Inverter-based standalone power systems (ISPSs), with limited inertia/damping, are prone to significant changes in frequency indicators encompassing frequency deviation and rate of change of frequency (RoCoF), which can easily exceed the pertinent relay thresholds and cause power outages. Limited by estimating the disturbance and system inertia/damping deficiency, existing controls cannot ensure system frequency stability. To overcome this issue, a frequency trajectory planning (FTP) based strategy is developed in this article to improve frequency stability of droop-controlled ISPS. This frequency-indicator-oriented control relates system frequency with several pre-defined planning parameters, decoupling from system's disturbances and inertia/damping deficiency that are difficult to evaluate. During normal operation or when the disturbance level is insignificant, the inverter operates in standard droop mode since the system intrinsic inertia/damping features suffice to regulate the frequency. In the event of a large disturbance, an FTP block is triggered by detected frequency indicators, and a marginally safe frequency trajectory is planned according to the requirement of the grid code. In this case, by tracking the planned frequency trajectory, the inverter provides suitable inertia/damping support needed by the system, thereby guaranteeing frequency stability of the ISPS. Finally, simulation and experimental results proved the effectiveness and advancement of the FTP based strategy.

中文翻译：

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基于频率轨迹规划的策略，提高基于下垂控制逆变器的独立电力系统的频率稳定性


基于逆变器的独立电力系统（ISPS）具有有限的惯性/阻尼，频率指标（包括频率偏差和频率变化率（RoCoF））容易发生显着变化，很容易超过相关继电器阈值并导致断电。受干扰估计和系统惯量/阻尼不足的限制，现有控制无法确保系统频率稳定性。为了克服这个问题，本文开发了一种基于频率轨迹规划（FTP）的策略，以提高下垂控制 ISPS 的频率稳定性。这种面向频率指示器的控制将系统频率与几个预定义的规划参数相关联，从而与难以评估的系统干扰和惯性/阻尼缺陷脱钩。在正常运行期间或当扰动水平不明显时，逆变器以标准下垂模式运行，因为系统固有的惯性/阻尼特性足以调节频率。当发生较大扰动时，检测到的频率指标会触发FTP块，并根据电网规范的要求规划出边际安全的频率轨迹。在这种情况下，逆变器通过跟踪规划的频率轨迹，提供系统所需的合适的惯性/阻尼支持，从而保证ISPS的频率稳定性。最后，仿真和实验结果证明了基于FTP的策略的有效性和先进性。