Methods of controlling cooling in a microwave heating apparatus and apparatus thereof

Abstract

A microwave heating apparatus and methods of controlling cooling of a microwave heating apparatus are provided. The microwave heating apparatus typically includes a microwave source for generating microwaves, a cooling unit for cooling the microwave source and a control unit. According to one embodiment, the control unit is configured to receive operational data from a measuring device indicative of the measured power of microwaves transmitted from the magnetron and receive operational data from the measuring device indicative of the measured anode current of the magnetron. A calculating device calculates an efficiency of the magnetron as a function of the measured power of the transmitted microwaves and the measured anode current, to define a determined efficiency. The control unit controls the cooling unit and cools the magnetron based on the determined efficiency.

Claims

1. A microwave heating apparatus comprising: a magnetron for generating microwaves; a cooling unit for cooling the magnetron; a control unit: configured to receive operational data indicative of a measured power of transmitted microwaves from the magnetron; configured to receive operational data indicative of a measured anode current of the magnetron; configured to determine an efficiency of the magnetron as a function of the measured power of the transmitted microwaves from the magnetron and the measured anode current, to define a determined efficiency; and configured to control the cooling unit and cool the magnetron based on the determined efficiency.

2. The microwave heating apparatus of claim 1, further comprising a sensor for detecting a temperature of the magnetron to define a detected temperature.

3. The microwave heating apparatus of claim 2, further comprising a calculating device that calculates a calculated temperature time derivative based on, in part, the detected temperature of the magnetron.

4. The microwave heating apparatus of claim 3, wherein the determined efficiency of the magnetron is further determined based on the calculated temperature time derivative.

5. The microwave heating apparatus of claim 1, wherein the magnetron is adapted to feed the transmitted microwaves from the magnetron to a cavity of the microwave heating apparatus via a transmission line.

6. The microwave heating apparatus of claim 1, wherein the control unit is configured to receive the measured power of microwaves reflected back to the magnetron and control the cooling of the cooling unit based on the determined efficiency of the magnetron and the measured power of reflected microwaves.

7. The microwave heating apparatus of claim 1, wherein the control unit is configured to determine a cooling demand based on the determined efficiency to define a determined cooling demand, and control the cooling unit based on the determined cooling demand.

8. The microwave heating apparatus of claim 7, further comprising controlling the cooling unit based on the determined efficiency and reducing a noise generated by the cooling.

9. The microwave heating apparatus of claim 1, wherein the efficiency of the magnetron is a function of a ratio between the measured power of the transmitted microwaves from the magnetron and the measured anode current.

10. The microwave heating apparatus of claim 1, wherein the operational data indicative of the measured anode current of the magnetron is further indicative of a power supplied to the magnetron.

11. A microwave heating apparatus comprising: a magnetron for generating microwaves; a cooling unit for cooling the magnetron; a measuring device for measuring power of transmitted microwaves from the magnetron and measuring anode current of the magnetron; a control unit configured to receive operational data from the measuring device indicative of the measured power of transmitted microwaves from the magnetron and receive operational data from the measuring device indicative of the measured anode current of the magnetron; and a calculating device configured to calculate an efficiency of the magnetron as a function of the measured power of the transmitted microwaves from the magnetron and the measured anode current, to define a determined efficiency; wherein the control unit controls the cooling unit and cools the magnetron based on the determined efficiency.

12. The microwave heating apparatus of claim 11, further comprising a sensor for detecting a temperature of the magnetron to define a detected temperature.

13. The microwave heating apparatus of claim 12, wherein the calculating device calculates a calculated temperature time derivative based on, in part, the detected temperature of the magnetron.

14. The microwave heating apparatus of claim 13, wherein the determined efficiency of the magnetron is further determined based on the calculated temperature time derivative.

15. The microwave heating apparatus of claim 11, wherein the magnetron is adapted to feed the transmitted microwaves from the magnetron to a cavity of the microwave heating apparatus via a transmission line.

16. The microwave heating apparatus of claim 11, wherein the control unit is configured to receive a measured power of microwaves reflected back to the magnetron and control the cooling of the cooling unit based on the determined efficiency of the magnetron and the measured power of microwaves reflected back to the magnetron.

17. The microwave heating apparatus of claim 11, wherein the control unit is configured to determine a cooling demand based on the determined efficiency to define a determined cooling demand, and control the cooling unit based on the determined cooling demand.

