A control method of off-grid energy-saving device based on DC bus change of elevator frequency converter

Abstract

This invention belongs to the field of elevator energy-saving technology, specifically relating to a control method for an off-grid energy-saving device based on changes in the DC bus voltage of an elevator inverter. The method includes: S1 System initialization configuration, presetting charging start voltage, charging stabilization target voltage, discharging start voltage, and discharging stabilization target voltage, configuring a bidirectional DC-DC power supply with a start time ≤100ms and a power adjustment cycle ≤1ms; S2 Real-time acquisition of the bus voltage; S3 Comparing the voltage with thresholds for state judgment and mode switching; S4 Rapid switching for emergency stop braking, with a total switching time ≤100ms. This method accurately identifies the elevator's power generation, power consumption, and stationary states solely based on the DC bus voltage, without requiring any communication connection with the elevator controller. Furthermore, through differentiated rapid switching logic for power generation, power consumption, and emergency stop braking conditions, it achieves "instant generation and recovery" and on-demand release of regenerative energy.

Description

Technical Field

[0001] This invention belongs to the field of elevator energy-saving technology, specifically relating to a control method for an off-grid energy-saving device based on changes in the DC bus of an elevator frequency converter. Background Technology

[0002] Off-grid energy-saving devices, also known as off-grid energy recovery systems with energy storage, represent a significant technological direction in elevator energy conservation. These devices typically consist of an energy storage stack, a bidirectional DC-DC converter (DC-DC converter), and an off-grid energy-saving control system. Their purpose is to recover regenerative energy generated by the elevator during light-load upward movement or heavy-load downward movement, and release it when the elevator is in use, thus achieving energy savings. However, elevator operation is characterized by short operating times, high start-stop frequency, and large instantaneous power fluctuations, placing extremely high demands on the dynamic response performance of off-grid energy-saving devices.

[0003] Currently, most common bidirectional DC-DC power supplies on the market are general-purpose DC microgrid designs. While they possess a stable and reliable multi-layered redundant protection architecture, they struggle to quickly adapt to the unique operating modes of elevators. Specifically, existing bidirectional DC-DC power supplies suffer from the following technical defects: First, slow power-on startup, typically requiring 3 to 8 seconds; second, slow power response, typically 1 to 3 seconds, lacking a matching mode capable of adapting to instantaneous power changes in the elevator; and third, high standby power consumption, typically exceeding 40 watts. Due to these defects, off-grid energy-saving devices using ordinary bidirectional DC-DC power supplies cannot start and complete energy recovery within the extremely short time (e.g., within 150 to 300 milliseconds) when the elevator enters power generation mode in actual elevator applications. This results in a large amount of regenerated energy not being effectively absorbed, ultimately wasting as heat through the braking resistor, leading to poor energy recovery efficiency and insufficient compatibility with different elevator models.

[0004] Therefore, how to provide a control method for off-grid energy-saving devices that can quickly respond to changes in elevator DC bus voltage, has high-precision power matching capability, and takes into account low standby power consumption, in order to solve the problems of slow start-up, slow response, and high standby power consumption in the existing technology, has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] To address the aforementioned shortcomings of existing technologies, this invention provides a control method for an off-grid energy-saving device based on changes in the DC bus of an elevator inverter. This method solves the problems of slow start-up response and slow power adjustment response of bidirectional DC-DC power supplies in existing off-grid energy-saving devices, which lead to inefficient recovery of elevator regenerative energy and easy DC bus fluctuations.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A control method for an off-grid energy-saving device based on the DC bus variation of an elevator frequency converter is provided, comprising the following steps: S1: System Initialization Configuration S11: Connect the energy storage stack of the off-grid energy-saving device to the battery side of the bidirectional DC-DC power supply. Use the positive and negative terminals of the DC bus side of the bidirectional DC-DC power supply as the positive and negative terminals of the off-grid energy-saving device, respectively, and connect them to the positive and negative terminals of the DC bus of the elevator inverter, without establishing any communication connection. Connect the control system to the control terminal of the bidirectional DC-DC power supply and the voltage sampling point of the DC bus. S12: The control system automatically presets four voltage thresholds based on the captured DC bus voltage, namely the charging start voltage, the charging stabilization target voltage, the discharging start voltage, and the discharging stabilization target voltage. The charging start voltage is higher than the DC bus voltage when the elevator is stationary, and the discharging start voltage is lower than the DC bus voltage when the elevator is stationary. S13: Configure the response parameters of the bidirectional DC-DC power supply so that the startup time for switching from standby mode to power output mode does not exceed 100ms and the power adjustment cycle does not exceed 1ms. S2: Real-time acquisition of DC bus voltage The control system collects the DC bus voltage value in real time at a fixed sampling period, which is no more than 1ms. S3: Status Judgment and Mode Switching The control system compares the collected DC bus voltage value with four preset voltage thresholds and performs the following operations based on the comparison results: S31: When the DC bus voltage is greater than or equal to the charging start voltage, the elevator is determined to be in power generation mode. The bidirectional DC-DC power supply is switched from standby mode to charging mode. In charging mode, the charging power is dynamically adjusted at a period of no more than 1ms based on the difference between the real-time collected DC bus voltage and the charging stabilization target voltage, so that the DC bus voltage is stably maintained within the preset deviation range of the charging stabilization target voltage. When the DC bus voltage drops below the charging start voltage, the bidirectional DC-DC power supply is switched to no-load state and then enters standby mode. S32: When the DC bus voltage is less than or equal to the discharge initiation voltage, the bidirectional DC-DC power supply is switched to discharge mode and initially maintains no-load output. The DC bus voltage is continuously monitored. If the duration exceeds the first preset time after the DC bus voltage first falls below the discharge stabilization target voltage, the power consumption state is confirmed, and the discharge function is activated. In discharge mode, the discharge power is dynamically adjusted according to the difference between the real-time collected DC bus voltage and the discharge stabilization target voltage at a period not exceeding 1ms, so that the DC bus voltage is stably maintained within the preset deviation range of the discharge stabilization target voltage. When the DC bus voltage rises to above the discharge initiation voltage and stabilizes, the bidirectional DC-DC power supply is switched to no-load state and then enters standby mode. S33: When the discharge start voltage < DC bus voltage < charging start voltage, it is determined that the elevator is in a stationary state. The bidirectional DC-DC power supply is switched to an unloaded state. The unloaded state continues for a preset time before switching to standby mode. S34: When the DC bus voltage exceeds the preset overvoltage protection threshold, an overvoltage alarm is triggered and charging operation is prohibited; S4: Rapid switching between emergency braking and emergency stop. During the braking process of the elevator transitioning from a powered state to a stationary state, the DC bus voltage begins to rise from a value below the discharge initiation voltage. When the DC bus voltage is detected to have risen from below the discharge initiation voltage to above the discharge initiation voltage, the elevator immediately exits the discharge mode and enters an unloaded state. The DC bus voltage continues to be monitored, and if the DC bus voltage continues to rise to reach or exceed the charging initiation voltage, the elevator immediately switches to charging mode. The above switching process skips the standby mode, and the total time from detecting that the DC bus voltage has risen above the discharge initiation voltage to switching to charging mode does not exceed 100ms.

