Thermal mass energy storage system power grading adjustment method based on virtual asynchronous machine control

Abstract

The invention discloses a thermal mass energy storage system power grading adjustment method based on virtual asynchronous machine control, and belongs to the technical field of thermal mass energy storage systems, and the method comprises the steps: converting the alternating current output by a power grid side into direct current in the process of injecting power into a thermal mass energy storage system by the power grid side based on a virtual asynchronous machine control method; according to the direct current-alternating current converter control method based on the V / f control strategy, power frequency alternating current of a power grid is improved to high-frequency alternating current so as to be matched with power pulsation of a heat storage device side; electric energy of high-frequency alternating current is converted into heat energy to be stored by a heat and mass energy storage system based on Rankine cycle; different heat capacity intervals are divided for the current heat mass energy storage working medium temperature according to the heat mass energy storage device, the virtual inertia coefficient of the virtual asynchronous machine is adjusted, an adjustment instruction is output based on the electric power level, and the power injected or released into the heat mass energy storage system is dynamically adjusted. According to the method, power dynamic balance and frequency support between the power grid and the Rankine cycle heat and mass energy storage system are realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of thermal mass energy storage systems, and relates to a power grading regulation method for a thermal mass energy storage system based on virtual asynchronous machine control. BACKGROUND

[0002] In recent years, with the rapid development of high-proportion renewable energy access in new power systems, thermal mass energy storage systems gradually become an important supporting link for load peak shaving and valley filling. The thermal mass energy storage device based on the Rankine cycle has good power response characteristics due to its high thermal-electric conversion efficiency, wide selection range of heat storage medium, and strong flexibility of system structure. In the control layer of the electric-thermal coupled system, the virtual asynchronous machine control technology is introduced into the thermal mass energy storage system, which simulates the frequency-torque response characteristics of the traditional asynchronous motor, realizes the dynamic adjustment of the electric heating power injection path, and can effectively alleviate the frequency oscillation problem caused by the rapid change of electric load. With the complication of system operation scenarios and the evolution of microgrid structure, in order to cope with the problems such as low execution efficiency and insufficient thermal capacity protection of traditional continuous power regulation method in actual control, a hierarchical power control idea based on "operation section classification" is introduced, that is, by identifying the temperature range (thermal capacity interval) of the thermal storage system, the corresponding power execution logic is configured for each interval, so that the coordinated operation of the electric-thermal side is realized without increasing the calculation complexity. This method is suitable for integration with the virtual asynchronous machine control model, providing stable inertia support capability and power execution mechanism within the section for the energy storage system.

[0003] In the electric-thermal integrated system with high-proportion renewable energy grid connection, thermal mass energy storage technology (such as Carnot battery) plays an increasingly important role in load peak shifting and energy transfer, but the traditional "heat dominant" or "electric dominant" operation mode has its own limitations: the former prioritizes thermal load, and the electric side responds slowly, which is difficult to meet the second-level frequency support; the latter improves the adaptability of the power grid, but it is too dependent on the control of thermal storage capacity, which easily leads to over-temperature or annealing failure of the thermal storage medium under frequent load disturbance. The existing continuous proportional regulation or fixed temperature threshold method cannot balance the fast inertia support of the electric side and accurately protect the safety of the thermal storage, and the common response disconnection and energy mismatch problems are "fast electric side support, slow thermal side amplitude limiting" or "excessive thermal side amplitude limiting, insufficient electric side support". Although the virtual asynchronous machine control can provide power grid inertia by simulating the machine-electricity difference, its output power is only based on the frequency deviation, and it is not linked with the dynamic boundary of the thermal side temperature or the thermal storage capacity, which may exceed the safety limit of the thermal storage system or weaken the frequency support due to excessive amplitude limiting, thereby aggravating system instability. Therefore, there is an urgent need for a power grading regulation method for a thermal mass energy storage system based on virtual asynchronous machine control. SUMMARY

[0004] To solve the above problems, the technical scheme adopted by the present application is: a power grading regulation method for a thermal mass energy storage system based on virtual asynchronous machine control, comprising:

[0005] Based on the virtual asynchronous machine control method, the rectifier is controlled during the process of injecting power from the grid side to the thermal mass energy storage system, and the alternating current output from the grid side is converted into direct current.

[0006] Based on the V / f control strategy of the DC-AC converter control method, the grid power frequency alternating current is raised to high frequency alternating current to match the power pulsation of the thermal storage device side.

