Improved Seamless Switching Control Strategy for AC/DC Hybrid Microgrid

Abstract

Aiming at the problems of transient over-current and over-voltage in the switching process of AC/DC hybrid microgrid in grid-connected mode and island mode, which leads to the sudden change of transmission power and seriously affects the power transmission quality. In this paper, an improved seamless switching control strategy of droop control with disturbance observer is designed. The main work is as follow: according to the diffident power transmission calculation methods of droop control in gridconnected mode and island mode, the adaptive switching is realized by detecting the current and frequency at Point of Common Coupling(PCC) of public power grid. Secondly, the switching from island mode to grid-connected mode will cause impact due to the difference of frequency, phase and amplitude between microgrid and public grid, and even cause system collapse. So the pre-synchronization control of frequency, phase and amplitude is designed. Based on the droop control, the disturbance observation(DOB) is added, which can quickly track the sudden change of system current, and suppress the sudden change by the difference between the tracking value and the actual value, so as to realize the smooth switching from island to grid. Finally, the effectiveness and feasibility of the control strategy are verify in Matlab/Simulink.

Operation and coordination control scheme of an enhanced AC–DC hybrid microgrid under abnormal distribution network

“…In most studies, once DN faults are detected, HMG systems will be disconnected from the grid immediately [11, 12]. While this practice is easy to operate, it inevitably leads to unexpected switching between the grid‐tied mode and the islanded mode, which will cause the following drawbacks: Unable to guarantee an uninterrupted and high‐quality power supply for HMG users [13]; The strategies of interface converters for DGs also need to be changed, such as switching from the maximum power point tracker (MPPT)‐based control scheme to the droop‐based control scheme [14], which increases the running cost; The reconnection process is complicated, needs to design the grid‐connected pre‐synchronization algorithm, and may lead to the occurrence of transient impact current, which will affect the safety of the HMG [15]. …”

Energy Management Strategy of AC/DC Hybrid Microgrid Based on Solid-State Transformer

“…To satisfy the power consumers in ERbased low-voltage distribution networks and to achieve maximum economic benefits, EP should be considered. A novel active power control strategy for the converters based on the bidirectional droop characteristic is proposed in [13]- [15] to realize power balance and independent power sharing. But the proposed converter to connect the DC and the AC microgrids is a conventional AC/DC bidirectional converter that does not comprise the multiple functions of the SST.…”

State Feedback Control Based Seamless Switch Control for Microgrid Inverter

“…Recently, some switch control algorithms were presented in [13][14][15][16][17][18][19][20]. 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.…”