Mistake-3 Selection of inverter 12 Major mistake continuation
What are the Major mistakes of off grid system and How to avoid , Mistake number- 03
Mistake Selection of Inverter
1) What is inverter?
An inverter in an devise that converts the DC voltage to an AC voltage. In most cases, the input DC voltage is usually lower while the output AC is equal to the grid supply voltage of either 110 volts and 60 Hz, or 230 Volts and 50 Hz depending on the country.
There are different types of inverters based on the shape of the switching waveform. These have varying circuit configurations, efficiencies, advantages and disadvantages
An inverter provides an ac voltage from dc power sources and is useful in powering electronics and electrical equipment rated at the ac mains voltage. In addition they are widely used in the switched mode power supplies inverting stages. The circuits are classified according the switching technology and switch type, the waveform, the frequency and output waveform.
2) Basic inverter operation
The basic circuits include an oscillator, control circuit, drive circuit for the power devices, switching devices, and a transformer.
The conversion of dc to alternating voltage is achieved by converting energy stored in the dc source such as the battery, or from a rectifier output, into an alternating voltage. This is done using switching devices which are continuously turned on and off, and then stepping up using the transformer. Although there are some configurations which do not use a transformer, these are not widely used.
The DC input voltage is switched on and off by the power devices such as MOSFETs or power transistors and the pulses fed to the primary side of the transformer. The varying voltage in the primary induces an alternating voltage at secondary winding. The transformer also works as an amplifier where it increases the output voltage at a ratio determined by the turn’s ratio. In most cases the output voltage is raised from the standard 12 volts supplied by the batteries to either 110 Volts or 230 volts AC.
The three commonly used Inverter output stages are, a push-pull with centre tap transformer, push-pull half-bridge, or push-pull full bridge. The push pull with centre tap is most popular due to its simplicity and, guaranteed results; however, it uses a heavier transformer and has a lower efficiency.
A simple push pull DC to AC inverter with center tap transformer circuit is a shown in the figure below.
3) Inverter output wave forms
The inverters are classified according to their output waveforms with the three common types being the square wave, the pure sine wave and the modified sine wave.
The square wave is simple and cheaper, however, it has a low power quality compared to the other two. The modified square wave provides a better power quality (THD~ 45% Total harmonic distortion (THD) ) and is suitable for most electronic equipment. These have rectangular pulses that have dead spots between the positive half cycle and the negative half cycle (THD about 24%).
Inverters are used for a variety of applications that range from small car adapters to household or office applications, and large grid systems.
- Uninterruptible power supplies
- As standalone inverters
- In solar power systems
- As a building block of a switched mode power supply
5) What is solar inverter?
A solar inverter or PV inverter, is a type of electrical converter which converts the variable direct current (DC) output of a photovoltaic (PV) solar panel into a utility frequency alternating current (AC) that can be fed into a commercial electrical grid or used by a local, off-grid electrical network.
6) What are the Major type of solar inverter available in Market?
There are 3 type of inverter used in solar industry
a) Off-grid/ Standalone Inverters – works independently of the grid and requires battery storage, From the solar power the inverter stored in batter DC power, while the power failure the Off grid inverter change the DC power to AC power as supply voltage of either 120 volts, or 230 Volts depending on the country.
Pros:
- Time-tested technology – used widely for storage in Battery solar systems around the world
- Countless product options available
- Modular nature lends to greater system design flexibility
- Long history of use in off-grid and stand-alone power systems means most units are exceptionally sturdy and durable
- Can be relatively easily retrofitted onto existing solar PV systems for addition of battery storage
Cons:
- The system used in domestic purpose of upto one kva the efficiency very low
b) On-grid/ Grid-tied Inverters – The Grid tie inverter connected the input from solar PV and the out put connected to the Grid connection, From the PV panel to inverter connection maximum voltage are vary based on the country regulation , Voltages as high as 600 volts in North America and 1,000 volts in Europe are common: voltages that can very easily be fatal on contact. grid This type of inverter are dependent upon the grid.
Pros:
- Time-tested technology – used widely in grid-connected solar systems around the world
- Countless product options available
Cons:
- Possible to include battery storage, but battery side of the system will require a separate inverter
- Separate energy management system may be required to maximise overall system efficiency
c) Hybrid Inverters – In the context of residential solar + storage systems, a hybrid inverter (sometimes referred to as a multi-mode inverter) is an inverter which can simultaneously manage inputs from both solar panels and a battery bank, charging batteries with either solar panels or the electricity grid (depending on which is more economical or preferred). Their capabilities may go beyond this however – some devices also handle inputs from wind turbines, generators and other power sources.
