Discharge circuit

Abstract

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

Description

[0001] Discharge circuit

[0002] Field of the invention

[0003] The present invention relates to a discharge circuit, in particular a bipolar discharge circuit for an induction cooking zone.

[0004] Background art

[0005] International patent application WO 2022 / 096122 A1 discloses a circuit arrangement for discharging an intermediate circuit capacitor for induction coils of a cooking hob and to lower peak currents in the circuit during discharge. The circuit arrangement utilizes a separate discharge circuit for discharging the intermediate circuit capacitor during a predetermined time period when a mains voltage is positive between two zero crossings thereof.

[0006] European patent application EP 3 768 042 A1 discloses a system and method for controlling the provision of electric power to an induction coil of an induction hob. The system comprises circuitry including an input for receiving rectified AC-voltage, at least one switching element for providing pulsed electric power to an induction coil, a capacitor being connected in parallel to the switching element and a discharging entity being configured to enable a discharging of said capacitor. The system further comprises a control entity, wherein the control entity is configured to perform subsequent control cycles, wherein in said control cycle the control entity is configured to discharge the capacitor based on the discharging entity and, after discharging the capacitor, to start a switching operation of the switching element in order to provide pulsed electric power to the induction coil.

[0007] Summary of the invention

[0008] The present invention seeks to provide an improved discharge circuit, in particular a bipolar discharge circuit for an induction cooking zone for reducing acoustic noise when the induction cooking zone is activated for heating cookware or when the induction cooking zone detects cookware. The bipolar discharge circuit of the present invention further improves durablity and longgevity of electronic components, reduces energy losses as well as electromagnetic emmisions.

[0009] According to the present invention, a bipolar discharge circuit as mentioned above is provide comprising a line mains terminal for connection to a mains line of a mains AC source and a neutral mains terminal for connection to a mains neutral of the mains AC source; a rectifier having a line connection connected to the line mains terminal and a neutral connection connected to the neutral mains terminal, and a positive DC connection and a negative DC connection; a DC bus capacitor having a positive capacitor terminal and a negative capacitor terminal, wherein the positive capacitor terminal is connected to the positive DC connection via a positive DC line and wherein the negative capacitor terminal is connected to the negative DC connection via a negative DC line, and wherein the positive capacitor terminal and the negative capacitor terminal are configured for connection to an induction cooking zone for heating and detecting cookware; and a 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 a first positive wave period connection connected to the line mains terminal and a second positive wave period connection connected the neutral mains terminal, and a first negative wave period connection connected to the neutral mains terminal and a second negative wave period connection connected to the line mains terminal; and wherein the switching circuit is configured to provide a first switch state in which the DC bus capacitor is dischargeable via the first positive wave period connection and the second positive wave period connection; a second switch state in which the DC bus capacitor is dischargeable via the first negative wave period connection and the second negative wave period connection; a third switch state in which the DC bus capacitor is disconnected from the first positive wave period connection, the second positive wave period connection, the first negative wave period connection and the second negative wave period connection.

[0010] The bipolar discharge circuit of the present invention, and in particular the switching circuit, allows the DC bus capacitor to be solely discharged via the line mains terminal and neutral mains terminal, thereby avoiding discharging the DC bus capacitor via an induction cooking zone connected to the positive capacitor terminal and the negative capacitor terminal. So in contrast to discharging the DC bus capacitor via the induction cooking zone, solely discharging the DC bus capacitor via the switching circuit, and through the mains AC source via the line mains terminal and neutral mains terminal, eliminates high discharge (peak) currents flowing through the induction cooking zone and electronic components thereof. This, in turn, avoids power dissipation and thermal losses by the induction cooking zone and as such prevents excessive heat accumulation that could damage the electronic components of the induction cooking zone. Therefore, discharging the DC bus capacitor through the switching circuit and mains AC source increases durability and longevity of the induction cooking zone and further reduces acoustic noise.

[0011] The first switch state and the second switch state of the switching circuit allows the DC bus capacitor to be discharged via the line mains terminal and the neutral mains terminal when the line mains terminal exhibits positive polarity during the first switch state or negative polarity during the second switch state. Therefore, the DC bus capacitor can be discharged in faster succession, e.g. two times during a single sinusoidal wave period of the mains AC source connected to the line mains terminal and neutral mains terminal. Being able to discharge the DC bus capacitor more than once during a single sinusoidal wave period also enables high frequency detection of cookware without acoustic noise.

[0012] The third switch state provided by the switching circuit allows the DC bus capacitor to be disconnected from the line mains terminal and neutral mains terminal once the DC bus capacitor is sufficiently discharged. In this third switch state, cookware detection and normal operation of the induction cooking zone for heating or detecting cookware can start or resume.

[0013] Short description of drawings

[0014] The present invention will be discussed in more detail below, with reference to the attached drawings, in which

[0015] Figure 1 shows a bipolar discharge circuit connected to a mains AC source and an induction cooking zone according to an embodiment of the present invention;

[0016] Figure 2 shows an example of a bipolar discharging circuit in operation and switch states thereof relative to a mains AC voltage according to an embodiment of the present invention;

[0017] Figure 3A and 3B show a positive period switching part and a negative period switching part as used by the bipolar discharge circuit according to an embodiment of the present invention.