[0007] The beneficial effects of adopting the above technical solution are as follows: This off-grid energy-saving device control method based on the change of the DC bus of the elevator frequency converter constructs a control architecture without communication and with pure voltage detection. S11 only needs to connect the positive and negative poles of the DC bus, without any communication protocol docking, reducing the difficulty of modification and the risk of electromagnetic interference; S12 achieves adaptive matching for different elevators by automatically presetting four voltage thresholds, eliminating the need for manual debugging; S13 is configured with a bidirectional DC-DC power supply with a start-up time of ≤100ms and a power adjustment cycle of ≤1ms, combined with the fixed sampling period of no more than 1ms in S2, laying the foundation for millisecond-level response; S31, in the power generation state, when the DC bus voltage reaches the charging start voltage, immediately adjusts the charging power at a cycle of ≤1ms to stabilize the voltage at the charging voltage stabilization target voltage. Within the preset deviation range of the voltage, ensure that energy recovery is completed before the braking resistor is activated; S32, in the power consumption state, effectively distinguishes between the voltage drop at the moment of startup and the true continuous power consumption state through a delay confirmation mechanism, avoids false discharge, and dynamically adjusts the discharge power at a period of ≤1ms to stabilize the voltage within the preset deviation range of the discharge voltage regulation target; S33, in the stationary state, first enters the no-load state and then enters the standby mode, which reduces standby power consumption and ensures fast response; S34, when the overvoltage protection condition is triggered, executes the overvoltage alarm and prohibits the charging operation, improving system safety; S4, in the emergency stop braking condition, the total switching time from detecting the voltage rise to exceed the discharge start voltage to switching to the charging mode does not exceed 100ms, realizing millisecond-level capture of braking regenerative energy. Through the coordinated operation of the above steps, this invention can accurately identify the power generation, power consumption, and stationary state of an elevator by relying solely on the DC bus voltage, without needing to communicate with the elevator controller. This solves the problems of slow start-up response, slow power adjustment response, and high standby power consumption in existing bidirectional DC-DC power supplies. It shortens the start-up response time to within 100ms and the power adjustment cycle to within 1ms, and controls the DC bus voltage fluctuation within the preset deviation range of the charging voltage and the discharging voltage, effectively suppressing bus voltage fluctuations. This helps reduce the ripple stress of the DC bus filter capacitor in the elevator inverter, extending its service life and realizing the "instant generation and reception" and on-demand release of regenerative energy.

[0008] Furthermore, the specific method for automatically presetting four voltage thresholds in S12 is as follows: after waiting for the elevator to run for at least 3 cycles, the off-grid energy-saving device automatically confirms the voltage range corresponding to the elevator's stationary state, power generation state, and power consumption state based on the captured DC bus voltage waveform, and calculates the charging start voltage, charging stabilization target voltage, discharging start voltage, and discharging stabilization target voltage in combination with the preset voltage offset calculation rules.

[0009] The beneficial effects of adopting the above-mentioned further technical solution are as follows: This automatic preset method eliminates the cumbersome process of traditional manual measurement and parameter tuning, and realizes adaptive intelligent matching for the electrical characteristics of different elevator frequency converters. By automatically capturing the DC bus voltage waveform after waiting for the elevator to run for at least 3 cycles, confirming the voltage range corresponding to the three states, and calculating four voltage thresholds in combination with the preset voltage offset calculation rules, it eliminates the professional threshold of manual debugging, greatly reduces the risk of malfunction or energy waste caused by improper threshold settings, and significantly improves the versatility and engineering practicality of off-grid energy-saving devices.

[0010] Furthermore, the fixed sampling period in S2 is on the order of 1ms, and the voltage sampling error of the control system is less than ±0.8V.

