A lithium-ion battery super capacitor composite power supply What is to design you?


  Author :Iflowpower – Portable Power Station Supplier

If the energy density of the super capacitor cannot be greatly improved, it is more difficult to use alone in electric cars. Even if there is a relatively large bus, it is more cumbersome. It has been in the actual operation.

Its posture is this: only relying on the passenger's time and get off the bus, it is not enough, so you have to wait for charging; there is a vehicle to block the charging position, you must wait, parking Charging at a specific location; the site must be intensive, it is best not to exceed 2-3km spacing. One stop is a charge, in practical applications, there is a lot of difficulties. Relatively speaking, combining the supercapacitor and the power supply with high energy density, each of which is more practical.

Taking lithium-ion battery and supercapacitance as an example. Advantage of electric vehicle composite power supply combined with supercapacitor and power lithium-ion battery cell energy storage device, it is important to consider the following points: 1) The purpose of combining power lithium ion batteries and super capacitors is to solve a single energy storage device. Insufficient comparison of power and longer energy; 2) can minimize the frequency of the battery large current charge, thereby reducing the heat generation and energy loss of the battery, so that the operating conditions of the battery are improved, the efficiency is improved; 3) Composite power system Give full play to the high-rate fast charge and discharge, high-specific power, and the super capacitor can quickly absorb the instantaneous power braking energy, improve the energy utilization of the vehicle system; 4) When the same power and energy, composite The cost, volume and weight of the power system are far better than a single power supply.

1 General topology of composite power supply At present, super capacitors and battery composite power vehicles are important to use in parallel structure, battery and supercapacitor connection, and corresponding control strategies are also different. The connection method of the composite power supply is divided into the following four, the first in parallel, the most simple structure, the number of devices, the number of devices, but because there is no two-way DC / DC converter, super capacitance and battery have the same voltage at any time. At this time, the assignment of the power size is important depending on the internal resistance of each power supply.

The DC bus side voltage variation range is limited by the battery-side voltage, and the supercapacitor can only output and absorb fluctuations when the battery voltage changes rapidly, so this kind of The mode limits the high power charge and discharge capacity of the super capacitor, and it is not possible to give full play to the advantages of supercapacitance and load matching. In the second parallel manner, the battery and the load are connected directly, and the supercapacitor is connected to the load through a two-way DC / DC converter. In this form of structure, the DC bus voltage of the battery connection is relatively small during the system charging and discharge process, and the battery is substantially operated in a constant current, and the charge and discharge current of the battery is optimized.

Under the third parallel mode, the battery can be connected to the load connection, and the battery can optimize the input and output characteristics of the battery; the supercapacitor is connected directly to the load. At this time, the super capacitor can quickly supply electric bus start / acceleration Power output and brake energy recovery when decelerating the brake. However, due to the change in the supercapacitor terminal voltage, the form of the supercapacitor is particularly improved, and it is difficult to give full play to the characteristics of supercapacitance instantaneous power charge and discharge.

Under the fourth parallel mode, the supercapacitors and the battery are connected to the load through the two-way DC / DC converter. At this time, the voltage regulation range is large, the flexibility is high, but due to the use of two DC / DC converters, the entire system Added difficulty in complexity and control, reducing the efficiency of the system, and the cost of the system is added. 2 Bidirectional DCDC Use the two-way DC / DC converter used in the composite power system: 1) Stable voltage.

The voltage of the DC bus is stabilized to the appropriate voltage required by the DC / DC converter; 2) Transmission power. Adjust the output power of each power supply by two-way DC / DC converters to meet the needs of energy and power; 3) High efficiency. The power converter has a high conversion efficiency, minimizing its own energy loss; 4) faster response speed.

Regarding the case where only the supercapacitor loop is connected in series DCDC, when the battery is connected to the DC bus, when the transplantria is instantaneously changed, if the transducer response speed is can't keep up, the supercapacitor cannot prompt the peak power of the battery output. In addition, the supercapacitor needs to undertake the instantaneous large current charge charge to protect the battery, and thus the same branch DC / DC converter, to undertake changes in the large current and instantaneous voltage; 5) In order to improve the energy utilization of electric vehicles, The energy recovery of regenerative brakes to supercapacitor. Therefore, the DC / DC converter required to be in series with the supercapacitor must be inverse of the current bidirectional.

3 Important Issues Designed by Compound Power System 3.1 How to determine how supercapacitance and lithium-ion batteries first look at the needs of vehicles, according to the established strategy, from discharge and braking energy recycling two processes to consider the number of two types of power supplies. For example, the discharge process, first reflect the most common system operating status and power fluctuation amplitude according to the relevant experience, and the system power is calculated; the system power average is calculated; finally determine the working mechanism of the supercapacitor and lithium-ion battery pack.

