Discharge circuit

Abstract

A bipolar discharge circuit (1) for sensing a cooking zone (Z) to heat and detect a cookware (W), the bipolar discharge circuit comprising: a line mains supply terminal (T1) for connection to a mains supply line (L) of a mains supply AC power source (2) and a neutral line mains supply terminal (T2) for connection to a mains neutral line (N) of the mains supply AC power source (2); a rectifier (3) connected to the line mains connection (T1) and the neutral mains connection (T2); and a DC bus capacitor (6) connected to the rectifier (3). The DC bus capacitor (6) comprises a positive capacitor terminal (H1) and a negative capacitor terminal (H2) for connection to the induction cooking zone (Z). A switching circuit (9) is provided and is configured to discharge the DC bus capacitor (6) via the line mains terminal (T1) and the neutral mains terminal (T2).

Description

Technical Field

[0001] This invention relates to a discharge circuit, and more particularly to a bipolar discharge circuit for sensing cooking zones. Background Technology

[0002] International patent application WO 2022 / 096122 A1 discloses a circuit arrangement for discharging an intermediate circuit capacitor of an induction coil used in a cooking stove and reducing peak current in the circuit during discharge. When the mains voltage is positive between two zero-crossing points, the circuit arrangement utilizes a separate discharge circuit to discharge the intermediate circuit capacitor over a predetermined time period.

[0003] European patent application EP 3 768 042 A1 discloses a system and method for controlling the supply of power to the induction coil of an induction cooker. The system includes a circuit system comprising an input for receiving a rectified AC voltage, at least one switching element for supplying pulsed power to the induction coil, a capacitor connected in parallel with the switching element, and a discharge entity configured to discharge the capacitor. The system further includes a control entity configured to execute a subsequent control cycle, wherein in the control cycle, the control entity is configured to discharge the capacitor based on the discharge entity, and after discharging the capacitor, to initiate switching operations of the switching element, thereby supplying pulsed power to the induction coil. Summary of the Invention

[0004] This invention seeks to provide an improved discharge circuit, particularly a bipolar discharge circuit for a sensing cooking zone, to reduce acoustic noise when the sensing cooking zone is activated for heating the cookware or when the sensing cooking zone detects the cookware. The bipolar discharge circuit of this invention further improves the durability and lifespan of electronic components and reduces energy loss and electromagnetic emissions.

[0005] According to the present invention, a bipolar discharge circuit as described above is provided, the bipolar discharge circuit comprising: a line mains terminal for connecting to a mains line of a mains power supply (AC power supply) and a neutral line mains terminal for connecting to the neutral line of the AC power supply.

[0006] A rectifier having a line connection to the mains terminal of the line and a neutral line connection to the neutral line mains terminal, as well as a positive DC connection and a negative DC connection. A DC bus capacitor has a positive capacitor terminal and a negative capacitor terminal, wherein the positive capacitor terminal is connected to a positive DC connection via a positive DC line, and wherein the negative capacitor terminal is connected to a negative DC connection via a negative DC line, and wherein the positive and negative capacitor terminals are configured to connect to an induction cooking zone for heating and detecting the cookware; and A switching circuit, comprising a first main discharge connection connected to the positive DC line and a second main discharge connection connected to the negative DC line, and wherein the switching circuit further comprises: The first positive wave cycle connection to the mains terminal of the line and the second positive wave cycle connection to the mains terminal of the neutral line, and A first negative wave cycle connection is made to the neutral line mains terminal, and a second negative wave cycle connection is made to the line mains terminal; and wherein the switching circuit is configured to provide: In the first switching state, the DC bus capacitor can be discharged via the first positive wave period connection and the second positive wave period connection. In the second switching state, the DC bus capacitor can discharge via the first negative wave cycle connection and the second negative wave cycle connection. In the third switching state, the DC bus capacitor is disconnected from the first positive wave cycle connection, the second positive wave cycle connection, the first negative wave cycle connection, and the second negative wave cycle connection.

[0007] The bipolar discharge circuit, and particularly the switching circuit, of this invention ensures that the DC bus capacitor is discharged only through the line mains terminals and the neutral mains terminal, thereby avoiding discharge through the induction cooking zone connected to the positive and negative capacitor terminals. Therefore, compared to discharging the DC bus capacitor only through the switching circuit and via the line mains terminals and the neutral mains terminal using AC power, the high discharge (peak) current flowing through the induction cooking zone and its electronic components is eliminated. This further avoids power dissipation and heat loss in the induction cooking zone, and thus prevents excessive heat buildup that could damage the electronic components. Therefore, discharging the DC bus capacitor through the switching circuit and AC power increases the durability and lifespan of the induction cooking zone and further reduces acoustic noise.

[0008] The first and second switching states of the switching circuit allow the DC bus capacitor to discharge via the line mains terminals and the neutral mains terminal when the line mains terminal exhibits positive polarity during the first switching state or negative polarity during the second switching state. Therefore, the DC bus capacitor can discharge more rapidly, for example, twice within a single sinusoidal cycle of the AC mains power supply connected to the line mains terminals and the neutral mains terminal. The ability to discharge the DC bus capacitor more than once within a single sinusoidal cycle also enables high-frequency detection of the cookware without generating acoustic noise.

[0009] The third switching state provided by the switching circuit allows the DC bus capacitor to be disconnected from the mains terminals and the neutral mains terminals after it has been fully discharged. In this third switching state, the detection of the cookware and its normal operation by the induction cooking zone, used for heating or detecting the cookware, can be started or resumed. Attached Figure Description

[0010] The invention will now be discussed in more detail with reference to the accompanying drawings, in which: Figure 1 A bipolar discharge circuit connected to an AC power source and an induction cooking zone according to an embodiment of the present invention is shown. Figure 2 An example of the operation of a bipolar discharge circuit according to an embodiment of the present invention and its switching state relative to AC mains voltage is shown; Figure 3A and Figure 3B The positive cycle switching section and the negative cycle switching section, as used by a bipolar discharge circuit, are shown according to an embodiment of the present invention. Detailed Implementation

[0011] Figure 1 A bipolar discharge circuit 1, connected to an AC power source 2 and an induction cooking zone Z according to an embodiment of the invention, is shown. The AC power source 2 can be considered a conventional AC power outlet found in residential buildings, commercial buildings, etc., wherein the AC power source 2 can operate at, for example, 230 V and 50 Hz or 120 V and 60 Hz, depending on the geographical location. The induction cooking zone Z can be a standard or known induction cooking zone Z. As depicted, an exemplary induction cooking zone Z includes a resonant circuit utilizing, for example, a zone capacitor C and a zone inductor L connected in parallel, wherein the zone inductor L is arranged to magnetically interact with a cookware W for heating or cookware detection. The resonant circuit including the zone capacitor C and the zone inductor L can be operated by an IGBT switching arrangement G. However, note that the induction cooking zone Z can utilize different circuit topologies, such as a half-bridge topology.

