EN
One of the quickest-growing renewable energy technologies is wind power; however it has a fundamental problem - it is not predictable. Output voltage from a wind turbine varies constantly in direct response to changes in wind speed, gusts and turbulence. This is not acceptable for grid connected systems where voltages must be kept within very tight tolerances and for independent industrial loads which could be damaged by over-voltage or under-voltage events. Three phase voltage regulators convert the erratic AC power from a turbine to stable usable power by doing the following.
Compensating for Rapid Wind Speed Variations
Wind speed can vary by several meters per second within seconds; gusting which will cause the rotor to speed up and hence increase generator voltage, or dying away causing voltage sag. This rapidly varying voltage—at ±15–30 percent—of nominal, is beyond the capabilities of most equipment; pumps, motors and control circuits can trip out or fail, causing an undesirable event. A three phase voltage regulator designed for wind applications uses fast response SCR (thyristor) or servo motor driven tap-changing technology to continuously monitor output voltage and vary regulator tap or firing angle in 20 to 40 milliseconds—much faster than the mechanical response of the turbine. As wind speed changes wildly, the regulator keeps voltage at within 3 to 5 percent of setpoint and protects vulnerable loads from nuisance tripping for use with wind-diesel hybrid systems or small grid-connected turbines.
Handling Unbalanced Input from Turbine Asymmetry
Three phase wind turbine generators, (particularly permanent magnet) do not typically produce perfectly balanced voltage; imbalance, possibly 5–15% between phases, caused by blade asymmetry, yaw misalignment, or partially shaded rotor, leads to overheating in three phase motors, reduced rectifier efficiency and harmonic current generation. A three phase voltage regulator offers independent phase control; the system will regulate the three phases individually compensating for imbalance by either boosting or bucking each line individually. An imbalance of 5–15% can be reduced to 1–2% at the regulator output. For those wind turbines that power three phase loads, such as water pumps, compressors or battery charges, it is undesirable for this imbalance to reach the load and damage or degrade equipment. The power quality factor is improved, a value increasingly specified by grid code.
Protecting Against Overspeed Over-Voltage Events
During storm conditions when wind speeds rise above rated, generator voltage can surge to a level far above the nominal value—often to 130–150% of rated voltage. If sustained this level of voltage damages electrical insulation, over-excites transformers, and destroys sensitive electronic loads such as Variable Frequency Drives or inverters. A three phase voltage regulator will control over-speed over-voltage conditions by limiting the output. During such an event the input voltage is monitored; when it exceeds set limits (typically 110-115% of nominal) the output is dropped to a lower tap value, or at extremes, disconnected from the load using an internal bypass contactor. Some units give a signal to the wind turbine controller to implement turbine braking or pitch control, ensuring the catastrophic failure of the equipment is prevented in storm conditions or if, due to grid failure for example, it is unable to output its power.
Smoothing Output for Battery Charging and Inverter Input
For off grid applications a battery bank is often charged from the wind turbine or power is directed to an inverter supplying AC loads; both battery charging and inverter inputs require stable voltage levels. At the elevated voltages during charging, excessive charging currents flow at such high levels, causing batteries to gas and shortening their lifespan. Inverter inputs are highly sensitive to voltage ripple, generating harmonic currents which will reduce power efficiency. By placing a three phase voltage regulator between the turbine and the battery charger or inverter, the turbine output is conditioned. For inverter driven loads, this means much cleaner sine waves and lower harmonics. Ripple at the output is reduced by factors of between 5 and 10. This means that, at low wind speeds, the battery is supplied at the required charge voltage, thus prolonging life by between 20 and 30% over a direct connected turbine. Low voltage disconnect protection is also included in order to prevent battery over-discharge during calms.
We provide three phase voltage regulators that, compensate for rapid wind speed changes, handle unbalanced input from turbine asymmetry, protect against overspeed over-voltage events and smooth the output voltage of batteries and inverter inputs. We have over 20 years’ experience and over 50,000 square meters of manufacturing space together with our own component design, intellectual property rights and role as a national standard maker for the industry, and we supply three phase voltage regulators to ensure wind power is usable and dependable.