lower level loading

Simple and reliable control is conducted by PLC in lower level, and by adopting virtual instrument in upper level for complex loading control.

下位机采用PLC进行简单可靠控制，上位机采用虚拟仪器进行复杂的加载控制。

The lower-level problem is to maximize the loading margin under a load change direction and the upper-level problem is to find the closest critical point subject to the constraints of load change.

下层问题求解某个负荷变化方向上的最大负载裕度，上层问题考虑负荷变化方向的约束，寻找最近的电压稳定临界点。