Challenges in Distributed Energy Resources (DER)

Environmental concerns, global warming, climate changes are spurring l growth of solar energy, power quality has become a countries to shift to environmental friendly Renewable energy resources. Windmill and solar found to be the alternative primary source of energy.

?But with exponential Growth of these renewable sources of energy. Integration has become a serious power quality issue. There is need to have a fresh look at the power conditioning options for successful deployment.

New standards have been established like the IEEE-1547-2018 as a guide for solar and windmill Installation.

Introduction to solar technologies:

?The latest technologies adopted is Multilevel Inverters, with various topologies like the clamped diode, flying capacitor and Cascaded H bridge Multi level Inverters (CHBMLI)

?Some of the unique feature of these technologies are :

a.???Smaller common mode voltage avoiding noise.

b.???Input current: Multi level frequency converters can draw input current with low distortion.

c.????Low commutation and switching losses. Multilevel inverters can switch at low switching. High frequency switching increases losses.

d.???Fault tolerance : The fault levels of .multi level Inverters are higher.

e.???Some smarter inverters are designed to cancel harmonic generated in electrical network.

There are several switching techniques such as, Space Vector Pulse width modulation (SVPWM), to improve the performance of Inverters and minimise the THD. Some inverters employ selective Harmonic elimination to ensure harmonics are not generated at the input.

However, manufacturers of solar inverters hide more than they reveal on Power quality.

The challenges:

1. As a current source of power solar installation technically is not a load. But however current source inverters are vulnerable and susceptible to power quality on the source distribution grid into which they are feeding energy.
2. The assumption that he solar equipment manufacturer can withstand the same system generation conditions is not invariably given.
3. A careful consideration must be made against known grid tie conditions. Deployment of power conditioning equipment may be necessary in certain conditions.
4. High density Industrial environment poses several challenges of high harmonics and other power quality challenges due to growth of nonlinear loads generating low frequency and high frequency harmonics (Supra harmonics > 2000Hz.)

Major Power quality issues are:

#High level of grid voltage distortion level above the IEEE-519, IEEE -1547 8% and 5% respectively. The presence of high voltage distortion can trigger nuisance tripping. Equipment malfunction or even damage of the equipment. This can lead to mundane operational issues.

#Over excitation / Under excitation and co-ordination. Over voltage fluctuation beyond the operating ranges, may be outside the solar inverter ability to operate and function properly.

# Transient and surge consideration: as with any power electronic equipment transients and surges protection to clamp surge voltage with inverter immunity levels. To depend on grid operators to provide such protection is imprudent and impractical.

#Temporary Over voltage (TOV) can occur during fault conditions and their control as defined by IEEE C62-92.6.

If the load of the solar Systems consists of Phase -N load that are more than 33% of the inverters rating no treatment is necessary. But if it is less than 33% a supplemental grounding source is required. This could mean installation of Zig zag transformer also called zero sequence impedance transformer. A cost effective solution and provide a low Impedance path for the Triplen Harmonics as well as common mode noise. If these Triplen Harmonics are not effectively blocked, these currents can overload the supplemental grounding equipment.

#Leakage Current in Inverters:

In transformer less Inverters leakage current flows through the parasitic capacitances (between the ground and the PV panel and the ground inductance. Capacitances in the distribution network and long cables and capacitor cable banks without detuned anti resonant reactors can cause harmonic resonance when the small harmonic currents interacts with the harmonics of the electrical network causing voltage disturbance, most likely a leading power factor.?

Some possible Solutions:

Some devices that can be deployed to surmount these problems are:

?1.???Advanced Passive Harmonics Filter capable of filtering Harmonics form the 5th to the 500th order harmonics.

2.???LC or LCL filters for filtering harmonics beyond the PQ range >2000Hz.

3.???Zero sequence Impedance transformer for effective grounding.

4.???Common mode noise filter.

5.???Active Harmonic filter with Output LCL filters.

Conclusion:

Despite the innovations in complex switching technique and filtering techniques so as not of distort voltages and current waveforms, some issues remain to be resolved with advanced techniques. The Technologies continue to evolve to resolve many of these issue. Selecting the right Inverter and to be compatible with IEEE -1547 is the best option for solar installers.

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OUR RANGE OF PRODUCTS:

1. WAVEFORMS TERMINATOR?- ADVANCE PASSIVE HARMONICS FILTER.
2. WAVEFORMS HYBRID HMT?- HARMONICS MITIGATION TRANSFORMER.
3. WAVEFORMS SINEWAVE FILTER?- SINE FILTER FOR OUTPUT SIDE OF VFD.
4. WAVEFORMS TRIPLEN ELIMINATOR?- FOR 3RD,9TH, 15TH..... HARMONICS (Neutral Harmonics Eliminator)
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