Porto Velho Back-to-Back Converter Station

The Porto Velho Back-to-Back HVDC project is an important component of the larger Rio Madeira HVDC system in Brazil. This back-to-back station is located at the Porto Velho converter station, in the state of Rondônia.

Technical Specifications

The Porto Velho Back-to-Back station consists of two converter blocks, each rated at 400 MW, for a total capacity of 800 MW. These converters use Capacitor Commutated Converter (CCC) technology, which was chosen over conventional converters to provide better voltage and power control in the weaker power networks of northwest Brazil.

The back-to-back converters operate at a voltage of 230 kV AC on both sides, connecting the local Acre-Rondônia AC network to the main HVDC system. This configuration allows for the transmission of power between two asynchronous AC systems without the need for a long-distance DC transmission line.

Purpose and Functionality

The primary function of the Porto Velho Back-to-Back station is to supply power to the surrounding 230 kV AC network in the Acre-Rondônia region. This is particularly important because the local AC system is characterized by very long transmission lines and limited generation capacity, resulting in a weak grid with low short-circuit power.

The CCC technology used in these converters offers several advantages for this application. It eliminates the need for synchronous condensers, which were initially proposed in the project's base design. Additionally, it improves voltage and power stability in the weak AC network and reduces temporary overvoltages and the risk of resonance at low frequencies. Furthermore, it allows for operation with very low Short Circuit Ratios (SCR), with simulations indicating satisfactory performance at SCR values as low as 0.2.

Control System

The back-to-back converters employ an advanced control scheme that includes various components. There is a main control loop for constant alternating voltage operation, using measurements from the filter bus. The system also features a transient direct-current controller that can be activated during disturbances in the connected AC network. Additionally, a transient commutation margin control is in place to prevent commutation failures. This control system allows the converter to generate or absorb reactive power from the connected AC system, enabling appropriate control of the alternating voltage at the commutating bus.

Integration with the Rio Madeira HVDC System

The Porto Velho Back-to-Back station is part of the larger Rio Madeira HVDC system

The back-to-back station works in conjunction with the main HVDC converter station at Porto Velho, which contains the rectifier terminals for the two ±600 kV bipoles.

Construction and Commissioning

The Porto Velho Back-to-Back station was built by ABB as part of Lot 1 of the Rio Madeira HVDC project. It was commissioned in 2013, along with the Bipole 1 converter stations.

In conclusion, the Porto Velho Back-to-Back was an innovative solution for integrating a weak local AC network with a large-scale HVDC transmission system. Its use of CCC technology and advanced control systems makes it well-suited to the unique challenges of power transmission in the Amazon region of Brazil.