Abstract
Southwest China Grid (SCG) is one of the hydropower-rich power grids around the world. SCG has recently been into asynchronous operation mode, it is expected to face challenges in low inertia and frequency stability issues caused by the hydraulic turbine governing system (HTGS), which brings profound changes to the validity and stability for the multi-area automatic generation control (AGC) power systems. This article analyzes the frequency control problems of SCG according to the operation data from asynchronous operation tests. To overcome the large overshoot and reverse regulation for external disturbances, frequency-based segment values of frequency bias for areas under TBC mode are developed considering multi-deadband effects, and a switching method of control modes for supporting large-disturbance recovery is proposed. Based on the complex and nonlinear of AGC systems, a fuzzy PD+I controller is proposed to reduce the excessively large overshoot. Furthermore, the rule for tuning D gain is established by the sign of change of area control error (ACE), and flexible I-part is applied to the control process based on the relationship between ACE and frequency. Then, we also provide filter-based control strategies with adaptive parameters to effectively coordinate hydropower and thermal power generators. The filter coefficients are computed considering various delays within AGC systems. Some case studies and actual operating conditions demonstrate the efficiency and accuracy of the proposed ideas compared with current control strategies.
Highlights
The reverse distribution of energy resources and electricity demands exists in China. 80% of hydro resources are mainly distributed in the southwest provinces of China (e.g. Sichuan and Yunnan provinces), and over 70% of the energy is consumed by East China and Central China where primary energy resources are scared
The UHVAC/UHVDC hybrid power grids are established by the SGCC in these provinces to transmit large-scale electricity eastward [1], [2]
To ensure the safety of energy supply and emission reduction [3], the Chongqing-Hubei back-to-back flexible HVDC interconnection project has been put into operation on June 24, 2019, Southwest China Grid (SCG) becomes asynchronously interconnected to the Central China-North China AC interconnection system
Summary
The reverse distribution of energy resources and electricity demands exists in China. 80% of hydro resources are mainly distributed in the southwest provinces of China (e.g. Sichuan and Yunnan provinces), and over 70% of the energy is consumed by East China and Central China where primary energy resources are scared. The reverse distribution of energy resources and electricity demands exists in China. The UHVAC/UHVDC hybrid power grids are established by the SGCC in these provinces to transmit large-scale electricity eastward [1], [2]. To ensure the safety of energy supply and emission reduction [3], the Chongqing-Hubei back-to-back flexible HVDC interconnection project has been put into operation on June 24, 2019, SCG becomes asynchronously interconnected to the Central China-North China AC interconnection system. Renewable energy resources have a rapid growth in SCG, such as wind and photovoltaic, which affect the operational needs for small-scale power systems [5]. The operation characteristics of SCG have faced profound changes, which brings great challenges and security risks to the safety grid operation. One of the main concerns is that a very large frequency deviation would occur after a UHVDC transmission line bipolar blocks
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