Patent Publication Number: US-2017373487-A1

Title: Starting and protecting induction motors

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of priority from pending U.S. Provisional Patent Application Ser. No. 62/384,721, filed on Sep. 8, 2016, and entitled “DRIVER AND PROTECTOR OF INDUCTION MOTORS BY SLIP,” which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     The present disclosure generally relates to induction motors, and particularly, to methods for starting and protecting induction motors by electronic circuits. 
     BACKGROUND 
     An important problem of single-phase induction motors is the absence of a starting torque. To create a starting torque, an auxiliary coil is used, which is then removed from the circuit when the motor starts working. To activate and deactivate the auxiliary coil in single-phase induction motors, a mechanical centrifugal switch is used. The centrifugal switch may include a clutch and platinum. In this mechanism, when the motor speed reaches the desired amount, the auxiliary coil is deactivated. But centrifugal switches have their own problems and can cause damage on single-phase induction motors. For example, if the induction motor cannot rotate for any reason, the centrifugal switch is incapable of cutting the electricity current and the high current can damage the auxiliary coil and also the motor itself. In some cases, the binding of the clutch and also the large distance between the contacts of platinum centrifugal switches or the contacts that stick together prevent the keys from functioning, which can also damage the auxiliary coil and the motor. Single-phase induction motors also require protection against overload or under voltage. 
     In three-phase induction motors, there is no starting issue; however, protection is still required to protect against overload, under voltage, or phase separation. Different ways are used to reduce the initial current, such as the star-delta method. In this method, first the motor is launched in the star state, and after a certain time (determined by an industrial timer) the motor switches into the delta state. For this purpose, a power circuit, a complex control circuit and an industrial timer is required. 
     There is therefore a need for a simple method and circuit to start and protect induction motors, without a need for complex control procedure and circuitry. There is also a need for an integrated method that enables starting and protecting both single-phase and three-phase induction motors without adding complex procedures. A need also exists for a circuit that can perform operations needed for starting and protecting both single-phase and three-phase induction motors in different working conditions. 
     SUMMARY 
     This summary is intended to provide an overview of the subject matter of the present disclosure, and is not intended to identify essential elements or key elements of the subject matter, nor is it intended to be used to determine the scope of the claimed implementations. The proper scope of the present disclosure may be ascertained from the claims set forth below in view of the detailed description below and the drawings. 
     In one general aspect, the present disclosure describes an integrated method for starting and protecting an induction motor. The method may include starting the induction motor, detecting an initialization fault, monitoring operation of the induction motor, detecting an operation fault while monitoring operation of the induction motor, and stopping the induction motor if the initialization fault or the operation fault is detected. In some implementations, starting the induction motor may include using a first switch and a second switch. Furthermore, stopping the induction motor may include using the first switch and the second switch. 
     The above general aspect may include one or more of the following features. In some implementations, the initialization fault and the operation fault may include a speed of the induction motor at a given time after starting the induction motor. In some cases, the speed of the induction motor may include a value lower than a first speed threshold. In some cases, monitoring operation of the induction motor may include measuring a speed of the induction motor. In some implementations, measuring the speed of the induction motor may include measuring a voltage of a Hall effect sensor at a time lapse. In some examples, the Hall effect sensor may be placed on the induction motor. In some cases, each of the first switch and the second switch may include an electromechanical relay or a solid state relay. In addition, each of the first switch and the second switch may be controlled by a processing unit. In some implementations, the processing unit may include a microprocessor. In some cases, the induction motor may include a three-phase induction motor. In other cases, the induction motor may include a single-phase induction motor. In some implementations, the single-phase induction motor may include a main coil and an auxiliary coil. 
