| 1. |
- Barenthin, Märta, et al.
(author)
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Validation of stability for an induction machine drive using power iterations
- 2005
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In: Proceedings of the 16th IFAC World Congress, 2005. - Prague. - 9783902661753 ; , s. 892-897
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Conference paper (peer-reviewed)abstract
- This work is an extension of the paper (Mosskull et al., 2003), in which the modelling, identification and stability of an nonlinear induction machine drive is studied. The validation of the stability margins of the system is refined by an improved estimate of the induced L2 loop gain of the system. This is done with a procedure called power iterations where input sequences suitable for estimating the gain are generated iteratively through experiments on the system. The power iterations result in higher gain estimates compared to the experiments previously presented. This implies that more accurate estimates are obtained as, in general, only lower bounds can be obtained as estimates for the gain. The new gain estimates are well below one, which suggests that the feedback system is stable. The experiments are performed on an industrial hardware/software simulation platform. in this paper we also discuss the power iterations from a more general point of view. The usefulness of the method for gain estimation of nonlinear systems is illustrated through simulation examples. The basic principles of the method are provided.
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| 2. |
- Mosskull, Henrik
(author)
-
Robust Control of an Induction Motor Drive
- 2006
-
Doctoral thesis (other academic/artistic)abstract
- This thesis considers robust control of an induction motor drive, consisting of an input filter, a voltage source inverter and one or several induction motors in parallel. The motor torque is here controlled by using the method Indirect Self Control (ISC), and power oscillations between the inverter and the input filter are damped by means of a stabilization controller in an outer feedback loop. Closed-loop performance with ISC is analyzed under the assumption of a stiff inverter input voltage. It is shown how parameter errors influence the torque loop and the conclusion is that the motor leakage inductance should not be overestimated, especially not with a large desired control bandwidth. It is also shown that model errors enhance cross coupling, but that the performance is quite insensitive even to large parametric errors. Based on the closed-loop model, expressions for the controller parameters are derived to obtain required stability margins. For design of the stabilization controller to suppress oscillations between the inverter and the input filter, it is shown that the effects of time delays and limited torque (or current) control bandwidth are important and cannot be neglected. From models including these non-ideal properties of the control system, explicit expressions for stabilization controllers to use with ISC as well as field-oriented control (FOC) are derived. This is valuable as stabilization often is designed through costly and time-consuming manual tuning. In the controller design, the trade-off between tight torque control and stability of the DC-link is also explicitly considered. In this way reasonable stability margins are obtained, while minimizing the negative effects on torque control. Stability of the closed-loop drive with the proposed stabilization is validated through realistic hardware-in-the-loop simulations using real control HW and SW. Using models obtained from frequency domain system identification, stability of the non-linear closed-loop drive is verified by combining stability results for linear systems with the small gain theorem for the non-linear model errors. This thesis considers the input filter dynamics in connection with torque control of an induction motor. The key result is a model-based framework for simultaneous treatment of DC-link stability and efficient torque control.
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| 3. |
- Mosskull, Henrik, et al.
(author)
-
Stabilization of induction motor drives with poorly damped input filters
- 2007
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In: IEEE Transactions on Industrial Electronics. - : IEEE. - 0278-0046 .- 1557-9948. ; 54:5, s. 2724-2734
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Journal article (peer-reviewed)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.
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| 4. |
- Mosskull, Henrik
(author)
-
μ-Analysis of indirect self control of an induction machine
- 2005
-
Conference paper (peer-reviewed)abstract
- Robust stability and performance of an induction machine controlled with Indirect Self Control (ISC) are examined through μanalysis. The analysis indicates poor robust performance at higher rotor speeds. Using reasonable parameter deviations between plant and controller, the predicted bad performance is however hard to verify through simulations. The tested parameter variations seem not to generate the worst case model errors. in simulations, the ISC therefore outperforms linear controllers optimized with respect to the robust performance criterion (at dispense of nominal performance). The large predicted sensitivity to model errors however explains the large impact on performance due to seemingly small differences in the implementation of the ISC control.
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