Electricity: motive power systems – Synchronous motor systems
Reexamination Certificate
2001-10-05
2003-02-04
Fletcher, Marlon T. (Department: 2837)
Electricity: motive power systems
Synchronous motor systems
C318S720000
Reexamination Certificate
active
06515446
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a motor controller that adequately regulates a voltage applied from a power source to a coil of a motor, thereby controlling operation of the motor, and also to a corresponding motor controlling method.
BACKGROUND ART
Various motors are used for industrial machinery and railcars. Recently proposed hybrid vehicles also use a motor as part of the power source. The motor is rotated by interaction of magnetic fields generated by a stator and a rotor. At least one of the magnetic fields is generated by power supply to a motor coil. In the case of a permanent magnet-type synchronous motor, permanent magnets are attached to a rotor, whereas a coil is wound on a stator. Supply of a multi-phase alternating current through the coil of the stator produces a revolving magnetic field on the stator. In the synchronous motor, the rotor is rotated synchronously with the revolving magnetic field thus generated.
The motor operation is controlled by regulating the voltage applied to the coil and thereby regulating the electric current running through the coil. For example, in order to output a large torque, the control increases the voltage applied to the coil to enhance the electric current and generate a strong magnetic field. In order to output a small torque, on the other hand, the control decreases the voltage applied to the coil to reduce the electric current and generate a weak magnetic field.
An inverter is often used to regulate the voltage applied to the coil. The inverter is a circuit of converting a DC voltage into an AC voltage and has pairs of switching elements, where the switching elements in each pair respectively connect with the source and the sink of a power source of a fixed voltage. The voltage applied to the coil is varied by changing a duty, that is, the on rate of the switching elements per unit time. Raising the duty on the source side increases the output voltage. Lowering the duty, on the other hand, decreases the output voltage. In order to regulate the voltage applied to the coil to a desired value, it is required to drive the inverter at an appropriate duty according to the source voltage.
The prior art technique sets a target voltage to be applied to the motor coil in response to a required torque and specifies the duty based on a source voltage measured with a sensor, in order to attain the setting. The motor operation is then controlled through the on-off operation of the switching elements included in the inverter at the specified duty.
The prior art control method may not, however, sufficiently control the motor operation. The sensor used for measuring the source voltage may cause an error for example, due to the factors of the environment, in which the motor is used. The error arises as an offset error where the observed value is deviated from a true value in either the positive direction or in the negative direction. The quantity of the offset is varied by the environmental and other factors.
The prior art technique controls the motor operation without considering the potential effects of the offset error. As mentioned above, the voltage applied to the motor coil is regulated by adjusting the duty of the inverter on the basis of the source voltage. An error included in the source voltage interferes with application of a desired voltage to the coil. The prior art control technique thus does not ensure accurate output of the required torque.
The detection error of the source voltage further causes the following troubles in the control of the synchronous motor. As discussed previously, the synchronous motor is driven by the revolving magnetic field, which rotates at a speed synchronous with the revolving speed of the rotor. In order to generate such a magnetic field, power supply to the coil is required according to the electrical rotational angle of the rotor, that is, the electrical angle. A sensor like a Hall element is generally used for detection of the electrical angle. The technique of sensor-less detection of the electrical angle has also been proposed to simplify the structure of the motor controller and thereby enhance the reliability.
The process of sensor-less detection of the electrical angle tentatively estimates the electrical angle to a certain value and applies a preset electrical angle detection voltage to the motor coil. The process then measures the electric current running through the coil in response to the applied electrical angle detection voltage. The relationship between the voltage and the current is expressed by a voltage equation. When no error is included in the estimated electrical angle, this equation is equal to zero. When the estimated electrical angle includes some error, the result of the voltage equation is deviated from zero according to the quantity of the error. An error or a difference between the estimated electrical angle and a true value may be specified, based on the deviation of the result of the voltage equation.
Application of the electrical angle detection voltage with a high accuracy is required for accurate sensor-less detection of the electrical angle. The value of the electrical angle detection voltage is also regulated by adjusting the duty according to the source voltage. The prior art technique does not take into account the value of source voltage in the process of application of the electrical angle detection voltage. The value of the electrical angle detection voltage is thus varied, due to the detection error of the source voltage. This may lower the accuracy of detection of the electrical angle. The lowered accuracy of detection of the electrical angle may cause troubles, such as pulsation of the torque, and damage the smooth operation of the motor.
A variety of apparatuses with a motor have been proposed recently, and there has been a high demand to enhance the accuracy of the motor operation control. Under such circumstances, the decrease in accuracy due to the error of the source voltage is thus not negligible. In some apparatuses using the motor as the power source, the power source may have an extremely high voltage. In such apparatuses, the effect of the error included in the source voltage is especially significant.
DISCLOSURE OF THE INVENTION
The object of the present invention is thus to provide a technique that relieves the drawbacks due to a detection error of a voltage applied to a motor coil and thereby adequately controls motor operation. In order to attain this and the other related objects, the present invention is arranged as discussed below.
The present invention is directed to a motor controller that regulates a voltage applied from a power source to a coil of a motor and thereby controls operation of the motor. The motor controller includes: a voltage estimation unit that estimates a voltage of the power source; a detection voltage application unit that applies a preset detection voltage to the coil, based on the estimated voltage; an electric current detection unit that measures a value of electric current running through the coil in response to the applied detection voltage; an error specification unit that specifies an error included in the estimated voltage, based on the estimated voltage and the observed value of electric current; and an operation control unit that reflects the specified error on control of the operation of the motor.
The motor controller of the above arrangement reflects the error included in the source voltage on the control. For example, when the absolute value of the error is greater than a preset value, the technique of the invention determines the occurrence of some abnormality and carries out a separately provided control process. The separately provided control process may be an additional process that is carried out in addition to a general control procedure or a substitutive process that is carried out in place of the general control procedure. The additional process that is carried out in addition to the general control procedure is, for example, a process of calibrating the source voltage or a proce
Kawabata Yasutomo
Koide Satoshi
Yamada Eiji
Fletcher Marlon T.
Toyota Jidosha & Kabushiki Kaisha
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