GB2263592A - Improving stability of power supply system voltage by controlling timing of increase/decrease in power consumption of a load - Google Patents

Abstract

A device controls a load so that the load can only turn on, or increase its power consumption, if the instantaneous (or short term average) value of the amplitude of the voltage of an A.C. or D.C. supply system is above a first threshold, and so that the load can only turn off, or decrease its power consumption, if the instantaneous amplitude is below a second threshold. The first and second thresholds may be equal to one another and equal to the long term average of the supply voltage, (Figs 1, 2). Alternatively, the first threshold may be less than the second or vice versa, (Figs 7, 8) and both may be adjusted in dependence on the highest and lowest values of the supply voltage in a given time interval. In an appliance with microcomputer control to maintain a target value of a certain parameter, the additional deviation from the target value due to the power-switching delay inherent in use of the device of the invention may be compensated by microcomputer calculation of the on-delay and off-delay averages and by advancing monitoring for suitable on/off time points by such average period ahead of the times when the microcomputer estimates that an upcoming on or off command will next be given in response to deviation from the target value.

Description

ADEQUATE POWER-SWITCHING TIMING-CONTOL DEVICE ERR LARGE POWER-CONSUMPIIOL ELECTRICAL APPLIANCE The present invention relates to a device which, in order to assist the automatic control function of an electrical appliance, can adequately select an optimal timing for switching ON/OFF the power, or increasing/decreasing power-consumption of the appliance. In an electrical appliance without an automatic controller and operated manually, the present invention assures the function for an adequate timing control, too.

As known, the line-voltage in a public power supply system, due to freely the end users' usages of electrical appliances (broad definition of electrical appliance includes electrical mechanics which are driven by motor, heater, electromagnetic device, or large power-consumption electronic devices, etc.) and the unpredictability of when each electrical appliance will switch to any state of power-on, power-off, speed up, speed down, increasing power-consumption, or decreasing powerconsumption in its automatic control, will result in a supply of varying voltage. This kind of line-voltage difference, caused by the variable instantaneous power-consumptions in local area, can't be avoided absolutely no matter how stable a generator can control. And the poor quality of power supply which each end user disgusts becomes an outstanding problem.

The instability of the supplying line-voltage urges users who require stable voltage supply for electrical appliances such as computers to resolve the problem by themselves as to adopt voltage-stabilizers or unstop-power-suppliers (UPS). However, they cost money and can be used only at occasions with small variance in power-consumption. For example, the starting current of a motor can be up in seconds to 4 times operating current, under this circumstance, a voltage-stabilizer or an UPS system can not guarantee a stable voltage. Besides, since adoption of these kinds of voltage-stabilizing equipments, as they themselves still consume power and will certainly affect voltage in the supply system, thus, it will not improve the quality of power supply thoroughly.

Since the random change in line-voltage, while at a low-voltage state (the instantaneous voltage is lower than the average voltage), if an electrical appliance (such as a motor) suddenly turns on or increases its power-consumption, then the appliance not only consume a larger current than that of the rating-current while at a standard-voltage, but also induce the voltage of the supply line to a much lower state. This may prompt the total consumed-current of all electrical appliances to exceed the allowed total consuming-current, and burn off the fuse or break off a protecting breaker and shut down the power supply.

Similarly, while at a high-voltage state (the instantaneous voltage is higher than the average voltage), if an electrical appliance suddenly turns off, then the line-voltage will rise because of the decreasing of powerconsumption. This will generate an unstable power-consumption such as a sudden-bright in a lamp, or a sudden-speed in the revolution of a motor, connected in the line. Moreover, it can affect life time of an electrical appliance, and produce feedback effect which will hamper the control of the power generating system and influence a partial or the whole power system. Therefore, ideally, each electrical appliance shall consider the voltage status of the power source while turning itself on or off.

