Abstract: This paper introduces the design of a multi-functional variable frequency energy-saving control system for escalators, using an OMRON CPM1A-20CDR-A-V1 PLC and an Inovance MD320 frequency converter as examples. Based on the basic principles of escalators, the paper outlines the selection of components and the design of the hardware circuit, as well as the design of the system control program.
Keywords: escalator; PLC ; variable frequency energy saving; control system
Abstract: Based on the Omron CPM1A-20CDR-A-V1 PLC controller and Inovance MD320 frequency converter, the design for Multi-frequency energy-saving control system of escalator has been introduced. According to the basic theory of energy-saving control, the choice of fittings and design of hardware circuit has been carried out. In the end, the program of control system has been analyzed.
Key words: Escalator; PLC; Frequency energy-saving; Control system
1 Introduction
Escalators are widely used in large shopping malls, supermarkets, airports, subways, hotels, and other venues. Most escalators operate at their rated speed when passenger flow is high, and continue running at the rated speed even when there are no passengers, resulting in high energy consumption, severe mechanical wear, and short service life. The adoption of energy-saving control systems combining PLC and frequency converter control has become the development direction of escalator control technology.
Energy-saving escalators have the following characteristics:
(1) When no one is using the escalator, the escalator will automatically and smoothly transition to energy-saving operation, running at 1/5 of the rated speed (the function of automatically stopping the escalator when no one is using it can be selected);
(2) When someone is riding the escalator, the escalator will immediately and smoothly transition to its rated speed.
(3) Because the speed is very low during energy-saving operation, the wear and tear on the mechanical parts is greatly reduced, thus extending the service life of the escalator;
(4) The adoption of frequency conversion technology has greatly reduced the impact on the power grid when the escalator starts.
Most energy-saving escalators currently available are limited in form and function, only capable of simple fast/slow or fast/stop cycles. The highlight of this system is that the fast/slow and fast/slow/stop cycles can be freely selected via a program. The system also integrates functions such as protection against lost steps, broken drive chain, reverse rotation, and fault output. Furthermore, the status of auxiliary relays within the program can monitor the escalator's operating status, making on-site debugging very convenient.
2. Variable frequency energy-saving control method for escalators
2.1 Variable frequency drive (VFD) non-self-starting (fast/slow cycle)
2.1.1 Function Description
By adding a frequency converter to control the speed of the escalator, when there are passengers on the escalator, the escalator runs at high speed (e.g., rated speed) to increase passenger flow. When the passenger detection device does not detect passengers passing by for a period of time, the escalator begins to decelerate and switch to low speed (e.g., 0.2m/s, parameter can be set). At this time, it is always in standby operation, which is non-self-starting energy saving.
2.1.2 Description of Operating Status
Variable frequency control; low speed when unattended, high speed when occupied. The high-speed operation time is denoted as TQ, which can be set via PLC program; the specific time depends on the lifting height and speed of the elevator.
2.1.3 Operating Procedures
(1) When the escalator stops waiting after being powered on, and starts running in a direction (such as going up), the escalator will start running at a low speed to save energy and enter standby waiting.
(2) The passenger detection device in the lower machine room detects whether someone passes through. When someone passes through, the high-speed running time counter (denoted as TC) inside the controller is cleared to zero. At this time, the escalator begins to slowly accelerate to high speed.
(3) The high-speed running time counter (denoted as TC) starts counting. When TC
(4) When no one rides the escalator for a period of time, i.e., TC≥TQ, the escalator will slow down and enter a low-speed standby state, and this cycle will repeat.
Figure 1 is a timing diagram of the fast and slow cycle control of the escalator.
Figure 1. Timing diagram for escalator fast/slow cycle control
2.1.4 Function Implementation
Passenger detection devices installed at the escalator entrances detect whether anyone is riding the escalator.
