Energy storage type low-grade waste heat power generation automatic grid connection device, power generation system and operation method of power generation system

Abstract

The invention discloses an energy storage type low-grade waste heat power generation automatic grid-connected device, a power generation system and an operation method thereof, and the device comprises a rectification unit which is connected with an engine end and is used for rectifying an alternating current generated by a power generator into a direct current and transmitting the direct current to an energy storage unit; the energy storage unit is used for storing the direct-current electric energy output by the rectifying unit and continuously providing a stable direct-current power supply when the output current of the generator is reduced due to the decline of the heat source; the rectification inversion unit is respectively connected with the energy storage unit and an external power grid and is used for executing a corresponding working state according to an operation requirement so as to realize mutual conversion between the direct-current voltage of the energy storage unit and the power frequency three-phase alternating-current voltage of the power grid and electric energy uploading; and the detection / control / protection unit is used for monitoring state parameters in real time, diagnosing an abnormal state, generating a pulse width modulation (PWM) signal through a preset control strategy, and outputting the PWM signal to the rectification inversion unit to drive and control a high-speed switch so as to realize dynamic adjustment.

Description

Technical Field

[0001] The present invention belongs to the technical field of waste heat power generation, and in particular relates to an energy storage type low-grade waste heat power generation automatic grid-connected device, a power generation system and an operation method thereof. Background Art

[0002] In the production process of industrial enterprises in the fields of metallurgy, petrochemicals, etc., there are a large number of waste heat dissipations in various forms; waste heat power generation is to recover waste heat, generate steam, drive steam turbine generators to generate electricity, achieve energy conservation and emission reduction, and has been widely used with remarkable results. However, in the field of low-grade waste heat utilization, due to the low grade, discontinuity and low energy of waste heat resources, the steam generated by the recovery has large flow fluctuations and unstable parameters, which seriously affects the operating efficiency and stability of steam turbine generators.

[0003] Figure 1 The following is a typical application diagram of low-grade waste heat power generation, including primary equipment such as low-grade heat source, steam turbine, synchronous generator, grid-connected circuit breaker, and secondary equipment such as speed control, excitation, synchronization and protection devices. After the unit is started, the generator outlet generates a voltage with the same frequency, phase and amplitude as the grid connection point through the adjustment of the speed control device, excitation device, synchronization device, etc., so that the grid-connected circuit breaker can be closed to realize the generator grid-connected power generation. The following problems often occur in the production process of low-grade waste heat power generation:

[0004] 1. Before the generator is connected to the grid, the unstable heat source affects the generator speed control and adjustment effect, resulting in a long synchronization adjustment process and difficulty in connecting to the grid;

[0005] 2. During the operation of the generator, when the heat source drops significantly in a short period of time, the generator will be forced to shut down and restart when the heat source is restored; frequent shutdown and restart will affect the equipment life and operating efficiency. Summary of the invention

[0006] To solve the above problems, the purpose of the present invention is to provide an energy storage type low-grade waste heat power generation automatic grid-connected system and its operation method, which is suitable for low-grade waste heat power generation scenarios and solves the problems of difficulty in grid connection and frequent start and stop of synchronous generators.

[0007] The present invention provides an energy storage type low-grade waste heat power generation automatic grid-connected device, which is characterized by comprising: a rectifier unit, an energy storage unit, a rectifier inverter unit, a detection / control / protection unit,

[0008] The rectifier unit is connected to the engine end and is used to rectify the alternating current generated by the generator into direct current and transmit it to the energy storage unit;

[0009] The energy storage unit is used to store the DC power output by the rectifier unit and continue to provide a stable DC power supply when the heat source decreases, causing the output current of the generator to decrease;

[0010] The rectifier and inverter units are connected to the energy storage unit and the external power grid respectively, and are used to execute corresponding working states according to operation requirements to realize the mutual conversion between the DC voltage of the energy storage unit and the three-phase AC voltage of the power grid and the uploading of electric energy, ensure the synchronous connection of the generator and the power grid, and realize charging and discharging when the generator is shut down;

[0011] The detection / control / protection unit is used to monitor state parameters in real time, diagnose abnormal states, generate pulse width modulation (PWM) signals through a preset control strategy, and output the signals to the rectifier and inverter units to drive and control high-speed switches to achieve dynamic regulation.

