17-08-2012, 01:11 PM
DESIGN & IMPLEMENTATION OF AN INTELLIGENT SOLAR HYBRID INVERTER IN GRID ORIENTED SYSTEM
[attachment=31840]
Abstract:
This paper demonstrates the implementation of a prototype of IPS (instant power supply) system to ensure
continuous output current to load in residential application utilizing both Photovoltaic (PV) energy and AC
Grid. Utility interfacing PWM inverter designed here to operate by both solar energy and storage batteries that
highly satisfies the necessity in rural areas where National Grids are hardly available and power cut problem
reduces the effectiveness of IPS. Solar energy gets priority here to charge storage battery rather than AC source
that may save hundreds of mega watts power every day. To extend the battery lifetime and keep system
components hazard-free, it includes exact battery-level sensing, charging-current controlling by microcontroller
unit (MCU) and a cumulative DC/AC MPPT (Maximum Power Point Tracking) charging to congregate
maximum PV energy from AC Solar Modules. Investigation on improvement of power-interfacing control and
optimization of overall system operation assent to intend usage recommendation in this exposition. Computer
simulations and experiment results show the validity of this proposed system to have high power conversion
efficiency and low harmonic distortions.
Introduction
Gigantic population and comprehensive electrical energy consumption have made power crisis one of the
gravest national problems in the developing countries like Bangladesh. Excessive demand of power is always
difficult to meet and as a result national economy is being hampered severely due to this deregulation of
electricity. Alternative power sources that can deliver output currents in absence of grid supply are now
automatic choices in home grid-connected system. In urban areas, IPS (Instant Power Supply) system is being
used massively to cope up with load shedding. But in the large context, it is worsening the situation roughly
since it consumes huge power from grid to charge its storage battery. Unfortunately most IPS system has poor
charge controlling mechanism which makes it a massive power consumer. Now-a-days, the practical cost of
solar panel and the consumers’ awareness to preserve AC power have stimulated the demands of high effective
Grid connected power sources.
Starting from the utilization of solar energy and digital power conversion application, this paper
demonstrates such a solution of implementing PV energy in existing isolated IPS system. When AC main fails,
inverter section will provide uninterrupted AC power supply which should be maintained by the storage
batteries. These storage batteries will be charged efficiently by the solar source(s) when sunlight is available
regardless of the AC line status. While, in dark night or cloudy weather AC grid source will charge the batteries.
These are schematically represented in Table 1. Since PV array of medium capability has been used in this
prototype, usage of PV energy here are only restricted to charge the battery and being miniature amount,
harvested AC will not be reflected to Grid which is left open for future.
Description
The proposed system schematically showed in Fig. 1 basically consists of three tiers: a) Input power section, b)
Intelligent processing section and c) Output power section. The core part of this system is the intelligent
switching circuit which is composed of PIC 16f876A based MCU unit which ensure uninterrupted output power
based on the available input. This pre-programmed section intelligently not only maintains maximum AC output
power with greater efficiency but also DC supply to small DC load that may reduce pressure of AC output. The
following sub-sections give the details of entire system.
Input Power and Switching Section
Input power section allows three different sources of energy like grid line, storages battery and Photovoltaic
energy (controlled by MPPT charge controller). To minimize the burden on the grid line, the system is designed
as follows: when Grid supply is present, switching circuitry gets informed about its availability from AC main
sensing section and passes AC main’s signal to inverter output socket. In absence of AC grid supply, switching
circuitry takes DC input from storage battery and turns on inverter circuit i.e. composition of oscillator, MOS
driver, output amplifier and transformer section and AC low-pass filter. Oscillator section generates 50 Hz MOS
driver signal that gets amplified, sent to inverter transformer using MOSFET switching and transforms into AC
and injects AC energy to the AC-side output connection. Such periodical switching ON/OFF of MOSFET starts
an alternating current with 50Hz frequency at primary winding of step-up transformer that results in 220V AC
supply at the secondary winding. All these functionalities are done here by implementing PIC 16f876A MCU
unit that resembles the change-over section of commercial IPS section implementing by analog circuitry.