2.2 Variable frequency self-start (fast, slow, and stop cycle)
2.2.1 Functional Description
By adding a frequency converter to control the speed of the escalator, when there are passengers on the escalator, the escalator runs at high speed (e.g., rated speed) to increase passenger flow. When the passenger detection device does not detect passengers passing by for a period of time, the escalator begins to decelerate and switch to low speed (e.g., 0.2m/s, parameter can be set). When the passenger detection device does not detect passengers riding the escalator for a period of time, the escalator begins to stop and wait, which is self-starting energy saving.
2.2.2 Description of Operating Status
The elevator is controlled by a frequency converter. It stops when no one is using it for an extended period and runs at high speed when someone is using it. The high-speed running time is denoted as TQ, and the low-speed running time is TS. Both parameters can be set via a PLC program, and the specific times depend on the elevator's lifting height and speed.
2.2.3 Operating Steps
(1) When the escalator is powered on and stops waiting, and then starts running in a direction (such as upward), the escalator enters the upward stop waiting running state.
(2) The photoelectric detection device in the lower machine room detects whether someone passes through. When someone passes through, the high-speed running time counter (denoted as TC) inside the controller is cleared to zero. At this time, the escalator begins to slowly accelerate to high speed.
(3) The high-speed running time counter (denoted as TC) starts timing. When TC
(4) When no one rides the escalator for a period of time, i.e., TC≥TQ, the escalator begins to decelerate and enters a low-speed operation state.
(5) The low-speed running time counter (referred to as TSC) starts timing. When TSC < TS, if someone enters at this time, TC is reset to zero and timing restarts. The escalator accelerates to the high-speed running state and then enters the high-speed running state again.
(6) When no one rides the escalator for a period of time, i.e., TSC≥TS, the escalator stops running and enters a waiting state, and this cycle repeats.
Figure 2 is a timing diagram for the escalator's fast, slow, and stop cycle control.
Figure 2. Timing diagram for escalator fast/slow/stop cycle control
2.2.4 Function Implementation
Passenger detection devices installed at the escalator entrance detect whether anyone is riding the escalator. However, to ensure passenger safety, according to GB16899-1997 "Safety Code for the Manufacture and Installation of Escalators and Moving Walks," self-starting escalators should start operating before the user reaches the intersection line of the comb teeth. Therefore, the passenger detection device should meet the following requirements:
(1) Requirements that the detection device should meet
• The beam should be positioned at least 1.3m ahead of the intersection line of the comb teeth;
• The contact pads should have their outer edges positioned at least 1.8 m before the intersection of the comb teeth, and their length along the running direction should be at least 0.85 m. They should respond before a load of 150 N is applied to any point on their surface of 25 mm².
(1) In actual design, you can choose
• Photoelectric diffuse emission device installed at the entrance and exit of the handrail;
• A light column installed at the inlet of the cover plate;
• This is achieved through a self-starting device installed under the cover plate.
The system was designed with a photoelectric diffuse reflection device to ensure that every passenger coming from different directions can be effectively detected, thus enabling the system to start automatically.
3 System Design
3.1 Control System Composition
Figure 3 Control System Block Diagram
As shown in Figure 3, the system mainly consists of the following parts: power supply, PLC, frequency converter, etc. The PLC is the core of the control system. The PLC determines the output of the high-speed operation command based on whether the input photoelectric signal is valid. The frequency converter controls the running speed of the escalator according to the high-speed operation command of the PLC, and completes the fast and slow and fast and slow stop cycle of the escalator.
3.2 Hardware Selection
Taking the variable frequency non-self-starting (fast and slow cycle) escalator as an example, its escalator control system actually requires 11 inputs and 7 outputs. The PLC main controller adopts the Omron CPM1A-20CDR-A-V1 type PLC. This type of PLC is equipped with corresponding programming software CX-Programmer for programming and monitoring. It can be programmed not only by handheld programmers but also by personal PCs. During the operation of the escalator, the elevator operation status can be monitored by the status of the auxiliary relays inside the program, making on-site debugging very convenient. [1]
The inverter used is the Huichuan MD320 inverter. The MD series inverter has complete input and output interfaces, and the entire series can be installed in independent air ducts and in or out of the heat sink cabinet. It can provide a solution with protection close to IP54. Its system design is particularly suitable for constant torque loads. [2]
4 System Design
4.1 Variable Frequency Control Main Circuit
Figure 4 Variable frequency control main circuit
Figure 4 shows that the main circuit is mainly composed of main circuit breaker ZK, phase sequence protection relay JXW, safety contactor JAQ, running contactor JYX, main motor MT, etc.