[0012] Preferably, the input end of the rectifier unit is connected to the synchronous generator, and the output end of the rectifier unit is connected to the energy storage unit, wherein the rectifier unit adopts a three-phase full-bridge rectifier circuit composed of diodes to convert the three-phase AC voltage emitted by the synchronous generator into a DC voltage, output it to the energy storage unit, and charge the battery in the energy storage unit.

[0013] Preferably, the energy storage unit comprises a battery pack, wherein the battery pack comprises a plurality of batteries connected in series to match the system voltage, and the batteries connected in series are connected in parallel to expand the overall capacity to store electrical energy and stabilize the DC voltage.

[0014] Preferably, the rectifier-inverter unit comprises three bridge arms, each bridge arm is composed of two IGBTs connected in series to form a three-phase bridge rectifier-inverter integrated circuit, which operates in two states of inverter and controlled rectification as needed. By controlling the switching state of the IGBT on each bridge arm, three-phase AC power is converted into DC power in the rectification state, and DC power is converted into three-phase AC power in the inverter state.

[0015] Preferably, the detection / control / protection unit adopts voltage and current transformers, temperature sensors and digital signal processors, wherein the detection unit is used to detect real-time voltage, current, temperature, switch status and related operating parameters; the protection unit is used to record and analyze the detected operating parameters, diagnose abnormal conditions, issue alarm signals, and achieve safety protection by shutting down the IGBT or external circuit breaker; the control unit is used to make abnormal judgments based on the detected operating parameters, generate pulse width modulation signals through a preset control strategy, output them to the rectifier inverter unit, drive the IGBT to control the high-speed switch, and achieve dynamic adjustment.

[0016] The present invention also provides a power generation system using an energy storage type low-grade waste heat power generation automatic grid-connected device, comprising the above-mentioned energy storage type low-grade waste heat power generation automatic grid-connected device, a low-grade heat source, a steam turbine, a synchronous generator and a grid-connected circuit breaker.

[0017] The present invention also provides an operation method of a power generation system using the above-mentioned energy storage type low-grade waste heat power generation automatic grid-connected device, comprising:

[0018] Before the engine is started, the isolation circuit breaker is closed and the energy storage type low-grade waste heat power generation automatic grid-connected device is installed. Currently, the IGBT is in the off state and the generator is not connected to the grid;

[0019] The low-grade waste heat steam is introduced into the steam turbine, the speed of the steam turbine is gradually increased to the rated speed, and the excitation system of the synchronous generator is adjusted to generate a three-phase AC voltage at the generator end;

[0020] When the generator end is connected to the rectifier unit, the three-phase AC voltage is converted into a DC pulsating voltage through the rectifier unit to charge the battery of the energy storage unit;

[0021] When the charging energy reaches the operating conditions, the rectifier inverter unit works in the inverter grid-connected mode, and the IGBT is turned on in an orderly manner according to the predetermined strategy, converting the DC voltage in the battery into a three-phase AC voltage. The output end generates a three-phase AC sinusoidal waveform that is exactly the same as the grid voltage at the grid connection point, realizing the circuit connection of the generator-automatic grid-connected device-grid. The current output by the generator is injected into the grid through the automatic grid-connected device, completing the generator grid-connected power generation.

[0022] As a preferred method, the method includes: during the operation of the generator, when the heat source decreases and the generator cannot supply power to the power grid, the charging current is output through the rectifier unit to convert the waste heat recovered by the system into electrical energy and store it in the battery, thereby realizing the recovery of waste heat and waste energy;

[0023] When the heat source decreases and the turbine cannot maintain its speed, the voltage at the turbine terminal drops significantly. Based on the unidirectional conductivity of the rectifier unit circuit, the output current path of the generator is naturally cut off by the diode, and the charging current output by the rectifier unit is reduced to zero, so that the generator is automatically decoupled.

[0024] After the generator is disconnected, the energy storage unit continues to output electric energy to the grid through the rectifier inverter unit, avoiding fluctuation interference to the grid caused by the generator shutdown;

[0025] When the energy in the energy storage unit is exhausted, the rectifier inverter unit enters the stop mode, the IGBT is turned off, and the current path between the energy storage unit and the grid is cut off, so there is no need to disconnect the grid circuit breaker, and the conditions for reconnection to the grid are available at any time.