Lithium-ion batteries with high energy density, ideal, responsible for supplying power average and electric energy below the average; when the load is spike, the supercapacitor is used to fill the peak portion, try to exert the advantages of its power performance. Corresponding, regenerative braking process, generally require supercapacitance to completely bear the responsibility of its energy recovery. In the system of simultaneous use of the battery, the battery pack should meet the following important parameters: rated voltage, operating voltage range, rated power, peak power, maximum recovery current, and total energy (total endurance mileage).

In the power system with supercapacitor participation, the battery is important to meet the requirements of voltage and total energy. Therefore, the number of super capacitors should take the maximum value of the electricity and energy recovery, and the number of batteries is determined by the electric power consumption rate and battery life requirements. 3.

2 How to consider the size of the brake energy recovery power brake recovery power, directly affect the number of supercapacitance, so in the composite power system, the amount of braking energy recovery must be more accurately estimated. The regenerative braking energy of the vehicle is determined by the vehicle's own physical parameters, brake strategy, and vehicle speed, and is affected by various factors in the energy transfer chain. The greater the quality of the vehicle, the higher the vehicle speed, the greater the inertia of the vehicle, the greater the braking force.

But not all braking power is reversed by the motor, it is important for safety considerations. When the pure electric bus using a hybrid brake system is braked, the ratio between the regenerative braking and the friction power determines the power of the regenerative braking, the larger the proportion, the more power, the power of the brake, the brake The less frictional loss, the more energy recovered by the energy storage system, the higher the energy recovery efficiency. Transfer chain of braking energy: Brake system to the motor to the battery.

The brake system dispensses brakes according to the vehicle operation; the motor converts the braking force into electrical energy, reverse delivery to the energy storage device, which is supercapacitor; supercapacitor is as possible to store the maximum proportion of power. During the process, the power distribution ratio, motor power generation efficiency, supercapacitor charging efficiency, will affect the power of ultimately charged in the super capacitor. 3.

3 How to consider supercapacitor group arrangement determined the number of supercapacitor monomers and the number of M and strings, and different capacities, and different capacities after determining the number of supercapacitor monomers and the number N value of the sum number m and strings, and different capacities. The arrangement of monomer capacitors take into account group problems. After the first string, I was still in the first string, maybe starting with the entrance, we have already used it first and then string, so this problem is no longer as a problem.

There is a research surface, the skewers are directly affected by the reliability of the module after the group. Direct conclusions, we are commonly used in the form of structural forms, related to the string and form, with higher reliability, and larger the number of skewers, the more obvious effect. Since the supercapacitor monomer has an ineffective capacitance deviation, when the supercapacitance is arranged, it is best to measure the capacitance deviation of the supercapacitor, which is not used with a single body value.

The capacitance deviation is in the allowable range, the smallest capacitance or the largest supercapacitor monomer cannot be connected in parallel in parallel, and can be arranged from small to large (or from large to small) according to the small to large (or from large to small) according to the small to large (or from large to small). Make grouping, and then perform alignment of supercapacitor arrays in the way compared to the value-value lift. 4 Energy Distribution Strategy Policy Bus Composite Energy System Power Allocation Policy should be met: Battery and supercapacitance in the composite energy storage system can exert its own advantages in the premise of ensuring the power of the vehicle, and promote the shortage of avoidance; Fill in the field, reduce the impact of large currents on the battery, extend battery life, improve charge and discharge efficiency; maximum recycled braking energy, improve energy usage rate.

Composite energy storage system power distribution strategies have three categories: deterministic policies, non-deterministic strategies, and inspirational strategies. Based on the analysis of the information that has been learned, the deterministic control policies are determined, the most typical is the most typical logic threshold control strategy and the logical threshold control strategy containing filter ideas. The method is based on the average power of the driving road condition, and the car is supplied by the battery in the normal driving process, super capacitor supply spike or exceeded part of the power.

Heuristic control policies, based on the assumptions or formulas reflecting the basic principles, the corresponding values ​​are derived according to these hypothetical or formulas. The biggest advantage of this control method is to achieve simple, as long as the general information of the system components (such as the maximum charge and discharge current allowed by the battery and supercapacitor), not to prepare the driving road conditions information. The most typical heuristic control method is to use the power allocation control strategy based on the current vehicle speed, the steady-state power of the bus in the speed of the bus is supplied by the battery, supplied by the super capacitor.

Non-definitective control strategy is based on algorithms such as random methods, fuzzy logic or neural networks, and realize real-time optimization of power distribution during driving. Although the non-deterministic control strategy is very suitable for solving complex optimization problems expressed in difficult to use mathematical expressions, it is impossible to ensure that the bus adopted such control strategy can apply for each driving condition. In addition, this method is very complicated, the most typical type of control strategy is to use a fuzzy logic control strategy to blur a reasonable allocation of the power of the bus to the power of the bus and the supercapacitor to achieve the reasonable allocation of demand power.

Most of the non-deterministic control strategy is mostly determined or an inspiratory control policy. .

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