Power Quality Optimizer

The Power Quality Optimizer (PQO) is an electronic device ensuring a stable voltage in rural low-voltage networks.

For historical reasons, low voltage distribution networks in rural areas often have relatively high impedances. Values of more than 0.5 Ω per phase may occur. Traditionally, excessive voltage drops due to increasing loads were mitigated by inserting automatic voltage controllers based on autotransformers. Whereas this is a suitable solution for the steady-state voltage level and for three-phase loads, transient phenomena and voltage asymmetries are not compensated. They are even aggravated because the transformers add additional impedance to the system. Such a system is relatively sensitive to flicker.

The advent of loads which take intermittent currents from the network, such as small welding appliances and photocopiers, results in unacceptable flicker levels. The traditional method of mitigating the flicker is to replace long LV cables by an MV cable plus a new distribution transformer, or to replace the LV cable by a cable with a bigger cross-section. Both methods are very uneconomic if compared to the income obtained by delivering electricity through the network. The Power Quality Optimizer (PQO) is a local electronic compensator ensuring a stable voltage at a fraction of the cost of a network upgrade.

A PQO is in essence a three-phase inverter with a small energy buffer, connected in parallel to the distribution network at the specific location at which improvement of the voltage quality is required. It will absorb or inject active as well as reactive power, to the extent needed to enforce only gradual changes in the rms voltage. In addition the PQO continuously absorbs harmonics from the network.

Since LV networks supply power to predominantly single-phase loads, the PQO provides compensation for each phase independently.

The PQO was developed and tested in cooperation with ENECO Netbeheer (now Stedin BV), Rotterdam.