[0026] Preferably, when the heat source is restored, the generator operates at rated speed, the generator terminal voltage is restored, the output current of the rectifier unit increases, and the charging amount of the energy storage unit increases. When the charging energy is higher than the operating lower limit, the rectifier inverter unit re-enters the inverter grid-connected mode, the IGBT is turned on, and grid-connected power generation is restored.

[0027] Preferably, when the generator is in a shutdown state, the diode in the rectifier unit is not conducting, and there is no current path between the generator and the energy storage unit, the energy storage unit and the rectifier inverter unit form an energy storage device and operate as an energy storage system.

[0028] Due to the adoption of the above technical solution, the present invention has the following advantages and positive effects compared with the prior art:

[0029] 1. Improve grid-connected efficiency and stability: Through the energy storage type low-grade waste heat power generation automatic grid-connected device, the generator can be connected to the grid more efficiently. The rectifier inverter unit can convert direct current into three-phase alternating current when needed to ensure that the generator output current matches the grid voltage, thereby improving the stability and reliability of the grid connection.

[0030] 2. Reduce the adjustment time and accuracy requirements during the grid connection process: In traditional methods, the generator grid connection requires precise adjustment of parameters such as voltage, frequency, phase sequence, amplitude and phase. In the present invention, only the voltage parameter needs to be close to the rated value, which greatly simplifies the adjustment process and shortens the grid connection time.

[0031] 3. Improve energy recovery efficiency: When the heat source decreases or is interrupted, the system can convert the recovered waste heat into electrical energy and store it in the battery, thereby maximizing the utilization of waste heat and waste energy; even when the heat source is extremely reduced, the unidirectional conductivity of the rectifier unit circuit can naturally shut off the generator output current to avoid energy waste.

[0032] 4. Enhance the adaptability and flexibility of the system: The system can automatically adjust the operating status according to the changes in the heat source without manual intervention. When the heat source is restored, the system can automatically restart the grid-connected power generation, improving the automation level and operating efficiency of the system.

[0033] 5. Reduce the impact on the power grid: After the generator is disconnected, the energy storage unit continues to output electric energy to the power grid through the rectifier inverter unit, avoiding the fluctuation interference of the generator shutdown on the power grid and protecting the stable operation of the power grid.

[0034] 6. Improve economic benefits: By optimizing energy utilization and improving system operation efficiency, enterprises can reduce operating costs and improve economic benefits. At the same time, energy storage systems can also achieve peak load shifting and valley filling, and absorb surplus electricity, further increasing economic benefits. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The specific embodiments of the present invention are further described in detail below with reference to the accompanying drawings, wherein:

[0036] Figure 1 It is a schematic diagram of a typical application of energy storage type low-grade waste heat power generation described in an embodiment of the present invention;

[0037] Figure 2 It is a schematic diagram of the energy storage type low-grade waste heat power generation automatic grid-connected device described in an embodiment of the present invention;

[0038] Figure 3 Schematic diagram of a power generation system using an energy storage type low-grade waste heat power generation automatic grid-connected device in an embodiment of the present invention. DETAILED DESCRIPTION

[0039] The present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the following description and claims. It should be noted that the drawings are all in a very simplified form and use non-precise ratios, which are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention.

[0040] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0041] The present invention provides an energy storage type low-grade waste heat power generation automatic grid-connected device, including: a rectifier unit, an energy storage unit, a rectifier inverter unit, and a detection / control / protection unit. The principle is shown in Figure 2 As shown,

[0042] The rectifier unit is connected to the engine end and is used to rectify the alternating current generated by the generator into direct current and transmit it to the energy storage unit;

[0043] The energy storage unit is used to store the DC power output by the rectifier unit and continue to provide a stable DC power supply when the heat source decreases, causing the output current of the generator to decrease;

[0044] The rectifier and inverter units are connected to the energy storage unit and the external power grid respectively, and are used to perform corresponding working states according to operation requirements to realize the mutual conversion between the DC voltage of the energy storage unit and the three-phase AC voltage of the power grid and the uploading of electric energy, ensure the synchronous connection of the generator and the power grid, and realize the charging and discharging of the energy storage device when the generator is shut down;

[0045] The detection / control / protection unit is used to monitor state parameters in real time, diagnose abnormal states, generate pulse width modulation (PWM) signals through a preset control strategy, and output the signals to the rectifier and inverter units to drive and control high-speed switches to achieve dynamic regulation.