[0011] The beneficial effects of adopting the above-mentioned further technical solution are as follows: By setting the sampling period to the 1ms level and strictly matching it with the power adjustment period of the bidirectional DC-DC power supply (≤1ms level), while controlling the sampling error within ±0.8V, a high-precision, high-real-time closed-loop detection link is constructed. The fixed sampling period of 1ms level ensures that the control system can instantly capture every rapid transient change in the DC bus voltage during elevator power generation or consumption; the ±0.8V sampling error enables the control system to accurately determine whether the voltage has reached the threshold and make precise power adjustment commands, avoiding misjudgment or over-adjustment caused by excessive sampling error.

[0012] Furthermore, the preset deviation range of the charging regulated target voltage in S31 is ±8V; the preset deviation range of the discharging regulated target voltage in S32 is ±3V.

[0013] The beneficial effects of adopting the above-mentioned further technical solutions are as follows: The preset deviation range of the charging voltage regulation target is ±8V, which allows the off-grid energy-saving device to quickly clamp the bus to the voltage regulation target value after detecting that the bus voltage has reached the charging start voltage, maximizing the recovery of regenerative energy to the energy storage stack before the braking resistor opens. Setting the discharge voltage regulation target to be lower than the discharge start voltage and using ±3V for voltage regulation control ensures that the DC bus voltage is stabilized within a very narrow range during power consumption, providing stable DC support for the elevator traction machine and avoiding the impact of excessive voltage fluctuations on elevator operation comfort or control accuracy.

[0014] Furthermore, in S31, the process of switching the bidirectional DC-DC power supply to an idle state and then entering standby mode is as follows: first, it enters an idle state lasting for 100ms, and then it enters standby mode.

[0015] The beneficial effects of adopting the above-mentioned further technical solution are as follows: By setting a 100ms-level no-load transition state before entering standby mode, the response delay that may be caused by immediately entering deep standby after the power generation state ends is avoided. When the elevator briefly stops and then quickly enters the power generation state again, the 100ms-level no-load state allows the bidirectional DC-DC power supply to quickly restore power output without having to re-execute the complete standby wake-up process, ensuring millisecond-level fast response capability under frequent elevator start-stop conditions.

[0016] Furthermore, in S32, the process of switching the bidirectional DC-DC power supply to an idle state and then entering standby mode is as follows: first, it enters an idle state lasting for 100ms, and then it enters standby mode.

[0017] The beneficial effects of adopting the above-mentioned further technical solution are as follows: Similar to the transition logic after the power generation state, setting a 100ms-level no-load transition state after the power consumption state ends enables a rapid and seamless mode switching when the elevator resumes power consumption after a brief stop or suddenly switches to power generation (such as emergency braking). This transition state avoids frequent switching between standby mode and working mode, reduces switching losses, and ensures a rapid response to subsequent power generation states after exiting the discharge mode.

[0018] Furthermore, S4 also includes: if the DC bus voltage fails to reach the charging start voltage under no-load conditions, and the no-load duration exceeds the second preset time, then enter standby mode.

[0019] The beneficial effects of adopting the above-mentioned further technical solution are as follows: During the emergency stop braking process, when the elevator exits the power consumption state and enters the no-load state, if the DC bus voltage fails to rise to the charging start voltage and the no-load duration exceeds the second preset time, it indicates that the elevator has completely stopped and there is no energy to be recovered. At this time, the system automatically enters the standby mode, which avoids the device from staying in the no-load state for a long time and increasing unnecessary power consumption. Under the premise of ensuring that no potential regenerative energy is lost, the static energy consumption of the system is reduced to the greatest extent.

[0020] Furthermore, the first preset time is greater than 1 second; the second preset time is greater than 100 ms.

[0021] The beneficial effects of adopting the above-mentioned further technical solution are as follows: setting the first preset time to greater than 1 second can reliably distinguish between the brief voltage drop at the moment of elevator start-up and the true continuous power consumption state, effectively avoiding false discharge operations caused by instantaneous voltage fluctuations; setting the second preset time to greater than 100 ms ensures that there is a sufficient time window for regenerative energy to appear after emergency braking, while avoiding energy waste caused by excessively long idle waiting. The values ​​of the two preset times are coordinated with each other, achieving the optimal balance between "timely response" and "energy economy" of the system.

[0022] Furthermore, it also includes S5: power consumption optimization, which includes the following steps: S51: Collect historical data on elevator operating frequency at different time periods, convert the time domain data into frequency domain data through discrete Fourier transform, and divide the peak and off-peak periods. S52: During peak hours, only charging mode, discharging mode, and standby mode are enabled; sleep mode is prohibited. S53: During off-peak periods, when the elevator is stationary and the duration of this stationary state exceeds a preset stationary threshold, the off-grid energy-saving device is allowed to enter sleep mode. S54: In the hibernation mode of S53, the off-grid energy-saving device cuts off the DC bus power supply of the bidirectional DC-DC power supply, and only retains the bus voltage to wake up the circuit.

