Space vector pulsewidth modulation (SVPWM) algorithms for cascaded H-bridge multilevel (CHB ML) inverter usually provide the possibility of using several combinations of active voltage vectors to generate the same output voltage vector. For preselected H-bridges, some of them may generate output voltages opposite to the assumed direction. This results in the change of the dc-link voltages of these H-bridges in the opposite direction to the assumed direction in the ordering algorithm. Consequently, these algorithms are characterized by undue constraints and narrow possibilities of dc-link voltage balancing. In the proposed control algorithm, CHB ML inverter is treated as groups of successively activated three-level inverters; depending on the length of the reference voltage vector. These three-level inverters consist of three H-bridges selected from each phase. The proposed extended selection method enables firm-grip control of the dc-link voltages. For a given direction of phase currents, the possibility of using H-bridges with lowest and highest dc-link voltages is simultaneously analyzed. Additionally, each of the three-level inverters is controlled by one of three proposed alternative modulation methods for which both the attainable output voltage vectors and unbalanced dc-link voltages are predicted. Simulation and experimental results confirm the correctness of the algorithm execution.

Given the recent available IGBT switch modules up to 6.5 kV, 1200 A rating, the prospect of the diode-free variant topology of the three-level neutral-point-clamped (3-level, T-type) inverter in certain medium voltage applications is bright; due to its small part count and low conduction losses compared to the diode-clamped NPC inverter. However, within this voltage range, the input dc voltage rating of 50% of the switches per inverter phase-leg still poses limitations to the deployment of 3-level T-type inverter. In view of these limitations, a reconfigured four-switch per phase-leg power circuit for 3-level inverter (F-type) is presented in this paper. The common node of the bidirectional switch in T-type inverter is explored to have only one power switch rated at input dc voltage and 3 switches rated at half the input dc voltage, per inverter-leg. This reduced voltage stress has inverter cost and loss implications. The performances and competitiveness of the three-level, F-type inverter are analyzed in detail and demonstrated with a hardware prototype. Results reveal that it has the potentials of being considered a real alternative to 3-level, T-type inverters for certain low- and medium-voltage applications.

The paper presents the control possibility of five phase induction machines. In the proposed solution the machine model vector form is not transformed to the (dq)-coordinate system, that is connected to rotor flux vector, but utilizes the stationary system ( $\alpha\beta$ ). Moreover, the nonlinear model linearization is based on demonstrated nonlinear variables transformation for i-orthogonal ( $\alpha\beta$ )(n) planes. By introducing the backstepping approach, the independent stabilization of electromagnetic torque and rotor flux in each plane is obtained. A practical stability analysis of the proposed controller for a multi-phase machine is illustrated as well. Finally, experimental test results are demonstrated for a specific speed sensorless five phase induction motor test setup

This paper presents an analysis of the two speed observer structures which are based on the backstepping and sliding super twisting approach. The observer stabilizing functions result from the Lyapunov theorem. To obtain the observer tuning gains the observer structure is linearized near the equilibrium point. The rotor angular speed is obtained from non-adaptive dependence. In the sensorless control system structure the classical PI controllers and transformation to the multi-scalar variables are applied. The theoretical derivations are verified in experimental waveforms. Comparison of both speed observer structures is presented for nominal speed, load torque injections while regenerating mode, very low speed range and the uncertainties of nominal parameters of induction machine.

In the sensorless control system of an induction machine, the rotor speed value is not measured but reconstructed by an observer structure. The rotor speed value can be reconstructed by the classical adaptive law with the integrator. The second approach, which is the main contribution of this article, is the nonadaptive structure without an integrator. The proposed method of the rotor speed reconstruction is based on an algebraic relationship – the rank of the mathematical model of the observer system is not increased. However, the problem with the stabilization of the observer structure does exist. For near to zero rotor speed or in the regenerating mode of an induction machine, the speed observer structure can be unstable. Therefore, in this article, the new stabilization functions are proposed. The stability is provided by the Lyapunov theorem and the practical stability theorems in which the uncertainty of parameters is considered. In the proposed solution, the newly introduced stabilization functions guarantee observer stability during both the motoring and regenerating conditions at the chosen low rotor speed ranges and for different load torque values. All the theoretical considerations were confirmed by simulation and experimental tests during the chosen working modes and uncertainties of nominal parameters of the induction machine.

The paper presents an analysis of the speed observer which is based on the backstepping and sliding mode approach. The speed observer structure is based on the extended mathematical model of an induction machine. The observer structure is based on the measured phase stator currents and transformed to ( $\alpha \beta$ ) coordinate system. The stator voltage vector components are treated as known values. Additionally, such an observer structure is extended to the integrators. The observer stabilizing functions contain the appropriate sliding surfaces which result from Lyapunov function. The rotor angular speed is obtained from non-adaptive dependence. Stability analysis of the observer structure based on Lyapunov theory is presented in order to guarantee the estimation errors decay to zero.