VSG-VDG-based AC-DC hybrid microgrid interconnection converter autonomous control method and device

Abstract

The invention discloses a VSG-VDG-based autonomous control method and device for an AC-DC hybrid micro-grid interconnection converter. The equipment comprises a direct-current micro-grid, an alternating-current micro-grid and an interconnection converter connected with the direct-current micro-grid and the alternating-current micro-grid. The direct current microgrid is provided with a direct current side VDG control module which is used for controlling a direct current converter to adjust direct current power supply output by collecting internal voltage and current signals; the AC micro-grid is provided with an AC side VSG control module which is used for controlling on-off of a switching tube of a three-phase full-bridge inverter by collecting internal voltage and current signals so as to adjust AC three-phase voltage output. The interconnection converter is provided with an interconnection converter control module which is used for connecting the direct-current bus and the alternating-current bus through the bidirectional interface converter and adjusting energy balance in the subnet through bidirectional energy flow. According to the method, the robustness of the AC / DC micro-grid system is enhanced, and the fault self-healing capability of the system under extreme conditions and the transient and steady-state stability of a controlled system are improved.

Description

Technical Field

[0001] The present invention relates to the field of AC-DC hybrid microgrid, and in particular to a VSG-VDG-based AC-DC hybrid microgrid interconnected converter autonomous control method and device. Background Art

[0002] Under the background of "dual carbon", a large number of distributed power sources, mainly wind turbines and photovoltaics, are connected to microgrids (or microgrid clusters). Among them, AC microgrids are suitable for large-scale energy access, but the control is often more complicated; while DC microgrids do not need to consider frequency and voltage phase issues, have high transmission efficiency and are easy to control, but have high construction costs. When a single microgrid supplies power, there are often inherent defects such as poor power quality and the lack of guarantee of power supply system safety and reliability. The AC / DC hybrid microgrid group formed by interconnecting AC / DC microgrids has the advantages of both AC microgrids and DC microgrids, but is limited by the limited internal capacity and inertia of a single area. The AC / DC hybrid microgrid has insufficient resilience when dealing with disturbances such as power mutations, and the voltage and frequency fluctuations are still serious. The existing inverter control technology is difficult to effectively cope with complex operating environments, resulting in insufficient system stability, and disturbance oscillations will be accumulated and transmitted within the hybrid system until the system becomes unstable. Summary of the invention

[0003] In order to overcome the shortcomings of the prior art, the present invention provides an autonomous control method and device for an AC / DC hybrid microgrid interconnected converter based on VSG-VDG, so as to realize adaptive dual droop control of an AC / DC microgrid based on a virtual synchronous generator on the AC side and a virtual DC motor on the DC side.

[0004] According to one aspect of the present invention, there is provided an autonomous control device of an AC / DC hybrid microgrid interconnected converter based on VSG-VDG, comprising a DC microgrid, an AC microgrid and an interconnected converter connecting the DC microgrid and the AC microgrid; the DC microgrid is provided with a DC side VDG control module for controlling the DC converter to adjust the DC power output by collecting internal voltage and current signals; the AC microgrid is provided with an AC side VSG control module for controlling the on and off of the switch tube of the three-phase full-bridge inverter by collecting internal voltage and current signals to adjust the AC three-phase voltage output; the interconnected converter is provided with an interconnected converter control module for connecting the DC bus and the AC bus through a bidirectional interface converter, and adjusting the energy balance within the subnet through bidirectional energy flow.

[0005] As a further technical solution, the DC side VDG control module includes a DC voltage bus regulation module, a virtual DC generator control module, a DC droop control module and a current tracking control module;

[0006] The DC droop control module is used to calculate the active power inside the DC microgrid by collecting the DC bus voltage and current, and allocate the bus reference voltage inside the DC microgrid according to the droop coefficient based on the difference between the calculated active power and the set active power of the DC microgrid;

[0007] The DC voltage bus regulation module is used to adjust the virtual DC generator control voltage by collecting the voltage of the DC bus, combining the bus reference voltage calculated by DC droop, and accumulating it through the PI regulator;

[0008] The virtual DC generator control module is used to obtain mechanical power by multiplying the current value by the port voltage given value, and then obtain mechanical torque after dividing it by the rated speed of the DC motor, and then obtain the port current given value after calculating the DC motor mechanical equation and the electromotive force balance equation;

[0009] The current tracking control module is used to control the virtual DC generator by controlling the switch tube of the DC converter.

