AC-AC frequency converter control method based on virtual asynchronous machine

Abstract

The invention provides an AC-AC frequency converter control method based on a virtual asynchronous machine, and the method comprises the following steps: building a rectifier control technology based on the virtual asynchronous machine, carrying out the real-time power balance control of a power grid side, and achieving the frequency dynamic response when the energy storage demand of a load side changes; based on the real-time temperature of the circulation type heat mass energy storage system, the inertia coefficient of temperature change is adopted to adjust the temperature response of the load side, and real-time control over the electric heating energy system is achieved; according to the inverter control method based on V / f control, power frequency alternating current is converted into high-frequency alternating current; according to the Carnot battery energy storage system based on heat storage medium circulation, a power grid is connected with the Carnot battery energy storage system, so that electric energy is converted into heat energy to be stored. According to the virtual asynchronous machine control provided by the invention, the power grid frequency and the rotor frequency do not need to be known, and the frequency can automatically change along with the change of the power, so that when the load power changes, the virtual asynchronous machine control can automatically optimize the frequency of the alternating current side.

Description

Technical Field

[0001] The present invention relates to the technical field of virtual asynchronous machine control, and in particular to a method for controlling a cycloconverter based on a virtual asynchronous machine. Background Art

[0002] In recent years, with the construction and development of new power systems dominated by renewable energy, circulating thermal mass energy storage systems have been recognized as a promising direction in modern energy supply systems. With their significant economic benefits, high flexibility, outstanding environmental benefits, and strong safety, these systems offer tremendous potential for improving the comprehensive utilization and effective management of energy resources. However, in meeting thermal storage needs, the real-time power balance between the grid and the energy storage system has become a key challenge to the stable operation of the system, posing a severe test for the electric heat storage of circulating thermal mass energy storage systems.

[0003] In the process of optimizing dispatch in new energy systems, to address the multi-dimensional uncertainties on the source and load sides, the dispatch process is typically divided into multiple stages, each operating collaboratively at different time scales to gradually reduce the impact of uncertainty on optimal dispatch. However, due to the difficulty of standardizing time scales in multi-energy systems, current methods primarily focus on minute- and hourly-scale power optimization and dispatch. Real-time power balancing between supply and demand has become a pressing challenge to ensure stable system operation.

[0004] In recent years, the design of power balancing strategies has focused on adjusting power or heat output under coupled electric and thermal conditions. Cyclic thermal mass energy storage systems typically operate in two modes: heat-dominated and electricity-dominated. The heat-dominated mode prioritizes meeting real-time energy storage needs, with power generation as a secondary priority. However, this mode lacks power flexibility. In contrast, combined heat and power operation strategies in the electricity-dominated mode have been widely researched and applied. However, in large-scale regional thermal storage system networks, strategies that rely solely on a single control variable are insufficient to meet the flexibility requirements of power regulation. Furthermore, due to the widespread use of power electronic converters, microgrids face the challenge of low inertia. Frequent load changes and the intermittent operation of distributed power systems lead to large frequency fluctuations, which seriously affect the efficiency and stability of microgrids. Traditional power balancing strategies struggle to achieve power balancing within seconds, making it difficult to meet the requirements for efficient renewable energy consumption and stable power system operation. Summary of the Invention

[0005] In accordance with the technical problems mentioned in the above background technology, a control method for an AC-AC frequency converter based on a virtual asynchronous machine is provided. The present invention proposes an AC-AC frequency converter control technology based on a virtual asynchronous machine. By simulating the operating characteristics of the asynchronous motor to design a control strategy, it is applied to the AC-AC frequency converter to achieve the balance of power on both sides of the source and the load when the industrial frequency AC power grid transmits energy to the circulating thermal mass energy storage system. This technology has the advantages of adapting to load power fluctuations and suppressing frequency oscillations. In addition, the control technology introduces an adaptive inertia control algorithm based on temperature changes, which significantly improves the electrothermal response performance, and establishes a unified mathematical expression, further optimizing the control effect of the system.

[0006] The technical means adopted in the present invention are as follows:

[0007] A method for controlling an AC-AC frequency converter based on a virtual asynchronous machine comprises the following steps:

[0008] S1. Establish rectifier control technology based on virtual asynchronous machines to control real-time power balance on the grid side and achieve dynamic frequency response when energy storage demand changes on the load side;

[0009] S2. Based on the real-time temperature of the circulating thermal mass energy storage system, the inertia coefficient of temperature change is used to adjust the temperature response of the load side to achieve real-time control of the electric thermal energy system;

[0010] S3, an inverter control method based on V / f control, which converts industrial frequency AC power into high frequency AC power;

[0011] S4. A Carnot battery energy storage system based on a heat storage medium cycle. The grid is connected to the Carnot battery energy storage system, so that electrical energy is converted into thermal energy for storage.

[0012] Furthermore, in S1, the rectifier control technology based on the virtual asynchronous machine is based on the physical model of the asynchronous motor and includes the following steps:

[0013] S11: Under idealized assumptions, the input power P on the AC side is calculated in real time by collecting the voltage and current signals on the AC side;

[0014] The power signal is controlled by the power outer loop and the current inner loop to generate the AC electromotive force reference value e on the d-axis and q-axis respectively. qref and e dref ,

[0015] AC electromotive force reference value e qref and e dref Then, the AC electromotive force reference value e of the asynchronous motor in the abc reference frame is obtained through the inverse Park transformation. abc ;

[0016] S12: The AC electromotive force reference value of the asynchronous motor in the abc reference frame is modulated by PWM to generate a switch trigger signal of the rectifier, thereby realizing the control of the virtual asynchronous machine converter and further realizing real-time power balance control on the electric energy side.

