MXPA00008468A - Motor conroller - Google Patents

Abstract

A motor controller utilizes sensors to detect the rotational speed and relative position of the motor rotor and generates a voltage vector to maintain the motor current in phase with the EMF before a voltage limit is reached. The approximate actual speed is calculated and position signals are generated by the calculator. The actual speed is compared with a command speed signal and any difference gives rise to an error signal. A proportional integrator receives the error signal and produces a correction signal for a vector rotator corresponding to the desired vertical voltage component necessary to achieve the command speed. After the voltage limit is reached, any further speed increase desired is achieved by rotation of the voltage vector with it's amplitude unchanged.

Description

MOTOR CONTROLLER FIELD OF THE INVENTION This invention relates to a motor controller and is particularly related to a motor controller for high speed brushless DC motors, to allow the motor speed to be controlled between the minimum and maximum speed with optimum efficiency. International Patent Application No. PCT / AU98 / 00035 discloses a high speed brushless DC motor that was designed particularly for the handling of a refrigerant compressor or the like. This motor has a rotor formed with a rare earth magnet (NdFeB) inside a non-magnetic sleeve and a very low inductance stator coil to allow the near factor of the power unit to be reached between the base speed and the maximum engine speed. The present invention allows an engine of the type described in the aforementioned international patent application or engines of similar design to be controlled without the need to use relatively expensive and complex control equipment. In order for the engine speed to be controlled within the desirable limits using inexpensive control components, it is necessary to devise an engine controller that is able to take advantage of the low inductance design of the stator coils. Therefore, it is desirable to provide an engine controller that is capable of controlling the speed of a high-speed DC motor having low inductance stator coils.

It is also desirable to provide a motor controller of relatively low cost but effective to provide the necessary speed control required for a refrigeration compressor or the like. It is also desirable to provide an engine controller that can be used in relation to structurally-engineered engines and of ordinary dimensions in commercial manufacturing. It is also desirable to provide a motor controller that is capable of controlling the speed of the motor in accordance with load demands.

SUMMARY OF THE INVENTION In accordance with one aspect of the invention, there is a motor controller provided for a high speed DC electric motor, which includes sensors for detecting the relative position of the motor rotor, the speed calculation means for receiving the position signals of the sensors and to calculate from them the approximate relative position and rotation speed of the rotor, a vector rotor that receives the existing speed and the position signals of the speed calculation means, a signal generator of error to generate an error signal corresponding to any difference detected between a signal of the control speed and the signal of the existing speed, a proportional integrator to receive any error signal and produce a signal for the vector rotor corresponding to the desired vertical component of the voltage vector required to achieve the command speed and the means of tadio of power to amplify the output of the vector rotor to supply the motor.

The controller of this invention is particularly designed to be used in connection with high speed electric motors having a low inductance stator coil to stay close to the power unit factor over the range of operating speeds. Said electric motor as described in the aforementioned International Patent Application No. PCT / AU 98/00035 was designed for use in a refrigeration system in which the rotational speed of the centrifugal compressor is dependent loading. Refrigeration systems invariably run less than the total load capacity for a relatively long part of their operating time. The controller of the invention ensures that the engine power requirements result in maximum efficiencies in the total operating speed of the compressor. This is done by the controller that generates a voltage vector in response to the sensors to keep the motor current substantially in phase with the electric motive force (EMF) before the voltage limit is reached. Any additional increase in the required velocity after the voltage limit is reached is achieved by rotation of the voltage vector while keeping the amplitude constant. In a preferred embodiment of the invention, the position sensors determine the rotating position of the rotor and its instantaneous rotation speed. The instantaneous velocity determinations can not detect the acceleration between the sensor positions so that the calculated existing rotor speed can include a degree of approximation. Any difference, however, between the detected speed and the existing speed is not significant for the purpose of calculating the speed.

The calculated existing speed is compared to a signal of the command speed to detect any difference. The signal of the control speed can be derived from a control circuit of the cooling system that produces a speed signal corresponding to the load of the detected system. A vector rotor generates control voltages to the horizontal and vertical components of which reflects the modified speed control by the difference with the detected speed. Preferably, a conditional switch is provided in the controller so that the voltage amplitude and the voltage angle are kept commensurate with the command speed signal to maintain a minimum energy for a given torque output. The conditional switch, in one position, applies a function of the existing rotor speed according to the horizontal component and the load demand according to the vertical component of the vector rotor. The switch moves to a second position when the horizontal and vertical components of the voltage vector satisfy the condition μq2 + μd2 = 1 and ßl weakening of the field originates and any additional increase in velocity causes the vector rotor to rotate the voltage vector with the amplitude of the vector without change. In this case, the power factor stays close to the unit. The sensors that detect the relative position of the rotor comprise three position sensors placed at 120 ° from each other. Because the sensors detect the instantaneous position of a magnetic field rotating with the rotor and as the rotation speed can vary between the sensors, the existing position of the measured rotor necessarily approaches due to the speed changes between the sensor positions . However, at rotation speeds between 20,000 rpm and 55,000 rpm, the approach can be ignored for the purposes of the controller of the invention. For the invention to be understood more quickly, one embodiment thereof is described with reference to the accompanying drawing.