[0010] As a further technical solution, the AC side VSG control module includes a power calculation module, a virtual rotor module including primary frequency modulation, a virtual excitation module including primary voltage regulation, a dual closed-loop control module and a first PWM modulation module;

[0011] The power calculation module is used to calculate the instantaneous power of the AC microgrid by collecting the three-phase AC voltage and current inverted by the DC power supply, and construct a steady-state AC microgrid output power;

[0012] The virtual rotor module with primary frequency modulation is used to collect the angular frequency of the three-phase AC power between the filter capacitor and the load, combine it with the difference with the rated frequency, allocate the adjustment power, and obtain the electromagnetic power in combination with the set AC microgrid output power, and obtain the deviation power by the frequency difference through the active droop control law, and then change the mechanical power to adjust its output frequency;

[0013] The virtual excitation module with primary voltage regulation is used to simulate the excitation regulation function of the synchronous motor, and adjusts the terminal voltage and reactive power output thereof by adjusting the excitation current;

[0014] The dual closed-loop control module includes a voltage outer loop and a current inner loop. The voltage outer loop is used to compare the actual output voltage value of the three-phase AC side with a given reference voltage value, and the error value between the two is passed through a PI regulator, and the error value is output as the expected amplitude of the current inner loop; the current inner loop is used to track the grid side voltage phase according to the static error;

[0015] The first PWM modulation module obtains the switch tube duty cycle signal of the three-phase full-bridge inverter based on the comparison between the target three-phase voltage signal and the carrier signal, and outputs it to the three-phase full-bridge inverter to adjust the output terminal voltage of the three-phase full-bridge inverter.

[0016] As a further technical solution, the interconnected converter control module includes a bus normalization module, a dead zone adaptive control module, a reference power generation module, a feedforward control module and a second PWM modulation module;

[0017] The bus standardization module is used to standardize the DC microgrid bus voltage and the AC microgrid bus frequency;

[0018] The dead zone adaptive control module is used to determine whether the per-unit deviation of the AC / DC microgrid exceeds the limit, and start the interconnected converter control when the per-unit deviation exceeds the limit;

[0019] The reference power generation module is used to compare the reference active power after PI adjustment with the actual active power to generate the reference active power;

[0020] The feedforward control module is used to obtain a voltage command reference by feedforward control of the reference power;

[0021] The second PWM modulation module is used to generate a switch tube signal based on a voltage command reference to adjust the output voltage of the interconnected converter and thus control its power change.

[0022] As a further technical solution, the AC microgrid further includes a circuit breaker for controlling the interconnection of the AC and DC microgrids. When the circuit breaker is in an open state, the AC and DC microgrids operate in an island state.

[0023] According to one aspect of the present invention, a method for autonomous control of an AC-DC hybrid microgrid interconnected converter based on VSG-VDG is provided, comprising:

[0024] Construct a DC side VDG control module to control the DC-DC converter to adjust the DC power output by collecting internal voltage and current signals; construct an AC measurement VSG control module to control the on / off of the three-phase full-bridge inverter to adjust the AC three-phase voltage output by collecting internal voltage and current signals; construct an interconnected converter control module to connect the DC bus and the AC bus through a DC / AC bidirectional interface converter, which adjusts the energy balance in the subnet through bidirectional energy flow;

[0025] When the AC and DC microgrids are each stable at the steady-state equilibrium point, the DC microgrid uses the droop law to allocate power and bus voltage, and the AC grid uses the droop law to allocate power and bus frequency;

[0026] After the dual droop control is completed, the bus voltage of the DC microgrid and the bus frequency of the AC microgrid are normalized through the interconnected converter control module to determine whether the per-unit value deviation of the AC / DC microgrid is over-limit, and the interconnected converter control is started when the per-unit value deviation is over-limit, so that the AC / DC microgrids can each stabilize at a new steady-state equilibrium point.

[0027] As a further technical solution, in a DC microgrid, the output droop characteristics show dynamic characteristics consistent with those of a DC motor; in an AC microgrid, the active-frequency link obtains the deviation power through the active droop control law from the frequency difference, and then changes the mechanical power to adjust its output frequency; the reactive-voltage control of VSG control is used to simulate the excitation regulation of a synchronous motor, and adjusts its terminal voltage and reactive output by adjusting the excitation current.

[0028] As a further technical solution, in a DC microgrid, a switch tube signal of a DC converter is generated through PWM modulation according to a current command to control the DC power supply output; in an AC microgrid, a voltage reference value of a voltage loop is obtained according to the amplitude and voltage phase of a voltage command, and after double closed-loop control, a voltage command reference is obtained, and the voltage command reference is modulated by PWM to generate a switch tube signal to control the output voltage of the output terminal.

