Wind Power Applications:
The VSI Generator has a direct application to wind power generation. In fact, when the VSI Generator is made commercially available, it will displace virtually all-synchronous, induction and doubly fed wound rotor generators used for wind power. This is significant because a number of studies have found that within the decade, commercial wind power generation costs will be lower than all other power technologies except hydro and geothermal. With the use of VSI Generators, wind power generation costs can be reduced even further.
A. Increased Efficiency and Operating Range
The most important advantage the VSI Generator has is that it allows the turbine to increase or decrease in speed as the wind speed varies. Existing wind machines use synchronous or induction generators, which must “lock-in” to a very narrow rpm, range to effectively generate power compatible with the utility grid. This severely limits the wind machine's ability to use the power of the wind resource. A wind machine, which operates in a narrow rpm range, suffers from a reduction in efficiency. Because the actual power available in wind triples with a single-fold increase in wind speed, a turbine, which must operate within a narrow rpm range, cannot effectively use wind speeds, which cause the generator to exceed synchronous speed. Therefore, in such cases the range within which wind power can be effectively harnessed is reduced. The VSI Generator, on the other hand, can be loaded to maximize wind energy conversion over a wide rpm range. The "wind speed cube law" can be used to advantage by allowing the turbine to achieve maximum power points at various wind speeds. In this way, as in the case of hydro, turbine-generator efficiency is made more optimal.
This superior coupling of wind turbine efficiency and generator output has been sought after for a number of years. It has been accomplished to some extent with the use of direct current (DC) generators, which can operate at various speeds. When this power is converted to alternating current (AC), however, losses in efficiency occur.
Thus, DC wind machines, when used to provide AC power, provide marginal increases in overall wind generation efficiency. Existing generator technology cannot approach the efficiency of VSI Generators for wind energy production.
B. Propeller Pitch and Speed Control/Synchronization Equipment Not Needed
The VSI Generator has additional advantages, which stem from its ability to always match the utility grid's AC frequency when driven at variable speeds. Synchronous and doubly fed wound rotor generators must use elaborate propeller pitch control and speed control mechanisms to ensure appropriate generator speed is maintained. These mechanical systems are costly and have historically shown to be a limiting component in terms of wind machine reliability. An example of this is U.S. Windpower's wind turbines in Altamont Pass, which have had extensive problems with the failure of propeller pitch control mechanisms. The VSI Generator can very effectively harness wind power without the use of propeller pitch and speed control equipment. In the event of utility system outages, however, some type of braking device must be used to prevent overspeeding that can occur when generator load is suddenly eliminated. By comparison, the cost of braking equipment is small. As with induction and synchronous generators used for hydro generation, synchronizing equipment must be used to switch off wind generators when they move out of phase with the utility frequency. Moreover, induction generators that overspeed and get “out-of-step” with the utility system incur the "closed door effect" and must be reintegrated with the grid before effective power generation can resume. To cope with these problems, tradeoffs with mechanical and economic inefficiencies must be made. With the VSI Generator, there is no need for synchronizing equipment, and the problematic "closed door effect" need not be considered. Furthermore, wind turbine propellers can be optimally sized to equal maximum generator load capabilities. In contrast, induction generator wind machines usually undersize turbine propellers so that generator load can never be exceeded, which would cause overspeeding and the "closed door effect" to occur.
An additional advantage of the VSI Generator for wind power is its ability to be self-protecting. The phase-angle adjustment mechanism can be used to essentially turn off the generator if an undervoltage or overvoltage condition occurs in the utility system. In comparison, existing wind machines must employ costly and complicated protection equipment to guard against this possibility. In sum, the VSI Generator has the potential to displace virtually all AC generators currently used for wind energy production of utility compatible power. Wind power production can be revolutionized and made more cost-effective through use of the VSI Generator.
Starting purposes:
The VSI Generator can be used for starting purposes, for wind turbines and other turbines. The unit acts as an induction motor, but with one difference, it does not require the 6 to 8 times full load rated inrush current to develop full torque and thus has a major advantage over other machines in this respect. The VSI Generator can be designed to make the output watts curve follow the "cube" law to a remarkable degree. No other equipment approaches this parameter without excessively complex and costly controls.
|
