Choosing the appropriate sampling resistor for Microchip's dsPIC33EP series drone drive control system requires comprehensive consideration of multiple parameters such as resistance, power, accuracy, and packaging. The following are key parameters and suggestions compiled based on some practical application solutions.
The table below summarizes the core parameters of the sampling resistor in the FOC (Field Oriented Control) electrical tuning scheme for unmanned aerial vehicles based on dsPIC33EP32MC204.
| parameter category | Recommended parameters | Explanation and Interpretation |
|---|---|---|
| resistance value | 1mΩ | Choosing a low resistance value aims to reduce power consumption and heat generation, but it will generate weak voltage signals that require subsequent circuit coordination. |
| precision | ±1% | High precision resistors can ensure the accuracy of current sampling values, which is crucial for the control accuracy of FOC algorithms. |
| rated power | 3W | Actual power consumption needs to be calculated based on the maximum current of the system, with a margin left. For example, the power consumption at 44A peak current is about 1.9W, and the solution may use multiple resistors in parallel or rely on short-term overload capacity. |
| encapsulation | one thousand two hundred and twenty-five | A larger packaging size is more conducive to the heat dissipation of resistors. |
| Solution Type | Dual shunt resistor | Place a sampling resistor in each phase A and B, and calculate the current of the third phase. This method has better dynamic response and simpler algorithm than the single resistor scheme. |
In addition to the core parameters in the table, you also need to pay attention to the following points when finalizing and designing:
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Power calculation verification:
The actual power consumption of the resistor is P=I ² × R. Taking the recommended parameters as an example, at a peak current of 44A, the instantaneous power on a single resistor is (44A) ² × 0.001 Ω=1.936W, which is much higher than its rated power of 0.5W. This means that in practical design, either multiple resistors are connected in parallel to share power, or the short-term pulse overload capability of the resistors is relied upon (the peak current during drone operation is usually transient). You need to carefully evaluate and select the appropriate power resistor based on the continuous operating current and peak current duration of the ESC.
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Resistance type selection:
It is recommended to use non inductive wound resistors or metal sheet resistors. The parasitic inductance of this type of resistor is extremely low, which can avoid severe voltage spikes at high-speed PWM switching frequencies, thereby ensuring the authenticity of the sampled waveform.
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Layout and signal processing:
The PCB layout of sampling resistors is crucial.
- Kelvin Connection or four wire connection should be used to separate the current signal detection wiring from the power current path, in order to reduce measurement errors caused by the resistance of the connecting wires.
- Due to the small voltage drop across a 1m Ω resistor (e.g. only 10mV at 10A current), it is highly susceptible to noise interference. Therefore, it is necessary to place it close to the operational amplifier (such as OPA2191 mentioned in the scheme) and use differential routing as much as possible to reduce the interference of common mode noise.
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Error calibration:
Even if high-precision resistors are used, in actual production, due to factors such as PCB layout and soldering, there may still be gain and offset errors in the entire sampling channel. It is recommended to reserve a calibration interface in the software, for example, to calibrate the scaling factor of the entire system by measuring a known load current.
I hope the above information can help you choose the appropriate sampling resistor for the dsPIC33EP drone drive control scheme. If you could share more specific application scenarios (such as continuous operating current, target cost, etc.), perhaps I can provide more targeted suggestions.