     In some examples, starting the single-phase induction motor may include applying an AC voltage to the single-phase induction motor, and activating the main coil and the auxiliary coil. In some cases, starting the single-phase induction motor may further include deactivating the auxiliary coil when a speed of the single-phase induction motor reaches a second speed threshold. In some implementations, the second speed threshold may include three quarters of a nominal speed of the single-phase induction motor. In some cases, activating the main coil may include connecting the main coil to the first switch. In some implementations, activating the auxiliary coil may include connecting the auxiliary coil to the second switch. In some implementations, deactivating the auxiliary coil may include disconnecting the auxiliary coil from the second switch. In some examples, stopping the single-phase induction motor may include deactivating the main coil and deactivating the auxiliary coil. In some implementations, deactivating the main coil may include disconnecting the main coil from the first switch. 
     In some cases, starting the three-phase induction motor may include activating a power supply contactor, and applying an AC voltage to the three-phase induction motor through the power supply contactor. In some examples, activating the power supply contactor may include connecting the power supply contactor to the first switch. In some implementations, stopping the three-phase induction motor may include deactivating the power supply contactor. In some examples, deactivating the power supply contactor may include disconnecting the power supply contactor from the first switch. 
     In some cases, starting the three-phase induction motor may include activating a main contactor and a star contactor at an initial moment, and activating a delta contactor and deactivating the star contactor when an initialization time passes, or when a speed of the three-phase induction motor reaches a third speed threshold. In some implementations, the third speed threshold may be set to a nominal speed of the three-phase induction motor. In some examples, activating the main contactor may include connecting the main contactor to the first switch. In some cases, activating the star contactor may include connecting the star contactor to the second switch. In some implementations, activating the delta contactor may include connecting the delta contactor to the second switch. In some cases, deactivating the star contactor may include disconnecting the star contactor from the second switch. In some examples, stopping the induction motor may include deactivating the main contactor. In some cases, deactivating the main contactor may include disconnecting the main contactor from the first switch. 
     In another general aspect, the present disclosure describes a circuit for starting and protecting an induction motor. In an implementation, the induction may motor include a three-phase induction motor, or a single-phase induction motor. In an example, the single-phase induction motor may include a main coil and an auxiliary coil. In some implementations, the circuit may include a processing unit, a power source, a Hall effect sensor, a plurality of switches, and a plurality of contactors. In a case, the processing unit may include a microprocessor. In some examples, the Hall effect sensor may measure a speed of the induction motor at a time lapse. In a configuration, the Hall effect sensor is placed on the induction motor. In some cases, the plurality of switches may include a first switch and a second switch. In some implementations, the first switch and the second switch may include an electromechanical relay or a solid state relay. In some examples, the plurality of switches may be controlled by the processing unit. In some cases, the plurality of contactors may include a main contactor, a star contactor, and a delta contactor. In some implementations, the plurality of contactors may be controlled by the processing unit. In some examples, the processing unit may be configured to perform a set of operations. The set of operations may include starting the induction motor, detecting an initialization fault, measuring a speed of the induction motor by the Hall effect sensor, detecting an operation fault while measuring the speed of the induction motor, and stopping the induction motor if the initialization fault or the operation fault is detected. 
     The above general aspect may include one or more of the following features. In some implementations, starting the single-phase induction motor may include connecting the power source to the single-phase induction motor, activating the main coil by connecting the main coil to the first switch, activating the auxiliary coil by connecting the auxiliary coil to the second switch, and deactivating the auxiliary coil by disconnecting the auxiliary coil from the second switch when a speed of the single-phase induction motor reaches a second speed threshold. In some examples, the second speed threshold may include three quarters of a nominal speed of the single-phase induction motor. In a case, the nominal speed may be stored in the processing unit. 
     In some implementations, starting the three-phase induction motor may include connecting the power source to the three-phase induction motor through the main contactor, activating the main contactor by connecting the main contactor to the first switch, activating the star contactor by connecting the star contactor to the second switch, activating the delta contactor by connecting the star contactor to the second switch, and deactivating the star contactor by disconnecting the star contactor from the second switch. In some examples, activating the delta contactor and deactivating the star contactor may be performed when an initialization time passes, or when speed of the three-phase induction motor reaches a third speed threshold. In some cases, the third speed threshold may include a nominal speed of the three-phase induction motor. 
     In some implementations, the initialization fault and the operation fault may include the speed of the induction motor at a given time after starting the induction motor. In some cases, the speed of the induction motor may include a value lower than a first speed threshold. 
     In some configurations, stopping the single-phase induction motor may includes deactivating the main coil and deactivating the auxiliary coil. In some implementations, deactivating the main coil may include disconnecting the main coil from the first switch. In some cases, stopping the three-phase induction motor may include deactivating the main contactor. In some examples, deactivating the main contactor may include disconnecting the main contactor from the first switch. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The drawing figures depict one or more implementations in accord with the present teachings, by way of example only, not by way of limitation. In the figures, like reference numerals refer to the same or similar elements. 
         FIG. 1  is a flowchart illustrating an implementation of an integrated method for starting and protecting an induction motor. 
         FIG. 2  illustrates an implementation of a circuit configured to start and protect a single-phase induction motor. 
         FIG. 3  illustrates an implementation of a circuit configured to start and protect a three-phase induction motor, according to a direct starting method. 
         FIG. 4  illustrates an implementation of a circuit configured to start and protect a three-phase induction motor, according to a star-delta starting method. 
         FIG. 5  illustrates an implementation of a circuit configured to start and protect a single-phase induction motor and a three-phase induction motor. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description is presented to enable a person skilled in the art to make and use the methods and devices disclosed in exemplary implementations of the present disclosure. For purposes of explanation, specific nomenclature is set forth to provide a thorough understanding of the present disclosure. However, it will be apparent to one skilled in the art that these specific details are not required to practice the disclosed exemplary implementations. Descriptions of specific exemplary implementations are provided only as representative examples. Various modifications to the exemplary implementations will be readily apparent to one skilled in the art, and the general principles defined herein may be applied to other implementations and applications without departing from the scope of the present disclosure. The present disclosure is not intended to be limited to the implementations shown, but is to be accorded the widest possible scope consistent with the principles and features disclosed herein. 
     Disclosed herein is an integrated method and circuit for both starting and protecting induction motors. The method and circuit may be used to start and protect a single-phase induction motor, as well as a three-phase induction motor. Starting the induction motors may include activating coils or contactors by using switches, and deactivating the coils or switches after an initialization time passes or the speed of the induction motors reaches a given threshold. Protecting the induction motors may include detecting an initialization fault (when the induction motor is started) or an operation fault (while the induction motor is operating), and stopping the induction motor when an initialization fault or an operation fault is detected. 
       FIG. 1  illustrates an implementation of an integrated method  100  for starting and protecting an induction motor. The integrated method  100  may include starting the induction motor (step  101 ), detecting an initialization fault (step  102 ), monitoring operation of the induction motor (step  104 ), detecting an operation fault while monitoring operation of the induction motor (step  106 ), and stopping the induction motor if the initialization fault or the operation fault is detected (step  108 ). In some implementations, starting the induction motor (step  101 ) may include using a first switch and a second switch. In addition, stopping the induction motor (step  108 ) may include using the first switch and the second switch. 
     In some implementations, the initialization fault and the operation fault may include a speed of the induction motor at a given time after starting the induction motor (step  101 ). In some implementations, the speed of the induction motor may include a value lower than a speed threshold Nr. In an implementation, the speed threshold Nr may be calculated by the following equation: 
         Nr =(1− s )× Ns    (Equation 1)
 
