F1's 2014 electronics revolution explained

Since KERS was introduced in 2009, one of the less-talked-about parts of energy-recovery systems has been the battery and the electronics needed to manage the electrical energy passing from the Motor Generator Units.

With the huge increase in the potential power from ERS for 2014, the design of these systems is ever more critical, doubly so given the limit of five of each of the energy store and control electronics per driver per season. This means reliability is paramount if teams are to avoid grid penalties for busting their allowance later in the season.

The Energy Store (ES) is, in the most simplistic terms, the battery. This unit plays the key role of storing energy harvested by both the kinetic (ERS-K) and heat (ERS-H) energy-recovery systems.

On the ERS-K, the storage has gone up from a 0.5MJ limit last year to 4MJ this year. On top of this, there is no cap on energy being recovered from the ERS-H.

At the battery's terminals, voltage is in the hundred-of-volts bracket and limited to 1000v. Electrical current is in the tens of amps. So this is a high-power system, and the battery has to be sized to accommodate the use of both systems simultaneously.

Within the ES enclosure is a large array of lithium-ion cells. These are ostensibly similar to mobile-phone batteries, but set up in a far more sophisticated manner. To package the dozens of cells inside the enclosure, either cylindrical or pouch-type cells can be used.

Making the battery small enough to fit neatly under the fuel-tank area and also meet the 20-25kg min/max weight rule, while still achieving the power and energy targets, is a tough design challenge.

Aside from housing the cells, the energy store also has electronics to manage the condition of the individual cells. Hundreds of cells' parameters are monitored, including temperatures, voltage and current. Cells can be taken out of use if they are failing, but not every manufacturer has this functionality on their energy store.

With the ES storing its energy in a DC electrical format and the MGUs on the engine using three-phase AC power, there needs to be an electrical conversion between the two systems. This is achieved with the control electronics (CE).

Typically there is one control unit for both the ERS-K and ERS-H. When harvesting energy, the MGU will send its AC power via three high-current cables to the control unit.

Inside, a series of high-current switches called IGBT (Insulated Gate Bipolar Transistors) take the power and pass it through capacitors to convert it to DC format. From here the DC power is sent via two cables to the ESS. Sending power from the ESS to the MGU is the reverse of this method.

These electronic units also provide the car with its 12-24v supply for the usual electronics, ignition and fuel injection. No longer do the cars need to have alternators and a separate battery.

The packaging of these two control units varies among engine manufacturer and team. They can be either housed within the ES enclosure or separately in the sidepods. Being separate provides more design freedom, but is heavier due to the cable and cooling pipework.

The inversion process from AC to DC and back again creates losses, which take the form of heat. Equally, the charging and discharging of the cells in the ESS creates heat. So both systems need cooling.

Typically, this is done with a dedicated water-cooling circuit, requiring a reasonably sized radiator in the sidepod.

Although cooling is critical, in order to operate at maximum efficiency the batteries need to run within a narrow operating temperature. This is hotter than ambient temperature, so pre-warming of the water inside the cooling circuits is required before a session, just as the engine itself is pre-warmed before being fired up.

Equally, the batteries prefer to work with a specific state of charge (SOC). This is the amount of energy the batteries hold at any specific point.

SOC needs to be looked after carefully. It is necessary to charge and maintain the ES within a tight operating window. This allows the battery to be pre-charged before a session, but not during the session due to regulations.

The ES can also be rapidly brought up to a good SOC on the out-lap or early laps of a session. It's not the FIA's intention to have this process used as a performance advantage, so teams do not have sophisticated pre-charging equipment in their garages.

As part of the rules for the new power units, there are five distinct sub-systems of which the team can use five sets during the year. Two of these sub-systems are the ES and CE.

Such is the nature of these units that any problem will fry the hardware. As Renault Sport F1's Rob White sums it up: "When something goes wrong, it ends up in instant electrical death and there's no way back from that."

Soon, these unseen pieces of hardware will become newsworthy as their failure starts to inflict grid penalties.