Modern and comfort solution for PVP power factor correction

There are several ways of addressing the issue of power factor correction of photovoltaic power plants with a different impact on the complexity, convenience, time, maintenance, efficiency and economy and therefore we offer a comparison of different methods of compensation while addressing compensation according to VONSCH.

Control of active and reactive power can be provided in the following ways:

• directly by using inverters, assuming that the inverters support this feature
• by active compensation units
• by passive compensation units
• by combination of active and passive compensation units

Control of active and reactive power by inverters

The fact that VONSCH inverters of FOTO CONTROL family allow direct control of active and reactive power comes from their construction: they are solved on the basis of controlled rectifier (Active Front End), which is always phased to the grid and parameters such as active and reactive current appear directly in its control structures. Some suppliers of passive compensation for PV installations exclude the possibility that the power factor is managed directly by inverters, respectively they state that it is possible to control the power factor at the cost of reducing the active power only. Some PV inverters (e.g. VONSCH) are able to do this, because its power electronics is designed for increased output current, therefore reactive power control at full active power is possible. For changing the power factor from 1.00 to 0.95, it is required to increase the apparent power by approximately 50 kVA.

Main advantages of compensation made by inverters:

• firmware upgrade or installation of control system is much cheaper than installation of passive filter
• they allow compensation to 0.95 capacitive even from 0.95 inductive and vice versa.
• passive filter losses are minimally 0.75% higher than losses resulting from increasing apparent power by several kVA during power factor correction
• passive filters for complete capacitive-inductive correction require several enclosures with weight of 3000 kg or more
• compensation by inverter does not require any further device
• inverters allow continuous control of power factor, therefore allowing accurate control of reactive power

Control of active and reactive power by active compensation units

For PVP, which are not equipped with inverters allowing adjustable reactive power compensation, VONSCH offers active units of UNIKOMPENZATOR series, based on active filters. In addition, there are two power options with output currents 80 and 250 A (at 400 V output network 55 and 170 kVAr). Larger performances are solved by parallel combination.

Comparison of active and passive compensation:

• active compensation units allow continuos control of power factor, therefore allowing accurate control of reactive power. Passive filters are discrete, therefore it is only possible to select from several compensation steps
• lower weight and lower space requirements and easier manupulation. For compensating 1MW PVP by , two enclosures with dimensions of 2000 x (2 x 1000) x 500mm and weight 2 x 300 kg are required. On the contrary, passive compensation would require more enclosures with total weight of approximately 3000 kg.
• The downside of active compensation units deployment is higher base price of active compensating units. However, lower installation costs eliminate part of this disadvantage.

It is possible to set power factor setpoint and power reduction setpoint not only continuously by analog input, but also in discrete steps. The rate of change of setpoint is always limited by ramp, therefore no fast transient changes are introduced to the distribution grid.

Control of active and reactive power by combination of active and passive compensation units

This combines the advantages of both solutions. The largest part of the reactive power is compensated by passive filter, active filter compensates only remaining reactive power. It can deliver its reactive power continuously, therefore it can provide more precise adherence to the setpoint. The disadvantage remains large weight compensatory unit, advantage is a lower price compared to the active units designed for full power. When designing a suitable compensation, it is good to remember that each case is different. As a first step it is necessary to convert the measurement of electrical parameters of PVP and according to the results of measurement start designing appropriate compensation. When designing and choosing between active and passive unit it is appropriate to consider all the circumstances: not only price, but also transportation, space location, installation costs and technical specifications.

More information can be provided by our professionals.