Brushless excitation is an excitation system that does not need slip rings and carbon brushes.Medium and small three-phaseSynchronous generatorIt is mainly divided into brushless excitation system and brushless excitation system.
The brushless excitation system is composed ofVoltage regulatoryesAC exciterExciterArmature windingThe generated AC is rectified by the rotating rectifier and then used for excitation of the field winding of the main generator.
Brushless excitation system has its own irreplaceable advantages. It can operate stably under dangerous conditions. It is the preferred excitation mode for modern small and medium-sized motors and large brushless excitation systems.[1]
In the early 1960s, foreign countries began to use medium generatorsAC exciterThe mode of adding semiconductor rectificationSynchronous generatorExcitation has achieved good results, and semiconductor excitation mode has been widely used.It is also divided into separately excited semiconductor excitation system and self excited semiconductor excitation system.Separately excited semiconductor excitation system according toSemiconductor rectifierStatic or rotating is divided into separately excited static semiconductor excitation system and separately excited rotating semiconductor excitation system.The former eliminates the problem of reversing spark.But the system still needs slip rings and carbon brushes.The latter is due to the fact that the semiconductor and AC exciter rotate together with the main generator on the same axis.Slip rings and carbon brushes are not required.Therefore, it is called brushless excitation system.
The excitation winding of brushless excitation is powered by the auxiliary exciter through the thyristorAC exciterFor power supply, the auxiliary exciter generally selects the motor with higher AC frequency.The on-off of thyristor controllable converter is controlled by the excitation controller. In the era of developed digital chips, the excitation controller can be built by DSP chips.It can greatly improve the cost performance of the control circuit.The excitation winding of the exciter generates corresponding excitation current to excite the AC exciter.AC exciter armature voltage frequency is generally 1 to 2 times higher than power frequency.The potential induced by the AC exciter is rectified by an uncontrolled rectifier bridge, and the DC current generated is used to supply power to the generator excitation winding.[2]
Principle of brushless excitation structure
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The shaft end of brushless excitation generator is aalternatorThe rotor is a generator winding, and the current generated is led to the silicon rectifier tube fixed on the shaft through the wire fixed on the generator shaft. The rectified DC directly enters the rotor winding, where there is no rectifier brush, so it is called brushless excitation.It used to be popular for some time, but the rectifier tube had to be shut down when it was broken, so it has been used very little, and the self compound excitation system is basically used.
Brushless in general small and medium-sizedSynchronous generatorIn, most of the auxiliary exciters are omitted.The auxiliary winding or main winding tap in the host stator replaces the auxiliary excitation to provide the excitation power of the AC exciter.
Among three-phase brushless synchronous generators, the types of AC exciters include armature synchronous generator, asynchronous generator and rotating phase compound excitation transformer, etc., but the armature three-phase synchronous generator type AC exciter is the most widely used.The three-phase exciter has a high utilization coefficient, which is conducive to reducing the volume.
Brushless generatorThe disadvantage is that the electromagnetic inertia of the excitation system is large, so the dynamic characteristics are relatively poor.In order to improve the dynamic characteristics, the measures taken areAC exciterMedium frequency is adopted. Due to the restriction of generator size and required excitation power, most marine brushless generator exciters have a frequency of 100~150 Hz.In addition, the brushless generator has high requirements for the manufacturing and installation process of the rotating rectifier.
Brushless excitation characteristics
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Features of brushless excitation mode:
(1) Brushless excitation has no contact parts, carbon brushes and slip rings, which are simple to maintain, high reliability, long-term continuous operation and can achieve less or no maintenance.
(2) Since there are no rotating contact conductive parts, which will not produce sparks, it is suitable for operation in harsh environmental conditions such as flammable gas and dust.
(3) The excitation power is small, and the reliability design of AVR is easy to realize.
