Page 173 - Renewable Energy Devices and System with Simulations in MATLAB and ANSYS

160 Renewable Energy Devices and Systems with Simulations in MATLAB and ANSYS ®
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6. Predictable transient and steady-state loads
7. Proximity of the public network

The SEIG performance is affected by the random character of many variables related to the
instant availability of primary energy and the way consumers use the load, in particular, on the fol-
lowing aspects:

• Parameters of the induction machine
• Operating voltage
• Rated power
• Rated frequency used in the parameter measurements
• Power factor of the machine
• Rotor speed
• Isolation class
• Operating temperature
• Carcass (cylindrical yoke) type
• Ventilation system
• Service factor
• Noise level
• Resonant conditions
• IG self-exciting process
• Degree of iron saturation of the generator caused by capacitors
• Fixed or controlled self-excitation process
• Speed control
• Load parameters
• Rated voltage
• Starting torque and current
• Maximum torque and current
• Power factor
• Generated harmonics
• Load connected directly to the distribution network or through converters
• Load type: passive, active, linear, and nonlinear
• Load evolution over time
• Type of primary source (in order to define the shaft power)
• Wind or hydro for small-scale applications
• Primary machine conditions for acceleration or deceleration
• Needs for energy storage

The induction machine parameters are related to their iron magnetization characteristics and
consequently to their degree of iron saturation and operating rotor speed. Therefore, experimen-
tal tests are required to obtain their magnetization curve. The designer of a SEIG needs a setup
capable of keeping the shaft speed constant for several conditions of the applied voltage. By
experiments, it is easy to find out the correct excitation capacitor for the measured magnetiza-
tion curve.
In the case of stand-alone operation (in small power plants), the connection of a capacitor
bank across the IG terminals is necessary to supply their needs for reactive power, as illustrated in
Figure 7.6. To keep the phase voltage balanced, it is advisable to connect each excitation capacitor C
across each generator winding; one should keep the same capacitor connection of the winding
machine wiring, either both in Δ−Δ or in Y−Y connection. Furthermore, every load can be individu-
ally compensated by a capacitor in such a way that whenever it is connected to the generator, it will
not change the necessary excitation capacitance and the output voltage will remain nearly constant.