[0018] Detailed description of embodiments

[0019] Figure 1 shows a bipolar discharge circuit 1 connected to a mains AC source 2 and an induction cooking zone Z according to an embodiment of the present invention. The mains AC source 2 may be viewed as a regular mains AC power socket found in residential buildings, commercial buildings and the like, wherein the mains AC source 2 may operate at e.g. 230V and 50 Hertz or 120V and 60 Hertz depending on geographical location. The induction cooking zone Z may be a standard or known induction cooking zone Z. As depicted, an exemplary induction cooking zone Z comprises a resonant circuit utilizing a zone capacitor C and zone inductor L, e.g. in parallel, wherein the zone inductor L is arranged to magnetically interact with cookware Wfor heating or detection thereof. The resonant circuit comprising the zone capacitor C and zone inductor L may be operated by an IGBT switch arrangement G. However, do note that the induction cooking zone Z may utilize different circuit topologies, such as half bridge topologies,

[0020] As further shown in Figure 1 , the bipolar switching circuit 1 comprises a line mains terminal T 1 for connection to a mains line L of the mains AC source 2 and a neutral mains terminal T2 for connection to a mains neutral N of the mains AC source 2. The mains line terminal T 1 and neutral mains terminal T2 may be configured or adapted for connection to a regular mains AC power socket.

[0021] The bipolar switching circuit 1 further comprises 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 further comprises a positive (+) DC connection 5a and a negative (-) DC connection 5b.

[0022] Further, a DC bus capacitor s is provided and comprises 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. As shown in Figure 1 , in an exemplary embodiment, the negative DC line 8 will be grounded. The positive capacitor terminal H1 and negative capacitor terminal H2 are then configured for connection to the induction cooking zone Z for heating and detecting cookware W.

[0023] It is important to note that in other embodiments it is possible that the bipolar discharge circuit 1 comprises a further DC bus capacitor 6’ having a further positive capacitor terminal H1’ and further negative capacitor terminal H2’, wherein the further positive capacitor terminal H1’ is connected to the positive DC connection 5a via the positive DC line 7 and wherein the further negative capacitor terminal H2’ is connected to the negative DC connection 5b via the negative DC line 8. As depicted in Figure 1 , a further induction cooking zone Z’ may be connected to the further positive capacitor terminal H1’ and the further negative capacitor terminal H2’.

[0024] Like the induction cooking zone Z, the further induction cooking zone Z’ may comprise a similar resonant circuit utilizing a further zone capacitor C’ and further zone inductor L’, e.g. in parallel, wherein the further zone inductor L’ is arranged to magnetically interact with cookware, e.g. further cookware W’, for heating or detection thereof. The further resonant circuit may be operated by a further IGBT switch arrangement G’.

[0025] The bipolar switching circuit 1 as shown in Figure 1 further comprises a switching circuit 9, wherein the switching circuit 9 comprises 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 further comprises a first positive wave period connection 11a connected to the line mains terminal T1 and a second positive wave period connection 11 b connected the neutral mains terminal T2, and a first negative wave period connection 12a connected to the neutral mains terminal T2 and a second negative wave period connection 12b connected to the line mains terminal T1 .

[0026] As will be explained in further detail below, the naming scheme “positive wave period” used for the first and second positive wave period connection 11a, 11 b refers to a period when the line mains terminal T1 exhibits positive polarity and the term “negative wave period” used for the first and second negative wave period connection 12a, 12b refers to a period when the line mains terminal T1 exhibits negative polarity.

[0027] The switching circuit 9 is configured to provide, or comprises, a first switch state (see e.g. S1 in Figure 2) in which the DC bus capacitor s is dischargeable via the first positive wave period connection 11 a and the second positive wave period connection 11 b. In particular, in the first switch state the DC bus capacitor s is dischargeable via the first main discharge connection 10a, the first positive wave period connection 11a, the second positive wave period connection 11 b, and the second main discharge connection 10b. Note that in the first switch state, the DC bus capacitor 6 is disconnected from the first negative wave period connection 12a and the second negative wave period connection 12b.

[0028] Further, the switching circuit 9 is configured to provide, or comprises, a second switch state (see e.g. S2 in Figure 2) in which the DC bus capacitor s is dischargeable via the first negative wave period connection 12a and the second negative wave period connection 12b. In particular, in the second switch state the DC bus capacitor s is dischargeable via the first main discharge connection 10a, the first negative wave period connection 12a, the second negative wave period connection 12b, and the second main discharge connection 10b. Note that in the second switch state, the DC bus capacitor s is disconnected from the first positive wave period connection 11a and the second positive wave period connection 11 b.

[0029] The switching circuit 9 is further configured to provide, or comprises, a third switch state in which the DC bus capacitor s is disconnected from the first positive wave period connection 11a, the second positive wave period connection 11 b, the first negative wave period connection 12a and the second negative wave period connection 12b.

[0030] According to the present invention, the bipolar discharge circuit 1 and in particular the switching circuit 9, allows the DC bus capacitor 6 to be solely dischargeable via the line mains terminal T 1 and neutral mains terminal T2, and subsequently through the mains AC source 2. Solely discharging the DC bus capacitor s via the switching circuit 9 and the mains AC source 2, but not through the induction cooking zone Z, eliminates high discharge (peak) currents flowing through the induction cooking zone Z and electronic components thereof. This, in turn, avoids power dissipation by the induction cooking zone Z and as such prevents excessive heat accumulation that could damage the electronic components. Therefore, discharging the DC bus capacitor 6 solely through the switching circuit 9 and the mains AC source 2 increases durability and longevity of the induction cooking zone Z, and also reduces acoustic noise when discharging the DC bus capacitor 6.