[0007] The high-frequency alternating current is converted into thermal energy by the thermal mass energy storage system based on the Rankine cycle.

[0008] According to the division of different heat capacity intervals of the thermal mass energy storage device for the current thermal mass energy storage working medium temperature, the virtual inertia coefficient of the virtual asynchronous machine is adjusted, the output adjustment instruction is based on the electric power level, and the power injected or released by the thermal mass energy storage system is dynamically adjusted based on the adjustment instruction.

[0009] Further, the virtual asynchronous machine control method, during the process of injecting power from the grid side to the thermal mass energy storage system, controls the rectifier, and converts the alternating current output from the grid side into direct current as follows:

[0010] The voltage v abc and current i abc of the grid side are sampled in real time, converted to the synchronous rotating coordinate system through Park transformation, and v d , v q and i d , i q are obtained.

[0011] On this basis, the input power P of the alternating current side is calculated; and the power signal is processed through the power outer loop and the current inner loop to generate the d-axis and q-axis electromotive force reference values u qref and u dref .

[0012] Then, the d-axis and q-axis electromotive force reference values u qref and u dref are converted to the electromotive force reference values u abc in the abc reference system through inverse Park transformation.

[0013] Subsequently, the electromotive force reference u abc is PWM modulated to generate the rectifier switch trigger signal, realizing real-time power balance of the electric energy side, and improving the dynamic response of the system frequency when the alternating current side load fluctuates.

[0014] Further, the DC-AC converter control method based on the V / f control strategy is as follows:

[0015] Firstly, the grid point voltage is collected in real time and compared with the preset reference value, the adjustment signal is calculated by the PI controller and transmitted to the pulse width modulator, the modulation coefficient is dynamically adjusted, the load power demand in the microgrid is determined according to the frequency difference and the voltage difference, and then the output power is adjusted, the active power and the reactive power are represented by the following formula:

[0016]

[0017] In the formula, K p , K Q , μ p , μ Q are control parameters, f ref , U ref are the reference values of frequency and voltage amplitude respectively, and f m , U m are the measured values of frequency and voltage amplitude respectively.

[0018] The transfer function of voltage regulation under V / f control is:

[0019]

[0020] In the formula, k p and k i are proportional and integral gains respectively;

[0021] When sinusoidal pulse width modulation is adopted, the relationship between the effective value of the inverter output fundamental phase voltage and the DC side voltage U DC and the modulation coefficient P m is as follows:

[0022]

[0023] Further, the thermal mass energy storage medium is selected from water, heat conducting oil or molten salt.

[0024] Further, the current working medium temperature is divided into three stages in different heat capacity intervals:

[0025] The first stage is the safety zone, when the medium temperature is lower than the preset lower limit, the thermal mass energy storage system has sufficient heat storage capacity,

[0026] The second stage is the buffer zone, when the medium temperature is greater than or equal to the preset lower limit and less than or equal to the preset upper limit, the thermal mass energy storage system enters the normal operation range;

[0027] The third stage is the critical zone, when the medium temperature reaches or exceeds the pre-trial upper limit, the thermal energy storage system enters a high-risk protection state.

[0028] Further, the determination process of the virtual asynchronous machine virtual inertia coefficient is as follows:

[0029] When , it indicates that the energy storage system temperature is in a stable state and there is no significant deviation from the set value, at this time the adaptive inertia coefficient remains at the nominal inertia value J0;

[0030] When the energy storage system temperature deviates from the set temperature, that is According to the adaptive inertia coefficient formula, a relatively large inertia

[0031] When the energy storage system temperature stabilizes to the set temperature as soon as possible, that is According to the adaptive inertia coefficient formula, a relatively small inertia

[0032] Further, the expression of the adaptive inertia coefficient J is as follows:

[0033]

[0034] Where: ξ T = ξ·sign(T es -T set ), ξ is a positive inertia compensation coefficient, and sign is a sign function;

[0035] T es is the temperature of the heat storage tank, T set is the set temperature of the heat storage tank, T high and T low are the maximum and minimum values of the temperature of the heat storage tank, respectively, J0 is the initial inertia coefficient, is the rate of change of the temperature of the heat storage tank with respect to time t.