[0046] Specifically, the input end of the rectifier unit is connected to the synchronous generator, and the output end of the rectifier unit is connected to the energy storage unit, wherein the rectifier unit uses a three-phase full-bridge rectifier circuit composed of diodes to convert the three-phase AC voltage emitted by the synchronous generator into a DC voltage, output it to the energy storage unit, and charge the battery in the energy storage unit. It can be understood that the unit connects the generator end and the energy storage unit, uses diodes to form a classic three-phase full-bridge rectifier circuit, converts the three-phase AC voltage emitted by the generator into a DC voltage (AC-DC), outputs it to the energy storage unit, and charges the battery therein.

[0047] Specifically, the energy storage unit includes a battery pack, which includes a plurality of batteries connected in series to match the system voltage, and the batteries connected in series are connected in parallel to expand the overall capacity to store electric energy and stabilize the DC voltage. It can be understood that the battery pack is composed of a large-capacity battery pack. Since the voltage and capacity of a single battery are limited, in order to meet the system voltage and capacity requirements, multiple groups of batteries are connected in series to match the system voltage, and the overall capacity is expanded by connecting the batteries in parallel, so as to store electric energy and stabilize the DC voltage.

[0048] Specifically, the rectifier inverter unit includes three bridge arms, each bridge arm is connected in series by two IGBTs, forming a three-phase bridge rectifier inverter integrated circuit, which operates in the two states of inverter and controllable rectification according to needs, and converts three-phase AC into DC in the rectification state, and converts DC into three-phase AC in the inverter state by controlling the switch state of the IGBT on each bridge arm. It can be understood that the unit connects the energy storage unit with the external power grid, uses the turn-off power electronic device IGBT, and forms a three-phase bridge rectifier inverter integrated circuit, which can operate in the two states of inverter and controllable rectification according to needs, realizing the mutual conversion of the DC voltage of the energy storage unit and the three-phase AC voltage of the power grid, the charging of the energy storage unit by the power grid, and the uploading of the stored electric energy to the power grid.

[0049] Specifically, the detection / control / protection unit uses voltage, current transformer, temperature sensor and digital signal processor, wherein the detection unit is used to detect real-time voltage, current, temperature, switch state and related operating parameters; for example, the voltage and current transformer are used to monitor the voltage, current and other electrical parameters of the generator in real time; the temperature sensor is used to monitor the temperature change of the system to ensure that the equipment operates within a safe temperature range; the switch state sensor is used to monitor the switch state of key equipment such as grid-connected circuit breakers. The protection unit is used to record and analyze the detected operating parameters, diagnose abnormal conditions, issue alarm signals, and achieve safety protection by shutting down IGBT or external circuit breakers; for example, the collected analog signal is converted into a digital signal after filtering, and this process is usually completed by an AD converter, such as the AD7606 chip, which supports 8-channel, 16-bit high-precision acquisition. The digital signal processor (DSP) receives these digital signals and performs further analysis and processing. The control unit is used to make abnormal judgments based on the detected operating parameters, generate pulse width modulation signals through a preset control strategy, output them to the rectifier inverter unit, drive the IGBT to control the high-speed switch, and achieve dynamic adjustment. For example, during fault diagnosis, the DSP performs real-time analysis on the collected data to determine whether there are abnormal conditions, such as overvoltage, undervoltage, overcurrent, overheating, etc.; when an abnormal condition is detected, the DSP will record the relevant data and prepare to take corresponding protective measures. When the alarm function is implemented, once an abnormal condition is diagnosed, the DSP will immediately issue an alarm signal to notify the operator or control system; the alarm signal can be conveyed through sound and light alarms, display screens or remote communication modules. Control strategy formulation: According to the operating requirements of the generator and the actual situation of the power grid, a complete set of grid-connected control programs is preset. These programs include strategies for starting grid connection, normal operation, decoupling, and dealing with various abnormal situations. The control strategy contains detailed algorithms and logical judgments to ensure that correct decisions can be made under different working conditions. PWM signal generation: When it is necessary to dynamically adjust the rectifier inverter unit, the DSP will calculate the appropriate PWM signal according to the preset control strategy and current operating parameters. PWM signal is a technology that adjusts the output voltage or current by changing the pulse width. In this system, PWM signals are used to control the conduction and shutdown of power electronic devices such as IGBTs. DSP outputs the calculated PWM signal to the driving circuit of the rectifier inverter unit, driving IGBT and other devices to turn on and off in an orderly manner according to the predetermined strategy. When the above units are dynamically adjusted and executed, the rectifier inverter unit responds: after receiving the PWM signal from DSP, the rectifier inverter unit adjusts its working state according to the change of the signal; in the inverter mode, the rectifier inverter unit converts the DC voltage in the battery into a three-phase AC voltage and injects it into the power grid; in the controllable rectifier mode, the rectifier inverter unit can adjust the current size and direction input to the energy storage unit.System feedback and optimization: The system will continuously adjust the control strategy and PWM signal according to the current operating status and feedback information to achieve the best dynamic adjustment effect; through closed-loop control, the system can automatically adapt to changes in external conditions and maintain efficient and stable operation.