Normally, the power supply system, protection devices (such as fuse) and power lines in a building or a production line have been settled and passed the security check while being installed. Any amendment afterwards causes additional efforts. Yet, with the rising in living standard or requirements of a higher productivity, it is frequently that the user or plant manager will adopt more and more electrical appliances, thus the power-consumption will easily reach to the limit of the contracted-power in a building or a production line. Under this circumstance, any improper ON/OFF timing can generate overloading situation.Furthermore, most of the modern electrical appliances have equipped with automatic controller such as a timer, program selector, sequence selector, status selector or feedback control, however, there's no such device which can detect the voltage status of power supply system, or control itself correspondingly. In this case, if many electrical appliances simultaneously turn ON at a low-voltage status or OFF at a high-voltage status, a poor quality of power supply will happen and this can even cause a disaster of power shut-down. In an electrical appliance which does not equip with any automatic controller and is switched ON/OFF manually, a similar situation still exists, as a man either does not recognize when an appropriate timing is to switch ON or OFF an electrical appliance.Moreover, since the power supply networks relate to each other, any sudden change of power consumption in an area can affect other users more or less, this will do harm to all electrical appliances and users, too.

Generally, if an electrical appliance turns ON (such as speeds up, heats up, increases the power-consumption, etc.) while in its high-voltage state; or turns OFF (such as speeds down, decreases the powerconsumption, etc.) while in a low-voltage state, since it will lower the peak of the instantaneous voltage or rise the bottom of the instantaneous voltage, therefore, the breaker will not break off, fuse will not burn off, power will not shut down. And thus at starting, the electrical appliance needs only a smaller starting current (especially for electrical appliance with motor), and can run smoothly. Therefore, a safer ON/OFF is secured, the leap time of a START/STOP will become shorter, and the life of an electrical appliance will last longer. Undoubtedly, a positive effect in the quality of power supply achieves.

The operational methodology of the present invention is to detect in a shorter period (such as 3 minutes, the time interval can be adjusted) the average line-voltage which varies by time-sequence or the variation range of the line-voltage in a larger interval (such as 1 hour), and compare that with the instantaneous voltage of the line where the electrical appliance is about to ON/OFF. If a instantaneous voltage is higher than the average voltage or is located in a higher portion of the variation range, then it allows the electrical appliance to be switched on or speed-up by connecting the electrical appliance with the power source through a relay or solid-state switch (such as SCR or TRIAC, etc.).

Certainly, the controller by this time is giving an "ON" or powerconsumption INCREASING (thereinafter, as ON) command; if otherwise, an "OFF" or power-consumption DECREASING (thereinafter, as OFF) command is signalled, then the present invention will delay temporarily the OFF-timing of the electrical appliance, till it detects that a instantaneous voltage of the power source is lower than the average voltage or a threshold voltage. Contrarily, if it detects that the instantaneous voltage is lower than the average voltage or is located in a low threshold region, then it permits the electrical appliance to be switched OFF.Of course, by this time, the control device of this electrical appliance is giving an 'OFF' command; and it will delay temporarily the 'ON' command, till the instantaneous voltage of the power source is higher than the average voltage or a preset threshold voltage.

Currently, electrical appliance in use or in the market does not equip with any kind of power-switching timing-control device. As the more people rely on the electrical appliance, and as the more automatic controllers are used in the work places and production lines, the worse the quality of power supply (especially those users at the end of a supply network). As comparison, the present invention provides functions not only in protecting the electrical appliance itself, prolonging its life time, increasing the security, but also in raising quality of power supply in the power lines. After popularly adapted, the present invention will effectively stabilize voltage in power supply systems.Moreover, it will avoid the necessity of facilitating a much larger capacity in a power plant, and prevent the power generator to break off or a public transformer to explode due to overload caused by inappropriate timings in switching power.

The present invention can be installed in each kind of electrical appliance: to any electrical appliance with large power consumption, AC or DC, high-voltage or low-voltage, especially an inductive appliance (such as motor) on a line in a network system as large as a plant, a ship, etc., or as small as a house or a vehicle. The objectives and characteristics will be thereinafter described in detail in the following embodiments.

FIG. I is an electrical circuit illustrating how voltage is detected in one embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of the average voltage, instantaneous voltage, and output signal of a comparator, of FIG. 1.

FIG. 3 is a system diagram illustrating a (micro)computercontrolled electrical appliance equipped with the present invention.

FIG. 4 is a schematic diagram illustrating a statistical compensation to the power-switching delay in a microcomputer-controlled automatic appliance equipped with the present invention.

FIG. 5 is a composition diagram of a manual-switching electrical appliance equipped with the present invention.

FIG. 6 is a diagram showing the voltage level and switching-signal in the circuit of FIG. 5.

FIG. 7 is a diagram illustrating another embodiment of the present invention.

FIG. 8 is a diagram illustrating the comparison of voltages, and controlling of the microcomputer of FIG. 7.

