WO2008031560A1 - Induction heating device - Google Patents

Abstract

1. Induction heating device. 2.1. The invention relates to an induction heating device. 2.2. The induction heating device according to the invention comprises a mains AC voltage terminal (100a, 100b) for connecting a mains AC voltage, at least one induction coil (101 - 104) and at least one frequency converter (105-112, 114-121, 113, 136), which generates a high-frequency drive voltage for the at least one induction coil (101 - 104) from the mains AC voltage, wherein the mains AC voltage terminal (100a, 100b) is connected to a first outer conductor (L1) and a second outer conductor (L2) of a three-phase mains during operation of the induction heating device. 2.3. Use for domestic appliances, for example.

Description

 Description Induction heater

The invention relates to an induction heater according to the preamble of claim 1.

Induction cooking appliances or induction cookers are becoming increasingly popular. Advantageous are their high efficiency and the rapid response to a change in the cooking level. The disadvantage is the higher price compared to glass ceramic hobs with radiant heaters.

Induction cooking appliances usually comprise one or more induction heating devices associated with a respective cooking area with an induction coil which is supplied with an alternating voltage or an alternating current, whereby eddy currents are induced in a cookware to be heated which is magnetically coupled to the induction coil. The eddy currents cause heating of the cookware.

For controlling the induction coil, different circuit arrangements and control methods are known. All circuit or process variants have in common that they produce a high-frequency drive voltage for the induction coil from a low-frequency power input voltage. Such circuits are referred to as frequency converters.

For conversion or frequency conversion, it is usual to first rectify the mains input or mains alternating voltage with the aid of a rectifier into a DC supply voltage or DC link voltage, and then to generate the high-frequency voltage. th drive voltage using one or more switching means, generally insulated gate bipolar transistors (IGBT) prepared. At the output of the rectifier, ie between the DC link voltage and a reference potential, a so-called DC link capacitor for buffering the DC link voltage is usually provided.

A converter variant which is widespread in Europe comprises a so-called half-bridge circuit comprising two IGBTs, wherein the induction coil and two capacitors, which are connected in series between the intermediate circuit voltage and the reference potential, form a series resonant circuit. The induction coil is connected to a connection with a connection node of the two capacitors and with its other connection to a connection node of the two half-bridge forming IGBTs. This converter version is powerful and reliable, but relatively expensive due to the two IGBTs required.

Another converter variant is the so-called full bridge circuit consisting of four IGBTs. In each case, two IGBTs form a switching transistor pair, which is looped in between the intermediate circuit voltage and the reference potential. The inductor and a capacitor are connected in series or in parallel between a connection node of the two IGBTs forming the first switching transistor pair and a connection node of the two IGBTs forming the second switching transistor pair. This converter variant is very flexible, powerful and reliable, but due to the four required IGBTs the most expensive variant.

Therefore, a variant optimized from a cost point of view uses only one switching means or an IGBT, wherein the induction coil and a capacitor form a parallel resonant circuit. Between the The rectifier's output connections are parallel to the DC link capacitor, the parallel resonant circuit consisting of induction coil and capacitor and the IGBT are connected in series.

The conventional induction heating devices are usually operated in a so-called star connection, i. As AC mains voltage or mains input voltage of the induction heater, a voltage difference between a so-called outer conductor or phase strand and a so-called neutral conductor of a three-phase network is used, i. a mains AC voltage connection of the induction heating device is connected in its operation with one of the three outer conductor of the three-phase system and the neutral conductor of the three-phase network.

The three-phase system has a single neutral conductor and three outer conductors, each carrying sinusoidal voltages, which have a phase difference of 120 degrees to each other. In Germany, for example, an effective value of the voltage between any of the three outer conductors and the neutral conductor is 230V.

Usually in star connection, i. via one of the three outer conductors and the neutral conductor, two hotplates per mains AC voltage connection, i. two induction coils, supplied. With a mains voltage of 230V, approx. 3.7kW of power is available per mains AC voltage connection. Thus, if one of the two induction coils is to be operated at the full power of 3.7kW, then the other of the two induction coils remains "cold", i. there is no power available for them.