[0017] Furthermore, the idealized assumptions include:

[0018] a. Without considering space harmonics and cogging effect, assuming that the three-phase windings are arranged symmetrically and the electrical angle interval is 120°, the generated air gap magnetomotive force presents a sinusoidal distribution;

[0019] b. To simplify the modeling, it is assumed that the magnetic circuit does not saturate and the self-inductance and mutual inductance of each winding maintain linear changes;

[0020] c. Ignore core loss;

[0021] d. Consider the effects of temperature and frequency on winding resistance;

[0022] e. Assume that after the rotor parameters are converted to the stator side, the number of turns per phase is equal.

[0023] Furthermore, the S12 includes the following steps:

[0024] S121: Get the basic characteristics of the asynchronous motor; the slip rate of the asynchronous motor is defined as:

[0025]

[0026] Among them, ω s 、ω r and ω slip They represent synchronous frequency, rotor frequency and slip frequency respectively;

[0027] Using space vector notation, the stator voltage V of an asynchronous machine with a short-circuited rotor is s and rotor voltage V r The equation is:

[0028] V s =(R s I s +L s p)i s +L mag pI r ;

[0029] V r =(R r I r +L r (p-jω))I r +L mag (p-jω)I s ;

[0030] Where p represents the differential operator, r and s represent the rotor and stator respectively, and the stator inductance L s =L es +L mag , rotor inductance L r =L er +L mag ;L er 、L es and L mag Represent rotor leakage inductance, stator leakage inductance and magnetizing inductance respectively; R s Represents the stator resistance, R r Indicates the rotor resistance, I s Represents the stator current, I r represents the rotor current, ω represents the system angular velocity, j represents the complex imaginary part, and j 2 =-1;

[0031] Air gap power P gap The calculation formula is:

[0032]

[0033] Among them, |I r | represents the absolute value of the rotor current, SLIP represents the slip; the output of the asynchronous motor is converted into mechanical power P m and torque T e The estimation formula is:

[0034]

[0035] The frequency of the induction motor automatically adjusts to the power changes;

[0036] S122: The matrix form of the voltage equation of the asynchronous motor is:

[0037]

[0038] Among them, R s represents the stator resistance, u sA 、u sB 、u sC Represent the three-phase stator phase voltage, i sA 、i sB 、i sC Indicates the instantaneous value of the three-phase stator current, Indicates the instantaneous value of the three-phase stator flux, R r represents the rotor resistance, i ra 、i rb 、i rc represents the instantaneous value of the three-phase rotor current, Indicates the instantaneous value of the three-phase rotor flux, ura 、u rb 、u rc Represent the three-phase rotor phase voltage respectively;

[0039] The flux linkage of the three-phase stator and rotor windings is equal to the sum of their self-inductance flux linkage and the mutual inductance flux linkage of other windings. The flux linkage equation of each phase winding is expressed as:

[0040]

[0041] in, represents the three-phase stator flux, Represents the three-phase rotor flux, L AA 、L BB 、L CC 、L aa 、L bb 、L cc Represents the self-inductance of each winding, L AB 、L AC 、L Aa 、L Ab 、L Ac 、L BA 、L BC 、L Ba 、L Bb 、L Bc 、L CA 、L CB 、L Ca 、L Cb 、L Cc 、L aA 、L aB 、L aC 、L ab 、L ac 、L bA 、L bB 、L bC 、L ba 、L bc 、L cA 、L cB 、L cC 、L ca 、L cb represents the mutual inductance of the corresponding windings, i A 、i B 、i C 、i a 、i b 、i c Indicates the current flowing through each winding; L maxs Indicates the maximum mutual inductance flux linked to one phase of the stator winding, called stator mutual inductance; L maxrIndicates the maximum mutual inductance flux linked to one phase of the rotor winding, which is called the rotor mutual inductance. Since the number of turns of the stator and rotor windings is equal after the motor conversion, the mutual inductance flux between the windings passes through the air gap, and the magnetic resistance is equal, the stator mutual inductance is equal to the rotor mutual inductance, that is:

[0042] L maxs =L maxr ;

[0043] For each phase winding, the inter-link magnetic flux in the motor is formed by the mutual inductance magnetic flux and the leakage magnetic flux. Therefore, the corresponding self-inductance of the stator is expressed as:

[0044] L AA =L BB =L CC =L maxs +L es ;

[0045] Among them, L es Indicates the stator leakage inductance;

[0046] The self-inductance of each phase of the rotor is:

[0047] L aa =L bb =L cc =L maxs +L er ;

[0048] Among them, L er represents the leakage inductance of the rotor. The mutual inductance relationship between the internal windings of the motor can be divided into two categories: the first is the mutual inductance between stators and rotors, and the second is the mutual inductance between the stator and the rotor. Assuming that the spatial phase difference of the three-phase winding axes is 120° and the air gap flux is distributed in a sinusoidal law, the specific expression of the first type of mutual inductance is:

[0049] L AB =L AC =L BA =L BC =L CA =L CB =L maxs cos(120°);

[0050] L ab =L ac =L ba =L bc =L ca =L cb =L maxs cos(-120°);

[0051] Among them, cos represents the cosine function;

[0052] Since the relative position between any phase of the motor stator and any phase of the motor rotor is not fixed, the second-type mutual inductance is not a constant, but a function of the spatial angular displacement variable θ:

[0053] L Aa =L aA =L Bb =L bB =L Cc =L cC =L maxs cosθ;

[0054] L Ab =L bA =L Bc =L cB =L Ca =L aC =L maxs cos(θ+120°);

[0055] L Ac =L cA =L Ba =L aB =L Cb =L bC =L maxs cos(θ-120°);

[0056] The equivalent model of the asynchronous motor on the dq axis is:

[0057]

[0058]

[0059] Among them, ω syn and Δω represent the synchronous frequency and slip frequency respectively; u sd ,u sq ,i sd ,i sq , and Represent the dq axis voltage, current and stator flux respectively;

[0060] The control expressions of the rotor and stator flux links are expressed as:

[0061]

