## 1 Introduction  
To combat climate change, the production of greenhouse gas emissions must be reduced to significant levels and shift to the use of Renewable Energy Sources (RES) must be accomplished. In numbers, the European Union's (EU) Nationally Determined Contribution (NDC) under the Paris Agreement is to reduce greenhouse gas emissions by at least 40% by 2030 when compared to 1990 [1]. RES are connected to the power system through Power Electronic (PE) converters. However, PE converters do not possess inherent inertial response characteristics. Until now, the integration of RES to the power system has not created major problems since the stability of the system is maintained by the synchronous machines in power plants. Traditionally, the inertia for the power system is provided by these synchronous machines connected to the network. However, an increase in RES in the future causes an increase in PE converter based generation units. Simultaneously, the synchronous machines in conventional power plants need to be disconnected from the network. This makes the power systems weak due to low short circuit power and low system inertia. Therefore, the consequence of disconnecting the synchronous generators leads to the requirement of the PE converter based generation units to take up the role of governing the stability of the power system. The major contributing source among the available RES is wind energy. Specifically, offshore wind energy is predicted to be the most significant source of energy among the North Sea countries by 2040 [2]. As a result, the deployment of offshore wind energy technology is expected to grow further. With the increase in integration of offshore wind energy, the inherent characteristics of offshore wind energy conversion systems will affect the nature of the power system. The vulnerable wind speed conditions due to the uncertain behaviour of wind could lead to variations in the supply and demand, and therefore, fluctuations in voltages and frequency are bound to occur. Moreover, as the power systems become weak due to the decommissioning of synchronous generators in conventional power plants that use non-renewable sources, the integration of offshore wind power plants to such weak power systems pose various research challenges on the power system stability. One of the challenges is related to voltage stability. The continuous variation in offshore wind speed causes a constant change in the active power output of the offshore wind power plant. This could lead to an increase in the reactive power output and consequently, the voltage at the point of common coupling (PCC). The conventional current control methods using Proportional Integral (PI) controllers in the modern Wind Generators (WGs) are capable of providing voltage control by injecting reactive currents when connected to a strong network (SCR = SC\({}_{MVA}\)/P; where SCR is the Short Circuit Ratio, SC\({}_{MVA}\) is the Short Circuit power of the network and P is the active power generation. If SCR = 100 to 250, it is a strong grid. If SCR = 5 to 25, it is a weak grid). However, these controllers are not suitable for operation in highly PE converter dominated grids as the connected network is weak and is not capable of absorbing the injected currents. Furthermore, during the scenario of islanding, voltage control by the conventional current controllers is ineffective due to the absence of continuous voltage control, and the deviation in voltage is not high enough to activate an effective voltage reduction mechanism. There are challenges in terms of frequency stability as well since the conventional current controllers in the WGs are not equipped to provide frequency control of the network during islanding. The drawback of these control strategies with respect to parallel operation of converters is that they require an already existing reference voltage. There are control strategies that create the reference voltage and are termed as voltage control strategies.