Abstract:
A control and protection apparatus for an electric motor, comprising an inverter ( 3 ), a first converter ( 1 ), a temperature detection apparatus ( 7 ), and a second converter ( 2 ). The first converter ( 1 ) is used for generating, on the basis of an input signal, a first control signal to control working of the inverter ( 3 ). The temperature detection apparatus ( 7 ) is used for detecting the temperature of the electric motor ( 4 ) and for acquiring a temperature signal. The second converter ( 2 ) is used for generating a second control signal on the basis of the temperature signal detected and for providing the second control signal to the inverter ( 3 ). The inverter ( 3 ) is used for controlling wording of the electric motor ( 4 ) on the basis of the first control signal and of the second control signal. The control and protection apparatus for the electric motor is low in costs and high in safety and reliability.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an electric motor and, more particularly, to a control and protection apparatus for an electric motor. 
       BACKGROUND OF THE INVENTION 
       [0002]    An electric motor has been widely used in various fields such as industry and agriculture. In practical applications, the electric motor may experience over temperature due to overload, winding faults or abnormal power voltage so as to damage or destroy the electric motor, and thus the over temperature protection for the electric motor is needed. In addition, the electric motor should be safely stopped when it is in abnormal operation status. That is, a STO (safe torque off) should be applied manually to make the electric motor stop work. 
         [0003]    In order to stop the electric motor when it is over temperature or a safe torque off signal is received, the existing control and protection apparatus is usually provided with a control unit comprising a thermistor, an OR gate circuit and a safety circuit, wherein the two input ends of the OR gate circuit are configured to receive the electric motor&#39;s temperature signal detected by the thermistor and the safe torque off signal (or safe stop signal) respectively. When the temperature of the electric motor is too high and/or the safe torque off signal applied manually is received, the safety circuit makes the insulated gate bipolar transistor (IGBT) in an inverter stop work, and thus makes the electric motor stop work. In the control and protection apparatus above, the OR gate circuit and the safety circuit need ATEX certification, which may increase the cost of the apparatus. On the other hand, upon a failure of the OR gate circuit, the applied safe torque off signal and/or over temperature of the electric motor will not be able to stop the electric motor, which means the performance of the OR gate circuit must meet higher requirements. 
       SUMMARY OF INVENTION 
       [0004]    In view of the foregoing, an object of the present invention is to provide a control and protection apparatus for an electric motor. The control and protection apparatus for the electric motor comprises a frequency transformer, a first converter, a temperature-detection device and a second converter, wherein the first converter is configured to generate a first control signal from an input signal to control the operation of the frequency transformer, the temperature-detection device is configured to detect the temperature of the electric motor and generate a temperature signal, the second converter is configured to generate a second control signal from the temperature signal, and provide the second control signal to the frequency transformer, and the frequency transformer is configured to control the operation of the electric motor based on the first control signal and the second control signal. 
         [0005]    Preferably, the frequency transformer comprises a switch tube driver and an inverter, and the switch tube driver is configured to provide a pulse width modulation signal to the inverter. 
         [0006]    Preferably, the first converter is configured to generate a first stop signal when receiving a safe torque off signal in order to make the switch tube driver stop work, and provide a first work signal to the switch tube driver for when receiving no safe torque off signal in order to make the switch tube driver work. 
         [0007]    Preferably, the second converter is configured to convert the temperature signal of the electric motor to a second stop signal when the temperature of the electric motor is higher than a threshold in order to make the switch tube driver stop work, and convert the temperature signal of the electric motor to a second work signal when the temperature of the electric motor is not higher than the threshold in order to make the switch tube driver work. 
         [0008]    Preferably, the first stop signal is a pulse width modulation disenable signal input to the switch tube driver, and the first work signal is a pulse width modulation enable signal input to the switch tube driver. 
         [0009]    Preferably, the second work signal is a pulse width modulation input signal input into the switch tube driver, and the second stop signal is a voltage signal to make the switch tube driver stop work. 
         [0010]    Preferably, the frequency transformer further comprises a switch power supply, which is configured to provide a required direct current to the switch tube driver. 