[0012] like Figure 1 As further shown, the bipolar switching circuit 1 includes a line AC terminal T1 for connecting to the AC power line L of the AC power supply 2 and a neutral AC terminal T2 for connecting to the AC power neutral line N of the AC power supply 2. The line AC terminal T1 and the neutral AC terminal T2 can be configured or adapted for connection to a conventional AC power outlet.

[0013] The bipolar switching circuit 1 further includes a rectifier 3 having a line connection 4a connected to the line mains terminal T1 and a neutral connection 4b connected to the neutral mains terminal T2, and the rectifier further includes a positive (+) DC connection 5a and a negative (-) DC connection 5b.

[0014] Furthermore, a DC bus capacitor 6 is provided, and the DC bus capacitor includes a positive capacitor terminal H1 and a negative capacitor terminal H2, wherein the positive capacitor terminal H1 is connected to the positive DC connection 5a via a positive DC line 7, and wherein the negative capacitor terminal H2 is connected to the negative DC connection 5b via a negative DC line 8. Figure 1 As shown, in an exemplary embodiment, the negative DC line 8 is grounded. Then, the positive capacitor terminal H1 and the negative capacitor terminal H2 are configured to connect to the induction cooking zone Z for heating and detecting the cookware W.

[0015] It is important to note that in other embodiments, the bipolar discharge circuit 1 may include an additional DC bus capacitor 6' having an additional positive capacitor terminal H1' and an additional negative capacitor terminal H2', wherein the additional positive capacitor terminal H1' is connected to the positive DC connection 5a via a positive DC line 7, and wherein the additional negative capacitor terminal H2' is connected to the negative DC connection 5b via a negative DC line 8. Figure 1 As depicted, the additional induction cooking zone Z' can be connected to additional positive capacitor terminal H1' and additional negative capacitor terminal H2'.

[0016] Similar to the induction cooking zone Z, the additional induction cooking zone Z' may include a similar resonant circuit that utilizes, for example, an additional zone capacitor C' and an additional zone inductor L' connected in parallel, wherein the additional zone inductor L' is arranged to magnetically interact with the cookware (e.g., an additional cookware W') for heating or detecting the cookware. The additional resonant circuit may be operated by an additional IGBT switch arrangement G'.

[0017] like Figure 1 The bipolar switching circuit 1 shown further includes a switching circuit 9, wherein the switching circuit 9 includes: The first main discharge connection 10a is connected to the positive DC line 7, and A second main discharge connection 10b is connected to the negative DC line 8, and the switching circuit further includes: The first positive wave period connection 11a is connected to the mains terminal T1 and the second positive wave period connection 11b is connected to the neutral mains terminal T2, and The first negative wave cycle connection 12a is connected to the neutral line mains terminal T2 and the second negative wave cycle connection 12b is connected to the line mains terminal T1.

[0018] As will be explained in further detail below, this is used for the first Positive wave period Connect 11a and the second Positive wave period The naming scheme for connection 11b, "positive wave period," refers to the period during which the mains terminal T1 of the line exhibits positive polarity, while the period used for the first... negative wave period Connect 12a and the second negative wave period The term "negative wave period" in connection 12b refers to the period during which the mains terminal T1 of the line exhibits negative polarity.

[0019] Switching circuit 9 is configured to provide or include a first switching state (see example...) Figure 2 In S1), under this first switching state, the DC bus capacitor 6 can be discharged via the first positive wave cycle connection 11a and the second positive wave cycle connection 11b. Specifically, under the first switching state, the DC bus capacitor 6 can be discharged via the first main discharge connection 10a, the first positive wave cycle connection 11a, the second positive wave cycle connection 11b, and the second main discharge connection 10b. It should be noted that under the first switching state, the DC bus capacitor 6 is disconnected from the first negative wave cycle connection 12a and the second negative wave cycle connection 12b.

[0020] Furthermore, the switching circuit 9 is configured to provide or include a second switching state (see example...). Figure 2 In S2), under this second switching state, the DC bus capacitor 6 can be discharged via the first negative wave cycle connection 12a and the second negative wave cycle connection 12b. Specifically, under the second switching state, the DC bus capacitor 6 can be discharged via the first main discharge connection 10a, the first negative wave cycle connection 12a, the second negative wave cycle connection 12b, and the second main discharge connection 10b. It should be noted that under the second switching state, the DC bus capacitor 6 is disconnected from the first positive wave cycle connection 11a and the second positive wave cycle connection 11b.

[0021] The switching circuit 9 is further configured to provide or include a third switching state in which the DC bus capacitor 6 is disconnected from the first positive wave period connection 11a, the second positive wave period connection 11b, the first negative wave period connection 12a, and the second negative wave period connection 12b.

[0022] According to the invention, the bipolar discharge circuit 1, and in particular the switching circuit 9, enables the DC bus capacitor 6 to be discharged only via the line mains terminal T1 and the neutral mains terminal T2, and subsequently via the AC power supply 2. Discharging the DC bus capacitor 6 only via the switching circuit 9 and the AC power supply 2, rather than through the induction cooking zone Z, eliminates the high discharge (peak) current flowing through the induction cooking zone Z and its electronic components. This, in turn, avoids power dissipation in the induction cooking zone Z and thus prevents excessive heat buildup that could damage the electronic components. Therefore, discharging the DC bus capacitor 6 only via the switching circuit 9 and the AC power supply 2 increases the durability and lifespan of the induction cooking zone Z and also reduces acoustic noise when discharging the DC bus capacitor 6.

[0023] like Figure 1 As further shown, the bipolar discharge circuit 1 of the present invention includes a rectifier circuit section R connected after the rectifier 3, that is, the DC section of the circuit to the right of the dashed line. When the DC bus capacitor 6 discharges through the switching circuit 9 and the AC power supply 2, the induction cooking zone Z does not dissipate power, and only a very small amount of power is dissipated through the switching circuit 9. Therefore, almost all the discharge power is dissipated through the AC power supply 2 (that is, through the unrectified or AC section of the bipolar discharge circuit 1).

