A high-temperature photo-thermal energy storage power generation system for emerging energy power generation

Abstract

This invention discloses a high-temperature solar thermal energy storage power generation system for emerging energy generation, belonging to the field of high-temperature solar thermal energy storage power generation technology. The system includes a solar field heat collection unit, a high-temperature fluid circuit, a generator set, a converter, and a transformer. An active common-mode cancellation circuit is connected in parallel between the positive and negative DC bus of the converter. The system is also equipped with a temperature sensor group, a common-mode voltage sensor, and a controller. The controller calculates the common-mode equivalent impedance based on the temperature signal of the high-temperature conductive fluid and calculates the compensation voltage based on the detected transient common-mode voltage. It drives the active common-mode cancellation circuit to output a compensation voltage with opposite polarity and equal amplitude to the transient common-mode voltage and injects it into the common-mode coupling node. This suppresses the common-mode voltage from the electrical conversion source of the converter, cuts off the high-frequency leakage current path formed by the parasitic capacitance coupling between the high-temperature conductive fluid and the pipe wall, suppresses the electrochemical corrosion of the pipeline of the high-temperature solar thermal energy storage system, and extends the service life of the system. It is suitable for high-temperature solar thermal energy storage grid-connected power generation systems.

Description

Technical Field

[0001] This invention relates to the field of high-temperature solar thermal energy storage power generation technology, specifically to a high-temperature solar thermal energy storage power generation system for emerging energy power generation, and more particularly to a system structure and implementation method for suppressing the common-mode voltage of the full-power converter in the system, thereby cutting off the high-frequency leakage current path formed by the parasitic capacitive coupling between the high-temperature conductive fluid and the heat collector tube wall. Background Technology

[0002] High-temperature solar thermal energy storage power generation systems typically consist of a solar field heat collection unit, a high-temperature heat transfer and storage circuit, a generator set, and a grid-connected converter unit. The high-temperature heat transfer and storage circuit is a closed loop formed by sequentially connecting heat collection pipes, a heat storage tank, and a heat exchanger. High-temperature molten salt or liquid metal is used as the heat transfer and storage medium in the circuit. This type of medium exhibits good electrical conductivity at the operating temperature and is essentially an electrolyte or a metallic conductor. The AC power generated by the generator set must be converted from AC to DC to AC by the H02M7 full-power converter before it can be connected to the grid. The converter generally uses high-frequency pulse width modulation technology to drive power semiconductor devices to perform high-speed switching operations.

[0003] The closest existing technology to this invention is a conventional full-power converter combined with passive corrosion protection and grounding treatment: the converter inverter bridge uses conventional modulation to generate the switching vector, without actively controlling the common-mode voltage component. The common-mode voltage excited by the high-frequency switching action is coupled through the parasitic capacitance formed between the pipe wall and the high-temperature fluid, thus forming a high-frequency leakage current in the fluid circuit. Existing solutions only delay the corrosion rate by passively increasing the pipe wall thickness, adding corrosion-resistant alloy linings, or setting ground points at multiple locations in the pipeline, and regularly inspect and replace the pipeline.

[0004] The aforementioned existing technologies only address the issue of common-mode voltage after it has already been coupled into the fluid circuit. They do not suppress the generation of common-mode voltage from the source of electrical conversion in the converter, resulting in high treatment costs and limited suppression effects. High-temperature fluid pipelines still face the problem of accelerated electrochemical corrosion and high-frequency electromigration damage, shortened service life, and frequent maintenance and replacement. Summary of the Invention

[0005] The technical problem to be solved by this invention is that in existing high-temperature solar thermal energy storage power generation systems, the common-mode voltage generated by the high-frequency switching action of the full-power converter is coupled through the parasitic capacitance between the high-temperature conductive fluid and the heat collector tube wall, forming a high-frequency leakage current in the fluid circuit. This current, together with the high-temperature environment, accelerates the electrochemical corrosion and electromigration damage of the tube wall. Existing technologies can only address this issue post-event by upgrading materials or passively grounding, failing to cut off the generation of common-mode voltage at the source of the converter's electrical conversion. This approach is costly and has limited effectiveness.

