Improvement in battery charging system in Solar Charge Controller-A Case Study

TECHNOLOGY ISSN (O) :- 2349-3585

Improvement in battery charging system in Solar Charge Controller-A Case Study

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Akash Kadam ¹ ,Chandrakant Shinde ²

Electrical Department, Yadavrao Tasgaonkar College of Engineering & Management, Karjat, Maharashtra , India

ABSTRACT:This paper presents an intelligent solar charging system control method. With the scarce energy source and the worsening environmental pollution, how to create and use a clean and never exhausted energy is becoming very important day by day. This solar charging system is composed of a solar cell, a charger, batteries, a buck converter and a digital signal processor. PV modules are increasingly used in battery charging applications in home inverter systems due to the power crisis faced in developing countries. This work aims at maximizing the use of solar energy by charging the battery as well as by supplying it to the loads when in excess. This system is implemented using two subsystems namely a charge controller and a Power Flow Management System (PMS).

The charge controller is used to control the power flow from the PV module to the battery by operating in two modes. The Maximum Power Point Tracking mode (MPPT) extracts maximum power from PV panels and the Voltage Control Mode prevents overcharging of the battery.

Keywords: PV modules, The Maximum Power Point Tracking mode (MPPT), PWM charge controller

1.INTRODUCTION

Charge controllers manage interactions and energy flows between a PV array, battery, and electrical load. Limits the rate at which electrical current added from electrical batteries.

It prevent overcharging & may prevent against overvoltage, which can be improve battery performance to use of Charge controller. PWM and MPPT charge controllers are both widely used to charge batteries with solar power. The PWM controller is in essence a switch that connects a solar array to the battery. The result is that the voltage of the array will be pulled down to near that of the battery.The MPPT controller is more sophisticated (and more expensive): it will adjust its input voltage to harvest the maximum power from the solar

array and then transform this power to supply the varying voltage requirement of the battery plus load. Thus, it essentially decouples the array and battery voltages so that there can be, for example, a 12 volt battery on one side of the MPPT charge controller and panels wired in series to produce 36 volts on the other. It is generally accepted that MPPT will outperform PWM in a cold to temperate climate, while both controllers will show approximately the same performance in a subtropical to tropical climate. In this paper, the effect of temperature is analyzed in detail, and a quantitative performance comparison of both controller topologies is given.

2. SYSTEM DESCRIPTION

Some charge controllers are relay-operated. These charge controllers seldom meet the exact requirements of PV systems and their current flow capabilities are also not good. So in this case PIC microcontroller based designs are favorable for intelligent control with an internal program written in it.

Fig -1: A typical standalone system showing a solar charge controller.

Fig -1 shows a typical standalone PV system. There are two

switches in a charge controller. The first switch is used for the

connection or disconnection between the PV array and battery

and the second switch is used for the connection or

disconnection between battery and the load. Now when the

first switch connects, the battery starts charging. When the 2nd

switch connects, the battery starts discharging. When both the

switch is connected the system is in the charging and

discharging mode state. To eliminate overcharge and over discharge, resulting from the oscillatory process, hysteresis control has been introduced into the circuit so that the array will not reconnect to the batteries until the batteries have discharged somewhat or load will not reconnect to the batteries until the batteries have some prescribed voltage left.

The Sulfation effects occur when a battery is fully charged frequently. Proper battery and array sizing with the periodic equalization charges can reduce the onset of sulfation effects.

A. STAND-ALONE CHARGE CONTROLLERS

Charge controllers are sold to consumers as separate devices, often in conjunction with solar or wind power generators, for uses such as RV, boat, and off-the-grid home battery storage systems. In solar applications, charge controllers may also be called solar regulators. Some charge controllers/solar regulators have additional features, such as a low voltage disconnect (LVD), a separate circuit which powers down the load when the batteries become overly discharged (some battery chemistries are such that over-discharge can ruin the battery). A series charge controller or series regulator disables further current flow into batteries when they are full. A shunt charge controller or shunt regulator diverts excess electricity to an auxiliary or "shunt" load, such as an electric water heater, when batteries are full. Simple charge controllers stop charging a battery when they exceed a set high voltage level, and re-enable charging when battery voltage drops back below that level. Pulse width modulation (PWM) and maximum power point tracker (MPPT) technologies are more electronically sophisticated, adjusting charging rates depending on the battery's level, to allow charging closer to its maximum capacity. A charge controller with MPPT capability frees the system designer from closely matching available PV voltage to battery voltage. Considerable efficiency gains can be achieved, particularly when the PV array is located at some distance from the battery. By way of example, a 150 volt PV array connected to an MPPT charge controller can be used to charge a 24 or 48 volt battery. Higher array voltage means lower array current, so the savings in wiring costs can more than pay for the controller. Charge controllers may also monitor battery temperature to prevent overheating. Some charge controller systems also display data, transmit data to

remote displays, and data logging to track electric flow over time.

