The usage of variable frequency drives (VFDs) to control induction motors is extremely relevant for industrial applications because of their low cost. The switching behavior of the inverter in the VFD generates common-mode voltages which can cause a common-mode current to flow in the system. This common-mode current can propagate through the protective earth connection and causes the unwanted trigger of safety devices such as residual current breakers. Because of the relevance of the common-mode current, many different filter topologies have been developed to reduce the common-mode on the motor side. A suggested topology is the so-called commonmode transformer, which adds a fourth winding to a classic common-mode choke. In this work, a passive common-mode transformer is proposed with a simulation model to evaluate the reduction of the common-mode current in a system with a long cable. The developed topology is then validated with a simulation in the frequency domain and its effect on the common-mode current and common-mode voltage is analyzed. The simulation model is developed by using a lumped element representation of the motor to simulate the common-mode impedance of the motor. The cable model is obtained through a finite element model to represent the capacitive and inductive parameters of the cable. The proposed simulation model allows a good evaluation of the common-mode current flowing in the system and tests the effectiveness of the filter topology. The application of the common-mode transformer ensures the reduction of both the common-mode voltage and common-mode current in the system.

Transformers are fundamental and widely used electric components in the industrial area and the power system. Modeling of transformers is also an essential issue. To analyze the global losses of transformers concerning harmonics conditions, this paper proposes a circuit-level simulation approach up to a few kilohertz range, which considers both the frequency-dependent magnetization phenomenon and the capacitive coupling among windings. The core model is based on the permeance capacitance analogy, the material and the geometry information of the core are also considered for an accurate estimation.

This paper investigates the soft starter torque and flux control (STFC) algorithm for braking induction motors driven by them. In comparison to classic phase angle control approaches, the STFC algorithm considers the rotor flux during the firing pulse generation, additional to the grid voltage. The algorithm and the additional control structure is explained and discussed in detail. Different measurements compare the behaviour with a classic phase swap approach. A special focus lies on the requirements to the constellation of motor and load for a robust performance. A huge advantage of this new braking approach is that no additional equipment such as contactors or rectifiers is necessary, even for braking very high inertias.

This paper presents a new model predictive algorithm for induction motors driven by a soft starter. The predictive algorithm idea and equations that are used for the calculation of the system behaviour are discussed in detail. Decision criteria are introduced and defined for different aspects. Measurements of predictive and classic start-ups are done under different load conditions and then compared. Also, the capabilities, the advantages and opportunities of the new approach are discussed.

Nonlinear voltage distortion of the inverter affects the control performance of an AC drive, especially during low speed operations. For implementing advanced control algorithm such as sensorless control, compensation of the nonlinearity of the inverter is crucial. Thus, the availability of precise phase voltage measurement has great advantages. However, because of the switching nature of the PWM phase voltages, accurate phase voltage sensing is not trivial. In this paper, a novel direct measurement of the PWM phase voltages for a PMSM drive is introduced. The proposed method combines oversampling based on delta-sigma modulation and digital filtering. The implementation of the approach is based on high speed ADC and FPGA, actually well-known from current measurement and adapted to voltage measurement in this paper. The effectiveness and reliability of the proposed method are verified with experimental results.

In this paper a Finite Control Set Model Predictive Controller (FCS-MPC) is developed and implemented in real time on an FPGA platform. The common reference tracking squared l2-norm cost function is redefined in order to reduce the inverter losses directly instead of reducing the switching frequency. Different combinations of switching and conduction losses are considered in the proposed cost function aiming at more effective reduction of inverter losses. Experimental results show that, with the proposed cost function the switching operations happen more frequently when the corresponding phase current is small and avoided when it is high. This results in less inverter losses with the same average switching frequency compared to common cost function as well as lower DC-Link current ripple. In other words, with the same inverter losses, the proposed cost function has higher average switching frequency resulting in better current THD and torque TDD and consequently lower Induction Machine (IM) losses. The new cost function requires however, more FPGA resources.

An accurate real time parameter estimation of permanent magnet synchronous machines (PMSMs) is essential to achieve a high performance of a drive system. However, the accuracy of the estimation is affected by the nonlinearity of the inverter. In this paper, an approach for parameter identification based on model reference adaptive system (MRAS) with considering the nonlinearity of the inverter is proposed. Compared to conventional compensation strategies, different turn-on and turn-off delay time of the high- and low-side IGBTs is considered, which makes the compensation more accurate. With the proposed method, the voltage disturbance of the inverter can be successfully compensated and the identification accuracy can be significantly improved. In addition, the total harmonic distortion (THD) of the phase currents and voltages can be greatly reduced, which improves further the performance of the drive. Experimental results demonstrate the effectiveness of the proposed method.

This paper deals with modeling and control strategy for a dual active bridge (DAB) converter. The generalized average modeling method is used to obtain the state-space representation of the DAB, in which the DC and the fundamental harmonic in the Fourier series expansion of state variables are considered. Transfer functions from control-to-output are determined, which will be used to define two controllers for the output current and the output voltage in a cascaded control structure. Simulations and experiments will be used to validate the operation of the proposed method.