The Impact of UPS Input Power Factor on the Grid and Load
As a critical component of the power supply system, the Uninterruptible Power Supply (UPS) also plays a significant role in the power grid. Like other electrical loads, its input power factor is a key performance indicator that determines whether it contributes to grid pollution. A low input power factor indicates that the UPS draws both reactive and active power from the grid, leading to higher operational costs.
For example, if a UPS with an input power factor of 0.8 and a power capacity of 100 kVA is used, when the UPS is fully loaded, it will consume 80 kW of active power and 60 kVAR of reactive power from the grid. As a result, the system would need to support a total power capacity of 150 kVA. If diesel generators are used as a backup power source, they must have 2 to 4 times the capacity to meet this demand. Additionally, the capacity and cost of power distribution equipment, such as switches, transformers, and transmission lines, would increase significantly.
The input power factor of a UPS varies depending on the circuit design. For backup and online-interactive UPS systems, the input power factor matches that of the output load. Under normal grid conditions, these systems do not regulate the power factor but also do not introduce additional distortion to the grid. On the other hand, the input power factor of traditional double-conversion UPS systems, which use a controllable rectifier and filter circuit, is typically low—around 0.8—due to the influence of higher-order harmonics, and it remains unaffected by the nature of the output load.
However, modern double-conversion UPS systems with high-frequency rectification and those incorporating high-frequency conversion series-parallel compensation circuits have a significantly higher input power factor, often reaching up to 0.99 over a wide range of input voltages and loads, regardless of the output load characteristics.
Utility companies often set minimum input power factor requirements for electrical equipment, especially for high-power devices. Typically, the input power factor should be at least 0.95. If this threshold is not met, passive or active power factor correction systems must be installed. For instance, upgrading the UPS’s AC/DC converter from a 6-pulse to a 12-pulse rectifier and adding the appropriate inductor-capacitor filtering can raise the input power factor above 0.95. However, this can increase the overall cost by approximately 20%. Additionally, if the input voltage waveform is highly distorted, it may cause instability in the input filter circuit, posing a risk to both the UPS system and the connected load.