Abstract
During the design of the conventional current controller for a grid-connected inverter with LCL filter, the parameter mismatches and disturbances are generally neglected, which may seriously affect the control performance, even result in instability. In order to improve the ability of disturbance rejection and ensure a desired control performance, this paper proposes an Adaptive PID (APID) controller with the self-learning ability based on the Disturbance Observer (DOB). First, the full state-feedback and state observer are utilized to achieve active damping and eliminate the effect of computational delay. Then, aiming to estimate and compensate the lumped disturbance, a DOB is designed. Beneficial from DOB, the steady-state performance is almost not affected by model uncertainties and unmodeled dynamics, however, the transient performance is still deteriorated inevitably due to the limitation of DOB. Thus, an online adaptive method using APID is finally proposed to further improve grid-injected current dynamics. The control parameters can be automatically adjusted in real time by adaptive learning rule, which significantly improves the system robustness and the control performance. Simulation and experiments are provided to demonstrate the effectiveness of the proposed strategy.
Highlights
The LCL filter has been widely adopted in grid-connected inverters since they can provide improved attenuation on the pulse width modulation switching harmonics compared with the L filter [1], which allows the use of smaller inductance to satisfy the stringent harmonic requirements [2], [3]
In order to achieve excellent performances and address global stability, various control strategies have been proposed, such as PI-based control [4], [5], Repetitive Control (RC) [6], [7], Sliding Mode Control (SMC) [8], [9], The associate editor coordinating the review of this manuscript and approving it for publication was Snehal Gawande
Motivated by the aforementioned limitations, this paper proposes an Adaptive PID (APID) controller with the selflearning ability based on Disturbance Observer (DOB)
Summary
The LCL filter has been widely adopted in grid-connected inverters since they can provide improved attenuation on the pulse width modulation switching harmonics compared with the L filter [1], which allows the use of smaller inductance to satisfy the stringent harmonic requirements [2], [3]. In [19], DOB-based feedforward scheme was proposed by introducing the estimation of fluctuations into the reference of the inner loop, which can remarkably attenuate disturbance effects both in structure and external power Among these DUEA strategies above, owing to its relatively simple structure and prominent performance [21]–[23], DOB, combining with other controller, is increasingly adopted in the applications of inverters to improve the ability of disturbance rejection. Since the grid-injected current ig(k), PCC voltage ug(k) are measured and the inverter output voltage ui(k) is internally known, the remaining state variables can be estimated precisely, i.e. where the subscript ‘‘ˆ’’ denotes the estimated value, L = l1 l2 l3 T is the observer gain vector. Aiming to improve the ability of disturbance rejection, a DOB is constructed
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