MOTOR CONTROL PROCESSING WITH A FLAT PULSE WIDTH MODULATION SCHEME

Abstract

The invention relates to a motor control processing unit for a motor control device which comprises a voltage source inverter unit, configured to control the voltage source inverter unit to provide a motor voltage following a pulse-width modulation, PWM, scheme, wherein the motor control processing unit is configured to control the voltage source inverter unit according to a flat PWM scheme, which comprises a flat-bottom or flat-top PWM scheme, at least at some times in order to provide a precise motor control with minimized losses. The invention also relates to a corresponding method.

Claims

1. A motor control processing unit for a motor control device having a voltage source inverter unit, the motor control processing unit configured to control the voltage source inverter unit to provide a motor voltage by using a pulse-width modulation (PWM) scheme, characterized in that: the motor control processing unit is configured to control the voltage source inverter unit according to a flat PWM scheme, which comprises a flat-bottom or flat-top PWM scheme, at least at some times.

2. The motor control processing unit according to claim 1, characterized in that: the motor control processing unit is configured to automatically activate and/or deactivate the flat PWM scheme at runtime.

3. The motor control processing unit according to claim 1, characterized in that: the motor control processing unit is configured to activate and/or deactivate the flat PWM scheme in dependence upon a parameter representing an operating condition, in particular a measured value.

4. The motor control processing unit according to claim 3, characterized in that: the motor control processing unit is configured to activate the flat PWM scheme if the parameter representing the operating condition is equal to or greater than a preset value, and to deactivate the flat PWM if the parameter representing the operating condition is smaller than the preset value.

5. The motor control processing unit according to claims 3, characterized in that: the motor control processing unit is configured to activate and/or deactivate the flat PWM scheme with a delay, where the delay can be given by a preset amount of time and/or by another operating condition.

6. The motor control processing unit according to claim 1, characterized in that: the motor control processing unit is configured to set the duty cycle provided by the voltage source inverter unit in dependence upon a first time constant characterizing the rising edge of the duty cycle and/or a second time constant characterizing the falling edge of the duty cycle.

7. The motor control processing unit according to claim 6, characterized in that: the motor control processing unit is configured to set the duty cycle such that, in each PWM cycle, an integral of the voltage provided by the voltage source inverter unit over time depends linearly on the voltage commanded by the motor control processing unit for any value of the voltage commanded by the motor control processing unit.

8. A motor control device with a voltage source inverter unit and a motor control processing unit according to claim 1, or a motor device with such a motor control device and/or with such a motor control processing unit.

9. A robotic device with the motor control device or motor device of claim 8.

10. A method for controlling a motor control processing unit of a motor control device with a voltage source inverter unit, comprising: controlling the voltage source inverter unit to provide a motor voltage following a pulse-width modulation, PWM, scheme, using a flat PWM scheme, which is a flat-bottom PWM or a flat-top PWM scheme, as PWM scheme at least at some times.

11. The motor control processing unit according to claim 3, wherein the operating parameter is one or more of a measured velocity, a measured power output, a measured temperature, or a setpoint.

12. The motor control processing unit according to claim 3, wherein the setpoint is one or more of a torque setpoint, a velocity setpoint, or a power setpoint.

Description

[0034] Exemplary embodiments are further described in the following by means of schematic drawings. Therein,

[0035] FIG. 1 shows an exemplary embodiment of a motor control processing unit in a motor control device with a motor; and

[0036] FIG. 2, shows an illustration of exemplary commanded voltage and exemplary voltage generated with an ideal voltage source inverter unit, and exemplary voltage generated with a real voltage source inverter unit.

[0037] In FIG. 1, a motor control processing unit 1 is part of a motor control device 2 that is connected to a three-phase motor 3, via respective terminals a, b, and c. The motor control device 2 further comprises a voltage source inverter unit 4 that is configured to provide a motor terminal voltage comprising three motor terminal voltages via the terminals a, b, c following a pulse width modulation, PWM, scheme. The motor control device 2 is connected to a power line d and also features a control terminal e to control the motor control processing unit 1. The motor control processing unit 1 is configured to control the voltage source inverter unit 4 according to normal PWM scheme or flat PWM scheme, in the present case either a flat-bottom PWM scheme or a flat-top PWM scheme, at least at some times of the operation of the motor 3.

[0038] FIG. 2 depicts the exemplary course of the voltage over time during one PWM period at one of the terminals a, b, c of the motor 3.

[0039] In the first panel a) of the present example, during the duty cycle characterized by T.sub.DUTY, the voltage is set to the DC link voltage V.sub.DC. Apart the duty cycle, the voltage is set to ground GND in the PWM period T.sub.PWM. The course A of the voltage V over the time t in the first panel a) indicates the commanded voltage at a respective inverter unit output terminal in the known state of the art, which should be achieved in order to arrive at an intended course of the motor current, for example a sinusoidal course, in motor 3.

[0040] The second panel b) shows the course B of the voltage V over time t corresponding to the top panel generated with an ideal motor control device, namely a motor control device with an ideal voltage source inverter unit, that is, a voltage source inverter unit with ideal switching components in which the switch turns on an off immediately and with 0 delay. Note that, evidently, the integral of the generated voltage V over time t in panel b) depends linear on the commanded voltage V of panel a).

[0041] The third panel c) shows an exemplary voltage generated in a real voltage source inverter unit, that is, a voltage source inverter unit for with real switching components. The course C of the voltage V in the third panel therefore features two areas X, X′ where the integral of the generated voltage V over time t is not linearly dependent from the commanded voltage V of panel a). This is due to a finite first time constant characterizing the rising edge Y of course C of the voltage V (at the start of the duty cycle) and a finite second time constant characterizing the falling edge Y′ of course C of the voltage V (at the end of the duty cycle). As the time constants are not equal in the shown example, both effects do not cancel out each other, resulting in a deviation between actual motor current and commanded motor current. So, said non-linearity leads to higher motor current ripples and motor current disturbances.

[0042] These effects are minimized by adjusting the effective duty cycle T′.sub.DUTY based on the respective first and second time constants such that the integral over time over one PWM period in panel c) matches the integral of the duty cycle the duty of the commanded voltage shown in panel a). So, the commanded voltages as known from the state of the art are used as a basis for the computation of the required or effective duty cycles for the inverter units’ switching components in a way that the integral of the real generated voltage is linear with the commanded voltage.