"The conceptual model of the buck converter is best understood in terms of an inductor's "reluctance" to allow a change in current. the load (not shown) -> the motor (with resistance and induced voltage).the capacitor C -> no direct correspondence (but you can think of EMI filter and CLL).the inductance L -> the total inductance (in power stage, motor choke and motor). the diode D -> the diodes of the power stage.the switch S -> the MOSFETs of the power stage.the output voltage V o -> the voltage applied to the motor U mot.the input voltage V i -> the constant supply voltage V cc of the controller.Slightly simplified, a PWM power stage is essentially a step-down DC-DC converter or Buck converter. Do not use the supply current for calculating the heating or torque of the motor. The most important result is that motor currents should be measured at the output of the controller's power stage. The motor voltage depends on the required speed and the load and is controlled by the PWM duty cylce D=(t on /(t on + t off). Since no energy is stored, we have (except for the losses): P in = P out or I cc = (U mot/V cc) * I mot. Power conversionīasically, a PWM power stage is a power converter that transforms the input power of the supply P in = V cc * I cc into an output power that is applied to the motor P out = U mot * I mot. PWM power stages act similar to power transformers. Thus it is wise to measure the motor current at the controller output and not at the power supply.
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