Escalator energy-saving system and control method

Abstract

The escalator energy-saving system comprises a first escalator and a second escalator which are opposite in running direction, are driven by a first frequency converter and a second frequency converter respectively and are provided with an energy-saving device. The energy-saving device comprises a first connecting end and a second connecting end which are respectively connected with DC buses of two frequency converters, an energy storage unit, and a first power conversion unit and a second power conversion unit which are connected between the connecting ends and the energy storage unit. The control unit detects bus voltage at the two ends and the state of the energy storage unit in real time and controls the working mode of the power conversion unit according to the bus voltage, and when one escalator goes down for power generation and the bus voltage rises, the control unit controls the corresponding unit to store energy into the energy storage unit; and when the bus voltage is reduced due to the ascending power consumption of the other escalator, the corresponding unit is controlled to release the energy in the energy storage unit for compensation. Automatic cyclic utilization of energy between the two escalators is achieved, electric energy is effectively saved, energy waste is avoided, a power grid is not polluted, the structure is simple, and implementation is convenient.

Description

An escalator energy-saving system and control method Technical Field

[0001] This invention belongs to the field of escalator energy utilization, and particularly relates to an escalator energy-saving system and control method. Background Technology

[0002] Escalators, as an efficient and convenient continuous transportation tool, are widely used in public places such as shopping malls, subway stations, airports, and large supermarkets. In these places, escalators are usually arranged in pairs, one going up and one going down, to form a continuous flow of people.

[0003] The energy flow characteristics of an escalator during operation are closely related to its direction of travel. When the escalator carries passengers upwards, its drive motor operates as a motor, absorbing electrical energy from the power grid. When the escalator carries passengers downwards, due to gravity, the motor is actually in a generator state, producing regenerative energy. Existing methods for handling this energy generated during downward travel mainly fall into two categories: one is consumption-type, which dissipates the regenerative energy as heat through a braking resistor; the other is feedback-type, which feeds the regenerative energy back to the power grid or other electrical equipment for utilization.

[0004] Currently, escalators commonly use frequency converters for speed control. Theoretically, if a four-quadrant frequency converter is used, the regenerative energy generated during descent can be fed back into the power grid. However, this method injects harmonics into the grid, causing grid pollution, and is therefore subject to strict restrictions or even prohibitions by relevant national power grid standards.

[0005] In practice, most escalators use two-quadrant frequency converters, which are cheaper and simpler in structure. The two-quadrant frequency converter topology is shown in Figure 1. Three-phase AC power is rectified by a three-phase diode rectifier bridge and filtered by capacitors to obtain smooth DC power. This DC power is then inverted into variable frequency and voltage AC power by a three-phase inverter unit composed of IGBTs and other switching devices to drive the motor. A braking unit (switch Q1) and a braking resistor (R1) are connected in parallel on the DC bus of this topology. When the motor generates electricity, causing the DC bus voltage to be too high, the braking unit controls Q1 to conduct, dissipating the excess energy in resistor R1. The disadvantages of this method are obvious: usable regenerative energy is wasted, converted into useless heat, and it also increases heat dissipation costs and equipment space occupation.

[0006] To effectively utilize the energy generated during elevator descent, some manufacturers separate the rectification, filtering, and inversion functions of two-quadrant frequency converters, allowing multiple elevators to share the same rectification and filtering unit. This means that each elevator's three-phase inverter unit draws power from the same DC bus. As shown in Figure 1, the energy of the three-phase inverter unit primarily originates from capacitor C1. For a single two-quadrant frequency converter, the rectification, filtering, and inversion units are all housed in the same enclosure, allowing for real-time energy replenishment of the inverter unit. However, when using a single rectification and filtering unit to power multiple inverter units, if the inverter units are installed close to the escalator motors, the energy replenishment for the inverter units requires a long line from the rectification and filtering unit, potentially preventing the inverter units from driving the motors in real-time and affecting the elevator's normal operation. Conversely, if multiple inverter units are placed close to the rectification and filtering unit, the distance between the inverter units and each escalator motor becomes significant, resulting in substantial voltage drops in the lines and further energy loss, impacting motor output. Therefore, this multi-inverter scheme with a shared DC bus is difficult to implement in escalator engineering practice.

