WO2003096523A1

WO2003096523A1 - Reduced energy multiple-function digital controller for motors and appliances

Info

Publication number: WO2003096523A1
Application number: PCT/PH2002/000005
Authority: WO
Inventors: Andrew F. Risso; Hilary L. De Leon; Jonathan C. Chua; Ricardo B. Dalumpines, Jr.
Original assignee: Risso Andrew F; De Leon Hilary L; Chua Jonathan C; Dalumpines Ricardo B Jr
Priority date: 2002-04-23
Filing date: 2002-04-23
Publication date: 2003-11-20
Also published as: AU2002306033A1

Abstract

An electronic controller using digital technology performs various functions in controlling the energy consumption of low power single-phase AC motors and providing protection and power conditioning to household appliances. It reduces energy consumption by automatically adjusting the voltage applied to the motor based on the poewr factor or phase angle between voltage and current. During low loads, motor efficiency is low and the phase angle is high so that the applied AC voltage is reduced, thereby saving on energy consumption. When the motor is fully loaded, the controller automatically applies full voltage. Furthermore, the digital controller also protects the load from over-voltage, under-voltage, overload, high starting currents, surges and transients. It also performs the functions of power-on delay, to prevent damage to the load when power interruption occurs and auto-volt operation, to allow operation over a wide range of voltages.

Description

REDUCED ENERGY MULTIPLE-FUNCTION DIGITAL CONTROLLER FOR MOTORS AND APPLIANCES

Background - Field of Invention

This invention relates to energy control and power conditioning for electric motors and household appliances.

Background - Description of Prior Art

The energy consumption of AC motors can be reduced by sensing the power factor or phase angle of the AC voltage and current and automatically reducing the applied voltage to the motor if the power factor is low or the phase angle is large. This is accomplished using an electronic switch, such as a silicon controlled rectifier ortriac, in series with the motor, a phase angle detector and a feedback control circuit. This approach is the basis of patent no.4,052,648 to Nolan, patent no. 4,704,570 to Hopkins, patent no. 4,455,521 to Day, et al, patent no. 5,637,975 to Pummer and patent no. 5,389,869 to Anderson.

The limitations of the prior art is that being analog designs, the application is limited to a single function, namely, energy reduction. Although other functions can be added, the cost will be too high for the consumer market. There is also a lack of flexibility since the functionality will be hard-wired.

Other patents which use digital methods include patent no. 5,801 ,935 to Sugden which uses a digital comparator and DC bus voltage and patent no.

5,631 ,550 to Castro, et al, which use digital sequential circuits. These are also limited in functionality and do not use microprocessors or microcontrollers.

Electric motors and electronic appliances also require some form of protection against the many abnormalities that can occur on an AC power supply source, Examples of these are voltage fluctuations, transients, surges and power interruptions. Such abnormalities or disturbances can cause serious damage to the motor or appliance load. To provide protection, separate devices are normally used that address each type of disturbance. By using a microcontroller chip, it is possible to perform all the functions of energy reduction, soft start, protection against voltage fluctuations and transients, protection against power interruptions and motor overloading all on a single low-cost device.

Brief Summary of the Invention

The invention is an energy saver and multi-function power protector that is based on a digital microcontroller with the appropriate peripheral circuits that is designed and programmed to perform the following functions: save energy when motors are operating at low loads, provide over and under voltage protection, provide current overload protection, allow operation over a wide range of voltages, provide surge and transient protection, provide power-on delay functions during power interruptions and perform soft start operation for motor loads.

