Nested control loop design for differential boost inverter using generalized averaged model in photovoltaic applications

Abstract

To use photovoltaic energy, voltage source inverters are playing an important role. The most of local AC loads such as AC motors need higher voltage than solar panel output voltage. Differential boost inverter produces an AC voltage that is greater than the DC input voltage in a single power stage. This inverter consists of two DC‐DC bilateral boost converters in which work via time‐variant duty cycles to produce sinusoidal voltage, and this feature causes complexity in control design. To deal with this complexity, new modeling so‐called generalized averaged model is used to achieve a linear time‐invariant model. In this paper, a nested control loop is designed. This control strategy consists of two control loops in which the inner loop is designed by linear quadratic regulator theory to displace poles in proper location and the second loop uses a PI‐PR controller to track desired voltage and reject disturbances. To evaluate the proposed control method, the sliding mode controller is applied and compared as well. As shown by simulations, the proposed control strategy has more reliable performance and provides higher robustness in comparison with sliding mode control technique in rigid situations such as dealing with nonlinear load, parameters values changes, and external disturbances.

Nonlinear robust‐optimal control of boost converter in photovoltaic applications

“…Equation (11) shows a standard form of state equation for using LQR technique. Equation (13) expresses the new standard feedback control law and new performance index equation (14).…”

“…As a common method, matrices Q and R can be tuned for use in performance index (14) in a regular LQR problem. It should be noted, by using this common method, LQR can stabilize the system with nominal values of parameters and provides good results in both steady and transient states.…”

“…In the inner loop, by means of getting feedback from state variable i L , a virtual resistance is added to the system which acts as active damping and diminishes undesired oscillations. The outer control loop aims at tracking the desired voltage in a rigid situation such as input voltage drop which is an inevitable result of the shading effect in photovoltaic energy 14 . Both controllers coefficients are computed optimally via a robust LQR approach.…”

“…This controller consists of two loops: the inner loop includes a state feedback controller and the second loop utilizes an output feedback controller. 14 To enhance the robustness of this system in dealing with parametric uncertainties, the coefficients of both controllers are computed with a robust linear quadratic regulator (LQR) technique. The most important advantage of this technique is providing at least a 60 • phase margin and almost infinite gain margin of closed-loop system.…”

“…In this study, a robust optimal controller is proposed to achieve an output voltage with good results in both steady and transient states in rigid situations. This controller consists of two loops: the inner loop includes a state feedback controller and the second loop utilizes an output feedback controller 14 . To enhance the robustness of this system in dealing with parametric uncertainties, the coefficients of both controllers are computed with a robust linear quadratic regulator (LQR) technique.…”