[0031] As further shown in Figure 1 , the bipolar discharge circuit 1 of the present invention comprises a rectified circuit part R connected after the rectifier 3, i.e. a DC part of the circuit to the right of the dotted line. When the DC bus capacitor s is discharged through the switching circuit 9 and the mains AC source 2, then the induction cooking zone Z dissipates no power and only very little power is dissipated by the switching circuit 9. So almost all discharged power is dissipated via the mains AC source 2, i.e. via the unrectified or AC part of the bipolar discharge circuit 1.

[0032] From Figure 1 it can be seen that the first and second positive wave period connections 11a, 11 b and the first and negative wave period connections 12a, 12b circumvent the use of a discharge circuit loop D comprised by the rectified circuit part R for discharging the DC bus capacitor 6. For example, prior art induction cooking systems would typically utilize the discharge circuit loop D comprising the DC bus capacitor s and the induction cooking zone Z for discharging the DC bus capacitor s. However, the depicted discharge circuit loop D causes power dissipation by the induction cooking zone Z, resulting in unwanted heat absorption by electronic components thereof.

[0033] In other prior art systems as disclosed in EP 3 768 042 A1 mentioned earlier, a discharge circuit loop may be utilized comprising a DC bus capacitor and a discharging entity, wherein the discharging entity is arranged parallel to a resonance circuit such that discharge currents do not flow through the resonance circuit. Like the prior art induction cooking systems mentioned above, this discharge circuit loop is entirely comprised by a rectified AC-voltage part of the system. Consequently, when discharging the DC bus capacitor, discharge currents flow through the discharge circuit loop and power must be dissipated by the discharging entity. However, the discharging entity would still not allow the DC bus capacitor to be discharged in fast succession over extended periods of time without risking damaging electronic components thereof due to excessive heat accumulation.

[0034] From the above it follows that the bipolar discharge circuit 1 of the present invention circumvents discharging the DC bus capacitor s only at the side of the rectified circuit part R as this requires a discharge circuit loop comprised by the rectified circuit part R. Such a discharge circuit loop will need to dissipate power and as a result may suffer from excessive heat accumulation by electronic components thereof. In particular, the bipolar discharge circuit 1 provides a positive wave period circuit loop Dp in the first switch state, so wherein the DC bus capacitor 6 is dischargeable via the first positive wave period connection 11a and the second positive wave period connection 11 b, and a negative wave period circuit loop Dn in the second switch state, so wherein the DC bus capacitor s is dischargeable via the first negative wave period connection 12a and the second negative wave period connection 12b. Therefore, discharging the DC bus capacitor s is achieved through the line mains terminal T1 and the neutral mains terminal T2 external from the rectified circuit part R, thereby minimizing power dissipation by the bipolar discharge circuit 1 .

[0035] The first switch state and the second switch state of the switching circuit 9 allows the DC bus capacitor s to be discharged via the line mains terminal T1 and the neutral mains terminal T2 when the line mains terminal T1 exhibits positive polarity during the first switch state or negative polarity during the second switch state. As a result, the first switch state and the second switch state allow the DC bus capacitor 6 to be discharged in faster succession, e.g. two times during a single wave period of the mains AC source 2. Being able to discharge the DC bus capacitor 6 more than once during the single wave period enables high frequency detection of cookware without acoustic noise, which is often experienced as loud “ticking” noises.

[0036] In the third switch state, the DC bus capacitor s is disconnected from the line mains terminal T1 and neutral mains terminal T2 once the DC bus capacitor s is sufficiently discharged just before the induction cooking zone Z is activated for heating or cookware detections.

[0037] Conventionally, many prior art circuit arrangements fordriving the induction cooking zone Z activate a resonant circuit thereof multiple periods of a mains frequency of the mains AC source 2. However, each time an IGBT circuit arrangement G is disabled for longer periods, the DC bus capacitor 6 charges fully, e.g. up to 325V. Once the IGBT circuit arrangement G is activated again for operating the induction cooking zone Z, energy stored in the DC bus capacitor s has to be discharged first via the induction cooking zone Z by switching the IGBT circuit arrangement G, thereby causing acoustic noise, high electromagnetic emissions and energy losses, as well as reduced lifetime of electronic components. The switching circuit 9 and the switchable connections 11a, 11 b, 12a, 12b as mentioned above eliminate the need for discharging the DC bus capacitor s via the induction cooking zone Z and as such avoiding the aforementioned problems.

[0038] In an exemplary embodiment as depicted in Figure 1 , in the first switch state, the first main discharge connection 10a is connected to the first positive wave period connection 11a, and the second main discharge connection 10b is connected to the second positive wave period connection 11 b, and wherein 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.

[0039] In the second switch state, the first main discharge connection 10a is connected to the first negative wave period connection 12a, and the second main discharge connection 10b is connected to the second negative wave period connection 12b, and wherein the first main discharge connection 10a is disconnected from the first positive period wave connection 11a, and the second main discharge connection 10b is disconnected from the second positive wave period connection 11 b.

[0040] 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 wherein the second main discharge connection 10b is disconnected from the second positive wave period connection 11 b and the second negative wave period connection 12b.

[0041] This embodiment provides two disjoint pathways for discharging the DC bus capacitor 6, so either via the first and second positive wave period connection 11 a, 11 b, or via the first and second negative wave period connection 12a, 12b. Advantageously. The first and second positive wave period connection 11a, 11 b can be utilized for discharging the DC bus capacitor during a positive wave period, i.e. when the line mains terminal T1 exhibits positive polarity, and wherein the first and second negative wave period connection 12a, 12b can be utilized for discharging the DC bus capacitor 6 during a negative wave period, i.e. when the line mains terminal T 1 exhibits negative polarity.

