What are those nonlinear loads in real microgrids/grids?
What kind of loads generate these kinds of waveforms? If your switching power on and off and not just a regular rectifier then you are probably a nonlinear load. Loads like LED's and diodes that only draw power from one half of the cycle are also non-linear. Anything that switches power on and of more than the cycle time is also nonlinear. 


  Modern industrial facilities are characterized by the widespread
  application of nonlinear loads. These loads can make up a significant
  portion of the total facility loads and inject harmonic currents into
  the power system, causing harmonic distortion in the voltage. This
  harmonic problem is compounded by the fact that these nonlinear loads
  have a relatively low power factor. Industrial facilities often
  utilize capacitor banks to improve the power factor to avoid penalty
  charges. The application of power factor correction capacitors
  can potentially magnify harmonic currents from the nonlinear loads,
  giving rise to resonance conditions within the facility.
  
  Nonlinear industrial loads can generally be grouped into three
  categories:  
  
  1) Three-phase power converters (
    2) Arcing devices
    3) Saturable devices    


Source: Harmonic Sources from Industrial Loads I

Three-phase electronic power converters


  Three-phase electronic power converters differ from single-phase
  converters mainly because they do not generate third-harmonic
  currents. This is a great advantage because the third-harmonic current
  is the largest component of harmonics.    


Source: Harmonic Sources from Industrial Loads I

Arcing Devices


  This category includes arc furnaces, arc welders, and discharge-type
  lighting (fluorescent, sodium vapor, mercury vapor) with magnetic
  ballasts. As shown in Fig. 4.17, the arc is basically a voltage clamp
  in series with a reactance that limits current to a reasonable value.
  The voltage-current characteristics of electric arcs are nonlinear.
  Following arc ignition, the voltage decreases as the arc current
  increases, limited only by the impedance of the power system. This
  gives the arc the appearance of having a negative resistance for a
  portion of its operating cycle such as in fluorescent lighting
  applications. In electric arc furnace applications, the limiting
  impedance is primarily the furnace cable and leads with some
  contribution from the power system and furnace transformer. Currents
  in excess of 60,000 A are common.  


Source:Harmonic Sources from Industrial Loads II 

Saturable devices


  Equipment in this category includes transformers and other
  electromagnetic devices with a steel core, including motors. Harmonics
  are generated due to the nonlinear magnetizing characteristics of the
  steel  


Source:Harmonic Sources from Industrial Loads II