Task and solution The invention is therefore based on the object to provide an induction heater available that allows a high power output under all operating conditions.

The invention solves this problem by an induction heater according to claim 1.

Advantageous and preferred embodiments of the invention are the subject of the other claims and are explained in more detail below. The wording of the claims is incorporated herein by express reference.

The induction heating device according to the invention comprises a mains AC voltage connection for connecting an AC mains voltage, at least one induction coil and at least one frequency converter, which generates from the mains AC voltage a high-frequency drive voltage for the at least one induction coil. During operation of the induction heating device, for example, when the induction heating device is installed in a hob, the line AC voltage connection is connected to a first outer conductor and a second outer conductor of a three-phase system. Compared to the conventional circuit, in which the mains AC voltage connection is connected to the neutral conductor and one of the three outer conductors or phases of the three-phase network, significantly more connected load is available in the induction heater according to the invention. Thus, for example, a hotplate can be operated with greater heating power. If the induction heating device is provided for heating more than one hotplate, ie more than one induction coil is present, for example, two hotplates can be operated simultaneously with high power. In a further development, the induction heating device comprises at least three, in particular at least four, induction coils, wherein the frequency converter has only a single drive unit, which is designed such that it from the AC line voltage depending on a high-frequency drive voltage for an associated one of the at least three, in particular at least four, Induced induction coils. The circuit according to the invention of the mains AC voltage connection with the first outer conductor and the second outer conductor of the three-phase network makes it possible to operate a plurality of burners with a common induction heating, since due to the wiring, a sufficient power supply is ensured. In conventional induction heaters usually two induction coils are operated on an outer conductor. In an induction hob with four burners, each associated with an induction coil, consequently, usually two of the four induction coils are supplied by a first outer conductor and the remaining two of the four induction coils by a further, second outer conductor. There is therefore no common reference potential between the circuit parts associated with the first two inductors and the circuit parts associated with the remaining two inductors. If the four induction coils are to be controlled as a function of one another in order, for example, to ensure as quiet a operation as possible and / or to operate power management, information or signals must be exchanged between the circuit parts operated on different outer conductors. Due to the different reference potentials, elements for electrical isolation, for example so-called optocouplers, must be used for this purpose in conventional induction heating devices. Since the induction heating device according to the invention has a common reference potential for all circuit parts which are assigned to the induction coils, elements for galvanic isolation are not required. Consequently, it is without additional components effort possible to control the induction coils in dependence on each other, for example, to allow quiet operation and / or to operate a power management.

In a development, the induction heater comprises at least four induction coils. The frequency converter includes first to eighth capacitors, wherein the first and second capacitors, the third and fourth capacitors, the fifth and sixth capacitors, and the seventh and eighth capacitors are serially connected between an intermediate circuit voltage and a reference potential. Furthermore, the frequency converter comprises first to eighth switching transistors, wherein the first and the second switching transistor, the third and the fourth switching transistor, the fifth and the sixth switching transistor and the seventh and the eighth switching transistor are connected in series between the intermediate circuit voltage and the reference potential. The first inductor is connected between a connection node of the first and second switching transistors and a connection node of the first and second capacitors, the second inductor is connected between a connection node of the third and fourth switching transistors and a connection node of the third and fourth capacitors, the third Induction coil is connected between a connection node of the fifth and the sixth switching transistor and a connection node of the fifth and the sixth capacitor and the fourth induction coil is connected between a connection node of the seventh and the eighth switching transistor and a connection node of the seventh and the eighth capacitor. The converter comprises a common drive unit, which is designed to drive the first to eighth switching transistors. The first and second, third and fourth, fifth and sixth and seventh and eighth transistors form a half-bridge circuit as a pair of transistors in each case in connection with the first and second, third and fourth, fifth and sixth or seventh and eighth capacitors, wherein all the transistors are driven by the common drive unit for generating a respective high-frequency drive voltage for the associated induction coil.