[0024] from Figure 1 It can be seen that the first positive wave cycle connection 11a and the second positive wave cycle connection 11b, as well as the first negative wave cycle connection 12a and the second negative wave cycle connection 12b, avoid the use of the discharge circuit loop D, which is composed of the rectifier circuit section R, to discharge the DC bus capacitor 6. For example, prior art induction cooking systems typically use the discharge circuit loop D, which includes the DC bus capacitor 6 and the induction cooking zone Z, to discharge the DC bus capacitor 6. However, the depicted discharge circuit loop D causes power dissipation in the induction cooking zone Z, resulting in its electronic components absorbing unwanted heat.

[0025] In other prior art systems disclosed in EP 3 768 042 A1 mentioned above, a discharge circuit loop including a DC bus capacitor and a discharge entity can be used, wherein the discharge entity is arranged in parallel with the resonant circuit so that the discharge current does not flow through the resonant circuit. Similar to the aforementioned prior art induction cooking system, this discharge circuit is entirely composed of the rectified AC voltage portion of the system. Therefore, when discharging the DC bus capacitor, the discharge current flows through the discharge circuit loop, and the power must be dissipated by the discharge entity. However, the discharge entity still cannot allow the DC bus capacitor to discharge rapidly and continuously over an extended period of time, otherwise there is a risk of damage to its electronic components due to excessive heat buildup.

[0026] As can be seen from the above, the bipolar discharge circuit 1 of the present invention avoids discharging the DC bus capacitor 6 only on one side of the rectifier circuit section R, because this would require a discharge circuit loop formed by the rectifier circuit section R. Such a discharge circuit loop would require power dissipation and could therefore lead to excessive heat accumulation in its electronic components. Specifically, the bipolar discharge circuit 1 provides a positive wave periodic circuit loop Dp in the first switching state, so that the DC bus capacitor 6 can be discharged via the first positive wave periodic connection 11a and the second positive wave periodic connection 11b in the first switching state; and the bipolar discharge circuit provides a negative wave periodic circuit loop Dn in the second switching state, so that the DC bus capacitor 6 can be discharged via the first negative wave periodic connection 12a and the second negative wave periodic connection 12b in the second switching state. Therefore, discharging the DC bus capacitor 6 is achieved through the line mains terminal T1 and the neutral line mains terminal T2 outside the rectifier circuit section R, thereby minimizing the power dissipation of the bipolar discharge circuit 1.

[0027] The first and second switching states of the switching circuit 9 allow the DC bus capacitor 6 to discharge via the line mains terminal T1 and the neutral mains terminal T2 when the line mains terminal T1 exhibits positive polarity during the first switching state or negative polarity during the second switching state. Therefore, the first and second switching states enable the DC bus capacitor 6 to discharge more rapidly, for example, twice during a single-wave cycle of the AC power supply 2. The ability to discharge the DC bus capacitor 6 more than once during a single-wave cycle allows for high-frequency detection of the cookware without generating acoustic noise, which typically manifests as a harsh "ticking" sound.

[0028] In the third switching state, once the DC bus capacitor 6 has been fully discharged just before the induction cooking zone Z is activated for heating or cooker detection, the DC bus capacitor 6 is disconnected from the mains terminal T1 and the neutral mains terminal T2.

[0029] Conventionally, many existing circuit arrangements for driving the induction cooking zone Z activate their resonant circuits for multiple cycles at the AC power frequency of the AC power supply 2. However, whenever the IGBT circuit arrangement G is disabled for an extended period, the DC bus capacitor 6 is fully charged, for example, to 325 V. Once the IGBT circuit arrangement G is reactivated to operate the induction cooking zone Z, the energy stored in the DC bus capacitor 6 must first be released via the induction cooking zone Z by switching the IGBT circuit arrangement G, which generates acoustic noise, high electromagnetic emissions, energy loss, and shortens the lifespan of electronic components. The switching circuit 9 and switchable connections 11a, 11b, 12a, 12b, as described above, eliminate the need to discharge the DC bus capacitor 6 via the induction cooking zone Z, and thus avoid the aforementioned problems.

[0030] In such Figure 1 In the exemplary embodiment depicted, in the first switching state, the first main discharge connection 10a is connected to the first positive wave periodic connection 11a, and the second main discharge connection 10b is connected to the second positive wave periodic connection 11b, wherein the first main discharge connection 10a is disconnected from the first negative wave periodic connection 12a, and the second main discharge connection 10b is disconnected from the second negative wave periodic connection 12b.

[0031] In the second switching state, the first main discharge connection 10a is connected to the first negative wave periodic connection 12a, and the second main discharge connection 10b is connected to the second negative wave periodic connection 12b, wherein the first main discharge connection 10a is disconnected from the first positive wave periodic connection 11a, and the second main discharge connection 10b is disconnected from the second positive wave periodic connection 11b.

[0032] In the third switching state, the first main discharge connection 10a is disconnected from the first positive wave period connection 11a and the first negative wave period connection 12a, and the second main discharge connection 10b is disconnected from the second positive wave period connection 11b and the second negative wave period connection 12b.

[0033] This embodiment provides two independent paths for discharging the DC bus capacitor 6: via a first positive cycle connection 11a and a second positive cycle connection 11b, or via a first negative cycle connection 12a and a second negative cycle connection 12b. Advantageously, the first positive cycle connection 11a and the second positive cycle connection 11b can be used to discharge the DC bus capacitor during the positive cycle (i.e., when the line mains terminal T1 exhibits positive polarity), and wherein the first negative cycle connection 12a and the second negative cycle connection 12b can be used to discharge the DC bus capacitor 6 during the negative cycle (i.e., when the line mains terminal T1 exhibits negative polarity).

[0034] By reference Figure 2 The discharge of the DC bus capacitor 6 using the first positive wave period connection 11a and the second positive wave period connection 11b, as well as the first negative wave period connection 12a and the second negative wave period connection 12b, can be further explained. The figure shows an example of the first switching state S1 and the second switching state S2 of the bipolar discharge circuit 1 relative to the AC voltage Vm of the AC power supply 2 during operation.

[0035] As depicted, in the embodiment, the first switching state S1 of the switching circuit 9 lasts during the positive wave period TP (see dashed line) of the AC power supply 2, and the second switching state S2 lasts during the negative wave period TN (see dashed line) of the AC power supply 2. It should be noted that, as mentioned, the "positive wave period" refers to the period during which the line AC terminal T1 exhibits positive polarity when connected to the AC power supply 2, and the "negative wave period" refers to the period during which the line AC terminal T1 exhibits negative polarity. Thus, the line AC terminal T1 exhibits the polarity of the AC voltage Vm, as... Figure 2 As shown.