[0006] To solve the above-mentioned technical problems, the present invention provides a high-temperature solar thermal energy storage power generation system for emerging energy power generation, including a solar field heat collection unit, a high-temperature fluid circuit, a generator set, a converter, and a transformer;

[0007] The high-temperature fluid circuit includes a heat collection tube, a heat storage tank, and a heat exchanger connected in sequence to form a closed loop, which contains a high-temperature conductive fluid.

[0008] The output terminal of the generator set is connected to the AC input side of the converter.

[0009] The converter includes a rectifier bridge, a DC bus, and an inverter bridge. The output terminal of the rectifier bridge is connected to one end of the DC bus, the other end of the DC bus is connected to the input terminal of the inverter bridge, and the output terminal of the inverter bridge is connected to the input terminal of the transformer.

[0010] The system also includes an active common-mode cancellation circuit, a temperature sensor group, a common-mode voltage sensor, and a controller;

[0011] The active common-mode cancellation circuit is connected in parallel between the positive and negative buses of the DC bus. The active common-mode cancellation circuit includes a compensation bridge arm, and the output end of the compensation bridge arm is connected to the common reference point of the output end of the inverter bridge via an isolation coupling network.

[0012] The temperature sensor group is installed on the heat collection pipe to collect the temperature signal of the high-temperature conductive fluid.

[0013] The common-mode voltage sensor is disposed between the output terminal of the inverter bridge and the grounding network, and is used to detect the transient common-mode voltage at the output terminal of the inverter bridge;

[0014] The controller is connected to the temperature sensor group, the common-mode voltage sensor, the inverter bridge, and the compensation bridge arm, respectively. It is used to calculate the common-mode equivalent impedance between the high-temperature conductive fluid and the pipe wall based on the temperature signal, and to calculate the compensation voltage based on the transient common-mode voltage. It drives the compensation bridge arm to output the compensation voltage with opposite polarity and equal amplitude to the transient common-mode voltage, and injects the compensation voltage into the common reference point to cancel the transient common-mode voltage.

[0015] The technical effects that this invention can achieve include:

[0016] Firstly, without replacing the corrosion-resistant alloy pipes or altering the original mechanical structure of the collector pipes and storage tanks, the common-mode voltage is actively suppressed from the source of electrical conversion of the converter, cutting off the path of high-frequency leakage current flowing through the high-temperature conductive fluid via parasitic capacitance coupling, thereby suppressing the electrochemical corrosion and electromigration damage of the pipe wall.

[0017] Secondly, by mapping the temperature signal of the high-temperature conductive fluid to the common-mode equivalent impedance parameter in real time, the compensation voltage can be adaptively adjusted according to the wide temperature range of fluid conditions.

[0018] Third, the compensation bridge arm and the main inverter bridge are topologically independent and decoupled in control. The operation of the compensation circuit does not participate in the main power transmission and does not affect the main power conversion efficiency and stability.

[0019] Fourth, by correcting the residual common-mode voltage through closed-loop feedback, the common-mode voltage suppression effect can be kept converging during the continuous operation of the system, thereby extending the service life of the high-temperature solar thermal network, reducing the frequency of operation and maintenance replacement, and reducing the cost per kilowatt-hour of the solar thermal energy storage power station. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the high-temperature solar thermal energy storage power generation system of the present invention;

[0021] Figure 2 This is a flowchart of the common-mode voltage suppression method of the present invention. Detailed Implementation

[0022] The following is in conjunction with the appendix Figure 1-2 The specific embodiments of the present invention will be further described below. It should be noted that the description of these embodiments is for the purpose of helping to understand the present invention, but does not constitute a limitation of the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0023] The high-temperature solar thermal energy storage power generation system of this embodiment includes a solar field heat collection unit, a high-temperature fluid circuit, a generator set, a converter, a transformer, an active common-mode cancellation circuit, a temperature sensor group, a common-mode voltage sensor, and a controller.