B. INTEGRATED CHARGE CONTROLLER CIRCUITRY

Circuitry that functions as a charge regulator controller may consist of several electrical components, or may be encapsulated in a single microchip, an integrated circuit (IC) usually called a charge controller IC or charge control IC.

Charge controller circuits are used for rechargeable electronic devices such as cell phones, laptop computers, portable audio players, and uninterruptible power supplies, as well as for larger battery systems found in electric vehicles and orbiting space satellites.

a. Why need of charge controller:-

1. Open cell batteries can lose water quickly if overcharged. If electrolyte falls below the top of the plates, damage occurs.

2. Sealed batteries may be ruined if frequently overcharged.

3. To prevent damage to batteries from excessively deep discharge (purpose of discharge control).

b. Causes of controller failure:-

1. Nearby lightning strikes. The controller switch is directly in the path of induced voltages in the long wire connecting the panel and the battery.

2. High temperatures caused by blocking the ventilation around the controller or placing it in a hot location

3. Damage by technicians and users 4. Insect damage

5. Corrosion of circuit boards due to poor design associated with salt exposure, high humidity and high temperatures.

c. Voltage drop:-

1. Long conductors between a charge controller and a battery bank have resistance that causes voltage drops. Voltage drops affect the voltage measured by the charge controller.

2. There should NEVER be more than 2 meters (6 feet) of wire connecting the controller to the battery and if possible, it should be shorter than that. The wire should be the same size as the panel wire or larger.

3. Longer wires between the battery and controller result in inaccurate sensing of battery voltage by the controller and improper operation.

d. Protection scheme:-

1. over charge protection

Charge controllers protect batteries from overcharge by terminating or limiting charging current.

2. over discharge protection

Charge controllers protect batteries from over discharge by controlling discharge current.

3. Diversionary charge protection

a diversionary charge controller regulates charging current by diverting excess power to an auxiliary load when the battery is fully charged.

4. Hybrid charge protection

Charge controllers designed for hybrid pv systems must manage multiple current source simultaneously.

5. Equalization charge protection

The equalization set point brings the battery voltage to a level that is higher than the normal charge regulation voltage.

3. BASIC TYPES OF CHARGE CONTROLLER 1. SHUNT CONTROLLER:-

Placed between the panels and the battery. To prevent overcharge, the output from the panel is shorted by the controller using a semiconductor switch Because the panel wires go to the battery, a blocking diode has to be installed or shorting the panel output would also short the battery.

Fig.2- shunt controller Advantage-

1. Simple and cheap. Lends itself to local production

2. Less likely to be damaged by excess current flow than series switching control.

Disadvantage-

1. All the panel power is shorted through the controller and

converted to heat. So large panels generate a great deal of heat and it is a problem to get rid of it. Shunt controls are therefore best suited to small (under 50Wp) PV systems.

2. Sensitive to lightning.

3. Requires a blocking diode with its attendant power loss.

2. SERIES CONTROLLER:-

Placed between the panels and the battery. A transistor switch or a relay is used to disconnect the panel from the battery so overcharging cannot occur.

Fig.3.-series controller 4. BATTERY CHARGING SYSTEM

Single-stage battery charging is simpler to manage, but multistage battery charging brings battery to a higher state of charge.

i.Multiple Arrays:-

Larger PV system often use independent charge controllers for each array source circuit.

ii.Battery Banks With Charge Controllers:-

Separate charge controllers are usually recommended for charging independent battery banks.

iii.Battery Banks with One Charge Controller:-

In some cases, a single charge controller may be used to charge independent battery banks.

iv.Battery Temperature Sensors:-

Temperature probes are placed between batteries and connect

to a charge controller to compensate for the charge regulation

set point.