[0062] Among them, the stator inductance L s =L es +L mag And the rotor inductance L r =L er +L mag ;

[0063] Virtual torque T of virtual asynchronous machine v Expressed as:

[0064]

[0065] Furthermore, it is assumed that in steady state, the virtual rotor flux is aligned with the d-axis, i.e. The virtual torque is reformulated as:

[0066]

[0067] The formula and equation simplify to:

[0068]

[0069] Where ρ represents the slip frequency, and Δω represents the change in angular velocity;

[0070] According to the above formula:

[0071]

[0072] Substituting in, we get:

[0073]

[0074] Among them, δ r =L r / R r ;The mechanical power of the asynchronous motor is:

[0075]

[0076] Where J represents the inertia coefficient of the temperature change of the electrothermal energy system, D represents the friction damping coefficient, ω r represents the virtual rotor electrical angular velocity, T mech represents the mechanical torque, and:

[0077] T mech =T L +Dω r ;

[0078] That is, the mechanical power of the asynchronous motor is:

[0079]

[0080] T L It represents the rotor mechanical torque and is calculated as follows:

[0081]

[0082] Among them, P aC-DC represents the exchange power between the DC side and the AC side, κω (ω norm -ω norm,0 ) represents the virtual regulator part, ω norm,0 represents the rated set point of the AC microgrid frequency, κ ω Indicates active power coefficient;

[0083] Δω r Let the virtual rotor frequency ω r Deviation from the initial value ω0, the formula becomes:

[0084]

[0085] It has the characteristics of a first-order low-pass filter in the frequency domain, namely:

[0086]

[0087] Synchronous speed ω norm and the angle reference θ can be obtained by ω0, Δω r And the angular velocity difference Δω gives:

[0088] ω norm =ω0+Δω r +Δω;

[0089] θ=∫(ω0+Δω r +Δω)dt.

[0090] Furthermore, in S2, based on the real-time temperature of the circulating thermal mass energy storage system, the temperature response of the energy storage side is adjusted by using the inertia coefficient of temperature change to achieve real-time control of the electrothermal energy system, including the following steps:

[0091] S21: The temperature-dependent adaptive inertia coefficient J yields:

[0092]

[0093] Among them, τ T =τsign(T sys -T norm ), τ represents the positive inertia compensation coefficient, sign represents the sign function; T sys represents the temperature of the liquid working medium heat storage tank of the thermal energy storage system, T norm represents the set temperature of the liquid working medium heat storage tank of the thermal energy storage system, T max and T min They represent the maximum and minimum temperatures of the liquid working medium heat storage tank of the thermal energy storage system, J0 represents the initial inertia coefficient, It represents the rate of change of the temperature of the liquid working medium heat storage tank of the thermal energy storage system relative to time t.

[0094] Furthermore, the step S3 includes the following steps:

[0095] S31: When applying the V / f control strategy, the power required by the load in the microgrid is calculated by detecting the frequency difference and voltage difference, and the system output is adjusted accordingly; the expressions for active power and reactive power can be derived as follows:

[0096]

[0097] Among them, k p 、k q 、k i Represents controller parameters; f ref 、u ref Indicates reference value; f o 、u o Indicates the measured value;

[0098] S32: To achieve stable voltage control, the V / f strategy generally superimposes an outer voltage loop control on the basis of the inner current loop control. At the same time, filter capacitor current feedback and PCC voltage feedforward terms are added to the inner loop design. The improved voltage and current control equations are finally formed as follows:

[0099]

[0100] Among them, i 1q l、i 1d lω represents the feedback amount of the filter capacitor current; v q cω、v d cω represents the PCC voltage feedforward; u dref 、u qref Indicates the given value of dq axis voltage; u d 、u q Indicates the measured value of dq axis voltage; i d 、i q Indicates the measured values of the dq axis of the inner current loop.

[0101] Furthermore, S4 includes the following steps:

[0102] S41: The AC port type of the Carnot battery thermal mass cycle system connected to the power grid is 380V-660V high-frequency AC power; i represents the AC port of the i-th node in the power grid, and the active and reactive power output of this node is:

[0103]

[0104] Among them, P i,t , Q i,t They represent the active power and reactive power output by node i in period t respectively; G ij 、B ijRepresent the real and imaginary parts of the node admittance matrix respectively; V i,t ,θ ij,t Represent the node voltage amplitude and voltage phase difference respectively;

[0105] S42: Construct a Carnot battery thermal cycle energy storage system model.

[0106] Furthermore, the Carnot battery thermal cycle energy storage system includes: 1 electric boiler, 1 storage tank for the hot and cold sides of the liquid working medium, 1 storage tank for the hot and cold sides of the gas working medium, 2 heat exchangers under different operating conditions and an expander; the 2 heat exchangers under different operating conditions include a single-phase heat exchange working medium cooler and a gas heater.

[0107] Compared with the prior art, the present invention has the following advantages:

[0108] (1) The virtual asynchronous machine control proposed in the present invention does not require knowledge of the grid frequency and the rotor frequency, because the frequency automatically changes with the power. When the load power changes, the virtual asynchronous machine control can automatically optimize the AC frequency.

[0109] (2) Different from the minute-level and hour-level power optimization scheduling methods of traditional electrothermal coupled energy storage systems, the virtual asynchronous machine control proposed in the present invention using large inertia heat and fast response speed electricity can achieve real-time power balance.

[0110] (3) Compared with the virtual synchronous generator control strategy, the virtual asynchronous machine method has the advantages of adapting to load power changes and suppressing frequency oscillations. BRIEF DESCRIPTION OF THE DRAWINGS

[0111] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0112] Figure 1 The figure is a schematic diagram of the control method of the AC-AC converter based on the virtual asynchronous machine according to the present invention.

[0113] Figure 2 Schematic diagram of the rectifier circuit of the present invention.