As shown in FIG. 1, one embodiment of the present invention comprises two transformers 1 and 2 connected with power lines AC, the output voltage of these two transformers can be the same, or of different, according to the connecting resistors 6 and 9 and the required voltagedrop. The output ports of transformers 1 and 2 are connected to two bridge-rectifiers 4 and 5. In which, the output DC voltage from rectifier 4 will be filtered and damped by a RC-circuit composed with a variableresistor 6 and variable-capacitor 7, and provided to an operational amplifier 8 as an average voltage Va which is stable in a long period. In order to ascertain that this average voltage can represent an average of line voltage in a long period, the time-constant of the variable-resistor 6 and variable-capacitor 7 is designed to a quite large value.Though the output voltage of rectifier 5 is a DC voltage, there is still ripples, and it is filtered by a smaller RC-value circuit, that is, a filtering circuit composed by a smaller fixed resistor 9 and a smaller fixed capacitor 10.

Its output voltage Vb also leads to the operational amplifier 8 which is a voltage comparator with an output voltage Vc, as shown in FIG. 2, a non-periodical square-wave.

FIG. 2 shows, with time axis T, the average voltage Va, instantaneous voltage Vbof a power source, and the generated output voltage Vc by comparing Va with Vb. The output voltage Vc of the comparator is a non-periodical square-wave, it decides when the highvoltage level H that allows an electrical appliance to be switched ON is; and when the low-voltage level L that prohibits an electrical appliance to be switched ON is. In a word, an electrical appliance which is not originally ON is permitted to be turned ON while at a high-voltage level H; after being turned ON, it is permitted to be turned OFF at a lowvoltage level L only.

FIG. 3 shows an embodiment of the present invention which applies to an electrical appliance 21 controlled automatically by a microcomputer 11. The above mentioned voltage Vc, which determines whether the line voltage of a power source is adequate for the electrical appliance 21 to be switched ON or OFF, is connected with an interrupt pin INT of the processing unit (CPU) in the microcomputer 11.The microcomputer 11 according to the ON or OFF requirement of the electrical appliance 21 (where the requirement of ON or OFF is a comparison result of a sensed value with a default value; or a timer reads, or a status or sequence shows, that it shall be ON or OFF; which is of general automatic control technique, and will not be described in detail herein), judges that whether voltage Vc of the current power source is on a status which allows the ON or OFF, then sends a control command to a power switch such as a relay 12, etc.That is, if an electrical appliance 21 gets a signal of an ON or OFF command, the microcomputer 11 will consider simultaneously that whether, at that time, the electrical appliance is in an ON-appropriate or OFF-appropriate state, and find an adequate timing for the electrical appliance to be switched ON or OFF which will ascertain that at a high-voltage state to allow more electrical appliances to consume power, at a low-voltage state to decline the use of power, thus provides a voltage-stabilizing effect and generates without over-current or over-voltage situations in the process.

FIG. 4 shows a compensation manner for minimizing the deviation caused by the power-swtiching delay of the present invention, which is used in an electrical appliance controlled by a microcomputer. The wave C indicates the deviation of control around a target value Xm. The deviation AX1+AX2 is caused by waiting for adequate timings, e.g. at 2, bk 2 -2 as shown, to switch the power.That is, in a general system without the invented device (As long as a control command sends, the electrical appliance will immediately switch ON or OFF, no matter if a power source is in an appropriate state to be ON or OFF.), the deviation is AX- (Axl+Ax2) and in the invented system which considers whether a power source is appropriate to be switched ON or OFF, this value increases to Ax. The microcomputer may calculate the average ON-delaying time

where ax are ak-2, ak-1, etc. as shown; or take the last ON-delaying time ak-l for compensation to the next timing of ON-control.That is, estimating that there will be an upcoming ON command, the microcomputer will start executing the ON-timing monitoring by this delaying-time ahead, so that smaller ON-time ak, ak' and less deviation AX' can be met. Similarly, an average OFF-delaying time

where bx are bk-3, bk 2 bk-l, etc. as shown; or the last OFF-delaying time but 1 can be taken for compensation to the next timing of OFFcontrol. That is, upon estimating an upcoming OFF command, the microcomputer will start executing the OFF-timing monitoring by this delaying-time ahead, so that smaller OFF-delaying time bk, bk' and less deviation AX' can be met.