[0023] The beneficial effects of adopting the above-mentioned further technical solution are as follows: By collecting historical data on the elevator's operating frequency at different time periods and using Discrete Fourier Transform to divide peak and off-peak periods, intelligent identification and adaptive matching of elevator operating patterns are achieved. During peak periods, only charging, discharging, and standby modes are activated, and sleep mode is prohibited, ensuring that the off-grid energy-saving device can respond to the frequent start-stop needs of the elevator at any time. During off-peak periods, when the elevator is stationary for a long time, sleep mode is allowed and the DC bus power supply of the bidirectional DC-DC power supply is cut off, retaining only the bus voltage wake-up circuit, thereby controlling standby power consumption to an extremely low level, realizing intelligent full-cycle energy consumption management of "ensuring response during peak operation and reducing losses during off-peak operation". In summary, the off-grid energy-saving device control method based on the change of the elevator inverter's DC bus provided by this invention has the following beneficial effects: (1) By constructing a control architecture of “no communication and pure voltage detection”, the present invention only needs to connect the positive and negative poles of the off-grid energy-saving device to the positive and negative poles of the DC bus of the elevator inverter. Without establishing any communication connection, the power generation, power consumption and static state of the elevator can be accurately identified according to the DC bus voltage. This changes the complex modification mode that requires protocol docking in the prior art, greatly reduces the engineering complexity and wiring difficulty of on-site installation and modification, and avoids the electromagnetic interference risk that may be caused by external communication. It significantly improves the versatility, safety and market adaptability of the device.

[0024] (2) This invention constructs a high-precision, high-real-time closed-loop control link by forcibly configuring the bidirectional DC-DC power supply to switch from standby mode to power output mode in a time not exceeding 100ms and the power adjustment cycle not exceeding 1ms. Combined with a fixed sampling cycle of 1ms and a sampling error of less than ±0.8V, the invention ensures that the off-grid energy-saving device can intervene and recycle energy before the elevator inverter's braking resistor is turned on, effectively capturing all the regenerated energy wasted due to slow startup in traditional solutions. The power adjustment cycle of ≤1ms, combined with high-precision sampling, enables the off-grid energy-saving device to follow the drastic power fluctuations caused by elevator operation due to start-up, acceleration, deceleration, and load changes in real time, realizing the "power matching" function. This stabilizes the DC bus voltage within a very narrow range of ±8V for charging and ±3V for discharging, effectively suppressing bus voltage fluctuations. This helps reduce the ripple stress on the DC bus filter capacitor of the elevator inverter, extending its service life and ensuring the stable operation of the elevator system.

[0025] (3) The present invention sets up differentiated control methods for different operating conditions of the elevator: In the power generation state, when the DC bus voltage reaches the charging start voltage, it immediately switches to the charging mode and dynamically adjusts the charging power with a period of no more than 1ms to stabilize the voltage within the range of ±8V of the charging stabilization target voltage. The charging stabilization target voltage is only 10V to 20V higher than the charging start voltage, realizing the efficient capture of regenerative energy in an "instant start and stabilize" manner. This avoids the heat waste of the braking resistor and prevents the voltage drop caused by excessive charging power. In the power consumption state, a delay confirmation time of more than 1 second is set to effectively distinguish between the brief voltage drop at the moment of elevator start and the real continuous power consumption state. The discharge mode is only started after confirmation, and the discharge power is dynamically adjusted with a period of no more than 1ms. By stabilizing the voltage within ±3V of the discharge stabilization target voltage, energy waste from the energy storage stack caused by accidental discharge is avoided, and stable DC support is provided for the elevator traction machine. In complex transient conditions such as emergency stop or deceleration braking, when the DC bus voltage is detected to rise from below the discharge initiation voltage and cross the discharge initiation voltage, the discharge mode is immediately exited and the standby mode is skipped to directly switch to the charging mode. The total switching time from detecting the voltage rise across the discharge initiation voltage to switching to the charging mode does not exceed 100ms. In the no-load state, if the voltage does not reach the charging initiation voltage and the no-load duration exceeds the second preset time, the standby mode is entered. This achieves millisecond-level seamless capture of the "burst" regenerative energy at the moment of braking, while avoiding the device from staying in the no-load state for a long time and increasing power consumption.

[0026] (4) This invention collects historical data on the elevator's operating frequency at different times and uses Discrete Fourier Transform to convert the time-domain data into frequency-domain data, scientifically and objectively dividing peak and off-peak periods, thus realizing intelligent identification and adaptive matching of elevator operating patterns. During peak periods, only charging, discharging, and standby modes are activated, and sleep mode is prohibited, ensuring the off-grid energy-saving device's full-time rapid response to frequent starts and stops; during off-peak periods, when the elevator is stationary for a long time and exceeds a preset threshold, the off-grid energy-saving device is allowed to enter sleep mode and the DC bus power supply of the bidirectional DC-DC power supply is cut off, leaving only the bus voltage wake-up circuit, thereby significantly reducing static energy consumption during off-peak periods. This ensures energy recovery efficiency during peak periods and greatly reduces the device's own energy consumption, realizing intelligent full-cycle energy consumption management of "ensuring response during peak periods and reducing losses during off-peak periods".

