This invention relates to appliances, and more specifically, to a range having a power management system for detecting the source line voltage and adjusting load device currents of the range.
This invention relates generally to electronic power control systems for electrical loads which may be subject to a plurality of different supply voltages or to substantial swings relative to a nominal supply voltage. Cooking performance can be influenced by the line voltage. The standard line voltage for a range is 240 VAC, but there are certain locations where only 208 VAC is supplied on the line. This drop in line voltage can have a negative impact on cooking performance.
In different geographic areas within the U.S. as well as among various countries throughout the world, the nominal supply voltages can differ significantly. Typical nominal RMS supply voltages are 208, 220, 240 volts. In addition, voltages can vary from the nominal supply value. In resistive heating elements such as may be employed in cooking appliances, relatively large output power changes can occur with relatively small changes in input voltages since output power varies with the square of the voltage. Similar changes can occur with non-resistive loads such as electric motors for washing machines, or inverter circuits for induction cooktops.
Rather than design a different control system for each different nominal supply voltage it would be desirable to provide a single cost effective control system for an appliance, for example, which would allow the appliance to be used with any of the various power supplies. To be attractive for such applications the control system should either automatically adapt to the applied voltage, or at least be readily and simply pre-settable to various supply voltages in the factory or during installation. If the range is able to sense that 208 VAC is being supplied on the line, it can use cooking parameters that are specifically tailored to lower voltage (208 VAC) operation. providing uniform cooking settings independent of the line voltage.
In addition, it would be desirable to provide a control system for an appliance which automatically compensates for over-voltage or under-voltage conditions without any apparent difference in performance thereby preventing damage to the appliance, avoiding a potential safety hazard, all without interrupting use and enjoyment of the appliance.
In the preferred embodiment of the invention, an improved power management system is provided for controlling the total amount of current provided to at least a first and a second load device of an appliance. The power management system is comprised of a microprocessor, an alternating current voltage source, a voltage regulating circuit, a clamping circuit, a clamping circuit, at least two load devices, and a MOC and a triac for each of the at least two load devices. The clamping circuit outputs a fixed voltage of 5.7 volts during the positive portion of the ac cycle and a fixed voltage of −0.7 volts during the negative portion of the ac cycle. These voltages are input to a microprocessor so the microprocessor knows when the ac voltage crosses the zero threshold from one portion to another. The microprocessor utilizes these inputs to control the amount of time the current is turned on to each of the at least first and second load devices. The current is turned on to each of the at least first and second load devices by an output from the microprocessor provided to the associated MOC which in turn controls the associated triac for turning the current on to the associated load for the amount of time determined by the microprocessor. One of the at least first and second loads has a sensing circuit which monitors the current drawn by the load. A surge or rise in the current drawn will cause an output from the sensing circuit which is input to the microprocessor. The microprocessor will adjust according to pre-programmed instructions the amount of time the current is turned on and hence the average voltage applied to each of the at least first and second loads so that the total current drawn by all of the at least first and second loads does not exceed a pre-determined value. This requires that the microprocessor reduce the average voltage and current provided to the at least second load to account for the increased amount of current used by the first load.
In the description to follow, the control arrangement of the present invention is applied in a power control system for an electric cooktop appliance. The invention may, however, be employed to control a variety of other types of electrical loads including but limited to, ranges where a cooking oven is included, a cooktop where the surface burners are exposed, microwave ovens, wall ovens or a combination of electrical appliances. Further, the description herein in conjunction with the cooking appliance is not to be interpreted as limiting the invention to such appliances.
In the description to follow, the designators 230-236 shall be understood to refer to the heating units disposed under patterns 130-136 respectively. Each of heating units 230-236 comprises an open coil electrical resistance element designed when energized at its rated power to radiate primarily in the infrared (1-3 micron) region of the electromagnetic spectrum. Such heating units are known and not described in further detail. Each of heating units 230-236 are designed to operate at 100% of rated power when energized by a specific input voltage, for example of 208 volts RMS.
The power control system 260 controls the power applied to the heating units by controlling the rate at which gate pulses are applied to the triac gate terminals in accordance with power setting selections for each heating unit entered by user actuation of the control and display panel 150.
The zerocross circuit 210 shown in
In the illustrative embodiment gate signals are applied to triacs 240-246 to couple power pulses to the heating units. Each pulse is a full cycle of the 60 Hz AC power signal; however, power signals of different frequencies, such as 50 Hz, could be similarly used.
For example the equations used to approximate line voltage at 60 Hz are shown in the following Table 1:
Equations used to approximate line voltage at 50 Hz are shown in Table 2:
These equations are plotted in
Power control system 260 is arranged to operate each heating unit at one of a plurality of discrete power levels. These levels are available to adjust the power applied to the heating unit 230-236 such as, for example, to overdrive the heating units when operating in a transient heat up mode to rapidly heat the units to radiant temperature. The power control system uses power pulse repetition to provide an expected heat output at a user specified power setting. Power pulse repetition is known and will not be described in further detail.
While in accordance with the Patent Statutes specific embodiments of the present invention have been illustrated and described herein, it is realized that numerous modifications and changes will occur to those skilled in the art. For example, the invention could also be used in other applications as well, such as power control for induction cooktops or as a motor control in a clothes washing appliance. It is therefore to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit and scope of the invention.