[0042] Utilization of the first and second positive wave period connections 11a, 11 b and the first and second negative wave period connections 12a, 12b for discharging the DC bus capacitor s can be further explained by referring to Figure 2, showing an example of the first switch state S1 and the second switch state S2 of the bipolar discharging circuit 1 in operation relative to a mains AC voltage Vm of the mains AC source 2.

[0043] As depicted, in an embodiment the first switch state S1 of the switching circuit 9 extends during a positive wave period TP (see dotted line) of the mains AC source 2 and wherein the second switch state S2 extends during a negative wave period TN (see dotted line) of the mains AC source 2. Note that it has already been mentioned that the “positive wave period” refers to a period when the line mains terminal T1 exhibits positive polarity when connected to the mains AC source 2, and where the “negative wave period” refers to a period when the line mains terminal T1 exhibits negative polarity. As such, the line mains terminal T1 exhibits the polarity of the mains AC voltage Vm as shown in Figure 2.

[0044] In an embodiment, the positive wave period TP may be defined to start when the line mains terminal T1 is at a predetermined first positive voltage Vp1 and ends 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 to start when the line mains terminal T1 is at a predetermined first negative voltage Vn1 and ends 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.

[0045] The first switch state S1 allows the DC bus capacitor s to discharge via the line mains terminal T1 and neutral mains terminal T2 as the mains AC voltage Vm decreases from first positive voltage Vp1 to the second positive voltage Vp2. Likewise, the second switch state S2 allows the DC bus capacitor 6 to discharge via the line mains terminal and T1 and neutral mains terminal T2 as the mains AC voltage Vm increases from first negative voltage Vn1 to the second negative voltage Vn2.

[0046] When the mains AC voltage Vm operates at 50 Hertz, it will be understood that a single sinusoidal wave period is considered to last 1 / 50 = 20 milliseconds, so that the depicted positive wave period TP and the negative wave period TN lie in a time window of 20 / 4 = 5 milliseconds. Alternatively, having a main AC voltage Vm operating at 60 Hertz changes the time window to 1 / (60*4) milliseconds for the positive wave period TP and the negative wave period TN.

[0047] The positive wave period TP and the negative wave period TN can be defined in a further embodiment. Let T be a time period of a single sinusoidal wave of the mains AC source 2, i.e. a single sinusoidal wave of the mains AC voltage Vm, then the positive wave period TP is further defined to start between T / 4 and 1 ,2*T / 4 as measured from a first zero crossing ZC1 and ends when a DC capacitor voltage Vdc over the positive capacitor terminal H1 and the negative capacitor terminal H2 lies between 0V and 30V. Likewise, the negative wave period TN may be further defined to start between T / 4 and 1 ,2*T / 4 as measured from a second zero crossing ZC2 and ends when the DC capacitor voltage Vdc over the positive capacitor terminal H1 and the negative capacitor terminal H2 lies between 0V and 30V. Here, the first and second zero crossing ZC1 and ZC2 each define a voltage-time point, e.g. Vm(t), as shown in Figure 2, at which the mains AC voltage Vm is substantially zero and changes polarity as time progresses. At the first zero crossing ZC1 the mains AC voltage Vm changes from negative polarity to positive polarity and at the second zero crossing ZC2 the mains AC voltage Vm changes from positive polarity to negative polarity. In an exemplary embodiment, T = 1 / 50 milliseconds or T = 1 / 60 milliseconds, thus corresponding to an operating frequency of the mains AC source 2 of 50 Hertz or 60 Hertz, respectively.

[0048] Note that in an embodiment, the positive wave period TP may end when a DC line voltage (not depicted) between the positive DC line 7 and the negative DC line 8 lies between 0V and 30V, and wherein the negative wave period TN may also end when the DC line voltage lies between 0V and 30V. Referring to Figure 1 , an embodiment is conceivable wherein a filtering inductor Lf may be connected in series with the DC bus capacitor 6 between the positive DC line 7 and the positive capacitor terminal H1. However, it will be understood that the filtering inductor Lf has no influence on DC voltage and as such the DC line voltage will be substantially the same as the DC capacitor voltage Vdc.

[0049] When the positive wave period TP starts between T / 4 and 1 ,2*T / 4 from the first zero crossing ZC1 , and the negative wave period TN starts between T / 4 and 1 ,2*T / 4 from the second zero crossing ZC2, provides flexibility to efficiently switch particular semiconductor technology for optimized operation of the switching circuit 9. That is, for particular semiconductor components it may be beneficial to switch somewhat later then T / 4 milliseconds as measured from the first or second zero crossing ZC1 , ZC2.

[0050] When the DC bus capacitor 6 is discharged, it is preferrable that the DC capacitor voltage Vdc (or DC line voltage) is 0V. However, to protect the switching circuit 9 for being active too long, an embodiment is provided wherein the positive wave period TP and the negative wave period TN end before the DC capacitor voltage Vdc reaches 0V. Should the switching circuit 9 remain active after the mains AC voltage Vm passed the first or second zero crossing ZC1 , ZC2, this may cause excessive currents to 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 lies between 10V and 20V.

[0051] From Figure 2 it follows that an embodiment is conceivable wherein duration of the positive wave period TP and the negative wave period TN both equal T / 4 as shown by solid vertical lines for TP and TN, so from a maximum mains AC voltage Vm to a mains AC voltage of 0V. In practice, however, duration of the positive wave period TP and the negative wave period TN may be less than T / 4 as explained earlier.

