04-12-2012, 12:14 PM
Wind Turbine Driven by Permanent Magnet Synchronous Generator
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ABSTRACT
A permanent magnet synchronous generator (PMSG) variable speed wind turbine connected to an electrolyzer and a battery model system is presented in this paper. Hydrogen gas could be produced from the model system, when a variable wind speed is applied to the PMSG driven variable wind turbine. The simulation results presented shows the nature of some of the variables of the PMSG wind driven turbine and the hydrogen gas produced as the wind speed varies with time.
INTRODUCTION
Variable speed operation of modern wind turbine enables an optimization of the performance, reduces the mechanical loading, and at the same time delivers various options for active power plant control [1, 2]. Megawatt class wind turbines equipped with a permanent magnet synchronous generator (PMSG) have been announced by Siemens Power Generation and GE Energy. In this concept, the PMSG can be directly driven or have smaller gearboxes or even gearless and is connected to the AC power grid through the power converter [3, 4].
In PMSG, the excitation is provided by permanent magnets instead of field windings. Permanent magnets machines are characterized as having large air gaps, which reduce flux linkage even in machines with multi-magnetic poles [5, 6]. As a result, low rotational speed generators can be manufactured in relatively small sizes with respect to their power ratings. Moreover, a gearbox can be omitted due to the low rotational speed in PMSG wind generators resulting in low cost.
WIND TURBINE DRIVEN GENERATORS
There are three main types of wind turbines currently in use: the fixed speed wind turbine with Squirrel Cage Induction Generator (IG), the variable speed wind turbine with Doubly Fed Induction Generator (DFIG), and the variable speed wind turbine with Permanent Magnet Synchronous Generator (PMSG) [14]. A brief distinction of the 3 types of wind turbine driven generators is given below.
Fixed Speed Squirrel Cage Induction Generator
This generator consumes reactive power and cannot contribute to voltage control. For this reason, although static capacitor control may allow wind farms with this type of generators are doomed to disappear from wind turbines. Below are the schematic diagram and the equivalent
circuit of the fixed speed squirrel cage induction
generator used in wind turbine technology as
shown in Figures 1 and 2, respectively. Details
and nomenclature of the equivalent circuit of this
type of generator can be found in [1, 15].
Model System of Study
The simulation model of the system under study
is shown in Figure 7, where the wind turbine is
connected to the hydrogen generator model with
an electrolyzer and a battery system. The rated
capacity of the PMSG is 3MVA.
From Figure 7; W represents the rotor speed of
the PMSG; Wopt represents the optimum rotor
speed of the PMSG; Pref represents the
maximum power point tracking (MPPT) reference
active power of (Figure 8); Vw represents the
input wind speed; and the voltmeter and the
power meter takes the root mean square (r.m.s)
voltage, the active and reactive power at the
PMSG terminals, respectively.
CONCLUSION
The paper presented the modeling and control design of the variable speed wind turbine (VSWT) driven by a permanent magnetic synchronous generator (PMSG). The modeling of the wind turbine maximum power point tracking is also described. The modeling and control strategy for the generator rotor side frequency converter are presented.
The control topologies are suitable for improving the dynamic analysis of the VSWT-PMSG driven, to be able to generate a constant voltage despite the stochastic nature of the input wind energy. Hydrogen gas for fuel purpose can also be generated, when an electrolyzer is connected via a hydrogen generator to the VSWT-PMSG system as shown by the simulation results in PSCAD/EMTDC. The hydrogen gas production in the system is possible because the VSWT-PMSG driven has the ability to provide and absorb reactive power to the network system, through its high frequency converter controls despite the varying nature of the wind energy, thus maintaining a constant voltage supply.