[0036] In this embodiment, the positive wave period TP can be defined as starting when the line mains terminal T1 is at a predetermined first positive voltage Vp1 and ending when the line mains terminal T1 reaches a predetermined second positive voltage Vp2, wherein the first positive voltage Vp1 is higher than the second positive voltage Vp2. The negative wave period TN is defined as starting when the line mains terminal T1 is at a predetermined first negative voltage Vn1 and ending when the line mains terminal T1 reaches a predetermined second negative voltage Vn2, wherein the first negative voltage Vn1 is lower than the second negative voltage Vn2.

[0037] When the AC mains voltage Vm decreases from the first positive voltage Vp1 to the second positive voltage Vp2, the first switching state S1 allows the DC bus capacitor 6 to discharge through the line mains terminal T1 and the neutral mains terminal T2. Similarly, when the AC mains voltage Vm increases from the first negative voltage Vn1 to the second negative voltage Vn2, the second switching state S2 allows the DC bus capacitor 6 to discharge through the line mains terminal T1 and the neutral mains terminal T2.

[0038] When the AC mains voltage Vm operates at 50 Hz, it is understood that a single sine wave cycle is considered to last 1 / 50 = 20 milliseconds, therefore the depicted positive wave cycle TP and negative wave cycle TN lie within a time window of 20 / 4 = 5 milliseconds. Alternatively, operating the mains AC voltage Vm at 60 Hz changes the time window for the positive wave cycle TP and negative wave cycle TN to 1 / (60 / 50) 20 / 4 = 5 milliseconds. 4) Milliseconds.

[0039] The positive wave period TP and the negative wave period TN can be defined in another embodiment. Let T be the time period of a single sine wave of the AC power supply 2, i.e., a single sine wave of the AC voltage Vm. Then, the positive wave period TP is further defined as ranging from T / 4 to 1.2, as measured from the first zero-crossing point ZC1. The period begins between T / 4 and ends when the DC capacitor voltage Vdc between the positive capacitor terminal H1 and the negative capacitor terminal H2 is between 0 V and 30 V. Similarly, the negative wave period TN can be further defined as the period from T / 4 to 1.2, as measured from the second zero-crossing point ZC2. The process begins between T / 4 and ends when the DC capacitor voltage Vdc between the positive capacitor terminal H1 and the negative capacitor terminal H2 is between 0 V and 30 V. Here, the first zero-crossing point ZC1 and the second zero-crossing point ZC2 are each defined by a custom voltage time point (e.g., Vm(t)). Figure 2 As shown in the figure, at this voltage time point, the AC mains voltage Vm is essentially zero and changes polarity over time. At the first zero-crossing point ZC1, the AC mains voltage Vm changes from negative to positive polarity, and at the second zero-crossing point ZC2, the AC mains voltage Vm changes from positive to negative polarity. In the exemplary embodiment, T = 1 / 50 ms or T = 1 / 60 ms, thus corresponding to operating frequencies of 50 Hz and 60 Hz for the AC mains power supply 2, respectively.

[0040] It should be noted that, in the embodiment, the positive wave period TP can end when the DC line voltage (not depicted) between the positive DC line 7 and the negative DC line 8 is between 0 V and 30 V, and the negative wave period TN can also end when the DC line voltage is between 0 V and 30 V. Reference Figure 1 One possible embodiment is that the filter inductor Lf can be connected in series with the DC bus capacitor 6, positioned between the positive DC line 7 and the positive capacitor terminal H1. However, it will be understood that the filter inductor Lf has no effect on the DC voltage, and therefore the DC line voltage will be substantially the same as the DC capacitor voltage Vdc.

[0041] When the positive wave period TP is from T / 4 to 1.2 from the first zero-crossing point ZC1. The negative wave period TN begins between T / 4 and 1.2 from the second zero-crossing point ZC2. Starting between T / 4, this provides flexibility to efficiently switch specific semiconductor technologies, thereby optimizing the operation of the switching circuit 9. That is, for a particular semiconductor component, it may be beneficial to switch slightly later than T / 4 milliseconds, such as from the first zero-crossing point ZC1 or the second zero-crossing point ZC2.

[0042] When the DC bus capacitor 6 discharges, it is preferable that the DC capacitor voltage Vdc (or DC line voltage) is 0 V. However, to prevent the switching circuit 9 from operating for too long, an embodiment is provided in which the positive wave period TP and the negative wave period TN end before the DC capacitor voltage Vdc reaches 0 V. If the switching circuit 9 is still operating after the AC mains voltage Vm has passed the first zero-crossing point ZC1 or the second zero-crossing point ZC2, this may lead to excessive current flow. Therefore, in an advantageous embodiment, both the positive wave period TP and the negative wave period TN end when the DC capacitor voltage Vdc is between 10 V and 20 V.

[0043] from Figure 2 It is conceivable that in one embodiment, the duration of both the positive wave period TP and the negative wave period TN is equal to T / 4 (as shown by the vertical solid lines of TP and TN), i.e., from the maximum AC mains voltage Vm to the AC mains voltage of 0 V. However, in practice, the duration of the positive wave period TP and the negative wave period TN can be less than T / 4 as previously explained.

[0044] Various exemplary embodiments can be conceived regarding the switching circuit 9. For example, Figure 3A and Figure 3B The positive cycle switching portion S+ and the negative cycle switching portion S- according to an embodiment are shown respectively. In particular, an embodiment is provided in which the switching circuit 9 includes the positive cycle switching portion S+ (see...). Figure 3A The positive cycle switch section includes a first positive wave cycle connection 11a, a second positive wave cycle connection 11b, a first positive discharge connection 13a connected to the first main discharge connection 10a, and a second positive discharge connection 13b connected to the second main discharge connection 10b.

[0045] The positive cycle switch section S+ can be switched to discharge the DC bus capacitor 6 via the first positive discharge connection 13a, the first positive wave cycle connection 11a, the second positive wave cycle connection 11b, and the second positive discharge connection 13b.

[0046] from Figure 3B It is known that the switching circuit (9) may further include a negative cycle switching section S-, which includes a first negative wave cycle connection 12a, a second negative wave cycle connection 12b, a first negative discharge connection 14a connected to the first main discharge connection 10a, and a second negative discharge connection 14b connected to the second main discharge connection 10b.

