Blade Pitch Control

Comparison of Electric and Hydraulic Blade Pitch Control

	Hydraulic	Electric
Design / composition	Consists of a Hydraulic Power Unit (HPU) in the nacelle and three actuators with control valves and accumulators in the hub	Includes three sets of motors/gears, drives, controllers, and energy storage units. Consists of from 3 to 8 switchgear cabinets depending on what functions are assembled in one cabinet.
Strengths	High forces, no need for gears No backlash Fail-safe powered by accumulator	Low energy consumption Quiet operation (no pump)
Weaknesses	Management of hydraulic fluid, possible oil leakage High energy consumption as pump runs continuously Repetitive maintenance as filtration and oil replacement. Fluid Rotary Union required. Accumulator pressure loss	Maintenance of batteries Backlash Increased probability of failure due to higher number of components (energy storage unit, motor/gear, controller)
Cost	Initial cost lower; running cost higher due to higher maintenance cost	Initial cost higher; running cost lower due to lower maintenance cost
Maintenance	Cylinder seals need to be replaced every 7 to 10 years	Largely maintenance-free except battery change
Working Environment	Noisy due to pump Risk of oil leakage	Little room for movement in hub
Image	Highly reliable due to proven fail-safe functionality	Environmentally friendly system