PMSMs Torque Estimation Using Pulsating HF Current Injection

Abstract

Torque estimation in permanent magnet synchronous machines (PMSMs) is highly desirable in many applications. Torque produced by a PMSM depends on the permanent magnets' (PM) flux and dq-axis inductances. Consequently, precise knowledge of these parameters is required for proper torque estimation. This paper proposes the use of a high frequency (HF) signal for PM flux and dq-axis inductances estimation. The HF signals will be injected in the stator via inverter superposed on top of the fundamental excitation. Appealing properties of this method include operation in real time, without interference with the normal operation of the machine and independent of machine working condition. 1

Enhancement of Permanent-Magnet Synchronous Machines Torque Estimation Using Pulsating High-Frequency Current Injection

“…As shown in (2), electromagnetic torque (T syn ) estimation requires knowledge of PM flux, λ pm . D-axis inductance can be used for this purpose as it has been shown to vary almost linearly with PM flux [23], [25]. λ pm variation with d-axis inductance can be expressed as (5).…”

“…D-axis inductance (6) is a function of the fundamental current, d and q-axis currents, and PMs remanent flux, which varies with its temperature T r [22]. I and with PM remanent flux due to saturation, the remanent flux being affected by magnet temperature [19], [23]. Equation 6…”

“…Implementation and experimental results A) Implementation and experimental setup Fig. 5 shows the general block diagram used for the implementation of the proposed method [23]- [22], including inverter control and injection of pulsating HF signals; torque estimation requires the injection of two pulsating HF signals to estimate L dHF and λ pm , and to estimate L qHF respectively. It must be noted that the frequency of the HF signals in a stationary reference frame will be, ω r + ω hf , which should be smaller than half of the switching frequency (i.e.…”

“…Implementation details are summarized in Table I. The d and q-axis HF impedances are estimated using (12) and (22), the d and q-axis HF inductances are estimated using (13) and (23), the PM flux is estimated using (15) and the output torque, T out , is finally estimated using (26), by adding (16) and (25). Note that the proposed method does not require knowledge of PM temperature.…”

“…In addition PM remanent flux variation changes the daxis saturation level (assumed that the PMs are aligned with the d-axis), making the d-axis inductance to change [22]. Injection of fundamental dq-axes current changes the dq-axes saturation level, resulting therefore in dq-axes inductances variation [22], [23]. Therefore, to obtain reliable torque estimation, knowledge of parameters variation with machine operating conditions would be required.…”