     where, s is a slip threshold and Ns is a synchronous speed of the induction motor. In some implementations, induction motors may be designed to operate with low values of slip (about 0.02 to 0.05). Therefore, in some implementations of the integrated method  100 , the slip threshold s may be set to about 0.05. 
     Referring again to  FIG. 1 , if an initialization fault is detected (step  102 , Yes), the process  100  moves to stop the induction motor (step  108 ). If, however, an initialization fault is not detected (step  102 ,  100  No), the process  100  moves to monitor operation of the induction motor (step  104 ). Moving forward, if an operation fault is detected while monitoring operation of the induction motor (step  106 , Yes), the induction motor is stopped (step  108 ). If an operation fault is not detected while monitoring operation of the induction motor (step  106 , No), the process  100  returns to step  104  to continue to monitor the operation of the induction motor. 
     In some implementations, monitoring operation of the induction motor (step  104 ) may include measuring a speed of the induction motor. In some implementations, measuring the speed of the induction motor may include measuring a voltage of a Hall effect sensor at a time lapse, beginning from a given moment after starting the induction motor (step  101 ). In some examples, the Hall effect sensor may be placed on the induction motor. In a case, the Hall effect sensor may be placed near the shaft of the induction motor, and a magnet may be placed on the shaft. The sensor voltage may change once at each rotation of the shaft, as the magnet becomes close to the Hall effect sensor. In some implementations, the speed of the induction motor may be calculated by counting the number of voltage changes in the Hall effect sensor at every second. 
     In some examples, each of the first switch and the second switch may include an electromechanical relay or a solid state relay. Furthermore, each of the first switch and the second switch may be controlled by a processing unit. The processing unit may include a microprocessor. 
     In one implementation, the induction motor may include a three-phase induction motor. In another implementation, the induction motor may include a single-phase induction motor. The single-phase induction motor may include a main coil and an auxiliary coil. The single-phase induction motor may be started (step  1 ) by applying an AC voltage to the single-phase induction motor, and activating the main coil and the auxiliary coil. In some implementations, starting the single-phase induction motor (step) may further include deactivating the auxiliary coil when a speed of the single-phase induction motor reaches a speed threshold. The speed threshold may be set to three quarters of the nominal speed of the single-phase induction motor. The nominal speed of the single-phase induction motor may be stored in the processing unit. In some implementations, the voltage of the Hall effect sensor may be loaded to the processing unit to calculate the speed of the induction motor and detect the initialization fault or the operation fault. In some examples, the processing unit may generate an alarm (such as a visual alarm or an audible alarm) if the initialization fault or the operation fault is detected. 
     In some implementations, activating the main coil may include connecting the main coil to the first switch and activating the auxiliary coil may include connecting the auxiliary coil to the second switch. In some implementations in which electromechanical relays are used as the first switch or the second switch, a snubber circuit may also be included to protect the switches. In an implementation, a path to an AC power source may be provided to the main and auxiliary coils when connected to the corresponding switch, to activate each coil. 
     In some implementations, stopping the single-phase induction motor (step  108 ) may include deactivating the main coil and deactivating the auxiliary coil. Deactivating the main coil may include disconnecting the main coil from the first switch. Deactivating the auxiliary coil may include disconnecting the auxiliary coil from the second switch. 
     In another implementation, as noted above, the induction motor may include a three-phase induction motor. Starting the three-phase induction motor (step) may include activating a power supply contactor, and applying an AC voltage to the three-phase induction motor through the power supply contactor. The power supply contactor may be activated by connecting the power supply contactor to the first switch. In some implementations, stopping the three-phase induction motor (step  108 ) may include deactivating the power supply contactor. The power supply contactor may be deactivated by disconnecting the power supply contactor from the first switch. 
     In some implementations, starting the three-phase induction motor (step) may include activating a main contactor and a star contactor at an initial moment, and activating a delta contactor and deactivating the star contactor when an initialization time passes, or when a speed of the three-phase induction motor reaches a speed threshold. The speed threshold may be set to a nominal speed of the three-phase induction motor. The main contactor may be activated by connecting the main contactor to the first switch. The star contactor may be activated by connecting the star contactor to the second switch. The delta contactor may be activated by connecting the delta contactor to the second switch. Furthermore, the star contactor may be deactivated by disconnecting the star contactor from the second switch. In other words, the star contactor and the delta contactor may be connected to a same switch. Therefore, deactivating the star contactor by disconnecting it from the second switch may connect the delta contactor to the second switch, which may activate the delta contactor. Hence, in some implementations, deactivating the star contactor and activating the delta contactor may be simultaneously performed by a single command to the second switch from the processing unit. 
     In some examples, stopping the induction motor (step  108 ) may include deactivating the main contactor. The main contactor may be deactivated by disconnecting the main contactor from the first switch. 
