Method and circuit assembly for current control in 3-phase motors
A method and circuit assembly are provided for controlling the motor current in an electric 3-phase motor, in particular in a 3-phase stepper motor, by a chopper process. For at least two of the three motor connections a respective chopper phase is cyclically activated, while a target motor current supplied for the motor connection in question is injected into the motor connection by a chopper process, while the two other motor connections are connected to each other.
1. Method for controlling the motor current in an electrical 3-phase motor, with a first, a second and a third motor connection, comprising
activating a first, a second and a third chopper phase in cyclically alternating fashion, wherein during each chopper phase the motor is connected between a supply voltage and ground, namely with one of the first, the second and the third motor connection and with two other motor connections of the first, the second and the third motor connection which are connected with each other, and
injecting, during at least two of the three chopper phases, a target current supplied for the one of the first, second, and third motor connection into the one of the first, second, or third motor connection by a chopper process, and
comparing, during each chopper phase, a supplied instantaneous motor target current for the one motor connection with a de facto instantaneous motor current at this motor connection, and activating, dimensioning, and combining through the chopper process, in dependence on a difference between these two currents, ON and FD motor current phases so that the de facto motor current follows the motor target current.
2. Method according to claim 1 , comprising connecting, during a chopper phase, either the one of the first, second and third motor connection with a supply voltage and the other two motor connections with each other to ground, or the one of the first, second and third motor connection to ground and the other two motor connections connected to each other with the supply voltage.
3. Method according to claim 1 , activating between two chopper phases an SD motor current phase by all three motor connections being connected with each other.
4. Method according to claim 1 , activating, during a chopper phase, only one motor current phase.
5. Method according to claim 4 , terminating a chopper phase and activating a next chopper phase when a motor current phase in the chopper phase is terminated by the chopper process.
6. Method according to claim 1 , wherein a frequency of switching from one chopper phase to the next is higher than a frequency of the supplied motor target currents.
7. Method according to claim 1 , wherein a sequence of activating the three chopper phases is chosen to coincide with a rotational direction of the motor.
8. Method according to claim 1 , comprising increasing the supplied instantaneous motor target current by a preset hysteresis before it is compared with the de facto instantaneous motor current.
9. Circuit assembly for controlling motor current in an electrical 3-phase motor with a first, a second and a third motor connection, comprising
a driver circuit controlled by a chopper, by which driver circuit a cyclic alternating switching takes place between at least two chopper phases, wherein during each chopper phase, in one of the motor connections of the first, the second, and the third motor connection, by a chopper process, a motor current is injected which corresponds to a motor target current which is supplied for the one motor connection, wherein two other motor connections of the first, the second, and the third motor connections are connected with each other via the driver circuit; and
a comparator with two inputs for comparing a de facto motor current with a supplied motor target current as well as an output that is connected with the chopper.
10. Circuit assembly according to claim 9 , comprising a first adder and an inverter for adding and inverting a supplied first and second motor target current (IsU, IsV) for generating the third motor target current (IsW) according to the formula IsW=−(IsU+IsV).
11. Circuit assembly according to claim 9 , comprising a multiplexer with three inputs, to which the first, the second and the third motor target current (IsU, IsV, IsW) are applied, as well as an output, which is connected to one of the inputs by means of a chopper switching signal for switching between the chopper phases.
12. Circuit assembly according to claim 9 , comprising a second adder for adding a hysteresis value to the supplied motor target currents.
13. Circuit assembly according to claim 9 , wherein, by the driver circuit controlled by the chopper, all three motor connections can be connected with each other between two chopper phases.