[0007] In summary, there are obvious contradictions in the existing technologies: the solution of using a two-quadrant frequency converter with a braking resistor is reliable and low-cost, but it cannot recover energy, resulting in waste; while using a four-quadrant frequency converter to feed back to the grid or adopting a centralized rectification solution has the disadvantages of polluting the grid or making the project difficult to implement.

[0008] Therefore, there is an urgent need for a solution that can efficiently recover and utilize the regenerative energy of escalator descent without affecting power grid quality and is easy to implement in engineering. Summary of the Invention

[0009] This invention aims to overcome the energy waste problem caused by the consumption of downstream regenerated power through braking resistors in existing two-quadrant frequency converter schemes, avoid the harmonic pollution caused by the four-quadrant frequency converter grid feedback scheme, and provide an easy-to-install and implement local energy balancing scheme to solve the problems of large voltage drop, high loss and unstable operation caused by long cables in the multi-escalator DC bus scheme. While achieving energy recovery, it aims to minimize changes to the core structure and control method of the original frequency converter and motor, reduce or eliminate external braking resistor boxes, thereby reducing system complexity and overall cost.

[0010] To address the aforementioned technical problems, this invention provides an escalator energy-saving system, comprising a first escalator and a second escalator arranged side-by-side with opposite operating directions. The first and second escalators are driven by a first frequency converter and a second frequency converter, respectively. The system includes an energy-saving device comprising: a first connection terminal connected to the DC bus of the first frequency converter; a second connection terminal connected to the DC bus of the second frequency converter; an energy storage unit for storing and releasing electrical energy; a first power conversion unit connected between the first connection terminal and the energy storage unit; a second power conversion unit connected between the second connection terminal and the energy storage unit; and a control unit for detecting the voltages of the first and second connection terminals, the state of the energy storage unit, and controlling the operating modes of the first and second power conversion units. Specifically, when one escalator is in a downward generating state, causing its frequency converter's DC bus voltage to rise, the control unit controls the corresponding power conversion unit to store excess energy in the energy storage unit. When another escalator is in an upward motoring state, causing its frequency converter's DC bus voltage to drop, the control unit controls the corresponding power conversion unit to release energy from the energy storage unit for compensation.

[0011] Furthermore, both the first power conversion unit and the second power conversion unit are bridge arms composed of two switching transistors connected in series, and the midpoint of the bridge arm is connected to the energy storage unit through an inductor.

[0012] Furthermore, the control unit includes: a voltage and current detection module for real-time detection of the DC bus voltage and current on both sides and the energy storage unit voltage; an MCU for processing the detection data and generating a PWM control signal through a PID algorithm; and a drive circuit for driving the switching transistors in the power conversion unit according to the PWM control signal.

[0013] Furthermore, the rated voltage of the energy storage unit is lower than the minimum operating voltage of the DC bus of the first and second frequency converters. The energy storage unit is a battery, a capacitor, or a combination of both.

[0014] Furthermore, the energy-saving device is physically installed on one of the escalators and connected to the DC bus of the inverter of the other escalator via a cable.

[0015] Furthermore, the first and second connection terminals of the energy-saving device are directly connected to their respective inverter DC buses. Alternatively, an electrical isolation module is provided between the first and second connection terminals of the energy-saving device and their respective inverter DC buses.

[0016] A control method for the aforementioned escalator energy-saving system is also provided, comprising the following steps: real-time monitoring of the DC bus voltages Udc1 and Udc2 of the first and second frequency converters and the voltage Ucb of the energy storage unit; determining the operating status of the two escalators; if Udc1 is higher than a first threshold and Udc2 is lower than a second threshold, then determining that the first escalator is in a power generation state and the second escalator is in a motoring state; controlling the first power conversion unit to operate in BUCK mode to store energy on the DC bus of the first frequency converter into the energy storage unit; controlling the second power conversion unit to operate in BOOST mode to release energy in the energy storage unit to the DC bus of the second frequency converter; and automatically switching the operating modes of the first and second power conversion units when a state reversal is detected.