       FIG. 2  depicts an implementation of a circuit  200  configured to start and protect a single-phase induction motor, according to an implementation of the integrated method  100 . In some implementations, the single-phase induction motor may include a main coil  202  and an auxiliary coil  204 . In some examples, starting the single-phase induction motor (step) may include applying an AC voltage to the single-phase induction motor, and activating the main coil  202  and the auxiliary coil  204 . In some implementations, starting the single-phase induction motor (step) may further include deactivating the auxiliary coil  204  when a speed of the single-phase induction motor reaches a speed threshold. The speed threshold may be set to three quarters of the nominal speed of the single-phase induction motor. 
     The main coil  202  may be activated by connecting the main coil  202  to the first switch  206 . The auxiliary coil  204  may be activated by connecting the auxiliary coil  204  to the second switch  208 . In some implementations in which electromechanical relays are used as the first switch  206  or the second switch  208 , a snubber circuit may also be included to protect the switches. In an implementation, a path to an AC power source  212  may be provided to the main and auxiliary coils  202  and  204  when connected to the corresponding switch, to activate each coil. 
     In some implementations, the first switch  206  and the second switch  208  may be controlled by the processing unit  210 . The processing unit  210  may include a microprocessor. In an example, the nominal speed of the single-phase induction motor may be stored in the processing unit  210 . In some implementations, the voltage of the Hall effect sensor  214  may be loaded to the processing unit  210  to calculate the speed of the induction motor and detect the initialization fault or the operation fault. In some examples, the processing unit  210  may generate an alarm  216  (such as a visual alarm or an audible alarm) if the initialization fault or the operation fault is detected. 
     In some examples, stopping the single-phase induction motor (step  108 ) may include deactivating the main coil  202  and deactivating the auxiliary coil  204 . The main coil  202  may be deactivated by disconnecting the main coil  202  from the first switch  206 . The auxiliary coil  204  may be deactivated by disconnecting the auxiliary coil  204  from the second switch  208 . 
       FIG. 3  depicts an implementation of a circuit  300  configured to start and protect a three-phase induction motor, according to an implementation of the integrated method  100 . In some implementations, starting the three-phase induction motor (step) may include activating a power supply contactor  302 , and applying an AC voltage to the three-phase induction motor through the power supply contactor  302 . Starting the three-phase induction motor according to the implementation of  FIG. 3  may also be referred to as “direct starting.” The power supply contactor  302  may be activated by connecting the power supply contactor  302  to the first switch  206 . The first switch  206  may include an electromechanical relay, or a solid state relay and may be controlled by the processing unit  210 . 
     In some implementations, stopping the three-phase induction motor (step  108 ) may include deactivating the power supply contactor  302 . The power supply contactor may be deactivated by disconnecting the power supply contactor  302  from the first switch  206 . 
       FIG. 4  depicts an implementation of a circuit  400  configured to start and protect a three-phase induction motor, according to an implementation of the integrated method  100 . In some implementations, starting the three-phase induction motor (step) may include activating a main contactor  402  and a star contactor  404  at an initial moment, and activating a delta contactor  406  and deactivating the star contactor when an initialization time passes, or when a speed of the three-phase induction motor reaches a speed threshold. The speed threshold may be set to a nominal speed of the three-phase induction motor. Starting the three-phase induction motor according to the implementation of  FIG. 4  may also be referred to as “star-delta starting.” 
     The main contactor  402  may be activated by connecting the main contactor  402  to the first switch  206 . The first switch  206  may include an electromechanical relay or a solid state relay. The star contactor  404  may be activated by connecting the star contactor  404  to the second switch  208 . The second switch  208  may include an electromechanical relay or a solid state relay. The delta contactor  406  may be activated by connecting the delta contactor to the second switch  208 . 
     In some implementations, deactivating the star contactor  404  may include disconnecting the star contactor  404  from the second switch  208 . In other words, in some examples, the star contactor  404  and the delta contactor  406  may be connected to a same switch. Therefore, deactivating the star contactor  404  by disconnecting it from the second switch  208  may connect the delta contactor  406  to the second switch  208 , which may activate the delta contactor  406 . In some implementations, the first switch  206  and the second switch  208  may be controlled by the processing unit  210 . Hence, in some implementations, deactivating the star contactor  404  and activating the delta contactor  406  may be simultaneously performed by a single command to the second switch  208  from the processing unit  210 . 
     In some examples, stopping the induction motor (step  108 ) may include deactivating the main contactor  402 . The main contactor  402  may be deactivated by disconnecting the main contactor  402  from the first switch  206 . 
     EXAMPLE 1 
     A Starter and Protector Circuit for a Single-Phase Induction Motor and a Three-Phase Induction Motor 
       FIG. 5  illustrates an implementation of a circuit  500  configured to start and protect a single-phase induction motor and a three-phase induction motor, according to an implementation of the integrated method  100 . TABLE 1 includes the description of elements that are used in the circuit  500 . 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Description of elements that are used in the circuit 500  
               
