Bachelor thesis

Solar module optimizer

Arne Schmidt

Balcony power plant

Microinverter

MPP tracker

Free programmable?

Idea & motivation

Closed source

Own development

Microcontroller

Mircopython

Power electronics

Solar module optimizer

Concept

Maximum power point

Concept

Performance adjustment

Concept

Power adjustment

Concept

Power adjustment

Concept

Concept

Concept

Concept

Concept

Concept

Interactive with mouse and enter

Boost converter

Boost converter

Circuit diagram

Boost converter

.

On time $dT_{s}$

Boost converter

.

Turn-off time $(1-d)T_{s}$

Boost converter

Boost converter

Input resistance

Boost converter

max dutycycle $$ d_{max} = 1 - \frac{U_{in}}{U_{out}} = 1 - \frac{15V}{50V} = 0,7 $$

min dutycycle $$ d_{min} = 1 - \left(\frac{U_{in}}{U_{out}}\right) \cdot (1-d_{max}) \\ 1 - \left(\frac{30V}{15V}\right) \cdot (1-0,7) = 0,4 $$

Boost converter

Inductor $$ L = \frac{U_{max}d_{min}}{\Delta i_{L} f_{s}} = \frac{30V \cdot 0,4}{2,5A \cdot 50 kHz} = 96 \mu H $$

Output Capacitor $$ C_{out} = \frac{I_{out}D_{max}}{\Delta U_{out} f_{s}} = \frac{2A \cdot 0,7}{0,1V \cdot 50 kHz} = 280 \mu F $$

Implementation


first schematic

Implementation


final schematic

Microcontroller

Microcontroller

  • Raspberry Pi Pico RP2040
  • 26 GPIO Pins
  • 4 Analog-Digital-Converter
  • 16 pulse width modulation
  • big flash storage
  • greate documentation
  • Micropython

Mikrocontroller

Voltage measurement

Voltage measurement

Voltage divider

Voltage measurement

\[\begin{aligned} U_{out} = U_{in}\frac{R_{2}}{R_{1}+R_{2}} \\\\ 0V < U_{in/out} < 50V \\ 0V < U_{adc} < 3.3V \\\\ R_{1} = 36k \\ R_{2} = 2,2k \end{aligned} \]

Voltage measurement

Voltage measurement

Translate function ADC:

\[\begin{aligned} U_{digital} = U_{analog} \cdot \frac{U_{sys}}{Auflösung ADC} \end{aligned} \] 

							from machine import Pin, ADC

							adcScaleFac = 3.2 / 2**16
							voltDiv = 36 / 2.2

							adc1 = ADC(Pin(26))

							while(True):
								voltage = adc1.read_u16() * adcScaleFac * voltDiv
								print(voltage)

Current measurement

Current measurement

Hall effect sensor

Current measurement

Current measurement

Current measurement

Transferfunction:

\[\begin{aligned} U_{out} = I_{in} \cdot S + U_{out,0A} \end{aligned} \] 

							from machine import ADC, Pin

							adc = ADC(Pin(27))
							
							sensivity = 0.2 
							zero_current_output = 3.2 * 0.5
							adcScaleFac = 3.2 / 2**16
							
							while(True):
								voltage = adc.read_u16() * adcScaleFac
								current = (voltage - zero_current_output) / sensivity
								print(current)

Filter

Lowpassfilter

Lowpassfilter

Problem: noisey signal

$$ C_{filter} = \frac{1}{2\pi R_{filter} f_{c}} $$ $$ R_{filter} = 10k $$ $$ f_{c} = 75 Hz $$ $$ \rightarrow C_{filter} = 220 nF $$

Lowpassfilter

Software Filter

Pythoncode:


							class FilterAvg():
							def __init__(self, adc: ADC, samples: int):
								self.buf = 0.
								self.samples = samples
								self.adc = adc
						
							def calc(self):
								for sample in range(self.samples):
									self.buf += self.adc.read_u16()
								filtered = self.buf/self.samples
								self.buf = 0.
								return(filtered)

Mosfet and Driver

Mosfet and Driver

Mosfet and Driver

Pulse with modulation

Pythoncode:


							from machine import Pin, PWM

							pwm = PWM(Pin(6))  
							pwm.freq(50000)
							pwm.duty_u16(35000)

							enable = Pin(7, Pin.OUT)
							enable.on()
							
							def setDutyCycle(self, duty):
								'''Set mosfet dutycycle for boost converter'''
								self.duty = int(((100 - duty) / 100) * 65536)
								self.pwm.duty_u16(self.duty)

Snubbercircuit

Snubbercircuit

Snubbercircuit

Snubbercircuit

Note: poor picture Nyquist–Shannon sampling theorem violated

Implementation

Algorithms

Algorithms

Observe & Perturb

Algorithms

Observe & Perturb


							while(True):
								device.getfilteredADC()
								device.calcADCData()
								power_delta = device.power[0] - power_pre
								voltage_delta = device.voltage[0] - voltage_pre
								power_pre = device.power[0]
								voltage_pre = device.voltage[0]

								if power_delta >= 0:
									if voltage_delta > 0:
										device.vRef -= 1
									else:
										device.vRef += 1
								elif power_delta < 0:
									if voltage_delta > 0:
										device.vRef += 1
									else:
										device.vRef -= 1

								device.vRef = clamp(device.vRef)
								device.setDutyCycle(device.vRef)

Algorithms

Observe & Perturb

Interactive with mouse

Algorithms

VI-Scanner

Algorithms

VI-Scanner


							power_curve =[] 

							while(True):
								for duty in range(70):
									device.setDutyCycle(duty)
									time.sleep_ms(50)
									device.getfilteredADC()
									device.calcADCData()
									time.sleep_ms(50)
									power_curve.append(device.power[0])
									device.printOut()
									if device.voltage[0] < 12:
										print('Abbruch ', device.voltage[0])
										break

								power_max = max(power_curve)
								duty_max = power_curve.index(power_max)
								power_curve.clear()
								time.sleep_ms(500)
								devive.setDutyCycle(duty_max)
								print('power_max:{}W duty_max:{}'.format(power_max, duty_max))
								time.sleep(10)

Algorithms

VI-Scanner

Interactive with mouse

PV emulator

PV emulator

PV emulator

PV emulator

shaded

PV Emulator

shaded

PV emulator

Practical experiment

Perturb & Observe

not shaded

Perturb & Observe

shaded

VI-Scanner

not shaded

VI-Scanner

shaded

Thank you for your attention!