18. The microwave heating apparatus of claim 17, further comprising controlling the cooling unit based on the determined efficiency and reducing a noise generated by the cooling.

19. The microwave heating apparatus of claim 11, wherein the efficiency of the magnetron is a function of a ratio between the measured power of the transmitted microwaves from the magnetron and the measured anode current.

20. The microwave heating apparatus of claim 11, wherein the operational data indicative of a measured anode current of the magnetron is further indicative of a power supplied to the magnetron.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, with reference to the appended drawings, in which:

(2) FIG. 1 schematically shows a microwave heating apparatus according to an embodiment of the present invention;

(3) FIG. 2 schematically shows a microwave heating apparatus according to another embodiment of the present invention;

(4) FIG. 3 is a general outline of a method of controlling cooling of a microwave source in a microwave heating apparatus in accordance with embodiments of the present invention; and

(5) FIG. 4 is a general outline of a method of controlling cooling of a microwave source in a microwave heating apparatus in accordance with another embodiment of the present invention.

(6) All the figures are schematic, not necessarily to scale, and generally only show parts which are necessary in order to elucidate the invention, wherein other parts may be omitted or merely suggested.

DETAILED DESCRIPTION

(7) The present invention relates to the field of microwave heating, and in particular to methods for controlling cooling in a microwave heating apparatus.

(8) With reference to FIG. 1, there is shown a schematic view of a microwave heating apparatus according to an embodiment of the present invention.

(9) The microwave heating apparatus 100 comprises a microwave source 110 (e.g. a magnetron), a transmission line 120 and a cavity 130. The microwave source 110 is arranged at a first end, or extremity, of the transmission line 120 while the cavity 130 is arranged at a second end, opposite to the first end, of the transmission line 120. The microwave source 110 is adapted to generate microwaves, e.g. via an antenna 112, and the transmission line 120 is configured to transmit the generated microwaves 112 from the (antenna 112 of the) microwave source 110 to the cavity 130.

(10) The microwave heating apparatus further includes a cooling unit 190 for cooling the microwave source 110 (as schematically represented by the airflow illustrated by an arrow in FIG. 1) and, optionally, any other parts subject to a temperature increase induced by the operation of the microwave source 110. The cooling unit 190 may for example comprise a fan associated with a motor and pipes for guiding air from the fan to the microwave source 110 or for circulating the air around the microwave source 110. The microwave heating apparatus 100 further includes a control unit 170 configured to control the cooling unit 190.

(11) According to an embodiment, the control unit 170 may determine the need of cooling as a function of the efficiency of the microwave source 110. The cooling of the microwave source 110 via the cooling unit 190 is then adjusted or regulated accordingly. Several types of regulation of the cooling unit 190 may be envisaged. For the purpose of illustration, in a basic implementation with only two different levels of regulation of the cooling unit, the determined efficiency may be compared with a threshold and if the efficiency is above the threshold, the cooling system is operated at a first level and if the efficiency is below the threshold, the cooling system is operated at a second, higher than the first, level. In other embodiments, the cooling unit may be regulated based on a plurality of regulation levels. Further, the central unit 170 may include a lookup table correlating a specific efficiency with a specific regulation level, thereby providing a more sensitive control of the cooling (depending on the number of regulation levels included in the lookup table). The regulation may also be based on extrapolation of a regulation level even if the efficiency is not included in the lookup table, i.e. by extrapolation of an intermediate value between two subsequent values of the lookup table, thereby providing a more continuous type of regulation.

(12) According to a first alternative, the control unit 170 may determine the efficiency of the microwave source based on a temperature time derivative. For this purpose, the microwave heating apparatus 100 may be equipped with a temperature sensor 180 arranged at or in proximity to the microwave source 110. In this respect, the sensor 180 is preferably arranged directly at the anode outer mantle or on the radiator fin assembly used to cool down the microwave source (somewhat shielded behind the anode). The fan may then be arranged on the opposite side of the anode. The control unit 170 may then receive the temperature measurements from the temperature sensor 180 and by using a calculating or computing device to measure the power of microwaves. The calculating or computing devices can be a microprocessor or code stored within the memory system of a computer containing a processor where the code is capable of measuring the power of microwaves. The device is typically a directional coupler, (not shown), which calculates the temperature time derivative. The microwave heating apparatus 100 may then further include a clock (not shown) to track the time elapsed between two subsequent temperature measurements. The calculating device and the clock may be part of the control unit 170. However, it may also be envisaged that the calculating device and the clock are provided as separate entities or integrated in the temperature sensor 180 itself.