            
           
           
               
               
               
            
               
                 Element  
                 Description  
                 Value/Model 
               
               
                   
               
            
           
           
               
               
               
               
               
            
               
                 R 1 -R 9   
                 ¼  
                 W Resistor  
                 4.7  
                 kΩ 
               
               
                 R 10 -R 11   
                 ¼  
                 W Resistor 
                 220  
                 Ω 
               
               
                 R 12 -R 13   
                 ¼  
                 W Resistor  
                 1  
                 kΩ 
               
               
                 R 14   
                 ¼  
                 W Resistor 
                 2.2  
                 kΩ 
               
               
                 R 15   
                 ¼  
                 W Resistor  
                 1  
                 kΩ 
               
               
                 R 16 -R 18   
                 ¼  
                 W Resistor 
                 47  
                 Ω 
               
               
                 R 19   
                 1  
                 W Resistor 
                 100  
                 kΩ 
               
               
                 R 20   
                 ¼  
                 W Resistor 
                 4.7  
                 kΩ 
               
            
           
           
               
               
               
               
            
               
                 C 1 -C 5   
                 Capacitor  
                 100  
                 nF  
               
               
                 C 6 -C 9   
                 400 V Capacitor  
                 1  
                 μF 
               
               
                 C 10   
                  63 V Capacitor  
                 330  
                 μF 
               
               
                 L 1 -L 2   
                 Inductor  
                 100  
                 nH 
               
            
           
           
               
               
               
            
               
                 D 1 , D 4 , D 5 , D 6   
                 Diode  
                 1N4007  
               
               
                 D 2 , D 3 , D 8   
                 Light emitting diode  
                 LED3R-LED3G  
               
               
                 D 7   
                 TVS diode  
                 P6.5KE24A  
               
               
                 Q 1 , Q 2   
                 Transistor  
                 BD137  
               
               
                 J 1 -J 9   
                 Jumper  
                 DS1027-2BB  
               
               
                 REL 1 , REL 2   
                 Electromechanical relay  
                 HJQ-15F-1-S-Z  
               
               
                 B 1   
                 2 A Diode bridge  
                 2KBP04M  
               
               
                 U 1   
                 Voltage regulator  
                 7805  
               
               
                 U 2   
                 Microcontroller  
                 ATmega8  
               
               
                 U 3   
                 Dual op-amp  
                 LM358  
               
               
                 U 4   
                 Optocoupler  
                 SFH615-2  
               
               
                 P 1   
                 10-pin Terminal  
                 PHOENIX-10 PIN-RA  
               
               
                 H 
                 Hall effect sensor  
                 UGN3503 
               
               
                   
               
            
           
         
       
     
