1. System Design and Matching
◆ Compressor Selection and Parameter Consistency
Model Uniformity: When installing
electric compressors in parallel, it is crucial to select the same model to ensure consistency in technical parameters such as displacement, power, and performance curves. Variations in compressor power may lead to uneven load distribution, where one compressor bears a greater load while others remain underutilized or even inactive, reducing overall system efficiency and lifespan. Additionally,
high-efficiency energy-saving compressors that meet EV HVAC requirements should be prioritized, with variable-frequency compressors preferred for enhanced adjustability.
Redundancy Design: It is recommended to incorporate one standby compressor to support fault isolation and redundancy operation. This ensures that the system can continue functioning even if a single compressor fails, enhancing overall system reliability.
◆ Pressure Balancing and Pipeline Design
Symmetrical Flow Path Layout: Proper pipeline sizing and layout are essential to maintaining balanced resistance across the system. Excessive pipeline length and sharp bends increase pressure losses, negatively impacting overall system efficiency. Equal-length and equal-diameter designs should be used for both intake and exhaust pipelines to minimize pressure loss differentials (≤3%). Large-radius bends (R≥3D) should be preferred to reduce resistance losses and optimize refrigerant flow, minimizing turbulence and pressure fluctuations.
Pressure Equalization Control: The intake and exhaust pipelines of compressors in a parallel configuration must be properly designed to ensure balanced intake and discharge pressures for each unit, preventing localized pressure variations that could overload individual compressors. A common manifold should be used to connect the discharge ports, while pressure sensors and proportional control valves should be installed to dynamically adjust pressure differentials within ±5%. For multi-stage compression systems, precise pressure regulation strategies must be implemented to ensure stable refrigerant distribution.
◆ Refrigerant and Lubrication Oil Distribution
Proper refrigerant distribution is a critical concern in parallel compressor systems. The pipeline design must ensure an even distribution of refrigerant to each compressor to prevent issues such as overheating or insufficient lubrication, which could lead to seizure or failure.
Uniform Distribution Mechanism: A liquid distributor and expansion valves should be installed before the compressor inlet to maintain refrigerant flow deviation within ≤3%. A centralized oil separator and equalization valve should be used to control oil level deviations within <10%, preventing premature wear caused by insufficient lubrication in certain compressors.
Lubrication System: Proper lubrication is essential for reducing friction and ensuring efficient compressor operation. The oil circulation design must ensure adequate distribution among all compressors to prevent failures due to insufficient lubrication. An oil distribution system should be used to maintain uniform oil levels across all units.
Oil Return Management: Oil return pipelines should be installed with a minimum inclination angle of ≥3° to prevent oil accumulation and lubrication failure. Additionally, oil level monitoring devices should be used to ensure oil levels remain within the required operating range.
2. Mechanical Installation and Thermal Management
◆ Installation Height Consistency
All compressors should be installed at the same height, as height differences can lead to pressure imbalances in discharge and oil return pipelines, affecting system performance and efficiency. In parallel configurations, variations in installation height can cause uneven refrigerant and oil flow, leading to unbalanced compressor loads, unstable operation, and premature equipment wear.
◆ Support and Vibration Control
Vibration and noise issues must be addressed in parallel compressor installations. Vibrations generated during operation may affect system stability or even cause mechanical damage. Anti-vibration mounts or isolation devices should be used to minimize vibration.
Vibration Mitigation: High-strength vibration damping brackets (acceleration limit ≤0.5g) and isolation devices should be used to prevent resonance or mechanical fatigue during long-term operation. Bolts should have anti-loosening designs (e.g., thread-locking adhesives), and M10 bolts should be tightened to 30-40 N·m torque.
Noise Optimization: The compressor spacing should be ≥150mm, and sound-absorbing materials should be placed around the units to reduce noise and vibration. The system's NVH performance should meet passenger vehicle standards (target noise level <65dB).
◆ Check Valve Installation
Check valves must be installed at the suction and discharge ports of each compressor to ensure unidirectional refrigerant flow. This prevents backflow or flow reversal, which could lead to compressor overload, reduced efficiency, or equipment damage. Each compressor's suction and discharge ports must be equipped with check valves to maintain stable refrigerant flow under varying operating conditions. The check valve selection should be based on compressor operating characteristics, refrigerant flow rate, and working pressure.
Related reading: Compressor Efficiency and How Better Compressors can Improve EV Range?
◆ Thermal Management Design
Cooling Strategy: Parallel-installed scroll compressors often require additional cooling measures to prevent performance degradation or damage due to high temperatures. An appropriate cooling circuit or airflow system should be designed to ensure uniform heat dissipation. A forced air cooling channel (air velocity ≥2m/s) or liquid cooling plate should be implemented to maintain compressor surface temperatures ≤80°C. In high-temperature regions, thermal insulation shields can be installed to prevent heat accumulation and improve efficiency.
