The performance of anisotropic electrical machines is strongly dependent on the current loop characteristics. The problems for achieving robustness and fast response, without overshoot and oscillations, are mainly related to different values and behaviour of the direct and quadrature inductances (Ld, Lq), as well as to high output frequencies. In this paper, a novel current controller structure based on Internal Model Control (IMC) method is presented, taking into account the magnetic anisotropy (Ld != Lq). The model of salient machines is derived directly in the discrete domain and used to obtain a model-based controller. The controller derivation does not rely on transport-delay approximations, which enables improved decoupling of axes dynamics and the closed-loop robustness for very high output frequencies. The presented controller enables enhanced response for higher current loop bandwidth and output frequencies than the state-of-the-art methods. The experimental verification is performed on a 3-phase synchronous machine, using a standard industrial 3-phase inverter.

Performance of conventional digital current controllers is constrained by transport delays within the feedback acquisition chain, as well as by delays inherent to the pulse width modulation. In this paper, we introduce a novel current controller which provides a very high closed-loop bandwidth, improves the robustness and disturbance rejection, and eliminates the noise and sampling errors in the feedback path. In order to achieve these goals, we suppress the transport delays by introducing an improved execution schedule of the control interrupt and by inserting a cascaded multiplier of differential character. With the novel gain setting rule, the closed loop bandwidth reaches 17% of the sampling frequency, disturbance rejection capability is doubled, the step response has a negligible overshoot, and the robustness is characterized by the vector margin of 0.65. Experimental verification is performed using an experimental setup with a three-phase inverter, digital controller, and a permanent magnet synchronous motor.

Harmonic currents disturb the operation of ac grids with electronically controlled and distributed sources and loads. Harmonic suppression methods in grid-connected inverters exhibit finite attenuation of low-order harmonics, weak suppression of high-order harmonics, and dynamic coupling between current controllers and harmonic controllers, which all impair overall performance. The developed harmonic controller suppresses residual harmonics to at least sixty decibels below rated current. The structure includes a new error-free harmonic estimator and an original controller that eliminates mutual coupling with the fundamental current controller. The system is experimentally tested in industrial inverter units connected to an ac grid rich in harmonics with artificially introduced unbalances.

The paper presents the design of an induction motor speed estimator based on rotor slot harmonics (RSH), with a focus on analysis of its integration within the current and speed control loops. In the literature, RSH-based methods are dominantly used for speed estimation for monitoring purposes, without further discussion of their use in control loops. The proposed estimator consists of a PLL and digital adaptive filters, and the design is based on the requirements of the speed control loop. The estimator has negligible steady-state error and a low delay. An analytical model of the estimator and a linear stability analysis is provided. The estimation and control algorithms are implemented on a single processor with no additional software or hardware requirements or modifications. Experimental results demonstrate sensorless vector closed-loop operation of a three-phase 2.2 kW induction motor, with speed closed-loop bandwidth of up to 15 Hz and high disturbance rejection capability. Operation is presented over a wide speed range, from nominal speeds to very low speeds. The presented method can be applied to any IM capable of generating RSHs. The performance can be guaranteed if the RSH is represented with a minimum of 5 ADC quantization levels.

Vector control principles enable independent flux and torque control of an AC machine by means of only two stator d-q currents. This means that in AC machines with a phase number greater than three there exist additional degrees of freedom, which are nowadays most frequently looked at as a mean of enhancing the overall torque production of a multiphase machine through injection of higher harmonics. However, these additional degrees of freedom can be used to control independently other machines within a multimotor drive system. In order to do so, it is necessary to connect in series stator windings of all the multiphase machines, with an appropriate phase transposition, and supply the stator windings of the multimachine set from a single current controlled voltage source inverter (VSI). The concept is introduced in this paper using the general theory of electrical machines. Verification of the proposed seven-phase three-motor system is provided by simulation. The main advantage of the proposed drive configuration over the standard three-phase solution is the reduction of the number of inverter legs from nine to seven.