Brief Description of Drawings Fig. 1 is the block diagram of the invention

Fig. 2 is the circuit diagram of the microcontroller, LED displays and other elements

Fig. 3A is the circuit diagram of the voltage zero crossing detector

Fig. 3B is the circuit diagram of the current zero crossing detector

Fig. 4 is the circuit diagram of the switching circuit Fig. 5 is the circuit diagram of the auto-volt power supply

Fig. 6 is the flowchart of the main program of the invention

Fig. 7 is the flowchart of the voltage protection function

Fig. 8 is the flowchart of the current detection function Fig. 9 is the flowchart of the user interface function Fig. 10 is the flowchart of the power-on delay function Fig. 1 is the flowchart of the motor soft start function

5 Reference Numerals in Drawing

2 AC Input 280 Flash Over/Under Voltage

4 Transient & Surge Protection Indicator LED

8 Auto Volt Power Supply 282 Turn ON/OFF Piezo Buzzer

26 Transient Protection 284 Increment Second Counter

10 30 Over Current Detector 286 Second Counter = Delay ?

46 Load 288 Turn OFF Triac

50 Voltage Zero Cross Detector 290 Turn OFF Energy Saving LEDs

66 Over/Under Voltage Detector 292 Current Detection

80 Microcontroller Chip 293 Increment Current Counter

15 98 Current Zero Cross Detector 294 Input Current > Max ?

114 Switching Circuit 295 Current Counter = Current Max

122 LED Bar Graph display Setting ?

216 Piezo Buzzer 296 Turn OFF Energy Saving LEDs

222 Push Button Switch 298 Turn OFF Triac

20 230 Over/Under Voltage Indicator 300 User Interface

232 Over/Under Voltage 301 Button Timeout = Mode Timeout

234 Start 302 Button Press ?

236 Initialization 303 Load Type = Motor ?

238 Power On Delay Function and 304 Button Counter = Previous

25 Display Blinking LEDs Button Counter

240 Rea EEPROM 306 Button Press ?

242 Get Time Setting 307 Load Type = Motor

244 Time Setting = 0 ? 308 Increment Button Counter

246 Decrement Time Setting 309 Write Load Type EEROM

30 248 Display Blinking LEDs 310 Button Counter = 0 ?

250 Exit Function 311 Increment Button Timeout

252 Load type = Motor? 312 Display Current Time Setting

254 Motor Softstart 313 Button Timeout = Timeout Setting ?

256 Triac ON delay counter - 50 % 314 Button Counter = 1 ?

35 2581 ncrement Triac ON delay counter 316 Display 0 Minute Time Setting

260 Triac ON delay counter = 75 % 318 Button Counter = 2 ?

262 Delay 2 seconds 320 Display 1 Minute Time Setting

264 Display Energy Saving 322 Button Counter = 3 ?

266 A 324 Display 3 Minute Time Setting

40 268 Detect Voltage Zero Cross? 326 Write to EEPROM the new Time

270 Voltage Protection Setting

272 Voltage (>=Min1 and <=Max1) 328 Start Count Power Factor Width or (>=Min2 and <=Max2) ? 330 Detect Current Zero Cross?

274 Triac Turn OFF 332 Compute Power Factor

45 276 Increment Minute Counter 334 Generate Pulse Width Modulated

278 Counter = Setting ? Triac Gate Signal Detailed Description of the Invention

The main components of the reduced energy digital controller are shown in the block diagram of Fig. 1. The microcontroller chip 80 is the primary controlling element and is programmed to perform most of the functions of the invention. AC input 2 is the AC supply voltage from the mains and provides power to both the circuit and the load 46, which can either be a motor load or a non-motor appliance load such as a computer or television set. A transient and surge protection circuit 4 suppresses voltage spikes and unexpected surges in current, thereby protecting the load 46. Auto-volt power supply 8 provides the DC voltage needed by the various circuits and is designed to operate over a wide range of AC input voltages, from less than 100 volts to around 240 volts. At the output of power supply 8, a transient protection circuit 26 provides additional protection to the microcontroller 80 and the rest of the circuit.

The voltage zero cross detector 50 and current zero cross detector 98 are used to determine the points in time at which the sinusoidal voltage and current become zero. These points are used by the microcontroller 80 to compute the power factor or phase angle between the AC supply voltage and the load current. The microcontroller 80 then calculates the pulse width of the signal that drives the switching circuit 114. The voltage applied to the load is regulated by the switching circuit 114. When the computed phase angle is high, it means that the load is inefficient. In the case of motor loads, it is running at less than full load and the pulse width of the signal modulating the switching circuit 114 is then reduced, thereby saving on energy.