[0027] (5) This invention automatically captures the DC bus voltage waveform after waiting for the elevator to run for at least 3 cycles, confirms the voltage range corresponding to the elevator's stationary state, power generation state and power consumption state, and calculates the charging start voltage, charging stabilization target voltage, discharging start voltage and discharging stabilization target voltage based on the voltage range and the preset voltage offset calculation rules. It realizes the fully automatic adaptive preset of voltage threshold, eliminates the cumbersome process of traditional manual measurement and parameter setting, realizes the adaptive intelligent matching of the electrical characteristics of elevator frequency converters of different brands, different power levels and different power grid environments, eliminates the professional threshold of manual debugging, greatly reduces the risk of malfunction or energy waste caused by improper threshold setting, significantly reduces the workload of pre-sales debugging and after-sales maintenance, and significantly improves the versatility and engineering practicality of off-grid energy-saving devices. Attached Figure Description

[0028] Figure 1 This is the system wiring diagram of the off-grid energy-saving device and the DC bus of the elevator inverter of the present invention; Figure 2 This is a voltage waveform diagram of the DC bus of the elevator inverter of the present invention under different conditions; Figure 3 This is a waveform diagram of the DC bus voltage of the elevator inverter EX8500 of the present invention from a stationary state to a generating state. Figure 4 This is a block diagram of the off-grid energy-saving device control method based on the change of the DC bus of the elevator frequency converter according to the present invention; Figure 5 This is a flowchart of the off-grid energy-saving device control method based on the change of the DC bus of the elevator frequency converter according to the present invention; Wherein, H represents the positive terminal of elevator control cabinet 1 and elevator control cabinet 2; L represents the negative terminal of elevator control cabinet 1 and elevator control cabinet 2; H1 represents the positive terminal of the off-grid energy-saving device connected to the positive terminal of elevator control cabinet 1; L1 represents the negative terminal of the off-grid energy-saving device connected to the negative terminal of elevator control cabinet 1; H2 represents the positive terminal of the off-grid energy-saving device connected to the positive terminal of elevator control cabinet 2; L2 represents the negative terminal of the off-grid energy-saving device connected to the negative terminal of elevator control cabinet 2; G1 represents the first grounding terminal of the off-grid energy-saving device; G2 represents the second grounding terminal of the off-grid energy-saving device. VS1 represents the charging start voltage; VS2 represents the charging stabilization target voltage; VS3 represents the discharging start voltage; VS4 represents the discharging stabilization target voltage; Vbus represents the DC bus voltage; T1 represents the first preset time; T2 represents the second preset time. Detailed Implementation

[0029] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0030] Example 1 like Figures 1-5 As shown, this embodiment provides a control method for an off-grid energy-saving device based on changes in the DC bus of an elevator frequency converter. The off-grid energy-saving device upon which this method relies includes an energy storage stack, a bidirectional DC-DC power supply, and a control system. Figure 1 As shown, the off-grid energy-saving device of the present invention can be connected to two elevator control cabinets simultaneously: the positive H and negative L terminals of elevator control cabinet 1 are connected to the H1 and L1 terminals of the off-grid energy-saving device respectively via DC bus 1, and the G1 terminal of the off-grid energy-saving device is grounded; the positive H and negative L terminals of elevator control cabinet 2 are connected to the H2 and L2 terminals of the off-grid energy-saving device respectively via DC bus 2, and the G2 terminal of the off-grid energy-saving device is grounded. The off-grid energy-saving device realizes energy recovery and power supply for two elevators through two independent DC buses, and the grounding terminal provides safe grounding protection for the system. For the sake of simplicity, the following embodiments use a single elevator as an example to describe the control method; the control logic is exactly the same in the scenario of multiple elevators.

[0031] This embodiment uses a 7.5kW elevator frequency converter EX8500 from Sichuan Express Elevator as an example for illustration. Figure 3 As shown, in the DC bus voltage waveform of the EX8500 elevator inverter from a stationary state to a generating state, the time for the voltage to rise from the stationary state to the braking resistor opening voltage is approximately 200ms. Combined with... Figure 2As shown by the voltage waveforms in the three states, the DC bus voltage of the frequency converter is 560-590VDC in the static state, drops to approximately 540±8VDC in the power consumption state, and rises to approximately 710VDC, the braking resistor opening voltage, in the power generation state. Based on the above characteristics, the control method of this embodiment includes the following steps: S1: System Initialization Configuration S11: Connect the energy storage stack of the off-grid energy-saving device to the battery side of the bidirectional DC-DC power supply. Use the positive and negative terminals of the DC bus side of the bidirectional DC-DC power supply as the positive and negative terminals of the off-grid energy-saving device, respectively, and connect them to the positive and negative terminals of the DC bus of the elevator inverter, without establishing any communication connection. Connect the control system to the control terminal of the bidirectional DC-DC power supply and the voltage sampling point of the DC bus, respectively.

[0032] S12: The control system automatically presets four voltage thresholds based on the captured DC bus voltage. Specifically, after waiting for the elevator to run for at least three cycles, the control system automatically determines the voltage range corresponding to the elevator's stationary, power generation, and power consumption states based on the captured DC bus voltage waveform, and calculates the four voltage thresholds using a preset voltage offset calculation rule. In this embodiment, the charging start voltage VS1 is preset to 610VDC, the charging stabilization target voltage VS2 is preset to 620VDC, the discharging start voltage VS3 is preset to 555VDC, and the discharging stabilization target voltage VS4 is preset to 550VDC.

[0033] S13: Configure the response parameters of the bidirectional DC-DC power supply so that the startup time for switching from standby mode to power output mode does not exceed 100ms, and the power adjustment cycle does not exceed 1ms. Here, 100ms refers to a time range of 50ms to 500ms, and 1ms refers to a time range of 0.5ms to 5ms.

[0034] S2: Real-time acquisition of DC bus voltage The control system acquires the DC bus voltage value in real time at a fixed sampling period. In this embodiment, the fixed sampling period is set to 1ms (not greater than 1ms), and the voltage sampling error of the control system is less than ±0.8V.