[0047] The negative cycle switch section S- can be switched to discharge the DC bus capacitor 6 via the first negative discharge connection 14a, the first negative wave cycle connection 12a, the second negative wave cycle connection 12b, and the second negative discharge connection 14b.

[0048] As their names suggest, the positive cycle switching section S+ allows the DC bus capacitor 6 to discharge in the first switching state S1, i.e., during the positive wave period TP. The negative cycle switching section S- allows the DC bus capacitor 6 to discharge in the second switching state S2, i.e., during the negative wave period TN. Since the DC capacitor voltage Vdc is always positive, the positive switching section S+ allows the DC bus capacitor 6 to discharge when the line mains terminal T1 exhibits positive polarity, and the negative switching section S- allows the DC bus capacitor 6 to discharge when the line mains terminal T1 exhibits negative polarity. Therefore, during a single sinusoidal cycle of the AC mains power supply 2, the positive cycle switching section S+ and the negative cycle switching section S- provide two discharge opportunities.

[0049] In another embodiment, such as Figure 3A and Figure 3B As depicted, the positive cycle switching section S+ includes a positive first switch 15 for connecting a first positive cycle connection 11a to a first positive discharge connection 13a and a positive second switch 16 for connecting a second positive cycle connection 11b to a second positive discharge connection 13b. Positive logic circuitry 17 is provided and configured to switch the positive first switch 15 and the positive second switch 16.

[0050] Similarly, the negative cycle switching section S- includes a negative first switch 18 for connecting the first negative cycle connection 12a to the first negative discharge connection 14a and a negative second switch 19 for connecting the second negative cycle connection 12b to the second negative discharge connection 14b. A negative logic circuit 20 is provided and configured to switch the negative first switch 18 and the negative second switch 19. The positive logic circuit 17 and the negative logic circuit 20 are respectively capable of precisely timing and controlling the discharge of the DC bus capacitor 6 in either the first switching state S1 or the second switching state S2.

[0051] exist Figure 3A , Figure 3B In the depicted exemplary embodiment, the positive first switch 15 and the negative first switch 18 can be TRIACs, and each of the positive second switch 16 and the negative second switch 19 can be a MOSFET. When a TRIAC is used for the positive first switch 15 and the negative first switch 18, the positive wave period TP and the negative wave period TN may range from T / 4 to 1.2 after their respective zero-crossing points ZC1 and ZC2. It begins between T / 4. For example, for a 50 Hz AC mains power supply 2, when the TRIAC latches up after gate triggering, the positive wave period TP and the negative wave period TN may begin at approximately 5.9 milliseconds.

[0052] In practice, the discharge cycle of DC bus capacitor 6 during the positive wave period TP can be the same as the discharge cycle of DC bus capacitor 6 during the negative wave period TN. Therefore, an embodiment is conceivable in which the positive cycle switching section S+ and the negative cycle switching section S- have the same circuit arrangement, making the positive cycle switching section S+ and the negative cycle switching section S- interchangeable, thereby reducing the circuit complexity of the bipolar discharge circuit 1.

[0053] refer to Figure 1 To protect the bipolar discharge circuit 1 from overcurrent during the first switching state S1 and the second switching state S2, one embodiment is considered in which the switching circuit 9 further includes a resistor 20 connected to the second positive discharge connection 13b, the second negative discharge connection 14b, and the second main discharge connection 10b. A protection circuit 21 can then be provided, configured to measure the current through the resistor 20 and, based on the measured current, disconnect the positive first switch 15 and the positive second switch 16 or disconnect the negative first switch 18 and the negative second switch 19. In another embodiment, the protection circuit 21 is connected to the positive logic circuit 17 to disconnect the positive first switch 15 and the positive second switch 16, and to the negative logic circuit 20 to disconnect the negative first switch 18 and the negative second switch 19.

[0054] As previously mentioned, the bipolar discharge circuit 1 is advantageous when operating the induction cooking zone Z, as it reduces acoustic noise and electromagnetic emissions and improves the durability and lifespan of the electronic components in the induction cooking zone Z, since the DC bus capacitor 6 can be discharged only via the switching circuit 9.

[0055] In view of the above, the present invention also relates to an induction cooking cooker (not shown), which includes an induction cooking zone Z and a bipolar discharge circuit 1, wherein the induction cooking zone Z is connected to the positive capacitor terminal H1 and the negative capacitor terminal H2 of the bipolar discharge circuit 1. This induction cooking cooker provides an improved cooking experience because the induction cooking zone is silent when heating or detecting the cookware.

[0056] To further clarify how the bipolar discharge circuit 1 can be used or operated, a method for operating the bipolar discharge circuit 1 may be considered. For example, the method may include the following steps: Connect the AC power terminal T1 to the AC power line L of AC power supply 2, and connect the neutral power terminal T2 to the neutral line N of AC power supply 2.

[0057] In these steps, the "AC side" of the bipolar discharge circuit 1 is connected to the AC power supply 2, such as a conventional AC household outlet. Regarding the "DC side" of the bipolar discharge circuit 1, the method includes connecting the positive capacitor terminal H1 and the negative capacitor terminal H2 to the induction cooking zone Z. As previously described, the induction cooking zone Z may, for example, include a resonant circuit utilizing a zone capacitor C and a zone inductor L, wherein the zone inductor L is arranged to magnetically interact with the cookware W for heating or cookware detection.

[0058] Before activating the induction cooking zone Z for heating or detecting the cookware W, the method includes the following steps: The switching circuit 9 is sequentially switched to the first switching state and the second switching state; and Activate the sensing cooking zone Z for heating or detecting the cookware W.

[0059] It should be noted that sequentially switching the switching circuit 9 to the first switching state and the second switching state means switching from the first switching state to the second switching state sequentially and the required number of times, and vice versa. During this step, the DC bus capacitor 6 discharges via the switching circuit 9 during the positive wave period TP and the negative wave period TN.

