The energy efficiency improvement solution for FGI high-voltage variable frequency soft starters

As a general-purpose mechanical equipment, air compressors play a significant role in multiple industries. The high-voltage cascaded variable frequency soft start device developed by FGI Electronic Technology Co., Ltd. has successfully applied the soft start technology of the one-to-two variable frequency soft start device to the air compressor load, bringing outstanding economic benefits to users and ensuring the stable operation on site.

1. Brief introduction of the user's on-site situation

A certain chemical enterprise in Shandong has two air compressors, which are important equipment in the production process. The two motors on site are both 10kV and 4000kW. When the air compressor equipment starts, it should ensure that there will be no grid drop or grid fluctuation, short start-up time, convenient control and a series of other problems. In response to such situations, FGI Electronic Technology Co., LTD. (hereinafter referred to as "FGI") has provided a variable frequency soft starter one-to-two solution, which meets a series of on-site usage requirements. After on-site operation, it has demonstrated extremely high reliability, stability and convenience. To meet various on-site demands, the variable frequency soft start device has the following conditions:

The variable frequency soft start-up features high protection, high stability and high convenience, and can be fully unmanned throughout the process.

The variable frequency soft start device is a disturbance-free two-in-one switching device with reactor. The variable frequency soft start device can drive any one of the two motors to operate without any start sequence restrictions, ensuring the on-site process requirements. The start process of the variable frequency soft start device requires smoothness, large starting torque, and short start time for the air compressor, guaranteeing the on-site usage demands.

The variable frequency soft-start device is equipped with strict electrical interlocks and program interlock logic, strictly controlling the sequence of the knife switch during the disturbance-free switching process, and has complete fault alarm and protection measures to ensure the stability of the switching process.

The variable frequency soft start device is connected to the air compressor's electrical control system, meeting various functional interface and monitoring requirements, and ensuring that unexpected shutdowns will not occur due to parameter changes during operation. After repeated technical discussions and scheme evaluations, the FGI JD-BP38-2400FF2A type variable frequency soft start device was selected to carry out energy-saving and technological upgrades for the air compressor, achieving the expected goals.

2.Basic parameters of FGI JD-BP38-2400FF2A variable frequency Soft Starter Device

According to the on-site requirements, the FGI variable frequency soft start device needs to achieve the disordered start of two air compressors. The system should have basic functions such as heavy-load start, non-intrusive switching, logic protection, and communication interfaces. In addition, the FGI high-voltage variable frequency soft start device also has the following features:

It adopts a perfect harmonic-free unit series multi-level topology structure, featuring low grid current harmonics and meeting the strict requirements of the grid for power quality. There is no need to use output filters, and ordinary asynchronous motors can be used.

Oscillation suppression technology: When the motor is lightly loaded or unloaded, local instability may occur. At this time, the current amplitude fluctuates greatly, and the oscillation of the current may cause the system to trigger protection due to overcurrent or overvoltage. Our company adopts an advanced current oscillation suppression algorithm, which can effectively suppress the oscillation of current and ensure the stable and reliable operation of the system.

Neutral point drift function: After detecting a unit failure, the faulty unit can be bypassed within 100 μs, and the star point drift technology is executed to maintain the balance of output line voltage and maximize the voltage utilization rate.

Configuring the torque coordination function enables real-time control of the torque in multi-motor drive systems.

It can be configured with a current overload capacity of more than twice, which can meet the heavy-load start-up requirements of systems with large inertia.

The parameters are complete. The system provides and records all the parameters required for the motor operation process for on-site monitoring and protection.

Automatic output voltage regulation technology: The variable frequency soft start device detects the bus voltage of each unit in real time and adjusts the output voltage coefficient based on the bus voltage, thereby achieving the automatic voltage regulation function. This avoids the impact of grid fluctuations on the output voltage.

3.Control plan

A set of JD-BP38-2400FF2A high-voltage variable frequency speed regulation system produced by FGI Electronic Technology Co., Ltd. was adopted on site, with a rated voltage of 10kV, a rated current of 173A and a rated power of 2400kW. The main loop of the control scheme control variable frequency soft start device, easy field grid meet the demand of the scene space.

System diagram of the variable frequency soft starter one-to-two primary system

The on-site usage space is limited. The variable frequency soft start device designed this time features flexible design. The variable frequency soft start device can be set to start any air compressor according to the user's requirements. After starting, the motor will automatically switch to the industrial frequency operation without interference and then start the next motor. When a fault occurs during the start-up process of the variable frequency soft start device, It can be converted from fault to power frequency or directly started at power frequency according to the actual needs of the customer.