[0024] The solar field heat collection unit includes several sets of solar heat collection mirrors and corresponding heat collection tubes, which are used to gather solar radiation energy and convert it into heat energy. The high-temperature fluid circuit consists of heat collection tubes, heat storage tanks, and heat exchangers connected in sequence through pipelines to form a closed loop. The circuit contains a high-temperature conductive fluid. In this embodiment, the high-temperature conductive fluid is a high-temperature molten salt. In other embodiments, the high-temperature conductive fluid can also be a liquid metal. The operating temperature range is 600℃ to 1000℃. There is an insulating oxide layer and a heat insulation layer between the tube wall of the heat collection tube and the high-temperature conductive fluid contained inside. Together with the metal tube wall and the grounding network, they form a distributed parasitic capacitance coupling structure. This structure is the physical channel for high-frequency common-mode voltage coupling into the fluid circuit.

[0025] The generator set is used to convert the mechanical energy generated by the steam turbine driven by the heat-exchanged working medium into alternating current. The output end of the generator set is connected to the AC input side of the converter. The converter is composed of three cascaded parts: a rectifier bridge, a DC bus, and an inverter bridge. The output end of the rectifier bridge is connected to one end of the DC bus, and the other end of the DC bus is connected to the input end of the inverter bridge. The inverter bridge generates a switching vector drive signal according to the pulse width modulation method, which inverts the DC power on the DC bus into AC power. The output end of the inverter bridge is stepped up by a transformer and then connected to the power grid.

[0026] The active common-mode cancellation circuit is connected in parallel between the positive and negative buses of the DC bus. Its main body is a compensation bridge arm composed of wide-bandgap silicon carbide power devices. The output of the compensation bridge arm is connected to the common reference point of the inverter bridge output through an isolation coupling network to inject reverse zero-sequence compensation voltage into the common reference point. The compensation bridge arm is topologically independent from the main switch of the inverter bridge, and the two are decoupled in control. That is, the switching action of the compensation bridge arm does not participate in the main power transmission channel of the inverter bridge, but only undertakes the common-mode voltage cancellation function. Therefore, it will not affect the main power conversion efficiency and stability.

[0027] The temperature sensor group is installed on the pipeline of the heat collection tube to collect the temperature signal of the high-temperature conductive fluid in real time. The common-mode voltage sensor is installed between the output terminal of the inverter bridge and the grounding network to detect the instantaneous value of the three-phase output voltage of the inverter bridge relative to the reference ground in real time, thereby obtaining the transient common-mode voltage. The controller is connected to the temperature sensor group, the common-mode voltage sensor, the main switch of the inverter bridge, and the drive terminal of the compensation bridge arm, respectively. The controller is connected to the temperature sensor group and the common-mode voltage sensor for signal connection, and to the main switch and the compensation bridge arm for drive signal connection. The energy transmission channel is formed by the rectifier bridge through the DC bus to the inverter bridge, and then through the transformer to the power grid.

[0028] Regarding the dynamic modeling mechanism of the high-temperature fluid parasitic capacitance network, the cross-sectional structure of the heat collector tube, from the inside out, consists of a high-temperature conductive fluid, an insulating oxide layer and a thermal insulation layer, a metal tube wall, and a grounding network. The corresponding equivalent circuit is as follows: the high-temperature conductive fluid and the metal tube wall are represented by a parallel equivalent leakage resistance and equivalent parasitic capacitance. The metal tube wall is connected to the reference point of the grounding network through the grounding resistance. The whole system forms a parallel network that varies with temperature. The equivalent impedance of this network is the coupling path of the common-mode current. The current is excited by the common-mode voltage of the converter and flows to the grounding network through the equivalent parasitic capacitance and the equivalent leakage resistance.

[0029] The relationship between the conductivity of a high-temperature conductive fluid and temperature is described by the following function:

[0030] ;

[0031] In the formula, For high-temperature conductive fluid at absolute temperature The conductivity at that point This is the conductivity pre-conductivity factor, a constant related to the type of fluid material, which can be obtained through pre-calibration for specific fluid materials. The activation energy for fluid conductivity is a constant related to the fluid material. Boltzmann's constant, The real-time absolute temperature of the fluid is obtained in real time by a group of temperature sensors.