[0052] Regarding the switching circuit 9, a number of exemplary embodiments may be envisaged. For example, Figure 3A and 3B show a positive period switching part S+ and a negative period switching part S-, respectively, according to an embodiment. In particular, an embodiment is provided wherein the switching circuit 9 comprises a positive period switching part S+, see Figure 3A, comprising the first positive wave period connection 11a, the second positive wave period connection 11 b, 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.

[0053] The positive period switching part S+ is switchable for discharging the DC bus capacitor s via the first positive discharge connection 13a, the first positive wave period connection 11 a, the second positive wave period connection 11 b, and the second positive discharge connection 13b.

[0054] From Figure 3B it follows that the switching circuit 9 may further comprises a negative period switching part S- comprising the first negative wave period connection 12a, the second negative wave period connection 12b, and 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.

[0055] The negative period switching part S- is switchable for discharging the DC bus capacitor 6 via the first negative discharge connection 14a, the first negative wave period connection 12a, the second negative wave period connection 12b, and the second negative discharge connection 14b.

[0056] As the name suggests, the positive period switching part S+ allows the DC bus capacitor 6 to discharge in the first switch state S1 , so during the positive wave period TP. The negative period switching part S- allows the DC bus capacitor 6 to discharge in the second switch state S2, so during the negative wave period TN. Since the DC capacitor voltage Vdc is always of positive polarity, the positive switching part S+ allows discharging the DC bus capacitor 6 when the line mains terminal T1 exhibits positive polarity and the negative switching part S- allows discharging the DC bus capacitor 6 when the line mains terminal T1 exhibits negative polarity. So two discharge opportunities are provided by the positive and negative period switching parts S+, S- during a single sinusoidal wave period of the mains AC source 2.

[0057] In a further embodiment, as depicted in Figure 3A and 3B, the positive period switching part S+ comprises a positive first switch 15 for connecting the first positive wave period connection 11a to the first positive discharge connection 13a, and a positive second switch 16 for connecting the second positive wave period connection 11 b to the second positive discharge connection 13b. A positive logic circuit 17 is provided and configured for switching the positive first switch 15 and the positive second switch 16.

[0058] Likewise, the negative period switching part S- comprises a negative first switch 18 for connecting the first negative wave period connection 12a to the first negative discharge connection 14a, and a negative second switch 19 for connecting the second negative wave period connection 12b to the second negative discharge connection 14b. A negative logic circuit 20 is provided and configured for switching the negative first switch 18 and the negative second switch 19. The positive logic circuit 17 and the negative logic circuit 20 allow for precise timing and control for discharging the DC bus capacitor 6 in the first switch state S1 or the second switch state S2, respectively.

[0059] In the depicted exemplary embodiments of Figure 3A, 3B, the positive first switch 15 and the negative first switch 18 may be a TRIAC and wherein each of the positive second switch 16 and the negative second switch 19 may be a MOSFET. When using a TRIAC for the positive first switch 15 and the negative first switch 18, the positive wave period TP and the negative wave period TN may start between T / 4 and 1 ,2*T / 4 from respective zero crossings ZC1 , ZC2. For example, for a 50 Hertz mains AC source 2, the positive wave period TP and the negative wave period TN may start at around 5.9 milliseconds for the TRIAC to latch after gate triggering.

[0060] In practice, a discharging cycle of the DC bus capacitor 6 during the positive wave period TP may be identical to a discharging cycle of the DC bus capacitor 6 during a negative wave period TN. Therefore, an embodiment is conceivable wherein the positive period switching part S+ and the negative period switching part S- have identical circuit arrangements, so that the positive period switching part S+ and the negative period switching part S- are interchangeable, thereby providing reduced circuit complexity of the bipolar discharge circuit 1.

[0061] Referring to Figure 1 , to protect the bipolar discharge circuit 1 from overcurrent during the first and second switch states S1 , S2, an embodiment may be considered wherein the switching circuit 9 further comprises 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 may then be provided and configured for measuring a current through the resistor 20 and based on the measured current, opening the positive first switch 15 and the positive second switch 16, or opening the negative first switch 18 and the negative second switch 19. In a further embodiment the protection circuit 21 is connected to the positive logic circuit 17 and negative logic circuit 20 for opening the positive first switch 15 and the positive second switch 16, or opening the negative first switch 18 and the negative second switch 19.

[0062] As mentioned earlier, the bipolar discharge circuit 1 is advantageous when operating an induction cooking zone Z to reduce acoustic noise and electromagnetic emissions, and to improve durability and longevity of electronic components of the induction cooking zone Z as the DC bus capacitor 6 is solely dischargeable via the switching circuit 9.

[0063] In view of the above, the present invention also relates to an induction cooking hob (not shown) that comprises an induction cooking zone Z and a bipolar discharge circuit 1 , and 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. The induction cooking hob provides for an improved cooking experience as the induction cooking zone is silent when heating or detecting cookware.

[0064] To further clarify on how the bipolar discharge circuit 1 can be used or operated, a method may be considered for operating the bipolar discharge circuit 1 . For example, the method may comprise the steps of connecting the line mains terminal T1 to a mains line L of a mains AC source 2, and connecting the neutral mains terminal T2 to a mains neutral N of the mains AC source 2.

[0065] In these steps an “AC side” of the bipolar discharge circuit 1 is connected to the mains AC source 2, e.g. a regular AC domestic outlet. Regarding a “DC side” of the bipolar discharge circuit 1 , the method comprises the steps of connecting the positive capacitor terminal H1 and the negative capacitor terminal H2 to an induction cooking zone Z. As mentioned earlier, the induction cooking zone Z may, for example, comprise a resonant circuit utilizing a zone capacitor C and zone inductor L, wherein the zone inductor L is arranged to magnetically interact with cookware W for heating or detection thereof.