Fig.4- battery charging system A. MPPT TECHNOLOGY

MPPT Solar Charger Controller is a system with advanced MPPT (Maximum Power Point Tracking) Technology. The term “charge controller” refers either to a stand-alone device or a control circuitry integrated within a battery pack, battery- powered solar device or a battery recharger. This photovoltaic charge controller is the key component in off-grid or stand- alone solar power generation systems. It can track the maximum power point and transfer energy to various types of batteries. The build-in MPPT microprocessor enables the Solar Charge Controller to increase the energy transfer efficiency by upto 30% compared to traditional charge controllers. Easy installation with parallel connection capability makes MPPT Solar Charger Controller the perfect solution for your home as well as any large solar system application. Solar Charger Controller’s MPPT technology operates in a unique fashion. It calculates the maximum power voltage (V) at which the PV module delivers maximum power, and then the MPPT operates the module at a level, which extracts the maximum available power. The Solar Charger Controller continuously recalculates the maximum power voltage according to the changing operating conditions.

MPPT Controllers converts excess voltage into average.

Converting excess voltage into Amps, the charge voltage can be kept at an optimal level while the time required to charge the battery is reduced.MPPT Solar Charger Controller also regulates the rate at which electric current is added to or drawn from batteries. It prevents overcharging, over and variable voltage which if not controlled can reduce battery performance or life span and may pose a safety risk. It also prevents complete drainage (”deep discharge”) of a battery and facilitates controlled discharge thereby maintaining the battery’s longevity. Equipped with Micro controller and Digital Signal Processing (DSP) technology MPPT Solar Charger Controller is fully protected against transient over voltage and reverse the current flow, and can charge any type of battery.

Fig.5- charging system MPPT Protection against various parameters:- 1. Solar /battery reverse polarity.

2. Reverse current flow battery to solar array during night 3. Over charging current and short circuit.

4. Output over voltage

5. Excessive temperature of heat sink Features:-

1. Intelligent microprocessor control.

2.Silent, solid-state pulse Width Modulation (PWM Charging) process

3.User selectable configuration 12Vor 24V or 48 V configuration

4. Test point allows precise adjustment of settings 5. Electronic over current protection

6. Communication interface with PC or LCD modular for data

logging or parameter display

7. Protection against various parameters

8. Potentially increase the charging efficiency by 30%

9. Real time sensing of voltage and current to optimize charging.

Application:- 1. Solar portable light 2. Solar Home systems 3. Roof top solar solutions B. PWM TECHNOLOGY

Solar Charger Controller is a system with advanced MOSFET based PWM Technology. The term “charge controller” refers either to a stand-alone device or a control circuitry integrated one within a battery pack, battery-powered solar device or a battery recharger. The controller is for off-grid solar systems.

This protects the battery from getting over charged using the solar module and over discharged by the loads. The charging process has been optimized for long battery life and improved system performance. The comprehensive self-diagnostics and electronic protection functions prevent damage from installation mistakes or system faults.

Fig. 6- Chrging system of PWM FEATURES:-

1. Excellent EMC design

2. Nominal system voltage automatic recognition

3. High efficient Series PWM charging, increases battery life and improves the solar system performance

4. Use MOSFET as an electronic switch, without any mechanical switch

5. Widely used, automatically recognizes day/night

6. Graphics dot-matrix LCD screen and HMI (human-machine interface) with 4 buttons, integrated menu display and operation

7. Humanized design of browser interface, for convenience of operation

8. Full control parameters setting and modification, diversified load control mode

9. Gel, Sealed and Flooded battery type options

10. Adopt temperature compensation, correction algorithm for charging and discharging parameters automatically and improve battery life

11. Electronic protection from overheating, overcharging, over discharging, over load, and short circuit.

12. Reverse protection: any combination of solar module and battery.

5. RESULT & SOLUTION

The solution to improve MPPT controller performance at high cell temperatures is to increase panel voltage by increasing number of cells in series. Obviously, this solution is not applicable to PWM controllers: increasing the number of cells in series will reduce performance at low temperature. In case of the MPPT controller: replace the 12 V / 100 W panel by a 24 V / 100 W panel or by two 12 V / 50 W panels in series.

