The Application of High Voltage Inverter in Hamza Sugar Mill of Pakistan

I Project Overview

Hamza Sugar Mills Limited of Pakistan, formerly known as Hi-sons Sugar Mills established in 1969, was renamed to its current name in 1970. The company currently has a production scale of 38,000 tons of crushing capacity per day, making it the largest sugar mill in Asia. Its main products are sugar and raw materials for alcohol.

【Exterior View of Hamza Sugar Mill】

II Brief Introduction to Sugarcane Sugar Production Process

Sugarcane sugar production mainly includes four steps: pretreatment, pressing, clarification and evaporation, and sugar boiling. After pretreatment, the sugarcane enters the press through a conveying system, where it undergoes multiple squeezings to extract the juice. The juice then enters the clarification, evaporation, and sugar boiling processes to produce white sugar, while the pressed residue is processed separately.

The press is a crucial piece of equipment for extracting sugarcane juice using mechanical pressure. It mainly consists of a shredder and a main body containing three rollers, which are driven by a power device. The principle of juice extraction by pressing is to break the sugarcane cells and release the juice through squeezing. To improve extraction efficiency, the pressing process often uses multiple stages and may incorporate an imbibition process, which involves soaking the pressed bagasse in hot water or dilute juice to further extract residual sugar.

【Pressing Production Process Flow Chart】

III Reasons for Equipment Modification

The extraction rate of the press is a crucial factor affecting sugar absorption; for every 1% increase in the extraction rate, the total recovery rate can be improved by 0.88% to 0.92%. The main factors affecting the extraction rate include:

• Reabsorption during fiber expansion:

After pressing, the sugarcane fibers expand upon leaving the press, absorbing some of the extracted juice and causing sugar loss.

• Degree of crushing and morphology of cane material:

​ A good degree of crushing is a prerequisite for efficient pressing, promoting juice extraction and seepage.

• Moisture content of bagasse:

Lowering the moisture content of bagasse ensures a higher extraction rate.

• Uniformity of cane layer thickness:

Uneven cane layer thickness can lead to incomplete pressing or high bagasse moisture content, affecting the extraction rate.

• Wear of press rolls:

Wear of the press rolls in the later stages of the crushing season increases the gap between them, reducing the extraction rate.

【Original Steam Turbine Operation Scene】

The original press, driven by an inefficient and polluting back-pressure steam turbine (without a condenser, leading to high exhaust temperatures), also lacked adjustable speed. This resulted in suboptimal cane layer thickness about 10% of the time, lowering the average extraction rate below 95.4%, causing sugar loss and reduced output. Consequently, the user sought a modification for press speed regulation to improve extraction (theoretically by >0.2%) and save energy by reducing speed during insufficient cane layer thickness.

IV Modification Plan

According to on-site requirements, the modification plan adopts a high-voltage inverter + motor to replace the original steam turbine-driven press. The high-voltage inverter, as the motor's starting device, offers the following main advantages:

• Smooth start, protecting the motor and power grid: Reduces the impact of direct starting on the power grid, avoids motor winding overheating and insulation aging caused by instantaneous high starting current, and extends motor lifespan.
• Simple operation and easy maintenance.
• Convenient speed regulation to meet press process requirements.

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IV.I On-site Equipment Conditions

Each production line is equipped with 5 presses. The first press uses a one-to-one high-voltage inverter driving a high-voltage motor. This motor is a variable frequency three-phase asynchronous motor manufactured by Shanxi Electric Machinery Manufacturing. The first press has a heavier load, so its motor and inverter have higher power, while the remaining presses have lighter loads and correspondingly smaller equipment power.

The main advantages of using a variable frequency motor include:

• High balance quality and high-speed capability:

Vibration level R, high machining accuracy of mechanical parts, equipped with special high-precision bearings.

• Efficient and reliable cooling system:

​Uses imported axial flow fans for forced ventilation and heat dissipation, ensuring effective cooling of the motor at various speeds for long-term stable operation.

• Wider speed regulation range and higher design quality:

​Special magnetic field design suppresses high-order harmonic magnetic fields, meeting wide-frequency, energy-saving, and low-noise requirements, with wide-range constant torque and power speed regulation characteristics, stable speed regulation, and no torque pulsation.

IV.II On-site Modification of Main Circuit

【Simplified Diagram of Pressing Process】

According to on-site needs, each production line is equipped with 5 sets of presses. The variable frequency drive system for each press includes the following main components:

• Bypass cabinet: Serves as a standby power frequency starting device.
• Transformer cabinet.
• Power unit cabinet.
• Control cabinet: The panel is equipped with local/remote switching buttons, emergency stop buttons, and power frequency/variable frequency operation indicator lights.

This modification adopts the JD-BP38 series high-voltage inverter manufactured by FGI Electronic Technology Co., Ltd. The operating frequency of the variable frequency speed regulation system is set via a remote operation console, making it convenient for personnel in the electrical control room to monitor the system status and adjust the speed of the press according to production needs, thereby improving production efficiency.

【Main Circuit Diagram of On-site Modification】

The main circuit is equipped with knife switches K1, K2, and K3. During variable frequency operation, K1 and K2 are closed, and K3 is open; during power frequency operation, K1 and K2 are open, and K3 is closed. These three knife switches have strict mechanical and electrical interlock relationships to prevent simultaneous connection of power frequency and variable frequency power supplies, ensuring safe system operation.