[0114] Figure 3 This is a schematic diagram of the physical model of the asynchronous motor of the present invention.

[0115] Figure 4 This is a schematic diagram of the virtual asynchronous machine control structure of the present invention.

[0116] Figure 5Schematic diagram of the V / f control structure of the present invention.

[0117] Figure 6 This is a schematic diagram of the Carnot battery energy storage system of the present invention. DETAILED DESCRIPTION

[0118] In order to enable those skilled in the art to better understand the solutions of the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the embodiments described are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts should fall within the scope of protection of the present invention.

[0119] It should be noted that the terms "first", "second", etc. in the description and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that the numbers used in this way can be interchanged where appropriate, so that the embodiments of the present invention described herein can be implemented in an order other than those illustrated or described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0120] like Figure 1-6 As shown, the present invention provides an AC-AC converter control method based on a virtual asynchronous machine, comprising the following steps:

[0121] S1. Establishing a rectifier control technology based on a virtual asynchronous machine to control real-time power balance on the grid side and achieve dynamic frequency response when the energy storage demand on the load side changes. In S1, the rectifier control technology based on the virtual asynchronous machine is based on the physical model of the asynchronous motor and includes the following steps:

[0122] S11: Under idealized assumptions, the input power P on the AC side is calculated in real time by collecting voltage and current signals on the AC side. The idealized assumptions include:

[0123] a. Without considering space harmonics and cogging effect, assuming that the three-phase windings are arranged symmetrically and the electrical angle interval is 120°, the generated air gap magnetomotive force presents a sinusoidal distribution;

[0124] b. To simplify the modeling, it is assumed that the magnetic circuit does not saturate and the self-inductance and mutual inductance of each winding maintain linear changes.

[0125] c. Ignore core loss;

[0126] d. Consider the effects of temperature and frequency on winding resistance;

[0127] e. Assume that after the rotor parameters are converted to the stator side, the number of turns per phase is equal.

[0128] The power signal is controlled by the power outer loop and the current inner loop to generate the AC electromotive force reference value e on the d-axis and q-axis respectively. qref and e dref ,

[0129] AC electromotive force reference value e qref and e dref Then, the AC electromotive force reference value e of the asynchronous motor in the abc reference frame is obtained through the inverse Park transformation. abc ;

[0130] S12: The AC electromotive force reference value of the asynchronous motor in the abc reference frame is modulated by PWM to generate a trigger signal for the switch tube of the rectifier, thereby controlling the virtual asynchronous machine converter and further achieving real-time power balance control on the electric energy side. S12 includes the following steps:

[0131] S121: Get the basic characteristics of the asynchronous motor; the slip rate of the asynchronous motor is defined as:

[0132]

[0133] Among them, ω s 、ω r and ω slip They represent synchronous frequency, rotor frequency and slip frequency respectively;

[0134] Using space vector notation, the stator voltage V of an asynchronous machine with a short-circuited rotor is s and rotor voltage V r The equation is:

[0135] V s =(R s I s +L s p)I s +L mag pI r ;

[0136] V r =(R r I r +L r (p-jω))i r +L mag (p-jω)i s ;

[0137] Where p represents the differential operator, r and s represent the rotor and stator respectively, and the stator inductance L s =L es +L mag , rotor inductance L r =L er +L mag ;L er , L es and L mag Represent rotor leakage inductance, stator leakage inductance and magnetizing inductance respectively; R s Represents the stator resistance, R r Indicates the rotor resistance, I s Represents the stator current, I r represents the rotor current, ω represents the system angular velocity, j represents the complex imaginary part, and j 2 =-1;

[0138] Air gap power P gap The calculation formula is:

[0139]

[0140] Among them, |I r | represents the absolute value of the rotor current, SLIP represents the slip; the output of the asynchronous motor is converted into mechanical power P m and torque T e The estimation formula is:

[0141]

[0142]

[0143] The frequency of the induction motor automatically adjusts to the power changes;

[0144] S122: The matrix form of the voltage equation of the asynchronous motor is:

[0145]

[0146] Among them, R s represents the stator resistance, u sA 、u sB 、u sC Represent the three-phase stator phase voltage, i sA 、i sB 、i sC Indicates the instantaneous value of the three-phase stator current, Indicates the instantaneous value of the three-phase stator flux, R r represents the rotor resistance, i ra 、i rb 、i rc represents the instantaneous value of the three-phase rotor current, Indicates the instantaneous value of the three-phase rotor flux, u ra 、u rb 、u rc Represent the three-phase rotor phase voltage respectively;

[0147] The flux linkage of the three-phase stator and rotor windings is equal to the sum of their self-inductance flux linkage and the mutual inductance flux linkage of other windings. The flux linkage equation of each phase winding is expressed as:

[0148]

[0149] in, represents the three-phase stator flux, Represents the three-phase rotor flux, L AA , L BB , L CC , L aa , L bb , L cc Represents the self-inductance of each winding, L AB , L AC , L Aa , L Ab , L Ac , L BA , L BC , L Ba , L Bb , L Bc , L CA , L CB , L Ca , L Cb , L Cc , L aA , L aB , L aC , L ab , L ac , L bA , L bB , L bC , L ba , L bc , L cA , L cB , L cC , L ca , L cb represents the mutual inductance of the corresponding windings, i A 、i B 、i C 、i a 、i b 、i c Indicates the current flowing through each winding; L maxs Indicates the maximum mutual inductance flux linked to one phase of the stator winding, called stator mutual inductance; L maxrIndicates the maximum mutual inductance flux linked to one phase of the rotor winding, called rotor mutual inductance; since the number of turns of the stator and rotor windings are equal after the motor conversion, the mutual inductance flux between the windings passes through the air gap, and the magnetic resistance is equal, the stator mutual inductance is equal to the rotor mutual inductance, that is:

[0150] L maxs =L maxr ;