DESCRIPTION OF THE DRAWING Fig. 1 is a block diagram illustrating a form of the motor controller according to the invention.

DESCRIPTION OF THE PREFERRED MODALITY The motor controller of this mode is in the form of a micro controller 11 for controlling the motor 12 through a power stage 14. The motor controller is shown diagrammatically in Figure 1 where:? = existing speed? * = control speed μq = the vertical component of the voltage vector μ = the horizontal component of the voltage vector? = rotor position The relative position and the approximate speed of the rotor is detected by three position sensors 33 located around the rotor and spaced at 120 ° from each other. The position sensors 33 generate three drive trains in phase with the position of the rotor and are used by the position and the speed calculator 34 to calculate the existing speed? of the rotor and its position? at a given time, within a degree of approximation, depending on whether or not the change in speed between sensor positions occurs. The existing speed? is compared to a command speed? * by the error signal generator 36 to determine any difference between the existing speed? and the command speed? *. If a difference is detected, the error signal generator 36 generates an error signal e. The error signal e is used by the proportional integrator 37 to calculate the vertical component of the voltage vector μq which is used to control the vector rotor 31. The vector rotor 31 also receives the existing velocity signal? as well as the position of the rotor? of the speed and position calculator 34. The vector rotor 31 generates three control voltages V1, V2 and V3 which are a function of the vector field μq and which are amplified by the power stage 14 to provide the motor 12. The microcontroller 11 also includes a conditional switch 39 which is exchanged between position a and position b. The switch is in position a when μq2 + μd2 <; 1 and is in position b when μq2 + μd2 = 1. The multiplier 41 multiplies a correlation factor K with the existing rotor speed?, As determined by the position and the speed calculator 34. The product of this calculation, when the conditional switch 39 is in position a, is applied to the vector rotor 31 to give the horizontal component of the voltage vector. In this case the controller is able to vary the amplitude of voltage and the angle provided with the control speed? * To conserve the energy at its minimum for a given torque output before the voltage limit is reached. The correlation factor K is a constant constant speed and can vary between the base speed and the maximum speed of the motor. The K factor was developed by conducting tests at various engine operating speeds to determine the optimum value of K for engine conditions at various speeds. The results of the test were used to develop a polynomial curve, which was later used to determine the K factor for any given engine speed. Switch 39 moves to position b when the condition μq2 + μd2 = 1. When this condition occurs, the weakening of the field originates and any additional increase in the required velocity causes the voltage vector to rotate. The vertical component of the voltage vector generated by the proportional integrator 37 was applied to the calculator 42 that determines the horizontal component μd by: tt The μd component is applied to the vector rotor 31 through the position b of the switch 39. The vector rotor develops the necessary voltage vectors for the power stage 14. In the preferred form of the invention, the microcontroller 11 used in the Illustrated embodiment is a digital signal processor of Analog Devices AD MC 330. Of course, other processors may be used in the development of this invention. The motor controller of the invention allows the vertical and horizontal components of the voltage vector to be used to control the motor speed and at maximum voltage, when the additional speed increase is required, the weakening of the field originates causing the motor to rotate. voltage vector.

Claims (1)

1. CLAIMS A motor controller for a high-speed DC electric motor including sensors for detecting the relative position of the motor rotor, means for calculating the speed for receiving the position signals of the sensors and for calculating the relative relative position thereof. and the rotation speed of the rotor, a vector rotor that receives the existing speed and the position signals of the speed calculation means, an error signal generator to generate an error signal corresponding to any difference detected between a signal of the control speed and the existing speed signal, a proportional integrator to receive any error signal and produce a signal for the vector rotor corresponding to the desired vertical component of the voltage vector required to reach the control speed and the stadium means of power to amplify the output of the vector rotor to provide the motor. A controller according to claim 1, wherein said sensors that detect the relative position of the rotor, comprise three position sensors positioned at 120 ° to one another with respect to the rotor. A controller according to claim 2, wherein the sensors detect the instantaneous position of a magnetic field by rotating with the rotor and generating three pulse trains in phase with the position of the rotor and which are used by a position and the speed calculator. to calculate the existing speed? and its approach position? depending on whether or not a change in speed occurs between the sensor positions. A controller according to any of the preceding claims further comprising a conditional switch that provides an input signal to the vector rotor, whose input signal is either a function of the existing motor speed detected by the sensors or is a function of the vertical component of voltage. A controller according to claim 4, wherein when the switch is in a first position, it receives the output of a multiplier that multiplies a correlation factor K by the existing speed to produce the input signal of the vector rotor. A controller according to claim 5, wherein the switch moves from a first position to a second position when the maximum voltage is reached (when the square of the horizontal component plus the square of the vertical component is equal to one (1)) and in that second position, the weakening of the field originates and any additional increase in the required velocity causes the voltage vector to rotate. A controller according to claim 6, wherein the vertical component of the voltage vector generated by the proportional integrator is applied to a calculator that determines the horizontal voltage component μd by: tt onde: μq = the vertical component of the voltage vector μd = the horizontal component of the voltage vector.