IV.III Control System

【Control System Diagram】

For export requirements, the FGI inverter adopts an all-English design, including the interface and parameter settings, making it easy for users to understand. Its control system mainly consists of the following parts:

• Controller: The core control unit, including:
  • Optical fiber board: Transmits data signals bidirectionally between the optical fiber and the power unit. Each board controls the units of one phase, sending PWM signals and operating modes, and receiving fault codes.
  • Main control board: Adopts a high-speed DSP single-chip microcomputer to complete motor control, generate PWM three-phase voltage commands, and exchange status parameters and setting parameters with the human-machine interface via the RS232 interface.
  • Signal board.
  • Power board.
• Human-Machine Interface (HMI): Provides a user-friendly all-English operating interface, responsible for information processing and external communication, and can implement networked control with optional upper monitoring. It collects data through the main control board and PLC board, calculates and displays operating parameters such as current, voltage, power, and frequency, and has recording, overload, and overcurrent alarm protection functions. It is connected to the main control board via RS232 and to the PLC board via RS485 for real-time monitoring of the system status.

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【FGI Variable Frequency Control System Main Interface】

【Parameter Setting Interface】

• PLC board: Processes the internal switching signals of the inverter and on-site operation signals and status signals, enhancing application flexibility. It has the capacity for 4 analog inputs (processing analog signals such as flow and pressure from the field or setting signals) and 2 analog outputs (outputting frequency setting signals).
• Host computer: Communicates with the PLC board via the RS485 interface, facilitating user operation of the inverter and real-time monitoring of its operating parameters. It can be connected to a printer to record data. Operators can perform various operations in the monitoring room without needing to enter the high-voltage electrical control room, improving convenience and safety, reducing labor intensity, and enhancing work efficiency.

IV.IV Control Modes

The FGI inverter supports three control modes:

• Local Control: Operation of motor start/stop and all functions via the inverter's interface.
• Remote Control: Reception of on-site switch control signals through the built-in PLC board.
• Upper Control: Reception of control signals from the upper system via the RS485 interface and Modbus communication protocol.

This modification utilizes upper control, with operators adjusting frequency and monitoring running parameters on the host computer.

【On-site Control Box】

IV.V On-site Variable Frequency Modification of Press

This system comprises a high-voltage switchgear and a high-voltage inverter, with each line equipped with 5 sets of high-voltage inverters and high-voltage switchgears.

【Operation Screen Diagram】

IV.VI Technical Features of FGI JD-BP38 Series High Voltage Inverter

The FGI JD-BP38 series high-voltage inverter is a high-performance, high-high voltage source inverter featuring high-speed DSP control, speed sensorless vector control, and power unit series multi-level technology. It offers excellent power quality and motor protection and has been recognized as a China Famous Brand product. Its specific features include:

• High-speed DSP control: Faster calculation speed and more precise control.
• Flying start: Ability to recognize motor speed and start directly.
• Restart in rotation: Automatic operation after rapid recovery from power failure.
• Line voltage automatic equalization: Ensures balanced line voltage output during unit faults.
• Unit DC voltage detection: Optimizes voltage control, reduces harmonics, and improves accuracy.
• Long-life electrolytic capacitors: Utilizing patented technology, lifespan is increased by 1 time.
• High-reliability cooling structure: Low IGBT voltage stress and wide overvoltage range.
• Sudden phase-to-phase short circuit protection: Immediate equipment protection during short circuits.
• Current limiting function: Prevents overcurrent protection and reduces downtime.
• Fault auto-reset: Automatic recovery after overcurrent due to sudden load changes.

V Effects After Modification

The press modification has been well-received by users due to simplified operation and maintenance, and an improved working environment with reduced labor and steam emissions.

After modification and commissioning, the system offers the following advantages:

• Soft start: Adjustable start time and mode based on on-site conditions.
• High power factor: Achieves 0.95 or higher, eliminating the need for additional compensation.
• No harmonic pollution: Effectively reduces motor heating.
• Low torque pulsation: Minimizes mechanical resonance and wear on transmission mechanisms.
• Perfect output waveform: Distortion rate less than 4%.
• Reduced jamming and downtime: Lowers stoppages caused by excessive cane layer thickness.
• Improved extraction rate: Expected increase of over 0.2%, conservatively estimated at 0.1%, potentially increasing annual revenue by 119,000 yuan.
• Significant energy saving: Reduced power consumption per ton of cane from 33.02 kWh to 31.22 kWh, resulting in annual savings of 342,000 yuan.
• Reduced maintenance costs: Decreased downtime and maintenance expenses.

VI Conclusion

This variable frequency drive modification has not only saved energy but also enhanced system automation, reduced equipment wear, enabled demand-based speed control, lessened the labor intensity for workers, and significantly improved overall system efficiency. FGI will continue to pursue growth and innovation in the variable frequency drive industry, proactively consider user needs, and contribute to the upgrading and transformation of industrial electrical equipment in Pakistan.

Production Base: North of the middle section of Jincheng Road, Economic Development Zone, Wenshang County

R&D Center: No. 21, Gongye North Road, Baoshan Sub-district, Licheng District, Jinan City

Email: overseas@fengguang.com

Website: www.fengguang.com.