Method for operating an induction heating device and induction heating device

Abstract

The invention relates to a method for operating an induction heating device and to an induction heating device. The method for operating an induction heating device, wherein the induction heating device has a DC voltage intermediate circuit, which has a positive intermediate circuit branch, which guides a positive intermediate circuit potential, and a negative intermediate circuit branch, which guides a negative intermediate circuit potential, wherein there is an intermediate circuit DC voltage between the positive intermediate circuit branch and the negative intermediate circuit branch, a parallel resonant circuit, which has a capacitor and an induction heating coil, which is connected in parallel to the capacitor, wherein an alternating magnetic field can be generated for heating a cooking utensil by means of the induction heating coil, and a semiconductor switching device, wherein the parallel resonant circuit and the semiconductor switching device are connected in series in a loop between the positive intermediate circuit branch and the negative intermediate circuit branch, wherein the method comprises the following steps at the start of the heating: during a charging duration, the semiconductor switching device is actuated by means of a first PWM signal having a first frequency for charging the capacitor.

Description

Technical Field

[0001] The objective of this invention is to provide a method for operating an induction heating device and an induction heating device that enables the induction heating device to be operated in a manner that takes the most care of the components. Summary of the Invention

[0002] The method according to the invention is used to operate an induction heating device.

[0003] The induction heating device has a DC voltage intermediate circuit, which includes a positive intermediate circuit branch that guides the positive intermediate circuit potential and a negative intermediate circuit branch that guides the negative intermediate circuit potential. During operation of the induction heating device, an intermediate circuit DC voltage exists between the positive and negative intermediate circuit branches. The induction heating device also has a parallel resonant circuit, which has a capacitor and an induction heating coil connected in parallel with the capacitor, wherein an alternating magnetic field can be generated by means of the induction heating coil for heating cooking utensils.

[0004] The induction heating device also has a semiconductor switching device, especially exactly one semiconductor switching device, such as an IGBT.

[0005] The parallel resonant circuit and the semiconductor switching device are connected in series between the positive intermediate circuit branch and the negative intermediate circuit branch to form a loop.

[0006] The induction heating device also has a control unit, for example in the form of a microprocessor control device, which operates a semiconductor switching device to perform the method described below.

[0007] The method includes the step of (pre)charging the capacitor by means of a first PWM signal having a first frequency during the charging duration.

[0008] In one embodiment, the first frequency is in the frequency range between 200 kHz and 3 MHz.

[0009] In one implementation, the first PWM signal has a duty cycle of less than 20%.

[0010] In one embodiment, the charging duration is in the range of 0.5µs to 5µs. Alternatively, the charging duration can also be variably selected such that the voltage across the semiconductor switching device is less than a maximum voltage, for example less than 150 V, and particularly less than 100 V.

[0011] In one embodiment, the method includes subsequent steps after heating begins or after the steps described above: controlling the semiconductor switching device by means of a second PWM signal having a second frequency.

[0012] In one embodiment, the second frequency is in the range between 20 kHz and 65 kHz.

[0013] In one implementation, the second PWM signal has a duty cycle in the range of 15% to 25%.

[0014] In one embodiment, the induction heating device has a DC voltage supply device for generating the intermediate circuit DC voltage, particularly in a stabilized manner. The DC voltage supply device is preferably configured to generate the intermediate circuit DC voltage in a stabilized manner, such that the intermediate circuit DC voltage is generated independently of the load within a predetermined voltage range, for example, between 200 V and 240 V. Attached Figure Description

[0015] The invention will now be described in detail with reference to the accompanying drawings. In this case: Figure 1 A schematic circuit diagram of an induction heating device is shown; and Figure 2 Shown in Figure 1 The signal of the induction heating device shown over time. Detailed Implementation

[0016] Figure 1 A schematic circuit diagram of the induction heating device 100 is shown.

[0017] The induction heating device 100 has a DC voltage intermediate circuit 1, which has a positive intermediate circuit branch 1a that guides the positive intermediate circuit potential and a negative intermediate circuit branch 1b that guides the negative intermediate circuit potential. An intermediate circuit DC voltage 9 exists between the positive intermediate circuit branch 1a and the negative intermediate circuit branch 1b.

[0018] The induction heating device 100 also has a parallel resonant circuit, which has a capacitor 2 and an induction heating coil 3 connected in parallel with the capacitor 2, wherein an alternating magnetic field can be generated by means of the induction heating coil 3 for heating the cooking utensil 200.

[0019] The induction heating device 100 also has a semiconductor switching device 4 in the form of an IGBT, wherein the parallel resonant circuits 2 and 3 and the semiconductor switching device 4 are connected in series between the positive intermediate circuit branch 1a and the negative intermediate circuit branch 1b to form a loop.

[0020] The induction heating device 100 further includes a control unit 8, which controls the semiconductor switching device 4 to perform the method described below.

[0021] The induction heating device 100 also has a DC voltage supply device 10 for generating an intermediate circuit DC voltage 9 in a stable manner.

