Improved Predictive Control for an Asymmetric Multilevel Converter for Photovoltaic Energy

Abstract

This article proposes a 27-level asymmetric cascade H-bridge multilevel topology for photovoltaic applications, which considers a predictive control strategy that allows minimization of the commutations of the converter. This proposal ensures a highly sinusoidal and stable photovoltaic injection when there are solar irradiance disturbances, generating a low distortion in the current waveform and low switching losses. To validate the performance of the control and the proposed topology, the dynamic model of the alternating current (AC) and direct current (DC) side system is first obtained, which is checked by computational simulations. Subsequently, the implementation of a master–slave control is carried out, focused on the control of DC voltage and AC current. The proposal is simulated, and the total harmonic distortion (THD) is obtained in the voltage and current waveforms. Undesired commutations, typical of the predictive control, are eliminated in the AC voltage waveform, and a proper DC voltage tracking is achieved for the high-power cell. In order to demonstrate the performance of the proposed control strategy, a low-power proof-of-concept prototype is implemented, in which the energy is injected to the grid, under the event of solar irradiance disturbances (with DC control).Then, the undesired switching in the main cell is eliminated, generating THDs in the voltage and current signal of 7.76% and 2.65%, respectively.

Modeling Control and Robustness Assessment of Multilevel Flying-Capacitor Converters

“…Version March 25, 2021 submitted to Energies 27 of 37 "Multi_Step_Algorithm" attempts to keep the reduced voltage vector V c as close as possible to the desired reduced voltage vector V m0 , see (22). The main features of the "Multi_Step_Algorithm" are the following:…”

“…configuration S H will be applied in the first part of the PWM period when V HL = V dc − V s > 0, while configuration S L will be applied in the second part of the PWM period when V HL < 0, "Multi_Step_Algorithm" attempts to keep the reduced voltage vector V c as close as possible to desired reduced voltage vector V m0 , see (22). The main features of the "Multi_Step_Algorithm the following:…”

“…In [21], the control of modular multilevel converters is approached using model predictive control that is aided by disturbance observers with the objective of controlling the AC current and suppressing the circulating current in the converter. An asymmetric cascade H-bridge multilevel converter topology that is equipped with a predictive control strategy is instead proposed in [22]. The purpose of the latter is to minimize the converter commutations, while also exploiting the redundant states to equally distribute the load among the switches, thus equalizing their lifetime expectation.…”

“…Figure 26 provides the basic structure of the Variable-Step Control algorithm by means of a Matlab-like function called "Multi_Step_Algorithm(• • • )". This function is called at each activation time providing the following input parameters:∆V,Ṽ d , I out , T PW M , N s , V r0 .The "Multi_Step_Algorithm" attempts to keep the reduced voltage vector V c as close as possible to the desired reduced voltage vector V m0 , see(22). The main features of the "Multi_Step_Algorithm" are the following:…”

A nine-switch nine-level converter new topology with optimal modulation control

“…This will lead to the impracticality of this topology type since more isolated DC sources are required. Moreover, cascaded structures with asymmetric power supplies produce more voltage levels but many switches (in high voltage cells) need to withstand high voltage stress [12].…”