[0029] As a further technical solution, the method further includes:

[0030] The bus voltage of the DC microgrid and the bus frequency of the AC microgrid are normalized to per unit, and it is determined whether the per unit deviation of the AC and DC microgrids exceeds the limit, and the interconnected converter control is started when the per unit deviation exceeds the limit;

[0031] The reference active power is compared with the actual active power after PI adjustment to generate the reference active power, and the total reference power is obtained by combining the reference reactive power;

[0032] The reference power is fed-forward controlled to obtain a voltage command reference;

[0033] The switch tube signal is generated based on the voltage command reference to adjust the output voltage of the interconnected converter and control its power change.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. The AC / DC microgrid adaptive autonomous control device and method based on the virtual synchronous generator on the AC side and the virtual DC motor on the DC side proposed in the present invention can enhance the robustness of the AC / DC microgrid system without adding additional communication devices, can realize offline control, and has a simple and fast algorithm, which improves the system's ability to cope with faults under extreme conditions and the stability of the system.

[0036] 2. By utilizing the inertia and damping characteristics of VSG / VDG similar to those of synchronous generators, the three-phase voltage amplitude and phase output on the AC side and the single-phase bus voltage on the DC side will not change suddenly at the switching moment. When additional disturbances occur in the system, there is no need to modify the control parameters of the virtual synchronous machine. The disturbance of a single system has been absorbed within itself. At the same time, the damping effect of the interconnected converter further isolates high-frequency disturbances and prevents oscillations from being transmitted within the microgrid.

[0037] 3. After the dual droop control is completed, the AC and DC microgrids will each stabilize at a new steady-state equilibrium point. When a new disturbance occurs, the control module will autonomously determine whether to restart and reach a new working state so that the power it transmits can match the new system, ensuring the long-term stability of the hybrid system. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, a brief introduction is given below to the drawings used 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 work.

[0039] Figure 1 It is a schematic diagram of the overall framework of the control device provided by an embodiment of the present invention.

[0040] Figure 2 It is a waveform diagram of the bus frequency of an AC microgrid simulated by a sudden increase in line impedance of an AC / DC hybrid system provided by an embodiment of the present invention.

[0041] Figure 3 It is a waveform diagram of the DC microgrid bus voltage simulated by the sudden increase of line impedance of the AC / DC hybrid system provided by the embodiment of the present invention. DETAILED DESCRIPTION

[0042] It should be noted that:

[0043] The terms "including" and "having" and any variations thereof in the specification and claims of the present invention and the above-mentioned drawings are intended to cover non-exclusive inclusions, for example, a process, method, system, product or apparatus comprising a series of steps or units is not necessarily limited to the steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to these processes, methods, products or apparatuses.

[0044] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, 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 described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. In addition, the technical features in the various embodiments or single embodiments provided by the present invention are arbitrarily combined with each other to form a new technical solution. This combination is not restricted by the sequence of steps and / or the structural composition mode, but must be based on the ability of ordinary technicians in this field to achieve. When the combination of technical solutions is contradictory or cannot be achieved, it should be considered that this combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0045] The present invention provides an adaptive autonomous control device and method for an AC / DC microgrid based on a virtual synchronous generator VSG on the AC side and a virtual DC motor VDG on the DC side. The device and method do not require complex communication and are simpler to control. The method provides active support capabilities for a new power system with microgrids as an important component, and can quickly achieve power mutual assistance between AC / DC microgrids and the effect of smoothing disturbances between systems. After the autonomous (double droop) control is completed, the AC / DC microgrids will each stabilize at a new steady-state equilibrium point. If a new disturbance occurs, the interconnected converter control module will autonomously determine whether to restart. If the startup standard is met, a new working state will be reached so that the power transmitted by the microgrids can fit the new system.

[0046] Example 1

[0047] The present embodiment provides an AC / DC microgrid adaptive autonomous control device based on an AC-side virtual synchronous generator and a DC-side virtual DC motor. The present embodiment is described in detail below with reference to the accompanying drawings.

[0048] like Figure 1 The overall framework of the control device shown in the figure, the control device includes a medium DC power supply U1, a DC load, a single-phase LCL filter, a three-phase full-bridge inverter, an interconnected converter, a three-phase LCL filter, a circuit breaker, an AC load, an interconnected converter and an AC measurement VSG control module, a DC side VDG control module, and an interconnected converter control module.

[0049] The three-phase full-bridge inverter includes three sets of switch tube components connected in parallel, which converts DC power into three-phase AC power of the AC microgrid by controlling the corresponding switch tubes. The interconnected converter includes three sets of switch tube components connected in parallel, which balances the power between the DC microgrid and the AC microgrid by controlling the corresponding switch tubes. The single-phase LCL filter includes an inductor L f-dc and resistor R f-dc, the three-phase LCL filter includes an inductor L f-ac , resistor R f-ac and capacitor C f-ac The circuit breaker is used to control the on and off of the three-phase microgrid and the interconnected converter. When it is in the off state, the AC and DC microgrids each operate in an island state.

