2a and 2b so that the phases of the induction heating power supply devices 19a and 19b are matched. Adjusted. That is, when the phase of the current is a leading phase, the frequency is lowered to delay the phase, and when the phase of the current is a lagging phase, the frequency is increased to advance the phase. It is driven in synchronization with.

  A deviation between the detected current value a (I1) and the current command value Aa is obtained by the adder 4a and controlled so that the deviation becomes zero by the current regulator 5a. That is, the pulse width is adjusted by the pulse width control circuit 3a by the output of the current regulator 5a. As a result, the output voltage of the power converter 17a is adjusted, and the current I1 becomes equal to the command value Aa.

  However, when the heating coil connected to each induction heating power source is magnetically coupled, an induction voltage from another machine (19b) is generated. Accordingly, the load voltage increases accordingly, and if the maximum voltage that can be output by the power converter 17a is exceeded, the current cannot be controlled. That is, although the current command value Aa is given, the actual current does not increase but decreases. Therefore, the comparator 6a detects that the current detection value a (I1) has decreased from a value Ca smaller than the value in the normal use area, and stops the failure. Note that the fault output is masked in order to avoid erroneous fault detection when the current during stoppage is not flowing or when the current immediately after the start of operation is small.

The second embodiment has a configuration in which a comparator 7a for determining the magnitude of the output amount of the current regulator 5a is added to the first embodiment. When control becomes impossible, the output of the current regulator 5a has a value for maximizing the pulse width. In this example, the output of the current regulator 5a has a positive maximum value. This is a system in which this is detected by the comparator 7a, and a logical product with the output of the above-mentioned comparator 6a is obtained by the AND element 8a and used as a failure signal. Therefore, the set value Ba of the comparator 7a input may be set to a value slightly smaller than the value for maximizing the pulse width. Compared to the first embodiment, false detection can be reduced.
Here, depending on the system of the pulse width control circuit 3a, it can be configured to have a negative maximum value. That is, it is well known that the pulse width control circuit can be realized even when the control signal for maximizing the pulse width is positive maximum or negative maximum.

  In the above-described embodiment, an example in the case of a configuration with two power supplies is shown. However, three or more power supplies can be similarly realized.

DESCRIPTION OF SYMBOLS 1a, 1b ... Phase detector 2a, 2b ... Frequency adjustment circuit 3a, 3b ... Pulse width control circuit 4a, 4b ... Adder 5a, 5b ... Current regulator 6a, 6b, 7a 7b: Comparator 8a, 8b ... AND circuit 9 ... Reference oscillator 11 ... DC power supply 12a, 12b ... Capacitors 13a, 13b ... Internal resistors 14a, 14b ... Heating coil 15a , 15b ... mutual inductance 16a, 16b ... current detectors 17a, 17b ... power converters 18a, 18b ... control circuits 19a, 19b ... induction heating power supplies 17e1, 14e1 ... capacitors 17a1 -17a4, 17b1-17b4 ... IGBT

Claims (1)

In an induction heating power supply apparatus in which a common DC power supply is used as an input and a plurality of induction heating power supplies in which a series circuit of a heating coil and a resonant capacitor is connected to the output of the power converter, and each heating coil is magnetically coupled to each other,
A current detection means for detecting an output current of the power converter; a current regulator for inputting a deviation between a current detection value from the current detection means and an output current command value; and a pulse width by an output of the current regulator. A variable pulse width control means; and a current synchronization means for synchronizing the currents of the plurality of induction heating power supplies, wherein the current detection value is less than a predetermined value smaller than an output current command value during an operation period of the power supply device And detecting that the output value of the current regulator exceeds a predetermined value lower than a value for maximizing the pulse width , the failure is stopped.