[0032] The equivalent leakage resistance is determined by the fluid conductivity and the pipeline geometry, and the relationship is as follows:

[0033] ;

[0034] In the formula, This is the equivalent leakage resistance of the fluid. The effective length of the conductive path is determined by the pipe structure of the heat collector tube. The cross-sectional area for fluid conductivity is determined by the inner diameter of the heat collection tube. The meaning is the same as the previous one.

[0035] This leads to the equivalent impedance model of the common-mode channel:

[0036] ;

[0037] In the formula, For angular frequency Below, temperature The corresponding common-mode equivalent impedance, The imaginary unit, The equivalent parasitic capacitance between the pipe wall and the fluid is a fixed parameter determined by the pipe geometry and the dielectric properties of the insulation layer, and can be pre-calibrated. The model maps the real-time changes in fluid conductivity within the temperature range of 600℃ to 1000℃ to the input parameters of the controller's bottom control loop, which is the angular frequency corresponding to the high-frequency switching harmonic components of the converter. This enables the controller to adjust the compensation strategy according to the real-time operating conditions.

[0038] Regarding the active common-mode cancellation topology, in this embodiment, an active common-mode cancellation circuit composed of compensation bridge arms is connected in parallel between the positive and negative DC buses of the converter. The compensation bridge arms are composed of high-speed power devices. In this embodiment, wide-bandgap silicon carbide devices are preferred to obtain higher switching speed and lower switching losses. The output of the compensation bridge arms is connected to the common reference point at the output of the inverter bridge through an isolation coupling network, which is specifically used to inject reverse zero-sequence compensation voltage. The compensation bridge arms and the inverter bridge are topologically independent and decoupled in control. That is, the switching action of the compensation bridge arms does not participate in the main power transmission, but only undertakes the common-mode voltage cancellation task. Therefore, this circuit structure will not affect the main power conversion efficiency and stability. A common-mode voltage detection point is set between the output of the inverter bridge and the grounding network for the common-mode voltage sensor to collect transient common-mode voltage. The compensation voltage injection point is located between the isolation coupling network and the common reference point.

[0039] Regarding the adaptive zero common-mode pulse width modulation method, the controller drives the active common-mode cancellation circuit in the following manner to achieve active cancellation of common-mode voltage.

[0040] First, the controller calculates the current fluid conductivity based on the high-temperature conductive fluid temperature signal collected in real time by the temperature sensor group, according to the aforementioned conductivity function, and calculates the common-mode equivalent impedance under the current operating condition based on the aforementioned equivalent leakage resistance relationship and common-mode equivalent impedance relationship. This serves as the basis for dynamic parameters in subsequent compensation calculations.

[0041] Secondly, the controller calculates the transient common-mode voltage based on the instantaneous value of the three-phase output voltage of the inverter bridge detected in real time by the common-mode voltage sensor, using the following formula:

[0042] ;

[0043] In the formula, This refers to the transient common-mode voltage output by the inverter bridge. , , These are the instantaneous values ​​of the three-phase output voltage relative to the reference ground.

[0044] Then, the controller based on the detected data... The required reverse compensation voltage is calculated using the following formula:

[0045] ;

[0046] In the formula, The instantaneous value of the compensation voltage that the active common-mode cancellation circuit should output, its polarity is the same as... Conversely, they have equal magnitudes and are used to achieve voltage superposition and cancellation at the coupling node.

[0047] Furthermore, the controller converts the compensation voltage into a zero-sequence duty cycle adjustment coefficient, and accordingly corrects the action time distribution of the inverter bridge main switch vector. The relationship is as follows:

[0048] ;

[0049] In the formula, This is the zero-sequence duty cycle adjustment factor. The voltage of the DC bus is used to dynamically adjust the action time ratio of each basic vector in the pulse width modulation sector, so that the switching sequence of the main inverter bridge can be synchronized with the compensation action of the active common-mode cancellation circuit without affecting the effective power output.

[0050] The controller generates drive pulse signals for the compensation bridge arm based on the zero-sequence duty cycle adjustment coefficient, driving the compensation bridge arm to output compensation voltage within a preset time scale. It is then injected into the common-mode coupling node, where it is superimposed on and cancels out the common-mode voltage excited by the inverter bridge at that node.