[0036] Further, the process of outputting adjustment instructions based on the electric power level is as follows:

[0037] First, the measured original temperature of the heat storage tank is first-order filtered:

[0038]

[0039] Where: T[k] is the kth sampled medium temperature, is the filtered temperature, and γ is the filter coefficient;

[0040] Establish the corresponding section coefficient of different heat capacity partition power grading regulation:

[0041]

[0042] Wherein: β≈0.2~0.4 is the minimum scaling factor of the critical section, determined according to the material of the heat storage tank;

[0043] Adaptive coefficient of the buffer section The system temperature can be kept in the buffer section, and the coefficient decreases linearly with the increase of temperature, as follows:

[0044]

[0045] Wherein: the maximum coefficient of the buffer section at the low end is α max ≈1, and the minimum coefficient of the buffer section at the high end is α min ≈β.

[0046] Based on the section coefficient k(T), the actual limit is calculated:

[0047]

[0048] Wherein: the rated minimum active power limit is P min(0) , and the rated maximum active power limit is P max(0) .

[0049] The original instruction P raw of the VAM controller is limited to obtain the final output:

[0050]

[0051] Wherein: the original active power instruction of the virtual asynchronous machine control law output is P raw , and the closed-loop output instruction after limiting is P cmd .

[0052] Further, based on the adjustment instruction, the process of dynamically adjusting the power of the injected or released thermal mass energy storage system is as follows:

[0053] First, divide the power value by the synchronous speed to obtain the electromagnetic torque reference value required by the generator;

[0054] On the grid side, the torque reference value is input to the torque loop of the virtual asynchronous machine, and by controlling the on-off sequence and duty cycle of the semiconductor switch, the output voltage and current are adjusted, so that the generator generates electromagnetic torque consistent with the instruction at the grid frequency, thereby realizing accurate active injection or absorption of the grid;

[0055] In the thermal mass energy storage system side controller, the active power instruction generated by the virtual asynchronous machine controller is converted into the opening requirement of the corresponding steam valve; the thermal side controller calculates the corresponding valve opening ratio according to the valve flow characteristic curve, and adjusts the valve position through the driving of the pneumatic or electric actuator to change the steam flow into the expander, so that the thermal power output is consistent with the active power instruction.

[0056] The application provides a power grading regulation method for a thermal mass energy storage system based on virtual asynchronous machine control, which realizes accurate matching of power injection behavior and heat storage state by introducing a thermal capacity interval identification mechanism, and constructs an electric-thermal collaborative control scheme with temperature state identification capability and grading response logic. The method can be embedded in the existing inertia support framework based on virtual asynchronous machine, and provides an effective solution to the problems of power injection mismatch, increasing risk of over-temperature and controller response lag in the dynamic operation of the current thermal mass energy storage system. The application realizes grading execution control of power instruction through temperature interval division, can automatically identify whether the system is in a safe, overloaded or critical operation section according to the real-time thermal capacity state, dynamically adjusts the proportion of power injection without interrupting the operation, and effectively reduces the risk of thermal capacity overrun and control instability caused by large power fluctuations. In addition, combined with the response mechanism of the virtual asynchronous machine, an adaptive inertia strategy dominated by temperature is added, which further enhances the rapid response capability of the energy storage system to microgrid disturbances, ensures the safety of the boundary of the thermal storage equipment, and improves the flexible regulation capability of the electric-thermal system as a whole.

[0057] Based on the equivalent model of an asynchronous motor, a virtual asynchronous machine control method for AC-AC frequency converters is designed, which can simulate the torque-inertia characteristics of an asynchronous motor and realize power dynamic balance and frequency support between the power grid and the Rankine cycle thermal mass energy storage system.

[0058] It is proposed to divide the temperature of the heat storage medium into three stages of safe zone, buffer zone and critical zone, and set different power output limits in each stage. When the temperature is low, the maximum support is allowed, when the temperature is moderate, the output range is gradually reduced, and when the temperature approaches the upper limit, the output is strictly compressed, so as to balance the response capability and equipment safety.

[0059] In the control algorithm, a temperature adaptive inertia adjustment mechanism is introduced, so that when the temperature is low, a larger virtual inertia is provided to smooth the response, and when the temperature rises, the inertia is automatically reduced to protect the heat storage equipment first, and is linked with the partition limit logic to ensure that the electric-thermal system can stably operate under various working conditions.

[0060] The limited active power instruction is mapped into the electric side torque control signal and the thermal side steam valve opening instruction respectively, realizing the synchronous linkage of electric energy injection and heat energy release, so that the power grid frequency regulation and thermal storage energy management are collaboratively executed in the same control framework.