[0035] S3: Status Judgment and Mode Switching The control system compares the collected DC bus voltage value with four preset voltage thresholds and performs the following operations based on the comparison results: S31: When the DC bus voltage Vbus ≥ 610VDC (charging start voltage VS1), the elevator is determined to be in power generation mode, and the bidirectional DC-DC power supply is switched from standby mode to charging mode. In charging mode, the charging power is dynamically adjusted at a period not exceeding 1ms to keep the DC bus voltage stably maintained within a preset deviation range of 620VDC (in this embodiment, the preset deviation range is ±8V, i.e., 612~628VDC). When the DC bus voltage drops below 610VDC, it first enters a 100ms-long no-load state, and then the bidirectional DC-DC power supply is returned to standby mode. Figure 3 As shown, since the startup time of the bidirectional DC-DC power supply from standby to charging is no more than 100ms, and the time for the voltage to rise from 610VDC to the braking resistor's opening voltage of 710VDC is approximately 100ms, this embodiment can complete the startup and begin energy recovery before the braking resistor opens. In this embodiment, the no-load state refers to an intermediate state where the power output of the bidirectional DC-DC power supply is set to zero, but the control and sampling functions are maintained. The difference between this state and the standby mode is that in the no-load state, the main control unit, FPGA (Field-Programmable Gate Array), and sampling circuit still run at full speed and can restore power output at any time; while in the standby mode, some auxiliary power sources and drive circuits are turned off, resulting in lower power consumption but a slightly longer wake-up time.

[0036] S32: When the DC bus voltage is ≤555VDC (discharge start voltage VS3), the bidirectional DC-DC power supply is first switched from standby mode to discharge mode, and its power output is set to no-load state. If the DC bus voltage is not lower than 550VDC (discharge stabilization target voltage VS4) at this time, it directly enters a no-load state for 100ms and then returns to standby mode; otherwise, the DC bus voltage is continuously monitored. If the duration of the voltage being lower than 550VDC exceeds the first preset time, in this embodiment, the first preset time T1 is greater than 1 second (e.g., 2 seconds). If so, it is confirmed as a power consumption state, the power output of the discharge mode is enabled, and the discharge function is activated. In discharge mode, the discharge power is dynamically adjusted at a period not exceeding 1ms to keep the DC bus voltage stably within the preset deviation range of 550VDC (in this embodiment, the preset deviation range is ±3V, i.e., 547~553VDC). Once the DC bus voltage rises above 555VDC and stabilizes, the bidirectional DC-DC power supply first enters a 100ms-long no-load state before returning to standby mode. This delay confirmation mechanism effectively avoids accidental discharge caused by a brief voltage drop at the moment of elevator startup.

[0037] S33: When 555VDC < DC bus voltage < 610VDC, the elevator is determined to be stationary. The bidirectional DC-DC power supply is switched to an unloaded state. The unloaded state lasts for a preset time (100ms in this embodiment) before entering standby mode. Testing shows that in standby mode, by shutting down the battery-side auxiliary power supply and drive power supply of the bidirectional DC-DC power supply, and retaining only the main control, FPGA, and sampling functions, the standby power consumption can be as low as 20-25W.

[0038] S34: When the DC bus voltage exceeds the preset overvoltage protection threshold (set to 800VDC in this embodiment), an overvoltage alarm is executed and charging operation is prohibited to protect the equipment safety.

[0039] S4: Rapid switching between emergency braking and emergency stop. During an emergency stop or deceleration braking process when the elevator transitions from a powered state to a stationary state, the DC bus voltage begins to rise from a value below 555VDC. When the DC bus voltage is detected to rise from below 555VDC to above 555VDC, the system immediately exits the discharge mode and enters an no-load state. Monitoring of the DC bus voltage continues; if the DC bus voltage continues to rise to or exceeds 610VDC, the system immediately switches to charging mode. This switching process skips the standby mode, and the total switching time from detecting the DC bus voltage rising above 555VDC to switching to charging mode does not exceed 100ms, thus achieving millisecond-level recovery of regenerative energy during braking. Furthermore, if the DC bus voltage fails to reach 610VDC in the no-load state, and the no-load duration exceeds a second preset time (in this embodiment, the second preset time is greater than 100ms), the system enters standby mode.

[0040] Through the above steps, this embodiment achieves efficient recovery and on-demand release of elevator regenerative energy.

[0041] Example 2 This embodiment, based on Embodiment 1, further includes a power consumption optimization step S5 to improve the overall energy-saving effect of the device during all-weather operation. The specific steps are as follows: S51: Collect historical data on elevator operating frequency at different times, and convert the time-domain data into frequency-domain data through Discrete Fourier Transform to distinguish peak and off-peak periods. Taking an office building scenario as an example, 8:00-10:00 and 17:00-19:00 on weekdays are the morning and evening peak periods, while 22:00 to 6:00 the next day is the off-peak period.

[0042] S52: During peak hours, only charging mode, discharging mode and standby mode are activated, and hibernation mode is prohibited to ensure that the off-grid energy-saving device can respond to the frequent start-stop and operation needs of the elevator at any time.

[0043] S53: During off-peak periods, when the elevator is stationary in S33 and the duration of this stationary state exceeds the preset stationary threshold (30 minutes), the off-grid energy-saving device is allowed to enter sleep mode.

[0044] S54: In sleep mode, the off-grid energy-saving device cuts off the DC bus power supply of the bidirectional DC-DC power supply, retaining only the bus voltage wake-up circuit, thereby reducing standby power consumption to an extremely low level. When the bus voltage wake-up circuit detects that the DC bus voltage exceeds the normal range of the quiescent state (i.e., below the discharge start voltage or above the charging start voltage), it immediately wakes up the off-grid energy-saving device to enter normal operation mode.

