Seven-level packed U-cell (PUC7) is known as a cost-effective low-component multilevel inverter. However, PUC7 challenge is the capacitor voltage balancing; so, it conventionally needs an additional voltage control integrated into the current control loop. Because of extra variables, the control problem is further complicated for the grid-connected PUC7. This article proposes an optimized sliding-mode control (OSMC) based on the current dynamical model to track the load current reference and to self-balance the capacitor voltage in both grid-connected and stand-alone operations. By optimizing the OSMC control factor using a visual-based optimization method, PUC7 switching operation is controlled to self-balance the capacitor voltage while any extra voltage controller is needed. An adaptive control law has been also proposed for self-tuning of the PUC7 current reference to track the load and dc source variations. Experimental and simulation results of PUC7 prove the excellent performance of the proposed OSMC in achieving capacitor self-voltage balancing operation.

Switching-Based Optimized Sliding-Mode Control for Capacitor Self-Voltage Balancing Operation of Seven-Level PUC Inverter

Conventional PI controllers are vulnerable to changes in parameters and are difficult to tune. In this work, an artificial neural network (ANN) based controller is developed for the robust operation of a single-phase modified packed U-cell five-level inverter (MPUC-5) for solar PV application under variable insolation conditions. An MPUC-5 is a converter with a main and an auxiliary dc link of equal magnitude; although five-level operation is also still feasible with different voltages also. The maximum power point (MPP) of a PV array changes with the variation in the solar insolation. This results in a variable voltage at the output of the boost converter while maintaining the load line at the MPP. Consequently, the fundamental value of the output of the MPUC-5 also tends to change. Thus, it is required to produce angles that commit to an ac output voltage with a constant fundamental value and constrained to a minimum total harmonic distortion along with a third-order harmonic mitigation as per the grid codes, irrespective of the change in the dc-link voltages. A genetic algorithm is employed for this purpose. A large dataset is prepared for two-angle and four-angle operation of MPUC-5 under various dc-link voltages and constraints with which an ANN-based controller is trained. A neural network with a hidden layer is trained with the backpropagation technique; and once a correlation is developed, the network can be operated for a wide range of operating conditions. The robustness of the controller is verified through simulation in MATLAB/Simulink environment and validated by experimental emulation in an hardware in loop environment.

Robust ANN-Based Control of Modified PUC-5 Inverter for Solar PV Applications

This paper presents the current control design procedure of a single-phase grid-tied five-level packed U-cell inverter (PUC5) with an LCL output filter. The PUC5 inverter is used as an interface of renewable energy sources, such as solar applications. The LCL filter is calculated according to the grid-tied operation and converter ratings. An optimal controller, based on a linear quadratic regulator with integral action, is designed to inject a sinusoidal current with low harmonic distortion at unity power factor. For that design, the PUC5 inverter is modelled in the D – Q frame. The sensorless voltage control is incorporated into the switching technique to balance the PUC5 capacitor voltage and generate a five-level waveform at the output. Experimental tests are performed on a laboratory benchmark to confirm the theoretical design. The results prove the efficiency and accuracy of the adopted control strategy in a steady state and under transients of grid current, grid inductance, ac and dc voltage amplitudes.

LQR Control of Single-Phase Grid-Tied PUC5 Inverter With LCL Filter

An improved optimal integral sliding mode control for uncertain robotic manipulators with reduced tracking error, chattering, and energy consumption

This paper presents a binary hybrid multilevel inverter (BHMLI) based grid-connected solar energy conversion system (SECS), controlled by damped second-order generalized integral (DSOGI). The BHMLI architect has a cascaded half-bridge array, which modifies the DC-link of the H-bridge of the voltage source inverter, and results in approximate reference waveform. It reduces the dV/dt of the H-bridge switches and improves output waveform quality. The DSOGI control damps the oscillations and overshoots and provides longer service period of low power switches at transient conditions. It is implemented in the multilevel inverter application for the first time in literature. The SECS is designed to inject active power to the grid, and also mitigates the harmonic and reactive power demands of the load. The cascading of n' half-bridges and one H-bridge generate (2
 (nC1)
 - 1) output voltage levels. The maximum power extraction from solar photovoltaic (PV) array is achieved through incremental conductance (IC) algorithm based maximum point tracking (MPPT) operation of the DC-DC converter. An isolated single-input multiple-output single-ended primary inductance converter (SIMO-SEPIC) realizes it. SECS with 15-level BHMLI is analyzed with extensive simulation as well as with a hardware prototype. Moreover, the shunt active filter functionality of the system at various load conditions are verified and maintained the grid power quality within the IEEE-519 standard throughout the operation. The laboratory developed setup is tested for 5 kW, 400 V, three-phase system, and the experimental analysis at steady-state and dynamic variations of load-side and insolation variations validate the theoretical claims.

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Binary Hybrid Multilevel Inverter-Based Grid Integrated Solar Energy Conversion System With Damped SOGI Control

This paper presents a multifunctional single-stage residential photovoltaic power supply based on a linear quadratic regulator (LQR). The system makes use of a single-phase power converter connected to the grid through an LCL filter. A robust LQR with added integral action (LQRI) controller is designed to incorporate added functions such as a power line conditioner, an active power regulator, and a voltage stabilizer. The perturb-and-observe algorithm is used to generate the reference signal for the fluctuating dc bus voltage as well as to extract the maximum power from the solar panels. Full modeling of the converter in the D–Q reference frame is presented. An LQRI is designed to achieve the optimal multifunctionality operation of the residential power supply. Simulation and experimental results confirm the expected performance of the proposed controller for insolation and load variations.

A Multifunctional Single-Phase Grid-Integrated Residential Solar PV Systems Based on LQR Control

The aim of this paper is to present the design of a linear quadratic regulator (LQR) based on optimal control of single phase grid connected inverter with an LCL output filter used in solar applications. The converter model is set in the D-Q rotating reference frame where integral action is added to the grid current in order to cancel steady state error. The controller is tested in steady state, dynamic regime and for parameter variations. The simulation results carried out showed good performance and robustness of the adopted controller.

D-Q frame optimal control of single phase grid connected inverter with LCL filter

This work presents the direct current control scheme of shunt active power filter with an LCL output filter of a single phase energy distribution system feeding nonlinear loads connected at the PCC using an LQR. The model of SAPF-LCL is carried out in D-Q frame and the controller with added integral action is designed to compensate harmonics of the nonlinear loads and to keep the DC bus voltage at its reference value. Simulation and preliminary experimental results carried out confirmed the best performance in steady state of the implemented controller and the good tracking in dynamic regime to load and source voltage variations and robustness to large variation of source inductance.

Naima Arab

Papers

LQR Control of Single-Phase Grid-Tied PUC5 Inverter With LCL Filter

A Multifunctional Single-Phase Grid-Integrated Residential Solar PV Systems Based on LQR Control

D-Q frame optimal control of single phase grid connected inverter with LCL filter

Power quality enhancement in single phase energy distribution systems using DQ optimal control