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
Při provozu oběhového vodního čerpadla, když se průtok mění v důsledku procesních požadavků, je nutné upravit otevření výstupu a vstupu čerpadla, aby se změnil skutečný průtok čerpadla. Tato metoda nastavení se nazývá škrticí regulace. V tomto příkladu je otevření ventilu na výstupu a vstupu okolo 60 %. Z hlediska využití energie se jedná o velmi neekonomickou metodu nastavení.
3.2 Režim řízení po transformaci frekvenční konverze
Při provozu oběhového vodního čerpadla se při změně průtoku v důsledku procesních požadavků plně otevřou vstupní i výstupní ventily. Nastavením otáček motoru lze najít vhodný nový provozní bod pro dosažení odpovídajícího průtoku. V závislosti na skutečné situaci a potřebách na místě lze implementovat ruční nebo automatické ovládání. V tomto příkladu, protože není nutné často upravovat průtok, je skutečná provozní frekvence motoru stanovena na 40 Hz na základě skutečné situace a potřeb na místě a ruční ovládání se používá především z důvodu úspory energie.
4. Změny v provozu po použití systému regulace otáček s proměnnou frekvencí
Bylo dosaženo zcela měkkého startu. Při spuštění motoru se otáčky rotoru postupně zvyšují s frekvencí vstupního napájení, což vede k plynulému zvyšování otáček. Doba startu celého systému je nastavena na přibližně 20 sekund, což nezpůsobí žádný dopad na systém a je plynulejší než původní metoda startování.
Výrazně se snížil i proud používaný v elektrické síti, což zvyšuje bezpečnost používání elektrických zařízení. Zároveň se snižující se frekvencí snižuje i rychlost motoru, což snižuje mechanické opotřebení a výrazně snižuje pravděpodobnost poruch a náklady na údržbu. Transformátor, který dodává elektrickou energii vodnímu čerpadlu, ušetřil většinu kapacity zdroje napájení. Pouhým snížením aktivní zátěže se ušetří kapacita přibližně 50 kilowattů, což zlepšuje účinnost využití zařízení. Účiník motoru se také odpovídajícím způsobem zlepšil, což činí provoz motoru ekonomičtějším.
Použití technologie frekvenční konverze zlepšilo kvalitu produktů, snížilo spotřebu energie, ušetřilo energii a dále zvýšilo ekonomické přínosy podniků. Aplikace technologie frekvenční konverze pro regulaci rychlosti vyžaduje transformaci těchto zařízení za účelem dosažení úspory energie.