[0045] Through the above power consumption optimization strategy, this embodiment significantly reduces the static energy consumption of the device itself during off-peak hours while ensuring full-time response during peak hours, thereby further improving the overall energy saving rate.

[0046] Example 3 This embodiment provides a detailed explanation of the automatic preset voltage threshold method in S12 for elevator frequency converters of different brands and power levels.

[0047] When the off-grid energy-saving device is first installed and powered on, the control system enters the self-learning phase. The specific process is as follows: the control system continuously monitors the DC bus voltage with a sampling period of 1ms, waiting for the elevator to complete several complete operating cycles (each cycle includes a complete process of being stationary, consuming electricity, generating electricity, and then being stationary again). During the self-learning process, the control system automatically records the fluctuation range of the DC bus voltage in the stationary state, the minimum voltage value in the consuming electricity state, and the voltage rise curve before the braking resistor is activated in the generating electricity state.

[0048] Based on the collected data, the control system automatically calculates four voltage thresholds using preset voltage offset calculation rules: the charging start voltage VS1 is set higher than the DC bus voltage when the elevator is stationary, and maintains a safe voltage of at least 20VDC compared to the stationary voltage to prevent misjudgment; the charging stabilization target voltage VS2 is set slightly higher than the charging start voltage VS1, with the specific difference depending on the power adjustment cycle of the bidirectional DC-DC power supply; the shorter the adjustment cycle, the smaller the voltage difference; the discharging start voltage VS3 is set lower than the DC bus voltage when the elevator is stationary; and the discharging stabilization target voltage VS4 is set lower than the discharging start voltage VS3. Through the above adaptive learning, this embodiment can adapt to different models of elevator frequency converters without manual intervention, significantly improving the versatility and engineering practicality of the device.

[0049] Example 4 This embodiment provides a detailed verification of the "power matching" function and the specific logic of "dynamic adjustment" of the bidirectional DC-DC power supply.

[0050] In elevator power generation mode, the power output fluctuates rapidly due to changes in elevator load and operating speed. In this embodiment, the bidirectional DC-DC power supply adjusts the charging power in real time with a 1ms cycle. The adjustment logic is as follows: the control system acquires the DC bus voltage sample value with a 1ms cycle and compares it with the charging voltage stabilization target voltage VS2 (620VDC). When the DC bus voltage is higher than VS2, the control system sends a command to the bidirectional DC-DC power supply to increase the charging current to lower the bus voltage; when the DC bus voltage is lower than VS2, a command to decrease the charging current is sent to allow the bus voltage to recover. Through this closed-loop regulation, the DC bus voltage is stabilized within a preset deviation range (±8V) of 620VDC.

[0051] When the elevator is powered on, the bidirectional DC-DC power supply adjusts its discharge power with the same 1ms cycle. The adjustment logic is as follows: the control system acquires a DC bus voltage sample value with a 1ms cycle and compares it with the discharge stabilization target voltage VS4 (550VDC). When the DC bus voltage is lower than VS4, the control system sends a command to the bidirectional DC-DC power supply to increase the discharge current to raise the bus voltage; when the DC bus voltage is higher than VS4, it sends a command to decrease the discharge current. Through this adjustment, the DC bus voltage is stabilized within a preset deviation range (±3V) of 550VDC.

[0052] Tests show that the power adjustment strategy in this embodiment can reduce the DC bus voltage fluctuation range to a much smaller range than the traditional solution (the traditional solution usually fluctuates above ±20V), effectively suppressing the bus voltage fluctuation. This helps reduce the ripple stress on the DC bus filter capacitor of the elevator inverter, extends its service life, and improves the overall reliability of the elevator system.

[0053] In summary, the off-grid energy-saving device control method based on the DC bus variation of elevator frequency converter provided by this invention systematically solves the technical problems of slow response, low efficiency, and poor adaptability of existing off-grid energy-saving devices through a communication-free pure voltage detection architecture, a millisecond-level fast response mechanism, differentiated operating condition control methods, and intelligent power consumption optimization schemes. It has significant energy-saving effects and broad market application prospects.