4.2 PLC Input/Output Port Allocation
The input/output port allocation is shown in the attached table.
Appendix Input/Output Port Allocation Table
4.3 Operation Control Loop
Figure 5 shows the operation control loop.
Figure 5 Operation control loop
The operation control of escalators is accomplished by a PLC and a frequency converter. The following uses a frequency converter non-automatic start (fast and slow cycle) as an example to introduce the working principle of energy-saving operation of escalators.
The frequency converter monitors the output signal of the PLC in real time to determine the next step of the escalator's operation. For example, (1) escalator direction control: when the frequency converter's terminal DI1 receives the signal from the PLC, it outputs forward rotation, and the escalator moves upward; conversely, when terminal DI2 is active, it outputs reverse rotation, and the escalator moves downward. (2) High-speed operation control: the frequency converter has multiple speed control frequencies preset. When the escalator is running in energy-saving low-speed standby mode, only the running contactor (JYX) is engaged. When the PLC detects the photoelectric signal, it outputs a high-speed operation command signal. At this time, the high-speed operation contactor (VN) is engaged, the frequency converter's terminal DI3 is active, and the escalator immediately and smoothly accelerates to the set frequency for high-speed operation.
4.4 Typical Control Program Design
The following section will focus on introducing the two subroutines in the program: the operation mode and the energy-saving time control.
4.4.1 Selection of Variable Frequency Non-Self-Starting (Fast-Slow Cycle) and Self-Starting (Fast-Slow-Stop Cycle) Modes
The choice of method is shown in Figure 6.
Figure 6. Fast-slow loop and fast-slow-stop loop subroutines
By simply modifying the combination of SET and RSET in the program, you can switch between the two different operating modes.
Fast and slow cycle, set to SET 212.00 and RSET 212.01.
Fast, slow, stop loop, set to SET 212.00 and SET 212.01.
4.4.2 Control of energy-saving time
Figure 7. Subroutines for energy saving time
The express train operation holding time can be set by the aforementioned counter, thereby meeting the needs of escalators with different lifting heights and speeds (see Figure 7).
4.5 Experimental Data
To verify the energy-saving effect of this system, we conducted a field test. The traction motor power at the site was 7.5kW. We compared the power consumption of escalators controlled by variable frequency energy-saving control and those controlled by ordinary Y-Δ control. The escalators were tested for 4 hours each during passenger use and when unloaded. The actual test results showed that the energy-saving escalator consumed 25.3kWh under full load, while the escalator controlled by ordinary Y-Δ control consumed 26kWh; during unloaded operation, it consumed 1.8kWh, while the escalator controlled by ordinary Y-Δ control consumed 8.4kWh. This example demonstrates that the escalator controlled by variable frequency energy-saving control is 22% more energy-efficient than the escalator controlled by ordinary Y-Δ control.
If the escalator is stopped when no one is using it, energy savings of approximately 30% can be achieved compared to before the modification. In actual use, the longer the escalator slows down or stops, the more significant the energy-saving effect.
5. Conclusion
This design has been widely applied to energy-saving retrofits of escalators, with over 300 units installed and in use in major cities such as Wuhan and Shanghai. Practice has proven that the escalator energy-saving system based on PLC and frequency converter control is reliable, operates stably, and effectively saves users' operating costs.
References
[1] Programmable Logic Controller Operation Manual. Omron Automation (China) Co., Ltd., 1997.
[2] MD320 User Manual V2.2. Shenzhen Huichuan Technology Co., Ltd., 2008.
