Presentation on theme: "Main Topics Main topics: Solar panel description and characteristics"— Presentation transcript:
0DC to AC Inverter for Solar Panel Stanislav Arendárik, (Aug 2010)
1Main Topics Main topics: Solar panel description and characteristics Main parameters of the inverterStructure and block schematic of the inverterBlocks description
2Solar cell simple description Photons in sunlight hit the solar panel and are absorbed by semiconductor material – silicon.Electrons (negatively charged) are knocked loose from their atoms, allowing them to flow through the material to produce electricity. Due to special composition of solar cell, the electrons are only allowed to move in a single direction.An array of the solar cells converts solar energy into a usable amount of direct current (DC) electricity.source: wikipedia
3Solar cell characteristics A solar cell may be modeled by a current source in parallel with a diode, shunt and series resistances.IL represents the max current of the solar panel (short current)Diode forms the I-V characteristicShunt resistor represents the leakage currents (very small)Series resistance represents the wiring losses
4Solar cell characteristics - variations For most crystalline silicon solar cells the change in VOC with temperature is about -0.50%/°CImpact of the product of the series resistor and short-circuit current (ISCRS) is about 25mV/cell.Impact of the parallel resistance is small.
5Solar cell characteristics example The maximum power point (MPP) on the I-V curve varies with real working conditions – high dependency on the irradiance and lower dependency on the temperature.
6Maximum Power PointIn the technical parameters of the solar cell panel are defined:VMP – voltage at MPPIMP – current at MPPThe Inverter for the solar cell panel must achieve the operation on the MPP. This method is called as MPPT – maximum power point tracking.The presented inverter has implemented the P&O (perturb & observe) algorithm for MPPT.To get maximum power from a PV panel required operating at the optimum voltage.
7Selected range of the solar panels The amount of the solar cells is used to build one solar panel. Usually 72, 36, or other.For this design was selected panel with 72 cells, this implies MPP at 36V, which fairly corresponds to 3 x 12V lead acid batteries in series as the back-up for the power source for the inverter. This battery is used as the energy accumulator for the off-grid inverter usage.The characteristic of the selected solar panel:PMAX = 180WVSC = 44.4VVMP = 36VISC = 5.25AIMP = 5A
9Main Parameters of DC to AC Inverter Input voltage sourceVoltage level from solar panel VMP = +36VSolar energy can be stored in Lead-Acid batteriesBattery charger can be implemented (phase 2)Selected 3 pcs Lead-Acid batteries in seriesOutput voltageThis design aims 1-phase 230V 50Hz (115V 60Hz optional);Single design, just different power components;Tolerance +5% to -10%;Output power400VA;Harmonic distortion of the output voltageLower than 3%;Fault ProtectionOutput over-current, over-voltage, short-circuit;Input under-voltage;Signal outputSerial link RS-485 to main system
10Block Diagram of DC to AC Inverter Block Diagram of InverterThe whole DC to AC inverter consists of main power parts:MPP Tracking for solar panel output – software implementedDC low voltage to DC high voltage converterDC high voltage to AC sine output voltage inverterOutput filterIsolated RS-485 lineAssociated control and fault detection circuitsBoth DC-DC converter and DC-AC inverter is controlled by one DSC MC56F8023.
11DC to DC ConverterPush-Pull type with bridge rectifier on the isolated secondary sideAdvantage:Simple transformer windingsSimple controlGood efficiencyMPPT algorithm integrated in the software control loop
12DC to DC Converter Push-Pull type control signals: The duty-cycle for the PWM1 and PWM2 has the same valueThe PWM2 control signal is shifted of T/2 later against the PWM1 signalThe actual duty-cycle value D depends on the actual power transferred through the transformer
13DC to AC Inverter Full-bridge type inverter Advantages: Simple +400V DCBus used to generate 230V ACSimple PWM controlSimple reconstruction filter for AC line outputCan be controlled by half-bridge drivers or isolated gate transformersPower MOSFETs or IGBTs can be used
14DC to AC Inverter Full-bridge type inverter control signals: The PWM3 and PWM4 are complementaryThe duty-cycle varies ideal from zero to full period in sine amplitude and power line frequencyReal duty-cycle varies from 5% to 95% of the periodWhen the duty-cycle is <50%, the negative part of the output sine voltage is generatedWhen the duty-cycle is >50%, the positive part of the output sine voltage is generated
15Output filter Integrated output EMI filter used Advantages: Compact standard designGood EMI propertiesSufficient load properties
16Auxiliary Power Supplies Auxiliary power supplies power the on-board circuitryThe HW comparator enables the first DC/DC converter if the input voltage is > 18V DC from PV panelIf the battery is connected, the inverter runs from battery and battery is charged by the solar panelThe main +12V DC power supply acts as the source for all other DC/DC convertersTwo isolated power supplies provide the power for the isolated secondary side of the inverterThe control DSC is placed on the primary low voltage sideIsolated circuitry
17Control circuits DSC MC56F8023 used Controls the DC/DC converter and DC/AC inverterMPPT software algorithm for the solar panel implementedBattery charger control – as optionRS-485 line interface for supervisor’s line communicationOutput over-current, over-voltage, short-circuit and input under-voltage fuses implementedON-GRID or OFF-GRID mode
18Inverter view Battery connector Low power DC-DC converters For control circuitrySolar PanelConnectorsBatterypresentrelayFull-Bridge Inverter+ L-C FilterPush-PullPrimary sideDSC MC56F8023Control BoardDCBus +400VPowerOutputOutput FilterRS-485 LineBattery Charger HW
19Conclusion One standard DSC MC56F8023 used for whole inverter control Possibility of use as the ON-GRID or OFF-GRID connected inverterPossibility of use of wide range of the solar panels:One piece of the 36V type with the output power up to 450WTwo pieces of the 18V types in series with the total output power up to 450WInverters can be connected in parallel at the output to boost the output power in the OFF-GRID usageThe inverter starts run when the sufficient amount of the power is available from the solar panel (if battery not connected)The 3 x 12V lead-acid batteries in series are used as the energy accumulator
20DEMO Connection DEMO Start-up sequence: Switch OFF both switches (down position)Connect load bulb (60W to 100W) at outputConnect the solar panelThe green LED shines, red LED notPut OFF-GRID switch “ON” (up position)Switch ON the main switchThe “Fault” LED indicates the over-current – when shines, switch OFF the main switch, wait about sec and switch ON the main switch.