[0050] The DC microgrid includes a DC power supply U1, a single-phase LCL filter, and a DC load, which is connected to the interconnected converter through a DC bus and transmits power through it. The DC power supply U1 provides energy for the DC microgrid. The DC power supply outputs a single-phase DC voltage with a fixed voltage level. Its output is eliminated by a single-phase LCL filter module to retain the main fundamental wave and ensure continuous control of the power supply on the DC load. The DC microgrid has low inertia, weak damping, and weak self-regulation ability. It generally does not work alone and does not have a circuit breaker.

[0051] The VDG control module includes a DC voltage bus regulation module, a virtual DC generator control module, a DC droop control module and a current tracking control module.

[0052] The DC droop control module calculates the active power P inside the DC microgrid by collecting the DC bus voltage U2 and current I2. dc , according to the DC microgrid active power P r-dc0 The difference is used to distribute the bus reference voltage inside the DC microgrid according to the droop coefficient.

[0053] The DC voltage bus regulation module collects the voltage U2 of the DC bus and compares it with the voltage U2 calculated by the DC droop. r-dc , after being accumulated by PI regulator 1, the virtual DC generator control voltage is adjusted.

[0054] In the virtual DC generator control module, the current value I2 and the port voltage given value U r-dc The mechanical power is obtained by multiplying and then divided by the rated speed of the DC motor to obtain the mechanical torque T m-dc ; Then the port current given value I is obtained by calculating the DC motor mechanical equation and the electromotive force balance equation ref Inertia time constant H and AC side damping coefficient D ac It is an adjustable control parameter in virtual DC motor control and is selected according to the actual power supply and load response time.

[0055] The current tracking control module controls the switch tube of the DC converter through the control link and the modulation link to achieve the control purpose of the virtual DC generator.

[0056] The VSG control module includes a virtual rotor module including primary frequency modulation, a virtual excitation module including primary voltage regulation, a dual closed-loop control 1 module, a power calculation module and a PWM modulation 1 module.

[0057] The power calculation module collects the DC power supply U through the three-phase LCL filter module. ac The three-phase AC voltage u0 and current i0 are inverted to calculate the instantaneous power of the AC microgrid, and then the steady-state AC microgrid output power P is constructed through a low-pass filter. VSG , Q VSG .

[0058] The virtual rotor module with primary frequency modulation collects the angular frequency w of the three-phase AC power between the filter capacitor and the load, and calculates the angular frequency w according to the rated frequency. The difference between the frequency difference and the adjusted power is allocated. The electromagnetic power p is obtained by combining the set AC microgrid output power. The deviation power is obtained by the active droop control law, and then the mechanical power P is changed. m To adjust its output frequency.

[0059] The virtual excitation module with primary voltage regulation simulates the excitation regulation function of the synchronous motor and adjusts the terminal voltage and reactive power output thereof by adjusting the excitation current.

[0060] The dual closed-loop control 1 module consists of a voltage outer loop and a current inner loop. The voltage outer loop compares the actual three-phase output voltage value of the AC side with the given reference voltage value, passes the error value between the two through a PI regulator, and outputs the error value as the expected amplitude of the current inner loop; the current inner loop tracks the grid side voltage phase according to the static error, thereby achieving the effect of suppressing current distortion harmonics and improving the dynamic performance of the system.

[0061] The PWM modulation 1 module obtains the switch tube duty cycle signal of the three-phase full-bridge inverter based on the high and low comparison of the target three-phase voltage signal and the carrier signal, and outputs it to the three-phase full-bridge inverter to adjust the output terminal voltage of the three-phase full-bridge inverter.

[0062] The interconnected converter control module connects the DC bus and the AC bus through a DC / AC bidirectional interface converter. The bidirectional interface converter adjusts the energy balance in the subnet through bidirectional energy flow, and includes a bus standardization module, a dead zone adaptive control module, a reference power generation module, a feedforward control module and a PWM modulation 2 module.

[0063] The bus standardization module collects the DC microgrid bus voltage U2 and the AC microgrid bus frequency f, and completes averaging them to a value within -1 to 1 according to the maximum allowable deviation, so as to facilitate the DC voltage and the AC voltage to be of the same order of magnitude, so that they can be compared with each other and reflect the current operating status of the microgrid.

[0064] The dead zone adaptive control module determines whether the per-unit value deviation of the AC / DC microgrid is over the limit. If the per-unit value difference is too small, the disturbance is considered too weak and does not affect the steady-state operating point, and the interconnected converter control is not started; and the power mutual assistance priority of the AC / DC microgrid can be manually adjusted according to the weight coefficient to give priority to maintaining the bus amplitude of a special area in an emergency.

[0065] The reference power generation module generates a reference active power P according to the output reference active power P of the dead zone adaptive control module. ref , after passing through PI regulator 3, it is compared with the actual active power emitted by the interconnected converter to generate a reference active power.

