A method for switching hot plate relays at mains zero-crossing in vitroceramic cookers and system implementing the same

Abstract

The present invention relates to a method for switching hot plate relays in vitroceramic cookers by aligning the switching operation with the mains zero-crossing, and to a system implementing the said method. The mains sine wave signal is monitored by means of a zero-crossing circuit and relay feedback circuits, and the relay opening time is calculated by the controller. In the subsequent switching operations, the relay is engaged at the zero-crossing point, thereby achieving minimal current flow through the relay contacts. Thus, the economic life of the relay is extended, failures caused by high-current switching are prevented, and reliable operation is ensured. The said method improves the relay performance without the need for external current sensors and significantly reduces the failure rate.

Description

TECHNICAL FIELD

[0001] The present invention relates to switching methods of relays used in electric heaters, especially in vitroceramic cookers, used in kitchens. More specifically, the present invention relates to a hardware and method which ensure the switching of relays used in the vitroceramic cookers at the zero-crossing point of the mains sine wave signal.PRIOR ART

[0002] In recent years, significant developments and changes have occurred in cooking technologies used in kitchens. Among these technological advancements are induction heating cookers, which have become widely used in both domestic and professional kitchens in recent years, as well as vitroceramic cookers.

[0003] Like all electrically powered devices, vitroceramic cookers are typically energized with alternating mains voltage, which is 110 volts in North and Central America and 220-230 volts in nearly all other parts of the world. In these types of cookers, which are among the most commonly used electric cooker types in kitchens, the users can generally control the temperature of the heating zones using power levels ranging from 0 to 9. In the existing systems, the heating level of each zone is regulated by "on-off" switching of the corresponding relay. When the user selects a particular level, the cooker system divides the desired power level for this setting into a defined period and switches the relay on and off at certain intervals. This switching process is a fundamental method for controlling the temperature levels of the heating zones.

[0004] However, a significant problem exists in this system: Relay switching is performed without considering which phase of the mains sine wave the system is in. The mains voltage operates with alternating current (AC), and this current follows a sine wave form. The sine wave stars from zero and continuously oscillates between positive and negative peaks. Since in the state of the art, the switching operation can occur at any point of the sine wave, particularly when switching occurs at the peak points of the sine wave, high current passes through the relay contacts.

[0005] The peak of the sine wave is the point at which voltage, and therefore the current in the load, is at its maximum. Switching at this point results in a high amount of current flowing through the relay contacts, and this high current causes overheating, deformation, and eventual wear on the relay contacts. Continuous switching of the relay contacts under such high current leads to damage on the contact surfaces, potentially causing fragmentation and breakage. As a result, the performance of the relay decreases, the risk of failure increases, and the overall economic life of the relay is reduced.

[0006] Another disadvantage of the existing systems is that this high-current switching may lead to undesired consequences for the user in the course of time. When relay contacts become damaged, the hot plates do not function properly, which reduces the performance of the cooker and increases the number of service calls. Such relay failures can affect user satisfaction during the warranty period and increase service costs after the warranty expires.

[0007] Although various solutions related to the relay switching have been developed in the technical literature, the majority of the existing systems do not take into account the phase of the mains sine wave in which the relay switching is performed. Some systems use timers to open and close the relays at certain time intervals; however, these approaches do not aim to perform switching at the zero-crossing point of the sine wave, in other words, the moment when the current is at its minimum. Therefore, these systems cannot effectively resolve the problems caused by wear on relay contacts and the high current. As a result, the inability to precisely time the relay switching according to the mains sine wave in the state of the art constitutes a significant deficiency which adversely affects the economic life of the relays. This situation not only reduces the reliability of the device but also increases maintenance and repair costs in the long term.

[0008] In the state of the art Patent Application No. EP0989663A2, the relays are switched at zero-crossing points by following a specific pattern. When the switch of a load component is opened, the current flows from a nominal alternating power source to a zero-crossing detection circuit. In the zero-crossing detection circuit, the zero-crossing points of a current waveform are detected and are input to an output control circuit. The output control circuit preselects a sampling pattern and, by counting the zero-crossing points, generates a signal corresponding to this pattern, which is then input to an SSR. However, the patent application does not disclose an algorithm operating at the zero-crossing, and the relay is not switched exactly at the zero-crossing point.