     In an implementation, both single-phase and three-phase induction motors can be connected to the circuit  500  through a terminal P 1 . The coils or contactors of the induction motors can be connected to the first switch REL 1  and the second switch REL 2 , according to the implementations of  FIG. 2 - FIG. 4 . A first snubber circuit, including a resistor R 18  and a capacitor C 8 , may be coupled with the first switch REL 1 . A second snubber circuit, including a resistor R 16  and a capacitor C 6 , and a third snubber circuit, including a resistor R 17  and a capacitor C 7 , may be coupled with the second switch REL 2 . The snubber circuits may protect the switches against possible voltage spikes. Since two elements may be simultaneously connected to the second switch REL 2  (for example, the star contactor  404  and the delta contactor  406  in the implementation of  FIG. 4 ), two snubber circuits may be coupled to the second switch REL 2 , whereas one snubber circuit may be sufficient to protect the first switch REL 1 . In an example, a microcontroller U 2  drives the first switch REL 1  through a transistor Q 1  and the second switch REL 2  through a transistor Q 2 . A freewheeling diode D 5  may be coupled with the first switch REL 1  to protect the transistor Q 1  against voltage spikes on the first switch REL 1 . A freewheeling diode D 2  may be coupled with the second switch REL 2  to protect the transistor Q 2  against voltage spikes on the second switch REL 2 . The transistor Q 1  may be connected to the microcontroller U 2  through a resistor R 12 , to reduce the output current of the microcontroller U 2  that is injected to the transistor Q 1 . The transistor Q 2  may be connected to the microcontroller U 2  through a resistor R 13 , to reduce the output current of the microcontroller U 2  that is injected to the transistor Q 2 . In an implementation, when the circuit  500  is connected to a power source through a terminal P 1 , an input AC voltage is converted and reduced to about 5 v DC. The amplitude of the input AC voltage may be first reduced by an RC circuit, including a resistor R 19  and a capacitor C 9 . The AC voltage may be then rectified by a diode bridge B 1 . The rectified voltage may be converted to a 24 V DC voltage by a TVS diode D 7 . Ripples of the 24 V DC voltage may be removed by a capacitor C 10  that couples the output of the diode bridge B 1  to the ground. The 24 V DC voltage may be reduced to a 5 V DC voltage by a voltage regulator U 1 . The 5 V DC voltage may be further denoised by a denoising filter, including an inductor L 2 , a capacitor C 2 , and a diode D 6 . The 5V DC voltage may feed a Hall effect sensor H and the microcontroller U 2 . The sensor H may include three pins. A supply pin may be connected to the 5V DC voltage, a ground pin may be connected to the ground, and an output pin may include the output voltage of the sensor H. The signal on the output pin may be denoised by coupling the signal to the ground through a capacitor C 4 , and the signal on the supply pin may be denoised by coupling the signal to the ground through a capacitor C 5 . In the normal mode, the output voltage of the sensor H is about 2.5v. When a magnet becomes close to the backside of the sensor H, the output voltage of the sensor H increases. In an implementation, the output of the sensor H is connected to a first op-amp in the dual op-amp U 3 . A capacitor C 3  may couple the dual op-amp U 3  to the ground to denoise the signals of the dual op-amp U 3 . The first op-amp operates in the positive buffer mode. In an example, the output of the first op-amp is connected to the positive input of a second op-amp in the dual op-amp U 3 . A potentiometer POT 1 , supplied by the 5 V DC voltage, may be connected to the negative input of the second op-amp. The second op-amp may be used in the comparator mode. The sensitivity of the sensor H can be changed by changing the sensitivity of the potentiometer POT 1 . In an example, the output of the second op-amp may be connected to the input of an optocoupler U 4 . The output current of the second op-amp and the input current of the optocoupler U 4  may be reduced by coupling the second op-amp output and the optocoupler U 4  input to the ground through resistors R 14  and R 15 . The output of the optocoupler U 4  may be connected to the timer/counter input of the microcontroller U 2 . At each rotation of the induction motor, the output of the Hall effect sensor H is activated, causing the timer/counter input of the microcontroller U 2  to increment. A light emitting diode D 8  may be connected to the optocoupler U 4  input to monitor the rotation of the induction motor by emitting light upon each counting incident. A pull-down resistor R 20  may couple the optocoupler U 4  output to the ground. 