[0151] For each phase winding, the inter-link magnetic flux in the motor is formed by the mutual inductance magnetic flux and the leakage magnetic flux. Therefore, the corresponding self-inductance of the stator is expressed as:

[0152] L AA =L BB =L CC =L maxs +L es ;

[0153] Among them, L es Indicates the stator leakage inductance;

[0154] The self-inductance of each phase of the rotor is:

[0155] L aa =L bb =L cc =L maxs +L er ;

[0156] Among them, L er represents the leakage inductance of the rotor; the mutual inductance relationship between the internal windings of the motor can be divided into two categories: the first is the mutual inductance between stators and rotors, and the second is the mutual inductance between stators and rotors. Assuming that the spatial phase difference of the three-phase winding axes is 120° and the air gap flux is distributed in a sinusoidal law, the specific expression of the first type of mutual inductance is:

[0157] L AB =L AC =L BA =L BC =L CA =L CB =L maxs cos(120°);

[0158] L ab =L ac =L ba =L bc =L ca =L cb =L maxs cos(-120°);

[0159] Among them, cos represents the cosine function;

[0160] Since the relative position between any phase of the motor stator and any phase of the motor rotor is not fixed, the second-type mutual inductance is not a constant, but a function of the spatial angular displacement variable θ:

[0161] L Aa =L aA =L Bb =L bB =L Cc =L cC =L maxs cosθ;

[0162] L Ab =L bA =L Bc =L cB =L Ca =L aC =L maxs cos(θ+120°);

[0163] L Ac =L cA =L Ba =L aB =L Cb =L bC =L maxs cos(θ-120°);

[0164] The equivalent model of the asynchronous motor on the dq axis is:

[0165]

[0166] Among them, ω syn and Δω represent the synchronous frequency and slip frequency respectively; u sd ,u sq ,i sd ,i sq , and Represent the dq axis voltage, current and stator flux respectively;

[0167] The control expressions of the rotor and stator flux links are expressed as:

[0168]

[0169] Among them, the stator inductance L s =L es +L mag And the rotor inductance L r =L er +L mag ;

[0170] Virtual torque T of virtual asynchronous machine v Expressed as:

[0171]

[0172] Furthermore, it is assumed that in steady state, the virtual rotor flux is aligned with the d-axis, i.e. The virtual torque is reformulated as:

[0173]

[0174] The formula and equation simplify to:

[0175]

[0176] Where ρ represents the slip frequency, and Δω represents the change in angular velocity;

[0177] According to the above formula:

[0178]

[0179] Substituting in, we get:

[0180]

[0181] Among them, δ r =L r / R r ;The mechanical power of the asynchronous motor is:

[0182]

[0183] Where J represents the inertia coefficient of the temperature change of the electrothermal energy system, D represents the friction damping coefficient, ω r represents the virtual rotor electrical angular velocity, T mech represents the mechanical torque, and:

[0184] T mech =T L +Dω r ;

[0185] That is, the mechanical power of the asynchronous motor is:

[0186]

[0187] T L It represents the rotor mechanical torque and is calculated as follows:

[0188]

[0189] Among them, P AC-DC represents the exchange power between the DC side and the AC side, κ ω (ω norm -ω norm,0) represents the virtual regulator part, ω norm,0 represents the rated set point of the AC microgrid frequency, κ ω Indicates active power coefficient;

[0190] Δω r Let the virtual rotor frequency ω r Deviation from the initial value ω0, the formula becomes:

[0191]

[0192] It has the characteristics of a first-order low-pass filter in the frequency domain, namely:

[0193]

[0194] Synchronous speed ω norm and the angle reference θ can be obtained by ω0, Δω r And the angular velocity difference Δω gives:

[0195] ω norm =ω0+Δω r +Δω;

[0196] θ=∫(ω0+Δω r +Δω)dt.

[0197] S2. Based on the real-time temperature of the circulating thermal mass energy storage system, the inertia coefficient of temperature change is used to adjust the temperature response of the load side to achieve real-time control of the electric thermal energy system. In S2, based on the real-time temperature of the circulating thermal mass energy storage system, the inertia coefficient of temperature change is used to adjust the temperature response of the energy storage side to achieve real-time control of the electric thermal energy system, including the following steps:

[0198] S21: The temperature-dependent adaptive inertia coefficient J yields:

[0199]

[0200] Among them, τ T =τsign(T sys -T norm ), τ represents the positive inertia compensation coefficient, sign represents the sign function; T sys represents the temperature of the liquid working medium heat storage tank of the thermal energy storage system, T norm represents the set temperature of the liquid working medium heat storage tank of the thermal energy storage system, T max and T min They represent the maximum and minimum temperatures of the liquid working medium heat storage tank of the thermal energy storage system, J0 represents the initial inertia coefficient, It represents the rate of change of the temperature of the liquid working medium heat storage tank of the thermal energy storage system relative to time t.

[0201] S3, an inverter control method based on V / f control, converting industrial frequency AC power into high-frequency AC power; S3 includes the following steps:

[0202] S31: When applying the V / f control strategy, the power required by the load in the microgrid is calculated by detecting the frequency difference and voltage difference, and the system output is adjusted accordingly. The expressions for active power and reactive power can be derived as follows:

[0203]

[0204] Among them, k p 、k q 、k i Represents controller parameters; f ref 、u ref Indicates reference value; f o 、u o Indicates the measured value;

[0205] S32: To achieve stable voltage control, the V / f strategy generally superimposes an outer voltage control loop on the inner current control loop. At the same time, filter capacitor current feedback and PCC voltage feedforward terms are added to the inner loop design. The resulting improved voltage and current control equations are as follows:

[0206]

[0207] Among them, i 1q l、i 1d lω represents the feedback amount of the filter capacitor current; v q cω、v d cω represents the PCC voltage feedforward; u dref 、u qref Indicates the given value of dq axis voltage; u d 、u q Indicates the measured value of dq axis voltage; i d 、i q Indicates the measured values of the dq axis of the inner current loop.

