# State Feedback Control Based Seamless Switch Control for Microgrid Inverter
## 1 Introduction
In [13; 14], the voltage control loop, which acts as an inner loop, is cascaded by different outer control modules. The outer control loops are the power control loop in GC mode and voltage reference calculation in SA mode, respectively. The power control loop is either driven by a direct calculation method [13] or droop calculation method [14; 15]. When the inverter switches from GC mode to SA mode, the outer power control is switched to voltage reference calculation. However, the voltage reference calculation needs to be carefully designed to ensure the continuousness of the voltage reference. References [16; 17] adopted slide-mode control, whose sliding surfaces are defined differently for SA mode and GC mode to realize the voltage control in SA mode and current control in GC mode separately. The oscillation on the both sides of the sliding surfaces is a tough problem for slide-mode control. In [18], a generalized control algorithm was developed to enable the distributed generations (DGs) to operate in both modes with a single control structure, facilitating the seamless transition between the operating modes. Additionally, the effects of disturbances associated with the mode transitions are fully eliminated by dynamic compensation term. However, the compensation term includes differential operation which is hard to realize in digital control. A universal integrated synchronization and control were proposed in [19] to operate a single-phase dc/ac converter in both GC and SA modes and offer seamless transition between these modes without any reconfiguration of control structure. However, the definition of virtual powers in [19] excessively relies on the topology structure of filters and the precise parameters of a filter circuit. A unified control loop with a novel anti-derailing control is proposed in [20] for smooth and autonomous mode switch. An anti-derailing control and the power open loop control are paralleled as the outer loop of the inner current loop. The good performance of the switch control is achieved. A unified complex-based control with an added frequency control loop is proposed for the seamless switching control in [21]. However, the current controller is not designed and the frequency control loop will deteriorate the dynamic response. Generally, in present studies, both the current and voltage control are designed separately, and the current control and voltage control are two control systems. Hence, the switch actions are usually complicated. In this paper, with the fundamental work of [21], a new control frame based on complex-variable-design is proposed, the current controller is added by sharing one dynamic controller with the voltage controller and the frequency control loop is removed. A state feedback control is designed for the instantaneous control control. neous voltage and current control, a complex variable FLL is designed to realize the voltage and current reference computation. The voltage and current control share one resonant controller to ensure the smooth switch. The good performance of seamless switch is also achieved by the well-designed control method. Lastly, the proposed control strategy is verified through the built MG experiment platform.