[0066] Prior to activating the induction cooking zone Z for heating or detecting cookware W, the method comprises the steps of switching the switching circuit 9 to the first switch state and the second switch state sequentially; and, activating the induction cooking zone Z for heating or detecting cookware W.

[0067] Note that switching the switching circuit 9 to the first switch state and the second switch state sequentially refers to switching from the first switch state to the second switch state, and vice versa, in sequential manner and for a required number of times. In this step the DC bus capacitor 6 is discharged via the switching circuit 9 during the positive wave period TP and the negative wave period TN.

[0068] As explained earlier, the first switch state S1 and second switch state S2 may be provided by the positive period switching part S+ and the negative period switching part S- of the switching circuit 9. So when the bipolar discharge circuit 1 is in operation, switching to the first switch state S1 means that the DC bus capacitor 6 is discharged through the positive period switching part S+ and switching to the second switch state S2 means that the DC bus capacitor 6 is discharged through the negative period switching part S-. Therefore, in an embodiment, switching the switching circuit 9 to the first switch state S1 may comprise the step of discharging the DC bus capacitor s via the first positive wave period connection 11a and the second positive wave period connection 11 b when a mains AC voltage Vm of the line mains terminal T1 lies between a predetermined first positive voltage Vp1 and a predetermined second positive voltage Vp2, wherein the first positive voltage Vp1 is higher than the second positive voltage Vp2. Switching the switching circuit 9 to the second switch state S2 comprises the step of discharging the DC bus capacitor s via the first negative wave period connection 12a and the second negative wave period connection 12b when the mains AC voltage Vm of the line mains terminal T1 lies between a predetermined first negative voltage Vn1 and a predetermined second negative voltage Vn2, wherein the first negative voltage Vn1 is lower than the second negative voltage Vn2.

[0069] In view of the above, the present invention can now be summarised by the following embodiments:

[0070] Embodiment 1. A bipolar discharge circuit (1) for an induction cooking zone (Z) to heat and detect cookware (W), comprising a line mains terminal (T1) for connection to a mains line (L) of a mains AC source (2) and a neutral mains terminal (T2) for connection to a mains neutral (N) of the mains AC source (2); 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 a positive DC connection (5a) and a negative DC connection (5b); a 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 for connection to an induction cooking zone (Z) for heating and detecting cookware (W); a switching circuit (9) comprising 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 comprises a first positive wave period connection (11a) connected to the line mains terminal (T1) and a second positive wave period connection (11 b) connected the neutral mains terminal (T2), and a first negative wave period connection (12a) connected to the neutral mains terminal (T2) and a second negative wave period connection (12b) connected to the line mains terminal (T1); and wherein the switching circuit (9) is configured to provide: a first switch state in which the DC bus capacitor (6) is dischargeable via the first positive wave period connection (11a) and the second positive wave period connection (11 b); a second switch state in which the DC bus capacitor (6) is dischargeable via the first negative wave period connection (12a) and the second negative wave period connection (12b); a third switch state in which the DC bus capacitor (6) is disconnected from the first positive wave period connection (11a), the second positive wave period connection (11 b), the first negative wave period connection (12a) and the second negative wave period connection (12b).

[0071] Embodiment 2. The bipolar discharge circuit according to embodiment 1 , wherein, in the first switch state, the first main discharge connection (10a) is connected to the first positive wave period connection (11a), and the second main discharge connection (10b) is connected to the second positive wave period connection (11 b), and wherein 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); wherein, in the second switch state, the first main discharge connection (10a) is connected to the first negative wave period connection (12a), and the second main discharge connection (10b) is connected to the second negative wave period connection (12b), and the first main discharge connection (10a) is disconnected from the first positive period wave connection (11a), and the second main discharge connection (10b) is disconnected from the second positive wave period connection (11 b); wherein, in the third switch state, the first main discharge connection (10a) is disconnected from the first positive wave period connection (11 a) and the first negative wave period connection (12a), and wherein the second main discharge connection (10b) is disconnected from the second positive wave period connection (11 b) and the second negative wave period connection (12b).

[0072] Embodiment 3. The bipolar discharge circuit according to embodiment 1 or 2, wherein the first switch state extends during a positive wave period (TP) of the mains AC source (2) and wherein the second switch state extends during a negative wave period (TN) of the mains AC source (2), wherein the positive wave period (TP) is defined to start when the line mains terminal (T1) is at a predetermined first positive voltage and ends when the line mains terminal (T1) reaches a predetermined second positive voltage, wherein the first positive voltage is higher than the second positive voltage; and wherein the negative wave period (TN) is defined to start when the line mains terminal (T1) is at a predetermined first negative voltage and ends when the line mains terminal (T1) reaches a predetermined second negative voltage, wherein the first negative voltage is lower than the second negative voltage.

[0073] Embodiment 4. The bipolar discharge circuit according to embodiment 3, wherein the positive wave period (TP) is further defined to start between T / 4 and 1 ,2*T / 4 of a time period T of a single sinusoidal wave of the AC source (2) as measured from a first zero crossing (ZC1) and ends when a DC capacitor voltage (Vdc) over the positive capacitor terminal (H1) and the negative capacitor terminal (H2) lies between 0V and 30 V, and wherein the negative wave period (TN) is further defined to start between T / 4 and 1 ,2*T / 4 of the time period T as measured from a second zero crossing (ZC2) and ends when the DC capacitor voltage over the positive capacitor terminal (H1) and the negative capacitor terminal (H2) lies between 0V and 30V.