[0050] In the traditional grid-connected circuit, a new automatic grid-connected device is added between the generator and the grid-connected circuit breaker, that is, the energy storage type low-grade waste heat power generation automatic grid-connected device provided above, and the synchronization device is cancelled. The circuit breaker no longer directly switches the generator and only plays an isolation protection role. The configuration of the power generation system is shown in Figure 3 .

[0051] The present invention also provides a power generation system using an energy storage type low-grade waste heat power generation automatic grid-connected device, comprising the energy storage type low-grade waste heat power generation automatic grid-connected device, a low-grade heat source, a steam turbine, a synchronous generator and a grid-connected circuit breaker as described in the above embodiment.

[0052] The present invention also provides an operation method of a power generation system using the above-mentioned energy storage type low-grade waste heat power generation automatic grid-connected device, comprising:

[0053] 1. Generator start:

[0054] Before starting the generator, first close the isolating circuit breaker and put the automatic grid-connected device into operation; at this time, the output terminals of the rectifier inverter unit are connected to the grid, but because the power electronic device IGBT is in the off state, no current flows through the entire circuit and the generator is not connected to the grid.

[0055] The low-grade waste heat steam is introduced into the steam turbine, the speed of the steam turbine is gradually increased to the rated speed, and the excitation system is adjusted to generate a three-phase AC voltage at the generator end; unlike the traditional method of precisely adjusting the voltage frequency, phase sequence, amplitude, phase, etc., the voltage parameters of the generator in this patent can be close to the rated value. The generator end is connected to the rectifier unit of the automatic grid-connected device, and the three-phase AC voltage is converted into a DC pulsating voltage through the rectifier unit to charge the battery of the energy storage unit. When the charging energy reaches the operating conditions, the rectifier inverter unit works in the inverter grid-connected mode, and the power electronic device IGBT is turned on in an orderly manner according to the predetermined strategy, converting the DC voltage in the battery into a three-phase AC voltage. The output end generates a three-phase AC sinusoidal waveform that is exactly the same as the grid voltage at the grid connection point, realizing the circuit connection of the generator-automatic grid-connected device-grid, and the electric energy output by the generator is injected into the grid through the automatic grid-connected device to complete the generator grid-connected power generation.

[0056] Compared with the traditional synchronous grid-connected generator, the grid-connected technology adopted in the embodiment of the present invention has the advantages of short adjustment process, low precision requirement, fast grid-connected speed, etc., and is very suitable for the application scenario of low-grade waste heat power generation.

[0057] 2. Generator operation:

[0058] During the operation of the generator, the voltage at the generator terminal is maintained unchanged. When a short-term heat source drops, the output current drops accordingly until it reaches zero. In traditional technology, the generator needs to delay disconnection and the grid-connected circuit breaker trips and shuts down.

[0059] In the embodiment of the present invention, this problem is improved. Although the heat source is greatly reduced, resulting in the generator being unable to supply electricity to the power grid, as long as there is a minimum heat source to maintain the generator terminal voltage unchanged, the rectifier unit can still output a charging current, convert the waste heat recovered by the system into electrical energy and store it in the battery, thereby improving the recovery efficiency and realizing the collection of waste heat and waste energy. Only when the heat source is extremely reduced, the steam turbine cannot maintain the speed, and the terminal voltage drops significantly, based on the unidirectional conductivity of the rectifier unit circuit, the generator output current path is naturally turned off by the diode, and the charging current output by the rectifier unit is reduced to zero, at which time the generator is decoupled. Compared with the traditional method, the technology adopted in the embodiment of the present invention significantly improves the adaptability of the generator to load fluctuations and improves the continuity of operation; on the other hand, it achieves the purpose of accurately and smoothly decoupling the generator without disconnecting the grid-connected circuit breaker, effectively avoiding the reverse power phenomenon caused by untimely decoupling. After decoupling, the steam turbine generator set can choose to rotate or shut down according to the heat source situation.