In a further development, the induction heating device comprises first to fourth induction coils. The frequency converter comprises first to fourth capacitors, with one capacitor being connected in parallel or in series to an associated induction coil, and first to tenth switching transistors, the first and second switching transistors, the third and fourth switching transistors, the fifth and the sixth switching transistors , the seventh and eighth switching transistors, and the ninth and tenth switching transistors are serially connected between a DC link voltage and the reference potential. The first inductor is connected between a connection node of the first and second switching transistors and a connection node of the third and fourth switching transistors, the second inductor is connected between a connection node of the third and fourth switching transistors and a connection node of the fifth and sixth switching transistors, the third Induction coil is connected between a connection node of the fifth and the sixth switching transistor and a connection node of the seventh and the eighth switching transistor and the fourth induction coil is connected between a connection node of the seventh and the eighth switching transistor and a connection node of the ninth and the tenth switching transistor. Furthermore, a single drive unit is provided, which is designed to drive the first to tenth switching transistors. The switching transistors are preferably insulated-gate bipolar transistors.

In a further development, the induction heating device comprises a rectifier for generating an intermediate circuit voltage and / or a line filter. The rectifier and the line filter have a voltage tion strength, which is suitable for operation of the induction heater on the first outer conductor and the second outer conductor of the three-phase network.

Brief description of the drawings

Embodiments of the invention are shown schematically in the drawings and will be described in more detail below. Hereby shows:

Fig. 1 shows a first embodiment of an induction heater according to the invention with half-bridge circuits and

Fig. 2 shows a second embodiment of an induction heater according to the invention with full bridge circuits.

Detailed description of the embodiments

Fig. 1 shows a first embodiment of an induction heater according to the invention with half-bridge circuits. The induction heating device comprises a mains AC voltage connection with contacts 100a and 100b for connecting an AC mains voltage, four induction coils 101 to 104, a frequency converter, a rectifier 136 which generates an intermediate circuit voltage UZ from the AC mains voltage, and a mains filter 137 for interference suppression. The frequency converter comprises eight IGBTs 105 to 112 as switching transistors, eight capacitors 114 to 121 and a drive unit 113 for driving the IGBTs 105 to 112, the frequency converter each generating a high-frequency drive voltage for an associated induction coil 101 to 104 from the AC line voltage. The mains AC voltage connection is connected via its contacts 100a and 100b in the operation of the induction heater with a first outer conductor L1 and a second outer conductor L2 of a rotary power network, ie the contact 100a is connected to the outer conductor L1 and the contact 100b is connected to the outer conductor L2. It is understood that a combination of the outer conductors L1 and L3 or L2 and L3 can be used for the power supply of the induction heater.

The first and second capacitors 114 and 115, the third and fourth capacitors 116 and 117, the fifth and sixth capacitors 118 and 119, and the seventh and eighth capacitors 120 and 121 are connected in series between the intermediate circuit voltage UZ and a reference potential GND , The first and second IGBTs 105 and 106, the third and fourth IGBTs 107 and 108, the fifth and sixth IGBTs 109 and 110, and the seventh and eighth IGBTs 111 and 112 are serially connected between the intermediate circuit voltage UZ and the reference potential GND , The first inductor 101 is connected between a connection node of the first and second IGBTs 105 and 106 and a connection node of the first and second capacitors 114 and 115, the second inductor 102 is connected between a connection node of the third and fourth IGBTs 107 and 108 and a connection node The third inductor 103 is connected between a connection node of the fifth and sixth IGBTs 109 and 110 and a connection node of the fifth and sixth capacitors 118 and 119, and the fourth inductor 104 is connected between one Connection nodes of the seventh and eighth IGBTs 111 and 112 and a connection node of the seventh and eighth capacitor 120 and 121 looped.