Pros:
- All-in-one inverter solution for grid-connected solar-plus-storage systems
- Frequently intelligent and programmable for maximizing overall system efficiency and savings
- Can usually be installed without batteries for future expansion
- Long history of use in off-grid and stand-alone power systems
Cons:
- Less design flexibility than modular solutions which use separate PV and battery inverters
- Generally less efficient than dedicated solar-only or battery-only inverters
- More expansive
a) While selection of inverter there specification are not properly verified which cause lot of waste money as well as health hazard, some times serious injury, this can be avoided if properly select the inverter
i) Maximum AC output power (This is the maximum power the inverter can supply to a load on a steady basis at a specified output voltage. The value is expressed in watts or kilowatts)
ii) Peak output power :This is also known as the surge power; it is the maximum power that an inverter can supply for a short time. For example, some appliances with electric motors require a much higher power on start-up than when they are running on a continuous basis. Common examples are refrigerators, air-conditioning units, and pumps.
iii) AC output voltage
This value indicates to which utility voltages the inverter can connect. For inverters designed for residential use, the output voltage is 120 V or 240 V at 60 Hz for North America. It is 230 V at 50 Hz for many other countries
iv) Peak Efficiency
The peak efficiency is the highest efficiency that the inverter can achieve.
Most grid-tie inverters have peak efficiencies above 90%. The energy lost during inversion is, for the most part, converted into heat. It’s important to note what this means: In order for an inverter to put out the rated amount of power, it will need to have a power input that exceeds the output. For example, an inverter with a rated output power of 5,000 W and a peak efficiency of 95% requires an input power of 5,263 W to operate at full power
v) Maximum Input Current
This is the maximum direct current that the inverter can utilize.
If a solar array or wind turbine produces a current that exceeds this maximum input current, the excess current is not used by the inverter
vi) Maximum Output Current
This is the maximum continuous AC that the inverter supplies.
This value is typically used to determine the minimum current rating of the protection devices (breakers and fuses) and disconnects required for the output circuit.
vii) Peak Power Tracking or Pulse with modulation Voltage
This is the DC voltage range in which the inverter’s maximum power point tracker (MPPT) or Pulse with modulation (PWM) operates.
viii) Start Voltage
This value is the minimum DC voltage required for the inverter to turn on and begin operation.
This is particularly important for solar applications because the solar module or modules must be capable of producing the voltage. If this value is not provided by the manufacturer, the lower end of the peak power tracking voltage range can be used as the inverter’s minimum voltage.
ix) NEMA Rating or MNRE (Ministry of New and Renewable Energy) approval
This rating indicates the level of protection the inverter has against water intrusion. Most outdoor inverters are rated as National Electrical Manufacturers Association (NEMA) 3 for most weather conditions, check the Inverter is approved by MNRE in India
x) Total Harmonic Distortion (THD)
The total harmonic distortion (THD) is an indication of the purity, or the harmonic content, of the sinusoidal output of an inverter.
Most filtered sine waves still contain some harmonics that distort the waveform to a minor degree
xi) Weatherproof Enclosure
Most inverters, especially grid-tie inverters, are designed to be installed outdoors and have weatherproof enclosures.
xii) AC/DC Disconnects
Some inverters have built-in ac/dc disconnects for safety and to facilitate removing the inverter if it needs to be serviced.
xiii)Ground Fault Protection
The National Electric Code (NEC) requires that roof-mounted solar electric systems must be grounded. Most inverters have built-in ground fault protection.
xiv)Transfer Switch
A transfer switch is also known as a transfer relay. Grid-tie inverters usually feature a built-in load transfer switch for backup emergency power applications.
As long as utility power reaches the inverter’s AC input side, the transfer switch passes the AC grid power directly through the inverter to the load.
Sample specification for reference only
Also can check the difference between inverter and UPS below link
https://pmmsfs.blogspot.com/2020/09/difference-between-ups-inverter-and.html
ReplyDeleteThis kind of knowledge based content are actually required
which helps the customer to take correct decision while purchasing Solar inverter
Thanks for sharing with us.
Solar Inverter
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