Consultation on frequency converters

Reply 1# zhousun888: When the load on the equipment driven by the motor decreases, the speed of the motor can be controlled by changing its frequency, thereby adjusting the performance of the equipment to match the new operating conditions. This helps to reduce unnecessary loads (and the efficiency of the equipment also changes as a result), thus saving energy. The prerequisite is that the device has the capability to adjust its speed.

　　1. A frequency converter is a power control device that uses the on-off operation of power semiconductor devices to convert an industrial-frequency power supply into electrical energy of another frequency. 2. The principle of frequency conversion for energy savings: In production, the energy consumption of many devices is related to … 1. A frequency converter is a control device that uses the on-off operation of power semiconductor devices to convert AC power supply into electrical energy at another frequency. 　　2. Principle of frequency conversion for energy savings In production, the energy consumption of many devices is related to the speed of the machinery involved; oil and water pumps are particularly affected by this. These devices are usually selected based on the maximum load conditions that may occur during production, such as maximum flow rates and head pressures. However, the actual flow rate required in production is often much lower than the designed maximum value. If the motor used cannot adjust its speed, flow rate can only be controlled by adjusting the opening degree of valves, which results in significant energy losses at the valves. If valve regulation is not used instead and the motor operates at adjustable speeds, then when the required flow rate decreases, the motor’s speed drops as well, thereby reducing energy consumption significantly. 　　It can be seen that when the rotational speed is reduced by 1/2, the flow rate is reduced by 1/2, the pressure is reduced by 1/4, and the power is reduced to 1/8; in other words, the power decreases in proportion to the cube of the rotational speed. If instead of reducing the valve opening, the motor speed is lowered, then as the output pressure of the pump decreases, the power that was previously consumed by the valve can be completely avoided while maintaining the same flow rate. This is the principle behind saving energy through speed control. In simple terms, when no variable frequency drive is used, the discharge volume at the pump’s outlet is regulated by the outlet valve; this can cause the motor to overload. When the flow rate is low, the valve is closed to reduce the flow, which increases the resistance in the pipes and results in some energy being wasted on the pump’s outlet valve. By installing a variable frequency drive, it is possible to reduce the pump’s speed, and accordingly its head pressure as well. This leads to a reduction in the motor’s power consumption, thereby addressing the issue of energy loss that previously occurred at the pump’s outlet valve. Thanks to its constant torque characteristic, the motor torque remains unchanged after speed reduction via frequency conversion, and the driving torque stays constant, which ensures a consistent displacement and thus helps save electrical energy. 　　3. Examples of energy savings, taking water pumps as an example: When the frequency is reduced, the iron loss in the motor decreases. Since n=60f/2p, a decrease in rotational speed leads to a reduction in the motor’s output power. Thus, energy is saved. According to fluid mechanics, P (power) = Q (flow rate) × H (pressure); the flow rate Q is proportional to the first power of the rotational speed N, pressure H is proportional to the square of the rotational speed N, and power P is proportional to the cube of the rotational speed N. If the efficiency of the water pump remains constant, then when it is necessary to reduce the flow rate, the rotational speed N can be reduced proportionally, and as a result, the shaft output power P decreases in proportion to the cube of this reduction. That is, there is an approximately cubic relationship between the power consumption of the water pump motor and its rotational speed. For example: if a water pump motor has a power rating of 55 KW, its power consumption drops to 28.16 KW when the rotation speed is reduced to 4/5 of the original speed, resulting in a 48.8% reduction in energy use; when the rotation speed is reduced to 1/2 of the original speed, the power consumption is 6.875 KW, representing an 87.5% reduction in energy use. The application of Sanjing frequency converters for energy-saving upgrades in air compressors Air compressors are widely used in many sectors of the national economy and defense industry. In particular, they have become essential equipment in industries such as textiles, chemicals, and power generation, serving as key components in the manufacturing processes of numerous industrial fields. Providing compressed air with sufficient pressure for automated production is essential for ensuring smooth production processes; even brief drops in pressure can affect product quality. With the advancement of frequency conversion technology, inverters are being used more and more widely in the field of electrical drives. Its diversity of control methods, robust motor protection features, and unique advantages make it unmatched in the industrial control field at present. 　　I. Working Principle of Screw Air Compressors The operating process of screw air compressors consists of four stages: suction, sealing and delivery, compression, and exhaust. As the screw rotates within the housing, it engages with the toothed grooves of the housing. Air is drawn in through the intake port, along with engine oil. As the toothed grooves rotate, they seal the inhaled air and oil mixture and transport it toward the exhaust port. During this transportation process, the gap between the toothed grooves gradually decreases, compressing the air and oil mixture. When the toothed grooves rotate to the exhaust port of the housing, the high-pressure air and oil mixture is expelled from the engine. 　　II. Composition of the compressed air supply system and control principle of the air compressor Composition of the compressed air supply system: The air compression supply system in a factory generally consists of an air compressor, a cold dryer, filters, an air storage tank, pipelines, valves, and equipment that uses compressed air. 　　