(13) According to another alternative, the control unit 170 may determine the efficiency of the microwave source 110 based on the power level of the microwaves transmitted from the microwave source 110 to the cavity 130 and operational data indicative of the power supplied to the microwave source 110. For this purpose, the control unit 170 may be connected to a measuring device 140 adapted to measure the power of the microwaves transmitted in the transmission line 112 and a receiving device 150 adapted to receive and capable of receiving the operational data (e.g. the power supplied to the microwave source 110). The receiving device is typically linked to information about the power fed to the source itself. In the case of magnetron, this is, for example, the magnetron anode current. The magnetron anode current can be readily measured in the power supply feeding the magnetron either by using anode current data directly accessible in the case of an inventor or with an additional current clamp circuitry if a half-wave voltage doubler power supply is used.

(14) For a magnetron, the efficiency may be determined as a function of the ratio between the measured power of the transmitted microwaves and the anode current of the magnetron 110 (wherein the anode current is representative of the power supplied to the magnetron 110). It will be appreciated that for microwave ovens provided with inverters for controlling the anode current of the magnetron, such information may be directly obtained, normally via the inverter, by the control unit 170. However, it is also contemplated to apply the present invention to microwave ovens not comprising any inverter and for which the anode current may be derived via e.g. an external current meter connected to the (anode of the) magnetron 110. Measurements of the anode current in microwave ovens provided with regular high voltage transformers is preferably performed “outside” the tube of the magnetron 110 itself, e.g. in the supply circuit.

(15) In particular, in microwave ovens, the frequency of the microwaves varies as a function of the anode current (or as a function of a current from some power supply connected to the magnetron). Thus, if the anode current varies (for any reasons such as a change in output power from e.g. 900 W to 400 W), the oscillating frequency of the magnetron may vary (also refers to as the pushing factor), which may affect the efficiency of the magnetron. As the oscillation frequency is changed, the microwave source may then operate in sink phase. However, the pushing factor (i.e. a change in oscillating frequency because of a change in the average anode current) may also make the magnetron operate in anti-sink phase. The present invention takes care of the pushing factor in that the microwave heating apparatus 100 according to the present invention is configured to determine whether the efficiency of the microwave source 110 has changed and the cooling is regulated accordingly. Normally, if it is determined that the magnetron 110 operates in the sink phase (i.e. at relatively high efficiency), the cooling is decreased, and if it is determined that the magnetron 110 operates in anti-sink phase, the cooling is increased.

(16) The microwave heating apparatus 100 may include additional measuring devices 145 configured to measure the power level of microwaves reflected back towards the microwave source 110. In FIG. 1, the measuring device 140 and the additional measuring device 145 are integrated in a single entity, typically a directional coupler. Generally, microwaves transmitted to a cavity may be either absorbed by a load arranged in the cavity, absorbed by elements of the cavity (or other objects present in the cavity), or reflected back from the cavity (or feeding port). Indeed, if the coupling to the cavity 130 is not perfect, some microwave power may be reflected, e.g. through a feeding port, back into the transmission line 120 towards the microwave source 110. An advantageous, and thus preferred, way to control whether there is a satisfactory coupling to the cavity 130, is by measuring the power that is reflected from a feeding port of the cavity 130. In the example schematically shown in FIG. 1, the power of the reflected microwaves may be measured at the extremity of the transmission line 120 which is closest to the cavity 130. The powers of the reflected microwaves are, at least partly, representative of the amount of microwaves absorbed by the load 138 arranged in the cavity 130.

(17) According to an embodiment, the control unit 170 may determine the need of cooling as a function of the measured power of the reflected microwaves. In a basic implementation, the control unit 170 may be configured to set the cooling unit 180 at a first level of cooling capacity (e.g. using a first speed of the fan motor of the cooling unit) if the amount of reflected microwaves is below a predetermined threshold and at a second level of cooling, higher than the first level (e.g. using a higher speed of the fan motor), if the amount of reflected microwaves is above the predetermined threshold.

(18) Further, the control unit 170 may be configured to set the cooling level in accordance with the reflection coefficient (obtained by the ratio of the measured power level of the reflected microwaves and the measured power level of the transmitted microwaves) wherein a first cooling level may be set for a first range of reflection coefficients, e.g. between 0.5 and 0.7, a second cooling level may be set for a second range of reflection coefficients, e.g. between 0.7 and 0.9 and a third cooling level may be set for a third range of reflection coefficients, e.g. between 0.9 and 0.99. Advantageously, in the present example, the strength of the cooling increases from the first to the third cooling levels such that the microwave source 110 is more strongly cooled down for high reflection coefficients.

