Electricity: motive power systems – Constant motor current – load and/or torque control
Patent
1996-12-20
1998-02-03
Ro, Bentsu
Electricity: motive power systems
Constant motor current, load and/or torque control
318721, 318722, 318724, H02P 540
Patent
active
057148570
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a current regulation process for a three-phase, static-converter-fed, permanently excited synchronous machine.
BACKGROUND INFORMATION
European Patent Application No. 0 350 716 B1 describes a permanently excited synchronous machine with a trapezoidal magnet wheel voltage, driven by block-shaped phase currents. The regulating circuit of such a synchronous machine contains a current regulator with a pulse width modulator connected downstream. The actual value of the current at a given time is obtained using two measured phase currents and the actual value of the rotor orientation angle. Subsequently the regulating difference is calculated from a reference value and the measured actual value of the current. The control pulses for the power semiconductor of the power inverter, distributed to the corresponding bridge branches of the power inverter, are generated from the controller output voltage with the help of the pulse width modulator. If the synchronous machine is driven with exactly 120' long, rectangular currents and an ideal trapezoidal magnet wheel voltage, the torque ripple is equal to zero. Such operation of the machine is desirable, but cannot be achieved in practice, since it would require an infinitely high voltage due to the winding inductance needed to implement the block-shaped current with steep edges, and the power converter valves would require an infinitely high switching speed with no delays. In addition, the magnet wheel voltage of the permanently excited synchronous machine is not exactly trapezoidal.
Another disadvantage of this conventional type of regulation is that the current is affected in the phase not involved in switching. This results in strong pulsating torques and current harmonics on the DC input side of the power inverter, and thus in fluctuating input power. The European Patent No. 0 350 716 B1 describes a process for reducing such current disturbances.
The steeper the edge of the current block, the more the current approximates the ideal block current. Since a steeper edge requires more voltage reserves and increases the load on the supply lines and the winding of the permanently excited synchronous machine due to the steepness of the voltage, the steeper edge can be achieved to a certain degree. The current edge steepness has only a limited effect on the values obtained for power input and output, efficiency, and utilization. It strongly affects, however, the ripple of the intermediate circuit current, the battery current and the torque of a drive, especially of an electric vehicle drive. While a flat current edge is more advantageous for the intermediate circuit current and the battery current, it results in greater torque ripple.
Mr. Martin Schroder's 1986 dissertation entitled "High-speed brushless position drive with extremely low torque ripple" describes a current regulating process for a three-phase, static-converter-fed, permanently excited synchronous machine with a trapezoidal magnet wheel voltage. A device for implementing this current regulating process is illustrated in FIG. 1. Machine 2 is supplied from a four-quadrant pulse converter 4 with an intermediate voltage circuit equipped with field-effect power transistors. The reference values of the three phase currents are supplied to converter 4 in analog form as voltages. Phase current regulators 6, 8, and 10 are components of power inverter 4 as are current measurement points 12, 14, and 16. Since current regulation is based on a switching principle and the winding inductance is relatively small due to the large magnetic air gap, series reactors (not illustrated in detail) are required in the supply lines to the machine to smooth the current. These series reactors are also present in power inverter 4. An incremental phase angle sensor 18 is located on motor shaft 20 for measuring the actual values .omega..sub.ist and .epsilon..sub.ist of the rotation speed and the orientation angle, respectively; this incremental phase angle sensor supplies two outpu
REFERENCES:
patent: 4012679 (1977-03-01), Matsuda et al.
patent: 4468603 (1984-08-01), Vander Meer et al.
patent: 5097192 (1992-03-01), Iijima
Martin Schroder et al., "Hoctoutinger burstenloser Positionierantrieb mit extrem geringer Momentenwelligkeit", Institute fer Elektrische Maschinen und Antriebe der Universitat Stuttgart (1986).
Von Wolfgang Amrhein, "Die elektronische Reduktion von Drehmomentschwankungen an Permanentmagnetmotoren", 1155 Technische Rundschau 81, No. 10, Bern, Mar. 10 (1989).
Mannel Ulrike
Tolle Hans-Jurgen
Ro Bentsu
Siemens Aktiengesellschaft
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