The traditional piston air compressor mainly has two kinds of rotary electric motor drive and electromagnetic vibration type. At present, most of the piston compressors produced at home and abroad are driven by rotary electric machines. The main advantages of this type of compressor are mature technology, reliable performance and long life. The disadvantage is that the piston stroke is short, the piston reciprocating frequency is high, the structure is complex, the energy transmission link is many, the mechanical efficiency is low (the whole machine efficiency is generally 0.30~0.40), and the running noise is large. The electromagnetic vibrating compressor is driven by the principle of electromagnetic force and mechanical resonance, and directly pushes the reciprocating vibration of the piston to work. The advantages are: small volume, light weight, high mechanical efficiency, overpressure protection, easy to achieve oil-free lubrication. The disadvantages are: low efficiency of the whole machine (mainly low efficiency of the electromagnetic system), short stroke, high frequency, low exhaust pressure, and it is difficult to achieve large power.
The linear motor-driven piston compressor directly drives the compressor piston to reciprocate linear motion without the need of a crank-link mechanism and a mechanical transmission system. It has the following characteristics: (1) Replacing the electromagnetic spring resonance power system of the electromagnetic compressor with a linear induction motor, the piston compressor has made great progress in performance and mechanism.
(2) The efficiency of the cylindrical composite secondary linear motor is slightly lower than that of the rotary asynchronous motor, but the overall efficiency of the compressor is higher than that of the electromagnetic vibrating compressor and the rotary motor driven piston compressor.
(3) The piston stroke is long. The secondary stroke of the linear motor is not limited, so the compressor can select a longer piston stroke (more than 2 to 3 times the current stroke of the same cylinder). This also reduces the requirement for the reciprocating frequency of the piston (the piston frequency can be reduced by 2 to 3 times), thereby extending the mechanical life and greatly reducing the running noise.
(4) The piston speed can be designed as required.
2 basic structure
In the combined linear electric piston compressor structure, the secondary and the piston are integrally formed. The structural characteristics of this type of compressor: two cylinders are symmetrically installed at the two ends of the linear motor secondary, the piston reciprocates once, and the two cylinders each complete a compression cycle. The motor has a long secondary structure with no transmission system, and the mechanical loss is only the frictional resistance loss between the piston and the cylinder wall. The utility model has the advantages of simple structure, small volume, low cost, low noise and high efficiency.
Schematic diagram of the structure of the split linear electric piston air compressor. The structure is basically the same as the combination. Only the motor primary is separated from the cylinder. In this way, the diameter of the secondary part outside the cylinder is not limited by the inner diameter of the cylinder, which optimizes the structure of the motor and makes the performance of the motor better. At the same time, the heat dissipation effect of the secondary, piston and cylinder is also good. The disadvantage is that the installation accuracy of the linear motor and the cylinder is high.
3 power supply and control system
When the two-way thyristors TV4, TV5, and TV6 are in an open state, when TV1, TV2, and TV3 are triggered to be turned on, the piston runs to the left; when TV1, TV2, and TV3 are in an off state, and TV4, TV5, and TV6 are triggered to be turned on, The piston runs to the right. The thyristor is repeatedly turned on and off, and the piston reciprocates. The on/off of the thyristor is controlled by the signal detection circuit and the trigger circuit is completed.
In order to ensure the safe commutation of the motor power supply, the "delayed energization" commutation mode is adopted, that is, after a group of thyristors is powered off, the delay is delayed for a certain time, and the other group of thyristors is triggered to conduct again. This can ensure safe commutation, and a reasonable delay time can greatly reduce the starting current impact generated by the motor during commutation.
When the piston runs to the left to the position where K1 is located, K1 sends a power-off signal. TV1, TV2, and TV3 cannot get the trigger pulse. Since the motor is a resistive inductive load, TV1, TV2, and TV3 are disconnected after a delay. After the motor is powered off, after a delay, it is ensured that TV1, TV2, TV3 are completely disconnected, TV4, TV5, TV6 are triggered again, and the piston is subjected to the electromagnetic force in the right direction. When the piston reaches the K2 position to the right, K2 sends a signal, and TV4, TV5, and TV6 are delayed to turn off. After a delay, TV1, TV2, and TV3 are triggered to conduct, and the piston is subjected to the electromagnetic force to the left.
The position sensors K3 and K4 are safety protection switches. When the switch is actuated, the power is forcibly turned off and the power is reversed.
The control system also features phase loss automatic protection, SSR protection, short circuit and overload protection. When the operating frequency of the piston is relatively high, the single-winding motor is prone to commutation failure. A double-winding motor can be used, that is, the motor stator has two sets of windings. When the secondary is running in one direction, one set of windings is energized, and the secondary is reversed. During operation, another set of stator windings is energized, which can better solve the commutation problem, but the size of the motor becomes larger and the cost increases.
Two sets of windings are arranged in two forms. The structure of the motor has a larger stator diameter and requires more electromagnetic wires. The mutual inductance between the two sets of windings is too large, affecting the commutation. The slot is deep and affects the efficiency of the motor. The stator core of the motor is long and the utilization rate is not high.
4 test prototype and test results
Test sample: exhaust pressure: prototype 1 is 0.4MPa, prototype 2 is 0.1MPa; piston frequency: 5Hz; power supply: three-phase alternating current, rated voltage 220/380V, frequency 50Hz; motor synchronous speed: 3.0m / s; Gas volume: 0.1-0.3m 3 /min; control mode: manual adjustment of the commutation delay time; the linear motor secondary in the two prototypes are aluminum-iron composite structure.
5 Conclusion
The development of linear motor piston compressors is the first time at home and abroad. Compared with the traditional piston compressor, it has outstanding advantages. In some suitable situations, it will show unique advantages. Such as: simple structure, low cost, low noise, high efficiency of the whole machine, long piston stroke and so on.
Crisper
YANGZHONG HONGYUN BOTTLE CAPS MAKING FACTORY , https://www.hongyunyz.com