It is a common practice to use a series circuit power unit in hybrid automobiles. Internal combustion engine (ICE) is used as an electric generator drive which, in turn, is loaded onto a direct current traction motor. ICE works in an optimal regime on constant speed, and due to that consumes minimum fuel. Part of the energy produced by electric generator is used to charge buffer energy storage (which, as a rule, is realized on the basis of electrochemical supercapacitors). Buffer storage is used for a short-time (10-20 seconds) increase of electric motor output power at the moment of acceleration, when the vehicle takes off or overtakes, and it must provide high discharge current, short charging time and high endurance (hundreds of thousands charge-discharge cycles).
Storage mass-dimension characteristics and price are equally important. So, supercapacitor battery of a hybrid motor car meant for city cycle has 150 – 180 kg in weight, its volume is up to 90 litres, and its price is about 180 thousand roubles (this information can be found on the website of “Elton” company – one of the largest Russian supercapacitor manufactures. The replacement of the supercapacitor by a Li-ion accumulator battery will help to considerably ameliorate storage mass-dimension characteristics, but at the same time its price grows up to $12 000 and more.
Electronic separator SWEL-ES included in the supercapacitor discharge circuit, allows considerable decrease of chemical cell internal resistance due to the decrease of the polarization component of this resistance (or, rather, its activation part). This provides a more regular and efficient energy extraction in operating voltage range (U0–½U0) and also during a deeper supercapacitor discharge. It’s not difficult to realize such an inclusion of an electronic separator, because it doesn’t require any serious changes in the electrical circuit of a hybrid automobile. The ES efficiency in the energy storage of an electric car in different working modes reaches 115 – 150% (up to 135% for Li-ion batteries); mass-dimension and price characteristics of the storage can be reduced by 1.3 and more times.
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Electronic separator SWEL-ES is rather promising in complex with a battery of lead-acid or Ni-Cd (Ni-metal hydride) accumulators. Their advantage is much higher energy capacity, in comparison with electrochemical supercapacitors, that provides significant reduction of storage mass and dimensions. As for Li-ion accumulator batteries, their good mass-dimension characteristics are substantially leveled by their high cost (1 W*h of accumulated energy for a Ni-Cd accumulator costs 0.5$, the same for a Li-ion accumulator costs almost 10 times more).
Low endurance (less than 2000 charge-discharge cycles) is the main disadvantage of accumulators with aqueous electrolyte. It would seem that due to this problem they cannot be used for buffer energy storages in hybrid vehicle and electric cars. However, it is well-known that in cyclic partial accumulator discharge its service life increases dramatically (for a Ni-Cd accumulator at maximum discharge of 5% from rated capacity it reaches 100 000 and more cycles). Besides, an accumulator charged not to maximum voltage but to the level which corresponds to about 80% of its rated capacity, has no gassing during its charge (gassing is associated with decomposition of water molecules and the following emission of gaseous hydrogen and oxygen in the atmosphere via valve; it results in gradual electrolyte desiccation and reduction of accumulator service capacity).
Use of the electronic separator provides a more rapid and efficient charge of the accumulator, and also a much more effective (by half) energy extraction during its discharge. Thus, it becomes possible to realize a maintenance-free buffer energy storage on the basis of accumulators with aqueous electrolyte. Such a storage with power up to 50 kW for a hybrid motor car would have the following characteristics: weight (together with the electronic separator SWEL-ES) – up to 120 kg, price – less then 100 thousand roubles, endurance – up to 200 thousand cycles.
Similarly, the use of the electronic separator SWEL-ES gives considerable efficiency rise and helps to improve mass-dimension and price characteristics of buffer and traction accumulator batteries for electric cars and public electric transport. According to the type of the chemical cell, total gain can achieve 20 – 50% in mass and up to 2 times in price.
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