[0066] The feedforward control module obtains the corresponding dq axis reference current according to the reference power, and performs feedforward compensation on the output after the PI controller is adjusted according to the line inductance through feedforward decoupling control to obtain the dq axis command voltage, and then obtains the three-phase command voltage of the interconnected converter through inverse dq transformation. The feedforward control eliminates the influence of the coupling term, realizes the independent control of the d axis and the q axis, avoids the influence of the coupling current on the control performance, improves the control accuracy, and also enhances the stability and response speed of the system.

[0067] The PWM modulation 2 module obtains the switch tube duty cycle signal of the three-phase full-bridge inverter based on the comparison of the three-phase voltage signal of the interconnected converter instruction and the carrier signal, and outputs it to the interconnected converter to adjust the output voltage of the interconnected converter.

[0068] The embodiments of the present invention overcome the shortcomings of traditional dual droop control, such as sensitive response, frequent control signal activation, and easy propagation of high-frequency oscillations within each microgrid, and can achieve energy mutual assistance between AC / DC hybrid microgrids without communication.

[0069] Example 2

[0070] On the basis of Example 1, this embodiment provides an adaptive dual droop control method for an AC / DC microgrid based on an AC-side virtual synchronous generator and a DC-side virtual DC motor, the control method comprising:

[0071] Step 1, collect the bus voltage and current in the DC microgrid, collect the bus voltage and current in the AC microgrid, after normalization, pass through the dead zone adaptive control module to adjust the calculated response output, and finally obtain the reference output power of the interconnected converter through the PI integrator. After the internal loads of each microgrid are stably connected, the DC microgrid adopts the droop rule to allocate power and bus voltage, and the AC grid allocates power and bus frequency according to the droop rule. The allocation rule is shown in formula (1). Collect the voltage U2 and current I2 between the bus and the filter inductor in the DC microgrid, and collect the bus voltage u0 and current i0 between the load and the filter capacitor in the AC microgrid. After power calculation, the active power P2 of the DC microgrid and the active power P of the AC microgrid are obtained. VSG , reactive power Q VSG The AC microgrid frequency f is obtained by applying a phase-locked loop to the three-phase voltage.

[0072]

[0073] Where f0 represents the rated frequency of the AC microgrid, U0 represents the rated voltage of the DC microgrid, and K f is the primary frequency regulation droop coefficient of the AC microgrid, K f-dc is the primary voltage regulation droop coefficient of the DC microgrid, P r Represents the active reference power of the AC microgrid, P r-dc Represents the DC microgrid reference power.

[0074] Step 2: In the DC microgrid, the droop characteristics of its output show dynamic characteristics consistent with those of the DC motor, and its internal characteristics are shown in equations (2) and (3).

[0075] E=U m +IR a =C T φw dc (2)

[0076]

[0077] Formula (2) represents the electromotive force balance equation of the DC motor armature circuit, where E is the armature electromotive force of the DC motor, C T is the torque coefficient, φ is the magnetic flux, w dc is the mechanical angular velocity of the DC motor, is the mechanical angular velocity of the DC motor, U m is the terminal voltage; R a is the total equivalent resistance of the armature circuit. Equation (3) represents the mechanical rotation equation of the DC generator, where T m-dc and T e-dc are the electromagnetic and mechanical torques of the DC generator, is the rated mechanical angular velocity of the DC motor.

[0078] In the AC microgrid, the active-frequency link obtains the deviation power by the active droop control law, and then changes the mechanical power P m To adjust its output frequency; the reactive power-voltage control of VSG control is used to simulate the excitation regulation of the synchronous motor, and adjusts its terminal voltage and reactive power output by adjusting the excitation current. Its active power-frequency link is shown in formula (4):

[0079]

[0080] Where δ is the voltage phase output by the VSG control module, ω ac is the angular velocity of the virtual synchronous machine, P m is the virtual synchronous motor mechanical power, P e Virtual synchronous motor electromagnetic power, J is the rotor inertia, D ac is the damping coefficient of the virtual synchronous machine on the AC side.

[0081] Step 3: In the DC microgrid, according to the current command I ref , through PWM modulation, control the switch tube of the DC-DC converter to turn off. In the AC microgrid, according to the amplitude of the voltage command U V And the voltage phase δ, the voltage reference value of the voltage loop is obtained, and after the double closed-loop control 1, the voltage command reference is obtained. The time scale of the general current loop design is 0.01s. Since the tracking speed of the current inner loop is much faster than that of the power outer loop, in order to simplify the calculation, it can be regarded as a first-order inertia link, and the transfer function can be expressed as formula (5):

[0082]

[0083] In the formula, k p4 , k i4 is the proportional link and integral link coefficient of the PI controller of the voltage loop, T i is the time constant of the current loop, which is determined by the current loop PI parameters.

