Electricity: motive power systems – Induction motor systems – Primary circuit control
Reexamination Certificate
2001-07-30
2002-12-17
Dang, Khanh (Department: 2837)
Electricity: motive power systems
Induction motor systems
Primary circuit control
C318S802000, C318S811000, C318S782000
Reexamination Certificate
active
06495986
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to a drive controller for position and speed sensing for a three-phase motor without an integrated sensor system by means of an inverter. The inverter has electrical valves in bridge connection.
BACKGROUND OF THE INVENTION
When electrical drives are used in industrial automation technology, for example in the case of numerically controlled machine tools and robots, it is a prerequisite to provide the greatest possible protection for man and machine. With a “safe speed” function for the motor, it is intended to ensure that the electrical machine or motor remains controllable even in the event of a fault, with the result that, as far as possible, it cannot perform any hazardous movements.
Corresponding safety functions have so far been used mainly in the area of machine tools. One element conventionally forming the basis for the safety functions is a sensor system integrated in the motor for position and speed sensing. In other areas, for example, production machines etc., such safety functions are likewise becoming of greater interest. In these areas, usually sensor-free three-phase motors are used in connection with what are known as frequency inverters. However, such sensor-free, three-phase motors have not so far offered any significant safety functions. To date, only a “safe stopping” function has been used, in which the driving signals for the power transistors are “safely” inhibited, which prevents unwanted re-starting of the motor. One skilled in the art refers to this by the term “pulse inhibit”.
The word “safe” is intended here to express the idea that the respective requirements stipulated by the employers' liability insurance associations and their institutes for safety at work are satisfied. In this respect, there is a need with regard to fault detection for the protection of man and machine for such sensor-free, three-phase drives also to be provided with the “safe speed” function. Previous attempts to implement such a function have not been successful in respect of the accuracy or dynamics of the speed sensed (or calculated from current and voltage). To date, there has also not been any satisfactory solution found to the problem of recovering the stator frequency from the transistor driving signals for driving an inverter. It is therefore the object of the invention to provide a drive controller with safe speed monitoring for sensor-free three-phase drives.
SUMMARY OF THE INVENTION
According to the present invention, the aforesaid object is achieved by a drive controller for a three-phase motor which utilizes an inverter. The inverter has a first and a second system for generating a first set and second set of redundant control signals, to promote trouble-free operation for the electrical valves of the inverter. One system has a setpoint speed value applied to it, on the basis of which an essentially proportional setpoint frequency value can be derived for generating the first set of control signals, which can be provided for the other system via a communication interface for generating the second set of control signals. The respective setpoint frequency value in the respective system can be limited and/or can be monitored, wherein two fault detecting means are provided for monitoring the first and second sets of control signals, so that it is possible for a subset of corresponding control signals of the first and second sets of control signals to be compared with one another in the first fault detecting means and the remaining corresponding control signals of the first and second sets of control signals to be compared with one another in the second fault detecting means. In the case of corresponding control signals deviating from one another, the electrical valves of the inverter can be switched off in a two-channel mode by the respective fault detecting means.
If the inverter has electrical valves in bridge connection, it has been found to be particularly advantageous if, in the case of corresponding control signals deviating from one another, the pulses for the upper bridge arm of electrical valves can be inhibited by one fault detecting means and the pulses for the lower bridge arm of electrical valves can be inhibited by the other fault detecting means. In this case, it has been shown to be particularly effective for technical implementation if the setpoint stator frequency value, respectively, serves as the setpoint value essentially proportional to the setpoint speed value for generating the two sets of control signals.
A further preferred embodiment of the drive controller according to the present invention, is its application in an asynchronous motor, in which the system to which the setpoint speed value is applied comprise an arithmetical and logical means with an integrated speed controller. With knowledge of the motor data, the system supplies, on the basis of the setpoint speed value and the respective actual phase current values, not only the respective setpoint stator frequency value but also the respective setpoint slip frequency value, setpoint stator voltage value and load angle in the rotor flux system of coordinates. Based on this system, respective setpoint phase voltage values for driving a respective control unit for generating respective control signals can be generated by means of respective closed-loop control components of the two systems. In the case of a synchronous motor, the procedure is the same except that the slip frequency values are equal to zero for system-related reasons.
If the first fault detecting means monitors the corresponding control signals for the electrical valves of the upper bridge arm and the second fault detecting means monitors the corresponding control signals for the electrical valves of the lower bridge arm, a particularly simple fault detecting means can be achieved, and achieved particularly well when each fault detecting means performs a logic exclusive-OR operation on corresponding control signals that monitor the electrical valves. Thereafter, the results are logically combined to form a cumulative fault signal.
In a particularly low-cost technical implementation of the present invention, only one set of control signals for driving the electrical valves of the inverter is used.
By using respective optocouplers serving for the transmission of control signals to the electrical valves and a fault detecting means which allows the supply voltage of the optocouplers associated with the assigned control signals to be interrupted in the event of a fault, the safety of the drive controller can be further enhanced while the technical expenditure for switching off the control signals can be minimized. This system can be further simplified by a fault detecting means which allows the supply voltage of the optocouplers associated with the respectively assigned bridge arm to be interrupted in the event of a fault.
The safety of the arrangement according to the invention can be further increased by providing a means for enforced dynamization of the two pulse inhibiting paths. An interference signal can be applied to the setpoint value for generating the sets of control signals and the supply voltages for driving the electrical valves of the upper bridge arm and those of the lower bridge arm of the inverter can be read back. In this case, it has been shown to be particularly advantageous if the reading back of the supply voltages for driving the electrical valves of the upper bridge arm and those of the lower bridge arm of the inverter take place sequentially.
Safety may be further enhanced by utilizing an additional means for enforced dynamization of the setpoint value limitation, in particular of the setpoint stator frequency value, with which a respective test signal can be applied to the setpoint value for generating the sets of control signals in both systems; and the respectively generated limitation signals are compared, by crosswise data comparison.
REFERENCES:
patent: 4291265 (1981-09-01), Kawada et al.
patent: 5650708 (1997-07-01), Sawada et al.
Baker & Botts LLP
Dang Khanh
Siemens Aktiengesellschaft
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