[0061] Compared with the prior art, the present application has the advantages of:

[0062] (1) The virtual asynchronous machine control is organically integrated with the temperature grading strategy, the system closed-loop damping characteristics are optimized, the frequency and power fluctuations are reduced, the power balance of the power grid frequency mutation is achieved in seconds, and the regulation speed and accuracy are improved.

[0063] (2) Three-stage temperature zoning power output regulation and adaptive inertia control are adopted, which effectively prevents the overheat or overdischarge of the heat storage medium, and significantly improves the safety and service life of the heat storage system.

[0064] (3) All algorithms of the present application are implemented in the software level, without the need to add hardware or sensors, and the temperature boundary and inertia size can be quickly calibrated through simulation and field test, which has good engineering applicability and popularization value.

[0065] The method provided by the present application is a hierarchical power execution strategy that cooperatively integrates the heat storage temperature state and the virtual asynchronous machine inertia support, to realize the synchronous optimization of the power grid frequency rapid response and the heat storage safety limiting, eliminate the response disconnection and energy mismatch risk, and ensure the safe and stable operation of the electric-thermal coupling system under high dynamic conditions. BRIEF DESCRIPTION OF DRAWINGS

[0066] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0067] Figure 1 is a virtual asynchronous machine control block diagram of the method;

[0068] Figure 2 is a V / f control block diagram;

[0069] Figure 3 is a schematic diagram of a heat mass energy storage system based on Rankine cycle;

[0070] Figure 4 is a system power hierarchical regulation flowchart based on heat capacity interval grading.

[0071] Reference signs: 1, first state, 2, second state, 3, third state, 4, fourth state, 5, fifth state, 6, sixth state, 7, seventh state, 8, eighth state, 9, ninth state, 10, tenth state. DETAILED DESCRIPTION

[0072] It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0073] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The following description of at least one exemplary embodiment is merely illustrative and is in no way intended to limit the present invention or its application or use. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0074] Figure 1 This is a block diagram of the virtual asynchronous machine control for this method;

[0075] A method for graded power regulation of a thermal mass storage system based on virtual asynchronous machine control, characterized by comprising:

[0076] S1: Based on the virtual asynchronous machine control method, the rectifier is controlled during the process of power injection from the grid side to the thermal energy storage system, so as to convert the AC power output from the grid side into DC power.

[0077] S2: A DC-AC converter control method based on V / f control strategy, which boosts the grid frequency AC power to high frequency AC power to match the power pulsation on the thermal storage device side;

[0078] S3: High-frequency alternating current is converted into thermal energy and stored by a Rankine cycle-based thermo-mass energy storage system;

[0079] S4: Based on the thermal mass storage device, different heat capacity ranges are divided according to the current temperature of the thermal mass storage medium. The virtual inertia coefficient of the virtual asynchronous machine is adjusted, and an adjustment command is output based on the power level. Based on the adjustment command, the power injected into or released from the thermal mass storage system is dynamically adjusted. This method is used to regulate the real-time power balance on the grid side and to quickly respond to and stabilize the system frequency when the energy storage demand on the load side changes abruptly.

[0080] The steps S1 / S2 / S3 / S4 are executed sequentially;

[0081] The control equations for the virtual asynchronous machine are as follows:

[0082] The virtual torque τ of a virtual asynchronous machine v It is expressed as follows:

[0083]

[0084] where i qs is the stator q-axis current; the rotor inductance is l r rleak + l mg where l rleak and l mg are the rotor leakage and magnetizing inductances, respectively; the rotor flux is where i ds is the stator d-axis current, i dr is the rotor d-axis current.

[0085]

[0086] The mechanical power of the asynchronous motor is represented as follows:

[0087]

[0088] where J represents the inertia coefficient of the temperature variation of the electric thermal energy system, D represents the friction damping coefficient, Ω r is the virtual rotor electrical angular velocity, τ mec is the mechanical torque, and there is:

[0089] τ mec = τ load + DΩ r

[0090] That is, the mechanical power of the asynchronous motor is represented as follows:

[0091]

[0092] T L is the rotor mechanical torque, and its calculation formula is:

[0093]

[0094] where P AD is the exchange power between the DC side and the AC side, λ Ω (Ω set - Ω set0 ) is the virtual regulator part, Ω set0 is the rated set point of the AC microgrid frequency, and λ Ω is the active power coefficient.