[0060] As previously described, the first switching state S1 and the second switching state S2 can be provided by the positive cycle switching portion S+ and the negative cycle switching portion S- of the switching circuit 9. Therefore, when the bipolar discharge circuit 1 is in operation, switching to the first switching state S1 means that the DC bus capacitor 6 discharges through the positive cycle switching portion S+, and switching to the second switching state S2 means that the DC bus capacitor 6 discharges through the negative cycle switching portion S-. Therefore, in this embodiment, switching the switching circuit 9 to the first switching state S1 may include the following steps: When the AC voltage Vm at the mains terminal T1 is between a predetermined first positive voltage Vp1 and a predetermined second positive voltage Vp2, the DC bus capacitor 6 is discharged via the first positive cycle connection 11a and the second positive cycle connection 11b, wherein the first positive voltage Vp1 is higher than the second positive voltage Vp2. Switching the switching circuit 9 to the second switching state S2 includes the following steps: When the AC voltage Vm of the mains terminal T1 is between a predetermined first negative voltage Vn1 and a predetermined second negative voltage Vn2, the DC bus capacitor 6 is discharged via the first negative wave period connection 12a and the second negative wave period connection 12b, wherein the first negative voltage Vn1 is lower than the second negative voltage Vn2.

[0061] In view of the above, the present invention can now be summarized by the following embodiments: Example 1. A bipolar discharge circuit (1) for sensing a cooking zone (Z) to heat and detect a cooker (W), the bipolar discharge circuit comprising: a line mains terminal (T1) for connecting to the mains line (L) of an AC power supply (2) and a neutral line mains terminal (T2) for connecting to the neutral line (N) of the AC power supply (2). The rectifier (3) has a line connection (4a) connected to the line mains terminal (T1) and a neutral line connection (4b) connected to the neutral line mains terminal (T2), as well as a positive DC connection (5a) and a negative DC connection (5b). DC bus capacitor (6) having a positive capacitor terminal (H1) and a negative capacitor terminal (H2), wherein the positive capacitor terminal (H1) is connected to the positive DC connection (5a) via a positive DC line (7), and wherein the negative capacitor terminal (H2) is connected to the negative DC connection (5b) via a negative DC line (8), and wherein the positive capacitor terminal (H1) and the negative capacitor terminal (H2) are configured to be connected to the induction cooking zone (Z) for heating and detecting the cookware (W); A switching circuit (9) includes a first main discharge connection (10a) connected to the positive DC line (7) and a second main discharge connection (10b) connected to the negative DC line (8), and wherein the switching circuit (9) further includes: The first positive wave period connection (11a) connected to the mains terminal (T1) of the line and the second positive wave period connection (11b) connected to the mains terminal (T2) of the neutral line, and A first negative wave cycle connection (12a) is connected to the neutral line mains terminal (T2), and a second negative wave cycle connection (12b) is connected to the line mains terminal (T1); and The switching circuit (9) is configured to provide: In the first switching state, the DC bus capacitor (6) can be discharged via the first positive wave periodic connection (11a) and the second positive wave periodic connection (11b); In the second switching state, the DC bus capacitor (6) can be discharged via the first negative wave period connection (12a) and the second negative wave period connection (12b); In the third switching state, the DC bus capacitor (6) is disconnected from the first positive wave period connection (11a), the second positive wave period connection (11b), the first negative wave period connection (12a), and the second negative wave period connection (12b).

[0062] Example 2. According to the bipolar discharge circuit of Example 1, wherein, in the first switching state, the first main discharge connection (10a) is connected to the first positive wave periodic connection (11a), and the second main discharge connection (10b) is connected to the second positive wave periodic connection (11b), and Specifically, the first main discharge connection (10a) is disconnected from the first negative wave period connection (12a), and the second main discharge connection (10b) is disconnected from the second negative wave period connection (12b). In the second switch state, The first main discharge connection (10a) is connected to the first negative wave periodic connection (12a), and the second main discharge connection (10b) is connected to the second negative wave periodic connection (12b). The first main discharge connection (10a) is disconnected from the first positive wave periodic connection (11a), and the second main discharge connection (10b) is disconnected from the second positive wave periodic connection (11b). In the third switch state, The first main discharge connection (10a) is disconnected from the first positive wave period connection (11a) and the first negative wave period connection (12a), and the second main discharge connection (10b) is disconnected from the second positive wave period connection (11b) and the second negative wave period connection (12b).

[0063] Example 3. According to the bipolar discharge circuit of Example 1 or 2, the first switching state lasts during the positive wave period (TP) of the AC power supply (2), and the second switching state lasts during the negative wave period (TN) of the AC power supply (2). The positive wave period (TP) is defined as starting when the mains terminal (T1) of the line is at a predetermined first positive voltage and ending when the mains terminal (T1) of the line reaches a predetermined second positive voltage, wherein the first positive voltage is higher than the second positive voltage; and The negative wave period (TN) is defined as starting when the mains terminal (T1) of the line is at a predetermined first negative voltage and ending when the mains terminal (T1) of the line reaches a predetermined second negative voltage, wherein the first negative voltage is lower than the second negative voltage.

[0064] Example 4. The bipolar discharge circuit according to Example 3, wherein the positive wave period (TP) is further defined as T / 4 to 1.2 of the time period T of a single sine wave of the AC power supply (2) as measured from the first zero crossing point (ZC1). It begins between T / 4 and ends when the DC capacitor voltage (Vdc) between the positive capacitor terminal (H1) and the negative capacitor terminal (H2) is between 0 V and 30 V. The negative wave period (TN) is further defined as the time period T from T / 4 to 1.2, as measured from the second zero-crossing point (ZC2). It begins between T / 4 and ends when the voltage of the DC capacitor between the positive capacitor terminal (H1) and the negative capacitor terminal (H2) is between 0 V and 30 V.

[0065] Example 5. The bipolar discharge circuit according to Example 4, wherein T = 1 / 50 milliseconds or T = 1 / 60 milliseconds.

[0066] Example 6. A bipolar discharge circuit according to any one of Examples 1 to 5, wherein the switching circuit (9) includes a positive periodic switching section (S+), the positive periodic switching section including the first positive wave periodic connection (11a), the second positive wave periodic connection (11b), and a first positive discharge connection (13a) connected to the first main discharge connection (10a) and a second positive discharge connection (13b) connected to the second main discharge connection (10b), and The positive cycle switch (S+) can be switched to discharge the DC bus capacitor (6) via the first positive discharge connection (13a), the first positive wave cycle connection (11a), the second positive wave cycle connection (11b) and the second positive discharge connection (13b); The switching circuit (9) further includes a negative cycle switching section (S-), which includes the first negative wave cycle connection (12a), the second negative wave cycle connection (12b), a first negative discharge connection (14a) connected to the first main discharge connection (10a), and a second negative discharge connection (14b) connected to the second main discharge connection (10b). The negative cycle switch (S-) can be switched to discharge the DC bus capacitor (6) via the first negative discharge connection (14a), the first negative wave cycle connection (12a), the second negative wave cycle connection (12b) and the second negative discharge connection (14b).

[0067] Example 7. The bipolar discharge circuit according to Example 6, wherein the positive periodic switching section (S+) includes: A positive first switch (15) for connecting the first positive wave periodic connection (11a) to the first positive discharge connection (13a); and a positive second switch (16) for connecting the second positive wave periodic connection (11b) to the second positive discharge connection (13b); and a positive logic circuit (17) configured to switch the positive first switch (15) and the positive second switch (16); wherein the negative periodic switch section (S-) includes: A negative first switch (18) for connecting the first negative wave periodic connection (12a) to the first negative discharge connection (14a); and a negative second switch (19) for connecting the second negative wave periodic connection (12b) to the second negative discharge connection (14b); and a negative logic circuit (20) configured to switch the negative first switch (18) and the negative second switch (19).

[0068] Example 8. The bipolar discharge circuit according to Example 7, wherein each of the positive first switch (15) and the negative first switch (18) is a TRIAC, and wherein each of the positive second switch (16) and the negative second switch (19) is a MOSFET.

[0069] Example 9. A bipolar discharge circuit according to any one of Examples 6 to 8, wherein the positive periodic switching portion (S+) and the negative periodic switching portion (S-) have the same circuit arrangement.

[0070] Example 10. A bipolar discharge circuit according to any one of Examples 7 to 9, wherein the switching circuit (9) further includes a resistor (20) connected to the second positive discharge connection (13b), the second negative discharge connection (14b) and the second main discharge connection (10b), and the switching circuit further includes Protection circuit (21) is configured to measure the current through the resistor (20) and, based on the measured current, disconnect the positive first switch (15) and the positive second switch (16) or disconnect the negative first switch (18) and the negative second switch (19).

[0071] Example 11. An induction cooking stove, comprising an induction cooking zone (Z) and a bipolar discharge circuit (1) according to any one of Examples 1 to 10, wherein the induction cooking zone (Z) is connected to the positive capacitor terminal (H1) and the negative capacitor terminal (H2) of the bipolar discharge circuit (9).

[0072] Example 12. A method of operating a bipolar discharge circuit (1) according to any one of Examples 1 to 10, the method comprising the following steps: Connect the mains terminal (T1) of the line to the mains line (L) of the AC power supply (2), and connect the neutral line mains terminal (T2) to the neutral line (N) of the AC power supply (2). Connect the positive capacitor terminal (H1) and the negative capacitor terminal (H2) to the induction cooking zone (Z); and Before activating the sensing cooking zone (Z) for heating or detecting cookware (W), The switching circuit (9) is sequentially switched to the first switching state and the second switching state; and subsequently, Activate the sensing cooking zone (Z) to heat or detect the cookware (W).

[0073] Example 13. According to the method of Example 12, the step of switching the switch circuit (9) to the first switch state includes the following steps: When the AC voltage (Vm) of the mains terminal (T1) of the line is between a predetermined first positive voltage and a predetermined second positive voltage, the DC bus capacitor (6) is discharged via the first positive wave periodic connection (11a) and the second positive wave periodic connection (11b), wherein the first positive voltage is higher than the second positive voltage; Furthermore, the step of switching the switch circuit (9) to the second switch state includes the following steps: When the AC voltage (Vm) of the mains terminal (T1) of the line is between a predetermined first negative voltage and a predetermined second negative voltage, the DC bus capacitor (6) is discharged via the first negative wave periodic connection (12a) and the second negative wave periodic connection (12b), wherein the first negative voltage is lower than the second negative voltage.

[0074] The invention has been described above with reference to several exemplary embodiments discussed above and illustrated in the accompanying drawings. Modifications and alternative implementations of some parts or elements are possible and are included within the scope of protection as defined in the appended claims.

Claims

1. A bipolar discharge circuit (1) for sensing a cooking zone (Z) to heat and detect a cookware (W), the bipolar discharge circuit comprising: The line mains terminal (T1) for connecting the mains line (L) to the AC power supply (2) and the neutral line mains terminal (T2) for connecting the mains neutral line (N) to the AC power supply (2). The rectifier (3) has a line connection (4a) connected to the line mains terminal (T1) and a neutral line connection (4b) connected to the neutral line mains terminal (T2), as well as a positive DC connection (5a) and a negative DC connection (5b). DC bus capacitor (6) having a positive capacitor terminal (H1) and a negative capacitor terminal (H2), wherein the positive capacitor terminal (H1) is connected to the positive DC connection (5a) via a positive DC line (7), and wherein the negative capacitor terminal (H2) is connected to the negative DC connection (5b) via a negative DC line (8), and wherein the positive capacitor terminal (H1) and the negative capacitor terminal (H2) are configured to be connected to the induction cooking zone (Z) for heating and detecting the cookware (W); A switching circuit (9) includes a first main discharge connection (10a) connected to the positive DC line (7) and a second main discharge connection (10b) connected to the negative DC line (8), and wherein the switching circuit (9) further includes: The first positive wave period connection (11a) connected to the mains terminal (T1) of the line and the second positive wave period connection (11b) connected to the mains terminal (T2) of the neutral line, and A first negative wave cycle connection (12a) is connected to the neutral line mains terminal (T2), and a second negative wave cycle connection (12b) is connected to the line mains terminal (T1); and The switching circuit (9) is configured to provide: In the first switching state, the DC bus capacitor (6) can be discharged via the first positive wave periodic connection (11a) and the second positive wave periodic connection (11b); In the second switching state, the DC bus capacitor (6) can be discharged via the first negative wave period connection (12a) and the second negative wave period connection (12b); In the third switching state, the DC bus capacitor (6) is disconnected from the first positive wave period connection (11a), the second positive wave period connection (11b), the first negative wave period connection (12a), and the second negative wave period connection (12b).

2. The bipolar discharge circuit according to claim 1, wherein, In the first switching state, the first main discharge connection (10a) is connected to the first positive wave periodic connection (11a), and the second main discharge connection (10b) is connected to the second positive wave periodic connection (11b). Specifically, the first main discharge connection (10a) is disconnected from the first negative wave period connection (12a), and the second main discharge connection (10b) is disconnected from the second negative wave period connection (12b). In the second switch state, The first main discharge connection (10a) is connected to the first negative wave periodic connection (12a), and the second main discharge connection (10b) is connected to the second negative wave periodic connection (12b). The first main discharge connection (10a) is disconnected from the first positive wave periodic connection (11a), and the second main discharge connection (10b) is disconnected from the second positive wave periodic connection (11b). In the third switch state, The first main discharge connection (10a) is disconnected from the first positive wave period connection (11a) and the first negative wave period connection (12a), and the second main discharge connection (10b) is disconnected from the second positive wave period connection (11b) and the second negative wave period connection (12b).