The drive unit 113 controls the IGBTs 105 to 112 in accordance with a setpoint value set for the associated induction coils 101 to 104. Gabe, wherein the drive unit 113, the IGBTs 105 to 112 controls such that a low-noise operation of the induction heater is ensured and an optimized power distribution of the power AC voltage connection 100a and 100b available power is done. Since there is considerably more power available at the AC supply voltage connection 100a and 100b compared to a conventional induction heater, a single induction coil 101 to 104 can be supplied with higher electrical power and / or a plurality of induction coils 101 to 104 can be applied simultaneously with higher electrical power.

Fig. 2 shows a second embodiment of an induction heater according to the invention with full bridge circuits. Elements having functions corresponding to the functions of an element shown in Fig. 1 are given identical reference numerals. With regard to their function, reference is made to the comments on FIG. 1.

The induction heater shown in Fig. 2 differs from the induction heater shown in Fig. 1 essentially in that instead of the half-bridge circuits of Fig. 1, full-bridge circuits are used for frequency conversion.

The frequency converter of FIG. 2 for this purpose comprises first to fourth capacitors 122 to 125, wherein each one capacitor is connected in series with an associated induction coil, first to tenth switching transistors in the form of IGBTs 126 to 135, wherein the first and the second IGBT 126 and 127, the third and fourth IGBTs 128 and 129, the fifth and sixth IGBTs 130 and 131, the seventh and eighth IGBTs 132 and 133, and the ninth and tenth IGBTs 134 and 135 in series between the intermediate circuit voltage UZ and the reference potential GND are looped. Two of these IGBT pairs form a full bridge. The first induction coil 101 is connected between a connection node The first inductor 102 is connected between a connection node of the third and fourth IGBTs 128 and 129 and a connection node of the fifth and sixth IGBTs 130 and 131, the third inductor 103 is connected between a connection node of the fifth and sixth IGBTs 130 and 131 and a connection node of the seventh and eighth IGBTs 132 and 133, and the fourth inductor 104 is connected between a connection node of the seventh and the eighth IGBTs 132 and 133 and a connection node of the ninth and tenth IGBTs 134 and 135 are looped. The central drive unit 113 is designed to drive the first to tenth switching transistors 126 to 135. A low-noise operation of the induction heating device and an optimized power distribution of the power available via the mains AC voltage connection 100a and 100b are effected by the control device 113 as in FIG. 1.

The non-prepublished patent application DE 10 2005 038 525 describes an induction heater with full bridges. The content of this application is hereby incorporated by reference in its entirety into the content of the present description. An activation of the IGBTs 126 to 135 shown in FIG. 2 can take place corresponding to the activation described there. In this case, the drive device 113 is embodied such that a phase shift between a first drive signal pair assigned to a first half bridge and a second drive signal pair assigned to a second half bridge is set as a function of the set heating power. A first half-bridge, for example, form the transistors 126 and 127, and a second half-bridge form, for example, the transistors 128 and 129, said half-bridges 126 and 127 and 128 and 129 together forming a full bridge. outward Visible details of the control is referred to the said application.

In the embodiment shown in FIG. 2, all induction coils 101 to 104 are driven by full bridges. In a conventional induction heater, four IGBTs are required per induction coil, i. a total of sixteen IGBTs for four induction coils. Due to the specific arrangement or wiring shown in FIG. 2, a total of ten IGBTs suffice to form four full bridges, wherein all induction coils are operated or driven with identical fundamental frequency. The wiring shown enables independent power adjustment for all four inductors 101 to 104. Although the inductors 101 and 102 share the half bridge consisting of the IGBTs 128 and 129, a specific power setting for the inductor 101 is selected by selecting the drive signal for the IGBTs 126 and 127 possible. The specific power setting for the second inductor 102 is possible by selecting the drive signal for the IGBTs 130 and 131. Although the second induction coil 102 and the third induction coil 103 are commonly driven by the IGBTs 130 and 131, the power of the third induction coil 103 can be adjusted by appropriately driving the IGBTs 132 and 133. Finally, the IGBTs 134 and 135 enable an independent power setting for the fourth inductor 104. The wiring principle shown can also be applied to more than four inductors.