[0095] Let ΔΩ r be the deviation of the virtual rotor frequency Ω r from the initial value Ω0, and the formula becomes:

[0096]

[0097] The synchronous speed Ω set and the angle reference θ can be obtained from Ω0, ΔΩ r ​and the angular velocity difference ΔΩ, as shown below:

[0098] Ω set = Ω0+ ΔΩ r + ΔΩ

[0099]

[0100] The virtual asynchronous machine control method based on the process of injecting power from the grid side to the thermal mass energy storage system controls the rectifier, and the process of converting the alternating current output from the grid side to direct current is as follows:

[0101] By real-time sampling of the alternating current side voltage v abc and the current i abc , converting to the synchronous rotating coordinate system through Park transformation, v d , v q , i d , and i q are obtained.

[0102] On this basis, the alternating current side input power P is calculated; and the power signal is processed through the power outer loop and the current inner loop, and the outer loop and the current inner loop processing respectively generate the d-axis and q-axis electromotive force reference values u qref and u dref .

[0103] The d-axis and q-axis electromotive force reference values u qref and u dref are obtained through inverse Park transformation to obtain the electromotive force reference values in the abc reference system u abc .

[0104] Subsequently, the electromotive force reference u abc is PWM modulated to generate rectifier switch trigger signals, realizing real-time power balance on the power side, and improving the dynamic response of the system frequency when the alternating current side load fluctuates.

[0105] The electrical angle required for Park transformation is output by the virtual asynchronous machine control algorithm, and the control structure can simulate the dynamic characteristics of the traditional asynchronous generator, effectively improving the stability of the system.

[0106] The DC-AC converter control method based on the V / f control strategy is as follows:

[0107] Firstly, the grid-connected point voltage is collected in real time and compared with the preset reference value, the adjustment signal is calculated by the PI controller and transmitted to the pulse width modulator, the modulation coefficient is dynamically adjusted, so that the inverter output voltage can quickly track the reference value to eliminate the deviation; the fundamental frequency of the output voltage is determined by the modulation wave frequency generated by the virtual phase-locked loop, so as to realize the accurate and errorless control of the grid-connected point voltage. According to the difference value of the frequency and the voltage, the demand of the load power in the micro-grid can be determined, and then the output power is adjusted. The active power and the reactive power can be represented by the following formula:

[0108]

[0109] In the formula, K p , K Q , μ p , μ Q are control parameters, f ref , U ref are the reference values of frequency and voltage amplitude respectively, and f m , U m are the measured values of frequency and voltage amplitude respectively.

[0110] The voltage regulation block diagram under V / f control is shown in Figure 2 , wherein u abc represents the instantaneous value of the grid-connected point voltage, U represents the amplitude of the grid-connected point voltage obtained through the voltage measurement link, and P m is the modulation coefficient; the transfer function of the voltage regulation under V / f control is:

[0111]

[0112] In the formula, k p and k i are proportional and integral gains respectively; in order to prevent the saturation of the modulation signal, the PI controller is provided with a limiting logic, so that P m-max =1 and P m-min =-1.

[0113] When the sine pulse width modulation is adopted, the relationship among the effective value of the inverter output fundamental phase voltage , the DC side voltage U DC and the modulation coefficient P m is as follows:

[0114]

[0115] The thermal mass energy storage medium is selected from water, heat conducting oil or molten salt, the working medium for the organic Rankine cycle is an organic fluid working medium with low boiling point and chemical stability, and the cycle mode is the organic Rankine cycle.

[0116] The heat and mass energy storage system based on the Rankine cycle is established, and the process of converting electricity into heat energy for storage is as follows:

[0117] The model of the heat and mass energy storage system based on the Rankine cycle is shown in FIG. 1, and the construction process is as follows: Figure 3

[0118] Firstly, in the charging stage, the commercial power drives the compressor with 50 Hz AC power to compress the working medium from low-pressure saturated vapor into high-temperature and high-pressure gas (first state 1→second state 2), and then the high-temperature and high-pressure gas enters the heat pump condenser to exchange heat with the water medium in the heat storage system, so as to store the sensible heat in the high-temperature tank (second state 2→third state 3→fourth state 4);

[0119] After the pressure is reduced by the throttle valve (fourth state 4→fifth state 5), the working medium is vaporized in the heat pump evaporator to return to the compressor inlet (fifth state 5→first state 1) from the low-temperature flue gas, completing the heat energy storage of the heat pump cycle;

