Analysis and Exploitation of the Star-Point Voltage of Synchronous Machines for Sensorless Operation

Abstract

In the field of sensorless drive of synchronous machines (SMs), many techniques have been proposed that can be applied successfully in most applications. Nevertheless, these techniques rely on the measurement of the phase currents to extract the rotor position information. In the particular case of low-power machines, the application of such techniques is challenging due to the limited bandwidth of the available current sensors. An alternative is offered by those techniques that exploit the star-point voltage rather than phase currents. This work aims at providing a model of the dynamic behavior of the star-point voltage and presenting a technique for extracting the rotor electrical position needed for sensorless operation of SMs. Two different circuitries for measuring the star-point voltage are also presented and then compared. The presented mathematical analysis and the measurement methods are validated both numerically and experimentally on a test machine.

Analysis and Application of the Direct Flux Control Sensorless Technique to Low-Power PMSMs

“…Let us consider the electrical equation of an SM in the phase reference frame where the speed is considered zero. This hypothesis does not limit the validity of this presentation as shown in [23].…”

“…As shown in [23], it is possible to prove that these transfer functions are proper and of the second order given that the numerator and denominator polynomials have a root in zero. In addition, it is possible to calculate the coefficient of the maximum order of the numerator and denominator polynomials in s. Thus, it follows that the ratio between the maximum coefficients in s of the transfer functions G(s) is given by:…”

“…The mathematical description of the star-point voltage dynamics in synchronous machines has been presented extensively in [23]. In this work, after a brief recall of that mathematical framework, the theory is enhanced first by proposing a condition on the applicability of star-point voltage exploiting techniques to SMs and then with considerations concerning the structure of the machine inductance matrix L abc .…”

“…In [19] and in [20], a method to excite the machine for the DFC technique in order to obtain signals that can be used for the estimation of the rotor position has been proposed. In order to improve the quality of such measurements, a Fast resettable integrator circuit (FRIC) was presented in [21][22][23]. Another interesting usage of the zero-sequence voltage for sensorless operation of PMSMs is reported, firstly, in [24], where the machine is operated by exciting two machine phases and by measuring the induced voltage caused by magnetic saturation (IVMS) allowing for the estimation of the rotor position.…”

“…By considering the mathematical description of the star-point voltage dynamic behavior presented in [23], this work aims at presenting and discussing the applicability of star-point voltage exploiting sensorless techniques to the case of PMSMs. In particular, with reference to the DFC technique, given a mathematical description of a PMSM inductance matrix, similar to that of [26], this work aims at modeling the information that can be extracted from the machine star-point voltage with a particular focus on determining the conditions of the machine phase inductances under which no information can be extracted from the zero-sequence voltage.…”