[0017] Furthermore, both the BUCK mode and BOOST mode adopt constant current control. Additionally, protection steps are included: when the voltage Ucb of the energy storage unit is lower than the set minimum voltage threshold, all discharge operations are stopped; when the DC bus voltage of the inverter being charged drops to its rectified voltage, the charging operation is stopped.

[0018] Compared with the prior art, the escalator energy-saving system and its control method provided by the present invention have the following beneficial effects: (1) High efficiency and energy saving: Real-time energy transfer and reuse are realized between two escalators arranged in pairs at the same location, effectively recovering the regenerated electricity generated by the down escalator and supplying it to the up escalator, significantly reducing the operating power consumption of the escalator system.

[0019] (2) Clean and environmentally friendly: Energy is recycled within the system and no electrical energy is fed back to the power grid, thus eliminating harmonic pollution to the power grid and meeting the power grid quality standards.

[0020] (3) Strong engineering applicability: No need to modify the main topology and control logic of the original frequency converter, it can be realized by simply connecting the DC bus externally. The device can be installed nearby, avoiding the technical difficulties caused by long-distance DC power supply. The installation is flexible and easy to promote and apply in new construction or renovation projects.

[0021] (4) Reduced cost: Since most of the regenerative energy is consumed internally by the system, the load of the braking resistor in the original frequency converter is greatly reduced or even eliminated. Therefore, a smaller power braking resistor can be selected or the external braking resistor box can be completely eliminated, saving equipment cost, installation space and heat dissipation cost.

[0022] (5) Intelligent and reliable: The control system operates fully automatically without manual intervention. It adopts constant current charging and discharging control and voltage status judgment, ensuring stable and reliable operation without any adverse effects on the existing escalator's performance and safety. Attached Figure Description

[0023] Figure 1 shows the topology of a traditional two-quadrant frequency converter; Figure 2 shows the topology of an escalator energy-saving system; Figure 3 shows the block diagram of an intelligent energy-saving device. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] The escalator energy-saving system provided by this invention is based on an intelligent energy-saving device that is directly connected to the DC bus of the frequency converter of two escalators arranged in pairs and running in opposite directions. This enables the automatic transfer, storage and release of energy between the two escalators, thereby recovering downward energy and replenishing upward energy.

[0026] Referring to Figures 2 and 3, this embodiment provides an exemplary escalator energy-saving system. The system includes a first escalator (left side, including motor M1), a second escalator (right side, including motor M2), a first frequency converter (drive M1), a second frequency converter (drive M2), and an intelligent energy-saving device. Both the first and second frequency converters are conventional two-quadrant frequency converters, and their topology is shown in Figure 1, including a three-phase rectifier bridge, a filter capacitor C1, an inverter unit, and a braking circuit (switching transistor Q1 and braking resistor R1).

[0027] The main circuit ① of the intelligent energy-saving device includes: a first power conversion unit: a left bridge arm composed of switching transistors Q11 and Q12 connected in series, the midpoint of which is connected to the energy storage unit CB1 through an inductor L11.

[0028] The second power conversion unit consists of the right bridge arm formed by the series connection of switching transistors Q21 and Q22, and the midpoint of the bridge arm is connected to the energy storage unit CB1 through the inductor L21.

[0029] Energy storage unit CB1: In this embodiment, a 48V lithium battery pack is selected as the energy storage device. The rated voltage is lower than the minimum operating voltage of the DC bus of the first and second frequency converters. 48V is much lower than the DC bus voltage of about 540V after rectification of 380V AC power, ensuring that the BUCK / BOOST circuit works normally and safely.

[0030] The first connection terminals, bus1+ and bus1-, and the second connection terminals, bus2+ and bus2-, are directly connected to the DC buses of the first and second frequency converters via cables, respectively. During connection, bus1+ is connected to the positive terminal of the first frequency converter's DC bus, and bus1- is connected to the negative terminal; bus2+ is connected to the positive terminal of the second frequency converter's DC bus, and bus2- is connected to the negative terminal.

