Software implementation
The implementation of the software is the next important step for the development of the solar module optimizer. In this chapter we will look at how the software for the module optimizer is developed and implemented. The software is intended to control the RP2040 microcontroller so that the system is able to sample measurement data, process it, and be able to control the keying time.
In particular, the Micropython programming language and the required libraries will be discussed. The implementation is described in sections for the respective peripherals and the individual functions of the software are explained. The listings of the Micropython code are described in the text but shown without comments, this is based in the trivial properties of Micropython and the clarity. In order for the algorithm to access the peripherals of the microcontroller, a class MPPTController is created in Listing using object-oriented programming. These make it possible to define various methods and attributes.
Listing Controller Class
@singleton
class MPPTController():
''' Hardware abtraction layer for MPPTController'''
def __init__(self):
self.pwm = PWM(Pin(6, Pin.OUT))
self.pwm.freq(50000)
self.sd = Pin(7, Pin.OUT)
self.adc1 = ADC(Pin(26, Pin.IN))
self.adc2 = ADC(Pin(27, Pin.IN))
self.adc3 = ADC(Pin(28, Pin.IN))
self.adc4 = ADC(Pin(29, Pin.IN))
self.filter1 = FilterAvg(adc=self.adc1, samples=150)
self.filter2 = FilterAvg(adc=self.adc2, samples=150)
self.filter3 = FilterAvg(adc=self.adc3, samples=150)
self.filter4 = FilterAvg(adc=self.adc4, samples=150)
self.filtered = [0.,0.,0.,0.]
self.voltage = [0.,0.]
self.current = [0.,0.]
self.power = [0.,0.]
self.duty = 0
self.vRef = 0.
self.pid = PID(scale='ms')
The MPPTController class is implemented as a singleton to ensure that only one instance of this class exists to access the hardware. The singleton design pattern avoids collisions and inconsistencies when accessing the hardware resource and improves structure and maintainability.
In addition, implementation as a singleton provides the advantage of encapsulation between the peripheral and the algorithm that contains the logic for finding the MPP. The MPPTController class provides a hardware abstraction layer for the MPPT controller, and the device instance is later created from it. The attributes of this class provide access to various hardware components such as the PWM, a shutdown option SD, and four ADC, each of which is associated with a filter to ensure a noise-free signal.
In addition, the class has attributes for storing measured quantities such as voltage, current, power, and duty cycle. The voltage, current, and power are each stored for the input side and the output side respectively. In addition, a PID is initialized to regulate the output voltage to the setpoint vRef passed by the MPPT algorithm.