Thermal Expansion Compensation: Temperature variations during compressor operation cause expansion and contraction, which can impact pipelines and mounting structures. The installation must account for thermal expansion differentials among compressors to prevent system failures. Bellows or expansion joints should be incorporated into pipelines to absorb temperature-induced deformations, preventing stress concentrations that could lead to pipe cracks or leaks.
Related reading: Successful Implementations of High-Efficiency 900V AC Compressors in BTMS for Cranes
◆ Oil Volume Management
Optimized Oil Volume: Reducing oil volume can improve system efficiency and reduce energy consumption. For example, while conventional compressors require 200ml of oil, electric compressors may need only 120ml. In a parallel system, the total oil volume should be adjusted to (200ml + 120ml) × 70% = 224ml. However, this is a preliminary estimate—actual oil volume should be refined through extensive testing under various operating conditions.
◆ Pipeline and Layout Optimization
Low-Resistance Design: Sharp bends should be avoided, and Venturi structures should be used to optimize airflow. Symmetrical intake and discharge branch arrangements help minimize uneven flow distribution.
Maintenance Accessibility: Each compressor should be equipped with an independent isolation valve, allowing quick system switching to a redundant mode in case of failure, thereby improving maintenance efficiency.
3. Electrical Control and Protection Strategies
◆ Synchronization Control and Dynamic Adjustment
Startup Control: The startup method must be carefully designed to prevent excessive electrical load on the power system. Soft-start devices or star-delta starting methods should be used to limit inrush current. A central ECU and CAN bus should ensure speed synchronization (error ≤±2%), supporting soft-start operation (startup current ≤1.5× rated current) to prevent overloading the power grid or battery system.
Intelligent Load Distribution: Advanced control strategies such as variable frequency control or model predictive control (MPC) should be implemented to dynamically adjust compressor operation based on ambient temperature, vehicle speed, and cooling demand, ensuring high system efficiency and preventing compressor overload.
◆ Protection and Fault Diagnosis
Comprehensive Protection Mechanisms: Each compressor should be equipped with high/low-pressure protection, overload protection, and oil temperature protection devices (response time <10ms) to ensure timely shutdown or self-recovery in abnormal conditions. The protection mechanisms must be interconnected to maintain overall system safety.
Condition Monitoring: Vibration sensors (ISO 10816 standard) and temperature sensors should be integrated to monitor bearing wear and seal degradation in real time, ensuring stable system operation.
Related reading: Research on Control Strategies for Electric Compressors in Electric Vehicles
4. Commissioning and Maintenance Standards
◆ System Commissioning
No-Load Testing: Ensure compressor synchronization meets standards (speed error ≤±2%) and analyze vibration spectra to eliminate abnormal peaks.
Load Simulation: Conduct extreme temperature testing (-20°C to 40°C) to verify cooling capacity degradation rate, ensuring that system performance remains stable under extreme environmental conditions. Perform a continuous 72-hour high-load operation test to assess the reliability of compressors operating in parallel.
Refrigerant Charge Optimization: Proper refrigerant charging is essential for system performance. The ideal charge should be within ±3% of the calculated value to ensure stable operation while preventing overcharging (which may lead to liquid slugging) or undercharging (which can cause insufficient cooling and excessive compressor load).
Pressure and Leakage Testing: Perform a pressurization and vacuum leak test (holding pressure at 3.0 MPa for 24 hours) to verify the integrity of pipeline connections and prevent refrigerant leakage. Additionally, conduct an ultrasonic leak detection test to ensure system sealing meets industry standards.
◆ Maintenance and Servicing Guidelines
Routine Inspections: Periodic inspections should include checking for abnormal vibrations, noise levels, and operating pressures to detect early signs of wear or malfunction.
Lubrication and Oil Quality Monitoring: Regularly inspect oil levels and perform oil quality analysis every 5,000 hours of operation to ensure adequate lubrication and prevent excessive wear. If metal debris is found in the oil, investigate and replace worn components immediately.
Component Replacement and System Calibration: If any compressor fails, the entire system should be recalibrated after replacement. Conduct system load balancing and pressure equalization checks to ensure the newly installed compressor integrates seamlessly into the system.
Software and Control System Updates: The ECU firmware and software algorithms should be updated periodically to optimize performance, enhance fault diagnostics, and improve energy efficiency.
Conclusion
Parallel installation of
electric vehicle scroll compressors requires careful consideration of compressor selection, pipeline design, lubrication management, vibration control, electrical synchronization, and intelligent protection mechanisms. A well-engineered system ensures balanced operation, optimal energy efficiency, and long-term reliability. Implementing advanced thermal management, dynamic load control, and predictive maintenance strategies will further enhance system performance and extend service life.
