Test Case 8

8

Tran The Hoang, Quoc Tuan Tran (CEA)

2

Erigrid 2.0

01/12/2020

Evaluation of voltage control in distribution grids

With an ever-increasing penetration of renewable energy sources (RES), especially photovoltaic (PV systems), into distribution grids, the grid voltage may fluctuate in unacceptable ranges. The level of voltage fluctuation depends on grid topology, different operating conditions as well as level of RES penetration. Therefore, voltage control in distribution grids has become an essential task.

Indeed, effective voltage control strategies have a number of benefits:

• Reduce voltage fluctuation
• Improve quality of power supply
• Maximize the penetration of PV into the grid
• Participate in ancillary services
• Increase the flexibility of operation
• Reduce PV curtailment

There are a variety of voltage control strategies for distribution grids such as centralized, decentralized, or distributed. This Test Case is proposed to evaluate the distributed voltage control for distribution grids with high integration of single- and three-phase PV systems under different operating conditions.

• MAS-based distributed voltage-var control
• Reactive power capability of PV systems and their reactive power control modes for voltage control support

The amount of reactive power absorbed/injected by the PV systems can be controlled following the characteristic below (ENTSO EN 50438:2013 or ENTSO EN 50549-1:2019 “Requirements for micro-generating plants to be connected in parallel with public low-voltage distribution networks”):

In addition, the reactive power exchange capability of the PV systems must meet these requirements:

• follow a characteristic curve provided by the DSO (see 4.4) within the active factor cos ϕ = 0,90-under-excited to 0,90-over-excited when the active power output of the PV plants is more than or equal to 20 % of its nominal active power;
• not exchanging more reactive power than 10 % of the PV plant’s nominal active power when the active power output is less than 20 % of its nominal active power.

• Single-phase and three-phase PV inverters
• Multi-agent system (MAS)

• Electrical and electronic domains
• Control and ICT (time delays in sending/receiving controlling signals)

• To validate the performance of the MAS and PV systems for providing voltage control in a distributed manner
• To verify that the MAS and PV systems are able to maintain the grid voltage within the grid code requirement (±10% for LV distribution networks) under different operating conditions

In the Test Case, a distribution grid with a high penetration of single-phase and three-phase PV systems is taken into consideration. Below is the single-line diagram illustrating the interaction of the main components.

• Single-phase and three-phase PV inverters
• Single-phase load and three-phase loads
• Multi-agent system (MAS)
• Communication of MAS

• MAS-based distributed voltage-var control
• Communication functionality between the agents within the MAS
• Reactive power exchange capability and reactive power control modes of PV systems

• Voltage deviation must be maintained within limits (i.e., ±10% for LV networks) under different operating conditions
• Power losses
• The operating conditions of PV inverters must fulfil the protection requirements.

For PoI1:

• Reaction of MAS to grid voltage variation
• Information exchanged between agents of the MAS system
• Reaction of PV inverters to the controlling signals sent by their respective agents
• PV power characteristic according to the specifications

For PoI2:

• Voltage deviation
• PV curtailment
• Power losses

• Grid topology
• Main grid impedance
• PV penetration rate
• PV production
• Load consumption
• Influence of communication and control

• Voltage deviation within ±10%
• Reduction in power losses
• Increase of PV penetration