State-space current control enables high dynamic performance of a three-phase grid-connected converter equipped with an LCL filter. In this paper, observer-based state-space control is designed using direct pole placement in the discrete-time domain and in grid-voltage coordinates. Analytical expressions for the controller and observer gains are derived as functions of the physical system parameters and design specifications. The connection between the physical parameters and the control algorithm enables automatic tuning. Parameter sensitivity of the control method is analyzed. The experimental results show that the resonance of the LCL filter is well damped, and the dynamic performance specified by direct pole placement is obtained for the reference tracking and grid-voltage disturbance rejection.

Abstract-This paper deals with a speed and position estimation method for the sensorless control of permanent magnet synchronous motors. The method is based on a speed-adaptive observer. The dynamics of the system are analyzed by linearizing both the motor model and the observer, and the observer gain is selected to give improved damping and noise suppression. At low speeds, the observer is augmented with a signal injection technique, providing stable operation down to zero speed. The experimental results, obtained using a 2.2-kW interior magnet motor, are in agreement with the results of the analysis.

This paper addresses robust design of the active-power and dc-link control loops of powersynchronization control. Robustness is obtained by analytic gain selections which give large enough stability margins. The proposed design allows robust stability irrespective of the grid strength and of the operating point, the latter with one exception. The proposed design is compared to design based on the principle virtual synchronous machine. Experiments show that the time-domain results correlate well with the frequency-domain results.

This paper deals with discrete-time models and current control methods for synchronous motors with a magnetically salient rotor structure, such as interior permanent-magnet synchronous motors and synchronous reluctance motors (SyRMs). The dynamic performance of current controllers based on the continuous-time motor model is limited, particularly if the ratio of the sampling frequency to the fundamental frequency is low. An exact closed-form hold-equivalent discrete motor model is derived. The zero-order hold of the stator-voltage input is modeled in stationary coordinates, where it physically is. An analytical discretetime pole-placement design method for two-degrees-of-freedom proportional-integral current control is proposed. The proposed method is easy to apply: only the desired closed-loop bandwidth and the three motor parameters (R s , L d , L q ) are required. The robustness of the proposed current control design against parameter errors is analyzed. The controller is experimentally verified using a 6.7-kW SyRM drive. Index Terms-Current control, delay, discrete-time model, interior permanent-magnet synchronous motor (IPM), saliency, synchronous reluctance motor (SyRM), zero-order hold (ZOH). I. INTRODUCTIONS YNCHRONOUS motors with a magnetically salient rotor-such as interior permanent-magnet synchronous motors (IPMs), synchronous reluctance motors (SyRMs), and permanent-magnet (PM)-assisted SyRMs-are more and more applied in hybrid (or electric) vehicles, heavy-duty working machines, and industrial applications. In these applications, the maximum speeds and, consequently, the maximum operating frequencies can be very high (e.g., 12 000 r/min corresponding to the frequency of 1000 Hz for a ten-pole machine). Since the switching frequency of the converter feeding the motor Manuscript

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Abstract-This paper deals with reduced-order flux observers with stator-resistance adaptation for speed-sensorless induction motor drives. A general analytical solution for the stabilizing observer gain is given. The gain has two free positive parameters (which depend on the operating point), whose selection significantly affects the damping, convergence rate, robustness, and other properties of the observer. The general stability conditions for the stator-resistance adaptation are derived. An observer design is proposed that yields a robust and well-damped system and requires a minimal amount of tuning work. The proposed observer design is experimentally tested using a 45-kW induction motor drive; stable operation at very low speeds under different loading conditions is demonstrated.

Abstract-This paper deals with voltage model flux estimators for sensorless induction motor drives. In order to eliminate the drift problems, the pure integrator of the voltage model is replaced with a first-order low-pass filter, and the error due to this replacement is compensated in a very simple way.

This paper proposes a standstill method for identification of the magnetic model of synchronous reluctance motors (SyRMs). The saturation and cross-saturation effects are properly taken into account. The motor is fed by an inverter with a short sequence of bipolar voltage pulses that are first applied on the rotor d-and q-axes separately and then simultaneously on both the axes. The stator flux linkages are computed by integrating the induced voltages. Using the current and flux samples, the parameters of an algebraic magnetic model are estimated by means of linear least squares. The proposed method is robust against errors in the stator resistance and inverter voltage, due to the high test voltages (of the order of the rated voltage). The fitted model matches very well with the reference saturation characteristics, measured using a constant-speed method, and enables extrapolation outside the sample range. The method was tested with a 2.2-kW SyRM, whose shaft was uncoupled from any mechanical load, which is the most demanding condition for this method. The proposed method can be used for automatic self-commissioning of sensorless SyRM drives at standstill.