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The first is to consider reducing or adapt the power supply voltage, given that current ripple is directly proportional to this voltage. It is important, therefore, to keep current ripple as low as possible, and there are a number of ways in which we can do this.
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Iron losses have a direct impact on motor power, and it is easy to see, being a squared relationship, how a high ripple current can quickly generate significant iron losses.
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The ripple current also causes iron losses, forming circulation eddy currents that are proportional to the square of motor speed and to the square of motor current.
#BLDC TOOL PWM PORTABLE#
Since there are no brushes the ripple current doesn’t compromise the lifetime of the brushless DC motor as it would in a brushed DC motor, but it wastes energy (potentially compromising battery life in portable applications) and may require a heat sink, adding size and weight to the application. While the average current – established by the duty cycle of the switching electronics – defines the motor torque, the ripple current generates extra Joules losses (heat) and can have huge impact on the RMS (root mean square) current, without any corresponding increase in torque. Most notably, the switching on and off of the transistors leads to current rise and fall at each cycle, which can be problematic. It is useful, however, to understand some other basic physical phenomena to avoid unexpected performance issues. The switching frequency is a fixed parameter, making it easy for electronic designers to filter acoustic and electromagnetic noise generated. Most commonly, chopper amplifiers use a PWM (pulse width modulation) method, varying the duty cycle at a fixed frequency to adjust the voltage or current within the desired target value. This helps save on the battery life of the application, causes less heating and allows a smaller size of the electronics. The primary advantage is that it saves power when the transistor is off. In contrast, a chopper amplifier modulates the voltage (and current) by switching on and off the power transistors. It dissipates the power which is not delivered to the motor, resulting in the need for a large heat sink to dissipate the power, increasing the amplifier size and making it more difficult to integrate into the application. A linear amplifier adapts the power delivered to the motor by linearly changing the voltage or current. There are a number of different options for the amplifier. In any brushless DC motor driven system, the role of the control electronics, the amplifier, is to vary the supply voltage or the current, or both, to achieve the desired motion output of the motor. To solve this problem, I thought that I could use one PWM output of the PIC and a CMOS High speed 2 input 1 output AND gates, I would connect one input of each gate to the PWM output from PIC16F887, and each second input of each AND gate to one of the PIC pins so that when I would like that a gate outputs the PWM signal, the microcontroller should only drive highthe second input that is connected to it's pin.Schematic cross-section of a slotless brushless DC motor starting step 3. But the problem is that PIC16F887 has only two PWM outputs that are not independant. So, there should be only two PWMs activated at the same time, and also 6 PWM combinations possible, the PWMs should be independant. Since two windings are being driven at the same time, one High and one Low, there should be 6 possible current paths, phases are named A, B and C, so the six possible paths are: A to B, A to C, B to C, B to A, B to C, C to A. I'm using a PIC16F887 that has two CCP modules, I would like to drive a BLDC motor using PWM, this requires 6 PWM of same frequency and same duty.