Design of DC brushless motor

Design of DC brushless motor

The design task of DC brushless motor is to select appropriate materials according to the given rating and basic technical performance requirements, determine the size of each part of the motor, and calculate its performance, in order to meet the basic requirements of material saving, convenient manufacturing, good performance, and obtain greater economic benefits. There is no national standard for rating and technical requirements of DC brushless motor at present. Usually, the rating and technical requirements of DC brushless motor are negotiated by both parties according to the user's requirements and the factory's manufacturing conditions. Generally speaking, the main ratings and technical requirements are as follows.

I. Rating value

1, For a series of products, for the convenience of manufacturing, the power level of the motor should be increased by a certain proportional factor. The smaller the power increasing factor is, the more varieties to be selected by the user, and the less the over-installation capacity and over-installation cost will be. However, as the number of motor varieties increases, the motor manufacturing technology and equipment increase, and the production management is complicated, which leads to the increase of manufacturing cost. Therefore, the power level should be balanced between the requirements of production and use to make a reasonable decision. The increasing coefficient of power of direct current motor in China is 1.35. At present, the power of brushless DC is small. If you need to design a series of products, the power increasing coefficient can refer to the power increasing coefficient of general DC motor, and can also be determined according to the factory's own production conditions and market demand.

2, rated voltage U ɴ refers to the motor in the rated voltage of the state of runtime, the general use of dc rated voltage above 110 v, such as 160, 220, 440 v, and so on. The current application of brushless dc motor capacity is small, most of the use of low voltage, such as 6, 12, 24, 36 and 48V.

3. Rated speed refers to the speed under rated voltage and rated load. Table 4-1 lists the speed levels of common DC motors.

                   Table 4-1 dc motor speed level             (unit: r/min)

The speed of DC brushless motor is generally higher, usually more than a few hundred revolutions per minute. Common ones are 1000, 1500, 3000, 3600, 4800, 6000r/min or even higher.

Ⅱ, technical requirements

1. The operation mode is the same as the general DC motor, and the operation mode of the DC brushless motor has three kinds of continuous, short-time and intermittent. Continuous operation mode of the motor, according to its rating for a long period of continuous operation. Motors with short-time operation mode can be run for a specified duration starting from the actual cold state according to the rated value. The running time limit can be generally divided into four kinds: 10, 30, 60 and 90min. Intermittent operation mode of the motor, according to the rated value for a period of time, power off stop for a period of time, and then according to the same cycle of repeated operation, the standard persistence rate of 15%, 25%, 40%, 60% of four kinds. The so-called persistence rate refers to the ratio of power operation in a cycle time. For example, the persistence rate is 15%, which refers to the power operation in 15% of the time and the power shutdown in 85% of the time in a cycle. For the same power and the same temperature rise limit, the size of the motor in intermittent or short operation mode is smaller than that in continuous operation mode.

2. Protection type The protection type of the motor directly affects the structure and ventilation and heat dissipation of the motor, so full attention must be paid to it in the design. General DC motor protection types mainly include protective type and closed type, protective type mainly refers to the conductive part of the necessary insulation or mechanical shell protection, in order to prevent accidents such as accidental contact and short circuit of power supply, but does not significantly hinder the ventilation and heat dissipation of the motor. The structure of enclosed motor can prevent the free exchange of air inside and outside the enclosure, but does not require complete closure, mainly used in places with more dust.

3. During the operation of the motor, the temperature rise generates heat due to its own internal loss, which leads to the aging of the motor parts and the shortening of its life. The allowable temperature rise of the motor is mainly determined by the heat resistance grade of the insulating material. Table 4-2 shows the heat-resistant grades of two thousand insulating materials in China.

                Table 4-2 Heat resistance grades of insulation materials

4, efficiency The operation efficiency of the motor directly affects the effective use of electric energy, but also affects the temperature rise of the motor itself. It is one of the important indexes to measure the quality of motor. Therefore, the efficiency of each type of motor at rated operation is specified in the relevant technical conditions, and sometimes the efficiency tolerance is specified. The motor must be designed to achieve the required efficiency. Because the power of current DC brushless motor is small, the index of its energy consumption is not very prominent. On the premise of ensuring other performance indexes, sometimes the sacrifice of point efficiency is allowed.

5, Speed change rate of the motor When the winding approaches the working temperature and the terminal voltage remains unchanged, the applied load of the motor is gradually adjusted from the rated load to no load, and the speed change rate ∆ <e:2> % of the motor shall not exceed the provisions in Table 4-3. The tolerance of speed change rate is 20% of the guaranteed value.

                  Table 4-3 Speed change rate of DC motor

In addition to the above, the technical requirements of the motor should also meet the requirements of insulation strength, overload capacity, overspeed capacity, vibration, noise and installation size.