# Dual-Boost Inverter for PV Microinverter Application--An Assessment of Control Strategies
###### Abstract
Figure 1: Differential mode inverter scheme and principle of operation. The approach in the first family consists of controlling independently each boost converter (converters 1 and 2 of Figure 1) within the inverter, which has been achieved with linear and non-linear methods. The most popular strategy uses a cascaded linear control scheme, where the control objectives are the inductor's current (inner loop) and the output capacitor's voltage (external loop) for each boost converter. Two proportional-integral (PI) controllers are used to regulate the inductor's current and capacitor's voltage errors, as shown in [7, 8, 9]. However, the main issue with the PI controller in this application is the steady-state errors and phase shifts associated with controlling sinusoidal variables. Based on this idea, proportional resonant (PR) controllers have been implemented in the control scheme to solve the PI controller problems [10,11]. In addition, non-linear control techniques have been also proposed to regulate individually each boost converter. The first control proposal for this inverter was sliding mode control by [PERSON] [12], where the switching surface is formed by the error of the output capacitor voltage and inductor current of each boost converter. In [13], a dynamic linearizing modulator was employed to control the output capacitor voltage. The differential flatness theory was used to obtain a sinusoidal voltage on the output of each boost converter, through the regulation of the energy stored in the capacitor and inductor [14]. Another non-linear strategy is finite control set-model predictive control (FCS-MPC), which was proposed in [15]. In this strategy, the discrete model of the DBI is used to predict the behavior of the output capacitor's voltage, inductor's current, and AC output current. Then, an optimization algorithm is adopted to select the best control action for each boost converter. On the other hand, the sinusoidal output voltage or current of the inverter (\(v_{0}\) or \(i_{o}\)) is the main control goal of the second family, where the sliding mode approach has been proposed to achieve these objectives. In [16,17], a sliding mode control strategy based on the indirect regulation of the output voltage through the control of the difference between the inductor's current was presented. The control scheme is composed by two loops, which regulate the output voltage error of the inverter using a PI controller (external loop) and the difference between the inductor's current through sliding mode control (internal loop). Two strategies to control the output (AC) current were proposed in [18,19]. In the first work, the control scheme was composed by two loops considering a fixed input voltage for the DBI. The external control loop regulates the output (AC) current, and this loop is based on the PR controller, where an integral term is inserted to avoid a DC component in the output current of the inverter. Additionally, a phase compensator was introduced in this control loop to increase the controller's phase margin. Then, the internal control loop regulates the  
Figure 2: Control objectives for DBI: (**a**) Individual boost converter switching strategy. (**b**) Global switching strategy. difference between the inductor's current. In [19], the control goal was also the regulation of the inverter's output current, considering the inverter as a whole system with PV panels in the input. A control scheme composed by three cascaded loops was proposed, where a current mode control was used in the inner loop to regulate the difference between the inductor currents. The next loop is composed by a type III compensator for controlling the grid current, and the external loop regulates the PV (input) voltage through a PI controller. One advantage of controlling the system as a whole (inverter) and not independently (each DC-DC boost converter) is the reduction of the amount of control loops, which decreases the number of required sensors.