[0051] Subsequently, the controller uses a common-mode voltage sensor to detect the residual common-mode voltage after cancellation and calculates the residual error:

[0052] ;

[0053] In the formula, To eliminate the residual common-mode voltage error, it should ideally approach zero.

[0054] When residual error When the value exceeds the preset threshold, the controller uses proportional-integral feedback control to correct the compensation coefficient. The correction amount is calculated using the following formula:

[0055] ;

[0056] In the formula, This is the compensation correction amount output by the feedback controller. This is the proportional gain coefficient. This is the integral gain coefficient. This represents the historical error value within the integration interval.

[0057] The controller adds the correction amount to the original compensation voltage to obtain the corrected compensation voltage command:

[0058] ;

[0059] In the formula, The controller re-substitutes the compensation voltage command, after feedback correction, into the calculation formula for the zero-sequence duty cycle adjustment coefficient, and re-drives the compensation bridge arm to output the compensation voltage, forming a closed-loop iteration until the residual common-mode voltage... The signal converges to below the preset threshold, completing the cancellation process of one control cycle. Then, the next sampling cycle begins, and the temperature signal and common-mode voltage signal are reacquired and the above process is repeated to achieve continuous adaptive tracking of the dynamic operating conditions of high-temperature fluids over a wide temperature range.

[0060] Through the synergistic effect of the above system structure and control method, this embodiment actively cancels the common-mode voltage within the same time scale of the high-frequency switching action of the converter, thereby cutting off the high-frequency leakage current path at the source of the parasitic coupling channel between the fluid and the pipe wall, thus suppressing the electrochemical corrosion problem of the high-temperature solar thermal energy storage pipeline, without the need to replace the corrosion-resistant alloy pipe material or modify the mechanical structure of the heat collection pipe and the heat storage tank.

[0061] In another embodiment, a common-mode inductor can be superimposed on the converter output terminal based on the active common-mode cancellation circuit. By combining active cancellation with passive suppression, the residual common-mode voltage amplitude can be further reduced. This is suitable for applications with high system reliability and redundancy requirements. In yet another embodiment, the main power conversion circuit of the converter can be replaced with a midpoint clamping three-level topology. The characteristic of multi-level output to reduce the single-switching voltage change rate can be used to achieve a similar common-mode suppression effect in conjunction with the active common-mode cancellation circuit. This is suitable for applications with limited switching frequency. All of the above embodiments do not deviate from the technical concept of the active common-mode cancellation circuit and the temperature and common-mode voltage joint sensing and control mechanism of this invention, and all fall within the protection scope of this invention.

Claims

1. A high-temperature solar thermal energy storage power generation system for emerging energy generation, comprising a solar field heat collection unit, a high-temperature fluid loop, a generator set, a converter, and a transformer, wherein the high-temperature fluid loop comprises a heat collection tube, a heat storage tank, and a heat exchanger connected in sequence to form a closed loop, the closed loop containing a high-temperature conductive fluid, the output terminal of the generator set being connected to the AC input side of the converter, the converter comprising a rectifier bridge, a DC bus, and an inverter bridge, the output terminal of the rectifier bridge being connected to one end of the DC bus, the other end of the DC bus being connected to the input terminal of the inverter bridge, and the output terminal of the inverter bridge being connected to the input terminal of the transformer, characterized in that, It also includes an active common-mode cancellation circuit, a temperature sensor group, a common-mode voltage sensor, and a controller; The active common-mode cancellation circuit is connected in parallel between the positive and negative buses of the DC bus. The active common-mode cancellation circuit includes a compensation bridge arm. The output end of the compensation bridge arm is connected to the common reference point of the output end of the inverter bridge via an isolation coupling network. The temperature sensor group is installed on the heat collection tube and is used to collect the temperature signal of the high-temperature conductive fluid. The common-mode voltage sensor is disposed between the output terminal of the inverter bridge and the grounding network, and is used to detect the transient common-mode voltage at the output terminal of the inverter bridge; The controller is connected to the temperature sensor group, the common-mode voltage sensor, the inverter bridge, and the compensation bridge arm, respectively. It is used to calculate the common-mode equivalent impedance between the high-temperature conductive fluid and the pipe wall based on the temperature signal, and to calculate the compensation voltage based on the transient common-mode voltage. It drives the compensation bridge arm to output the compensation voltage with opposite polarity and equal amplitude to the transient common-mode voltage, and injects the compensation voltage into the common reference point to cancel the transient common-mode voltage.