[0074] Embodiment 5. The bipolar discharge circuit according to embodiment 4, wherein T = 1 / 50 milliseconds or T = 1 / 60 milliseconds.

[0075] Embodiment 6. The bipolar discharge circuit according to any of embodiments 1-5, wherein the switching circuit (9) comprises a positive period switching part (S+) comprising the first positive wave period connection (1 1 a), the second positive wave period connection (11 b), 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 wherein the positive period switching part (S+) is switchable for discharging the DC bus capacitor (6) via the first positive discharge connection (13a), the first positive wave period connection (11 a), the second positive wave period connection (1 1 b), and the second positive discharge connection (13b); wherein the switching circuit (9) further comprises a negative period switching part (S-) comprising the first negative wave period connection (12a), the second negative wave period connection (12b), and 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), and wherein the negative period switching part (S-) is switchable for discharging the DC bus capacitor (6) via the first negative discharge connection (14a), the first negative wave period connection (12a), the second negative wave period connection (12b), and the second negative discharge connection (14b).

[0076] Embodiment 7. The bipolar discharge circuit according to embodiment 6, wherein the positive period switching part (S+) comprises a positive first switch (15) for connecting the first positive wave period connection (11 a) to the first positive discharge connection (13a), and a positive second switch (16) for connecting the second positive wave period connection (11 b) to the second positive discharge connection (13b), and a positive logic circuit (17) configured for switching the positive first switch (15) and the positive second switch (16); wherein the negative period switching part (S-) comprises a negative first switch (18) for connecting the first negative wave period connection (12a) to the first negative discharge connection (14a), and a negative second switch (19) for connecting the second negative wave period connection (12b) to the second negative discharge connection (14b), and a negative logic circuit (20) configured for switching the negative first switch (18) and the negative second switch (19).

[0077] Embodiment 8. The bipolar discharge circuit according to embodiment 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.

[0078] Embodiment 9. The bipolar discharge circuit according to any of embodiments 6-8, wherein the positive period switching part (S+) and the negative period switching part (S-) have identical circuit arrangements.

[0079] Embodiment 10. The bipolar discharge circuit according to any of embodiments 7-9, wherein the switching circuit (9) further comprises 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 further comprising a protection circuit (21) configured for measuring a current through the resistor (20) and based on the measured current, opening the positive first switch (15) and the positive second switch (16), or opening the negative first switch (18) and the negative second switch (19).

[0080] Embodiment 11. An induction cooking hob comprising an induction cooking zone (Z) and a bipolar discharge circuit (1) according to any of embodiments 1-10, 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).

[0081] Embodiment 12. A method of operating the bipolar discharge circuit (1) according to any of embodiments 1-10, comprising the steps of: connecting the line mains terminal (T1) to a mains line (L) of a mains AC source (2), and connecting the neutral mains terminal (T2) to a mains neutral (N) of the mains AC source (2); connecting the positive capacitor terminal (H1) and the negative capacitor terminal (H2) to an induction cooking zone (Z); and prior to activating the induction cooking zone (Z) for heating or detecting cookware (W), switching the switching circuit (9) to the first switch state and the second switch state sequentially; and, subsequently, activating the induction cooking zone (Z) for heating or detecting cookware (W).

[0082] Embodiment 13. The method according to embodiment 12, wherein the step of switching the switching circuit (9) to the first switch state comprises the step of discharging the DC bus capacitor (6) via the first positive wave period connection (11a) and the second positive wave period connection (11 b) when a mains AC voltage (Vm) of the line mains terminal (T1) lies between a predetermined first positive voltage and a predetermined second positive voltage, wherein the first positive voltage is higher than the second positive voltage; and wherein the step of switching the switching circuit (9) to the second switch state comprises the step of discharging the DC bus capacitor (6) via the first negative wave period connection (12a) and the second negative wave period connection (12b) when the mains AC voltage (Vm) of the line mains terminal (T1) lies between a predetermined first negative voltage and a predetermined second negative voltage, wherein the first negative voltage is lower than the second negative voltage.

[0083] The present invention has been described above with reference to a number of exemplary embodiments discussed above and as shown in the drawings. Modifications and alternative implementations of some parts or elements are possible, and are included in the scope of protection as defined in the appended claims.

Claims

CLAIMS1 . A bipolar discharge circuit (1) for an induction cooking zone (Z) to heat and detect cookware (W), comprising a line mains terminal (T1) for connection to a mains line (L) of a mains AC source (2) and a neutral mains terminal (T2) for connection to a mains neutral (N) of the mains AC source (2); 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 a positive DC connection (5a) and a negative DC connection (5b); a 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 for connection to an induction cooking zone (Z) for heating and detecting cookware (W); a switching circuit (9) comprising 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 comprises a first positive wave period connection (11a) connected to the line mains terminal (T1) and a second positive wave period connection (11 b) connected the neutral mains terminal (T2), and a first negative wave period connection (12a) connected to the neutral mains terminal (T2) and a second negative wave period connection (12b) connected to the line mains terminal (T1); and wherein the switching circuit (9) is configured to provide: a first switch state in which the DC bus capacitor (6) is dischargeable via the first positive wave period connection (11a) and the second positive wave period connection (11 b); a second switch state in which the DC bus capacitor (6) is dischargeable via the first negative wave period connection (12a) and the second negative wave period connection (12b); a third switch state in which the DC bus capacitor (6) is disconnected from the first positive wave period connection (11a), the second positive wave period connection (11 b), 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 switch state, the first main discharge connection (10a) is connected to the first positive wave period connection (11a), and the second main discharge connection (10b) is connected to the second positive wave period connection (11 b), andwherein 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); wherein, in the second switch state, the first main discharge connection (10a) is connected to the first negative wave period connection (12a), and the second main discharge connection (10b) is connected to the second negative wave period connection (12b), and the first main discharge connection (10a) is disconnected from the first positive period wave connection (11a), and the second main discharge connection (10b) is disconnected from the second positive wave period connection (11 b); wherein, 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 wherein the second main discharge connection (10b) is disconnected from the second positive wave period connection (11 b) and the second negative wave period connection (12b).