[0060] After the generator is disconnected, the energy storage unit can continue to output electric energy to the grid through the rectifier and inverter unit, avoiding the fluctuation interference of the generator shutdown on the grid; when the energy of the energy storage unit is exhausted, the rectifier and inverter unit enters the stop mode, and the power electronic device IGBT is turned off, cutting off the current path between the energy storage unit and the grid; in this process, there is no need to disconnect the grid circuit breaker, and the conditions for reconnection to the grid are available at any time.

[0061] When the heat source is restored, the generator runs at rated speed, the terminal voltage is restored, the output current of the rectifier unit increases, and the charging capacity of the energy storage unit increases. When the charging energy is higher than the lower limit of operation, the rectifier inverter unit re-enters the inverter grid-connected mode, the power electronic device is turned on, and grid-connected power generation can be restored. This process is completed automatically without manual operation, which effectively improves the automation level of the enterprise, reduces the operating workload, and provides technical support for the unmanned and remote operation and maintenance of the system.

[0062] 3. Generator shutdown:

[0063] When the generator is shut down for a long time, the diode of the rectifier unit of the automatic grid-connected device is not conducting, and there is no current path between the generator and the energy storage unit of the automatic grid-connected device. The energy storage unit of the automatic grid-connected device and the rectifier inverter unit form a classic energy storage device, which operates as an energy storage system and realizes functions such as peak shaving and valley filling, surplus power consumption, smooth load curve, and peak-valley price difference profit as needed.

[0064] The embodiments of the present invention are described in detail above in conjunction with the accompanying drawings, but the present invention is not limited to the above embodiments. Even if various changes are made to the present invention, if these changes fall within the scope of the claims of the present invention and their equivalents, they still fall within the protection scope of the present invention.

Claims

1. An energy storage type low-grade waste heat power generation automatic grid-connected device, characterized in that: include: Rectification unit, energy storage unit, rectification and inverter unit, detection / control / protection unit, The rectifier unit is connected to the engine end and is used to rectify the alternating current generated by the generator into direct current and transmit it to the energy storage unit; The energy storage unit is used to store the DC power output by the rectifier unit and continue to provide a stable DC power supply when the heat source decreases, causing the output current of the generator to decrease; The rectifier and inverter units are connected to the energy storage unit and the external power grid respectively, and are used to execute corresponding working states according to operation requirements to realize the mutual conversion between the DC voltage of the energy storage unit and the three-phase AC voltage of the power grid and the uploading of electric energy, so as to ensure the synchronous connection of the generator and the power grid; The detection / control / protection unit is used to monitor state parameters in real time, diagnose abnormal states, generate pulse width modulation (PWM) signals through a preset control strategy, and output the signals to the rectifier and inverter units to drive and control high-speed switches to achieve dynamic regulation.

2. The energy storage type low-grade waste heat power generation automatic grid-connected device according to claim 1 is characterized in that: The input end of the rectifier unit is connected to the synchronous generator, and the output end of the rectifier unit is connected to the energy storage unit, wherein the rectifier unit adopts a three-phase full-bridge rectifier circuit composed of diodes to convert the three-phase AC voltage emitted by the synchronous generator into a DC voltage, output it to the energy storage unit, and charge the battery in the energy storage unit.

3. The energy storage type low-grade waste heat power generation automatic grid-connected device according to claim 1 is characterized in that: The energy storage unit includes a battery pack, which includes a plurality of batteries connected in series to match the system voltage, and the batteries connected in series are connected in parallel to expand the overall capacity to store electrical energy and stabilize the DC voltage.

4. The energy storage type low-grade waste heat power generation automatic grid-connected device according to claim 1 is characterized in that: The rectifier inverter unit includes three bridge arms, each bridge arm is connected in series by two IGBTs to form a three-phase bridge rectifier inverter integrated circuit, which operates in two states of inverter and controlled rectification according to needs. By controlling the switching state of the IGBT on each bridge arm, the three-phase AC power is converted into DC power in the rectification state, and the DC power is converted into three-phase AC power in the inverter state.

