Electric energy router energy storage and grid connection port inertia matching control method

Abstract

An electric energy router is used as a highly power electronic device and lacks the characteristic of inertia of a rotating rotor, so that power oscillation is easily caused, and stable operation of a system is influenced. According to the comprehensive inertia control method suitable for the electric energy router, two different inertia simulation modes are combined, and virtual direct current motor control and self-synchronization control based on capacitance inertia are adopted at an energy storage port and an alternating current grid-connected port of the electric energy router respectively. The virtual inertia is provided by embedding a virtual direct current motor algorithm, and the actual inertia of a direct current capacitor is utilized by the latter. The electric energy router connects alternating current frequency and direct current voltage through self-synchronization control of an alternating current port, so that alternating current side disturbance can be transmitted to a direct current side, and then inertia response is carried out. The established electric energy router inertia system can realize multi-port inertia response. Meanwhile, due to the different inertia simulation mechanisms of the two inertia simulation modes, the inertia matching mechanism under the two different inertia simulation modes is further explored.

Description

Technical Field

[0010] The present invention relates to the technical field of power system stability, and in particular to an inertia matching control method for energy storage and grid-connected ports of an energy router, which is used to improve the stability and anti-interference capability of the energy router. Background Art

[0011] With the transformation of the global energy structure and the rapid development of new energy technologies, power routers, as key interface devices in the power system, assume the important responsibility of efficient distribution and stable supply of electric energy. Through highly integrated power electronics technology, power routers achieve precise control and flexible management of electric energy, providing technical support for the access and utilization of distributed energy. However, since the power routers themselves lack the rotational inertia of traditional synchronous generators, when the system is disturbed, they cannot provide sufficient inertial response like traditional generators, thus affecting the stability and reliability of the entire power system. Especially in the context of large-scale access to new energy, this limitation of power routers is more prominent and has become a key issue restricting the safe and efficient operation of the power system.

[0012] In addition, when there are multiple devices that can provide inertia in the system, the problem of inertia matching needs to be considered. In actual operation, the inertia of the power router is generally provided by the energy storage port and the grid-connected port. Inertia mismatch may cause the power router to affect the dynamic response performance of the system when facing grid frequency fluctuations or load changes. Therefore, developing a control method that can achieve effective matching of the inertia of the energy storage and grid-connected ports is of great significance to improving the performance of the power router and ensuring the stable operation of the power system. Summary of the invention

[0013] Aiming at the deficiencies of existing electric energy routers in the configuration of energy storage and grid-connected port inertia, the present invention proposes a method for matching the energy storage and grid-connected port inertia.

[0014] This method designs the inertia parameters of the energy storage port and the grid-connected port, realizes the inertia response coordination between different ports of the power router, and effectively improves the system's adaptability and stability to grid disturbances.

[0015] The present invention introduces virtual DC motor control technology into the energy storage port of the power router. Compared with the traditional control method, the virtual DC motor control simulates the operating characteristics of the DC motor through an algorithm, providing virtual inertia support for the energy storage system. By adjusting the parameters of the virtual motor, the control strategy can flexibly set the required inertia size and damping ratio, thereby achieving precise control of the dynamic response characteristics of the energy storage system.

[0016] The two-port model of the buck / boost step-up / down circuit is simulated into a single-port model of a DC motor. The armature circuit equation of the simulated DC motor is shown as follows:

[0017] E=U2+I2R a =C T Φω

[0018] Where, E is the simulated DC motor armature electromotive force, C T is the torque coefficient, Φ is the magnetic flux, ω is the mechanical angular velocity of the DC motor; U2 and I2 are the terminal voltage and current of the two ports of the simulated front buck-boost circuit, and the terminal voltage and current of the simulated rear motor; Ra is the total equivalent resistance of the armature circuit.

[0019] For the mechanical power of the motor, there is the rotor motion equation:

[0020]

[0021] Where J is the moment of inertia, T m , T e are the mechanical torque and electromagnetic torque, D is the damping coefficient, and ω0 is the rated mechanical angular velocity.

[0022] The present invention adopts a self-synchronous control method based on DC capacitors at the grid-connected port of the power router. This method utilizes the natural inertia characteristics of DC capacitors and couples the frequency change on the AC side with the voltage change on the DC side through a control strategy, thereby realizing the transmission of disturbances on the AC side to the DC side.

[0023] In order to simulate the synchronization process of the generator, the DC voltage U dc The angular frequency ω of the inverter output r When coupled, the following relationship is established.

[0024]

[0025] Furthermore,

[0026]

[0027] Where U dcn with U dc are the rated value and actual value of DC voltage, ω ref With ω n are the reference value and rated value of the angular frequency on the AC side respectively, and K is the coupling coefficient between voltage and angular frequency.

[0028] Self-synchronous control not only exploits the natural inertia of the system, but also enhances the overall inertia response capability of the system through self-synchronization of voltage and grid frequency.

