Abstract:
The invention relates to a control method and system comprising an electronic control unit ( 11 ) controlling the electric current power supply from an electric power source to a motor-compressor arrangement ( 12, 13 ); the electronic control unit comprises a conversion means which is connected to an inversion means ( 15 ) to supply the voltage demanded by the motor ( 12 ). A PWM pulse width regulator ( 16 ) generates the switching signals for all the switching elements of the unit ( 11 ) relating to said demanded voltage.

Description:
OBJECT OF THE INVENTION 
       [0001]    The present invention relates to a method for governing and controlling the power supply from an electric power source to an assembly comprising an electric motor which can be connected to a hermetically encapsulated refrigeration compression unit. 
       STATE OF THE ART 
       [0002]    It is known that electric cooling apparatuses can be fed from electric power sources such as batteries which are charged by means of an electric generator activated from an internal combustion engine or from a photovoltaic cell panel or the like. 
         [0003]    A drawback of the aforementioned system is derived from the fact that the voltage level of the battery varies over time, i.e. the voltage level of the battery is greater than the rated voltage thereof when it is charged, and when the battery is discharged, its voltage decreases progressively, being less than the rated voltage thereof, and as a result the battery must be disconnected when its voltage level reaches a certain lower voltage level for the purpose of protecting the battery. 
         [0004]    It is consequently necessary to develop a control system for controlling the electric power supply from a battery to an assembly of an electric motor which can be connected to a hermetically encapsulated refrigeration compression unit such that the life of the battery is ensured. 
       CHARACTERIZATION OF THE INVENTION 
       [0005]    The present invention seeks to solve or reduce one or more of the aforementioned drawbacks by means of a control method for controlling the electricity supply as claimed in claim  1 . Embodiments of the invention are established in the dependent claims. 
         [0006]    An object of the present invention is to implement a method for controlling the electric power supply from an electric power source which can be connected to an electric motor through a control unit; wherein the control unit receives a voltage from the electric power source. A PID algorithm calculates the voltage which must be applied to the windings of the electric motor to reach the predetermined desired speed, and generates by means of a PWM modulator the switching signals relating to the calculated voltage signal, to be applied to each of the switching elements comprised in said control unit, so that the motor reaches the desired operating speed. 
         [0007]    Another object of the present invention is to conserve the life of the battery. 
         [0008]    Yet another object of the present invention is to maintain the temperature of a refrigerated enclosure without placing the battery at a disadvantage. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]    Devices embodying the invention will now be described only by way of example and with reference to the attached drawing, in which: 
           [0010]      FIG. 1  shows in a block diagram an electronic control unit connected to a hermetically encapsulated motor-compressor combination according to the invention. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0011]    A block diagram of an electronic control means  11  connected to a combination of an electric motor  12  and to a compression means  13  and to an electric power source is schematically illustrated below with reference to  FIG. 1 . 
         [0012]    The control unit  11  comprises an energy conversion means  14  receiving energy from the electric power source such as a battery or the like, not shown, which can be connected to an electric generator, not shown, the function of which is to recharge the battery. 
         [0013]    The converter  14  is carried out according to a boost topology, such as a boost converter. 
         [0014]    The control unit  11  also includes an inversion means  15  such as a three-phase inverter connected through a pair of input terminals to a pair of output terminals of the boost converter  14 . The control unit  11  also includes output terminals whereby it is connected to the windings of a direct current motor  12  without brushes and without sensors in the position of the rotor, which is in turn coupled to the compressor  13 . A capacitor  17  is connected in parallel to the input terminals of the three-phase inverter  15 . 
         [0015]    The boost converter  14  and the three-phase inverter  15  are widely known in the state of the art and their operation will not be described in detail. Both devices  14 ,  15  include switching elements such as MOSFET, IGBT field-effect transistors or the like working in cutoff and conduction mode. 
         [0016]    The control unit  11  includes a microprocessor, not shown, executing a PID (proportional-integral-derivative) algorithm to calculate the voltage demanded by the motor  12  which is necessary to reach and maintain a predetermined speed. 
         [0017]    The control unit  11  also includes a pulse width modulation (PWM) regulator  16  which is connected to all the switching elements of the control unit  11 , so as to generate the switching signals which are applied to each switching element at each instant from the demanded voltage, as a result a voltage will be generated which is applied at each instant to the windings of the motor  12 , the latter reaching the necessary speed so as to maintain the refrigeration conditions and conserve the life of the battery. 
         [0018]    The speed of the motor  12  can be predetermined and fixed or depend on the battery voltage, which is variable within a predetermined interval, i.e. when the battery voltage reaches its lower operating voltage value, the motor  12  must rotate at a predetermined minimum value and when the voltage reaches its upper operating voltage value, the motor must rotate at a predetermined maximum value. 
         [0019]    The speed can also be variable, calculated through an algorithm analyzing the temperature of the refrigerated enclosure or the work cycles of a thermostat maintaining said temperature. 
         [0020]    In summary, the speed at which the motor  12  must rotate is known at each instant. Once the speed is known, the PID algorithm calculates the voltage level which must be applied to the windings of the motor  12  so as to reach said speed. Once the necessary voltage value has been calculated, the PWM modulator  16  generates the corresponding switching signals for each switching element so that the motor  12  rotates at the desired speed. The switching signals make the switching elements of the control unit  11  work in cutoff and conduction mode. 
         [0021]    Two different circumstances can occur in any previously described case, which are that the voltage demanded by the motor  12 , namely calculated by the PID algorithm, is greater than the battery voltage and that the voltage demanded by the motor  12  is less than the battery voltage. 
         [0022]    In the event that the motor  12  demands a voltage value that is greater than the voltage value supplied from the battery, the voltage delivered to the boost converter  14  from the battery is transformed into a higher voltage. This transformation is controlled by the PWM modulator  16  generating a switching signal, a work cycle, at one of its outputs, which signal is applied to the switch of the boost converter  14  such that the converter  14  converts the received voltage into another higher voltage which is applied to the windings of the motor  12  through the three-phase inverter  15 , which works without modulation. 
         [0023]    In the event that the motor  12  demands a voltage value less than the voltage value supplied from the battery, the PWM modulator  16  generates a permanent cutoff signal which is applied to the switch of the boost converter  14 , such that said switch does not conduct and there is a transfer of non-converted power between the input and output of the boost converter  14 . In order to accommodate the voltage level received from the battery to the value demanded by the motor  12 , the PWM modulator  16  generates the corresponding modulated signals, work cycles, for each of the switching elements of the three-phase inverter  15 , such that the voltage received from the battery is substantially cut down to the voltage value demanded from the motor  12 . 
         [0024]    The embodiments and examples established in this specification are set forth as the best explanation of the present invention and its practical application and to thus allow the persons skilled in the art to put the invention into practice and use it. Nevertheless, the persons skilled in the art will admit that the description and the previous examples have been set forth for the purpose of illustration and only as an example. The description as it is set forth is not intended to be comprehensive or to limit the invention to the precise described form. Many modifications and variations are possible in the light of the previous teachings without departing from the essence and scope of the following claims.