5. The energy storage type low-grade waste heat power generation automatic grid-connected device according to claim 1 is characterized in that: The detection / control / protection unit adopts voltage and current transformers, temperature sensors and digital signal processors, wherein the detection unit is used to detect real-time voltage, current, temperature, switch status and related operating parameters; the protection unit is used to record and analyze the detected operating parameters, diagnose abnormal conditions, issue alarm signals, and achieve safety protection by shutting down IGBTs or external circuit breakers; the control unit is used to make abnormal judgments based on the detected operating parameters, generate pulse width modulation signals through preset control strategies, output them to the rectifier inverter unit, drive the IGBT to control high-speed switches, and achieve dynamic regulation.

6. A power generation system using an energy storage type low-grade waste heat power generation automatic grid-connected device, characterized in that: It comprises the energy storage type low-grade waste heat power generation automatic grid-connected device as described in any one of claims 1 to 5, a low-grade heat source, a steam turbine, a synchronous generator and a grid-connected circuit breaker.

7. An operating method of a power generation system using the energy storage type low-grade waste heat power generation automatic grid-connected device as claimed in any one of claims 1 to 5, characterized in that: include: Before the engine is started, the isolation circuit breaker is closed and the energy storage type low-grade waste heat power generation automatic grid-connected device is installed. Currently, the IGBT is in the off state and the generator is not connected to the grid; The low-grade waste heat steam is introduced into the steam turbine, the speed of the steam turbine is gradually increased to the rated speed, and the excitation system of the synchronous generator is adjusted to generate a three-phase AC voltage at the generator end; When the generator end is connected to the rectifier unit, the three-phase AC voltage is converted into a DC pulsating voltage through the rectifier unit to charge the battery of the energy storage unit; When the charging energy reaches the operating conditions, the rectifier inverter unit works in the inverter grid-connected mode, and the IGBT is turned on in an orderly manner according to the predetermined strategy, converting the DC voltage in the battery into a three-phase AC voltage. The output end generates a three-phase AC sinusoidal waveform that is exactly the same as the grid voltage at the grid connection point, realizing the circuit connection of the generator-automatic grid-connected device-grid. The electric energy output by the generator is injected into the grid through the automatic grid-connected device, completing the generator grid-connected power generation.

8. The method for operating the power generation system of the energy storage type low-grade waste heat power generation automatic grid-connected device according to claim 7 is characterized in that: include: During the operation of the generator, when the heat source decreases and the generator cannot supply power to the grid, the charging current is output through the rectifier unit to convert the waste heat recovered by the system into electrical energy and store it in the battery, thus realizing the recovery of waste heat and waste energy. When the heat source decreases and the turbine cannot maintain its speed, the voltage at the turbine terminal drops significantly. Based on the unidirectional conductivity of the rectifier unit circuit, the output current path of the generator is naturally cut off by the diode, and the charging current output by the rectifier unit is reduced to zero, so that the generator is automatically decoupled. After the generator is disconnected, the energy storage unit continues to output electric energy to the grid through the rectifier inverter unit, avoiding fluctuation interference to the grid caused by the generator shutdown; When the energy in the energy storage unit is exhausted, the rectifier inverter unit enters the stop mode, the IGBT is turned off, and the current path between the energy storage unit and the grid is cut off, so there is no need to disconnect the grid circuit breaker, and the conditions for reconnection to the grid are available at any time.

9. The method for operating the power generation system of the energy storage type low-grade waste heat power generation automatic grid-connected device according to claim 8, characterized in that: When the heat source is restored, the generator runs at rated speed, the generator terminal voltage is restored, the output current of the rectifier unit increases, and the charging amount of the energy storage unit increases. When the charging energy is higher than the operating lower limit, the rectifier inverter unit re-enters the inverter grid-connected mode, the IGBT is turned on, and grid-connected power generation is restored.

10. The method for operating the power generation system of the energy storage type low-grade waste heat power generation automatic grid-connected device according to claim 7, characterized in that: When the generator is in a shutdown state, the diode in the rectifier unit is not conducting, and there is no current path between the generator and the energy storage unit, the energy storage unit and the rectifier inverter unit form an energy storage device and operate as an energy storage system.

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