(19) Further, in accordance with further embodiments of the present invention, the control unit 170 may be configured to control the cooling based on a combination of the efficiency of the microwave source (either determined via the temperature time derivative or via the measured power level of the transmitted microwaves) and the heating efficiency as determined by the measured power level of the reflected microwaves.

(20) With reference to FIG. 2, there is shown a microwave heating apparatus 200, e.g. a microwave oven, having features and functions according to an embodiment of the present invention.

(21) The microwave oven 200 comprises a cavity 230 defined by an enclosing surface. One of the side walls of the cavity 230 may be equipped with a door 235 for enabling the introduction of a load, e.g. food, in the cavity 230. Further, the cavity 230 may be provided with a feeding port (or antenna) 233 through which microwaves are fed to the cavity 230 of the microwave oven 200. The feeding port may for instance be an antenna, such as a patch antenna or an H-loop antenna, or even an aperture in a wall (including sidewalls, the bottom and the ceiling) of the cavity 230. In the following, reference is made to the term “feeding port”.

(22) The microwave oven 200 further typically includes a microwave source 210, e.g. a magnetron, connected to the feeding port 233 of the cavity 230 by a transmission line or waveguide 220. The transmission line 220 may for instance be a coaxial cable.

(23) Further, the microwave oven 200 may include a first measuring unit (or measuring means) 240 for obtaining, or being adapted to obtain, a signal representative of the power transmitted from the microwave source 210.

(24) Further, the microwave oven 200 may also include a second measuring unit (or measuring means) 245 for obtaining, or being adapted to obtain, a signal representative of the reflected from the cavity 230 at the feeding port 233. The first measuring device 240 and the second measuring device 245 may e.g. be arranged at the feeding port 233, such as depicted in FIG. 2.

(25) Further, the microwave oven 200 may include a receiving device 250 (as discussed above in the context of FIG. 1) adapted to receive operational data (i.e. information) indicative of the power supplied to the microwave source 210.

(26) Further, the microwave oven 200 may include a temperature sensor 280 arranged at or near the microwave source 2i0 for measuring the temperature of the microwave source. For example, the temperature sensor may be arranged directly at the source (i.e. the anode) or at a heat sink (not shown and usually used to more efficiently cool down the microwave source) of the microwave source 210.

(27) Further, the microwave oven 200 includes a control unit 270 operatively connected to the first measuring unit 240, the second measuring unit 245, the receiving device 250 and the temperature sensor 280. The result of the measurements performed by the first measuring unit 240, the second measuring unit 245, the temperature sensor 280 and the information received by the receiving device 250 are transmitted to the control device or unit 270. The control unit 270 is then configured to determine the need of cooling based on either the efficiency of the microwave source 210, the measured level of the microwaves reflected back towards the microwave source 210 or a combination of both such information. The control unit is then configured to control a cooling unit 290 for cooling the microwave source 210 accordingly.

(28) Either one, or both, of the first measuring unit 240 and the second measuring unit 245 may be integrated as sub-units in the control unit 270. Alternatively, the measuring units 240 and 245 may be arranged as separate units connected to the control unit 270. For example, the sensing part(s) of the first measuring unit 240 and the second measuring unit 245 may be a probe comprising a field-sensor at its extremity for sensing the energy transmitted to or reflected from the cavity, respectively. As another example, the first measuring unit 240 and the second measuring unit 245 may be a directional coupler arranged in proximity to the feeding port 233 and in proximity to, or in connection with, the transmission line 220 connecting the microwave source 210 with the feeding port 233.

(29) It will be appreciated that the receiving device 250, although it is represented as a separate entity in FIG. 2, may be an integrated part of either one of the microwave source 210 or the control unit 270.

(30) Further, the respective powers of the transmitted and/or the reflected microwaves may be measured by the measuring units 240 and 245 at various time points during an operation cycle (for instance used for heating a load arranged in the cavity) of the microwave heating apparatus 200 and the cooling of the microwave source is regulated in accordance with any one of the above described embodiments. It is therefore contemplated that the first and second measuring units 240 and 245 may be adapted to, continuously or periodically, monitor the signals representative of the powers of the transmitted and reflected microwaves in order to dynamically determine the heating efficiency and thereby dynamically regulate the cooling of the microwave source during an operation cycle accordingly. For the synchronization of the power measurements in relation to, or within, the operation cycle, the microwave oven 200 may further include a clock system (not shown).