The over current detector 30 is connected in series with the load 46 and senses the current flowing trhough the load 46. It generates a DC voltage proportional to the current and the microcontroller's internal analog-to-digital converter transforms the analog input signal to digital. Microcontroller 80 determines if the load current exceeds a pre-set limit for a sustained period of time. If so, it will shut off the switching circuit 114, thereby turning off the load 46.

Push button switch 222 is used for setting the time delay duration of the power-on delay function of the device. In the event of an unexpected power interruption the load 46 is prevented from being energized immediately when the power is restored. A pre-set time delay is observed before the load is energized. This protects the load from current surges at the instant power is restored and from short and sudden power interruptions before the power stabilizes. By pressing push button switch 222, the duration of the time delay can be selected.

LED bar graph display 122 is used to indicate the status of the device's operation such as power-on delay setting, amount of energy saving and whether the device is operating or not.

Over/under voltage detector 66 monitors the AC supply voltage by generating a proportional DC voltage. This voltage is converted to digital by microcontroller 80 and compared with pre-set minimum and maximum values. Once these values are exceeded, the microcontroller signals the over/under voltage LED indicator 230 to flash. If this condition persists for a pre-set period of time, the microcontroller 80 activates the piezo buzzer 216, several seconds before shutting down the load through the switching circuit 114.

Fig. 2 is the circuit diagram of the microcontroller, LED display and some of the other components of the device.

Over current detector 30 uses a hall effect current sensor (32) for non- intrusive measurement of the load current. The sensor's AC output voltage is scaled down by resistor divider 34, 36 and 40. Diode 38 rectifies the AC voltage and capacitors 42 and 44 filters it thereby converting it to a DC voltage for input to the internal analog-to-digital converter of microcontroller 80.

Over/under voltage detector 66 scales down the AC supply voltage using resistor divider 68, 70 and 74, while diode 72 rectifies the AC signal. Capacitors 76 and 78 filters the rectified AC to generate the DC voltage input to the internal analog- to-digital converter of microcontroller 80.

Microcontroller 80 has a central processing unit and various functions integrated into its chip. These include a parallel input output digital port, a multichannel analog to digital converter, timers and counters, a clock oscillator, random access memory and non-volatile flash program memory. An example of this type of chip is the PIC micro controller family from Microchip Technology Inc., USA. Crystal 92 and capacitors 94 and 96 complete the internal clock oscillator circuit of microcontroller 80. LED bar graph display 122 consists of an array of 30 Light Emitting Diode's physically arranged into 2 bar graph displays of 15 LED's each. The 8 rows are driven by parallel outputs of microcontroller 80, while the columns are driven by 4 lines from microcontroller 80's parallel port, through transistors 164, 180, 198 and 214. For example to turn on LED 168 the microcontroller output line connected to resistor 126 is set to a high and transistor driver 180 is turned on by setting the microcontroller output line connected to resistor 142 also to high.

Piezo buzzer component 218 is connected in series with resistor 220 and one of the output lines of micro controller 80. Resistor 220 is used as current limiter.

Push button switch 226 is a normally open switch and pulled up by resistor 224, which is connected to an input line of microcontroller 80. The capacitor 228 is used to filter unwanted high frequency noise.

The circuit for the voltage zero crossing detector 50 is shown in Fig. 3A. The positive half cycle of the AC supply voltage input 2 is reduced by voltage divider resistors 52 and 56 and compared with a reference set by voltage divider resistors 58 and 60 by using operational amplifier comparator 62. The output of the op amp comparator is pulled up by resistor 64 and connected to one of the input lines of microcontroller 80.

