Determination of the rotor temperature of a permanent magnet synchronous machine

Abstract

Methods and apparatuses for determining a rotor temperature of a permanent magnet synchronous machine (PSM) of an electrically driven vehicle are described.

Claims

1. A method for determining a rotor temperature of a permanent magnet synchronous machine in an electrically driven vehicle, comprising: in a driving state in which no torque is demanded of the permanent magnet synchronous machine, operating a power electronics system supplying the permanent magnet synchronous machine with energy in a current regulation mode; regulating the power electronics system such that an alternating current on an AC side of the power electronics system is zero; while the alternating current on the AC side of the power electronics system is zero, measuring a direct voltage on a DC side of the power electronics system and an electrical angular velocity of the permanent magnet synchronous machine; calculating an alternating voltage applied to the AC side of the power electronics unit from the measured direct voltage and a duty cycle of the power electronics unit; and calculating the rotor temperature based on the measured direct voltage and the measured electrical angular velocity, wherein the rotor temperature is calculated from the calculated alternating voltage applied to the AC side of the power electronics unit and the measured electrical angular velocity of the permanent magnet synchronous machine according to rotor temperature≈alternating voltage divided by the measured electrical angular velocity.

2. The method according to claim 1, wherein the driving state, in which no torque is demanded of the permanent magnet synchronous machine, is a coasting mode.

3. An apparatus for determining a rotor temperature of a permanent magnet synchronous machine, comprising: a power electronics unit that feeds the permanent magnet synchronous machine with alternating current; at least one current sensor arranged on an AC side of the power electronics unit, which is configured to measure an alternating current in at least one phase supplying the permanent magnet synchronous machine; at least one voltage sensor arranged on a DC side of the power electronics unit, which is configured to measure a direct voltage applied to the DC side of the power electronics unit; at least one rotational speed sensor, which is configured to measure a rotational speed of the permanent magnet synchronous machine; and at least one device for controlling the power electronics unit and for receiving and processing the measured direct voltage and the measured rotational speed from the sensors, for calculating an alternating voltage applied to the AC side of the power electronics unit from the measured direct voltage and a duty cycle of the power electronics unit and for calculating the rotor temperature of the permanent magnet synchronous machine based on the measured direct voltage and the measured rotational speed, wherein the rotor temperature is calculated from the calculated alternating voltage applied to the AC side of the power electronics unit and the measured electrical angular velocity of the permanent magnet synchronous machine according to rotor temperature≈alternating voltage divided by the measured electrical angular velocity.

4. The apparatus according to claim 3, wherein the at least one device for controlling the power electronics unit and for receiving and processing the measured data from the sensors and for calculating the rotor temperature of the permanent magnet synchronous machine is configured to regulate an alternating current on the AC side of the power electronics unit to zero.

5. The apparatus according to claim 3, wherein the at least one device for controlling the power electronics unit and for receiving and processing the measured data from the sensors and for calculating the rotor temperature of the permanent magnet synchronous machine is configured to determine an electrical angular velocity of the permanent magnet synchronous machine from the rotational speed of the permanent magnet synchronous machine measured by the at least one rotational speed sensor.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

(1) FIG. 1 illustrates a drive train of an electric vehicle configured to carry out methods according to embodiments of the invention.

(2) FIG. 2 illustrates a schematic representation of stresses occurring in the drive train of FIG. 1 when carrying out methods according to embodiments of the invention.

DETAILED DESCRIPTION

(3) FIG. 1 schematically shows a drive train of an electric vehicle configured to carry out methods according to embodiments of the invention. The drive train comprises a permanent magnet synchronous machine (PSM) 10, a power electronics system 20 supplying the PSM 10 with electrical energy and a high-voltage (HV) battery 30. An AC side 21 of the power electronics system 20 has three phases connected to the PSM 10. A DC side 22 of the power electronics system 20 is connected to the HV battery 30.

(4) The power electronics system 20 comprises a current sensor 23 in one of the three phases to the PSM 10 on the AC side 21 and a voltage sensor 24 on the DC side 22. The measured values of these two sensors of the power electronics can be used in determining the rotor temperature.

(5) If the power electronics system 20 is operated in a current regulation mode and is regulated such that the alternating voltage on the AC side 21 is zero, the alternating voltage on the AC side 21 can be determined from the DC voltage measured by the voltage sensor 24 through conversion via the duty cycle of the power electronics system 20. This alternating voltage can be used to draw conclusions about the induced voltage of the permanent magnets.

(6) FIG. 2 schematically shows the alternating voltages occurring in the drive train of FIG. 1 on the AC side 21 when carrying out a method as described herein. The permanent magnets of the PSM 10 through their movement induce a voltage U.sub.1 on the AC side 21 of the power electronics system 20. In order to prevent a current flow, the power electronics system 20 generates a counter-voltage U.sub.2 of equal magnitude. The magnitudes of the alternating voltages U.sub.1 and U.sub.2 correspond to the alternating voltage u.sub.q.

(7) The rotor temperature T.sub.Rotor of the PSM 10 can be calculated from the alternating voltage u.sub.q and the electrical angular velocity ω.sub.el of the PSM 10 determined via a rotational speed sensor (not shown), according to T.sub.Rotor≈u.sub.q/ω.sub.el.

(8) German patent application no. DE 10 2019 126 268.2, filed Sep. 30, 2019, to which this application claims priority, is hereby incorporated herein by reference, in its entirety.

(9) Aspects and features of the various embodiments described above can be combined to provide further embodiments. These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled.