This paper introduces a comprehensive technical advantage of compensating pulse generators for inertial energy storage, electromechanical energy conversion and pulse shaping. A 20 MJ compensated pulse generator with rated speed of 12 000 r/min is developed and the key materials are studied. Includes options for shielding cylinders and shafts. On the basis of theoretical calculation and simulation analysis, the motor excitation circuit and armature winding are designed. A new compensation winding structure is proposed, that is, two sets of armature windings are placed on the stator. When the motor is discharged, the pulse current will be increased. The temperature will decrease and the magnetic field density will increase.
0 Preface
Compensated pulse generator (CPA) is a special synchronous generator that uses the principle of magnetic flux compression to reduce the armature inductance. When the motor is working, it will generate a large pulse current. It is currently recognized as a relative The practical value of the electromagnetic gun power supply uses the flywheel to store energy in mechanical form, overcomes the respective shortcomings of the capacitor and the single generator, and integrates the pulse energy supply of energy storage, conversion and regulation, which greatly reduces the load from the prime mover to the electromagnetic gun. The intermediate part of the power output has the comprehensive advantages of the unit parts. According to the research content of pulse power supply, design and manufacture the compensation pulse generator prototype with energy storage capacity above 20 MJ. Through the analysis of the internal magnetic field of the motor and the load test, the difficulty in compensating the pulse generator manufacturing is solved, and the motor is feasible for the electromagnetic gun. Sexual analysis lays the theoretical and engineering foundation for the next step to create a practical CPA.
1 basic parameters
Taking the motor volume and weight as the optimization goal, this paper designs and manufactures a hollow, self-excited mode, transition field structure, two-phase four-pole hollow selective passive with peak power of more than 300 MW, energy storage of 20 MJ and conversion efficiency of 15%. Compensate the pulse generator prototype. The main parameters of the motor are shown in Table 1.
2 basic structure
The compensation pulse alternator is a special synchronous generator. Through the research on the advantages and disadvantages of the current compensated pulse generator [4], the structure of the motor is determined as follows: two-phase four-pole, hollow, passive compensation, self-excitation Mode, transition structure.
The motor system structure includes a stator, a rotor, a brush, a slip ring, a bearing, an end cover, a power electronic device and a casing [5]. The rotor is composed of a rotating shaft, a rotor yoke, a field winding, a carbon fiber bandage, and an aluminum compensation cylinder. The titanium alloy rotor yoke fixed on the main shaft is connected by interference, the rotor excitation winding is bonded to the outer surface of the rotor yoke, and the outer part of the winding is fixed by a carbon fiber epoxy tying strap, and the outer band of the strap is an aluminum compensation cylinder; the stator is composed of a main armature winding, Glass fiber bandage, secondary armature winding, stator yoke, and casing. The stator yoke is fixed on the inner wall of the casing, the inner wall is bonded with the stator non-slotted armature winding (for excitation), and the carbon fiber epoxy banding bandage is between the secondary armature winding and the main armature winding (for discharge) The end of the stator slotless armature winding is covered by a shielding box, and the rotor is fixed in the stator through the support of the end cover bearing. One end of the main shaft is connected to the prime mover, and the other end of the main shaft is fixed with a slip ring and a brush.
3 rotor design
The basic size of the rotor is a motor with a hollow rotor structure. The optimal inner-outer radius ratio of the rotor flywheel is 0.45 [6]. The stored energy of the rotor is more than 95% of the energy stored in the solid rotor, which can save the rotor material and reduce the weight of the rotor.
The motor rotates at a very high speed, and the general ferromagnetic material cannot satisfy its mechanical effect, and is generally made of composite material or titanium. Titanium (Ti) is a silver transition metal. It is a non-magnetic metal and will not be magnetized in a large magnetic field. It also has excellent properties such as high temperature resistance and corrosion resistance [7].
Titanium alloys have high strength and low electrical resistivity, and maintain high strength at both high and low temperatures. Compared with composite materials, the use of titanium rotor structure can increase the energy storage density, reduce the volume of the rotor, and the process is relatively simple. Therefore, in this design, the rotor is made of titanium.
3.1 Selection of rotor yoke
The rotor yoke is composed of a titanium alloy. Titanium alloy material properties [8] are as follows: tensile strength: 1 000.0 MPa; tensile modulus: 116.7 GPa; specific strength:
221.2 MPa (g/cm3); specific modulus: 25.8 GPa (g/cm3); density:
4.52 g/cm3. When the motor rotates at 12 000 r/min, the outer diameter of the rotor is 0.088 m, the inner diameter of the rotor is 0.039 6 m, the rotor length is 0.326 m, and the mechanical angular velocity is 1 256.6 rad/s.
3.2 Selection of shaft material
The material type of the shaft is 25Cr2Ni4MoV. The main mechanical properties [9] index (tangential sampling) are as follows: the yield strength is 730~830 MPa; the tensile strength is σb≥1 000 MPa; the elongation is δb≥14%.
3.3 choice of bandages
The bandage is a composite material of carbon fiber and epoxy resin, and its performance [10] is as follows: tensile strength: 1 471.0 MPa; tensile modulus: 137.3 GPa; specific strength: 1 014.0 MPa (g/cm3); specific modulus : 94.7 GPa (g/cm3); density: 1.45 g/cm3.
3.4 Selection of shielding tube material
The choice of compensation tube material is an important part of the design of the motor. It must have good electrical conductivity and non-magnetic permeability [11]. When the work discharge is clicked, the armature reaction magnetic field is compressed because the compensation tube prevents the magnetic field from passing through. In the air gap between the stator and the rotor, the inductance of the armature winding is greatly reduced, and the instantaneous operating power of the compensation motor is greatly improved.
Based on the limitation of the compensation cylinder material, it must have good electrical conductivity and cannot be magnetically guided. Copper and aluminum meet the above requirements. However, when the motor is working normally, the motor rotates at a very high speed and has a large centrifugal force, so the mechanical performance and safety are obtained. Consider, choose aluminum.
For the compensation pulse generator, the thickness dimension of the compensation cylinder has a great influence on the performance of the motor. If the compensation cylinder is too thin, the compensation cylinder can not compensate the armature reaction flux very well when the motor is discharged, and the internal inductance of the armature winding in the motor is not When the requirements are met, the peak discharge current cannot be satisfied. If the compensation cylinder is too thick, the distance between the armature winding and the field winding is increased, and the coupling between the two is reduced. To achieve the same power, the motor needs to increase the excitation power to meet the requirements.
The thickness of the compensation cylinder directly affects the stability of the internal magnetic field and inductance of the motor. When its thickness is greater than 8 mm, the inductance of the armature winding is basically stable and will not change due to the thickness of the compensation cylinder, that is, the distribution of the magnetic field in the motor. becoming steady. Therefore, in order to minimize the gap of the motor, the thickness of the compensation cylinder of this design is 8 mm. Since the shield cylinder works at a high speed, it is necessary to select a high-strength cemented aluminum. The three-dimensional diagram of the rotor model of this design is shown in Figure 1.
Figure 1 Rotor model
4 stator design
The stator adopts a slotless winding, the inside is a circular cavity, and the stator yoke is made of a composite material, and the armature coil is fixed on the inner surface of the stator and connected through a terminating portion outside the stator.
(1) The inner diameter of the stator is 0.097 m, the outer diameter of the stator (outer diameter of the motor) is 0.138 m, the radial thickness of the stator yoke is 0.014 m, the thickness of the main armature winding and the thickness of the stator bandage are 0.005 m, and the thickness of the secondary armature winding is Is 0.017 m.
(2) The armature winding wire adopts a rectangular copper wire, and two wires are connected in parallel;
(3) The end of the winding is fastened with two aluminum rings, and the binding strip is used to fix the portion of the winding that protrudes from the core.
5 Structural optimization of armature winding
Since the pulse power is large when the motor is discharged, the temperature of the winding is very high. Therefore, in order to reduce the temperature rise of the winding, the equivalent resistance of the armature winding must be reduced. Therefore, the armature winding of the compensation pulse generator should be designed as a conductor cut. The area is relatively large and the number of turns is relatively small. However, due to the size, power and speed of the motor, the number of turns of the armature winding is relatively small and the output of the pulse power is limited, which prolongs the time for the motor to reach the self-excitation end point and reduces the efficiency of self-excitation.
In order to solve this problem, scholars use double armature windings when designing pulse generators, one winding for excitation and the other winding for motor discharge. The compensation pulse generator adopts a static field structure, that is, two sets of armature windings are installed on the rotor of the motor, and the centrifugal force generated by the high rotation speed of the motor is large, and the structure of the motor is grooveless. The fixing is basically fixed with a bandage. When the motor works, the centrifugal force will cause a great pressure on the bandage. Therefore, considering this factor, placing two sets of armature windings on the rotor increases the design and manufacturing difficulty.
Based on the above shortcomings, this design adopts the transition type, and puts the primary and secondary armature windings on the stator, so that the motor only needs a set of brush slip ring reversing system, which solves the design and manufacturing difficulty and solves the motor discharge. The contradiction between self-excitation time and discharge temperature rise, the structure of the transition field, the requirements on the brush and the slip ring are also reduced, and the stability of the system is correspondingly improved. Moreover, since the rotor has only the excitation winding, the magnetic field distribution inside the rotor changes during the operation of the motor, and the overall performance of the rotor is greatly improved.
The three-dimensional model of the stator is shown in Fig. 2. The primary and secondary armature windings are placed on the inner surface of the stator. The function of the main armature winding is to provide a discharge current, which is made of flat copper wire when it is emitted to the electromagnetic gun. The gap between the stator and the rotor can be reduced, the coupling between the armature winding and the field winding is increased, the cross-sectional area of ​​the flat copper wire is large, and the number of turns is small, so the inductance and resistance of the motor are low, which satisfies the requirements of the compensation motor. . The function of the secondary armature winding is to form a loop together with the excitation winding, which generates the magnetic field during discharge. It is made of ordinary round copper wire and has a large number of turns. When the motor works and the excitation winding work together, the excitation time is shortened and the excitation time is improved. Emission efficiency. The stator parameters are shown in Table 2.
Figure 2 Stator 3D
The main armature winding is mounted on the innermost side of the stator. The excitation winding and the compensation winding are fixed by epoxy adhesive tape and high-strength adhesive. The main armature winding is arranged such that it can be better coupled with the excitation winding on the rotor, so that the efficiency Further improve. Reducing the quality of the compensated pulse generator is also important for compensating the design of the pulse generator, which can increase the energy density and power density of the motor, so the stator yoke is made of high-strength glass fiber epoxy resin, which reduces the motor. The quality, at the same time, improves the stability of the motor.
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