It is understood that instead of the four induction coils shown, for example, three induction coils or more than four induction coils can be used. Furthermore, a Eintransistorumrichter can be used as a converter variant. The illustrated embodiments enable high power output under all operating conditions.

Claims

claims 1. induction heating device with a mains AC voltage connection (100a, 100b) for connecting an AC line voltage, at least one induction coil (101-104) and at least one frequency converter (105-112, 114-121, 113, 136), from the AC mains voltage, a high-frequency drive voltage for the at least one induction coil (101-104) generates, characterized in that the mains AC voltage connection (100a, 100b) in the operation of the induction heating device with a first outer conductor (L1) and a second outer conductor (L2) is connected to a three-phase network. 2. Induction heater according to claim 1, characterized by, at least three, in particular at least four, induction coils (101-104), wherein the frequency converter comprises a single drive unit (113) which is designed such that it from the AC line voltage depending on a high-frequency drive voltage for an associated one of the at least three, in particular the at least four, induction coils (101-104) generates. 3. Induction heater according to claim 1 or 2, characterized by at least four induction coils (101-104), wherein the frequency converter comprises: first to eighth capacitors (114-121), wherein the first and second capacitors (114, 115), the third and fourth capacitors (116, 117), the fifth and sixth capacitors (118, 119), and the seventh and eighth capacitors (120, 121) connected in series between one another Intermediate circuit voltage (UZ) and a reference potential (GND) are looped in, first to eighth switching transistors (105-112), wherein the first and the second switching transistor (105, 106), the third and the fourth switching transistor (107, 108), the fifth and sixth switching transistors (109, 110) and the seventh and eighth switching transistors (111, 112) are connected in series between the intermediate circuit voltage (UZ) and the reference potential (GND), the first induction coil (101) being connected between a connection node of the first and second switching transistors (105, 106) and a connection node of the first and second capacitors (114, 115) is looped, the second induction coil (102) between a connection node of the third and the fourth Scha The third inductor (103) is connected between a connection node of the fifth and the sixth switching transistor (109, 110) and a connection node of the fifth and the second transistor (107, 108) and a connection node of the third and fourth capacitors (116, 117) sixth capacitor (118, 119) is looped and the fourth induction coil (104) between a connection node of the seventh and the eighth Switching transistor (111, 112) and a connection node of the seventh and the eighth capacitor (120, 121) is looped, and a single drive unit (113), which is designed for driving the first to eighth switching transistors (105-112). 4. Induction heater according to claim 1 or 2, characterized by first to fourth induction coils (101-104), wherein the frequency converter comprises: first to fourth capacitors (122-125), wherein each capacitor is connected in parallel or in series with an associated induction coil first to tenth switching transistors (126-135), wherein the first and second switching transistors (126, 127), the third and fourth switching transistors (128, 129), the fifth and sixth switching transistors (130, 131), the seventh and the eighth switching transistor (132, 133) and the ninth and tenth switching transistors (134, 135) are serially connected between an intermediate circuit voltage (UZ) and a reference potential (GND), the first induction coil (101) being connected between a connection node of the first and second the second switching transistor (126, 127) and a connection node of the third and the fourth switching transistor (128, 129) is looped, the second induction coil (102) zwis connect a connection node of the third and the fourth switching transistor (128, 129) and a connection The third induction coil (103) is connected between a connection node of the fifth and the sixth switching transistor (130, 131) and a connection node of the seventh and the eighth switching transistor (132, 133) and the fourth inductor (104) is connected between a connection node of the seventh and eighth switching transistors (132, 133) and a connection node of the ninth and tenth switching transistors (134, 135), and a single drive unit (113) for driving the first to tenth switching transistors (126-135) is formed. 5. Induction heater according to claim 3 or 4, characterized in that the switching transistors are insulated gate bipolar transistors. 6. Induction heater according to one of the preceding claims, characterized by a rectifier (136) for generating an intermediate circuit voltage (UZ). 7. Induction heater according to one of the preceding claims, characterized by a line filter (137).