Electricity: single generator systems – Automatic control of generator or driving means – Speed or frequency of generator
Reexamination Certificate
2000-07-28
2002-11-12
Ramirez, Nestor (Department: 2834)
Electricity: single generator systems
Automatic control of generator or driving means
Speed or frequency of generator
C322S028000, C322S022000, C322S025000, C322S059000
Reexamination Certificate
active
06479971
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method for regulating a three-phase machine without a mechanical rotary transducer, in particular an asynchronous or synchronous machine, functioning under any operational conditions.
For high-precision regulation of three-phase machines, in particular asynchronous and synchronous machines, the latter either with permanent magnet excitation, through reluctance effect, i.e. different magnetic conductivity depending on the rotor position, or through a combination of permanent magnet excitation and reluctance effect, the position of the magnetic flux is used. For machine speeds above a certain minimum flux rate, the induced electric current (EMC) can be detected by various methods described in the literature, and from it the flux position can be determined. At low flux rates, the flux detection methods based on EMC fail. In this case methods can be used which detect the position or flux density-related magnetic conductivity in real-time, and determine the rotor or flux indicator position from it.
In asynchronous machines, the main magnetic flux in the machine affects the magnetic leakage conductivity through saturation of the metal, so that with real-time measurement of the magnetic leakage conductivity or a related coefficient the flux position can be determined. In synchronous machines, the magnetic flux is directly correlated with the rotor position, so that in synchronous machines the detection of magnetic flux or the detection of the rotor position can be used for field-oriented regulation. In synchronous machines with permanent magnet excitation without a significant reluctance effect, for example when permanent magnets are fixed to a cylindrical rotor, it is possible on saturation in the iron—as with asynchronous machines the saturation-related magnetic conductivity in relation to the flux position—to determine the flux position and also the rotor position using the leakage conductivity in machines with a damper or the main field factor in machines without a damper by means of real-time detection or by detection of a related coefficient. In synchronous machines with reluctance effect, the fluctuating magnetic conductivity depending on the rotor geometry is detected instead of the fluctuating magnetic conductivity depending on the saturation, and thus the rotor position is determined. In synchronous machines with permanent magnet excitation and reluctance effect, the sum effect of the conductivity fluctuation depending on saturation and depending on geometry is used.
As described by M. Schrödl in the VDI Progress Reports, Series 21, No. 117, VDI-Verlag, Düsseldorf 1992, “Sensorless Control of A.C. Machines”, by detection of the current space phasor and division by the voltage space phasor a complex value that fluctuates with the double rotor or flux position can be obtained, which delivers the rotor position or the flux position via trigonometric equations. The disadvantage of the method described there lies in the fact that for detection of the current space phasor the detection of at least two phase currents using expensive phase current sensors, e.g. transfo-shunts, is necessary.
The aim of the invention is to create a method of the type mentioned above, which on the one hand avoids the mentioned disadvantages, and on the other hand guarantees a better and more precise control of the machine.
The method according to the invention is characterised by the fact that in asynchronous machines the flow direction required for field- and rotor-oriented control, and in synchronous machines the rotor position are measured using the spatial magnetic conductivity fluctuations in the machine, whereby the conductivity fluctuations are detected using the parameters for the D.C. link, and in particular the D.C. link current and/or D.C. link voltage, and using the actual switching state of the inverter, and by the fact that this is followed by a mathematical evaluation. With this invention, it is for the first time possible to create a method for high-precision control of three-phase machines without a mechanical transducer, such as a position sensor or tachogenerator, which will work under any operating conditions, including low speeds and idle, whereby only parameters of the D.C. link such as D.C. link current or D.C. link voltage are measured. Thereby, using the actual inverter switching state, the ratio of phase current increases to the resulting voltages is determined, which corresponds with the flux or rotor position of the three-phase machine.
SUMMARY OF THE INVENTION
The basic idea is to detect the described conductivity fluctuations by measuring the current increases in the machine phases. The method according to the invention avoids expensive current sensors, since it does not require the full space phasor information, but only the projections of the current increase space phasor and the corresponding voltage space phasor on the motor phase axes. The ratio of these parameters (referred to as y with index of phase name) is proportional to the actual local magnetic conductivity in the relevant phase axis, and fluctuates with the double rotor or flux axis position. In accordance with the invention, a measurement of the increase in D.C. link current using the actual inverter switching state is used for detection of the phase current increases instead of a measurement of the phase current increases. Thereby, the inverter serves as an intelligent measuring point change-over switch that applies the different motor phases to the D.C. link current measuring module depending on the inverter state. Thereby, the operational inverter states—the machine control is not affected by the measurement—or forced inverter states—the machine control is affected by the measurement—can be used. If, for example, positive D.C. link voltage is applied to the inverter branch connected to phase U in a three-phase inverter, and negative D.C. link voltage is applied to the inverter branches connected to V and W, the phase current of phase U will necessarily flow in the D.C. link, and therefore this phase current will be detected via the D.C. link. At the same time, however, it is known that in this inverter combination the voltage space phasor applied to the machine points in the direction of phase U, so that the mentioned ratio of the projections of the current increase space phasor—in the mentioned case, this is the current increase in phase U—and the corresponding voltage space phasor—in this case the voltage space phasor in phase direction U—can be established on the motor phase axes. Therefore, yu is established. By means of a three-phase inverter and a three-phase machine, the mentioned ratios can therefore be established via six inverter states in the directions U, −U, V, −V, W, −W.
In accordance with a special feature of the invention, at least two measurements of the increase in D.C. link current are carried out, and the measured values of the two increases are entered into the stator voltage equations and linked mathematically. An important advantage of this method according to the invention is the fact that the same measuring module is always used, so that errors of measurement due to component leakage, etc., are compensated by the combination of several measurements and thus do not affect the result. With this embodiment of the invention with the combination of two measurements, the EMC can be eliminated and the conductivity measurement is therefore independent of speed. This is not possible in measurement of the current space phasor for at least two phase currents, since the involved current sensors have different errors of measurement that affect the result.
In accordance with a further embodiment of the invention, at least two conductivity measurements are carried out in spatially separate directions, and the angle &ggr; is calculated according to the known rules of calculation. If an induced voltage (EMC) occurs in the stator winding due to a turning rotor, the ratio y will be affected by the EMC.
Gonzalez Julio C.
Ramirez Nestor
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