For many years, DC has been the main variable power source for electric storage and handling equipment. DC drive has been widely used in electric equipment for a long time as a cheaper drive. However, the DC system itself has some inherent defects in performance, maintenance, etc., and AC and AC motors are far superior in this respect. Therefore, Fanda indoor handling equipment manufacturers have begun to commit to the research and development of AC technology applications.
In fact, since the end of the 19th century, AC power has been widely used. It is also the AC motor technology that has promoted the electrification process in industry, railways and other fields. Now, electrical 名媛直播 using communication technology are everywhere, and communication may have become the most widely tested and verified technology.
The advantages of communication technology are mainly reflected in the following aspects:
l The conversion between high and low voltage is simple.
2. The motor becomes powerful and efficient, and can withstand the impact of high current.
3. The number of motor parts is greatly reduced, and there is no wear, and it is durable.
4. Compared with DC motors, the cost reduction is significant.
However, the application of AC motors in battery-powered equipment such as forklifts is subject to certain restrictions. There are two main reasons: the low system voltage of 80V requires the conversion of DC to AC by high-energy semiconductors. This cost is high. The conversion process itself consumes energy, and the battery capacity is quite limited.
BT has now developed a new series of AC-powered reach forklifts-Reflex Aci. The new series of forklifts overcome the following problems and realize the full potential of AC technology, which reduces the operating cost of forklifts and significantly improves performance and reliability.
Below, we give a brief introduction to several existing motor technologies.
Series DC motor
This is the oldest and most traditional motor. The current is delivered to the battery and dried, and is transferred to the stator through the carbon brush. This method has two drawbacks: all current must be delivered through the carbon brush, and the performance depends on the physical size and wear of the carbon brush. The most important thing is that this limits the braking performance. In addition, the motor carbon brush as a wearing part must be replaced regularly, otherwise it will greatly affect the life of the motor. With this in mind, many manufacturers have equipped forklifts with devices that detect wear and issue warnings, which increases the cost of the forklift.
All motors will generate heat, but in DC motors, heat is mainly generated in the internal components of the motor, so most DC motors will also be equipped with a fan for heat dissipation.
Motor
This is a more advanced DC motor, the energy of the stator and armature is input separately. As with series motors, this technique has been used for quite a long time. The new technology uses separately excited parallel excitation magnetic field and armature, so that the performance control of the motor is much better than the series motor. This type of motor is often called a 4-quadrant motor because it can drive and brake in both directions. However, the defects of motor carbon brushes still exist.
Three-phase AC motor
Technically, this is the simplest type of motor. The principle is to send three-phase alternating current to a fixed coil, which produces a rotating magnetic field that induces a shorted voltage on the rotor. AC motors do not have brushes, nor do DC motors usually limit the maximum current, which means that the motor can get more energy and more braking torque in actual use, so it can run at a faster speed.
In the AC motor, the heat mainly occurs in the fixed sub-coil of the motor housing part, which is convenient for cooling and heat dissipation. If required, the rotor can be sealed. AC motors have no wearing parts that need to be replaced regularly. At the same time, they are more efficient, durable, and cost less than DC motors.
As mentioned earlier, there are two problems with the application of AC technology in battery equipment such as forklifts: a low system voltage of 80V and a correspondingly high current; and energy loss during DC-AC conversion.
Nevertheless, the application of AC power to forklifts is gradually expanding. However, most of the AC-powered forklifts provided by manufacturers are mainly used for the modification of DC forklifts in an explosion-proof environment, and the price is quite expensive. BT's Reflex series is different. It not only uses AC power, but also applies a new series of design concepts, so that the advantages of AC technology can be fully reflected and developed.
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 losses is to treat the forklift as a complete system, rather than focusing on just one component. Ultimately it comes down to making the energy loss during the conversion to AC equal to the energy loss of the carbon brush part of the DC motor (the AC motor has no carbon brush), and this process is achieved through advanced electronic systems.
cut costs
The next step is to maintain the low cost of the hardware part. This goal is finally achieved through extensive trials to find the best type and number of semiconductor components. In the process, the continuous decline in the price of electronic components also helps, and at the same time It proves the strategic prospect of communication technology.
However, the most important factor is the high braking torque of the AC motor based on the tributary technology. In fact, the braking capacity of the AC motor is equivalent to its acceleration capacity. Electrical braking can be achieved by changing the direction of travel. If you want more powerful brakes, you must use traditional brakes. Through careful study of the size of the motor, a braking torque that is much larger than the acceleration torque is obtained, making the electrical braking effect of the AC motor much stronger than that of the DC motor.
Efficient braking means that the traditional braking system can be greatly simplified. In BT's Reflex Aci, ordinary service brakes have been replaced by parking brakes. Whether the driver brakes with the brake pedal or switches in the direction of travel, the motor will stop and produce a generator-like effect. This means that the wear of the brake lining is minimized.
Energy recovery
As mentioned above, the efficiency of the AC motor in driving and braking is higher. When braking, the motor rotates in the reverse direction, that is, the frequency of the alternating voltage is lower than the rotor frequency, and the motor produces a discharge effect. The stronger the brake, the more energy is regenerated.
A forklift has two larger electric motors, one for driving and one for lifting. Both can produce energy regeneration. When a typical reach truck is used, all energy consumption can be divided into the following parts:
● 50% is used for driving.
● 4O% is used for lifting and other actions of the door frame and the goods.
● 10% is used for steering, fans, etc.
When the load is increased, the energy starts to be consumed. When the cargo drops with the fork, the energy is recycled. Field tests show that the energy consumption when the load is increased accounts for 19% of the total consumption.
BT's Reflex Aci series gives priority to the energy regeneration of the driving part, because this is the part that can significantly consume the most, and it does not need to increase the complexity of the system, that is, it can be achieved without adding any cost. Due to its high braking torque, almost all braking methods are produced with energy.
There are also electrical regenerative braking on some DC-powered forklifts, but it can only happen when a strong brake is applied, which also means that part of the regenerated energy is converted into heat in the brake lining part. In almost all situations, Aci will produce energy regeneration and continue to act until the forklift is completely stationary.
How much energy can be recovered is actually impossible to calculate, it depends on different usage conditions, the speed at the beginning of braking, etc. A more reasonable number is 10%-15%, which is 5%-7 of the overall energy consumption of the forklift %.
Improve performance
If the recovered energy cannot be used reasonably, its benefits are limited. The easiest way is to recharge the battery to extend the use time. In ReflexAci, BT uses this energy to improve the overall performance of the forklift. As a result, the maximum speed is increased by 10%, and the more obvious effect is reflected in the acceleration.
Reflex Aci only needs 15m to reach the maximum speed, while DC forklifts need at least twice the distance. Studies have shown that in most practical applications, the distance of a forklift truck from start to stop is less than 20m. Only the excellent acceleration of BT AC forklift makes it possible to achieve full-speed operation in such a short distance.
In summary, the application of AC technology to forklifts has improved the overall performance of forklifts, significantly reduced the rate of failure and event replacement, and greatly enhanced reliability. On the user side, it is reflected in higher productivity per unit time and lower operation and maintenance costs. The exchange technology is called the future technology in the battery forklift, and it will be more and more widely used.
