I believe michael8554 method is the best way to use PHEV.
And I would like to add a little bit of theoretical background of this method.
ICE engine burns Gasoline and it move the cylinder. When the material stays in gas state (not abbreviation of gasoline but a general of material existence state, like "Gas", "Liquid", "Solid"), material flying inside a volume as molecule state. We called it pressure. When gasoline burns together with oxygen (it is called combustion) inside cylinder, it creates "Heat". Combustion last only in less than a second and the created Heat by combustion provides molecules of material inside cylinder high energy level and molecules move in enormous speed and this is called High Pressure. High pressure pushes away only movable part of the cylinder, which is "Cylinder Head". Four cylinder Heads move in turns and it transfer push energy to crankshaft circular motion. We call it "Torque"
This energy of torque transferred to Transmission and rotate drive shaft and the car is moving. Transmission is essential because the combustion energy is Liner to gasoline consumption and this is restricted in a certain range, Cylinder size decides minimum energy to move cylinder and maximum energy to move cylinder head. The range is known as RPM, stands for "Round Per Minute". In each RPM, energy level is different. To get more efficiency, RPM vs numbers of tire rotate should be low. That is controlled by transmission. The reason why I explained is that during whole process from burning the gasoline to the car moving, there exist "Efficiency Of Combustion Engine". Government Official states that Efficiency of the Combustion is 12% to 30%. In early stage of the Combustion is less than 5%. This can be easily understood as "When you spend $100 for Gasoline, average $20 will be used for car moving. The rest money is for Heat, Vibration, and verity of mechanical friction energy all through the way to Tires.
Different with ICE, EV uses Electric Motor which uses different "Energy" to create torque. It is called Electro-Magnetic energy. Where there is flow of electric, magnetic power is created. When we apply electricity to rotor, it generates magnetic force and it has S and N. Surrounding rotor, there are lines of permanent magnetics and the magnetic force from rotor and permanent magnetic force are push and pull in tern and it creates circulation movement of rotor. There is no energy transition from liner movement to circular movement, not like ICE. Combustion energy moves Cylinder linearly and this linear movement transferred to crankshaft for circular movement, where there are lots of energy loss. And Rotor's circular movement is transferred to drive shaft and it turns tire. The difference of power transferring between ICE and Electric motor is that ICE required transmission to maximize the power efficiency, but electric motor doesn't. Since the power amount to transferred to tire can be controlled by the electricity supply quantity directly in EV. Thus, when we spend $100 of electricity, 80% to 90% of electricity is use for car moving. Heat, noise, mechanical friction is minimal compare to ICE.
Gasoline is very unstable material. However, we add a lots of safety device and control method to keep it in safe. EV uses electricity. It is unstable too, but we also apply safe device and control method to use it safely. Gasoline tank is rather safe rather than Electron Tank, which we say DC Battery. Both energy source is dangerous, but we are improving the tech to keep and use it safely.
Now we have to talk about Hybrid.
Engineers and inventers are keep studying how to move the car safely and efficiently, because the transportation is the top important issue in human society and car industry is big enough non to second.
Transportation is not simple activity in human. As it is not the concept of moving things, but it became the issue of HOW TO MOVE. There is a JOY of moving, Art of moving, Comfort of moving, Economy of moving, including memories of life with the car, ETC
Hybrid started from long time ago. But EV is totally rely on battery technology. Until we have enough of battery tech, EV is just an mirage. In 1997, Toyota finally showed us the first mass production of Hybrid car in the market. The Prius. Still the battery price is too high, full EV is still future industry. But spending as little money as possible, they grafted EV character to ICE car.
Toyota tried to minimize the loss of energy by deleting Idling ICE, start car with EV first, regenerate electric energy when stopping. These are 3 most wasting fuel in ICE car. Using electric motor with limited battery just run the car 12v system while idling, start the car with electric motor to minimize inefficiency of ICE by the Newton's Law, and charge the battery when stopping procedure. The energy efficiency increase 20% - 40% more than ICE only car.
As the Battery price goes down, engineers tried to apply bigger battery to maximize the effect of EV in Hybrid car. Concept is exactly same but install bigger battery. However, bigger battery cannot be charged enough from ICE during running, it should be charged by Grid. It is PHEV. As a result, more Battery use, less gasoline use, high gas mileage.
Charge mode in PHEV is a kind of derivative concept. Hybrid Engine generates electricity while running by using generator. However, the quantity of generated power is not enough to charge the PHEV battery while driving, since lots of power from generator already consumed by 12v circuit. Actually generating energy by ICE is not efficient. However, that energy loss will be regenerated by using EV, which has at least 80% of efficiency. That concept creates idea that use EV for 15 miles and the charge battery to 80% and then use EV again with high efficiency.
But I am a little spurious about this effectiveness because it could be related with battery life span, I am not sure. I am expecting the right answer about that 15 miles run and charge it and repeating this procedure is actually remarkably efficient, and this procedure is not affecting the life span of the battery.