[0009] In the state of the art Utility Model No. CN213635774U, a zero-crossing switching circuit of a small circuit breaker is disclosed, which is provided with an alternating current input port and an alternating current output port and comprises a microcontroller unit, the peripheral equipment of the microcontroller unit, and a zero-crossing detection circuit unit. In the zero-crossing detection circuit unit, a single-phase electric energy measurement chip is implemented. The microcontroller unit obtains a voltage sampling value from the zero-crossing detection circuit unit, determines a zero-crossing signal of the alternating current, and energizes a semiconductor switch element prior to the mechanical switch device. Regardless of whether the operation is opening or closing, since the switching is performed during the zero-voltage crossing, in principle, no current flows, and this is intended to protect the contact and extend the economic life. By using a triac in parallel with the relay, the current is conducted through the triac before reaching the relay. The hardware is designed such that a minimum (zero) current flows through the relay. No information is provided regarding algorithmic control.

[0010] In the state of the art Korean Patent Application No. KR20090061485A, a laundry treatment apparatus and a load control apparatus thereof are disclosed, aiming to eliminate electromagnetic interference distortion caused by harmonics or vibration by switching a motor or heater at the zero-crossing point, wherein the device comprises a load control apparatus, a load driving device, and a control device. The load driving device is located at the signal input terminal of the motor or the heater, and controls a signal input to the motor or heater as the motor or the heater is operated. The control device calculates the on / off time of the motor or the heater based on the response delay time of the load driving device and the zero-crossing point.AIMS OF THE INVENTION

[0011] An aim of the present invention is the realization of a system which solves the problems caused by switching the hot plates through the relays which draw high current, as is the case in the state of the art.

[0012] Another aim of the present invention is the realization of hardware and an algorithmic method which enable the relays to be switched at the zero-crossing of the mains sine wave.

[0013] Yet another aim of the present invention is the realization of a system wherein the current on relay contacts is shifted away from the maximum level, thereby extending the economic life of the relays and improving the user comfort.

[0014] Yet another aim of the present invention is the realization of a long-lasting vitroceramic cooker wherein the hot plate relays are switched at the mains zero-crossing point.BRIEF EXPLANATION OF FIGURES

[0015] The figures explained below aim to exemplify a method and system for a vitroceramic cooker wherein the hot plate relays are switched at the mains zero-crossing point, of which the advantages against the state of the art have already been summarized and will be explained in detail later.

[0016] The figures should not be interpreted as limiting the scope of protection defined in the claims, and should not be used separately to interpret the scope in the claims without referring to the technique in the description. Figure 1 - is the oscilloscope images of the measurement triggering performed at the moment of initial activation of the product in a vitroceramic cooker in an embodiment of the present invention. Figure 2 - is the view of the algorithmic steps of the measurement, wherein in the measurement triggering performed at the moment the product is first activated, the duration until the relay feedback signal is transmitted is determined as the relay opening time, in a vitroceramic cooker in an embodiment of the present invention. Figure 3 - is the oscilloscope images showing the actuation of the relays aligned with the zero-crossing point following the determination of the relay opening time, in a vitroceramic cooker in an embodiment of the present invention. Figure 4 - is the view of the algorithmic steps of actuating the relays aligned with the zero-crossing point in a vitroceramic cooker in an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] The elements illustrated in the figures are numbered as follows: 10) Mains voltage signal 11) Zero-crossing feedback signal 12) Relay pin trigger signal 13) Relay output signal 14) Relay output feedback signal 20) Measurement algorithm step 1 21) Measurement algorithm step 2 22) Measurement algorithm step 3 23) Measurement algorithm step 4 24) Measurement algorithm step 5 25) Measurement algorithm step 6 26) Measurement algorithm step 7 30) Mains voltage signal 31) Zero-crossing feedback signal 32) Relay pin controlled trigger signal 33) Relay output signal 34) Relay output feedback signal 40) Controlled trigger algorithm step 1 41) Controlled trigger algorithm step 2 42) Controlled trigger algorithm step 3 43) Controlled trigger algorithm step 4

