1 Introduction
With economic development and technological advancements, the use of escalators is increasing, and China currently has over one million escalators in operation. While providing convenience and speed, escalator systems also consume a significant amount of electricity. With the promotion of energy conservation and emission reduction, energy-saving measures for escalators are imperative. The "Regulations on Energy Conservation in Public Institutions," promulgated by the State Council on October 1, 2008, officially came into effect, guiding the development trend of energy-saving escalators in a legal form.
Escalators are widely used in public places such as shopping malls, airports, and subways. Once started, they operate at their rated speed. Even when no one is using them, the escalators continue to run at high speed, consuming a large amount of electricity and causing wear and tear on the mechanical parts. If the escalator's operating speed could be reduced or even stopped when no one is using it, electricity could be saved, wear and tear on the mechanical parts could be reduced, and the escalator's lifespan could be extended.
2. Analysis of Existing Escalator Systems
2.1 Non-energy-efficient escalator systems
Currently, the vast majority of escalators in operation use non-energy-efficient escalator control systems. These systems employ a PLC or dedicated control board as the core, and upon receiving a start signal, the control system activates the corresponding contactors, allowing the electrical grid to drive the escalator upwards or downwards. These systems typically include escalator protection logic, lubrication, and buzzer functions. Non-energy-efficient escalators can only be controlled to run at their rated speed or stop.
2.2 Y-△ Reduced-voltage Start Energy-saving Escalator System
In this design, when no one is using the escalator, the contactor is disconnected, the motor is de-energized, and the escalator stops. When someone is using the escalator, it starts rapidly using a Y-Δ reduced-voltage start. This system can save energy, but frequent starts and stops, even with Y-Δ reduced-voltage starting, still put a significant strain on the escalator and the power grid during startup. Therefore, this design is rarely used.
2.3 Energy-saving escalator system with universal frequency converter
Variable frequency drives (VFDs) have speed control capabilities, enabling soft starting of the motor and allowing escalators to operate at different speeds as needed. However, general-purpose VFDs lack built-in escalator control logic and require integration with other controllers. These controllers receive up/down photoelectric signals and output fast or slow speed commands to the VFD, which then drives the escalator at either speed. Since the system operates at variable frequency, it generates electricity during the escalator's downward movement, necessitating the inclusion of a braking resistor in the VFD. While such systems offer soft starting and low-speed energy savings, they are complex and costly.
3 HD5E Technical Features
The HD5E escalator-specific drive controller utilizes advanced customized design concepts, focusing on the needs of the escalator industry, and perfectly combining advanced motor control technology with escalator control logic. The product features multiple escalator operating modes, excellent bypass frequency conversion technology, comprehensive escalator control logic, and escalator fault protection, meeting the needs of various escalator retrofits and new escalator applications.
3.1 Multiple escalator operation modes
(1) Bypass frequency converter operation mode
When someone is riding the escalator, the drive controller accelerates the escalator to the mains frequency, and then the escalator switches from variable frequency drive to mains frequency drive; when no one is riding the escalator, the escalator is driven by variable frequency and runs at low speed.
(2) Full frequency conversion operation mode
Whether or not someone is using the escalator, it always operates under variable frequency drive, running at high speed when someone is using it and at low speed for energy saving when no one is using it.
(3) Power frequency Y-Δ operation mode
The escalator uses Y-Δ reduced voltage starting to minimize the impact on the escalator and the power grid. After starting, the escalator is driven by the mains frequency. When the inverter output is abnormal, the escalator system can operate in the mains frequency Y-Δ operation mode, providing two options for one system.
(4) Maintenance and operation
The maintenance and operation are divided into frequency conversion maintenance and power frequency Y-Δ maintenance, which involve checking the input and output signals and operating status of the escalator system in frequency conversion mode and power frequency mode, respectively.
3.2 Excellent bypass frequency conversion technology
When the escalator switches from variable frequency to mains frequency, the excellent phase locking technology ensures that the inrush current is small and the escalator does not shake.
When the escalator switches from power frequency to variable frequency, the ultra-smooth speed tracking technology enables shock-free start-up.
3.3 Three energy-saving operation modes
The HD5E offers three different energy-saving operation modes: low-speed operation when unattended, low-speed operation followed by a stop when unattended, and stop operation when unattended. It also provides user-configurable parameters such as forward express time, slow-speed operation time, express frequency, and slow-speed frequency, which can flexibly meet the energy-saving needs of different application scenarios.
3.4 Comprehensive escalator fault protection
In addition to the various protection functions of frequency converters, HD5E also provides escalator systems with comprehensive escalator fault protection logic, including safety circuit disconnection protection, anti-reverse protection, drive chain breakage protection, motor speed measurement protection, handrail belt speed measurement protection, step loss protection, contact adhesion protection, contactor contact feedback disconnection protection, and fire alarm protection. It fully meets industry standards and relevant national technical requirements, ensuring the safe and reliable operation of escalators.
