Department Of Electrical And Computer Engineering Design and Control of Photovoltaic inverter For Microgrid Application 3. MICROGRID POWER SYSTEM MODEL   3.1 DC boost converter DC boost converter can be used in a PV system, for stepping up the output voltage of PV array at a higher level, according to the requirement of connected loads. It consists of various elements like IGBT switch, diode, and inductor. The implementation of MPPT control in the boost converter varies the duty cycle of converter switch to generate an optimum reference voltage according to MPP condition. 3.2 Lead acid battery storage Battery storage plays an important role in residential level stand-alone microgrid power system, to provide reliable energy supply and backup power support in case of less or no PV power generation. 3.3 DC Bi Directional Charger Control DC bi-directional converter controls dc bus voltage at a steady level by permitting the battery to charge in case of excessive PV power generation and discharge during deficit or absence of PV power generation. The converter control system consists of two control loops; Voltage control loop with a PI controller which manages the voltage error signal and Current loop actuates buck switch (IGBT) during charge and boost switch (IGBT) during discharge condition. In this way, the two IGBT switches can be worked in corresponding with one Pulse Width Modulation (PWM) signal. To stay away overcharge or undercharge conditions of battery, the charge controller detaches the battery from the system when SOC is either more prominent than 80% or less than 30 3.4 Maximum power point Track (MPPT) control The I-V curve determines the performance characteristics of a PV cell. A convergence point in the I-V curve which the PV cell produces the greatest power for given sun oriented irradiance and cell temperature at specific electrical load is called as Maximum Power Point (MPP). To concentrate most extreme power from PV cell is a Perturb and Observe MPPT control algorithm was considered and executed in Simulink base PV model. The P&O MPPT control adjusts the PV array voltage as indicated by MPP voltage, 3.5 DC – AC Inverter A power inverter is an electronic device that changes direct current (DC) to alternating current (AC)   4 Maximum Power Point Tracking Algorithms(MPPT) : Figure 6 : P-V characteristics curve of photovoltaic cell [1] 4.1.1 Perturb & Observe Perturb & Observe (P&O) is the most straightforward technique. In this we utilise one and only sensor, that is the voltage sensor, to detect the PV array voltage thus the cost of execution is less and henceforth simple to implement. The time complexity of this calculation is less however on achieving near the MPP it doesn't stop at the MPP and continues perturbing on both the directions. At the point when this happens, the calculation has achieved near the MPP and we can set an appropriate error limit or can utilise a wait function which ends up increasing the time complexity of the algorithm. However, the strategy does not assess the fast change of irradiation level (because of which MPPT changes) and considers it as a change in MPP because of perturbation and ends up calculating the wrong MPP. To stay away from this issue we can utilise incremental conductance technique. 4.3 Perturb & Observe Algorithm The Perturb & Observe algorithm states that when the operating voltage of the PV panel is perturbed by a small increment, if the resulting change in power ∆P is positive, then we are going in the direction of MPP and we keep on perturbing in the same direction. If ∆P is negative, we are going away from the direction of MPP and the sign of perturbation supplied has to be changed.[1] Figure 7: Solar panel characteristics showing MPP and operating points A and B[1] The figure shows the plot of module output power versus module voltage for a solar panel at a given irradiation. The point marked as MPP is the Maximum Power Point, the theoretical maximum output obtainable from the PV panel. Consider A and B as two operating points. As shown in the figure above, the point A is on the left-hand side of the MPP. Therefore, we can move towards the MPP by providing a positive perturbation to the voltage. On the other hand, point B is on the right-hand side of the MPP. When we give a positive perturbation, the value of ∆P becomes negative, thus it is imperative to change the direction of perturbation to achieve MPP.   Appliances Rating Daily time of use Qty Daily use (Wh/day) Refrigerator 602kWh/year Whole day 1 1650 (300W) Freezer 88W Whole day 1 880 Electrical Stove 2100W 1-2hrs 1 2100 Microwave Oven 1000W 30 min to 1 hr 1 500 Rice cooker 400W 30 minutes 1 200 Toaster 800W 10 - 30 minutes 1 80 Ceiling Fan 65W 4 -5 hrs 5 1300 Fluorescent light 16W 6 - 8 hours 20 320 Washing machine 500W 1hr/week 1 71 Vacuum Cleaner 1400W 1hr/week 1 200 Air conditioner 1200W 1hr 3 1200 (Window) TV 32" LCD 150/3.5W 4 hrs 1 670 DVD player 17/5.9W 2 hrs 1 50 Cordless phone 4W Whole day 1 96 Computer 20W 4 - 5hrs 1 80 (Laptop) Clothe iron 1400W 15 - 30 minutes 1 350 Heater (Portable) 1200W 30 minutes 1 600 Hot Water System 1800W 3- 4 hrs 1 5400 Total: 15,747 5. Estimation of daily residential load   6. Sizing of Solar PV arrays : - Total Energy Consumption = 15.747 kwh/day 6.1 PV array Capacity [3] : - KWp = El/(S.W X Bη X conv.η X CT X CD ) equation (7) [3] El =daily energy consumption = 15.747 kwh/day S.W = Solar Window = 8 Bη = Battery Efficiency = 0.80 CT= cell Temperature factor = 0.88 Conv.η = efficiency of converter = 0.90 CD = Cell de-rate factor = 0.90 KWp = (15.747 kw)/(8 X 0.80 X0.88 X 0.90 X 0.90) KWp = 3.452 kw 6.2 PV module calculation[3] : - Max. voltage = Vmax = 48.3 V Max. current = Imax = 4.54 A Max. Power (Pmp) = 48.3 x 4.54 = 219.28 W No. of module = (PV array Capacity)/(Max Power) equation (8) [3] No. of module = (3.452 kw)/(219.28 ) No. of module = 15.74 We will consider the no. of module = 16 We will consider 2 modules in series per string and 8 strings in parallel 2 modules series x 8 strings in parallel = 16 6.3 Size of battery storage [3] : - Battery Capacity = (El x Dn)/(DoD X Batt.η X Inv.η X Batt.v) equation (9) [3] El =daily energy consumption = 15.747 kwh/day Dn= no. of day autonomy = 1 DoD = depth of discharge = 0.80 Inv.η = inverter efficiency = 0.95 Batt.v = Battery Voltage = 48v Batt.η = Battery Efficiency = 0.8 Battery Capacity = (15.747 X 1)/(0.80 X 0.80 X 0.95 X 48) Battery Capacity = 539.57 Ah Each lead acid battery with specification is 12V and 120Ah We will consider = 4 batteries in series and 5 strings in parallel Total bank Capacity = 600Ah   7. Simulation model: - figure 13 : Matlab/Simulink model of Photovoltaic System[16]