[0018] The teaching of the present invention relates to a zero-crossing-based hot plate relay driving method developed for use in vitroceramic cookers, and to a system which drives hot plates by implementing the same. This solution, which starts from the monitoring of the mains sine signal by using a zero-crossing detection structure and a relay feedback sampling structure for initial zero-crossing detection, comprises, in devices implementing the present invention, at least one input voltage sampling circuit, a zero-crossing feedback circuit, and at least one relay output feedback circuit, wherein the signal obtained from the zero-crossing circuit is used by the control unit to determine the relay opening time. It is characterized by an algorithm which ensures that the relay is switched at the zero-crossing point based on the relay opening time, and further in that the said algorithm ensures that the switching occurs at the zero-crossing point during each switching event by measuring the contact closing time of the relay. Thus, a method is proposed which protects the relay contacts without the need for an external current sensor, and by performing switching at the zero-crossing point, a durable and long-lasting vitroceramic solution is achieved by conducting minimal current through the relay contacts.

[0019] In a vitroceramic cooker solution proposed according to at least one embodiment of the present invention, the driving of the hot plate by relay triggering occurs as in other similar devices. The present invention comprises a control unit configured to perform operations such as algorithmic control, signal sampling, measurement, and relay driving. Moreover, according to the system proposed as part of the said solution, there is a mains signal sampling unit and a relay output signal sampling unit. Furthermore, the system also comprises a relay output feedback sampling unit. Due to the said structural components, the relationships between the mains voltage signal and other measurable characteristics of the operation of the vitroceramic cooker become comparable and controllable. Through the inclusion of a zero-crossing detection unit, zero-crossing feedback sampling becomes possible.

[0020] According to the teaching of the present invention, it is foreseen that a measurement triggering is initially performed by the control unit of the proposed vitroceramic cooker. Here, a sinusoidal signal formed by sampling the mains signal is received as a mains voltage signal (10). In each period, the regions where the voltage is near zero are considered zero-crossing points, and in synchronization with a zero-crossing feedback signal (11) to be generated at the said zero-crossing points, a relay pin trigger signal (12) reflecting the value of the relay pin is obtained. Upon triggering the relay pin, the relay is enabled to drive the hot plate mechanism, and together with this signal, which has a step-characteristic, a relay output signal (13) is generated. In the state of the art, the said relay pin trigger is activated arbitrarily, without regard to the zero-crossing moments of the mains voltage signal (10); however, the reason a measurement triggering is required is due to the benefit of knowing the relay trigger time (Δt on ), which is the time between the triggering of the relay pin and the acquisition of a feedback signal (14) from the relay output, which prevents relay wear due to maximum current by taking advantage of the relation to the zero-crossing point.

[0021] At the initial activation, the duration between the zero-crossing signal-based trigger and the acquisition of feedback from the relay is measured, which is considered the relay opening time (Δt on ). In an embodiment of the present invention, the difference between the moments at which the randomly triggered relay output is triggered such that the relay pin trigger signal (12) generated at the time of triggering and the relay output feedback signal (14) produce positive values, is calculated as the relay trigger time. According to a method proposed for this situation, the first step of a measurement triggering to be carried out according to the teaching of the present invention is to check whether the relay pin trigger time (Δt on ) is known (20). If it is known, measurement triggering is deemed unnecessary. However, in cases where this value is not known, as would be the case under the initial triggering conditions, the next step is to check the value received from the zero-crossing feedback signal (11) (21). Upon receiving this feedback, the relay pin is triggered (22), and a counter is started (23). Once the feedback from the relay output is received (24), the counter is stopped (25), and the value obtained from the counter is then accepted as the relay pin trigger time, or relay opening time (Δt on ) (26).

