PARMENANT MAGNET SYNCHRONOUS GENERATOR

BY JA’FAR R.A. AZIM Assem M.A. Al ighrair

 The modern history of permanent magnets stared about 1940 with the introduction of Alnico. Before this, the use of permanent magnets was limited to a few applications such as the compass and magneto whose very function depended on the permanent magnetic properties. With the introduction of Alnico, it became possible to replace electromagnets with permanent magnets and the use of magnets started to become widespread devices such as motors, generators and loud-speakers.

History of Permanent Magnets

   A permanent magnet synchronous generator is a generator where the excitation field is provided by a permanent magnet instead of a coil.

Synchronous generators are the majority source of commercial electrical energy. They are commonly used to convert the mechanical power output of steam turbines, gas turbines, reciprocating engines, hydro turbines and wind turbines into electrical power for the grid. They are known as synchronous generators because the speed of the rotor must always match the supply frequency.

In a permanent magnet generator, the magnetic field of the rotor is produced by permanent magnets. Other types of generator use electromagnets to produce a magnetic field in a rotor winding. The direct current in the rotor field winding is fed through a slip ring assembly or provided by a brushless exciter on the same shaft

Introduction

     They do not require an additional DC supply for the excitation circuit.

The permanent magnet synchronous generators avoid the use of slip rings, hence it is simpler and maintenance free.

Condensers are not required for maintaining the power factor in synchronous generators, as it is required in induction generators.

The generator is a brushless.

higher efficiency, as the copper losses in the rotor disappear.

Advantages of PMSG

 Large permanent magnets are costly.

 Uncontrolled air-gap flux density leads to over voltage and poor electronic control reliability.

 A persistent magnetic field imposes safety issues during assembly, field service or repair, such as physical injury, electrocution, etc.

 High performance permanent magnets, themselves, have structural and thermal issues.

Disadvantages of PMSG

 Uncontrolled air-gap flux density leads to over voltage and poor electronic control reliability.

 A persistent magnetic field imposes safety issues during assembly, field service or repair, such as physical injury, electrocution, etc.

 High performance permanent magnets, themselves, have structural and thermal issues.

Disadvantages of PMSG

Structure of the Permanent Magnet Machine

This model is similar to the conventional equivalent circuit of the synchronous machine, except there is no leakage inductance on the field.

EQUIVALENT CIRCUIT MODEL OF THE PMSG

This model is similar to the conventional equivalent circuit of the synchronous machine, except there is no leakage inductance on the field.

EQUIVALENT CIRCUIT MODEL OF THE PMSM

The demagnetization curve of the magnet that can be divided into three regions by three lines, called: no load, rated-load and excessive-load lines.

We always try to not enter the excessive load region; otherwise the magnet is in danger of being damaged.

Demagnetization curve



Small-Scale Wind Power Generation System

Wind power is an energy source whose industrial application in the world has grown at the fastest rate in the last 10-15 years. Installed capacity of wind power plants is continuously growing at a level of annual rate exceeding 30%. The European power market has been the main driving force in development of wind power industry for many years. In EU countries, a record installation of more than 6 180 MW new wind power generators was achieved in 2005. By the end of 2005, the capacity of wind energy generation reached a level of more than 40 500 MW in Europe and more than 59 300 MW worldwide. In Europe, the current targets of using wind capacity are 75 000 MW by 2010, 180 000 MW by 2020, and 300 000 MW by 2030.

Applications

 . A small-scale wind power turbine of the capacity 0.2-30 kW, with rotor diameters from 1 m up to 15 m may be used as a flexible and vital alternative for local power demand in isolated regions or locations.

Small-Scale Wind Power Generation System

 Permanent-magnet (PM) synchronous generators are one of the best solutions for small-scale wind power plants. Low speed multipole PM generators are maintenance-free and may be used in different climate conditions. It is possible to combine PM wind generators for hybrid technologies such as wind-diesel, wind photovoltaic etc.

Why PMSG

 Traditionally wind turbine generators have used gearboxes and pitch control to allow constant high-speed generation under varying wind speed conditions. In recent years contemporary power electronics of high efficiency, high reliability and decreasing cost offers the option to change the power frequency out of the generator to match the system frequency, which leads to the idea of variable speed direct-drive generators.

Why PMSG

 Traditionally wind turbine generators have used gearboxes and pitch control to allow constant high-speed generation under varying wind speed conditions. In recent years contemporary power electronics of high efficiency, high reliability and decreasing cost offers the option to change the power frequency out of the generator to match the system frequency, which leads to the idea of variable speed direct-drive generators.

Why PMSG

 Compared to a conventional gearbox coupled wind turbine generator, a direct drive generator has reduced overall size, lower installation and maintenance cost.

Why PMSG