[0031] The control system of the intelligent energy-saving device includes: voltage and current detection module ⑤: used to collect in real time the bus voltages Udc1 and Udc2 of the first connection terminal and the second connection terminal, the charging and discharging current, and the voltage Ucb of the energy storage unit CB1.

[0032] MCU③: Employs an LSC335 microcontroller operating at 150MHz. The MCU receives data from the detection module, executes its internal control algorithm (such as a PID algorithm), and generates PWM control signals.

[0033] Drive and control circuit ④: Receives the PWM signal from the MCU, isolates and amplifies it, and drives the switching transistors Q11, Q12, Q21, and Q22 in the main circuit.

[0034] Operation panel ⑥: Used to set parameters (such as charging and discharging current value, voltage protection threshold) and display system operating status.

[0035] The energy flow direction of the intelligent energy-saving device can be bidirectional, from left to right or from right to left; it can store energy first and then release it, or charge and release it simultaneously; the energy-saving process is completed automatically.

[0036] Escalators move in a left-right, up-down direction. Utilizing this characteristic, let's assume the initial state is that the first escalator is moving downwards (generating electricity) and the second escalator is moving upwards (electrically powered).

[0037] Energy recovery (charging): The generator M1 generates electricity, causing the DC bus voltage Udc1 of the first inverter to rise. The MCU③ of the control unit continuously monitors Udc1, Udc2, and Ucb. When Udc1 is higher than a set threshold (e.g., 700V) and Ucb has not reached its upper limit, the MCU determines that energy recovery is necessary. It controls the first power conversion unit to operate in BUCK mode: Q12 is normally off, and Q11 receives PWM drive. Electrical energy is regulated by choppers from the first connection terminal via Q11 and L11, and then charges the energy storage unit CB1 with a constant current (the current value can be set via the operation panel).

[0038] This process efficiently recovers the regenerative energy generated by the descending escalator into the energy storage unit, solving the problem of energy wasted by the braking resistor. Using constant current charging helps protect battery life and system stability.

[0039] Energy Compensation (Discharge): When motor M2 is in motor mode, it consumes electrical energy, causing the DC bus voltage Udc2 of the second frequency converter to decrease. When the MCU detects that Udc2 is low and Ucb has sufficient charge (above the set lower limit, such as 45V), it controls the second power conversion unit to operate in BOOST mode: Q21 is normally off, and Q22 receives PWM drive. The electrical energy of energy storage unit CB1 is boosted by L21 and Q22 and then replenished to the DC bus of the second frequency converter with a constant current, supporting the upward operation of the second escalator.

[0040] This process enables the on-site utilization of recovered energy, directly powering the upward escalator and achieving the goal of saving electricity. The energy circulates within the system and is never fed back to the grid, avoiding the grid pollution problems caused by four-quadrant frequency converters.

[0041] Furthermore, when the operating status of the two escalators changes (i.e., the first escalator goes up and the second escalator goes down), the MCU automatically identifies this transition by monitoring the voltage changes of Udc1 and Udc2, and immediately switches the operating modes of the two power conversion units: the second power conversion unit switches to BUCK mode to charge CB1, and the first power conversion unit switches to BOOST mode to discharge the first inverter bus.

[0042] This strategy ensures that the system can automatically optimize energy allocation regardless of the combination of escalator running directions, without affecting energy efficiency.

[0043] Throughout the process, if the CB1 voltage Ucb drops to the lower limit, the MCU will stop discharging to protect the energy storage unit. If the bus voltage drops due to load changes during charging, the MCU will also adjust or pause charging. The inverter's own braking unit Q1 serves as backup protection, only activating in extreme situations such as when the energy-saving device cannot fully absorb a sudden large current. This multi-layered protection mechanism ensures the system's high reliability and safety without any negative impact on the existing escalator's operating performance.

[0044] In Example 2, building upon Example 1, and considering the flexibility of on-site installation, the intelligent energy-saving device can be installed in or near the control cabinet of only one escalator (e.g., the first escalator). The DC bus of the inverter for the other escalator (the second escalator) is led to the installation location of the energy-saving device via a two-core power cable and connected to the second connection terminal (bus2+, bus2-). This method reduces redundant installation of equipment, lowers the overall cost, and avoids the voltage drop problem of long-distance AC lines.