(1) The control power is on and the knife switch operation is closed

The control power on the variable frequency soft start device detects that the high voltage is not ready, and the contactor status is met. Then, the isolation knives 1#QS1 and 1#QS2 can be operated, and the isolation knife operation is closed.

(2) Self-check of the variable frequency soft start device

Check whether the knife switch in the current variable frequency soft start device circuit is closed, whether the system is free of faults, and whether the external emergency stop and process permit signals are met. If all conditions are met, send out the "High Voltage Permit closing" signal.

(3)High-voltage power-on

The "closing Permit" is sent to the high-voltage cabinet, and the high-voltage cabinet is allowed to be powered on.

(4)Motor selection

After power-on is completed, the motor is selected based on the current control mode. There are three ways for this system to select the motor.

HMI control mode: Set the HMI number, and on the main interface, set the motor number to 1 or 2.
DCS/Remote Control Box Control Mode: Based on the terminal signal setting number, when the terminal input corresponding to the motor number is activated, it indicates that the selection is complete. If there is no input or multiple inputs, it is determined that the motor number selection is incorrect.
Host Computer Mode: Set communication parameters. The host computer can write the selected motor number by the frequency converter through communication. The frequency converter supports mainstream communication protocols such as Modbus, Profibus, Profinet, EtherCAT, and Ethernet.
Furthermore, regardless of the mode selection, both the human-machine interface and the upper computer will display the number of the currently selected motor.

(5) Contactor/circuit breaker closing logic

After the motor selection is completed, the contactor of the corresponding circuit is closed.

Taking the selection of Motor 1 in the variable frequency soft start device as an example. Choose 1 # machine, after determining the current circuit power frequency QF11 not closing, variable frequency soft start device trouble-free, output contactor KM1, KM01, KM3, in turn, closing, with signal frequency ready, site receives the signal frequency conversion is ready, waiting for the scene of the boot.

(6) guard signal

When the current running motor circuit is detected, the corresponding variable frequency soft start device alarm information will be activated. To ensure that the variable frequency soft start device is compatible with different types of motors in the later stage, a parameter backup and switching method is adopted to guarantee that there are different response strategies when the variable frequency soft start device selects different circuits, ensuring the stable operation on site.

4.The implementation effect of driving the air compressor with a variable frequency soft start device

Since the variable frequency soft starter device was debugged and officially put into use in April 2023, it has been operating stably and has maintained a zero-fault record to date.

(1) Convenience

The "one-to-two" technical solution enables the multi-loop seamless switching of the main body of the variable frequency soft-start device. The solid-state soft-start is used to achieve the design of one-to-many. This design has high cost and great difficulty. The customer's remote input signal can enable the rapid and seamless start of the air compressor, with no one on duty throughout the process. It perfectly solves the on-site problems and is highly practical and convenient.

(2) Efficiency

The variable frequency soft start device is a functional product based on the variable frequency converter. It has excellent dynamic and static performance, large starting torque, fast torque dynamic response, high speed regulation accuracy, and strong load capacity. It monitors the entire starting process, with no grid impact during the start-up, a smooth start-up process, and has won high praise from customers.

(3) Reliability

The internal structure of the variable frequency soft start device adopts a modular design and is equipped with high-level protection. The unit positions can be interchanged, making maintenance convenient. The device operates as a variable frequency starter, and internal optical fiber communication is used. The communication is reliable and the signals are stable, ensuring the stable operation of the equipment. When there is a fault during the operation of the variable frequency soft start device, it will automatically execute the neutral point drift technology to achieve unit failure without machine shutdown. When operating at power frequency, it is remotely controlled by contactors, allowing for direct start and stop by external control to meet various on-site requirements.

(4) Usability

This variable frequency soft start device supports the start-up of any motor number, which is conducive to on-site adjustment of the process. It also supports multi-parameter input for the motor, ensuring the stability of the equipment in multiple aspects.

In conclusion, the technical performance and on-site performance of the variable frequency soft start device, when applied to the manufacturing industry, greatly facilitate the promotion of this control method. It not only ensures the stability of the equipment to the greatest extent, but also maximally guarantees the convenience and reliability on-site.

5.Closing Remarks

After adopting the JD-BP38 series variable frequency soft start device produced by FGI Electronic Technology Co., Ltd. for the air compressor system, the on-site operation and production have been stable. The startup time of the air compressors meets the practical requirements. Combined with the on-site control, it has perfectly solved the complex problems of on-site control and greatly improved the convenience of the air compressor system. The actual application situation on site shows that using the advanced and reliable variable frequency soft start device from FGI to drive multiple loads such as air compressors can significantly enhance the on-site operation efficiency, reduce the on-site maintenance workload, and bring considerable economic benefits. It is worthy of wide promotion.