With the rapid growth of the installed capacity of renewable energy

the proportion of power electronic devices in the power system has gradually increased. At the same time

the share of synchronous generators has declined. This has led to a lack of support for voltage and frequency stability in the power system. To address the voltage construction issue in power systems with a high degree of power electronic integration

grid-forming (GFM) converters have attracted widespread attention and research from academia and industry. However

the definition and control structure of GFM converters have not yet reached a unified consensus

which has created challenges for related research. This paper first presents the definition of GFM converters based on the characteristics of voltage construction. It then systematically reviews the typical control frameworks for GFM converters from the perspectives of power constraints and current protection. Power constraints are reflected in the outer loop control

while current protection is addressed in the inner loop control. By integrating these two perspectives

this paper provides a unified research framework for existing control strategies

facilitating a better understanding and application of GFM converters in both academia and industry. Distinct from existing literature that predominantly derives GFM converter behavior from the perspective of emulated synchronous generators

this paper formulates the analysis directly based on the voltage source nature and operational constraints of converters. A unified control framework is proposed

offering valuable insights for future research and practical applications in related fields.