The authors discuss high-voltage power conversion. Conventional series connection and three-level voltage source inverter techniques are reviewed and compared. A novel versatile multilevel commutation cell is introduced: it is shown that this topology is safer and more simple to control, and delivers purer output waveforms. The authors show how this technique can be applied to either choppers or voltage-source inverters and generalized to any number of switches.<<ETX>>

Multi-level conversion : high voltage choppers and voltage-source inverters

In this paper, a short-circuit current-based adaptive perturb and observe maximum power point tracking algorithm is proposed to extract the maximum power from photovoltaic (PV) panel under sudden changes in the irradiance. This scheme is divided into two algorithms: 1) current perturbation algorithm; and 2) adaptive control algorithm. The current perturbation algorithm makes the PV panel operate at maximum power point. The adaptive control algorithm identifies the operating limit violation and sets a new operating point nearer to maximum power point. These limits are derived in terms of changes in the irradiance and current. The new operating point is set by estimating the short-circuit current. This algorithm proposes variable current perturbation, which varies continuously with the irradiance. A boost converter is used to realize the proposed algorithm. The proposed algorithm is compared with a conventional algorithm and validated for sudden changes in the irradiance through the experimental results.

A Novel Adaptive P&O MPPT Algorithm Considering Sudden Changes in the Irradiance

Multilevel inverters (MLIs) are nowadays extensively used in integration with renewable energy sources and in drives applications. The converter cost and voltage quality improvement are the utmost importance in such application of MLI. A six-switch seven-level reduced switch symmetrical MLI (6S-7L MLI) is proposed here. Compared to the conventional and similar existing MLI topologies, the proposed MLI uses less active switches and has less driver circuit requirement. A particle swarm optimisation (PSO)-based modified selected harmonic elimination technique is derived and analysed for computing optimal switching angles of proposed 6S-7L MLI to eliminate third- and fifth-order harmonics. Moreover, the performance of the proposed algorithm is compared with the two most commonly used PSO variants. The analysis shows the modified version of PSO is most suitable for optimising the output voltage of proposed MLI through targeted harmonic elimination. The proposed topology is investigated through simulation by applying the calculated switching angles using modified PSO algorithm. Finally, a single-phase experimental prototype is designed to verify the validity of the proposed structure.

https://ietresearch.onlinelibrary.wiley.com/doi/pdf/10.1049/iet-pel.2017.0697

Application of swarm optimisation-based modified algorithm for selective harmonic elimination in reduced switch count multilevel inverter

A multilevel inverter is a power electronic device that is used for high voltage and high power applications and has many advantages like, low switching stress, low total harmonic distortion (THD). Hence, the size and bulkiness of passive filters can be reduced. This paper proposes two new topologies of a 7-level cascaded multilevel inverter with reduced number of switches than that of conventional type which has 12 switches. The topologies consist of circuits with 9 switches and 7 switches for the same 7-level output. Therefore with less number of switches, there will be a reduction in gate drive circuitry and also very few switches will be conducting for specific intervals of time. The SPWM technique is implemented using multicarrier wave signals. Level Shifted triangular waves are used in comparison with sinusoidal reference to generate Sine PWM switching sequence. The number of level shifted triangular waves depends on the number of levels in the output. i.e. for n levels, n-1 number of carrier waves. This paper uses 1 KHz SPWM pulses with a modulation index of 0.8. The circuits are simulated using SPWM technique and the effect of the harmonic spectrum is analyzed. A comparison is made for the topologies with 9 switches and 7 switches and an effective reduction in THD has been observed for the circuits with less number of switches. The THD for 9 switches is 14% and the THD for 7 switches is 12.5%. The circuits are modeled and simulated with the help of MATLAB/SIMULINK.

Cascaded seven level inverter with reduced number of switches using level shifting PWM technique

Performance evaluation of a photoelectric–thermoelectric cogeneration hybrid system

The following paper validates an algorithm for Maximum Power Point Tracking using Perturb and Observe technique. The algorithm starts by setting the computed maximum power PMAX to an initial value (usually zero). Next the actual PV voltage and current are measured at specific intervals and the instantaneous value of PV power, PACT is computed. PMAX and PACT are compared. PMAX and PACT are compared. If PACT is greater than PMAX, it is set as the new value of PMAX. At every instant the PACT is calculated, and the comparison is continuously executed. Hence the final value of PMAX will be the point at which maximum power can be delivered to the load. For maximum power transfer across the load, the input impedance should be equal to the load impedance. Based on the mechanism of load matching the duty cycle of the converter is varied so that the output power will almost be equal to the input in practical systems. The system will be modelled with the help of MATLAB/SIMULINK.

Perturb and observe MPPT algorithm for solar PV systems-modeling and simulation

A multilevel inverter is a power electronic device that is used for high voltage and high power applications, with the added advantages of low switching stress and lower total harmonic distortion (THD), hence reducing the size and bulk of the passive filters. This paper proposes a new topology of a cascaded multilevel inverter that utilizes less number of switches than the conventional topology. Therefore with less number of switches in the circuit, there will be a reduction in the gate driver circuits and also in effect fewer switches will be conducting for specific intervals of time. The circuitry consists of smaller multilevel inverter blocks connected in series to achieve its characteristic output waveform. A seven level inverter will be simulated with the implementation of PWM techniques and its effect on the harmonic spectrum will be analyzed. The system will be modelled with the help of MATLAB/SEVIULINK.

Jacob James Nedumgatt

Papers

Perturb and observe MPPT algorithm for solar PV systems-modeling and simulation

A multilevel inverter with reduced number of switches