[0084] The voltage modulation wave after the double closed loop is modulated by PWM to generate a switch tube signal S1, which is input into the three-phase full-bridge inverter to adjust the inverter output voltage.

[0085] Step 4: When AC / DC microgrid power mutual assistance is required, the interconnected converter is started, and the voltage and current at the endpoints of the interconnected converter are collected to calculate the active power P on the interconnected converter side. VSG , reactive power Q VSG Collect and calculate the bus voltage per unit value f in the DC microgrid pu , AC microgrid bus voltage per unit value U dc.pu, as shown in formula (6),

[0086]

[0087] In the formula, f max 、f min are the maximum and minimum frequencies allowed by the AC sub-microgrid respectively; U dcmax , U dcmin are the maximum and minimum voltages allowed by the DC sub-microgrid respectively.

[0088] The difference is controlled by dead zone to obtain the active power difference that needs to be responded, as shown in formula (7).

[0089]

[0090] Where K is the deviation proportional coefficient, h is the dead zone threshold, and the larger the dead zone threshold, the smaller the minimum response deviation of the interconnected converter.

[0091] After the difference is accumulated by the PI regulator, the difference is calculated with the active power on the interconnected converter side to obtain the active power reference value for adjustment, and the reactive power of the interconnected converter is used as the reactive power reference value for adjustment, as shown in formula (8).

[0092]

[0093] The power reference value is adjusted after feedforward control to obtain the voltage command reference As shown in formula (9).

[0094]

[0095] In the formula, is the d-axis component of the command voltage, is the q-axis component of the command voltage, V d-ILC is the d-axis component of the three-phase voltage on the interconnected converter side after dq transformation, V q-ILC is the q-axis component of the three-phase voltage on the interconnected converter side after dq transformation, k p5 k i5 is the PI regulator 5 parameter for feedforward control, I d-ILC is the d-axis component of the three-phase current on the interconnected converter side after dq transformation, I q-ILC is the q-axis component of the three-phase current on the interconnected converter side after dq transformation, L ILC is the filter inductance of the interconnected converter, and w is the three-phase voltage angular frequency on the interconnected converter side.

[0096] The voltage command reference is transformed by inverse dq to obtain a three-phase voltage command reference value, and a switch tube signal S2 is generated through PWM modulation 2 to adjust the output voltage of the interconnected converter and control its power change.

[0097] The adaptive dual droop control module is also used for common disturbance conditions in other types of power systems. Once the disturbance acts on the AC / DC microgrid, causing its frequency and voltage to change, it will cause its corresponding per-unit value to change. When the generated deviation value is higher than the dead zone boundary value, the dual droop control algorithm is started to adjust the power output of the interconnected converter. Since the interconnected converter plays a connecting role, when it absorbs the active power of the AC microgrid, it will inevitably provide corresponding active power to the DC microgrid, that is, when the per-unit value of the AC microgrid frequency increases, the per-unit value of the DC microgrid voltage will inevitably decrease, and the difference between the two will gradually tend to zero. When the dual droop algorithm takes effect, due to the effect of a large number of inductors and capacitors in the system, the system power often has a small oscillation, and the proposed virtual synchronous machine algorithm on both sides of the AC and DC simulates the inertia and damping of the rotor. The power oscillation will not sensitively change the bus frequency and voltage due to their respective obstruction, thereby reducing the possibility of the bus per-unit value jumping, that is, the local oscillation generated by the disturbance will not be transmitted through the interconnected converter, thereby enhancing the robustness of the entire system.

[0098] Example 3

[0099] On the basis of Examples 1 and 2, in order to describe the beneficial effects of the present invention in detail, this example is explained through simulation experiments. An isolated AC / DC hybrid microgrid model is built, where the rated frequency of the AC microgrid is 50Hz, the rated voltage of the DC microgrid is 700V, the active load is a resistive load, and the reactive load is a resistive inductive load. At 1.4s, the line AC filter inductance suddenly increases (0.2pu→0.5pu), and the following is obtained: Figure 2 The waveform diagram of the frequency and value changing with time and the Figure 3 A waveform graph showing the voltage and value changing over time.

[0100] When the line parameter impedance increases, the bus frequency and voltage of the AC / DC microgrid both oscillate to a certain extent. The introduction of the VSG control module on the AC side can effectively improve the overshoot of the frequency oscillation, while the VDG control technology on the DC side mainly enables the frequency to approach the rated value after the final operating condition change faster, but due to its accompanying inertia, it will cause it to oscillate when approaching the rated value. Since the bus voltage of the DC microgrid is more sensitive, the addition of the proposed control strategy can reduce the new short-amplitude oscillation caused by approaching the rated value too quickly due to the constant filter value, and further reduce the adjustment time of the entire system. Compared with the traditional double droop control strategy, the proposed adaptive double droop control strategy takes into account the advantages of rapid response on the DC side and strong disturbance suppression ability on the AC side, significantly improving the robustness of the system.

