Robust Cascade MRAC for a Hybrid Grid-Connected Renewable Energy System

Abstract

Hybrid grid-connected renewable energy systems have gained significant importance in sustainably responding to an increased electrical energy demand. These are time-varying nonlinear dynamical plants, where the value of their parameters depends on changing weather conditions and the alternating grid voltage with randomly fluctuating amplitude. This paper proposes a robust cascade MRAC for nonlinear plants representing a class of these systems, which includes n renewable energy converts and a DC/AC single-phase full bridge inverter. The proposal reduces commissioning time by avoiding linearization and knowledge of the plant parameters. Moreover, it includes specific formulas for tuning the controller parameters that decrease their adjustments based on trial and error. Finally, it uses a direct adaptive method with adaptive laws having modification and an inner loop at least five times faster than the outer loop. The proposition validation includes the theoretical stability proof based on the Lyapunov stability method and Barbalat’s Lemma. Furthermore, it presents comparative simulation results with quoted cascade PI controllers for a monophasic system, including two renewable energy sources and injection. Both techniques effectively track setpoint changes of the energy sources’ currents and direct current bus voltage, showing the proposal similar or reduced ripple. At the same time, both ensure robustness against decreased photovoltage panels irradiance, increased fuel cells voltage, and grid voltage amplitude random fluctuations. However, the proposal does these things while avoiding prior linearization and unknowing the plant parameters.

Adaptive Control of M3C-Based Variable Speed Drive for Multiple Permanent-Magnet-Synchronous-Motor-Driven Centrifugal Pumps

“…The M3C modeled as (1) to (3) needs a cascade control system and the following cascade MRAC ( [12], Equations ( 14)-( 22)) ensures the outputs y o and y i tracks the references y * o and y * i :…”

“…Cascade MRAC ( 8)-( 10) applies to time-varying cascade systems of the following form ( [12], Equations ( 11)-( 13)):…”

“…. , n ( [12], Theorem 1). Finally, APBC adjusts the adaptive law fixed-gain ( [35], Equation ( 11)) as follows:…”

“…The books [9,10] describe the basis of MRAC for the single-input and single-output (SISO) and multiple-input and multiple-output (MIMO) cases, respectively. Based on the concepts given in [9], the work [11] proposes a cascade adaptive passivity-based controller (APBC), and [12] presents a cascade MRAC. This manuscript uses APBC and MRAC techniques together, considering the adaptive control advantages mentioned in ( [7], Section 4.5).…”

“…Presenting APBC in cascade with PBMRAC. It expands the cascade MRAC [12] and the cascade APBC [11]. The first uses an outer SISO controller, whereas the M3C outer loop requires an MIMO controller.…”