For many years, DC has been the main power source of electric storage and handling equipment. As a cheaper driving mode, DC drive has been widely used in electric equipment long ago. However, the DC system itself has some inherent defects in performance and maintenance, and the AC and AC motors are far better in this regard. Therefore, the manufacturers of fanda indoor handling equipment have begun to devote themselves to the research and development of the application of AC technology.
In fact, AC power has been widely used since the end of the 19th century. It is AC motor technology that promotes the electrification process in industry, railway and other fields. Now, electrical 名媛直播 using AC technology can be seen everywhere. Communication may have become the most widely tested and verified technology.
The advantages of AC technology are mainly reflected in the following aspects:
l. The conversion between high and low voltage is simple.
2. The motor becomes strong and efficient and can withstand the impact of high current.
3. The number of parts of the motor is greatly reduced, and there is no wear, solid and durable.
4. Compared with DC motor, the cost is significantly reduced.
However, the application of AC motor in battery powered equipment such as forklift truck is limited due to two main reasons: the low system voltage of 80V requires high-energy semiconductor to realize the conversion from DC to AC, and this cost is high; The conversion process itself consumes energy, and the battery capacity is quite limited.
BT company has developed a new series of AC powered forward forklift -- reflex ACI. The new series of forklifts overcome the following problems, realize all the potential of communication technology, reduce the operation cost of forklifts and significantly improve the performance and reliability.
Next, we will make a brief introduction to several existing motor technologies.
Series DC motor
This is the oldest and most traditional motor. The current is transmitted to the battery and dried, and transmitted to the stator through the carbon brush. This method has two defects: all current must be transmitted through the carbon brush, and the performance depends on the physical size and wear of the carbon brush. Most importantly, this limits the braking performance. In addition, the motor carbon brush, as a vulnerable part, must be replaced regularly, otherwise it will greatly affect the service life of the motor. With this in mind, many manufacturers will equip forklifts with wear detection and warning devices, which increases the cost of forklifts.
All motors will generate heat, but in DC motors, the heat is mainly generated in the internal parts of the motor, so most DC motors will be equipped with a fan for heat dissipation at the same time.
Separately excited motor
This is a more advanced DC motor. The energy of stator and armature is input respectively. Like the series motor, this technology has been used for quite a long time. The new technology uses separately excited shunt magnetic field and armature, so that the performance control of motor is much better than that of series motor. This kind of motor is usually called 4-quadrant motor because it can travel and brake in both front and rear directions. However, the defects of motor carbon brush still exist.
Three phase AC motor
Technically, this is the simplest kind of motor. The principle is that the three-phase alternating current is transmitted to a fixed coil to generate a rotating magnetic field and induce the voltage on the shorted rotor. AC motor has no hair brush, and there is no limit on the maximum current of DC motor, which means that the motor can get more energy and greater braking torque in practical use, so it can run faster.
In AC motor, heat mainly occurs in the fixed sub coil of the motor shell, which is convenient for cooling and heat dissipation. The rotor can be sealed if necessary. AC motor has no wearing parts that need to be replaced regularly. At the same time, it is more efficient, durable and lower cost than DC motor.
As mentioned earlier, there are two problems in the application of AC technology in battery equipment such as forklift: low system voltage of 80V and corresponding high current; Energy loss during DC-AC conversion.
Nevertheless, the application of AC power in forklift is still gradually expanding. However, the AC powered forklift provided by most manufacturers is mainly used for the modification of DC forklift in explosion-proof environment, and the price is quite expensive. BT's reflex series is different. It not only adopts AC power, but also applies a series of new design concepts, which fully reflects and develops the advantages of AC technology.
To achieve this goal, we must first solve three problems:
·Conversion energy loss.
·Hardware cost.
·Manufacturing technology of low voltage AC motor.
The corresponding measures are as follows:
Balance energy loss
The solution to converting energy loss is to treat the forklift as a complete system rather than focusing on only one component. Finally, it comes down to making the energy loss during flow to AC conversion equal to the energy loss of carbon brush part of DC motor (AC motor has no carbon brush). This process can be realized through advanced electronic system.
Reduce costs
The next step is to maintain the low cost of the hardware part. This goal is finally realized by finding the best type and quantity of semiconductor components through extensive experiments. In this process, the continuous decline in the price of electronic components is also very helpful, and proves the strategic prospect of AC technology.
However, the most important factor is that the whole vehicle design is based on tributary technology, and the high braking torque of AC motor is the key. In fact, the braking capacity of AC motor is equal to its acceleration capacity. Electric braking can be achieved by changing the driving direction. If you want more powerful brakes, you must use traditional brakes. Through the careful study of the motor size, the braking torque is much larger than the acceleration torque, which makes the electrical braking effect of AC motor much stronger than that of DC motor.
Efficient braking means that the traditional braking system can be greatly simplified. In the reflex ACI of BT, the ordinary service braking has been replaced by parking braking. Whether the driver brakes through the brake pedal or changes the driving direction, the motor will stop and produce a similar effect as a generator. This means that the wear of brake lining is minimized.
Energy recovery
As mentioned above, the efficiency of AC motor in driving and braking is higher. When braking, the motor rotates in reverse, that is, the frequency of AC voltage is lower than that of rotor, and the motor produces discharge. The stronger the brake, the more energy will be regenerated.
A forklift has two larger motors, one for driving and one for lifting. Both can produce energy regeneration. When a typical forklift truck is used, all energy consumption can be divided into the following parts:
● 50% for driving.
● 4o% used for lifting and other actions of gantry and cargo.
● 10% for steering, fans, etc.
When the load rises, the energy begins to be consumed. When the goods fall with the fork, the energy can be recycled. The field test shows that the energy consumption when the load rises accounts for 19% of the total consumption.
The reflex ACI series of BT gives priority to the energy regeneration of the driving part, because it is the part that can significantly consume the most, and does not need to increase the complexity of the system, that is, it can be achieved without increasing any cost. Due to its high braking torque, almost all braking modes are generated by the energy generated.
Electric regenerative braking is also available on some DC powered forklifts, but it can only occur when braking is strong, which also means that part of the regenerated energy is converted into heat in the brake lining. And in almost all cases,
Aci will generate energy regeneration and continue to act until the forklift is completely stationary.
In fact, it is impossible to calculate how much energy can be recovered. It depends on different use conditions and the speed at the beginning of braking. A reasonable number is 10% - 15%, that is, 5% - 7% of the overall energy consumption of forklift.
Improve performance
If the recovered energy can not be used reasonably, its benefits are limited. The simplest way is to recharge the upper battery to prolong the service time. In reflexaci, BT uses this energy to improve the overall performance of forklift. As a result, the maximum speed is increased by 10%, and the more obvious effect is reflected in the acceleration.
The reflex ACI only needs 15m to reach the top speed, while the DC forklift needs at least twice its distance. The research shows that in most practical applications, the distance from start to stop of forklift is less than 20m. Only the excellent acceleration of BT AC forklift makes it possible to realize full speed operation in such a short distance.
To sum up, the application of AC technology in forklift improves the overall performance of forklift, significantly reduces the replacement rate of faults and events, and greatly enhances the reliability. On the client side, it is reflected in higher productivity per unit time and lower operation and maintenance costs. AC technology in battery forklift is called the future technology, and will be more and more widely used.