[0208] S4: A Carnot battery energy storage system based on a heat storage medium cycle, wherein the grid is connected to the Carnot battery energy storage system, so that electrical energy is converted into thermal energy for storage. S4 includes the following steps:

[0209] S41: The AC port type of the Carnot battery thermal mass cycle system connected to the power grid is 380V-660V high-frequency AC power; i represents the AC port of the i-th node in the power grid, and the active and reactive power output of this node is:

[0210]

[0211] Among them, Pi,t , Q i,t They represent the active power and reactive power output by node i in period t respectively; G ij 、B ij Represent the real and imaginary parts of the node admittance matrix respectively; V i,t ,θ ij,t Represent the node voltage amplitude and voltage phase difference respectively;

[0212] S42: Construct a Carnot battery thermal cycle energy storage system model.

[0213] Furthermore, the Carnot battery thermal cycle energy storage system includes: 1 electric boiler, 1 storage tank for the hot and cold sides of the liquid working medium, 1 storage tank for the hot and cold sides of the gas working medium, 2 heat exchangers under different operating conditions and an expander; the 2 heat exchangers under different operating conditions include a single-phase heat exchange working medium cooler and a gas heater.

[0214] Charging process: The power grid inputs electric energy to the electric boiler to provide power heating. After the electric boiler heats the low-temperature liquid working medium in the liquid cold storage tank, the temperature of the low-temperature liquid working medium rises and becomes high-temperature liquid working medium, which enters the liquid hot storage tank of the heat storage system for storage;

[0215] Discharge process: The high-temperature liquid transfers heat to the low-temperature gas working fluid in the gas cold storage tank in the working fluid cooler. The low-temperature gas working fluid absorbs the heat energy of the high-temperature liquid working fluid in the gas heater, and is heated and pressurized to a high-temperature and high-pressure state. It then expands and performs work in the expander, converting mechanical energy into electrical energy and outputting it to the power grid. After performing work, the high-temperature and high-pressure gas becomes low-temperature and low-pressure gas and is returned to the gas cold storage tank of the heat storage system for storage.

[0216] The construction process of the electric boiler model is as follows:

[0217] Electric power consumed by electric boiler P eb As shown below:

[0218] P eb =P i,t

[0219] The heat release power of electric boiler is very high, which is linearly related to the power consumption. The output heating power Q of electric boiler is eb (t) is:

[0220] Q eb (t)=3.6μP eb

[0221] Where: μ is a constant, which represents the electric-to-heat conversion efficiency of the electric boiler.

[0222] The simplified expressions of the energy storage capacity and charge and discharge power of the Carnot battery thermal cycle energy storage system after the idealization of the model are:

[0223]

[0224] Where: H HS (t) is the thermal energy storage capacity in time period t; μ is the thermal energy self-release rate; η hch is the heat storage efficiency of the heat storage system during time period t; η edis is the discharge efficiency of the heat storage system during time period t; Q HS_ch (t) is the absorbed thermal power of the thermal mass energy storage system in time period t. ESS_dis (t) is the output electric power of the thermal mass energy storage system in time period t.

[0225] In the present application, the electric boiler: heats the low-temperature liquid working fluid by absorbing electrical energy, causing it to absorb heat and heat up to a high-temperature liquid working fluid. Liquid working fluid cold / hot storage tank: an insulated container for storing high-temperature / low-temperature liquid working fluid. Gas working fluid cold / hot storage tank: an insulated container for storing high-temperature / low-temperature gas working fluid. Heat exchanger: can efficiently enable the low-temperature working fluid to absorb heat from the electric boiler or transfer the heat of the high-temperature working fluid to the expansion agent to do work. Expander: during the expansion process, the gas releases its own internal energy in an adiabatic manner, accompanied by a substantial drop in pressure and temperature, and does work externally. The liquid working fluid in the system is water, heat transfer oil or molten salt, the gas working fluid is carbon dioxide, and the cycle is a transcritical carbon dioxide Rankine cycle or an organic Rankine cycle.

[0226] The serial numbers of the above embodiments of the present invention are for description only and do not represent the advantages or disadvantages of the embodiments.

[0227] In the above embodiments of the present invention, the description of each embodiment has its own focus. For parts that are not described in detail in a certain embodiment, reference can be made to the relevant descriptions of other embodiments.

[0228] In the several embodiments provided in this application, it should be understood that the disclosed technical content can be implemented in other ways. Among them, the device embodiments described above are only exemplary. For example, the division of the units can be a logical function division. In actual implementation, there may be other division methods, such as multiple units or components can be combined or integrated into another system, or some features can be ignored or not executed. Another point is that the mutual coupling or direct coupling or communication connection shown or discussed can be through some interfaces, indirect coupling or communication connection of units or modules, which can be electrical or other forms.

[0229] The units described as separate components may or may not be physically separate, and the components shown as units may or may not be physical units, that is, they may be located in one place or distributed across multiple units. Some or all of the units may be selected according to actual needs to achieve the purpose of the present embodiment.

[0230] In addition, the functional units in the various embodiments of the present invention may be integrated into a single processing unit, each unit may exist physically separately, or two or more units may be integrated into a single unit. The aforementioned integrated units may be implemented in the form of hardware or software functional units.

[0231] If the integrated unit is implemented in the form of a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of the present invention, or the part that contributes to the prior art, or all or part of the technical solution can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes several instructions for enabling a computer device (which can be a personal computer, server or network device, etc.) to perform all or part of the steps of the method described in each embodiment of the present invention. The aforementioned storage medium includes: U disk, read-only memory (ROM, Read-Only Memory), random access memory (RAM, Random Access Memory), mobile hard disk, magnetic disk or optical disk, etc. Various media that can store program codes.

