Stabilization of Induction Motor Drives With Poorly Damped Input Filters

Abstract

Abstract-Efficient torque control of induction motor drives in combination with resonant dc-link input filters can lead to a type of stability problem that is known as negative impedance instability. An often-proposed solution to this problem is the nonlinear system stabilizing controller (NSSC). Stability is usually analyzed under the simplifying assumption of perfect torque control. This indicates that the NSSC stabilizes the drive at any operating point. In this paper, however, we show power laboratory experiments where the NSSC stabilization fails. An improved framework for stability analysis and synthesis of stabilization, based on a linear feedback model of the drive, is therefore proposed. With this approach, effects of time delays can easily be included, and stability margins can be directly established from measurements. To solve the indicated problems with NSSC, a stabilization controller that considers the practical limitations of torque control is derived. In the design of the stabilization controller, the tradeoff between damping and acceptable torque control is also explicitly taken into account. The proposed stabilization scheme is implemented and evaluated on a hardware-in-the-loop simulator as well as in a power laboratory. The results show that the proposed method outperforms the NSSC method.

Performance and robustness evaluation of dc-link stabilization

“…Actually, with poor disturbance rejection, a non-zero transfer function G D in (1) may be large enough to stabilize the system (the assumption of a CPL is hence not valid). On the other hand, the "stabilization effect" of G D may also reduce robustness of the system as was shown in Mosskull et al (2007), where a non-zero G D caused instability of a motor drive at zero power, although a pure CPL would not destabilize the system, see further Subsection 4.6.…”

“…Magne et al (2012), Awan et al (2009) and Marx et al (2008), the linearized dynamics will be examined in this contribution. Although linear analysis may be valid only locally, it has the advantage of straightforward treatment of robustness to model errors, which allows prediction of stability problems as the one discussed in Mosskull et al (2007). Consequently, the non-linear power Eq.…”

“…Active stabilization for such systems have e.g. been presented in Mosskull et al, (2007), Bae et al (2001), Sudhoff et al, (1998) and Walczyna et al, (1996) with induction motor (IM) drives, in Magne et al (2012), Awan et al (2009), Marx et al (2008), Liu and Forsyth (2008b) and Liu et al (2008) with permanent magnet synchronous motor (PMSM) drives and in Liu et al, (2007), Forsyth (2005, 2008a) with brushless dcmotor (BLDC) drives. In these contributions, stabilization is usually proven using root loci with linearized models of the closed-loop system, where internal power control dynamics either are included (Mosskull et al, 2007;Liu and Forsyth, 2008b;Liu et al, 2008Liu et al, , 2007Mohamed et al, 2012;Delemontey et al, 1995) or neglected Magne et al, 2012;Awan et al, 2009;Mosskull, 2014).…”

“…The latter result is also verified for a real application using Hardware-in-the-Loop (HIL) simulations as well as power lab measurements. The Robust Stabilizing Controller (RSC) presented in Mosskull et al (2007) is finally reviewed as an option to improve robustness of the NSSC.…”

Modeling of multiport DC busses in power-electronic systems

“…In more advanced load admittance models, the effect of nonideal control loops has been considered [13], [14]. Furthermore, the sampling and pulse-width modulator (PWM) delays have been taken into account in [12], [15].…”