         [0011]    Preferably, the first stop signal is a pulse width modulation disenable signal input to the switch tube driver, and the first work signal is a pulse width modulation enable signal input to the switch tube driver; the second stop signal is a disenable signal for the switch power supply or a signal for turning-off the input of the switch power supply to make the switch power supply stop work, and the second work signal is an enable signal for the switch power supply or a signal for turning-on the input of the switch power supply to make the switch power supply work. 
         [0012]    Preferably, the first stop signal is a disenable signal for the switch power supply or a signal for turning-off the input of the switch power supply to make the switch power supply stop work, and the first work signal is an enable signal for the switch power supply or a signal for turning-on the input of the switch power supply to make the switch power supply work; the second stop signal is a pulse width modulation disenable signal input to the switch tube driver, and the second work signal is a pulse width modulation enable signal input to the switch tube driver. 
         [0013]    Preferably, the first stop signal is one of a disenable signal for the switch power supply and a signal for turning-off the input of the switch power supply to make the switch power supply stop work, and the second stop signal is the other one of the disenable signal for the switch power supply and the signal for turning-off the input of the switch power supply. 
         [0014]    Preferably, the switch tube driver is an IGBT driver. 
         [0015]    The control and protection apparatus for the electric motor of the present invention needs no ATEX certification and thus reduces the production cost. And the safety and reliability are improved for adopting two independent control signals to control the work status of the control switch driver. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0016]    The present invention will be further explained in combination with the embodiments with reference to the accompanying figures, wherein: 
           [0017]      FIG. 1  is a circuit diagram of a control and protection apparatus for an electric motor according to the first embodiment of the present invention. 
           [0018]      FIG. 2  is a circuit diagram of a control and protection apparatus for an electric motor according to the second embodiment of the present invention. 
           [0019]      FIG. 3  is a circuit diagram of a control and protection apparatus for an electric motor according to the third embodiment of the present invention. 
           [0020]      FIG. 4  is a circuit diagram of a control and protection apparatus for an electric motor according to the fourth embodiment of the present invention. 
       
    
    
     DENOTATION OF ACCOMPANYING DRAWINGS 
       [0021]      1  first converter 
         [0022]      2  second converter 
         [0023]      3  frequency transformer 
         [0024]      4  electric motor 
         [0025]      5  IGBT driver 
         [0026]      6  inverter 
         [0027]      7  thermistor 
         [0028]      8  switch power supply 
         [0029]      9  switch 
         [0030]      10  power supply 
         [0031]      22  second converter 
         [0032]      31  first converter 
         [0033]      32  second converter 
         [0034]      41  first converter 
         [0035]      42  second converter 
       DESCRIPTION OF EMBODIMENTS 
       [0036]    In the following parts, the present invention will be described in greater details with reference to the embodiments and the accompanying drawings so as to make its objects, solutions and advantages clearer. 
         [0037]      FIG. 1  is a circuit diagram of a control and protection apparatus for an electric motor according to the first embodiment of the present invention. As shown in  FIG. 1 , the control and protection apparatus for the electric motor comprises a first converter  1 , a second converter  2 , a frequency transformer  3  and a thermistor  7  within the electric motor  4 , wherein the frequency transformer  3  comprises a switch power supply  8 , a switch  9 , a power supply  10 , an IGBT driver  5  and an inverter  6 . The power supply  10  is connected to an input end of the switch power supply  8  through the switch  9 , and an output end of the witch power supply  8  is connected to a driving power supply end of the IGBT driver  5  to provide a required direct current to the IGBT driver  5 . The input end of the first converter  1  is used to receive a safe torque off (STO) signal, and the output end thereof is connected to an enable end of the IGBT driver  5 . The thermistor  7  is used to measure the temperature of the electric motor  4  and generate a temperature signal U t . An input end of the second converter  2  receives the temperature signal U t , and an output end thereof is connected to a pulse width modulation (PWM) input end of the IGBT driver  5 . An output end of the IGBT driver  5  is used to provide a PWM signal or a stop work signal to the IGBT (not shown in the Figures) in the inverter  6 , and an output end of the inverter  6  is connected to the electric motor  4 . 