[0232] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A control method for an AC-AC converter based on a virtual asynchronous machine, characterized in that: The following steps are involved: S1. Establish rectifier control technology based on virtual asynchronous machines to control real-time power balance on the grid side and achieve dynamic frequency response when energy storage demand changes on the load side; S2. Based on the real-time temperature of the circulating thermal mass energy storage system, the inertia coefficient of temperature change is used to adjust the temperature response of the load side to achieve real-time control of the electric thermal energy system; S3, an inverter control method based on V / f control, which converts industrial frequency AC power into high frequency AC power; S4. A Carnot battery energy storage system based on a heat storage medium cycle. The grid is connected to the Carnot battery energy storage system, so that electrical energy is converted into thermal energy for storage.

2. The AC-AC converter control method based on a virtual asynchronous machine according to claim 1, characterized in that: In S1, the rectifier control technology based on the virtual asynchronous machine is based on the physical model of the asynchronous machine and includes the following steps: S11: Under idealized assumptions, the input power P on the AC side is calculated in real time by collecting the voltage and current signals on the AC side; The power signal is controlled by the power outer loop and the current inner loop to generate the AC electromotive force reference value e on the d-axis and q-axis respectively. qref and e dref , AC electromotive force reference value e qref and e dref Then, the AC electromotive force reference value e of the asynchronous motor in the abc reference frame is obtained through the inverse Park transformation. abc ; S12: The AC electromotive force reference value of the asynchronous motor in the abc reference frame is modulated by PWM to generate a switch trigger signal of the rectifier, thereby realizing the control of the virtual asynchronous machine converter and further realizing real-time power balance control on the electric energy side.

3. The AC-AC converter control method based on a virtual asynchronous machine according to claim 2, characterized in that: The idealized assumptions include: a. Without considering space harmonics and cogging effect, assuming that the three-phase windings are arranged symmetrically and the electrical angle interval is 120°, the generated air gap magnetomotive force presents a sinusoidal distribution; b. To simplify the modeling, it is assumed that the magnetic circuit does not saturate and the self-inductance and mutual inductance of each winding maintain linear changes; c. Ignore core loss; d. Consider the effects of temperature and frequency on winding resistance; e. Assume that after the rotor parameters are converted to the stator side, the number of turns per phase is equal.

4. The AC-AC converter control method based on a virtual asynchronous machine according to claim 2, characterized in that: The S12 includes the following steps: S121: Get the basic characteristics of the asynchronous motor; the slip rate of the asynchronous motor is defined as: Among them, ω s 、ω r and ω slip They represent synchronous frequency, rotor frequency and slip frequency respectively; Using space vector notation, the stator voltage V of an asynchronous machine with a short-circuited rotor is s and rotor voltage V r The equation is: V s =(R s I s +L s p)I s +L mag pI r ; IN r =(R r AND r +L r (p-jω))I r +L mag (p-jω)I s ; Where p represents the differential operator, r and s represent the rotor and stator respectively, and the stator inductance L s =L es +L mag , rotor inductance L r =L er +L mag ;L er 、L es and L mag Represent rotor leakage inductance, stator leakage inductance and magnetizing inductance respectively; R s Represents the stator resistance, R r Indicates the rotor resistance, I s Represents the stator current, I r represents the rotor current, ω represents the system angular velocity, j represents the complex imaginary part, and j 2 =-1; Air gap power P gap The calculation formula is: Among them, |I r | represents the absolute value of the rotor current, SLIP represents the slip; the output of the asynchronous motor is converted into mechanical power P m and torque T e The estimation formula is: The frequency of the induction motor automatically adjusts to the power changes; S122: The matrix form of the voltage equation of the asynchronous motor is: Among them, R s represents the stator resistance, u sA 、u sB 、u sC Represent the three-phase stator phase voltage, i sA 、i sB 、i sC Indicates the instantaneous value of the three-phase stator current, Indicates the instantaneous value of the three-phase stator flux, R r represents the rotor resistance, i ra 、i rb 、i rc represents the instantaneous value of the three-phase rotor current, Indicates the instantaneous value of the three-phase rotor flux, u ra 、u rb 、u rc Represent the three-phase rotor phase voltage respectively; The flux linkage of the three-phase stator and rotor windings is equal to the sum of their self-inductance flux linkage and the mutual inductance flux linkage of other windings. The flux linkage equation of each phase winding is expressed as: in, represents the three-phase stator flux, Represents the three-phase rotor flux, L AA , L BB , L CC , L aa , L bb , L cc Represents the self-inductance of each winding, L AB , L AC , L Aa , L Ab , L Ac , L BA , L BC , L Ba , L Bb , L Bc , L CA , L CB , L Ca , L Cb , L Cc , L aA , L aB , L aC , L ab , L ac , L bA , L bB , L bC , L ba , L bc , L cA , L cB , L cC , L ca , L cb represents the mutual inductance of the corresponding windings, i A 、i B 、i C 、i a 、i b 、i c Indicates the current flowing through each winding; L maxs Indicates the maximum mutual inductance flux linked to one phase of the stator winding, called stator mutual inductance; L maxr Indicates the maximum mutual inductance flux linked to one phase of the rotor winding, which is called the rotor mutual inductance. Since the number of turns of the stator and rotor windings is equal after the motor conversion, the mutual inductance flux between the windings passes through the air gap, and the magnetic resistance is equal, the stator mutual inductance is equal to the rotor mutual inductance, that is: L maxs =L maxr ; For each phase winding, the inter-link magnetic flux in the motor is formed by the mutual inductance magnetic flux and the leakage magnetic flux. Therefore, the corresponding self-inductance of the stator can be expressed as: L AA =L BB =L CC =L maxs +L es ; Among them, L es Indicates the stator leakage inductance; The self-inductance of each phase of the rotor is: L aa =L bb =L cc =L maxs +L er ; Among them, L er represents the leakage inductance of the rotor. The mutual inductance relationship between the internal windings of the motor can be divided into two categories: the first is the mutual inductance between stators and rotors, and the second is the mutual inductance between the stator and the rotor. Assuming that the spatial phase difference of the three-phase winding axes is 120° and the air gap flux is distributed in a sinusoidal law, the expression of the first type of mutual inductance is: L AB =L AC =L BA =L BC =L CA =L CB =L maxs cos(120°); L ab =L ac =L ba =L bc =L ca =L cb =L maxs cos(-120°); Among them, cos represents the cosine function; Since the relative position between any phase of the motor stator and any phase of the motor rotor is not fixed, the second-type mutual inductance is not a constant, but a function of the spatial angular displacement variable θ: L Aa =L aA =L Bb =L bB =L Cc =L cC =L maxs cosθ; L Ab =L bA =L Bc =L cB =L Ca =L aC =L maxs cos(θ+120°); L Ac =L cA =L Ba =L aB =L Cb =L bC =L maxs cos(θ-120°); The equivalent model of the asynchronous motor on the dq axis is: Among them, ω syn and Δω represent the synchronous frequency and slip frequency respectively; u sd ,u sq ,i sd ,i sq , and Represent the dq axis voltage, current and stator flux respectively; The control expressions of the rotor and stator flux links are expressed as: Among them, the stator inductance L s =L es +L mag And the rotor inductance L r =L er +L mag ; Virtual torque T of virtual asynchronous machine v Expressed as: Furthermore, it is assumed that in steady state, the virtual rotor flux is aligned with the d-axis, i.e. The virtual torque is reformulated as: The formula and equation simplify to: Where ρ represents the slip frequency, and Δω represents the change in angular velocity; According to the above formula: Substituting in, we get: Among them, δ r =L r / R r ;The mechanical power of the asynchronous motor is: Where J represents the inertia coefficient of the temperature change of the electrothermal energy system, D represents the friction damping coefficient, ω r represents the virtual rotor electrical angular velocity, T mech represents the mechanical torque, and: T mech =T L +Dω r ; That is, the mechanical power of the asynchronous motor is: T L It represents the rotor mechanical torque and is calculated as follows: Among them, P AC-DC Indicates the exchange power between the DC side and the AC side, K ω (ω norm -ω norm，0 ) represents the virtual regulator part, ω norm，0 represents the rated set point of the AC microgrid frequency, κ ω Indicates active power coefficient; Δω r Let the virtual rotor frequency ω r Deviation from the initial value ω0, the formula becomes: It has the characteristics of a first-order low-pass filter in the frequency domain, namely: Synchronous speed ω norm and the angle reference θ can be obtained by ω0, Δω r And the angular velocity difference Δω gives: oh norm =ω0+δω r +See; θ=∫(ω0+Δω r +Dω)dt.