[0120] In the discharging stage, the high-temperature medium in the heat storage tank is first pressurized by the working medium pump to send the condensed saturated liquid into the Rankine cycle evaporator (seventh state 7→eighth state 8), where the liquid-vapor phase change is completed (eighth state 8→sixth state 6), and the generated high-temperature and high-pressure vapor drives the expander to do work (sixth state 6→seventh state 7), converting mechanical energy into electrical energy;

[0121] The AC port of the generator driven by the expander is high-frequency AC power of 380V-660V, which is connected to the public power grid through an inverter to complete the electrical energy feedback of the Rankine cycle;

[0122] The low-pressure vapor after expansion is then cooled to saturated liquid in the Rankine cycle condenser (seventh state 7→ninth state 9), and the condensed liquid is returned to the evaporator by the working medium pump (ninth state 9→tenth state 10), completing the closed cycle, so as to efficiently convert the heat energy in the heat storage medium and incorporate it into the power grid.

[0123] The current working medium temperature is divided into three stages according to different heat capacity intervals:

[0124] The first stage is the safety zone, when the medium temperature is lower than the preset lower limit, the heat and mass energy storage system has sufficient heat storage capacity, at this time the power limit can be cancelled, and the maximum power grid support capacity is preferentially provided;

[0125] The second stage is the buffer zone, when the medium temperature is greater than or equal to the preset lower limit and less than or equal to the preset upper limit, the heat and mass energy storage system enters the normal operating range, in order to balance the response speed and heat storage protection, the output power limit will be linearly tightened with the increase of the temperature-the closer the temperature is to the upper limit, the lower the maximum power allowed;

[0126] ​The third stage is a critical zone, when the medium temperature reaches or exceeds the upper limit of the pre-trial, the thermal energy storage system enters a high-risk protection state, and the output power is strictly compressed to the minimum level to prevent the thermal storage medium from overheating or the device from being damaged.

[0127] The preset upper and lower limit temperatures are determined according to the characteristics of the energy storage medium (such as water, heat conducting oil or molten salt) and the safety requirements of system operation. For example, when water is used as the thermal storage medium, the lower limit can be set to 60℃, and the upper limit can be set to 95℃; if heat conducting oil or molten salt is used, the corresponding upper and lower limit temperatures will be different.

[0128] The determination process of the virtual asynchronous machine virtual inertia coefficient is as follows:

[0129] When , it indicates that the temperature of the energy storage system is in a stable state and does not deviate significantly from the set value, and at this time the adaptive inertia coefficient remains at the nominal inertia value J0.

[0130] When the temperature of the energy storage system deviates from the set temperature, that is, According to the adaptive inertia coefficient formula, a relatively large inertia

[0131] When the temperature of the energy storage system stabilizes to the set temperature as soon as possible, that is, According to the adaptive inertia coefficient formula, a relatively small inertia

[0132] The expression of the adaptive inertia coefficient J is as follows:

[0133]

[0134] Wherein: ξ T = ξ·sign(T es -T set ), ξ is a positive inertia compensation coefficient, and sign is a sign function;

[0135] T es is the temperature of the thermal storage tank, T set is the set temperature of the thermal storage tank, T high and T low are the maximum and minimum values of the temperature of the thermal storage tank, J0 is the initial inertia coefficient, is the rate of change of the temperature of the thermal storage tank with respect to time t.

[0136] The process of outputting the adjustment instruction based on the electric power level is as follows:

[0137] The power grading regulation flow chart is as follows: Figure 4As shown, through three-stage partition, both high efficiency support at low temperature and smooth transition at medium temperature are ensured, and finally strong safety protection is provided at high temperature, effectively coordinating the contradiction between power grid frequency regulation and safe operation of thermal storage system.

[0138] Firstly, the measured original temperature of the thermal storage tank is first-order filtered:

[0139]

[0140] Wherein: T[k] is the medium temperature of the kth sampling, is the filtered temperature, and γ is the filtering coefficient;

[0141] The section coefficient corresponding to the power step adjustment of different heat capacity partitions is established:

[0142]

[0143] Wherein: β≈0.2-0.4 is the minimum scaling coefficient of the critical section, which is determined according to the material of the thermal storage tank;

[0144] Adaptive coefficient of buffer section The system temperature can be kept in the buffer interval, and the coefficient decreases linearly with the increase of temperature, as shown below:

[0145]

[0146] Wherein: the maximum coefficient of the buffer section at the low end is α max ≈1, and the minimum coefficient of the buffer section at the high end is α min ≈β;

[0147] Based on the section coefficient k(T), the actual limiting is calculated:

[0148]

[0149] Wherein: the rated minimum active power limit is P min(0) , and the rated maximum active power limit is P max(0) ;

[0150] The original instruction P raw of the VAM controller is limited to obtain the final output:

[0151]

[0152] Wherein: the original active power instruction of the virtual asynchronous machine control law output is P raw , and the closed-loop output instruction after limiting is P cmd .