         [0038]    The input end of the first converter  1  is used to receive an input signal, which may be a safe torque off signal (STO) or a voltage within a predetermined range. Herein the voltage within the predetermined range indicates that no safe torque off (STO) signals are received by the first converter  1 . The first converter  1  receives and processes the safe torque off (STO) signal, and outputs a pulse width modulation disenable signal to the enable end of the IGBT driver  5  so as to make the IGBT driver  5  stop work (or NOT work), and then cause the inverter  6  to stop work, finally make the electric motor  4  stop work. In this embodiment, the first converter  1  outputs a pulse width modulation enable signal when receiving no safe torque off (STO) signal. This pulse width modulation enable signal keeps the IGBT driver  5  in a working state. The pulse width modulation enable signal may be either a low-level voltage of 0 V, or a high-level voltage of 5 V or 3.3 V. In various embodiments, the voltage of the pulse width modulation enable signal may be defined according to the specification of the IGBT driver  5 , wherein the pulse width modulation disenable signal is at a low level when the pulse width modulation enable signal is at a high level, or vice versa. 
         [0039]    The thermistor  7  is used to measure the temperature of the electric motor  4  and output the acquired temperature signal U t  to the second converter  2 , wherein the acquired temperature signal U t  is an analog signal (such as an analog value of voltage). When the temperature of the electric motor  4  is higher than a threshold (such as the maximum working temperature the electric motor  4  can endure), the second converter  2  generates a turn-off voltage such as a fixed low voltage, and the IGBT driver  5  makes the IGBT in the inverter  6  turn off (i.e., makes the inverter stop work) in response to the turn-off voltage, and thus prevents the inverter  6  from supplying to the electric motor  4 , so as to make the electric motor  4  stop work. When the temperature of the electric motor  4  is within the working temperature range it can endure, a pulse width modulation input signal is output from the output end of the second converter  2  and provided to a pulse width modulation input end of the IGBT driver  5 , so that the inverter  6  provides an alternating current with a variable voltage amplitude and/or frequency to the electric motor  4 . In other embodiments of the present invention, the second converter  2  may be in the form of a single chip microcomputer. In the embodiments of the present invention, the safe torque off (STO) signal and the temperature signal U t  of the electric motor  4  (if the temperature of the electric motor  4  is higher than the threshold) are able to independently provide a control signal to the IGBT driver  5  through the first converter  1  and the second converter  2  respectively in order to make the IGBT driver  5  stop providing the pulse width modulation signal to the inverter  6 , which will improve the safety and reliability, and further avoid the ATEX certification to the OR gate circuit and the safety circuit, and thus reduce the production cost. 
         [0040]      FIG. 2  is a circuit diagram of a control and protection apparatus for an electric motor according to the second embodiment of the present invention, which is substantially the same as  FIG. 1 , but is different from  FIG. 1  in that an output signal of an output end of a second converter  22  is used for controlling the switch  9  to be switched on or off, and the pulse width modulation input end of the IGBT driver  5  receives a pulse width modulation (PWM) input signal. The thermistor  7  measures the temperature of the electric motor  4  and generates a temperature signal U t . When the temperature of the electric motor  4  is higher than the maximum working temperature it can endure (i.e., the electric motor  4  is over temperature), the output end of the second converter  22  outputs a signal for turning-off the input of a switch power supply. The signal for turning-off the input of the switch power supply controls the switch  9  to be switched off, so that the switch power supply  8  will not provide a required direct current to the IGBT driver  5 . Then the IGBT driver  5 , the inverter  6  and the electric motor  4  will stop work. In another embodiment, the output end of the second converter  22  is connected to an enable end (not shown in the Figures) of the switch power supply  8 . Likewise, when the electric motor  4  is over temperature, the output end of the second converter  22  will output a disenable signal for the switch power supply, which is used to make a switch tube (not shown in the Figures) of the switch power supply  8  stop work, and thus make the switch power supply  8  stop providing a required direct current to the IGBT driver  5 . In this embodiment, the voltage of the disenable signal for the switch power supply may be chosen according to the specific circuit structure of the switch power supply  8 . 