3. The bipolar discharge circuit according to claim 1 or 2, wherein the first switch state extends during a positive wave period (TP) of the mains AC source (2) and wherein the second switch state extends during a negative wave period (TN) of the mains AC source (2), wherein the positive wave period (TP) is defined to start when the line mains terminal (T1) is at a predetermined first positive voltage and ends when the line mains terminal (T1) reaches a predetermined second positive voltage, wherein the first positive voltage is higher than the second positive voltage; and wherein the negative wave period (TN) is defined to start when the line mains terminal (T1) is at a predetermined first negative voltage and ends when the line mains terminal (T1) 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 to start between T / 4 and 1 ,2*T / 4 of a time period T of a single sinusoidal wave of the AC source (2) as measured from a first zero crossing (ZC1) and ends when a DC capacitor voltage (Vdc) over the positive capacitor terminal (H1) and the negative capacitor terminal (H2) lies between 0V and 30 V, and wherein the negative wave period (TN) is further defined to start between T / 4 and 1 ,2*T / 4 of the time period T as measured from a second zero crossing (ZC2) and ends when the DC capacitor voltage over the positive capacitor terminal (H1) and the negative capacitor terminal (H2) lies between 0V and 30V.

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 of claims 1-5, wherein the switching circuit (9) comprises a positive period switching part (S+) comprising the first positive wave period connection (11a), the second positive wave period connection (11 b), and a first positive discharge connection (13a) connected to the first main discharge connection(IOa), and a second positive discharge connection (13b) connected to the second main discharge connection (10b), and wherein the positive period switching part (S+) is switchable for discharging the DC bus capacitor (6) via the first positive discharge connection (13a), the first positive wave period connection (11a), the second positive wave period connection (11 b), and the second positive discharge connection (13b); wherein the switching circuit (9) further comprises a negative period switching part (S-) comprising the first negative wave period connection (12a), the second negative wave period connection (12b), and 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), and wherein the negative period switching part (S-) is switchable for discharging the DC bus capacitor (6) via the first negative discharge connection (14a), the first negative wave period connection (12a), the second negative wave period connection (12b), and the second negative discharge connection (14b).

7. The bipolar discharge circuit according to claim 6, wherein the positive period switching part (S+) comprises a positive first switch (15) for connecting the first positive wave period connection (11a) to the first positive discharge connection (13a), and a positive second switch (16) for connecting the second positive wave period connection (11 b) to the second positive discharge connection (13b), and a positive logic circuit (17) configured for switching the positive first switch (15) and the positive second switch (16); wherein the negative period switching part (S-) comprises a negative first switch (18) for connecting the first negative wave period connection (12a) to the first negative discharge connection (14a), and a negative second switch (19) for connecting the second negative wave period connection (12b) to the second negative discharge connection (14b), and a negative logic circuit (20) configured for switching 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 wherein each of the positive second switch(16) and the negative second switch (19) is a MOSFET.

9. The bipolar discharge circuit according to any of claims 6-8, wherein the positive period switching part (S+) and the negative period switching part (S-) have identical circuit arrangements.

10. The bipolar discharge circuit according to any of claims 7-9, wherein the switching circuit (9) further comprises 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 further comprising a protection circuit (21) configured for measuring a current through the resistor (20) and based on the measured current, opening the positive first switch (15) and the positive second switch (16), or opening the negative first switch (18) and the negative second switch (19).

11. An induction cooking hob comprising an induction cooking zone (Z) and a bipolar discharge circuit (1) according to any of claims 1-10, 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 of claims 1-10, comprising the steps of: connecting the line mains terminal (T1) to a mains line (L) of a mains AC source (2), and connecting the neutral mains terminal (T2) to a mains neutral (N) of the mains AC source (2); connecting the positive capacitor terminal (H1) and the negative capacitor terminal (H2) to an induction cooking zone (Z); and prior to activating the induction cooking zone (Z) for heating or detecting cookware (W), switching the switching circuit (9) to the first switch state and the second switch state sequentially; and, subsequently, activating the induction cooking zone (Z) for heating or detecting cookware (W).

13. The method according to claim 12, wherein the step of switching the switching circuit (9) to the first switch state comprises the step of discharging the DC bus capacitor (6) via the first positive wave period connection (11a) and the second positive wave period connection (11 b) when a mains AC voltage (Vm) of the line mains terminal (T1) lies between a predetermined first positive voltage and a predetermined second positive voltage, wherein the first positive voltage is higher than the second positive voltage; and wherein the step of switching the switching circuit (9) to the second switch state comprises the step of discharging the DC bus capacitor (6) via the first negative wave period connection (12a) and the second negative wave period connection (12b) when the mains AC voltage (Vm) of the line mains terminal (T1) lies between a predetermined first negative voltage and a predetermined second negative voltage, wherein the first negative voltage is lower than the second negative voltage.

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