1.Introduction
On July 16, 2026, the PetroChina Dushanzi Petrochemical Tarim 1.2 million tons/year Phase II Ethylene Project achieved successful first-feed commissioning, marking the official commissioning of China's first ethylene plant with fully electric-driven compressors using indigenous technology. The core power equipment of this million-ton-class ethylene plant — the ethylene three-machine unit, consisting of the cracked gas compressor, propylene refrigerant compressor, and ethylene refrigerant compressor — directly determines the plant's continuous operation capability, energy consumption level, and operation and maintenance efficiency.
While traditional steam turbine drive technology is mature, it is associated with high energy consumption and carbon emissions. Under China's carbon peaking and carbon neutrality goals, the petrochemical industry is accelerating its “steam-to-electric” green transition. Variable frequency motor drive offers significant energy-saving advantages; however, ultra-large capacity medium voltage drive systems for ethylene three-machine units have long relied on overseas supply, leaving a gap in independent domestic control.
To achieve localization of major national equipment, with strong support from PetroChina Dushanzi Petrochemical Company, China Huanqiu Contracting & Engineering (Beijing) Company, and Shenyang Turbo-Machinery Company, Shanghai Nancal Electric Co., Ltd. overcame multiple technical bottlenecks and successfully developed ultra-large capacity, high-reliability medium voltage drives for the million-ton-class ethylene plant. The company provided a complete system solution, filling the domestic technology gap in fully electric-driven ethylene three-machine drive systems and offering a localized path for the electrification retrofit of the petrochemical industry.
Figure 1: Ethylene Three-Machine Unit
Figure 2: Medium Voltage Drive for Ethylene Three-Machine Unit
2.Drive Solution Technology Comparison
Ethylene plants require long-term continuous, uninterrupted production. A single unplanned shutdown would result in enormous economic losses. This places extremely high demands on the operational stability and energy efficiency regulation capability of compressor drive equipment. Both mainstream drive solutions have inherent technical limitations in practical applications.
For traditional steam drive, steam turbine performance is highly dependent on the thermal parameters of the plant's steam network. Fluctuations in steam temperature and pressure directly affect the speed regulation accuracy of the unit. The equipment requires a lengthy warm‑up process of 4 to 8 hours before startup, resulting in slow start-stop response. The thermal conversion process consumes high energy, and the load regulation range is limited, making it difficult to meet the energy-saving requirements of variable-load operation.
For electric drive, variable frequency motor drive offers advantages such as fast speed response, high regulation accuracy, and significant energy-saving potential. However, replacing traditional steam drive still requires systematic resolution of multiple engineering challenges: high-power long shaft systems are prone to torsional vibration, leading to fatigue damage; unexpected failures in the control system or main circuit power cells directly threaten production continuity; and the ultra-large capacity and medium voltage level of the equipment impose extremely high demands on hardware design and high performance control algorithm development. The ability to systematically overcome these challenges is critical to the successful deployment of the full-electric drive solution.
3.System Solution Overview
The fully electric-driven solution is not merely a drive technology upgrade; it is an inevitable path for industrial transformation that balances three core requirements: infrastructure investment, operation and maintenance management, and low-carbon emission reduction.
The medium voltage drive for this project adopts voltage source-type cell series multi-level water-cooling technology, featuring an innovative “2-operation and 1-standby” complete drive hot standby architecture (see Figure 3): two main drives and one standby drive, paired with brushless excitation synchronous motors for the million-ton-class ethylene three-machine unit. This design balances operational reliability and resource utilization, comprehensively meeting the stringent process requirements of long-term continuous operation and “zero unplanned shutdown” from the perspectives of hardware design, control strategy, and system architecture.
Figure 3: Medium Voltage Drive “2-Operation and 1-Standby” Complete Drive Hot Standby Architecture
“2-Operation and 1-Standby” complete drive hot standby architecture operating logic:
① Normal operating condition: The two main drives respectively drive the corresponding motors to keep the compressors running stably. The standby drive continuously collects real-time operating data from both motors and remains in hot standby status.
② Fault condition: When either main drive fails, the standby drive can complete fast switching and take over the main drive within 200 ms. After takeover, the motor speed no longer drops, ensuring continuous unit operation without shutdown.