If an electrical appliance is not controlled by a microcomputer controller, and instead is controlled by some general hardware control units, such as a thermostat, a frequency converter, a transponder, a humidity-equilibrator or any other controller which provides controlling functions (such as proportioning, integrating, ON-OFF, etc.), then the present invention will be connected in series with the signal output port of its control unit, as shown in port PB of FIG. 5. While at port PB, if there is an ON-command (can be a power-consumption INCREASING command such as speed-up, or current enlargement, as mentioned above), the electrical appliance will not switch on or speed up right away, rather, it will check if voltage of the power source is at an ONappropriate state, that is, whether Vc is on a high-voltage level at that time.

If it certifies that the voltage state is in an ON-appropriate state, then a SET signal is led to a self-hold relay 20 which will put through power that the electrical appliance 21 requires. After the electrical appliance 21 is ON, it can be OFF only till an OFF-command is sent out by PB, and the voltage level of the power source is checked to be at an OFF-appropriate state. In other words, while Vc is in a high-voltage level and the electrical appliance 21 is switched ON, then if Vc is back to a low voltage state and the controlling command is at an ON-state, then no matter how Vc is, the electrical appliance will remain on an ON-state temporarily, as shown in FIG. 6. Till PB gives an OFF-command and Vc drops to a low-voltage level, a RESET signal is sent to the electrical appliance which will then be switched OFF.The self-hold circuit for relay 20 which keeps an electrical circuit in the present state is of prior art and need not be described in detail herein.

The above described control signal of PB can be applied to any electrical appliance which has a manual ON-OFF switch. That is, even if the PB is a manual-switch, the operational methodology remains the same as described above.

FIG. 7 shows another embodiment of the present invention, which has a rectifier 15 that connects with power source AC. The output signal Vb of the rectifier 15 is a instantaneous voltage signal corresponding to the variance of the line voltage of the power source AC. The signal Vb is led to an analog-to-digital (A/D) converter 16 and through a processing unit (CPU) 17. A timer 18 provides time information that can be saved together with the corresponding digitized instantaneous voltage signal to a memory unit 19.The processing unit 17 will, according to comparison result of the ON/OFF requirement of an electrical appliance 21 and a user-preset higher voltage Vh and a lower voltage Vl which allow the electrical appliance 21 to be OFF and ON respectively, generate signal adequately to control the relay 12, so an ON-OFF range can be enlarged as shown in FIG. 8 (will be described later) and still maintains safety concerns.

FIG. 8 shows, in time axis T, a comparison of instantaneous voltage Vb in a power source with a higher voltage Vh and a lower voltage Vl which allow for the electrical appliance 21 (FIG. 7) to be switched OFF/ON respectively, in which, Vh and V1 can be set proportionally to the highest instantaneous voltage Vu and the lowest instantaneous voltage Vd in a specific time period: such as Vh=75% *1Vu-Vd Vl=25% * tVu-Vd where 75%, 25% are user-designated values. These values can be self-learned by the processing unit 17, too.That is, the processing unit 17 can retrieve from memory unit 19 each highest voltage Vu and each lowest voltage Vd in each time interval, and its variation of the voltage signal Vb at the ON and OFF state of the electrical appliance 21, and adjust automatically the Vh and V1 values. From the comparison, an ONappropriate time range Von and an OFF-appropriate time range Voff which allow an electrical appliance to be switched ON and OFF respectively are obtained. As shown in FIG. 8, the range Von and the range Voff overlaps in some time intervals, that means, under the basic restriction to maintaining a safe loading, a larger time range for power switching is obtained. Certainly, these two values Vh and V1 can be designated reversely so that a smaller time range for power switching can be obtained to some specific requirements.Also, these two values Vh and Vi can be set as a same value.

The electrical appliances that can be controlled by the present invention are inductive or resistive devices which consume large power such as motors, electromagnetic devices, magnetron, heaters, etc. While at the occasion of a DC power source rather than an AC, the present invention needs only to replace above mentioned transformers (1, 2) and rectifiers (4, 5, 15) with voltmeters.

The present invention allows an electrical appliance to be switched ON at a higher voltage state of a power source and not to be ON at a lower voltage state, so that the appliance obtains a smaller starting current which prevents itself from sudden overload at starting and avoids causing a power shut-down actuated by a power protection device such as a breaker. Since the electrical appliance is allowed to be switched ON at a higher voltage, it restricts the voltage of a power source from going too high; and as the appliance is switched OFF at a lower line voltage state, it raises the line voltage which stabilizes power supply system, and increases quality of power supply. It is good to each electrical appliance at the same power network because there will not have a too high voltage at starting an appliance, or a too high current at disconnecting.

