**4. The application of the DFIA**

It is well-known the principle of operation of the double-fed alternator [12, 14–16]. Electric machine of this type has been studied by scientists around the world since 1960. It has different applications, but in wind power it is used only for the last 10 years. The authors offer a unique design that they have developed for a row of wind power plants. The design has a Russian patent. It is described below.

The alternator consists of two electric machines. The main electric machine is a power alternator. It is the induction machine with a phase rotor. So, the stator and the rotor have three phase windings. The alternator has the inverse design. It means that the rotor is settled outside of stator. It is very comfortable for the windmill because it is possible to attach the blades to the rotor. The three phase rotor winding is supplied by an adjustable voltage source. The rotor creates the rotating magnet field. This magnet field generates the voltage in the stator winding. If the rotor is fixed the speed of rotation of magnet field depends only from frequency of voltage source. But if the rotor begins to rotate, the speed of magnet field is added to the speed of rotor rotation. So, the total speed of magnet field is combined with two parts. We can change the frequency of the adjustable three phase voltage sources. When the speed of rotor is variable we can choose the necessary frequency of voltage source and we will have the stable frequency in the stator winding. In this

way, we solve the problem of voltage frequency stabilization with different speed of rotor rotation. The amplitude of stator voltage is regulated by amplitude of rotor winding voltage.

But it is necessary to solve one serious problem to provide the reliability to windmill. It is impossible to use the sliding contact for windmill because it is very difficult to serve this device at height and in a difficult environment. The system has the second alternator (exciter) for brushless current supply. The brushless electric machine with combine excitation is used for the exciter. This type of electric machine has the stable external voltage with different speed of rotation. It is very comfortable in this case. In details, this type of electric machine is described in [1, 4, 19].

The sketch of alternator with exciter, 3D model and diagram of electronic control system is present in **Figures 10**–**12**. They allow understanding the principle of operation more carefully.

The electronic control system is built in to the alternators. This concept allows

*Application of an Asynchronous Synchronous Alternator for Wind Power Plant of Low, Medium…*

This idea was realized for the windmill 10 kW but the concept can be scaled to

The beginning of the work in the field of the theory of DFIA was initiated by the

research in the late 1960s — early 1970s by the laboratory of double feeding machines under the guidance of doctors of technical sciences M. Botvinnik and Yu.

The results of these works were the development of the foundations of the theory, structural schemes, principles of construction, as well as the creation of a

In a double-feed machine, energy is supplied (or withdrawn) to both the stator and rotor windings. This allows you to control the flow of active and reactive power of the dual-feed machine. The expediency of using DFIA is observed in the construction of alternator sets with a variable speed of rotation of the shaft, which is

The stator windings of the machine are connected to the power supply network (U1 = const, f1 = const), and the rotor windings are connected to a separate con-

There are various options for implementing a controlled power supply in the rotor circuit. A scheme of independent rotor power supply is interested in wind

The active Converter is a three-phase bridge circuit of the inverter, made on transistors. The main property of the active Converter is the ability to two-way transmission of active power. When transmitting power from an AC source, ASC acts as an active controlled rectifier (ACR). When transmitting power from the DC link, ASC acts as an Autonomous Inverter (AI). Such structures allow you to control the flow of active and reactive power between the supply network and

having very high efficiency and very low cost.

*DOI: http://dx.doi.org/10.5772/intechopen.89255*

**5. Theory of double-feed induction machine**

number of experimental and industrial installations.

trolled power source (active semiconductor converter ASC).

very important for wind power plants.

power plants (**Figure 13**).

the machine.

**11**

megawatts sizes.

*Diagram of electronic control system.*

**Figure 12.**

G. Shakaryan [20].

#### **Figure 10.**

*Sketch of double-fed alternator with exciter. (1, rotor of power alternator; 2, stator of power alternator; 3, rotor of excitation alternator; 4, stator of exciter alternator).*

**Figure 11.** *3D model of the windmill alternator.*

*Application of an Asynchronous Synchronous Alternator for Wind Power Plant of Low, Medium… DOI: http://dx.doi.org/10.5772/intechopen.89255*

**Figure 12.** *Diagram of electronic control system.*

way, we solve the problem of voltage frequency stabilization with different speed of rotor rotation. The amplitude of stator voltage is regulated by amplitude of rotor

But it is necessary to solve one serious problem to provide the reliability to windmill. It is impossible to use the sliding contact for windmill because it is very difficult to serve this device at height and in a difficult environment. The system has the second alternator (exciter) for brushless current supply. The brushless electric machine with combine excitation is used for the exciter. This type of electric machine has the stable external voltage with different speed of rotation. It is very comfortable in this case. In details, this type of electric machine is

The sketch of alternator with exciter, 3D model and diagram of electronic control system is present in **Figures 10**–**12**. They allow understanding the principle

*Sketch of double-fed alternator with exciter. (1, rotor of power alternator; 2, stator of power alternator; 3,*

*rotor of excitation alternator; 4, stator of exciter alternator).*

winding voltage.

*Aerodynamics*

described in [1, 4, 19].

**Figure 10.**

**Figure 11.**

**10**

*3D model of the windmill alternator.*

of operation more carefully.

The electronic control system is built in to the alternators. This concept allows having very high efficiency and very low cost.

This idea was realized for the windmill 10 kW but the concept can be scaled to megawatts sizes.