This will double the output voltage and the MPPT controller

will charge a 12 V battery with 66 W (5,1 A @ 13 V), at

100°C cell temperature. An additional advantage: because the

panel voltage has doubled, the panel current is reduced by half

(P = V x I and P has not changed but V has doubled). Ohm’s

law tells us that losses due to cable resistance are Pc (Watt) =

Rc x I², where Rc is the resistance of the cable. What this

formula shows is that for a given cable loss, cable cross

sectional area can be reduced by a factor of four when

doubling the array voltage. When using an MPPT charge

controller there are two compelling reasons to increase the PV

voltage (by increasing the number of cells in series): a)

Harvest as much power as possible from the solar array, even

at high cell temperature. b) Decrease cable cross sectional area

and therefore decrease cost. MPPT controller besides

performing the function of a basic controller, an MPPT

controller also includes a DC-to-DC voltage converter,

converting the voltage of the array to that required by the

batteries, with very little loss of power. An MPPT controller

attempts to harvest power from the array near its Maximum

Power Point, whilst supplying the varying voltage

requirements of the battery plus load. Thus, it essentially decouples the array and battery voltages, so that there can be a 12 volt battery on one side of the MPPT charge controller and two 12 Vpanels wired in series to produce 36 volts on the other. If connected to a PV array with a substantially higher nominal voltage than the battery voltage, an MPPT controller will therefore provide charge current even at very high cell temperatures or in low irradiance conditions when a PWM controller would not help much. As array size increases, both cabling cross sectional area and cable length will increase. The option to wire more panels in series and thereby decrease current, is a compelling reason to install an MPPT controller as soon as the array power exceeds a few hundred Watts (12 V battery), or several 100 Watts (24 V or 48 V battery).An MPPT charge controller is therefore the solution of choice:- a) If cell temperature will frequently be low (below 45°C) or very high (more than 75°C).

b) If cabling cost can be reduced substantially by increasing array voltage.

c) If system output at low irradiance is important.

d) If partial shading is a concern.

PWM controller When a solar array is connected to the battery through a PWM charge controller, its voltage will be pulled down to near that of the battery. This leads to a suboptimal power output wattage (Watt = Amp x Volt) at low and at very high solar cell temperatures. In times of rainy or heavily clouded days or during heavy intermittant loads a situation may occur where the battery voltage becomes lower than is normal. This would further pull down the panel voltage; thus degrading the output even further.At very high cell temperatures the voltage drop off point may decrease below the voltage needed to fully charge the battery. As array area increases linearly with power, cabling cross sectional area and cable length therefore both increase with power, resulting in substantial cable costs, in the case of arrays exceeding a few 100 Watts. The PWM charge controller is therefore a good low cost solution for small systems only, when cell temperature is moderate too high (between 45°C and 75°C).

7. CONCLUSION

In order to get the maximum out of a solar panel, a charge controller should be able to choose the optimum current-

voltage point on the current-voltage curve: the Maximum Power Point. An MPPT controller does exactly that. The input voltage of a PWM controller is, in principle, equal to the voltage of the battery connected to its output (plus voltage losses in the cabling and controller). The solar panel, therefore, is not used at its Maximum Power Point, in most cases.

8. REFERENCE

1.Charge Controller of Solar Photo Voltaic Panel Fed Battery, M.E.E (Master of Electrical Engineering), Thesis of T.Halder (Tapas Halder) submitted under the guidance of the Eminent Professor and Technologist Dr. Sujit K. Biswas in the year, 2001 in Jadavpur University. Kokata-32, INDIA.

2.V.Pop, H.J.Bergveld, D.Danilov, P.P.L.Regtien, P.H.L.Notten, "Battery Management Systems Accurate State- of-Charge Indication for Battery-Powered Applications",Philips Research Book Series-Volume 9, Springer Publications.

3.Duryea.S, Islam.S and Lawrance.W, "A battery management system for stand alone photovoltaic energy system", in Proceedings of Industry Applications Conference, 1999 and Thirty-Fourth IAS Annual Meeting 1999, vol.4, pp. 2649- 2654, 2009

4.Z.Jiang,Dougal.R.A, "Multiobjective MPPT/charging controller for standalone PV power systems under different insolation and load conditions", in Proceedings of the Industry Applications Conference and 39th IAS Annual Meeting, vol.

2,pp. 1154-1160, October 2004.

5.Reference of Su-Kam’s Solar Charger Controller system to implement MPPT & PWM technology.

6.www.victronenergy.com

Author Details :- 1. Akash Prakash Kadam

(Master of Engg.) Y.T.I.E.T., Karjat.

(Electrical Dept.)[email protected]

2.Chandrakant Gajendra Shinde

(Master of Engg.) Y.T.I.E.T., Karjat.

(Electrical Dept.)[email protected]