Abstract
Nowadays, behaving as constant power loads (CPLs), rectifiers and voltage regulators are extensively used in microgrids (MGs). The MG dynamic behavior challenges both stability and control effectiveness in the presence of CPLs. CPLs characteristics such as negative incremental resistance, synchronization, and control loop dynamic with similar frequency range of the inverter disturb severely the MG stability. Additionally, the MG stability problem will be more sophisticated with a high penetration level of CPLs in MGs. The stability analysis becomes more essential especially with high-penetrated CPLs. In this paper, the dynamic stability performance of an MG involving a high penetration level of CPLs is analyzed and investigated. An autonomous MG engaging a number of CPLs and inverter distributed generations (DGs) is modeled and designed using MATLAB. Voltage, current, and power controllers are optimally designed, controlling the inverter DGs output. A power droop controller is implemented to share the output DGs powers. Meanwhile, the current and voltage controllers are employed to control the output voltage and current of all DGs. A phase-locked loop (PLL) is essentially utilized to synchronize the CPLs with the MG. The controller gains of the inverters, CPLs, power sharing control, and PLL are optimally devised using particle swarm optimization (PSO). As a weighted objective function, the error in the DC voltage of the CPL and active power of the DG is minimized in the optimal problem based on the time-domain simulation. Under the presence of high penetrated CPLs, all controllers are coordinately tuned to ensure an enhanced dynamic stability of the MG. The impact of the highly penetrated CPLs on the MG dynamic stability is investigated. To confirm the effectiveness of the proposed technique, different disturbances are applied. The analysis shows that the MG system experiences the instability challenges due to the high penetrated CPLs. The simulation results confirm the effectiveness of the proposed method to improve the MG dynamic stability performance.
Highlights
Voltage, and power controllers are optimally designed to enhance the transient response of the autonomous MG considering constant power loads (CPLs)
Based on error curtailing in the DC voltage of the CPL and measured active power of the distributed generations (DGs), an optimal control design for the controllers of DGs, CPLs, and phase-locked loop (PLL) is presented
Several disturbances are applied to assess the optimal parameters impact on the MG stability
Summary
With high-level penetrations of CPLs, the MG stability will be more complicated and need more investigations Having advantages such as flexibility, redundancy, and expandability, droop control techniques are proposed to improve the low-frequency damping in both steady-state and transient modes and overcome the stability problems related to the sudden disturbances [3,12,28,29]. A coordinated virtual impedance control strategy for DGs units was presented to overcome the mismatched line impedance and avoid inaccurate power sharing and circulating current [28] Both virtual resistance and virtual inductance were simultaneously tuned to compensate the mismatched line impedance among DGs. The MG system stability was enhanced by increasing damping for the whole system.
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