The circuit for the current zero crossing detector 98 is shown in Fig. 3B. Its input is from MT2 which is the voltage across the triac 120 of Fig. 4. Since triac 120 is in series with the load, the voltage drop across it is representative of the load current. This input is connected to voltage divider resistors 100 and 104 and compared to a reference voltage set by divider resistors 106 and 108 by using operational amplifier comparator 110. The output of op amp 110 is pulled up by resistor 112 and connected to one of the input lines of microcontroller 80.

The diagram of the switching circuit is shown in Fig. 4. An output line from microcontroller 80 is connected to logic triac 118 through current-limiting resistor 116. The logic triac is used to drive the high current triac 120 which is in series with load 46. Triac 120's rating is set such that in can operate. The control signal is a pulse width modulated signal generated by the microcontroller and turns on and off logic triac 118 alternately. The longer the turn-on period, the greater the current flowing through load 46. This pulse is synchronized with the zero crossing of the AC supply voltage.

DC power to the whole circuit is provided by the Auto-volt power supply as shown in Fig. 5. The AC input voltage 2 can range from 80 Volts to 250 volts AC and the Vcc supply to the circuit shall remain fixed.

Metal oxide varistor 6 is connected across the AC input to provide transient protection to both load 46 and the device. The power supply consists of step-down transformer 10, bridge rectifier 12, low dropout voltage regulator 16 and capacitors 14, 22 and 24 for filtering purposes. Diodes 18 and 20 are used for protecting the voltage regulator. Since the voltage regulator is the low dropout type, its Vcc output remains constant even if the secondary voltage transformer 10 is reduced due to a low AC input voltage. Tranzorb 28 is connected across the Vcc and GND to protect the circuit against unexpected voltage spikes, especially if the load is a motor.

The succeeding figures describe the operation of the software which microcontroller 80 executes to perform the various functions of the device.

Fig. 6 is the flowchart of the main program and the energy saving function.

Upon power-up 234, the initialization function 236 sets up the microcontroller's input/output ports, the analog-to-digital converter, internal memory area and the variables needed by the program. The power-on delay function 238 is then performed and this is described by the flowchart of Fig. 10. The program then checks if the load type is a motor 252 by checking the load setting entered by the user. If it is a motor, the soft start module 254 is executed next.

The energy saving 264 is then displayed on one of the two LED bar graphs. The savings is determined by checking on the pulse width of the signal driving the triac gate. The narrower the pulse, the higher the savings and the more LED's on the bar graph display are turned on.

At this point the following modules are executed sequentially in a round-robin fashion: Voltage zero cross detect 268, Voltage protection 270, Current detection 292 and User interface 300. A timer in microcontroller 80 is programmed to generate interrupts at regular intervals and a module is called every interrupt until all the modules are called after which the cycle repeats. Once a voltage zero crossing 268 is detected, a counter is started 328 until the current zero cross is detected 330. The resulting count is proportional to the power factor 332. Based on this value, the pulse width of the signal driving the triac gate is estimated using a pre-programmed look-up table whose contents are established using empirical methods.

Fig. 7 illustrates the flowchart of the voltage protection module 270. The AC supply voltage is first checked if it is within the allowable range for 2 sets of operating voltages. The lower range is from Mini to Max1 and the higher range is from Min2 to Max2 272. If it is within range, the module returns to the main program.

If it is out of range and the triac is in the off state 274, the module repeats the loop. If the triac is on, it means that the load is energized, a time delay minute counter is then started 276 until the setting is reached 278. During this period, the over/under voltage LED indicator is flashed 280. The purpose of this delay is to assure that the condition persists, thereby preventing false shut downs which can cause further damage to the load or inconvenience to the user.

At the end of the minute count, the piezo buzzer is turned on 282 to warn the user that the load is about to be turned off. A second counter is started 284 until the pre-set delay is reached 286 after which the triac is turned off 288 and the load de- energized. The energy saving bar graph display is also turned off 290.

The current detection function 292 is shown in the flowchart of Fig. 8. The reading generated from the current sensor is compared with the pre-set maximum value 294. If the current exceeds the limit, a time delay is generated for a few seconds using the loop comprised of 293 and 295 to assure that it is not a momentary current surge. After the delay and the condition persists, the energy saving bar graph display is turned off 296 and then the triac is also turned off 298.