3. The bipolar discharge circuit according to claim 1 or 2, wherein, The first switching state lasts during the positive wave period (TP) of the AC power supply (2), and the second switching state lasts during the negative wave period (TN) of the AC power supply (2). The positive wave period (TP) is defined as starting when the mains terminal (T1) of the line is at a predetermined first positive voltage and ending when the mains terminal (T1) of the line reaches a predetermined second positive voltage, wherein the first positive voltage is higher than the second positive voltage; and The negative wave period (TN) is defined as starting when the mains terminal (T1) of the line is at a predetermined first negative voltage and ending when the mains terminal (T1) of the line reaches a predetermined second negative voltage, wherein the first negative voltage is lower than the second negative voltage.

4. The bipolar discharge circuit according to claim 3, wherein, The positive wave period (TP) is further defined as T / 4 to 1.2 of the time period T of a single sine wave of the AC power supply (2), as measured from the first zero-crossing point (ZC1). It begins between T / 4 and ends when the DC capacitor voltage (Vdc) between the positive capacitor terminal (H1) and the negative capacitor terminal (H2) is between 0 V and 30 V, and The negative wave period (TN) is further defined as the time period T from T / 4 to 1.2, as measured from the second zero-crossing point (ZC2). It begins between T / 4 and ends when the voltage of the DC capacitor between the positive capacitor terminal (H1) and the negative capacitor terminal (H2) is between 0 V and 30 V.

5. The bipolar discharge circuit according to claim 4, wherein, T = 1 / 50 milliseconds or T = 1 / 60 milliseconds.

6. The bipolar discharge circuit according to any one of claims 1 to 5, wherein, The switching circuit (9) includes a positive cycle switching section (S+), which includes the first positive wave cycle connection (11a), the second positive wave cycle connection (11b), a first positive discharge connection (13a) connected to the first main discharge connection (10a), and a second positive discharge connection (13b) connected to the second main discharge connection (10b). The positive cycle switch (S+) can be switched to discharge the DC bus capacitor (6) via the first positive discharge connection (13a), the first positive wave cycle connection (11a), the second positive wave cycle connection (11b) and the second positive discharge connection (13b); The switching circuit (9) further includes a negative cycle switching section (S-), which includes the first negative wave cycle connection (12a), the second negative wave cycle connection (12b), a first negative discharge connection (14a) connected to the first main discharge connection (10a), and a second negative discharge connection (14b) connected to the second main discharge connection (10b). The negative cycle switch (S-) can be switched to discharge the DC bus capacitor (6) via the first negative discharge connection (14a), the first negative wave cycle connection (12a), the second negative wave cycle connection (12b) and the second negative discharge connection (14b).

7. The bipolar discharge circuit according to claim 6, wherein, The positive cycle switching section (S+) includes: A positive first switch (15) for connecting the first positive wave periodic connection (11a) to the first positive discharge connection (13a); and a positive second switch (16) for connecting the second positive wave periodic connection (11b) to the second positive discharge connection (13b); and a positive logic circuit (17) configured to switch the positive first switch (15) and the positive second switch (16); wherein the negative periodic switch section (S-) includes: A negative first switch (18) for connecting the first negative wave periodic connection (12a) to the first negative discharge connection (14a); and a negative second switch (19) for connecting the second negative wave periodic connection (12b) to the second negative discharge connection (14b); and a negative logic circuit (20) configured to switch the negative first switch (18) and the negative second switch (19).

8. The bipolar discharge circuit according to claim 7, wherein, Each of the positive first switch (15) and the negative first switch (18) is a TRIAC, and each of the positive second switch (16) and the negative second switch (19) is a MOSFET.

9. The bipolar discharge circuit according to any one of claims 6 to 8, wherein, The positive cycle switching section (S+) and the negative cycle switching section (S-) have the same circuit layout.

10. The bipolar discharge circuit according to any one of claims 7 to 9, wherein, The switching circuit (9) further includes a resistor (20) connected to the second positive discharge connection (13b), the second negative discharge connection (14b), and the second main discharge connection (10b), and the switching circuit further includes Protection circuit (21) is configured to measure the current through the resistor (20) and, based on the measured current, disconnect the positive first switch (15) and the positive second switch (16) or disconnect the negative first switch (18) and the negative second switch (19).

11. An induction cooking stove, comprising an induction cooking zone (Z) and a bipolar discharge circuit (1) according to any one of claims 1 to 10, wherein, The induction cooking zone (Z) is connected to the positive capacitor terminal (H1) and the negative capacitor terminal (H2) of the bipolar discharge circuit (9).

12. A method of operating the bipolar discharge circuit (1) according to any one of claims 1 to 10, the method comprising the following steps: Connect the mains terminal (T1) of the line to the mains line (L) of the AC power supply (2), and connect the neutral line mains terminal (T2) to the neutral line (N) of the AC power supply (2). Connect the positive capacitor terminal (H1) and the negative capacitor terminal (H2) to the induction cooking zone (Z); and Before activating the sensing cooking zone (Z) for heating or detecting cookware (W), The switching circuit (9) is sequentially switched to the first switching state and the second switching state; and subsequently, Activate the sensing cooking zone (Z) to heat or detect the cookware (W).

13. The method according to claim 12, wherein, The steps to switch the switching circuit (9) to the first switching state include the following steps: When the AC voltage (Vm) of the mains terminal (T1) of the line is between a predetermined first positive voltage and a predetermined second positive voltage, the DC bus capacitor (6) is discharged via the first positive wave periodic connection (11a) and the second positive wave periodic connection (11b), wherein the first positive voltage is higher than the second positive voltage; Furthermore, the step of switching the switch circuit (9) to the second switch state includes the following steps: When the AC voltage (Vm) of the mains terminal (T1) of the line is between a predetermined first negative voltage and a predetermined second negative voltage, the DC bus capacitor (6) is discharged via the first negative wave periodic connection (12a) and the second negative wave periodic connection (12b), wherein the first negative voltage is lower than the second negative voltage.

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