[0029] Since the control strategy lacks a damping link, the system is prone to oscillation when disturbed, which interferes with the system synchronization speed and makes it impossible for the system to quickly reach stability.

[0030] A damping circuit is added to the control circuit. The damping provided by the damping circuit is the DC power multiplied by the damping coefficient, which is then added to the self-synchronous control process of the converter, as shown in the following formula:

[0031]

[0032] In order to ensure that the damping link does not affect the normal operation when the system is in steady state operation and plays a role in the dynamic process, a bandpass filter is added to the damping loop.

[0033] The reactive voltage circuit is controlled by the following formula:

[0034]

[0035] Where U rec is the reference voltage involved in modulation, U ref is the reference voltage of the droop control output, β is the AC voltage damping coefficient, U gn , U g They are the reference effective value and actual effective value of the AC voltage respectively.

[0036] The control strategy of the present invention can achieve inertia response under the following working conditions:

[0037] Photovoltaic power fluctuations;

[0038] DC load switching;

[0039] AC load switching;

[0040] The AC grid frequency fluctuates.

[0041] The present invention adopts two different inertia simulation mechanisms and involves the inertia transfer of the AC / DC cascade system. Therefore, the general inertia matching law cannot be used directly and the parameter design needs to be re-performed.

[0042] Derived from the armature circuit equation:

[0043]

[0044] Where R a *I value is much smaller than U dc , so it can be approximately ignored, and the above formula can be written as:

[0045]

[0046] Substitute the above formula into the rotor motion equation:

[0047]

[0048] At this time, the inertia equation of the virtual DC motor and the capacitor inertia equation have established the same dimension form. At this time, the inertia relationship between the two is linked through the inertia ratio r:

[0049]

[0050] The inertia ratio r represents the ratio of the inertia of the capacitor to the inertia of the virtual DC motor. The inertia ratio setting depends on the system conditions.

[0051] The beneficial effects of the present invention are:

[0052] The grid-connected port control proposed in the present invention does not need to rely on a phase-locked loop to track the grid frequency in the grid-connected mode, thus avoiding the adverse effects caused by the deterioration of the phase-locked loop accuracy under power disturbance;

[0053] In off-grid mode, it can also be used as a grid-type control to maintain the operation of the AC microgrid, avoiding the switching of operation modes;

[0054] Through self-synchronization, the disturbance on the AC microgrid can be transmitted to the DC side without communication, so that the DC side energy storage port participates in the inertia response;

[0055] The present invention explores the inertia matching mechanism of two inertia simulation methods, and provides a solution for the inertia configuration of AC / DC cascade systems and the interaction research between different inertia simulation mechanisms. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 It is the structure of a power router.

[0057] Figure 2 It is a virtual DC motor model.

[0058] Figure 3 This is the block diagram of the virtual DC motor control.

[0059] Figure 4 This is the self-synchronous control block diagram based on DC capacitor inertia. DETAILED DESCRIPTION

[0060] In the following statements, some specific system architectures and technical details are introduced for the purpose of explanation rather than limitation, in order to deepen the understanding of the embodiments of the present invention. However, it should be noted by those skilled in the art that the present invention can still be implemented even in the absence of these detailed descriptions. In order to highlight the innovation and features of the present invention, the explanation of some well-known systems, devices, circuits and methods will be shortened. Based on the technology and patent requirements mentioned in the uploaded files, the following is a complete description of the specific implementation method of the present invention.

[0061] Specific examples include Figure 1 The structure of the power router is shown in FIG. 1 , wherein the power router includes various converter ports and a DC bus.

[0062] The DC side port can realize plug-and-play of photovoltaic modules, energy storage modules, and DC load modules through DC / DC circuits.

[0063] The power router is connected to the AC side via an interconnected converter. The filter uses an LC filter. The AC side has a local AC load and is then connected to the large power grid through a transformer and a circuit breaker.

[0064] The AC side of the power router is connected to the AC microgrid, and the interconnected converter port realizes the function of bidirectional flow of AC and DC power. When connected to the grid, it controls the power exchange between the power router and the AC grid, and provides power support for the load of the AC microgrid when off the grid.

[0065] The photovoltaic array is connected to the power router through the Boost circuit. In order to maximize the use of renewable energy output, it is generally controlled in MPPT mode.

[0066] The energy storage system is connected to the DC bus through the Buck / Boost step-up and step-down circuit to achieve energy exchange between the energy storage battery and the DC bus.

[0067] The energy storage port adopts virtual DC motor control, such as Figure 2 As shown in the figure, the two-port model of the buck / boost step-up / down circuit is simulated into a single-port model of the DC motor.

[0068] U 2ref U1 and U2 are the DC voltage reference value and actual value respectively. T Φ is 2.228, R a Take 0.02, and select the corresponding values ​​of the moment of inertia J and the damping coefficient D according to factors such as system capacity and battery type.