[0101] After the double droop algorithm balances the disturbance of the system, the system reaches a steady state, and the bus voltage frequency per unit value on both sides is close to the same. At this time, the voltage standardization module no longer has an output, the interconnected converter works in a constant power state, and the power quality is stable. At this time, if the power grid encounters disturbances such as sudden load changes, under the control of the droop effect, the bus voltage / frequency will deviate from the original balance point, and reach a new steady-state point through adaptive double droop control. The output of the primary voltage and frequency regulation on the AC side and the virtual armature output on the DC side are adaptively adjusted according to the voltage and frequency changes of the power grid. Due to the damping effect inside each microgrid, the high-frequency disturbance caused by the disturbance is basically digested internally, and the low-frequency disturbance will only respond to the part higher than the dead zone control, and the system will be more robust.

[0102] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware or any combination thereof. When the use is implemented in whole or in part in the form of a computer program product, the computer program product includes one or more computer instructions. When the computer program instructions are loaded or executed on a computer, the process or function described in the embodiment of the present invention is generated in whole or in part. The computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions may be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions may be transmitted from one website site, computer, server or data center by wired (e.g., coaxial cable, optical fiber, digital subscriber line (DSL) or wireless (e.g., infrared, wireless, microwave, etc.) mode) to another website site, computer, server or data center. The computer-readable storage medium may be any available medium that a computer can access or a data storage device such as a server or data center that includes one or more available media integrated. The available medium may be a magnetic medium (e.g., a floppy disk, a hard disk, a tape), an optical medium (e.g., a DVD), or a semiconductor medium (e.g., a solid-state hard disk Solid State Disk (SSD)), etc.

[0103] 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 aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the technical solutions of the embodiments of the present invention.

Claims

1. The VSG-VDG-based AC-DC hybrid microgrid interconnected converter autonomous control device is characterized by: It includes a DC microgrid, an AC microgrid and an interconnected converter connecting the DC microgrid and the AC microgrid; the DC microgrid is configured with a DC side VDG control module, which is used to control the DC converter to adjust the DC power output by collecting internal voltage and current signals; the AC microgrid is configured with an AC side VSG control module, which is used to control the on and off of the switch tube of the three-phase full-bridge inverter by collecting internal voltage and current signals to adjust the AC three-phase voltage output; the interconnected converter is configured with an interconnected converter control module, which is used to connect the DC bus and the AC bus through a bidirectional interface converter, and adjust the energy balance in the subnet through bidirectional energy flow.

2. The VSG-VDG-based AC-DC hybrid microgrid interconnected converter autonomous control device according to claim 1 is characterized in that: The DC side VDG control module includes a DC voltage bus regulation module, a virtual DC generator control module, a DC droop control module and a current tracking control module; The DC droop control module is used to calculate the active power inside the DC microgrid by collecting the DC bus voltage and current, and allocate the bus reference voltage inside the DC microgrid according to the droop coefficient based on the difference between the calculated active power and the set active power of the DC microgrid; The DC voltage bus regulation module is used to adjust the virtual DC generator control voltage by collecting the voltage of the DC bus, combining the bus reference voltage calculated by DC droop, and accumulating it through the PI regulator; The virtual DC generator control module is used to obtain mechanical power by multiplying the current value by the port voltage given value, and then obtain mechanical torque after dividing it by the rated speed of the DC motor, and then obtain the port current given value after calculating the DC motor mechanical equation and the electromotive force balance equation; The current tracking control module is used to control the virtual DC generator by controlling the switch tube of the DC converter.

3. The AC / DC hybrid microgrid interconnected converter autonomous control device based on VSG-VDG according to claim 1 is characterized in that: The AC side VSG control module includes a power calculation module, a virtual rotor module including primary frequency modulation, a virtual excitation module including primary voltage regulation, a dual closed-loop control module and a first PWM modulation module; The power calculation module is used to calculate the instantaneous power of the AC microgrid by collecting the three-phase AC voltage and current inverted by the DC power supply, and construct a steady-state AC microgrid output power; The virtual rotor module with primary frequency modulation is used to collect the angular frequency of the three-phase AC power between the filter capacitor and the load, combine it with the difference with the rated frequency, allocate the adjustment power, and obtain the electromagnetic power in combination with the set AC microgrid output power, and obtain the deviation power by the frequency difference through the active droop control law, and then change the mechanical power to adjust its output frequency; The virtual excitation module with primary voltage regulation is used to simulate the excitation regulation function of the synchronous motor, and adjusts the terminal voltage and reactive power output thereof by adjusting the excitation current; The dual closed-loop control module includes a voltage outer loop and a current inner loop. The voltage outer loop is used to compare the actual output voltage value of the three-phase AC side with a given reference voltage value, and the error value between the two is passed through a PI regulator, and the error value is output as the expected amplitude of the current inner loop; the current inner loop is used to track the grid side voltage phase according to the static error; The first PWM modulation module obtains the switch tube duty cycle signal of the three-phase full-bridge inverter based on the comparison between the target three-phase voltage signal and the carrier signal, and outputs it to the three-phase full-bridge inverter to adjust the output terminal voltage of the three-phase full-bridge inverter.

