This paper attempts to analyze various charging schemes of electric vehicles, in order to find a practical and feasible charging scheme for electric vehicles in China.
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First, the role and function of the charging station
Charging stations generally have two functions: normal charging and emergency charging.
1. Normal state charging: equivalent to fuel vehicles must always go to the gas station to refuel, the daily charging of electric vehicles can be done by the charging station. But in fact, charging station normal charging has many drawbacks: household electric vehicle power battery 40-60AH, working voltage is 300V-400V, endurance capacity is in the range of 120-150km, commercial electric bus (public transportation or intercity traffic), power battery 400 -600AH, working voltage 350V-400V, its endurance capacity is 300-400km, that is to say, whether it is a household electric car with a charge of 150km on a single charge, or an intercity bus with a 400km battery life, it must be charged every day. Therefore, it cannot be applied. The fuel station's gas station theory mode selects the charging station as the normal charging mode of the electric vehicle. After all, the fuel vehicle can be refueled for 400-500km. It is usually necessary to add oil once every 5-7 days, and the refueling time is short. Every day, you must go to the charging station to charge, charging time is more than 1 hour, which is unacceptable to most car owners. In addition, in order to fully charge within 1 hour, you must use the "fast charge mode", that is, charging at a current of ≥1.0C. This charging mode has a high safety risk and the charging cannot exceed 80%, and we know that electric vehicles are now available. The electronic drift setting characteristics of the commonly used power lithium battery show that the key point to improve the battery output is charging to 80%-100% of the final charging interval of small current charging, charging station fast charging mode does not provide small current slow charging, and fast charging Up to 80% can't get 80% of the output, there is data showing that only 50%-60%, then, the normal slow-charge battery life of 150km, the normal state of charge with the charging station, the endurance will not exceed 100km! This shows that even if the electric vehicle is used for short-distance driving in the urban area, there may be a situation in which the charging station is charged once or more times per day, and thus the applicability of the electric vehicle will be greatly reduced. It can be concluded that the fast charging station cannot independently undertake the normal charging task.
2. Emergency charging: In the case of electric vehicles with occasional power shortage and unable to plug in and charge slowly, the short-time fast charging is implemented, so that the electric vehicle can quickly acquire the capacity of 30-50km. Obviously, this is the main function of the charging station. As an emergency system, a small number of fast charging stations and mobile fast charging vehicles must be built in advance.
Second, electric car peak and valley charging
According to the National Development and Reform Commission's new energy vehicle industry plan, China's new energy vehicles have reached 5-10% of production in recent years. In 2009, the annual output of automobiles reached 13 million, and 10% was 1.3 million. In the case of the same ratio, five years. The number of electric vehicles will reach 600-700 million, the required slow charging power will be 20-30 million kilowatts, and the fast charging power will reach 1.0-120 million kilowatts. In 2008, the national total installed capacity of electric power was hundreds of millions of kilowatts. The charging power of electric vehicles is equivalent to 15% of the national installed capacity. If you use a fast charging station to charge during the peak period, it may cause hundreds of billions of kilowatts of power gap. On the contrary, with hundreds of millions of installed machines, there will be 1/3 of the installed capacity in the valley, which is 2-250 million kilowatts. China's power grid is dominated by thermal power, and the ability to regulate peaks and valleys is poor. How to ensure the basic power load during the valley electricity period is a key factor to improve the quality of power grids.
Electric vehicle charging should choose the valley period. The valley electricity usually appears from 11:00 pm to 7:00 the next day. This time is especially suitable for plugging in and charging for 6-8 hours. The charging period coincides with the sleep time of the owner. Charging and replenishing, the best of both worlds! The electric vehicle is normally charged slowly, and the charging current should be 0.2-0.3C, which is about 1/5-1/4 of the fast charge. According to this, the vehicle with a relatively small power cut smart charger is used, and the AC power pile of the night parking lot is used. Complete the valley power slow charge, save money, but also ensure the quality of the charge, but also improve the peak-to-valley difference of the grid.
Third, the alternative emergency charging of electric vehicles
If the electric vehicle is charged with a car-mounted smart charger and the valley is plugged in slowly, we must look for an emergency solution for the alternative charging station:
One: battery rental replacement program, the idea of ​​this program is that the owner buys a car without a battery, the battery is rented separately, the battery rental company has a certain amount of battery backup, self-charged in the valley electricity period, after the electric vehicle battery discharge alarm Change the battery to the battery replacement station (like changing the gas bottle), and replace the battery to charge it and then make a backup.
The advantage of this scheme is that it can lower the threshold for purchasing electric vehicles. At the same time, the battery can be charged slowly, and it does not consume too much time for the owner. However, there are three problems: First, the battery company must have twice the number of batteries of the electric vehicle. Otherwise, the battery cannot be charged. Secondly, the battery specifications must have good interchangeability. In addition, the design of the vehicle must take into account the frequent replacement of the battery, which will cost a lot of space. At the same time, the owner must go to the battery station to change the battery every day. Station charging is no different, the owner will be annoying!
Second: the charging station + mobile charging car, like the road rescue, is responsible for the professional company. When receiving the rescue call, it receives the station fast charge or the charging car on the spot to help the emergency charge. The shortcoming of this solution is the difficulty of charging in the middle and long distance. And a one-time investment is large and the rescue is not timely, therefore, it is not suitable for a large number of choices, but a small amount of emergency.
The third: self-supplied generator program: the most typical is the General Chevrolet Volt, this car is a pure electric car, but with a small gasoline generator and a 10L spare fuel tank, can start the gasoline generator after the vehicle discharge alarm For the car charger to charge the battery, so that the electric car continues for 30-50 km (Volt's shortcoming is that the endurance is too small, only 60KM).
It is recommended that electric vehicle manufacturers choose their own gasoline generator solution. On the domestic passenger car, configure 3KW-5KW fuel generator, and if necessary, supply the vehicle-mounted 3KW-5KW charger to charge the power battery during operation. Understand as an alternative hybrid (only electric drive without fuel drive)
Fourth, the conclusion:
1. Electric car configuration 3-5KW car charger with the same power gasoline generator (cost 3-5 thousand yuan). Under normal circumstances, the AC power pile used in the night parking lot is used to charge the power battery during the valley power period. When there is no power on the way, many gas stations are used to refuel the generator and self-generate to charge the battery.
2. Commercial bus is equipped with 0.25C car charger, set AC power pile in the terminal parking lot, slow charging with car charger in the valley period, and set some fast charging stations in the middle according to the path, temporarily use 1-2C to quickly make up Electricity.
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