Fig. 9 shows the user interface function 300 which allows the user to set the load type and the power-on delay value which can be 0, 1 or 3 minutes. When the pushbutton is pressed 302, the button counter is set to the previous count 304. On the next button press 306, a button counter is incremented 308 until the button pressing stops and exceeds the timeout period 311 and 313. Based on the button counter number 310, 314, 318 and 322 the appropriate number of LED's on the running bar graph display is turned on 312, 316, 320, 324 and 326. The new time setting is then stored in the microcontroller's internal non-volatile memory or EEPROM 326.

If the button is pressed continuously 301 , it means that the function is to set the load type. The existing load type, is checked 303 and is set to motor if it is currently an appliance 307 and set to appliance if it is currently a motor 305. The load type is then stored in the EEPROM.

The flowchart for the power-on delay function 238 is illustrated in Fig. 10. The time setting is first read from the EEPROM 240 and 242. If it is zero, the module returns to the main program. If not, the time setting counter is decremented 246, the LED bar graph display blinks 248 and the loop repeats until the time setting is zero after which it returns to the main program.

Fig. 11 shows the flowchart for the motor soft start function 254. The pulse width modulation of the triac is set to 75% 256 and then incremented 258 until it reaches 100% 260. This allows a gradual application of voltage to the motor load. A delay of 2 seconds 262 is then implemented before the function returns to the main program.

Although the invention has been shown and described with respect to the best mode embodiment thereof, it should be understood by those skilled in the art that the foregoing and various other changes, omissions and deletions in the form and detail thereof may be made therein without departing from the spirit and scope of this invention.

Claims

ClaimsWhat is claimed is:

1. A single apparatus comprising: a microcontroller that is programmed to control the operations of all the elements of said apparatus;

a circuit for detecting the zero crossings of the AC supply voltage and the

AC load current;

a circuit for rectifying the AC supply voltage into a DC voltage signal; a circuit for amplifying and rectifying the AC load current into a DC voltage signal;

an analog-to-digital converter for converting the said DC voltage signals to digital form which are then used as inputs to said microcontroller; an intermediate electronic switch controlled by said microcontroller and used for activating the main switch connected in series with the electrical load;

an electronic switch which is connected in series with the electrical load; a solid state transient suppression device; a solid state surge suppression device; a plurality of light emitting diode (LED) displays to indicate the operation of the said apparatus;

a plurality of switches for setting the operation of said apparatus; a socket for plugging the electrical load to the said apparatus; a plug for attaching the apparatus to an AC supply outlet.

2. The apparatus of claim 1 wherein all the elements are housed in a single enclosure made of an impact resistant material.

3. A method of reducing the energy consumption of single phase AC induction motors comprising: measuring the phase angle by determining the time interval between the AC voltage and AC current zero crossing points;

generating a pulse width modulated signal which controls the electronic switch;

computing the pulse width based on the said phase angle; a table which relates phase angle with the pulse width of the gate control signal is used for this purpose.

4. A method of switching off the electrical load if the AC voltage supply exceeds a maximum pre-set limit or a minimum pre-set limit as determined by the microcontroller.

5. A method of controlling the sudden inrush of current to a motor load during starting by gradually applying the voltage across. The pulse width of the signal that controls the electronic switch is varied by the microcontroller.

6. A method of delaying the application of power to the load when the AC power supply is restored after a power interruption occurs. The electronic switch is turned off by the microcontroller during the delay period.

7. A method of setting the delay period of claim 6 through the use of a pushbutton switch and LED displays.

8. A method of allowing operation from 110 volts AC to 230 volts AC by maintaining a fixed supply voltage to all the circuits and using an electronic switch that can operate on a wide range of supply voltages.

9. A method of switching off the electrical load when the load current exceeds a certain pre-set maximum to prevent overloading. The microcontroller senses the current level and if it exceeds the maximum after a certain period of time it switches off the load.