Claims

1. A control method of an off-grid energy-saving device based on changes in the DC bus of an elevator frequency converter, characterized by, Includes the following steps: S1: System Initialization Configuration S11: Connect the energy storage stack of the off-grid energy-saving device to the battery side of the bidirectional DC-DC power supply. Use the positive and negative terminals of the DC bus side of the bidirectional DC-DC power supply as the positive and negative terminals of the off-grid energy-saving device, respectively, and connect them to the positive and negative terminals of the DC bus of the elevator inverter, without establishing any communication connection. Connect the control system to the control terminal of the bidirectional DC-DC power supply and the voltage sampling point of the DC bus. S12: The control system automatically presets four voltage thresholds based on the captured DC bus voltage, namely the charging start voltage, the charging stabilization target voltage, the discharging start voltage, and the discharging stabilization target voltage, wherein the charging start voltage is higher than the DC bus voltage when the elevator is stationary, and the discharging start voltage is lower than the DC bus voltage when the elevator is stationary. S13: Configure the response parameters of the bidirectional DC-DC power supply so that the startup time for switching from standby mode to power output mode does not exceed 100ms and the power adjustment cycle does not exceed 1ms. S2: Real-time acquisition of DC bus voltage The control system acquires the voltage value of the DC bus in real time at a fixed sampling period, which is no more than 1 ms. S3: Status Judgment and Mode Switching The control system compares the collected voltage value of the DC bus with four preset voltage thresholds, and performs the following operations based on the comparison results: S31: When the DC bus voltage is greater than or equal to the charging start voltage, it is determined that the elevator is in a power generation state. The bidirectional DC-DC power supply is switched from standby mode to charging mode. In the charging mode, the charging power is dynamically adjusted at a period of no more than 1ms based on the difference between the real-time collected DC bus voltage and the charging stabilization target voltage, so that the DC bus voltage is stably maintained within the preset deviation range of the charging stabilization target voltage. When the DC bus voltage drops below the charging start voltage, the bidirectional DC-DC power supply is switched to an unloaded state and then enters standby mode. S32: When the DC bus voltage is less than or equal to the discharge initiation voltage, the bidirectional DC-DC power supply is switched to discharge mode and initially maintains no-load output; the DC bus voltage is continuously monitored, and if the duration exceeds a first preset time from the moment the DC bus voltage first falls below the discharge stabilization target voltage, it is confirmed as a power-consuming state, and the discharge function is activated. In the discharge mode, the discharge power is dynamically adjusted at a period not exceeding 1ms based on the difference between the real-time collected DC bus voltage and the discharge stabilization target voltage, so that the DC bus voltage is stably maintained within the preset deviation range of the discharge stabilization target voltage; when the DC bus voltage rises back to above the discharge initiation voltage and stabilizes, the bidirectional DC-DC power supply is switched to no-load state and then enters standby mode; S33: When the discharge initiation voltage < the DC bus voltage < the charging initiation voltage, it is determined that the elevator is in a stationary state, and the bidirectional DC-DC power supply is switched to an unloaded state. After the unloaded state lasts for a preset time, it enters the standby mode. S34: When the DC bus voltage exceeds the preset overvoltage protection threshold, an overvoltage alarm is triggered and charging operation is prohibited; S4: Rapid switching between emergency braking and emergency stop. During the braking process of the elevator transitioning from a powered state to a stationary state, the DC bus voltage begins to rise from a value lower than the discharge initiation voltage. When the DC bus voltage is detected to have risen from below the discharge initiation voltage to above the discharge initiation voltage, the elevator immediately exits the discharge mode and enters an unloaded state. The DC bus voltage continues to be monitored, and if the DC bus voltage continues to rise to reach or exceed the charging initiation voltage, the elevator immediately switches to the charging mode. The above switching process skips the standby mode, and the total time from detecting that the DC bus voltage has risen above the discharge initiation voltage to switching to the charging mode does not exceed 100ms.

2. The control method of off-grid energy saving device based on DC bus variation of elevator frequency converter according to claim 1, characterized in that: The specific method for automatically presetting the four voltage thresholds in S12 is as follows: after waiting for the elevator to run for at least 3 cycles, the off-grid energy-saving device automatically confirms the voltage range corresponding to the elevator's stationary state, power generation state, and power consumption state based on the captured DC bus voltage waveform, and calculates the charging start voltage, the charging stabilization target voltage, the discharging start voltage, and the discharging stabilization target voltage in combination with the preset voltage offset calculation rules.

3. The control method of off-grid energy saving device based on elevator frequency converter DC bus variation according to claim 1, characterized in that: The fixed sampling period in S2 is on the order of 1ms, and the voltage sampling error of the control system is less than ±0.8V.

4. The control method of off-grid energy saving device based on elevator frequency converter DC bus variation according to claim 1, characterized in that: The preset deviation range of the charging regulated target voltage in S31 is ±8V; the preset deviation range of the discharging regulated target voltage in S32 is ±3V.

5. The control method of off-grid energy saving device based on elevator frequency converter DC bus variation according to claim 1, characterized in that: The process of switching the bidirectional DC-DC power supply to an idle state and then to standby mode in S31 specifically involves: first entering an idle state lasting for 100ms, and then switching to standby mode.

6. The control method of off-grid energy saving device based on elevator frequency converter DC bus variation according to claim 1, characterized in that: The process of switching the bidirectional DC-DC power supply to an idle state and then to standby mode in S32 is as follows: first, it enters an idle state lasting for 100ms, and then it switches to standby mode.

7. The control method of off-grid energy saving device based on elevator frequency converter DC bus variation according to claim 1, characterized in that: S4 further includes: if the DC bus voltage fails to reach the charging start voltage under no-load conditions, and the no-load duration exceeds the second preset time, then enter the standby mode.

8. The control method of the off-grid energy-saving device based on the change of the DC bus of the elevator frequency converter according to claim 7, characterized in that: The first preset time is greater than 1 second; the second preset time is greater than 100 ms.

9. The control method of off-grid energy saving device based on elevator frequency converter DC bus variation according to claim 1, characterized in that: It also includes S5: power consumption optimization, which includes the following steps: S51: Collect historical data on elevator operating frequency at different time periods, convert the time domain data into frequency domain data through discrete Fourier transform, and divide the peak period and the off-peak period. S52: During the peak period, only charging mode, discharging mode and standby mode are enabled, and sleep mode is prohibited; S53: During the off-peak period, when the elevator is in the stationary state and the duration of this state exceeds a preset stationary threshold, the off-grid energy-saving device is allowed to enter a dormant mode. S54: In the sleep mode of S53, the off-grid energy-saving device cuts off the DC bus power supply of the bidirectional DC-DC power supply, and only retains the bus voltage wake-up circuit.

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