One oversimplified view of lagging power pactor
is that one could merely add capacitance to compensate for a simple "lumped" value of equivalent inductance causing the lag. In truth, this may work with some types of motors in the first approximation. Yet, even then, with salient pole motors the effects are not truly sinusiod and, therefore, a simple capacitance will not make an ideal correction.
With other types of loads, such as with line-frequency chargers using triac controlled regulation (the most common) and with microwave ovens (which remove power from the input waveform only above set thresholds thereby causing "flat-topping") an overall lagging of the input current related to input voltage occurs with multiple harmonics and the resultant current and voltage waveforms are non-sinusiod.
It takes a compensating network of inductances and capacitors and resistors to properly make a correction and the size and expense is large for these components which is why you don't see such solutions outside of the military and industry. Consumers just woun't pay the price
...it would probably add 50% to the cost of an inverter/charger.
So, the reason that you will begin to see specifications indicating "harmonic line correction" or similar wording is because there is no simple specification for the number of degrees allowed between the input voltage and current sinusiods. There ARE, however, US and Eueropean standards for harmonic content allowed by a product connected to the power line.
Because the size of reactive components physically decrease as the square of frequency it is much more economically feasable to make corrections with high-frequency switch-mode power supplies. In addition, switch-mode supplies can be designed so as to extract energy from the entire conduction angles of the input voltage waveform and if done in a proper manner can cause the input current waveform to be in phase with the input voltage and be sinusiodal in nature. Electric
heaters and light bulbs do this, of course, by their very nature in that they are purely resistive loads (except for the fans). Motors do this as well yet change the angle between the current and voltage waveforms.
High tech motors today (up to hundreds of HP) use dc and, therefore, a properly designed off-the-line power supply can be a high-frequency switch-mode design to drive the motor
. The net result is a system having around 98% efficiency and automatic harmonic correction. They are being used in referigeration systems and diesel-electric drives.
,Panda and Onan (Cummins) make some high-tech generators using these principles. We will see this type of technology dominate the market if for no other reason than we cannot export products into the Eueropean markets without meeting harmonic standards and the old technology just will not compete.