Analysis of the walking uniformity of a five-phase hybrid stepping motor

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Where N is the number of series turns of each phase winding; NI is the magnetomotive force of each phase winding; Z2 is the number of teeth of the rotor; θ is the torque angle; Ad is the direct axis permeance; Aq is the cross axis permeance.
The maximum electromagnetic torque Tmax is proportional to the square of the magnetomotive force (or phase current) of each phase winding, so the stepper motor is a transmission motor that is very sensitive to the winding current.

The main circuit is shown in Figure 1. The constant value of the lower arm current is fixed at twice the rated current of the phase winding 2I. Taking half-step operation as an example, in the 20 power-on states of 4-5 excitation, 4-phase excitation and 5-phase excitation are alternately performed. According to the ring-division control logic, it is not difficult to analyze that the basic structure of the steady-state equivalent circuit of the main circuit is 4 beats per cycle, so the single-step response characteristic is also 4 beats per cycle. The drive control of the hybrid stepper motor is mainly reflected in the control of the torque vector, and the winding current is directly related to the torque. Taking the positioning torque T generated by the rated current I of one-phase winding as the benchmark, the change law of the adjacent 4-beat winding current and its corresponding derived positioning torque vector is first analyzed.

The derived positioning torque vector is:

The derived positioning torque vector is

The derived positioning torque vector is
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From the above analysis, it can be seen that the derived positioning torque vector changes unevenly, which is manifested in different sizes, and the torque fluctuation is quite obvious. The maximum value is 2.15 times the minimum value; the phase change is also uneven, and the 5-phase excitation produces an additional step error. These factors are reflected in the obvious "strong" or "weak" or "heavy" or "light" steps when the stepper motor runs at low frequency, which aggravates the low-frequency oscillation of the motor, which is not conducive to low-speed operation. In addition, the uneven step angle also affects the pulse equivalent of the system.

If the constant current value of the lower bridge arm constant current chopper changes with the winding excitation state, the uniformity of the positioning torque vector change can be improved. The specific analysis is as follows.

Condition: The constant current value of the constant current chopper of the lower bridge arm of the B phase is 2I; the constant current value of the constant current chopper of the lower bridge arm of the D phase is 1.5I. The current of each phase winding Condition


: The constant current value of the constant current chopper of the lower bridge arm of the D phase is 2I; the constant current value of the constant current chopper of the lower bridge arm of the B phase is 1.5I. The current of each phase winding

Condition: The constant current value of the constant current chopper of the lower bridge arm of the D phase is 2I; the constant current value of the constant current chopper of the lower bridge arm of the A and E phases is I; the current of each phase winding

It is not difficult to see from the above analysis that the uniformity of the derived positioning torque vector change is greatly improved, the torque fluctuation is quite small, the maximum value is only 1.11 times the minimum value, and there is no additional step error.

According to the improved scheme, the constant current value of the constant current chopper of each phase lower bridge arm changes with the excitation state of the winding. When the lower bridge arm is turned on, there are three values ​​of I, 1.5I and 2I according to the different excitation states. The circuit is shown in Figure 3. The required current setting value is obtained by changing the resistor voltage divider value through switch switching. The analog switches k1a and k2a can be implemented using the CD4066 integrated circuit.

The resistance values ​​of resistors R?0 and R?1 can be determined by formula (1).
When k1ak2a=10, the threshold value of the comparator U "+" terminal is

The resistance value of resistor R3 can be determined by the above formula.
Table 1 is the switch truth table corresponding to the entire five-phase current control switch and the ring-dividing signal. When the lower bridge arm of a phase is not turned on, the logical value in the table is an arbitrary value. The switch truth table can be implemented by devices such as EPROM or CPLD in combination with the ring-dividing signal.