Operational instability, or hunting, is widely observed in vapor compression systems (VCSs), negatively affecting the operational safety and efficiency. As one of the most significant challenges present in VCS operation and control, operational instability has been extensively studied for decades. This paper reviews the current research state on the operational instability of VCSs, including the mechanisms for triggering hunting, the measures to mitigate hunting and the related unsolved issues. Two different views, i.e. the inherent characteristics of two-phase evaporating flow and dynamic characteristics of expansion (EV)-evaporator control loop, were classified for explaining the causes of hunting. As the typical characteristics of two-phase evaporating flow, the present of slug flow upstream in an evaporator, the sudden variation of heat transfer mechanism or two-phase flow instability would trigger the unexpected change of refrigerant temperature at evaporator exit. Consequently, operational instability will be resulted in. The dynamic behaviours of the EV-evaporator control loop in terms of its nonlinearities were considered as another essential factor that would cause system instability. Superheat setpoint adjustment and adaptive superheat control were suggested as two effective measures for mitigating hunting. With the increasing applications of vapor compression cycle for electronic cooling and the multi-evaporator VCSs, more effects should be done to investigate their operational instability with the consideration of two-phase flow instability and the coupling influences of each EV-evaporator control loop.

在蒸汽压缩系统（VCS）中广泛观察到操作不稳定或波动，对操作安全性和效率产生负面影响。作为VCS操作和控制中存在的最重大挑战之一，数十年来，对操作不稳定的问题进行了广泛的研究。本文综述了VCS的运行不稳定性的研究现状，包括触发搜寻的机制，缓解搜寻的措施以及相关的未解决问题。对两种不同的观点进行了分类，即两相蒸发流的固有特性和膨胀（EV）-蒸发器控制回路的动态特性，以解释波动的原因。作为两相蒸发流的典型特征，蒸发器上游的团状流的存在，传热机理的突然变化或两相流的不稳定性将触发蒸发器出口制冷剂温度的意外变化。因此，将导致操作不稳定。EV蒸发器控制回路的非线性方面的动态行为被认为是导致系统不稳定的另一个重要因素。建议将过热设定点调节和自适应过热控制作为缓解波动的两种有效措施。随着用于电子冷却和多蒸发器VCS的蒸气压缩循环的应用不断增加，在考虑两相流不稳定性以及每个EV蒸发器控制回路的耦合影响的情况下，应采取更多措施来研究其运行不稳定性。