2. The high-temperature solar thermal energy storage power generation system according to claim 1, characterized in that, The compensation bridge arm is composed of wide bandgap silicon carbide power devices. The compensation bridge arm is topologically independent of the inverter bridge and decoupled from the inverter bridge in terms of control. The switching action of the compensation bridge arm does not participate in the main power transmission channel of the converter.

3. The high-temperature solar thermal energy storage power generation system according to claim 1, characterized in that, The controller is further configured to calculate the conductivity of the high-temperature conductive fluid according to the temperature signal and the exponential relationship between the conductivity of the high-temperature conductive fluid and temperature, calculate the equivalent leakage resistance according to the conductivity, the effective length of the conductive path and the cross-sectional area of ​​the fluid, and calculate the common-mode equivalent impedance according to the equivalent leakage resistance and the equivalent parasitic capacitance between the pipe wall and the high-temperature conductive fluid.

4. The high-temperature solar thermal energy storage power generation system according to claim 1, characterized in that, A common-mode voltage detection point is provided between the output terminal of the inverter bridge and the grounding network, and the injection point of the compensation voltage is located between the isolation coupling network and the common reference point.

5. The high-temperature solar thermal energy storage power generation system according to claim 1, characterized in that, The controller is also used to detect the residual common-mode voltage after the compensation voltage is injected. When the residual common-mode voltage is greater than a preset threshold, the compensation voltage is corrected by proportional-integral feedback regulation to obtain the corrected compensation voltage, and the compensation bridge arm is re-driven according to the corrected compensation voltage.

6. The high-temperature solar thermal energy storage power generation system according to claim 1, characterized in that, The transient common-mode voltage is calculated as one-third of the sum of the instantaneous values ​​of the three-phase output voltages of the inverter bridge relative to the reference ground.

7. A common-mode voltage suppression method, applied to the high-temperature solar thermal energy storage power generation system of claim 1, characterized in that, include: The temperature signal of the high-temperature conductive fluid is acquired, and the common-mode equivalent impedance between the high-temperature conductive fluid and the pipe wall is calculated based on the temperature signal. Detect the transient common-mode voltage at the output of the inverter bridge; The compensation voltage is calculated based on the transient common-mode voltage. The polarity of the compensation voltage is opposite to that of the transient common-mode voltage, and the amplitude is equal to that of the transient common-mode voltage. The zero-sequence duty cycle adjustment coefficient is calculated based on the compensation voltage, and the action time allocation of the inverter bridge main switch vector is corrected based on the zero-sequence duty cycle adjustment coefficient. The compensation bridge arm is driven to output the compensation voltage according to the zero-sequence duty cycle adjustment coefficient, and the compensation voltage is injected into the common-mode coupling node to cancel out the transient common-mode voltage.

8. The common-mode voltage suppression method according to claim 7, characterized in that, Also includes: The residual common-mode voltage error after the compensation voltage injection is detected. When the residual common-mode voltage error is greater than a preset threshold, proportional-integral feedback control is used to correct the compensation voltage to obtain a corrected compensation voltage command. The zero-sequence duty cycle adjustment coefficient is then recalculated based on the corrected compensation voltage command.

9. The common-mode voltage suppression method according to claim 7, characterized in that, Calculating the common-mode equivalent impedance based on the temperature signal includes: calculating the conductivity of the high-temperature conductive fluid based on the temperature signal; calculating the equivalent leakage resistance based on the conductivity, the effective length of the conductive path, and the cross-sectional area of ​​the fluid's conductive surface; and calculating the common-mode equivalent impedance based on the equivalent leakage resistance and the equivalent parasitic capacitance between the pipe wall and the high-temperature conductive fluid.

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