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.

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.

Galvanic isolation is a vital part of a grid-connected solar PV system. With the growth of multilevel inverters for grid-connected applications, the multilevel inverters having isolation are not sufficiently discussed in the literature. In this paper, a 15-level isolated multilevel inverter topology requiring only thirteen switches is proposed. The envisaged configuration includes two cells, designated as upper and lower cells. The upper cell includes a standard H-bridge, and the lower cell is switched capacitor based 5-level inverter. The outputs of the lower and upper cells are supplied to the load through single phase isolation transformers. The proposed single-phase isolated inverter requires reduced switches to generate 15-level ac output voltage with voltage gain of 7. In comparison to the MLIs mentioned in the literature, the switches connected in the proposed converter experienced less voltage stress. The proposed converter construction is contrasted to state-of-the-art MLIs described in the literature. PLECS software is used to simulate the proposed inverter under various working environments, the proposed MLI able to maintain capacitor voltage balance and generate good power quality even at low values of modulation index. The experimental results achieved on a low-power laboratory prototype are utilized to validate the proposed converter’s performance. The claimed efficiency of the converter calculated using simulation results is found to be 97.1%. However, the efficiency calculated using experimental results is 96.4% at 700W.