[0045] In Example 3, based on Example 1, to further improve the electrical safety and anti-interference capability of the system, a DC / DC isolation module can be added between the first and second connection terminals of the energy-saving device and the DC bus of the frequency converter. This module can achieve electrical isolation, preventing a failure of one frequency converter from affecting another frequency converter or energy-saving device through the DC bus.

[0046] Adding electrical isolation improves the system's safety and reliability. Of course, this also increases the system's size and cost; therefore, its adoption can be flexibly chosen based on the specific safety requirements and budget of the project.

[0047] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. An escalator energy-saving system, comprising a first escalator and a second escalator arranged side by side and running in opposite directions, wherein the first escalator and the second escalator are driven by a first frequency converter and a second frequency converter, respectively, characterized in that, It also includes an energy-saving device comprising: a first connection terminal connected to the DC bus of the first frequency converter; a second connection terminal connected to the DC bus of the second frequency converter; an energy storage unit for storing and releasing electrical energy; a first power conversion unit connected between the first connection terminal and the energy storage unit; a second power conversion unit connected between the second connection terminal and the energy storage unit; and a control unit for detecting the voltage of the first and second connection terminals, the state of the energy storage unit, and controlling the operating modes of the first and second power conversion units. Specifically, when an escalator is in a downward generating state, causing its frequency converter DC bus voltage to rise, the control unit controls the corresponding power conversion unit to store excess energy in the energy storage unit; when another escalator is in an upward motoring state, causing its frequency converter DC bus voltage to drop, the control unit controls the corresponding power conversion unit to release energy from the energy storage unit for compensation.

2. The escalator energy-saving system according to claim 1, characterized in that: Both the first power conversion unit and the second power conversion unit are bridge arms composed of two switching transistors connected in series, and the midpoint of the bridge arm is connected to the energy storage unit through an inductor.

3. The escalator energy-saving system according to claim 1, characterized in that, The control unit includes: a voltage and current detection module for real-time detection of the DC bus voltage and current on both sides and the energy storage unit voltage; an MCU for processing the detection data and generating a PWM control signal through a PID algorithm; and a drive circuit for driving the switching transistors in the power conversion unit according to the PWM control signal.

4. The escalator energy-saving system according to claim 1, characterized in that: The rated voltage of the energy storage unit is lower than the minimum operating voltage of the DC bus of the first and second frequency converters.

5. The escalator energy-saving system according to claim 1, characterized in that: The energy-saving device is physically installed on one of the escalators and connected to the DC bus of the frequency converter of the other escalator via a cable.

6. The escalator energy-saving system according to claim 1, characterized in that: The first and second connection terminals of the energy-saving device are directly connected to the DC bus of their respective frequency converters.

7. The escalator energy-saving system according to claim 1, characterized in that: An electrical isolation module is provided between the first and second connection terminals of the energy-saving device and their respective inverter DC bus.

8. A control method for the escalator energy-saving system according to any one of claims 1-7, characterized in that, The process includes the following steps: real-time monitoring of the DC bus voltages Udc1 and Udc2 of the first and second frequency converters, as well as the voltage Ucb of the energy storage unit; determining the operating status of the two escalators; if Udc1 is higher than a first threshold and Udc2 is lower than a second threshold, then the first escalator is determined to be in a power generation state and the second escalator is in a motoring state; controlling the first power conversion unit to operate in BUCK mode to store energy on the DC bus of the first frequency converter into the energy storage unit; controlling the second power conversion unit to operate in BOOST mode to release energy from the energy storage unit to the DC bus of the second frequency converter; and automatically switching the operating modes of the first and second power conversion units when a state reversal is detected.

9. The control method according to claim 8, characterized in that, It also includes protection steps: when the voltage Ucb of the energy storage unit is lower than the set minimum voltage threshold, all discharge operations are stopped; when the DC bus voltage of the inverter being charged drops to its rectified voltage, the charging operation is stopped.

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