(31) Any of the embodiments described above with reference to FIG. 1 for determining the efficiency of the microwave source 110 is applicable to the microwave heating apparatus described with reference to FIG. 2.

(32) With reference to FIG. 3, a method 3000 of controlling cooling of a microwave source in a microwave heating apparatus is described in accordance with exemplifying embodiments of the present invention.

(33) The method starts at step 3100 wherein the control unit may be in idle mode and waiting before starting the process. The process may be run on a periodic basis according to a specific time interval.

(34) According to a first alternative, the method includes the step of detecting 3200 the temperature of the microwave source and the step of calculating 3300 the temperature time derivative based on, in part, the detected temperature. The method then includes the step of determining 3400 the efficiency of the microwave source based on the calculated temperature time derivative.

(35) According to a second alternative, the method includes the step of measuring 3250 the power of microwaves transmitted from the microwave source and the step of receiving 3350 operational data indicative of the power supplied to the microwave source. The method then includes the step of determining 3400 the efficiency of the microwave source based on the measured power of the transmitted microwaves and the received operational data.

(36) Optionally, the method may further include the step of measuring 3500 the power of microwaves reflected back to the microwave source.

(37) The cooling is then controlled at step 3600 based on either the determined efficiency of the microwave source or a combination of the determined efficiency of the microwave source and the measured power of the reflected microwaves.

(38) It will be appreciated that any one of the embodiments described above for the first and second aspects of the present invention with reference to Figures land 2 is combinable and applicable to the method described herein with reference to FIG. 3.

(39) With reference to FIG. 4, a method 4000 of controlling cooling of a microwave source in a microwave heating apparatus comprising a transmission line via which microwaves generated by the microwave source are transmitted to a cavity is described in accordance with other exemplifying embodiments of the present invention.

(40) The method starts at step 4100 wherein the control unit may be in idle mode and waiting before starting the process. The process may be run on a periodic basis according to a specific time interval.

(41) The method includes the step of measuring 4200 the power of microwaves reflected back to the microwave source. Optionally, the method may also include the step of measuring 4300 the power of microwaves transmitted from the microwave source.

(42) The method then further includes the step of controlling 4400 the cooling based on the measured power of the reflected microwaves or a combination of the measured power of the reflected microwaves and the measured power of the transmitted microwaves (for example for computation of the reflection coefficient).

(43) It will be appreciated that any one of the embodiments described above for the third aspect of the present invention with reference to Figures land 2 is combinable and applicable to the method described herein with reference to FIG. 4.

(44) Further, it will be appreciated that in the methods described with reference to FIG. 3 or 4 the measurements (of the power levels and the temperature) and the regulation of the cooling are advantageously performed at a sufficient rate such that the cooling is adapted to any sudden changes, in particular in efficiency of the microwave source.

(45) The present invention is applicable for domestic appliances such as an oven, or more typically, a microwave oven using microwaves for heating. The present invention is also applicable for larger industrial appliances found in e.g. food operation. The present invention is also applicable for vending machines or any other dedicated applicators.

(46) While specific embodiments have been described, the skilled person will understand that various modifications and alterations are conceivable within the scope as defined in the appended claims.

(47) For example, the steps of the method described with reference to FIG. 4 may be performed in another order than that described above, in particular for steps 3200-3350 and for steps 4200 and 4300.

(48) It will be appreciated that the present invention is not limited to any specific range of frequencies for operation of the microwave heating apparatus. The present invention is therefore applicable for any standard microwave sources having mid-band frequencies of 915 MHz, 2450 MHz, 5800 MHz and 22.125 GHz.

(49) Further, it will be appreciated that the present invention is not limited to a microwave source being a magnetron. The microwave source may for example be a solid state microwave generator (or semiconductor-based microwave generator) including e.g. a varactor diode (having a voltage-controlled capacitance).

(50) Although a microwave heating apparatus including only one microwave source has been described above, it is also envisaged to apply the present invention to microwave heating apparatus including a plurality of microwave sources. The microwave sources may then be cooled down by use of a centralized cooling unit (connected to the microwave sources by a piping structure in order to provide cooled air to each of the microwave sources) or individual cooling units for one microwave source or a subgroup of microwave sources.