1 phase 25 kW bidirectional grid-tie wind inverter makes net metering possible for farm & industrial

Small and community-wind farms (25 to 100 kW) are fast growing markets in North America for wind-energy applications. But this great opportunity has drawbacks. For instance, farms are mostly supplied with split single phase power. Though single phase inverters are available for small wind turbines, such products are not practically usable at such power levels. Larger wind turbines at such power levels typically work on three-phase power which is not readily available in rural areas, so products that need it go unused.

Though the available wind inverters have many useful features, they can only supply power into a grid. Power can’t be taken from the grid for critical functions such as electrical breaking of a turbine during high winds or starting a turbine and overcoming its inertia under light winds. This issue forces turbine manufactures to design around the drawback by adding larger resistor and mechanical brakes which drives costs up.

A third issue is safety. To their knowledge, says a company spokesman, there are no UL 1741 certified bi-directional single phase 25 to 100-kW systems commercially available to the small and community-wind-turbine manufactures at this time.

Smart Power Systems Inc says it has developed a solution to the problems with the introduction of a 25 kW single phase bi-directional inverter. The SPS-Pavan 25 features minimum harmonic point tracking to reduce harmonic distortion, and a unity power factor operation while drawing or supplying power to a single-phase grid.

 

The inverter has passed UL 1741 certification tests at Metlabs Inc and is certified for production. The 25-kW model can be paralleled to produce 50 or 100 kW systems. Three such inverters can also be used to make 3 phase, high-power systems. The SPS Pavan-25 inverter is said to be a versatile unit that with minor modifications can be used for solar farms as well. Additional inverter features include

• Single phase grid tie in for generated power
• Bi-directional power conversion
• Net metering made possible for single-phase farm lines and small businesses.
• Useful where three-phase power is unavailable or prohibitively expensive
• Helps energy production under light wind conditions by starting a wind turbine from rest
• Provides assistance in shutting down the wind turbine under high wind conditions.
• Low harmonic distortions, less than 5 %
• Possible to add power generation capacity through modular approach. (up to 100 kW)

Smart Power Systems Inc.
www.smartpowerusa.com

What are the electrical & electronic components in a wind turbine?

Motors and drives: nacelles on utility scale turbines are filled with motors and drives. The latter devices are part of the turbine controls that tell motors what to do. Generally, electric motors pitch the blades on turbines with less than 1.5 MW outputs and point nacelles in appropriate directions. Utility-scale turbines can have up to eight yaw drives. Motor outputs on these turbines range from 2.2 to 22 kW. They attach to speed reducers to produce output torques from 2,000 to 50,000 nm.

 

Blade-load sensing leads to rotor monitoring and load measuring on the turbine hub. Such a system can be designed-in during manufacturing or retrofitted. The system detects operation and maintenance issues such as blade icing, in which the system lets operators predict when they ought to shut down turbines because “ice throw” is possible. Signaling when the ice has been shed from a blade also lets operators restart sooner.

 

Such controls and sensors would allow for adjustments to:

 

• Yaw misalignments. When running below rated power, a 10° yaw misalignment reduces power output by about 5%.

• Rotor imbalance. Sensors that provide data on mass and aerodynamic imbalances allow early action to maximize power generation and avoid damage.

• Blade damage. Sensors can detect damage affecting the structural or aerodynamic performance of a blade, allowing early remedial action.

 

Inverters

 

The output from a generator has three electrical characteristics: voltage, current, and frequency. Because wind speed changes constantly, a generator would produce these at variable rates as well. Hence, the inverter’s job is to steady two of the characteristics, and let only one of them vary. These electrical devices turn the variable current or voltage coming out of a generator into steady voltage and frequency that can contribute to power on the grid.

 

Transformers

 

These allow raising or lowering voltage in ac transmission lines. Transformers for wind turbine generators switch with solid-state controls to limit inrush current. While potentially aiding the initial energization, these electronic controls contribute damaging harmonic voltages that, when coupled with non-sinusoidal wave forms from the turbine, also contribute to overheating.

 

Standard voltage alternates at 60 Hz. When the transformer frequency differs, voltage peaks do not line up and do not produce the required amplification that would come from in-synch frequencies. The transformer tries to pass its voltage through the circuit, thereby causing extra loading. All electronics today send spikes on line. Transformers must handle the higher loading in frequency disturbances and spikes.

 

To handle potentially hazardous heat, one transformer manufacturer winds coils on a cruciform- mitered core. Circular windings have coolant flow ducts throughout which evenly spread radial and axial forces over their circumference, eliminating hot spots that lead to premature breakdown and ultimately transformer failure.

 

Transformers for wind turbines are usually designed so their voltage exactly matches the wind turbine’s output voltage. Generator output current is monitored at millisecond intervals. Operational limits allow up to 5% over-current for 10s before controls take a generator off the system. Because transformers used with wind turbine generators are intended to match generator output without overload sizing, the generator must function without extra capacity.

 

When using a rectifier-chopper system (the electronic controller in wind turbines) the transformer must handle harmonics similar to rectifier transformers. These harmonics are called “dirty” because they may contain high frequencies that wind-farm owners do not want to send to the grid because they affect other equipment.