Intelligent Processing and Battery Charging Section
In absence of solar energy, it is mandatory to use AC mains to charge storage battery. But, in daytime, it prefers
solar energy to AC grid in battery charging for power saving purposes. To ensure maximum possible PV energy,
some intelligence is applied in this proposed system. With a regular charge controller, if the batteries are low at
say 12.4 volts, then a 100 watt solar panel rated at 6 amps at 16.5 volts (6 amps times 16.5 volts = 100 watts)
will only charge at 6 amps times 12.4 volts or just 75 watts, losing 25% of panel’s capacity. Proposed MPPT in
this case compensates for the lower battery voltage by delivering closer to 8 amps into the 12.4 volt battery
maintaining the full power of the 100 watt solar panel. The intelligent charging section involves three level of
charging like absorption level charging, bulk level charging and float charging. A bulk level charging is
maintained for initializing charging process for a discharged battery. When Battery voltage exceeds a critical
level, charge controller maintains adsorption level charging. A full charged battery gets only float level charging
that maintains trickling current (i.e. one tenth of full charge current) causes available solar energy being unused.
Output Power section
Implementing such configuration described in previous section, maximum utilization of photovoltaic energy is
not yet confirmed practically. In semi-urban areas, where load-shedding are not much frequent, almost 80% of
available solar energy are being left unused. To utilize such power, this system contains an output pin that
supplies additional DC power to small loads likes in mobile charging application, DC fan, DC light, DC iron,
electric filters etc. This output DC power is obviously regulated in MPPT charge controller section to ensure
safe and maximum usages. Here we also implemented a fine adjuster of output DC voltage level to power large
possible and even tiny loads. A voltmeter is also integrated for this purpose at the output section to make this as
user-friendly as possible.
MPPT circuit description
This circuit utilizes a power BJT (Bipolar Junction Transistor) that works like a step-down converter. The circuit
operation can be divided into two modes. Mode 1 begins when transistor is switched on. The input current
which rises flowing through filter inductor, filter capacitor and load battery. And Mode 2 begins when transistor
is switched off. The freewheeling diode conducts due to energy being stored; inductor current continues to flow
through inductor, capacitor and load. Diode current falls until transistor is switched on again in the next cycle.
Here switching frequency is 25 KHz.
Working Circuit
Proposed system is such an online system that the inverter should always run if a load is connected. A lot of
configuration is deployed here for switching MOSFET (metal–oxide–semiconductor field-effect transistor-
IRFZ44N) [4,5,6]. A combination of two transistor pair like BC547, a NPN Transistor and BC557, another PNP
Transistor is used for safety that can ensure security for avoid miss pulse which cause the damage of MOSFET.
Additional diode, resistance and non-polar capacitor are also used for proper biasing of MOSFET (Fig.3). Since
maximum focus should be given to avoid the damage of MOSFET.
[attachment=31840]
Abstract:
This paper demonstrates the implementation of a prototype of IPS (instant power supply) system to ensure
continuous output current to load in residential application utilizing both Photovoltaic (PV) energy and AC
Grid. Utility interfacing PWM inverter designed here to operate by both solar energy and storage batteries that
highly satisfies the necessity in rural areas where National Grids are hardly available and power cut problem
reduces the effectiveness of IPS. Solar energy gets priority here to charge storage battery rather than AC source
that may save hundreds of mega watts power every day. To extend the battery lifetime and keep system
components hazard-free, it includes exact battery-level sensing, charging-current controlling by microcontroller
unit (MCU) and a cumulative DC/AC MPPT (Maximum Power Point Tracking) charging to congregate
maximum PV energy from AC Solar Modules. Investigation on improvement of power-interfacing control and
optimization of overall system operation assent to intend usage recommendation in this exposition. Computer
simulations and experiment results show the validity of this proposed system to have high power conversion
efficiency and low harmonic distortions.
Introduction
Gigantic population and comprehensive electrical energy consumption have made power crisis one of the
gravest national problems in the developing countries like Bangladesh. Excessive demand of power is always
difficult to meet and as a result national economy is being hampered severely due to this deregulation of
electricity. Alternative power sources that can deliver output currents in absence of grid supply are now
automatic choices in home grid-connected system. In urban areas, IPS (Instant Power Supply) system is being
used massively to cope up with load shedding. But in the large context, it is worsening the situation roughly
since it consumes huge power from grid to charge its storage battery. Unfortunately most IPS system has poor
charge controlling mechanism which makes it a massive power consumer. Now-a-days, the practical cost of
solar panel and the consumers’ awareness to preserve AC power have stimulated the demands of high effective
Grid connected power sources.
Starting from the utilization of solar energy and digital power conversion application, this paper
demonstrates such a solution of implementing PV energy in existing isolated IPS system. When AC main fails,
inverter section will provide uninterrupted AC power supply which should be maintained by the storage
batteries. These storage batteries will be charged efficiently by the solar source(s) when sunlight is available
regardless of the AC line status. While, in dark night or cloudy weather AC grid source will charge the batteries.