[0153] Based on the adjustment instruction, the process of dynamically adjusting the power of the heat storage system is as follows:

[0154] First, the power value is divided by the synchronous speed to obtain the electromagnetic torque reference value required by the generator;

[0155] On the grid side, the torque reference value is input to the torque loop of the virtual asynchronous machine, and the on-off sequence and duty cycle of the semiconductor switch are controlled to adjust the output voltage and current, so that the generator generates the electromagnetic torque consistent with the instruction at the grid frequency, thereby realizing accurate active power injection or absorption to the grid;

[0156] In the heat storage system side controller, the active power instruction generated by the virtual asynchronous machine controller is converted into the opening requirement of the corresponding steam valve; the heat side controller calculates the corresponding valve opening ratio according to the valve flow characteristic curve, and adjusts the valve position through the driving pneumatic or electric actuator to change the steam flow into the expander, so that the heat power output is consistent with the active power instruction. Finally, it should be pointed out that: the above embodiments are only used to illustrate the technical solutions of the present application, but not to limit it; although the present application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that: it can still modify the technical solutions recorded in the foregoing embodiments, or make equivalent replacement to part or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for graded power regulation of a thermal mass storage system based on virtual asynchronous machine control, characterized in that, The method comprises the following steps: The virtual asynchronous machine control method is used to control the rectifier during the process of injecting power from the grid side to the thermal mass energy storage system, and convert the alternating current output from the grid side into direct current; The DC-AC converter control method based on the V / f control strategy is used to convert the power frequency alternating current from the grid into high-frequency alternating current to match the power pulsation of the thermal storage device side; The high-frequency alternating current is converted into thermal energy by the thermal mass energy storage system based on the Rankine cycle; According to the current thermal mass energy storage medium temperature, different thermal capacity intervals are divided, the virtual inertia coefficient of the virtual asynchronous machine is adjusted, the output adjustment instruction is output based on the electric power level, and the power injected or released by the thermal mass energy storage system is dynamically adjusted based on the adjustment instruction.

2. The method of power staging for a thermal mass energy storage system based on virtual asynchronous machine control according to claim 1, wherein, The process of converting the alternating current output from the grid side into direct current by using the virtual asynchronous machine control method during the process of injecting power from the grid side to the thermal mass energy storage system is as follows: By real-time sampling of the AC side voltage v abc and current i abc on the grid side, converting to the synchronous rotating coordinate system through Park transformation, v d , v q , i d , and i q are obtained; On this basis, the AC side input power P is calculated; and the power signal is processed through the power outer loop and the current inner loop to generate d-axis and q-axis electromotive force reference values u qref and u dref ; The d-axis and q-axis electromotive force reference values u qref and u dref The electromotive force reference values u in the abc reference frame are obtained by inverse Park transformation abc ; The electromotive force reference u abc The PWM modulation generates the rectifier switch trigger signal, realizes the real-time power balance of the electric energy side, and improves the dynamic response of the system frequency when the AC side load fluctuates.

3. The method of power staging for a thermal mass energy storage system based on virtual asynchronous machine control according to claim 1, wherein: The process of converting the power frequency alternating current from the grid into high-frequency alternating current by using the DC-AC converter control method based on the V / f control strategy is as follows: Firstly, the grid-connected point voltage is collected in real time and compared with the preset reference value, the adjustment signal is calculated through the PI controller and transmitted to the pulse width modulator, the modulation coefficient is dynamically adjusted, the demand for load power in the microgrid is determined according to the difference between the frequency and the voltage, and then the output power is adjusted, the active power and the reactive power are represented by the following formula: where K p , K Q , μ p , μ Q are control parameters, f ref , U ref are reference values for frequency, voltage amplitude, respectively, f m , U m are measured values for frequency, voltage amplitude, respectively. The transfer function of voltage regulation under V / f control is: wherein: k p and k i are proportional and integral gains, respectively. When the sine pulse width modulation is adopted, the effective value of the fundamental phase voltage outputted by the inverter has the following relationship with the direct current side voltage U DC and the modulation coefficient P m .