4.Medium Voltage Drive Basic Configuration
5.Four Core Technologies for High Reliability
5.1 “2-Operation and 1-Standby” Complete Drive Hot Standby Architecture
An industry-first innovation that uses a single standby drive to provide redundancy for two main drives. The standby drive continuously collects voltage, frequency, and other signals from both motors. In the event of a fault, it quickly achieves phase-locked engagement and takes over, minimizing current disturbance during switching — solving the problems of slow switching and frequent shutdown issues in traditional solutions.
5.2 Main Control System Full Redundancy Design
Each drive's main control system features dual main control boards, redundant PLC, redundant communication, redundant control power supply, and redundant fiber optics — achieving true full-link redundancy of the main control system. This design ensures main control system switching time of less than 1 ms, supports online replacement of main control boards, eliminates single points of failure at the source, and achieves industry-leading main control system reliability.
Figure 4: Main Control System Redundancy Design Diagram
5.3 Centralized Power Cell Bypass Technology
The power cell fast bypass system employs an independent centralized bypass board, bypass control power supply, and dedicated communication link. The entire system is electrically isolated from the power cell main circuit. Even under extreme fault conditions such as complete power cell failure, control board power loss, or communication interruption, the system can still complete fast bypass of the faulty cell, ensuring continuous plant operation. At the same time, neutral point shift technology adjusts the neutral point position to maintain balanced three-phase output voltage and maximize voltage output utilization.
5.4 Torsional Vibration Identification and Active Suppression Technology
High-power compressor operation with variable frequency drives is susceptible to harmonic effects that can induce shaft torsional vibration. Long-term vibration can cause fatigue damage to the shaft system. Nancal Electric built a dual-motor back-to-back physical test bench to verify torsional vibration excitation, identification, and various suppression methods, ultimately developing torsional vibration identification and active suppression technology. This technology achieves active torsional vibration suppression based on the principle of electrical damping compensation, suitable for both single-motor and dual-motor drive scenarios. It can simultaneously suppress first-order and second-order torsional vibrations across the full speed range. Measured torsional vibration amplitude can be reduced to one-third of the pre-suppression level, significantly mitigating shaft fatigue risks and ensuring long-term safe and stable operation of the compressor unit.
In addition, the drive integrates Low Voltage Ride Through (LVRT), Prognostic and Health Management (PHM), real-time fault waveform recording, online condition monitoring, and other functions, fully adapting to the complex operating conditions of the petrochemical industry and the continuous production requirements of ethylene plants.
6.On-Site Verification
After completing full operating condition type tests at the factory, the medium voltage drive for this project underwent system integration commissioning, grid connection & load testing, and functional verification at the PetroChina Dushanzi Petrochemical Tarim 1.2 million tons/year Phase II Ethylene Project site. The entire process strictly followed petrochemical plant safety specifications and process requirements, successfully completing power-on, no-load commissioning, load trial operation, complete drive hot standby switching verification, and other critical steps.
On-site verification focused on main-standby drive switching performance. The switching time from faulty main drive to standby drive was less than 200 ms. During the switching process, motor speed remained stable without impact, fully meeting the continuous production process requirements of ethylene plants. Main control system switching, power cell fast bypass, and other functions were all verified under actual operating conditions. The complete drive operated stably with fast response.
The figure below shows the measured waveform of on-site main drive switching to standby drive, visually demonstrating the operating characteristics of the entire switching process.
Figure 5: Measured Waveform of Main-Standby Drive Switching
7.Application Value and Industry Significance
China's first medium voltage drive for fully electric-driven ethylene three-machine unit for this project is the largest-capacity drive ever supplied for ethylene electric-driven compressor units in the industry. Compared with traditional steam drive solutions, the complete plant occupies less floor space, features a simplified system architecture, and offers safer, more convenient start-up and routine operation and maintenance. Its overall energy consumption reaches industry benchmark levels while also enabling integration of green electricity, providing a replicable path for the “steam-to-electric” green transition of the petrochemical industry.
More importantly, this solution breaks the long-standing foreign technology monopoly, establishing fully localized, implementable, and scalable engineering experience. It can be applied to both new million-ton-class ethylene projects and retrofit upgrades of existing units. It not only directly promotes independent control of key petrochemical equipment but also provides solid support for ensuring the security of the energy industry and supply chain.
With this as a new starting point, Nancal Electric will continue to deepen its presence in the petrochemical sector, empowering the industry's green and low-carbon upgrade with high-reliability variable frequency drive solutions.