4. The VSG-VDG-based AC-DC hybrid microgrid interconnected converter autonomous control device according to claim 1 is characterized in that: The interconnected converter control module includes a bus normalization module, a dead zone adaptive control module, a reference power generation module, a feedforward control module and a second PWM modulation module; The bus standardization module is used to standardize the DC microgrid bus voltage and the AC microgrid bus frequency; The dead zone adaptive control module is used to determine whether the per-unit deviation of the AC / DC microgrid exceeds the limit, and start the interconnected converter control when the per-unit deviation exceeds the limit; The reference power generation module is used to compare the reference active power after PI adjustment with the actual active power to generate the reference active power; The feedforward control module is used to obtain a voltage command reference by feedforward control of the reference power; The second PWM modulation module is used to generate a switch tube signal based on a voltage command reference to adjust the output voltage of the interconnected converter and thus control its power change.

5. The VSG-VDG-based AC-DC hybrid microgrid interconnected converter autonomous control device according to claim 1, characterized in that: The AC microgrid also includes a circuit breaker for controlling the interconnection of the AC and DC microgrids. When the circuit breaker is in an open state, the AC and DC microgrids operate in an island state.

6. The autonomous control method of AC-DC hybrid microgrid interconnected converter based on VSG-VDG is characterized by: include: Construct a DC side VDG control module to control the DC-DC converter to adjust the DC power output by collecting internal voltage and current signals; construct an AC measurement VSG control module to control the on / off of the three-phase full-bridge inverter to adjust the AC three-phase voltage output by collecting internal voltage and current signals; construct an interconnected converter control module to connect the DC bus and the AC bus through a DC / AC bidirectional interface converter, which adjusts the energy balance in the subnet through bidirectional energy flow; When the AC and DC microgrids are each stable at the steady-state equilibrium point, the DC microgrid uses the droop law to allocate power and bus voltage, and the AC grid uses the droop law to allocate power and bus frequency; After the dual droop control is completed, the bus voltage of the DC microgrid and the bus frequency of the AC microgrid are normalized through the interconnected converter control module to determine whether the per-unit value deviation of the AC / DC microgrid is over-limit, and the interconnected converter control is started when the per-unit value deviation is over-limit, so that the AC / DC microgrids can each stabilize at a new steady-state equilibrium point.

7. The autonomous control method of the AC-DC hybrid microgrid interconnected converter based on VSG-VDG according to claim 6 is characterized in that: In a DC microgrid, the droop characteristics of the output show dynamic characteristics consistent with those of the DC motor; In the AC microgrid, the active-frequency link obtains the deviation power by the active droop control law, and then changes the mechanical power to adjust its output frequency. The reactive power-voltage control of VSG control is used to simulate the excitation regulation of synchronous motors, and to adjust the terminal voltage and reactive power output by adjusting the excitation current.

8. The autonomous control method of the AC-DC hybrid microgrid interconnected converter based on VSG-VDG according to claim 6 is characterized in that: In the DC microgrid, according to the current command, through PWM modulation, the switch tube signal of the DC converter is generated to control the DC power supply output; In an AC microgrid, the voltage reference value of the voltage loop is obtained according to the amplitude and voltage phase of the voltage command. After double closed-loop control, the voltage command reference is obtained. The voltage command reference is modulated by PWM to generate a switch tube signal to control the output voltage of the output terminal.

9. The autonomous control method of the AC-DC hybrid microgrid interconnected converter based on VSG-VDG according to claim 6 is characterized in that: The method further comprises: The bus voltage of the DC microgrid and the bus frequency of the AC microgrid are normalized to per unit, and it is determined whether the per unit deviation of the AC and DC microgrids exceeds the limit, and the interconnected converter control is started when the per unit deviation exceeds the limit; The reference active power is compared with the actual active power after PI adjustment to generate the reference active power, and the total reference power is obtained by combining the reference reactive power; The reference power is fed-forward controlled to obtain a voltage command reference; The switch tube signal is generated based on the voltage command reference to adjust the output voltage of the interconnected converter and control its power change.

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