4. The method of power rating adjustment of a thermal mass energy storage system based on virtual asynchronous machine control according to claim 1, wherein, The thermal mass energy storage medium is selected from water, heat-conducting oil or molten salt.

5. The method of power rating adjustment of a thermal mass energy storage system based on virtual asynchronous machine control according to claim 1, wherein, The current thermal mass energy storage medium temperature is divided into different thermal capacity intervals, which are divided into three stages: The first stage is the safety zone, when the medium temperature is lower than the preset lower limit, the thermal mass energy storage system has sufficient heat storage capacity, The second stage is the buffer zone, when the medium temperature is greater than or equal to the preset lower limit and less than or equal to the preset upper limit, the thermal mass energy storage system enters the normal operating range; The third stage is the critical zone, when the medium temperature reaches or exceeds the preset upper limit, the thermal mass energy storage system enters the high-risk protection state.

6. The thermal mass energy storage system power grading regulation method based on virtual asynchronous machine control according to claim 1, characterized in that: The determination process of the virtual inertia coefficient of the virtual asynchronous machine is as follows: When the energy storage system temperature is in a steady state and has no significant deviation from the set value, at which time the adaptive inertia coefficient is maintained at the nominal inertia value J0; The energy storage system temperature deviates from the set temperature A relatively large inertia is used according to the adaptive inertia coefficient formula when the temperature of the energy storage system stabilizes to the set temperature as soon as possible a relatively small inertia is used according to the adaptive inertia coefficient formula 7. The method of power rating adjustment of a thermal mass energy storage system based on virtual asynchronous machine control according to claim 1, wherein: The expression of the adaptive inertia coefficient J is as follows: wherein: ξ T = ξ · sign(T es -T set ), ξ is a positive inertia compensation coefficient, and sign is a sign function. T es is the temperature of the thermal storage tank, set is the set temperature of the thermal storage tank, high and T low are the maximum and minimum values of the temperature of the thermal storage tank, respectively, and J0is an initial coefficient of inertia, is the rate of change of the temperature of the thermal storage tank with respect to time t.

8. The method of power staging for a thermal mass energy storage system based on virtual asynchronous machine control of claim 1, wherein: The process of outputting the adjustment instruction based on the electric power level is as follows: Firstly, the measured original temperature of the heat storage tank is first-order filtered: Where: T[k] is the medium temperature at the kth sampling, is the filtered temperature, and γ is the filter coefficient. The section coefficient corresponding to the power grading regulation of different thermal capacity intervals is established: Where: β≈0.2-0.4 is the minimum scaling coefficient of the critical section, which is determined according to the material of the heat storage tank; Buffer segment adaptive coefficients The coefficients can be made to decrease linearly with temperature rise when the system temperature is within the buffer interval, as follows: Where: the maximum coefficient at the low end of the buffer section is a max ≈1, the minimum coefficient at the high end of the buffer section is a min ≈β; The actual amplitude is calculated based on the section coefficient k(T): wherein: the rated minimum active power limit is the rated maximum active power limit is The VAM controller raw instruction P raw The final output is obtained by limiting Wherein: the original active power instruction of the virtual asynchronous machine control law output is P raw , and the closed-loop output instruction after the amplitude limiting is P cmd .

9. The method of power rating adjustment of a thermal mass energy storage system based on virtual asynchronous machine control according to claim 1, wherein: The process of dynamically adjusting the power injected or released by the thermal mass energy storage system based on the adjustment instruction is as follows: Firstly, the power value is divided by the synchronous speed to obtain the electromagnetic torque reference value required by the generator; On the grid side, the torque reference value is input into the torque loop of the virtual asynchronous machine, the on-off sequence and duty cycle of the semiconductor switch are controlled, the output voltage and current are adjusted, the generator generates the electromagnetic torque consistent with the instruction at the grid frequency, and the accurate active power injection or absorption of the grid is realized. In the thermal mass energy storage system side controller, the active power instruction generated by the virtual asynchronous machine controller is converted into the opening requirement of the corresponding steam valve; the thermal side controller calculates the corresponding valve opening ratio according to the valve flow characteristic curve, and adjusts the valve position through the driving of the pneumatic or electric actuator to change the steam flow into the expander, so that the thermal power output is consistent with the active power instruction.

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