A unified theory for optimal feedforward torque control of anisotropic synchronous machines with non-negligible stator resistance and mutual inductance is presented which allows to analytically compute (1) the optimal direct and quadrature reference currents for all operating strategies, such as maximum torque per current (MTPC), maximum current, field weakening, maximum torque per voltage (MTPV) or maximum torque per flux (MTPF), and (2) the transition points indicating when to switch between the operating strategies due to speed, voltage or current constraints. The analytical solutions allow for an (almost) instantaneous selection and computation of actual operation strategy and corresponding reference currents. Numerical methods (approximating these solutions only) are no longer required. The unified theory is based on one simple idea: all optimisation problems, their respective constraints and the computation of the intersection point(s) of voltage ellipse, current circle or torque, MTPC, MTPV, MTPF hyperbolas are reformulated implicitly as quadrics which allows to invoke the Lagrangian formalism and to find the roots of fourth-order polynomials analytically. The proposed theory is suitable for any anisotropic synchronous machine. Implementation and measurement results illustrate effectiveness and applicability of the theoretical findings in real world.

This paper discusses nonlinear proportional-integral (PI) current control with anti-windup of reluctance synchronous machines (RSMs) for which the flux linkage maps are known (e.g. obtained by FEM analysis or measurements). Due to the nonlinear flux linkage, the current dynamics of RSMs are highly nonlinear and, so, to obtain an (almost) identical current closed-loop dynamics over the complete operation range, the controller parameters and the disturbance compensation terms must be adjusted online at each sampling instant. The model-based controller design is derived theoretically in state space. The theoretical results are illustrated and validated by simulation and measurement results.

This paper presents the pre- and post-fault stator current control structures for symmetrical dual three-phase reluctance synchronous machines (SDT-RSMs) with different neutral-point configurations. The effect of winding chording and rotor saliency on the space harmonic mapping among different subspaces is investigated. This proves on one hand that the control structure in the pre-fault case can be simplified, while on the other hand shows that the derived harmonic mapping in literature is insufficient to ensure high performance operation in the post-fault operation. Moreover, the machine non-linearities are identified, through which the maximum-torque-per-ampere (MTPA) loci are obtained and employed in the pre- and post-fault cases. The theoretical findings are corroborated with finite element simulations and experimental validations on a 3 kW SDT-RSM prototype.

A novel but simple machine map based modeling, identification and optimal feedforward torque control (OFTC) approach for induction machines (IMs) is presented. It is based on (i) a generic, nonlinear transformer-like machine model considering nonlinear flux linkages (with magnetic saturation and cross-coupling) and iron losses in the stator laminations in a novel, arbitrarily rotating but unique, robust & reproducible (d,q)-reference frame; (ii) a holistic machine identification procedure which evaluates steady-state measurements over a grid of (d,q) stator currents and produces temperature and frequency dependent machine maps for e.g. flux linkages, torque, iron resistance and efficiency; and (iii) a numerical offline optimization and extraction of different OFTC look-up tables (LUTs) for optimal current reference generation depending on reference torque and electrical frequency (and temperature). During the identification, stator winding temperature and electrical stator frequency of the IM are kept constant by an intelligent temperature and speed control system. The presented measurement results for a squirrel-cage IM confirm that compared to constant flux operation or scalar V/Hz control, efficiency can be increased particularly in part-load operation by up to 7% by Maximum Torque Per Losses (MTPL) minimizing copper and iron losses.

Analytical solutions for the optimal current references during maximum torque per current (MTPC; or maximum torque per Ampere (MTPA)), maximum torque per voltage (MTPV) and maximum torque per flux (MTPF) operation of anisotropic synchronous machines with non-negligible stator resistance and mutual inductance are presented. The analytical solutions allow for an (almost) instantaneous computation of the corresponding reference currents without neglecting stator resistance and/or mutual inductance (as usually done). Numerical methods (approximating these solutions only) are no longer required. The derived analytical solutions for MTPC, MTPV and MTPF operation are suitable for any anisotropic synchronous machine; even for nonlinear reluctance synchronous machines, as the presented measurement results illustrate.

Deep geothermal energy systems employ electric submersible pumps (ESPs) in order to lift geothermal fluid from the production well to the surface. However, rough downhole conditions and high flow rates impose heavy strain on the components, leading to frequent failures of the pump system. As downhole sensor data is limited and often unrealible, a detailed and dynamical model system will serve as basis for deeper understanding and analysis of the overall system behavior. Furthermore, it allows to design model-based condition monitoring and fault detection systems, and to improve controls leading to a more robust and efficient operation. In this paper, a detailed state-space model of the complete ESP system is derived, covering the electrical, mechanical and hydraulic subsystems. Based on the derived model, the start-up phase of an exemplary yet realistic ESP system in the Megawatt range—located at a setting depth of 950 $\mathrm{m}$ and producing geothermal fluid of 140 ${}^{\circ }\mathrm{C}$ temperature at a rate of 0.145 ${\mathrm{m}}^3{\mathrm{s}}^{-1}$ —is simulated in MATLAB/Simulink. The simulation results show that the system reaches a stable operating point with realistic values. Furthermore, the effect of self-excitation between the filter capacitor and the motor inductor can clearly be observed. A full set of parameters is provided, allowing for direct model implementation and reproduction of the presented results.