The power extracted from PV arrays is usually maximized using maximum power point tracking algorithms. One of the most widely used techniques is the perturb & observe algorithm, which periodically perturbs the operating point of the PV array, sometime with an adaptive perturbation step, and compares the PV power before and after the perturbation. This paper analyses the most suitable perturbation step to optimize maximum power point tracking performance and suggests a design criterion to select the parameters of the controller. Using this proposed adaptive step, the MPPT perturb & observe algorithm achieves an excellent dynamic response by adapting the perturbation step to the actual operating conditions of the PV array. The proposed algorithm has been validated and tested in a laboratory using a dual input inductor push-pull converter. This particular converter topology is an efficient interface to boost the low voltage of PV arrays and effectively control the power flow when input or output voltages are variable. The experimental results have proved the superiority of the proposed algorithm in comparison of traditional perturb & observe and incremental conductance techniques.

The concept of a multi-source inverter based on NPC topology was recently introduced for hybrid electric powertrains to connect several DC sources to the traction load in a single conversion stage without magnetics. This work proposes a new modulation algorithm that integrates the tasks of DC currents and AC voltages control at level of pulse-width modulation by means of the space-vector formalism. The proposed algorithm allows the multi-source inverter to have full control of the DC input currents and fundamental AC output voltages and enables a higher number of feasible operating modes, including load power sharing between sources and controlled recharging of one source from the other, both in motion and at standstill. Hence, improved control capability of the load and sources is achieved with respect to the state-of-literature modulation approach. To validate the proposed modulation under different operating conditions, steady-state and dynamic tests are performed on a small-scale traction system fed by a primary DC supply and a battery pack. The results are compared with those of the baseline control approach and show that the proposed technique improves the smoothness and flexibility of the control action, reduces the distortion of currents and voltages, while ensuring the same converter efficiency.

This study deals with direct torque control (DTC) of induction motor drives when a multilevel inverter is involved. The proposed control technique is finalised to reduce the amplitude of torque oscillations and to improve the motor dynamic response regardless of operating speed conditions while assuring a satisfactory input current distortion. This is achieved by using a special look‐up‐table built with a novel approach. The control itself is based on the application in each sampling interval of one or two voltage vectors suitably selected, in order to ensure low electromagnetic torque ripple in steady‐state operations and fast dynamic behaviour in transient operations. In the algorithm, the converter voltage vectors selection is carried out by using a novel look‐up table whose entry points are computed by means of a specialised relation, starting from the outputs of multilevel hysteresis controllers. The suggested method, suitable for a generic multilevel inverter, is detailed for a neutral point clamped three‐level inverter. The proposed algorithm is validated by several numerical results, and compared with a DTC algorithm based on a traditional three‐speed range look‐up tables. Finally, some experimental results, obtained with a scale laboratory setup, are shown, discussed and compared with the numerical ones.

This paper focuses on the performance analysis of a sensorless control for a Doubly Fed Induction Generator (DFIG) in grid-connected operation for turbine-based wind generation systems. With reference to a conventional stator flux based Field Oriented Control (FOC), a full-order adaptive observer is implemented and a criterion to calculate the observer gain matrix is provided. The observer provides the estimated stator flux and an estimation of the rotor position is also obtained through the measurements of stator and rotor phase currents. Due to parameter inaccuracy, the rotor position estimation is affected by an error. As a novelty of the discussed approach, the rotor position estimation error is considered as an additional machine parameter, and an error tracking procedure is envisioned in order to track the DFIG rotor position with better accuracy. In particular, an adaptive law based on the Lyapunov theory is implemented for the tracking of the rotor position estimation error, and a current injection strategy is developed in order to ensure the necessary tracking sensitivity around zero rotor voltages. The roughly evaluated rotor position can be corrected by means of the tracked rotor position estimation error, so that the corrected rotor position is sent to the FOC for the necessary rotating coordinate transformation. An extensive experimental analysis is carried out on an 11 kW, 4 poles, 400 V/50 Hz induction machine testifying the quality of the sensorless control.

The paper deals with isotropic PM-brushless drives in configuration “single-inverter, dual-motor” operating with unbalanced load-torques. After a short review of some control techniques based on the classical control methodologies of single-motor PM drives, an innovative control algorithm is presented. It is suitable to minimize the resultant armature current needed to obtain an assigned resultant motor torque, whatever is the load unbalance. Simplified analytical expressions are given in order to quickly evaluate optimized reference currents with good approximation. From these reference values, a predictive feeding algorithm evaluates the reference voltage space-vector for the inverter supplying the two motors in parallel. Current and torque oscillation, torque/current ratio, dynamic response and stability are the mainly observed quantities. Effectiveness of proposed control technique is highlighted.

The study deals with a novel torque derivative control of induction motor drives. The proposed technique is mainly finalised to improve the motor dynamic response regardless of speed operating conditions, ensuring satisfactory values of both motor currents distortion and torque ripple. The core of the discussed approach is a special look‐up table, in which the converter voltage space vectors are sorted with respect to their influence on the torque derivative, taking also into account their influence on the flux magnitude. The table is indeed accessed by a desired torque derivative value, obtained by properly processing the output of hysteresis controllers. Moreover, a variable duty‐cycle technique is implemented in order to ensure a satisfactory torque ripple in steady‐state conditions. The proposed algorithm, suitable for a general multilevel inverter, is numerically tested on a three‐level neutral point clamped inverter and its performance are compared with the ones obtained by a traditional direct torque control method based on three speed ranges look‐up tables. The control is then validated experimentally by means of a reduced scale laboratory prototype fixing the same condition used for numerical analysis.