4 HD5E Application Cases
4.1 HD5E Energy-Saving Retrofit Application Case
In retrofitting, the first step is to carefully analyze the original system's structure. Currently, most escalator control systems on the market are based on PLCs or dedicated control boards. During retrofitting, users generally require minimal changes to the original system; achieving energy-saving retrofitting with minimal modifications is a requirement in many retrofitting scenarios.
In this type of renovation, we chose a renovation solution based on full frequency conversion operation mode.
The system configuration diagram is as follows:
The above solution only requires extracting three signals—upward command, downward command, and stop command—from the original system. The escalator's protection logic remains the same as the original system, but the original system's main power is no longer output to the motor; the motor is driven by an HD5E frequency converter. The added upper and lower photoelectric sensors are installed at the upper and lower entrances of the escalator, respectively, to detect whether someone is riding the escalator. When someone is riding, the HD5E drives the escalator to run at high speed; when no one is riding, the HD5E drives the escalator to run at low speed for energy saving or stops.
This solution allows for simple energy-saving retrofitting of escalators. Because it operates entirely with variable frequency drives, energy is fed back to the HD5E when the escalator is carrying passengers downwards. A braking resistor is typically required to discharge this fed-back energy and prevent overvoltage faults in the HD5E. Additionally, it's important to note that the original system usually has speed protection, which is based on the rated escalator speed. When the escalator is running at low speed, the original system will report a speed protection fault. In this case, the original system's speed protection needs to be disabled, and the speed signal should be input to the HD5E for speed protection. The HD5E provides comprehensive speed protection, fully capable of protecting against any potential speed anomalies in the escalator.
4.2 HD5E New Elevator Application Case
In new elevator applications, the HD5E's advanced motor control performance and perfect escalator control logic can be fully utilized. The HD5E can handle both escalator control logic and variable frequency speed regulation of the motor. Escalator control systems built with the HD5E eliminate the need for other control devices, and this high degree of integration improves system reliability and maintainability.
In the new escalator application, a bypass frequency converter operation mode is adopted, and Y contactors and Δ contactors are equipped as backups. When the frequency converter output is abnormal, it can be switched to the power frequency Y-Δ operation mode to improve the reliability of the escalator system operation.
Wherein: KM1 is a frequency converter output contactor; KM2a is a grid up-line contactor; KM2b is a grid down-line contactor; KM3a is a Y contactor; and KM3b is a Δ contactor.
The escalator control system using the HD5E escalator-specific drive controller has the following advantages.
(1) The variable frequency speed regulation of the motor saves energy, reduces the impact and wear of the escalator, and improves the service life of the escalator.
(2) Bypass frequency conversion technology is adopted, which reduces the working time of HD5E frequency conversion output and increases the service life of HD5E. Since HD5E only outputs frequency during startup and low speed, it can be used at a lower speed to save system costs. When it is high speed, it switches to power frequency operation, so there is no need to configure a braking resistor, which saves control cabinet space and reduces heat generation.
(3) The integration of advanced motor control technology and perfect escalator control logic simplifies the system composition and improves the system's reliability and maintainability.
(4) A power frequency Y-Δ operation mode is provided as a backup for the system. When the frequency converter output is abnormal, the escalator can be driven by the power frequency, which further improves the reliability of the escalator system.
(5) Multiple energy-saving modes and flexible function parameter settings meet the needs of different applications.
4.3 Energy Saving Analysis of HD5E
The formula for calculating power P is as follows:
Where U is the line voltage and I is the phase current. The power factor is taken as an example. When the escalator is running at high speed with a 7.5kW motor under no-load at 50Hz, the output line voltage is 380V and the output phase current is 8A. The power factor is low when the motor is lightly loaded, which is assumed to be 0.5. The power P is calculated as follows.
When the escalator is running at a low speed of 10Hz under no-load, the output line voltage is about 80V and the output phase current is 8A. When running at low speed, the motor power factor increases slightly, which is assumed to be 0.7. The power P is calculated as follows.
Compared to 50Hz operation, running at a low speed of 10Hz can save nearly 2 kWh of energy per hour. Based on 5 hours of low-speed operation per day, this translates to a daily saving of 10 kWh. The escalator can also operate in a mode where it runs at low speed first and then stops when no one is using it, saving even more energy during the stop operation. These calculations demonstrate the significant energy-saving advantages of the HD5E. Of course, the energy-saving effect will vary depending on different applications, primarily related to the motor current and power factor when the escalator is unloaded.
5 Conclusion
Practice has proven that the HD5E escalator-specific drive controller has won customer recognition for its superior performance, rich and flexible functions, and reliable and stable operation in both old escalator retrofitting and new escalator applications. The HD5E will undoubtedly make its due contribution to the upgrading of escalator systems and the promotion of energy conservation and emission reduction.