Control principle of air compressors: In the control systems for air compressors in factories, pressure relays installed on the pipelines at the back end are commonly used to control the operation of the air compressors. When the air compressor starts, the loading valve is in a non-operational state, the loading cylinder does not move, the air inlet of the compressor head is closed, and the motor starts under no-load conditions. Once the air compressor starts operating, if the demand for air from the downstream equipment is high and the pressure of compressed air in the air storage tank and the downstream pipelines does not reach the maximum allowable value, the controller activates the loading valve to open the air inlet; the motor then operates, continuously generating compressed air to supply the downstream pipelines. If the gas-using equipment at the rear end stops using gas, the pressure of compressed air in the pipelines and storage tanks at the rear end gradually increases. When this pressure reaches the set upper limit, the pressure controller sends a unload signal; the loading valve stops functioning, the air inlet closes, and the motor operates without any load. 　　III. Variable-frequency transformation of screw air compressors Comparison between normal-frequency operation and variable-frequency operation of air compressors: Air compressor motors generally have high power, and the starting method that is most commonly used is the star-delta start under no-load conditions; both loading and unloading occur instantaneously. This results in a high starting current when the air compressor is started, as well as significant mechanical stress on the equipment during loading and unloading. It not only causes fluctuations in the power supply voltage but also leads to large variations in the compressed air supply. Additionally, this mode of operation accelerates wear and tear on the equipment, reducing its service life. Since the drive motor of a conventional air compressor cannot adjust its speed on its own, it is not possible to use changes in pressure or flow rate to reduce the speed and thus adjust the output power accordingly. The motor is not allowed to start frequently, which means that it continues to operate at no load even when the amount of air required is low, resulting in significant waste of electrical energy. 　　Conducting a variable-frequency conversion on the air compressor allows the motor to start and stop smoothly, reducing startup shock and extending the equipment’s service life. Meanwhile, since the motor’s operating frequency can be adjusted, the air compressor is able to automatically regulate its motor speed based on the amount of air required, which reduces frequent loading and unloading of the motor. This leads to a significant reduction in the motor’s operating power, helps maintain a constant pressure in the air supply system, and thus achieves energy savings. 　　IV. Design Principles for Variable Frequency Conversion Project 　　Based on the problems existing in the original operating conditions and taking into account the requirements of the production process, the system after the variable frequency conversion of the air compressor should meet the following requirements: 　　· The motor’s variable frequency operation should maintain a stable pressure at the outlet of the air storage tank, with the pressure fluctuation range not exceeding ±0.02 Mpa. 　　·The system should have two control circuits: one for variable frequency and one for mains frequency. 　　·According to the operating requirements of the air compressor, the system shall ensure that the motor has a constant torque operation characteristic. 　　·To prevent non-sinusoidal waves from interfering with the air compressor controller, effective measures to suppress electromagnetic interference should be in place at the input of the frequency converter. 　　·When the electrical load is low and the inverter is operating at a low frequency, it is necessary to ensure that the temperature of the motor windings as well as the noise level generated by the motor remain within acceptable limits. 　　·According to the production process requirements, after the frequency conversion upgrade, the supply pressure of the compressed air system should be appropriately reduced, changing the original high-pressure variable-flow air supply method to a frequency-controlled constant-pressure variable-flow air supply method. 　　V. Selection of the frequency converter 　In accordance with the principles mentioned above, the Guangzhou Sanjing Electric SAJ series of general-purpose frequency converters is selected; these converters are equipped with a function for switching between industrial and standard frequencies. By adding a pressure transmitter, a closed-loop control system can be established. The air pressure signal fed back by the sensor is directly sent to the input port of the PID regulator built into the frequency converter, while the pressure setting can be adjusted using the keyboard of the frequency converter, enabling this system to meet the aforementioned operational requirements. 　　Features of SAJ frequency converters: · Equipped with a 32-bit microprocessor dedicated to motor control, enabling high-precision frequency output. · Innovative power accumulation function, providing a more intuitive and convenient way to monitor energy savings. 　　·It has a built-in RS-485 interface, enabling network control via a computer. Multiple signal inputs, built-in simple PLC for more convenient automated control. 　　·The carrier frequency is adjustable, and it can operate in silent mode. 　　·It features diverse control methods and strong versatility. 　　·It features a built-in PID control function, enabling simple closed-loop control for low-speed rated torque output with stable operation. 　　·The keyboard is easy to use, allowing for online adjustment and setting of relevant parameters while it is running. 　　·Low-frequency torque output: 180%. Excellent performance at low frequencies. · Maximum output frequency of 600 Hz, enabling control of high-speed motors. · Comprehensive detection and protection functions (overvoltage, undervoltage, overload); ability to restart after sudden power outages. · Protection functions such as acceleration, deceleration, and stall prevention during operation. · Deceleration leads to a smooth stop, with automatic return to normal operation and DC braking. · Various parameters related to the inverter’s operating status are displayed, providing clear insight into control signals and load conditions. During the frequency conversion upgrade, we will strive to maintain the integrity of the main circuit and control circuit of the existing equipment, making no changes to these circuits. This facilitates the easy return of the air compressor to its original control mode in case of a failure or maintenance of the frequency converter, ensuring that the air compressor can operate both in frequency conversion mode and at normal frequency. 　　 Principle of frequency conversion energy saving

The frequency conversion is directly related to your power output; if the 2nd and 4th speed levels cannot meet the operational requirements \"directly,\" there will inevitably be losses, similar to backflow. Variable frequency can \"approximately\" meet the operating conditions, thus saving energy