Modeling and Design of $df/dt$ -Based Inertia Control for Power Converters
Modeling and Design of $df/dt$ -Based Inertia Control for Power Converters
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DOI：
10.1109/jestpe.2017.2703814
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发表时间：
2017-05
影响因子：
5.5
通讯作者：
D. Duckwitz;B. Fischer
中科院分区：
文献类型：
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作者：
D. Duckwitz;B. Fischer
基于逆变器的发电机组普及率较高的电力系统表现出较低的系统惯性。工厂停电或故障引起的系统分裂等故障会导致频率变化率增加，并可能导致频率不稳定。为电力电子转换器提供合成惯量的提议方案之一是基于频率导数 ($df/dt$) 的方法。采用这种方法的转换器注入与电网频率的导数成正比的有功电流，以模拟同步设备的惯性。目前正在讨论未来电网规范的合成惯性规范。在本文中，我们表明 $df/dt$ 控制器中的频率导数受到严格的带宽限制。为了避免由于谐波频率范围内的本地振荡模式的激励而导致的不稳定，大量的低通滤波是必不可少的。我们发现，具有通用参数的鲁棒稳定系统需要时间常数约为 1 s 的一阶滞后。引入并全面描述了一种新的准确表示采样效果的离散时间线性模型。提出了 $df/dt$ 控制设计，可实现鲁棒稳定的系统。模型和控制设计通过实验室实验进行验证，特别是在不稳定机制方面。本文的主要发现——应用$df/dt$控制器存在仅仅将系统范围频率不稳定的最初危险转移到局部稳定性问题的风险——对于发电厂制造商和系统运营商来说非常重要。
Power systems with high penetration rates of inverter-based generation units exhibit reduced system inertia. Faults like plant outages or fault-induced system splits then cause an increased rate of change of frequency and may lead to frequency instability. One of the proposed schemes to provide synthetic inertia with power electronic converters is the frequency-derivative-based ( $df/dt$ ) approach. Converters with this method inject an active current that is proportional to the derivative of the grid frequency to mimic the inertia of synchronous plants. Specification of synthetic inertia is currently being discussed for future grid codes. In this paper, we show that the frequency derivative in the $df/dt$ controller is subject to a severe bandwidth limitation. Considerable low-pass filtering is indispensable to avoid instability due to the excitation of local oscillation modes in the harmonic frequency range. We have found a first-order lag with a time constant around 1 s to be required for a robustly stable system with common parameters. A new discrete-time linear model that accurately represents sampling effects is introduced and comprehensively described. A $df/dt$ control design is proposed that leads to a robustly stable system. Model and control design are validated by laboratory experiments, especially regarding mechanisms of instability. The main finding of this paper—applying a $df/dt$ controller harbors the risk of merely shifting the initial danger of system-wide frequency instability to local stability problems—is important for power plant manufacturers as well as system operators.