[0022] This relay pin trigger time obtained by the present invention to synchronize the relay triggering with the zero-crossing is used in all operations other than the initial measurement triggering in order to regulate the temporal relationship between the mains voltage and the other structural components of the system (relay triggering, relay feedback, etc.). With reference to Figure 3, it can be seen that the mains voltage signal (30), which is a sinusoidal signal formed by sampling the mains signal, generates a zero-crossing feedback signal (31) induced by the zero-crossing points. Here, in contrast to the measurement triggering case, by using the determined relay pin trigger time, the relay pin trigger signal (12) is generated after a delay corresponding to the difference between 20 milliseconds (under 50Hz mains conditions) and the relay pin trigger time (20ms - Δt on ), following the triggering of the zero-crossing feedback signal (31). Under 60Hz mains conditions, this interval is 16.67 milliseconds. Since triggering the relay pin causes the relay to drive the hot plate mechanism, and since the generated relay output signal (13) is thereby made to occur close to the zero-crossing point, maximum current does not flow through the relays, and thus technical drawbacks such as deformation and component wear, which frequently occur under the maximum current conditions on the relay contacts, are eliminated. As a result, the economic life of the relays is stabilized, and the rate of faults caused by relay damage is reduced.

[0023] After the measurement triggering, each subsequent operation uses the duration from the zero-crossing signal-based triggering until the feedback is received from the relay, which is performed under a controlled trigger algorithm. According to a method proposed for this situation, a series of steps is carried out during the normal triggering by using the relay pin trigger signal value calculated through the measurement triggering according to the teaching of the present invention. In the first of these steps, it is checked whether the said relay pin trigger time is known (40). If it is known, the value of the zero-crossing feedback signal (31) is checked, and the presence of the feedback is evaluated (41). Upon receiving this feedback, a delay corresponding to the difference between 20 milliseconds and the relay pin trigger time (20ms - Δt on ) is observed (42), and then the corresponding relay pin is triggered (43).

Claims

1. A method executable by a controller which may be comprised in a vitroceramic cooker, comprising the steps of: a measurement triggering step wherein a relay opening time is determined for triggering at least one relay pin in synchronization with a mains signal zero-crossing and for energizing at least one hot plate, and a controlled triggering step wherein at least one relay is triggered, immediately after detecting the zero-crossing of the mains voltage, so as to correspond to a minimum current value based on the relay opening time determined in the previous step.

2. A method as in Claim 1, characterized by the said measurement triggering step comprising at least the following sub-steps: a first step (20) wherein it is tested whether the relay opening time is known, a second step (21) wherein, if the relay opening time is not known, it is tested whether a zero-crossing feedback is available, a third step (22) wherein, if feedback is present in the previous step, the relay pin is triggered, a fourth step (23) wherein a counter is started, a fifth step (24) wherein it is tested whether feedback is received from the relay output, a sixth step (25) wherein, if feedback is present in the previous step, the counter value is recorded, and a seventh step (26) wherein the relay opening time is calculated based on the recorded counter value.

3. A method as in any one of the above claims, characterized by the controlled triggering step comprising at least the following sub-steps: a first step (40) wherein it is tested whether the relay opening time is known, a second step (41) wherein, if the relay opening time is known, it is tested whether a zero-crossing feedback is available, a third step (42) wherein, if feedback is present in the previous step, a waiting period is executed corresponding to the difference between 20 milliseconds and the relay opening time, and a fourth step (43) wherein the relay pin is triggered.

4. A vitroceramic cooker comprising at least one hot plate, a relay associated with the said at least one hot plate, and at least one control unit, characterized in that the said vitroceramic cooker comprises at least one structure for generating zero-crossing feedback, at least one relay output signal, and a structure for generating relay output feedback, and the said at least one control unit is configured to execute a method comprising a measurement triggering step wherein a relay opening time is determined for triggering at least one relay pin in synchronization with a mains signal zero-crossing and for energizing at least one hot plate, and a controlled triggering step wherein at least one relay is triggered, immediately after detecting the zero-crossing of the mains voltage, so as to correspond to a minimum current value based on the relay opening time determined in the previous step.

5. A vitroceramic cooker as in Claim 4, characterized by at least one input voltage sampling circuit, a zero-crossing feedback circuit, and at least one relay output feedback circuit.

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