At present, there are 10 types of small wind turbines according to their rated power, which are 100W, 150w, 200w, 300w, 500W, 1kw, 2kw, 3kw, 5kW, and 10kw. Its technical characteristics are: 2 to 3 blades, side-bias speed regulation, upwind direction, and high-efficiency permanent magnet low-speed generators. The unit runs smoothly, has reliable quality, and has a design service life of 15 years. The maximum power coefficient of the wind wheel has been increased from about 0.30 in the initial stage to 0.38~0.42, and the starting wind speed is low, and the blade materials have been diversified: wood, iron, aluminum alloy, fiberglass composite type and all nylon type. The wind wheel adopts two kinds of fixed pitch and variable pitch, with the fixed pitch being the majority. The generator is equipped with a permanent magnet generator with low speed characteristics. The permanent magnet material is made of rare earth materials, which increases the efficiency of the generator from 0.50 to over 0.75, and some can reach 0.82. Most of the steering devices of small wind turbines use upwind tail wing steering. The speed control device adopts wind wheel offset and tail hinged shaft tilt type speed control, variable pitch speed control or wind wheel up-pitch speed control. Larger power units are also equipped with manual brakes to ensure the safety of wind turbines under strong winds or typhoons. The controller of the wind turbine generator has the functions of overcharging, overdischarging, AC unloading, overload and short circuit protection of the battery to extend the service life of the battery.
Small wind turbines mainly use low-speed permanent magnet generators. This is mainly because the wind wheels of small wind turbines are directly coupled to the generator shaft, eliminating the need for a speed-up mechanism, which requires the generator to have only a few hundred revolutions per minute. So use a low-speed generator.
Small wind turbines can be DC generators or AC generators. At present, most of the generators used in small wind turbines are three-phase AC generators. Due to the different forms of generating the magnetic field, three-phase AC generators have permanent magnet and excitation types. The three-phase AC generated by them is rectified by a rectifier diode to output DC. In order to facilitate installation and maintenance, when many small wind turbines use AC generators, the rectifier is installed in the controller.
Compared with the DC generator, the AC generator has the advantages of small size, light weight, simple structure, and good low-speed power generation performance. In particular, the interference to surrounding radio equipment is much smaller than that of a DC generator, so it is suitable for small wind generators. The AC generator is mainly composed of a rotor, a stator, a casing and a rectifier.
(1) Rotor. The rotor is a canine-tooth staggered magnetic pole, and the rotor magnetic pole of a permanent magnet generator is made of permanent magnets. The rotor magnetic poles of the excitation generator are made of two pieces of low carbon steel, and an excitation winding is installed in the cavity inside the magnetic poles. When the excitation current is applied, a magnetic field can be generated.
(2) Stator. The stator is composed of an iron core and a stator coil. The iron core is made of silicon steel sheet, and three sets of coils are wound in the iron core slot, connected according to the star method, and three-phase alternating current is generated in the coil when the generator is working.
(3) Case. The casing is the outer casing of the alternator, made of metal, and includes a casing and a front and rear end covers. If the rectifier is installed in the generator, the end cover with the rectifier is also called the rectifier end cover.
(4) Rectifier. The rectifier is composed of 6 silicon rectifier diodes to form a bridge-type full-wave rectification circuit. Its function is to convert three-phase alternating current into direct current, which can easily store electrical energy in the battery. Nowadays, many manufacturers use integrally packaged rectifier bridge modules, which simplifies the circuit, improves the reliability, and reduces the cost.
The rotor of a permanent magnet synchronous generator is a permanent magnet pole made of ferrite material, which is usually a low-speed multi-pole type without external excitation, which simplifies the structure of the generator, and thus has many advantages. A permanent magnet generator is a generator that changes the rotor of an ordinary synchronous generator into a permanent magnet structure. Commonly used permanent magnet materials include ferrite (BaFeO), samarium cobalt 5 (SmCo), and so on. Since the permanent magnet synchronous generator does not require external equipment excitation, it is also more convenient to maintain, but it also has its shortcomings:
(1) Since the magnetic field of the permanent magnet synchronous generator cannot be adjusted, after the motor is manufactured, the output voltage fluctuates with the change of wind speed. When the voltage is low, the electrical equipment cannot work normally, and when the voltage is high, it is easy to damage the electrical equipment.
(2) The technical performance of the permanent magnet material and the shape of the hysteresis curve have a great influence on the performance and operational reliability of the generator. The ferrite permanent magnet material is the main material for the manufacture of permanent magnet wind generators. The disadvantage is that the magnetic induction intensity is low, the magnetic load of the generator is limited, the amount of metal is increased, and the volume of the generator is larger.
(3) The permanent magnet is made of magnetic steel, but because the magnetic field performance cannot be accurately measured, the same batch of products cannot guarantee the same performance. During the operation of the wind turbine, due to the harsh conditions, it is inevitable that there will be vibration, overheating or overcooling, which will easily cause the magnet to lose magnetism, affect the efficiency of the generator, and cause damage to the generator in severe cases.