         [0041]      FIG. 3  is a circuit diagram of a control and protection apparatus for an electric motor according to the third embodiment of the present invention, which is substantially the same as  FIG. 1 , but is different from  FIG. 1  in that an output end of a first converter  31  is connected to an enable end of the switch power supply  8 , an output end of a second converter  32  is connected to the enable end of the IGBT driver  5 , and the pulse width modulation input end of the IGBT driver  5  receives a pulse width modulation (PWM) input signal. The first converter  31  is used to convert a safe torque off (STO) signal into a disenable signal for the switch power supply, which is used to make a switch tube (not shown in the Figures) of the switch power supply  8  stop work, and thus make the switch power supply  8  stop providing a required direct current to the IGBT driver  5 . When the temperature of the electric motor  4  is higher than the maximum working temperature it can endure, the output end of the second converter  32  outputs a pulse width modulation disenable signal, which makes the IGBT driver  5  stop work so as to make the inverter  6  and the electric motor  4  stop work. On the contrary, when the temperature of the electric motor  4  is not over a threshold, the output end of the second converter  32  outputs a pulse width modulation enable signal which makes the IGBT driver  5  work. In this embodiment, the IGBT driver  5  and thus the electric motor  4  will stop work when the electric motor  4  is over temperature or when a safe torque off (STO) signal is applied manually. In other embodiments of the present invention, the output signal of the output end of the first converter  31  may be used for controlling the switch  9  to be switched on or off, wherein the first converter  31  is used for converting a safe torque off (STO) signal into a signal for turning-off the input of a switch power supply. The signal for turning-off the input of the switch power supply controls the switch  9  to be switched off, so that the switch power supply  8  will not provide a required direct current to the IGBT driver  5 . 
         [0042]      FIG. 4  is a circuit diagram of a control and protection apparatus for an electric motor according to the fourth embodiment of the present invention, which is substantially the same as  FIG. 1 , but is different from  FIG. 1  in that an output end of a second converter  42  is connected to the enable end of the switch power supply  8 , the output signal of an output end of a first converter  41  is used for controlling the switch  9  to be switched on or off, and the pulse width modulation input end of the IGBT driver  5  receives a pulse width modulation (PWM) input signal. The first converter  41  generates a signal for turning-off the input of a switch power supply in response to a safe torque off (STO) signal. When the temperature of the electric motor  4  is higher than the maximum working temperature it can endure, the output end of the second converter  42  outputs a disenable signal for the switch power supply, otherwise it outputs an enable signal for the switch power supply. In other embodiments of the present invention, the output end of the first converter  41  is connected to the enable end of the switch power supply  8 , and the temperature signal when the electric motor  4  is over temperature is converted into a disenable signal for the switch power supply. Meanwhile, the output signal of the output end of the second converter  42  is used for controlling the switch  9  to be switched on or off. In this embodiment, the safe torque off (STO) signal and the temperature signal U t  are converted into control signals by the first converter  41  and the second converter  42  respectively so as to make the switch power supply  8  stop work, and thus make the IGBT driver  5  stop work. 
         [0043]    In the embodiments of the present invention, when there are no safe torque off (STO) signals or the temperature of the electric motor  4  is not higher than the threshold, the IGBT driver  5  provides a pulse width modulation signal to the inverter  6  to control the IGBT in the inverter  6  to be switched on or off, so as to provide a required alternating current to the electric motor  4 . 
         [0044]    In the above embodiments of the present invention, the IGBT driver  5  may be replaced with other semiconductor switch tube drivers, and accordingly, the IGBT in the inverter  6  may be replaced with corresponding semiconductor switch tubes. In other embodiments, the thermistor  7  may be replaced with other temperature-measuring devices. It is well known to a person skill in the art that the converters in above embodiments may adopt existing electronic components to realize the corresponding functions of the above converters. 
         [0045]    Embodiments of the present invention have been described in terms of the preferred embodiment, but the present invention is not limited to the embodiments described above, and various amendments and changes may be made within the scope of the present invention.