 

 

3-phase string inverter earns CSA approval

A manufacturer of renewable energy, and energy-efficient power conversion and power management equipment has received CSA-UL1741 approval for its Aurora 3-phase string inverter. The Aurora Trio, 10 & 12 kW string inverters have several differentiating features including two independent MPPT inputs, a wide input-voltage range, convection cooling, disconnect switches, and a NEMA-4X enclosure.

“This product provides design flexibility, productivity, and reliability,” says Paolo Casini, Power-One’s Vice President for Product Marketing. “Designed for commercial use, the 3-phase inverter can optimize the performance of a PV plant.”

In 2010, the European version of the Aurora 3-phase inverter received an A+ approval rating from the independent industry reviewer Photon Laboratory Magazine.

Power-One Inc.
www.Power-One.com

Inverter manufacturer starts production in Phoenix

A manufacturer of power inverters for the renewable energy industry, California-based Power-One, will open its first North American manufacturing facility in Phoenix. This marks the sixth such company to move to Greater Phoenix since January, drawn by the state’s landmark Renewable Energy Tax Incentive Program.

Production at the Phoenix facility starts October 2010 and will reach a capacity of 1 GW by mid 2011. The company makes Aurora brand power inverters with what they claim is up to 96% efficiency, or 99% when used with wind power.

Power-One manufactures renewable energy and energy-efficient power management equipment and holds 11% of the global photovoltaic inverter market share, according to IMS Research.

The company manufactures a range of inverters, which make electricity from solar and wind sources usable for residential, commercial, and utility-grade solar and wind markets. Power-One’s Phoenix facility will produce its photovoltaic and wind inverters, including single phase string inverters (2 to 6 kW), three phase string inverters, and NEMA 3R 250 kW, 300 kW, and 400 kW central inverters. For utility applications, products will include 2.5 MW inverters. Photovoltaic solar energy does not rely on vast amounts of water as steam-generating solar power does.

Power-One
power-one.com

7.2 kW inverter works at 99.4% efficiency

The power conversion efficiency rating of the Aurora Wind Interface model PVI-7200 W is 99.4%. It accepts three-phase input from a permanent-magnet generator (PMG) and outputs a max 7,200 W. The inverter has a fused wind input feature and an automatic brake function for the maximum 530 Vdc and an optional external brake resistor is available.
The PVI-7200 W, manufactured by Power-one, accepts an input of 0 to 400 Vac, an operating input voltage from the PMG of 40 to 400 Vac, and 0 to 600 Hz, a max operating input current of 16.6 A RMS, an input over-current (fuse-protected) 20 A RMS, a max out power (at 400 Vac PFC>0.7) of 7,200 W, and an output operating voltage range of 50 to 600 Vdc. Operating ambient temperature of the PVI-7200 W is -25°C to +55°C. It uses a NEMA 4X enclosure and generates and audible noise of less than 40 dBA. The unit complies with various set standards such as UL1741 and CSA C22.2, and N.107.1-01 for grid-connected usage, safety and electromagnetic features. Another inverter is rated for output power of 4 kW.

8 kW wind inverter comes with double standard warranty

An 8,000W inverter for wind turbines expands the Windy Boy lineup, which now consists of five models ranging from 3,000 to 8,000 W. The unit’s factory warranty, from SMA America, Rocklin, Calif. (sma-america.com) has also been increased to 10 years, with the ability to extend to 15 or 20 years.

The Windy Boy 8000US includes special firmware that permits a direct grid-tied operation with a broad range of wind turbines. Its longevity is enhanced by SMA’s patented OptiCool active temperature-management system and rugged cast-aluminum outdoor-rated enclosure. The inverter features a CEC weighted efficiency of 96%, resulting in exceptional energy yields. It is also certified to the UL 1741/IEEE1547 standard.

Designers can take advantage of the unit’s versatility. For instance, the wind inverter can be installed with a direct grid-tied connection or as part of a micro-grid in conjunction with the company’s Sunny Boy solar inverter, and Sunny Island battery inverter and management system, providing grid-quality power to remote locations.

Liquid cooled inverters ready for hot jobs

A liquid-cooled inverter provides optimal thermal performance in a compact design for applications unsuitable for air cooling. Manufacturer Magnetek Inc. says the liquid cooled inverters are ideal for sealed-structure applications such as near shore wind turbines or wind turbines installed in corrosive environments, as well as locations that require sustained operation at elevated ambient temperatures.

These liquid cooled inverters will also be available in utility-scale E-Force solar inverters, ideal for installation in solar power electrical equipment rooms and high ambient temperature solar power applications. Modular utility-scale E-Force inverters regulate and transform dc power generated by wind turbines or photovoltaic systems into utility-grade ac power, which is distributed to the power transmission grid. The inverters offer peak efficiencies when operating at full power and provide less current distortion by using high-frequency switching. The manufacturer says its compact design makes the inverters easier to install and service. Self-diagnostics and remote monitoring capabilities maximize energy generation. NEMA rated enclosures ensure electronics are protected from extreme temperatures and the elements.