Power Electronics - Wind and Solar Power Systems - page 196

TABLE 11-1

Maximum Voltage and Current Ratings of Power Electronic Switching Devices

Voltage Rating,
Volts

Current Rating,
Amperes Device Remark

BJT 1500 200 Requires large current signal to turn on

IGBT 1200 100 Combines the advantages of BJT,

MOSFET and GTO

MOSFET 1000 100 Higher switching speed

SCR 6000 3000 Once turned on, requires heavy turn-off

circuit

FIGURE 11-2

Variable-speed constant-frequency wind power system schematic.

the firing circuit. Although it has a distinct identity and many different
design features, it is generally incorporated in the main power electronic
component assembly.
In wind power system operating at variable speed for maximum annual
energy production, the output frequency and voltage of the induction gen-
erator vary with the wind speed. The variable-frequency, variable-voltage
output is converted into fixed voltage 60 Hz or 50 Hz terminal output to
match with utility requirement. In modern plants, this is accomplished by
power electronics scheme shown in Figure 11-2 . The variable frequency is
first rectified into DC, and the DC is then inverted back into the fixed
frequency AC. The increase in the energy production from the variable speed
wind turbine over the plant life more than offsets the added cost of the power
electronics.
In photovoltaic power systems, the DC power produced by the pv modules
is inverted into 60 or 50 Hz AC power using the inverter. The inverter circuit
in the pv system is essentially the same that is used in the variable speed
wind power system.
The main power electronic components of the wind and pv power systems
are, therefore, the rectifier and the inverter. Their circuits and the AC and
DC voltage and current relationships are presented in the following sections.