     In an implementation, the circuit  500  includes two sets of jumpers. The first set includes jumpers J 1 -J 4  that are configured to set the speed of the induction motor. The second set includes jumpers J 5 -J 9  that are configured to set the type of the induction motor, which includes a single-phase or a three-phase induction motor. The jumpers may be connected to the 5 V DC voltage. The 5 V DC voltage may be denoised by a denoising filter, including an inductor L 1 , a capacitor C 1 , and a diode D 1 . The jumpers J 1 -J 9  may be coupled to the ground through pull-down resistors R 1 -R 9 . In an example, the steps of starting and protecting the induction motor are determined by the microcontroller U 2 , based on the type of the induction motor. The direction of the rotation of the induction motors can be changed by changing the adjustments of the terminal P 1 . In one implementation, the sensor H is placed on the shaft of the induction motor and measures the speed of the induction motor. In an implementation, the microcontroller U 2  controls the induction motor via commands that are sent to the first switch REL 1  and the second switch REL 2 , according to the measured speed. The microcontroller U 2  may send a command to a light emitting diode D 2  to emit light, if an initialization fault or an operation fault is detected. The light emitting diode D 2  may be connected to the microcontroller U 2  through a resistor R 10 , to reduce the amount of current flowing through the light emitting diode D 2 . In addition, the microcontroller U 2  may send a command to a light emitting diode D 3  to emit light, if no fault is detected. The light emitting diode D 3  may be connected to the microcontroller U 2  through a resistor R 11 , to reduce the amount of current flowing through the light emitting diode D 3 . 
     While the foregoing has described what are considered to be the best mode and/or other examples, it is understood that various modifications may be made therein and that the subject matter disclosed herein may be implemented in various forms and examples, and that the teachings may be applied in numerous applications, only some of which have been described herein. It is intended by the following claims to claim any and all applications, modifications and variations that fall within the true scope of the present teachings. 
     Unless otherwise stated, all measurements, values, ratings, positions, magnitudes, sizes, and other specifications that are set forth in this specification, including in the claims that follow, are approximate, not exact. They are intended to have a reasonable range that is consistent with the functions to which they relate and with what is customary in the art to which they pertain. 
     The scope of protection is limited solely by the claims that now follow. That scope is intended and should be interpreted to be as broad as is consistent with the ordinary meaning of the language that is used in the claims when interpreted in light of this specification and the prosecution history that follows and to encompass all structural and functional equivalents. Notwithstanding, none of the claims are intended to embrace subject matter that fails to satisfy the requirement of Sections 101, 102, or 103 of the Patent Act, nor should they be interpreted in such a way. Any unintended embracement of such subject matter is hereby disclaimed. 
     Except as stated immediately above, nothing that has been stated or illustrated is intended or should be interpreted to cause a dedication of any component, step, feature, object, benefit, advantage, or equivalent to the public, regardless of whether it is or is not recited in the claims. 
     It will be understood that the terms and expressions used herein have the ordinary meaning as is accorded to such terms and expressions with respect to their corresponding respective areas of inquiry and study except where specific meanings have otherwise been set forth herein. Relational terms such as first and second and the like may be used solely to distinguish one entity or action from another without necessarily requiring or implying any actual such relationship or order between such entities or actions. The terms “comprises,” “comprising,” or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by “a” or “an” does not, without further constraints, preclude the existence of additional identical elements in the process, method, article, or apparatus that comprises the element. 
     The Abstract of the Disclosure is provided to allow the reader to quickly ascertain the nature of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in various implementations. This is for purposes of streamlining the disclosure, and is not to be interpreted as reflecting an intention that the claimed implementations require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed implementation. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separately claimed subject matter. 
     While various implementations have been described, the description is intended to be exemplary, rather than limiting and it will be apparent to those of ordinary skill in the art that many more implementations and implementations are possible that are within the scope of the implementations. Although many possible combinations of features are shown in the accompanying figures and discussed in this detailed description, many other combinations of the disclosed features are possible. Any feature of any implementation may be used in combination with or substituted for any other feature or element in any other implementation unless specifically restricted. Therefore, it will be understood that any of the features shown and/or discussed in the present disclosure may be implemented together in any suitable combination. Accordingly, the implementations are not to be restricted except in light of the attached claims and their equivalents. Also, various modifications and changes may be made within the scope of the attached claims.