5. The AC-AC converter control method based on a virtual asynchronous machine according to claim 1, characterized in that: In S2, based on the real-time temperature of the circulating thermal mass energy storage system, the temperature response of the energy storage side is adjusted by using the inertia coefficient of temperature change to achieve real-time control of the electric thermal energy system, including the following steps: S21: The temperature-dependent adaptive inertia coefficient J yields: Among them, τ T =τsign(T sys -T norm ), τ represents the positive inertia compensation coefficient, sign represents the sign function; T sys represents the temperature of the liquid working medium heat storage tank of the thermal energy storage system, T norm represents the set temperature of the liquid working medium heat storage tank of the thermal energy storage system, T max and T min They represent the maximum and minimum temperatures of the liquid working medium heat storage tank of the thermal energy storage system, J0 represents the initial inertia coefficient, It represents the rate of change of the temperature of the liquid working medium heat storage tank of the thermal energy storage system relative to time t.

6. The AC-AC converter control method based on a virtual asynchronous machine according to claim 1, characterized in that: The S3 includes the following steps: S31: When applying the V / f control strategy, the power required by the load in the microgrid is calculated by detecting the frequency difference and voltage difference, and the system output is adjusted accordingly; the expressions for active power and reactive power can be derived as follows: Among them, k p 、k q 、k i Represents controller parameters; f ref 、u ref Indicates reference value; f o 、u o Indicates the measured value; S32: To achieve stable voltage control, the V / f strategy generally superimposes an outer voltage control loop on top of the inner current control loop. Meanwhile, filter capacitor current feedback and PCC voltage feedforward terms are added to the inner loop design. The resulting improved voltage and current control equations are as follows: Among them, i 1q l、i 1d lω represents the feedback amount of the filter capacitor current; v q cω、v d cω represents the PCC voltage feedforward; u dref 、u qref Indicates the given value of dq axis voltage; u d 、u q Indicates the measured value of dq axis voltage; i d 、i q Indicates the measured values of the dq axis of the inner current loop.

7. The AC-AC converter control method based on a virtual asynchronous machine according to claim 1, characterized in that: S4 includes the following steps: S41: The AC port type of the Carnot battery thermal mass cycle system connected to the power grid is 380V-660V high-frequency AC power; i represents the AC port of the i-th node in the power grid, and the active and reactive power output of this node is: Among them, P i,t , Q i,t They represent the active power and reactive power output by node i in period t respectively; G ij 、B ij Represent the real and imaginary parts of the node admittance matrix respectively; V i,t ,θ ij,t Represent the node voltage amplitude and voltage phase difference respectively; S42: Construct a Carnot battery thermal cycle energy storage system model.

8. The AC-AC converter control method based on a virtual asynchronous machine according to claim 7, characterized in that: The Carnot battery thermal cycle energy storage system includes: an electric boiler, a storage tank for the hot and cold sides of the liquid working medium, a storage tank for the hot and cold sides of the gas working medium, two heat exchangers under different operating conditions, and an expander; the two heat exchangers under different operating conditions include a single-phase heat exchange working medium cooler and a gas heater.

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