These are schematically represented in Table 1. Since PV array of medium capability has been used in this
prototype, usage of PV energy here are only restricted to charge the battery and being miniature amount,
harvested AC will not be reflected to Grid which is left open for future.
Description
The proposed system schematically showed in Fig. 1 basically consists of three tiers: a) Input power section, b)
Intelligent processing section and c) Output power section. The core part of this system is the intelligent
switching circuit which is composed of PIC 16f876A based MCU unit which ensure uninterrupted output power
based on the available input. This pre-programmed section intelligently not only maintains maximum AC output
power with greater efficiency but also DC supply to small DC load that may reduce pressure of AC output. The
following sub-sections give the details of entire system.
Input Power and Switching Section
Input power section allows three different sources of energy like grid line, storages battery and Photovoltaic
energy (controlled by MPPT charge controller). To minimize the burden on the grid line, the system is designed
as follows: when Grid supply is present, switching circuitry gets informed about its availability from AC main
sensing section and passes AC main’s signal to inverter output socket. In absence of AC grid supply, switching
circuitry takes DC input from storage battery and turns on inverter circuit i.e. composition of oscillator, MOS
driver, output amplifier and transformer section and AC low-pass filter. Oscillator section generates 50 Hz MOS
driver signal that gets amplified, sent to inverter transformer using MOSFET switching and transforms into AC
and injects AC energy to the AC-side output connection. Such periodical switching ON/OFF of MOSFET starts
an alternating current with 50Hz frequency at primary winding of step-up transformer that results in 220V AC
supply at the secondary winding. All these functionalities are done here by implementing PIC 16f876A MCU
unit that resembles the change-over section of commercial IPS section implementing by analog circuitry.
Intelligent Processing and Battery Charging Section
In absence of solar energy, it is mandatory to use AC mains to charge storage battery. But, in daytime, it prefers
solar energy to AC grid in battery charging for power saving purposes. To ensure maximum possible PV energy,
some intelligence is applied in this proposed system. With a regular charge controller, if the batteries are low at
say 12.4 volts, then a 100 watt solar panel rated at 6 amps at 16.5 volts (6 amps times 16.5 volts = 100 watts)
will only charge at 6 amps times 12.4 volts or just 75 watts, losing 25% of panel’s capacity. Proposed MPPT in
this case compensates for the lower battery voltage by delivering closer to 8 amps into the 12.4 volt battery
maintaining the full power of the 100 watt solar panel. The intelligent charging section involves three level of
charging like absorption level charging, bulk level charging and float charging. A bulk level charging is
maintained for initializing charging process for a discharged battery. When Battery voltage exceeds a critical
level, charge controller maintains adsorption level charging. A full charged battery gets only float level charging
that maintains trickling current (i.e. one tenth of full charge current) causes available solar energy being unused.
Output Power section
Implementing such configuration described in previous section, maximum utilization of photovoltaic energy is
not yet confirmed practically. In semi-urban areas, where load-shedding are not much frequent, almost 80% of
available solar energy are being left unused. To utilize such power, this system contains an output pin that
supplies additional DC power to small loads likes in mobile charging application, DC fan, DC light, DC iron,
electric filters etc. This output DC power is obviously regulated in MPPT charge controller section to ensure
safe and maximum usages. Here we also implemented a fine adjuster of output DC voltage level to power large
possible and even tiny loads. A voltmeter is also integrated for this purpose at the output section to make this as
user-friendly as possible.
MPPT circuit description
This circuit utilizes a power BJT (Bipolar Junction Transistor) that works like a step-down converter. The circuit
operation can be divided into two modes. Mode 1 begins when transistor is switched on. The input current
which rises flowing through filter inductor, filter capacitor and load battery. And Mode 2 begins when transistor
is switched off. The freewheeling diode conducts due to energy being stored; inductor current continues to flow
through inductor, capacitor and load. Diode current falls until transistor is switched on again in the next cycle.
Here switching frequency is 25 KHz.
Working Circuit
Proposed system is such an online system that the inverter should always run if a load is connected. A lot of
configuration is deployed here for switching MOSFET (metal–oxide–semiconductor field-effect transistor-
IRFZ44N) [4,5,6]. A combination of two transistor pair like BC547, a NPN Transistor and BC557, another PNP
Transistor is used for safety that can ensure security for avoid miss pulse which cause the damage of MOSFET.
Additional diode, resistance and non-polar capacitor are also used for proper biasing of MOSFET (Fig.3). Since
maximum focus should be given to avoid the damage of MOSFET.