[0069] Through the control algorithm of the virtual DC motor, a current reference value I can be obtained. 2ref , this reference value is the current reference value of port 2, i.e., the current flowing into the DC bus, and the controlled inductor current is the current of port 1, and the two need to be calculated. Ignoring the converter loss, the output power of the two ports is equal, and the current is calculated as follows:

[0070]

[0071] The specific control block diagram of the virtual DC motor is as follows: Figure 3 shown.

[0072] The self-synchronous control of DC capacitor inertia is adopted for the AC port. According to the classification of the properties of the energy link state quantity in the power system, the capacitor and the rotor belong to the storage inertia, which provides buffering in the energy release and absorption process after the active disturbance. The specific control block diagram is as follows Figure 4 shown.

[0073] This control has a self-synchronization control process similar to that of the synchronous machine. Before explaining the self-synchronization process of the two, it is necessary to give the output power expressions of the synchronous machine and the converter.

[0074]

[0075] In the formula, ω g is the grid frequency, ω e ,ω rec are the electromagnetic angular frequency of the synchronous machine and the output angular frequency of the converter, m is the modulation ratio, δ is the power angle, and X is the sum of the grid-connected reactance, line reactance and equivalent grid impedance.

[0076] Taking the synchronization process of the grid frequency rising as an example, for the synchronous machine, the grid frequency rises, the power angle decreases, and the grid-connected power P e Decreases, the rotor angular velocity increases, and finally the synchronous machine output frequency increases until it is synchronized with the grid frequency; for the converter, the grid frequency increases, the power angle decreases, and the converter output AC frequency decreases. According to the power balance, it can be judged that the DC voltage will increase. At the same time, because the coupling relationship between angular frequency and voltage is constructed in the control link, the AC frequency of the converter output will eventually increase until it is synchronized with the grid frequency.

[0077] The above control strategy utilizes the converter equivalent capacitance to simulate the actual inertia and realizes the self-synchronization of the system DC voltage and AC angular frequency.

[0078] The above power router control strategy can realize multi-port inertia response, and its power balance formula is:

[0079]

[0080] Whether it is the frequency fluctuation on the AC side, the switching of the DC side load, or the disturbance of the photovoltaic module, it will directly affect the voltage change on the DC side, which will in turn cause the inertia response of the DC capacitor and the energy storage virtual DC motor, resisting the change of the system state quantity.

Claims

1. A method for controlling the inertia matching between energy storage and grid-connected ports of an energy router. It is characterized in that The method includes: Implement virtual DC motor control on the energy storage port of the power router, and set virtual inertia damping parameters through the control algorithm to provide inertia damping for the DC system; Implement self-synchronous control based on DC capacitors on the grid-connected port of the power router, couple the DC voltage with the AC angular frequency, and use the actual inertia of the DC capacitor to provide equivalent inertia for the AC side; The constructed power router can realize multi-port inertia response; The parameters of inertia matching are designed for the virtual inertia of the energy storage port and the actual inertia of the capacitor, and the inertia ratio is introduced to describe the inertia parameter configuration between the two ports.

2. According to claim 1, a method for controlling the energy storage and grid-connected port inertia matching of an electric energy router, It is characterized in that Self-synchronous control includes the following steps: Establish the coupling relationship between the DC voltage and the inverter output angular frequency, and use the actual inertia of the DC capacitor to provide equivalent inertia for the system; The angular frequency disturbance on the AC side is transmitted to the DC side, and the energy storage on the DC side participates in the inertia response; A damping loop based on DC power is added to the control to enhance the stability of the system when it is disturbed. The damping loop is shown in the following formula: Where U dcn with U dc are the rated value and actual value of DC voltage, ω ref With ω n are the reference value and rated value of the angular frequency on the AC side, respectively, and K is the coupling coefficient between voltage and angular frequency; A low-pass filter is added to the loop so that the loop only takes effect during the oscillation process.

3. According to claim 1, a method for controlling the energy storage and grid-connected port inertia matching of an electric energy router, It is characterized in that Able to realize multi-port inertia response, inertia response includes the following cases: The output of photovoltaic ports fluctuates; DC side load switching; Load switching on the AC side; The AC side grid frequency fluctuates.

4. According to claim 1, a method for controlling the energy storage and grid-connected port inertia matching of an electric energy router, It is characterized in that The parameter design of inertia matching includes the following steps: The armature circuit equation can be derived as follows: Where R a *I value is much smaller than U dc , so it can be approximately ignored, and the above formula can be written as: Substitute the above formula into the rotor motion equation: At this time, the inertia equation of the virtual DC motor and the capacitor inertia equation have established the same dimension form. At this time, the inertia relationship between the two is linked through the inertia ratio r: The inertia ratio r represents the ratio of the inertia of the capacitor to the inertia of the virtual DC motor. The inertia ratio setting depends on the system conditions.

Images