Against to the problems of low utilization rate of DC-side voltage of Cascaded H-bridge (CHB) multi-level inverter Carrier Disposition (CD) modulation strategy and unbalanced output power of each cascaded H-bridge units, a power balanced based In-Phase Disposition Trapezoidal Pulse Width Modulation (IPD-TPWM) strategy is proposed in this article. By selecting an appropriate trapezoidal wave triangulation rate δ, the modulation strategy can greatly increase the amplitude of the CHB inverter output voltage fundamental wave while ensuring the waveform quality of output phase voltage, and realize the power-balance of H-bridge units within a full modulation ratio range by changing the arrangement of triangular carriers in the vertical direction while using the carrier segment in the half carrier period of the IPD-TPWM strategy as the basic unit. Therefore, it has solved the problem of low utilization rate of DC-side voltage and unbalanced output power of each unit. At the same time, the Total Harmonic Distortion (THD) of output line voltage of the modulation strategy is lower than that of IPD-SPWM strategy in the whole modulation degree, which effectively improves the quality waveform of the output line voltage, and can be conveniently used in N-level CHB inverters. Moreover, the working stress of all the unit switching tubes is the same, the heat dissipation distribution is uniform, the switching loss is effectively reduced, and the service life and system reliability are improved. Finally, the Matlab/Simulink simulation model and experimental platform are established to verify the validity and practicality of the modulation strategy. INDEX TERMS Cascaded H-bridge multilevel inverter, trapezoidal pulse width modulation, DC voltage utilization, power-balance, triangulation rate δ, total harmonic distortion.

In response to the deficiencies that the Carrier Phase Shift (CPS-PWM) and Carrier In-Phase Disposition (IPD-PWM) modulation techniques are applied to Cascaded H-bridge (CHB) multilevel inverters, combined with the advantages of the two techniques, a Hybrid Multi-carrier PWM technique based on carrier reconstruction is proposed. The aforementioned technique uses the carrier segment in the half carrier period of the IPD-PWM technique as the basic unit and optimizes the modulation performance by periodically adjusting its arrangement in the vertical direction. When CHB multilevel inverter adopts Hybrid Multi-carrier PWM technique, as with CPS-PWM technique, the output power balance between the cascaded H-bridge cells is achieved naturally; at the same time, the harmonic spectrum of the output voltage is identical with that of the IPD-PWM technique, that is to say, the harmonic characteristics of the output line voltage of the inverters are effectively improved. In this paper, the CHB seven-level inverter is taken as an example, and the correctness of the relevant conclusions is verified by simulation and experimental results. INDEX TERMS Hybrid multi-carrier PWM, cascaded H-bridge inverter, power balance, harmonics analysis.

Compared with the traditional cascaded H-bridge multi-level inverters, the hybrid cascaded multi-level inverters have been receiving attention because they can generate more levels with the same number of power cells. However, with the general hybrid pulse width modulation (PWM), the output power distribution between the high-voltage and low-voltage H-bridge cells is extremely uneven in low amplitude modulation, and it may appear that the high-voltage cell feeds power into the lowvoltage cell in some modulation ratio intervals causing the low-voltage cell capacitor voltage boost. To avoid this problem, a method of a modified hybrid PWM strategy with power balance control is proposed. It has achieved the output power balance of H-bridge cells in full amplitude modulation, the occurrence of the phenomena of extremely uneven output power distribution between the high-and low-voltage cells in low amplitude modulation is avoided, and the performance of the inverter is improved. Simulation and experimental results verify the correctness and feasibility of the proposed strategy.

A five-level inverter composed of a single capacitor clamped three-level topology and a half-bridge is introduced, and a new SPWM control strategy for this topology is proposed. The strategy uses two modulation waves with opposite directions to modulate the positive and negative half-cycle interleaved carriers. By controlling the charging and discharging times of the clamping capacitor in each carrier cycle, the voltage balance control of the clamping capacitor is achieved. At the same time, a single-phase capacitor clamped fivelevel inverter is taken as an example to analyse the principle of the capacitor balance control strategy in detail, and to verify the correctness and feasibility of the control strategy through simulation research and experimental results. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

The drawback of modulation ratio limitation in selective harmonic elimination pulse width modulation (SHEPWM) technology based on Walsh function transformation. In order to solve this problem, a multiband SHEPWM control technology method for a multilevel inverter based on Walsh functions is proposed. By analyzing multiband SHEPWM for multilevel inverter voltage waveforms under a Fourier series transform, the unified nonlinear multiband SHEPWM equations for a multilevel inverter with a modulation index varying from 0 to 1 can be generalized. The equations can be solved by Walsh function transform. In this way, the difficulties faced in expanding the modulation index, online calculation, and real-time control are resolved simultaneously. A seven-level inverter is taken as the example, for which the piecewise linear equations of Walsh functions under different bands and the trajectories of switching angles are given. Meanwhile, the conditions for multiple sets of solutions at such a point where the modulation index is switched over are also taken into account. The feasibility of the proposed method is verified by simulation based on MATLAB and SIMULINK. Finally, the feasibility of the practical application is proved by the experiment based on Digital Signal Processor (DSP).