Suppliers of frequency converter energy feedback devices remind you that in modern industrial automation production, the application scope of pumps, fans and other equipment is becoming more and more extensive. Their consumption of electrical energy, throttling losses of baffles, valves and other equipment, as well as daily maintenance and repair costs, account for almost 20% of the cost. This is a considerable production expense. With the development of the economy, the deepening of reforms, and the intensification of market competition, energy conservation and consumption reduction have gradually become an important means to improve product quality and reduce production costs.
1. Basic Theory of Variable Frequency Energy saving Technology
The basic principle of frequency conversion technology is that for a long period of time, the frequency of the alternating current used by electrical equipment is maintained in a fixed state. The application of frequency conversion technology is to make the frequency a resource that can be adjusted and utilized freely. Nowadays, the most active and rapidly developing variable frequency technology is the speed regulation technology of variable frequency.
Frequency conversion technology includes computer technology, power electronics technology, and click transmission technology. It is a comprehensive technology that combines mechanical equipment and strong and weak electricity. It refers to the conversion of the signal of the power frequency current into other frequencies, which is mainly achieved through semiconductor components. Then, the alternating current is converted into direct current, and the inverter regulates the current and voltage while achieving stepless speed regulation of the electromechanical equipment. In summary, frequency conversion technology is to control the speed of a motor by changing the frequency of the current, thereby effectively controlling the motor equipment. These are all achieved on the basis of the year-on-year increase in current frequency and motor speed. The characteristic of frequency conversion technology is that it can ensure the smooth operation of the motor, automatically control acceleration and deceleration, and reduce energy consumption while improving work efficiency.
In the daily use of frequency converters, direct torque control and vector control are mainly used. In the future development of frequency converters, artificial neural networks and fuzzy self optimization control methods will be used. Moreover, as frequency converters continue to develop, their comprehensiveness will become increasingly high. In addition to completing basic speed regulation functions, they also have communication, programmable, and parameter identification functions set internally.
2. Energy saving principle of frequency converter
2.1 Variable frequency energy-saving methods
According to fluid mechanics, power=pressure * flow rate. Flow rate and speed to the power of one are proportional, pressure is proportional to the square of speed, and power is proportional to the cube of speed. If the efficiency of the water pump is fixed, when the flow rate decreases, the speed will decrease proportionally, and the output power will also decrease in a cubic relationship. Therefore, the speed of the water pump is approximately proportional to the power consumption of the motor. For example, when a 55kW water pump motor is turned to 80% of its original speed, its power consumption is 28kW/h, with a power saving rate of 48%. But if the speed is adjusted to 50% of the original, the power consumption becomes 6 kilowatts per hour, and the power saving rate reaches 87%.
2.2 Adopting power factor compensation for energy conservation
The reactive power not only causes equipment to heat up and increases wire wear, but most importantly, the decrease in power factor leads to a decrease in the active power of the power grid. As a result, a large amount of reactive energy is consumed in the power lines, leading to a decrease in equipment efficiency and serious waste. After using a variable frequency speed regulation device, the reactive power loss is further reduced due to the filtering capacitor inside the frequency converter, which increases the active power of the power grid.
2.3 Using soft start method for energy conservation
Due to the fact that the motor is started through Y/D or direct starting, the starting current is four to seven times the rated current, which can cause serious impact on the power grid and electromechanical equipment. Moreover, this requires a very high capacity of the power grid, generating a relatively large current during starting, and causing significant damage to valves and baffles during vibration, which is also very detrimental to the service life of pipelines and equipment. The use of frequency converters utilizes the soft start function of the frequency converter to start the current from zero, and the maximum value will not exceed the rated current. Therefore, the impact on the power grid and the requirements for power supply capacity are greatly reduced, and the service life of valves and equipment is greatly extended.
3. Application examples of variable frequency energy-saving technology
We used the installation of a variable frequency speed controller on a 160kW circulating water pump as an example to retrofit the variable frequency energy-saving equipment. We tested the electricity consumption before and after the retrofit and achieved very satisfactory results.
3.1 Control mode before frequency conversion transformation
In the operation of a circulating water pump, when the flow rate changes due to process requirements, it is necessary to adjust the opening of the pump outlet and inlet to change the actual flow rate of the pump. This adjustment method is called throttling adjustment. In this example, the valve opening of the outlet and inlet is around 60%. From the perspective of energy utilization, this is a very uneconomical adjustment method.
3.2 Control mode after frequency conversion transformation
In the operation of a circulating water pump, when the flow rate changes due to process requirements, both the inlet and outlet valves are fully opened. By adjusting the motor speed, a suitable and new operating point can be found to obtain the appropriate flow rate. According to the actual situation and on-site needs, manual or automatic control can be implemented. In this example, because there is no need to frequently adjust the flow rate, the actual operating frequency of the motor is determined to be 40Hz based on the actual situation and needs on site, and manual control is adopted mainly to save energy.
4. Changes in operation after using a variable frequency speed regulation system
The complete soft start has been achieved. When the motor starts, the rotor speed gradually increases with the frequency of the input power supply, resulting in a smooth increase in speed. The starting time of the entire system is set to about 20 seconds, which will not cause any impact on the system and is smoother than the original starting method.
The current used in the power grid has also been significantly reduced, making the use of electrical equipment safer. At the same time, as the frequency decreases, the speed of the motor also decreases, reducing mechanical wear and greatly reducing the probability of failure and maintenance costs. The transformer that provides electrical energy to the water pump has saved most of the power supply capacity. By simply reducing the active load, the saved capacity is approximately 50 kilowatts, improving the utilization efficiency of the equipment. The power factor of the motor is also correspondingly improved, making the operation of the motor more economical.
The use of frequency conversion technology has improved product quality, reduced energy consumption, saved energy, and further enhanced the economic benefits of enterprises. The application of frequency conversion speed regulation technology requires the transformation of these equipment to achieve energy conservation.