[0022] Figure 2 The voltage 11 at the collector 12 of the semiconductor switching device 4, the first PWM signal 5, and the second PWM signal 7 following the first PWM signal 5 are shown over time, wherein the PWM signals 5 and 7 are generated by means of the control unit 8 and are used to control the semiconductor switching device 4.

[0023] As shown, during the charging duration 6, the semiconductor switching device 4 is controlled by a first PWM signal 5 having a first frequency to charge the capacitor 2. The first frequency is in the range between 200 kHz and 3 MHz. The first PWM signal 5 has a duty cycle of less than 20%. The charging duration 6 is in the range between 0.5 µs and 5 µs.

[0024] After heating begins or after the charging duration 6 has expired, the semiconductor switching device 4 is controlled by means of a second PWM signal 7 having a second frequency. The second frequency is in the range between 20 kHz and 65 kHz. The second PWM signal 7 has a duty cycle in the range between 15% and 60% related to the heating power.

[0025] The present invention provides a method for controlling the gate terminal of an IGBT in conjunction with switching an induction heating device in a quasi-resonant manner, the induction heating device being powered from a stabilized DC voltage supply.

[0026] When not being heated, the intermediate circuit voltage is at a high level, which in conventional solutions results in a high collector current when the IGBT is turned on.

[0027] When the intermediate circuit is currently fed from a stabilized DC voltage supply device, the intermediate circuit does not need to be discharged because, unlike when the intermediate circuit is powered through a grid rectifier, there is no zero-crossing point of the AC grid that feeds the grid rectifier.

[0028] According to the present invention, when heating is started, the resonant circuit capacitor is charged by means of a high-frequency pulse mode, which protects the semiconductor switching device or IGBT from damage.

[0029] For example, multiple pulses can be used to control the IGBT to reduce the collector current during startup. The control frequency can be, for example, 1.55 MHz with a duty cycle of 17%.

[0030] After, for example, four pulses, the frequency can be changed to, for example, a normal operating frequency of 40 kHz with a duty cycle of 20%.

[0031] According to the present invention, the maximum collector current can be significantly reduced, thereby protecting the IGBT from damage. The method according to the present invention does not require changes to the conventional control topology.

Claims

1. A method for operating an induction heating device (100), -The induction heating device (100) wherein the induction heating device (100) has: - DC voltage intermediate circuit (1), the DC voltage intermediate circuit having a positive intermediate circuit branch (1a) that guides the positive intermediate circuit potential and a negative intermediate circuit branch (1b) that guides the negative intermediate circuit potential, wherein there is an intermediate circuit DC voltage (9) between the positive intermediate circuit branch (1a) and the negative intermediate circuit branch (1b). - A parallel resonant circuit having a capacitor (2) and an induction heating coil (3) connected in parallel with the capacitor (2), wherein an alternating magnetic field can be generated by means of the induction heating coil (3) for heating a cooking utensil (200), and - Semiconductor switching device (4). -The parallel resonant circuit (2, 3) and the semiconductor switching device (4) are connected in series to form a loop between the positive intermediate circuit branch (1a) and the negative intermediate circuit branch (1b). -The method described above includes the following steps at the start of heating: - During the charging duration (6), the semiconductor switching device (4) is controlled by means of a first PWM signal (5) having a first frequency to charge the capacitor (2).

2. The method according to claim 1, characterized in that, The first frequency is in the range between 200 kHz and 3 MHz.

3. The method according to any one of the preceding claims, characterized in that, The first PWM signal (5) has a duty cycle of less than 20%.

4. The method according to any one of the preceding claims, characterized in that, The charging duration (6) is in the range of 0.5µs and 5µs.

5. The method according to any one of the preceding claims, characterized in that, The method includes the following steps after heating begins: - The semiconductor switching device (4) is controlled by means of a second PWM signal (7) having a second frequency.

6. The method according to claim 5, characterized in that, The second frequency is in the range between 20 kHz and 65 kHz.

7. The method according to any one of claims 5 or 6, characterized in that, The second PWM signal (7) has a duty cycle in the range of 15% to 60%.

8. An induction heating device (100) comprising: - DC voltage intermediate circuit (1), the DC voltage intermediate circuit having a positive intermediate circuit branch (1a) that guides the positive intermediate circuit potential and a negative intermediate circuit branch (1b) that guides the negative intermediate circuit potential, wherein there is an intermediate circuit DC voltage (9) between the positive intermediate circuit branch (1a) and the negative intermediate circuit branch (1b). - A parallel resonant circuit having a capacitor (2) and an induction heating coil (3) connected in parallel with the capacitor (2), wherein an alternating magnetic field can be generated by means of the induction heating coil (3) for heating a cooking utensil (200). - Semiconductor switching device (4). -The parallel resonant circuit (2, 3) and the semiconductor switching device (4) are connected in series between the positive intermediate circuit branch (1a) and the negative intermediate circuit branch (1b) to form a loop, and - Control unit (8), which manipulates the semiconductor switching device (4) to perform the method according to any one of the preceding claims.

9. The induction heating device (100) according to claim 8, comprising: - A DC voltage supply device (10) is used to generate the DC voltage (9) of the intermediate circuit in a particularly stable manner.

Images