Therefore, the electrical appliance will not be burned through or break down, and can have a longer life. And with a better quality of power supply, the electrical appliance won't generate unstable situations such as luminance-changes, unwanted flash in a bulb or annoying noise in a motor.

In practical, for the possible few second's ON/OFF delay caused by the effect of the present invention, the resulted changes in the electrical appliance (such as the control of temperature, humidity, etc.) is limited and can be omitted through the sensitiveness of human body. As to an occasion which requires an immediate ON/OFF switching, the present invention will provide an unshown by-pass which will take control immediately and let the electrical appliance get or cut-off required power once it receives a control command. As to an electrical appliance with simple ON/OFF control, the present invention will certainly provide switch protection, besides, since the small switching current, a smaller rated-current switch can be adapted to reduce the cost.

Moreover, since the present invention can automatically compensate the power-switching delay, the variation of control will not get larger but reduced instead. And since the switch works more smoothly, the life of the switch will be prolonged, or, the switch times which can be operated during a same life time will be increased, and it will prolong life of the electrical appliance.

The foregoing descriptions of embodiments are provided for the purpose of illustration only and not for limitation. Any modification or variation under spirits of the present invention by the ones familiar with the art shall be included and are only restricted to the following claims.

Claims (10)

1. A power-switching timing-control device connected with a power supply control means of a large power-consuming electrical appliance which utilizes a power source for determining an adequate timing of said electrical appliance to switch ON, OFF, or to change power consumption, said device comprises: voltage-range detecting means, for detecting a voltage range or threshold values of said power source; instantaneous-voltage detecting means, for detecting any instantaneous voltage of said power source; a comparator for comparing said instantaneous voltage to said voltage-range or threshold values, generating an ON-appropriate signal while said instantaneous voltage is greater than a first threshold, and generating an OFF-appropriate signal while said instantaneous voltage is smaller than a second threshold; and a controller, for controlling switching time of said appliance in the following manner: a) upon receiving said ON-appropriate signal, allowing said electrical appliance to be switched on while it is OFF and to consume more power while it is already ON; and prohibiting said electrical appliance which is already ON to be switched off or to consume less power; b) upon receiving said OFF-appropriate signal, allowing said electrical appliance which is already ON to be switched off or to consume less power; and prohibiting said electrical appliance which is already OFF to be switched on, so as to improve stability and supply quality of said power source.

2. A device according to claim 1, in which said first and second thresholds are all an average voltages of said power source, said voltagerange detecting means is an average-voltage detecting device comprises a RC circuit with a larger time-constant resistor and capacitor; said instantaneous-voltage detecting means comprises a RC circuit with a smaller time-constant resistor and capacitor; said comparator and controller all comprise at least one of the following: operational amplifiers, electro magnetic devices, solid-state components, relays, and logic circuits.

3. A device according to claim 1, in which said ON-appropriate and OFF-appropriate signals from said comparator are inputted to a computerized controller of said electrical appliance, for judging together with control demands of said electrical appliance to generate adequate timing commands to switch ON, OFF, increase and decrease power consumption of said electrical appliance.

4. A device according to claim 1, in which said ON-appropriate and OFF-appropriate signals from said comparator are inputted to a logic circuit which composes said signals with output-signals of said power supply control means of said electrical appliance for detaining adequate power-switching timings1 and executing control through a self-hold switching means.

5. A device according to claim 3 in which said computerized controller will calculate an average ON-delaying time and use it to operate in advance for preparation to switching ON and OFF, so as to minimize deviation of control.

6. A device according to claim 4, in which said power supply control means of said electrical appliance is a manual ON-OFF switch.

7. A device according to claim 1, in which said first and second thresholds are predesignated critical-values of voltage, and these two values can be of the same.

8. A device according to claim 7, in which said voltage-range detecting means comprises a microcomputer for recording a highest and a lowest voltage of said power source, and variation of voltage of said power source while switching ON-OFF said electrical appliance, for automatically designating and adjusting said first and second thresholds.

9. A device according to claim 1, in which said power source comprises any of AC and DC powers.

10. An adequate power-switching timing-control device for large power-consumption electrical appliance, substantially as hereinbefore described with reference to the drawings.