A low communication three-level dc microgrid robust distributed control method and system

Abstract

The application discloses a low-communication three-level direct-current microgrid robust distributed control method and system, adopts a sparse communication cooperative control network layer and a converter local control layer, the converter local control layer is arranged between the sparse communication cooperative control network layer and a multi-node direct-current microgrid physical layer, each consistency distributed secondary controller in the sparse communication cooperative control network layer carries out limited information interaction with adjacent consistency distributed secondary controllers according to a preset communication topology, meanwhile, the communication topology is a non-directional connected communication topology, and it is unnecessary to establish a full-connection communication relationship with all the consistency distributed secondary controllers, and only normalized output currents and control state information are exchanged between the adjacent consistency distributed secondary controllers, so as to realize the consistency distributed secondary control function. Therefore, the number of required communication links and the communication data volume are reduced.

Description

Technical Field

[0001] This invention belongs to the field of power electronic converter and DC microgrid control technology, specifically relating to a robust distributed control method and system for a low-communication three-level DC microgrid. Background Technology

[0002] With the development of new energy power generation, energy storage systems, and DC loads, DC microgrids have attracted widespread attention due to their advantages such as fewer energy conversion stages, high operating efficiency, and ease of distributed power source integration. In multi-node DC microgrids, multiple distributed converter units are connected to their respective DC common coupling points and interconnected through DC distribution lines. To ensure stable system operation, it is necessary to achieve voltage balance among DC nodes and for each converter to share the load current according to its rated capacity. Existing secondary control methods for DC microgrids mainly include centralized control, decentralized control, and distributed collaborative control. Among them, centralized control relies on a central controller and is subject to single-point failure risk; decentralized control has lower communication requirements but struggles to achieve global voltage balance and precise current sharing; distributed collaborative control achieves global control objectives through information exchange between adjacent nodes, exhibiting better scalability and reliability.

[0003] However, most existing consensus-based distributed secondary control methods typically require adjacent converters to exchange information such as output current, common coupling point voltage, and average voltage estimates. As the number of nodes increases, the communication links and data volume also increase, easily introducing problems such as communication delays, data loss, communication failures, and DDoS attacks, thus affecting system stability and robustness. Furthermore, existing methods mostly focus on DC-DC converter interface-type DC microgrids, while research on constructing DC microgrids using three-phase three-level AC-DC converters is extremely limited. This involves not only DC-side voltage regulation and current distribution but also AC-side current control, modulation command generation, and midpoint potential balancing. Of course, the modulation technology used in converters employs a scheme that injects a zero-sequence voltage component into the modulation wave of sinusoidal pulse width modulation (SPWM), making it equivalent to SVPWM (space vector pulse width modulation). Compared to traditional SVPWM, SPWM based on zero-sequence component injection simplifies the calculation process and improves DC bus voltage utilization. Summary of the Invention

[0004] The technical problem to be solved by this invention is how to construct a distributed secondary control method with low communication requirements for a multi-node DC microgrid built with multiple three-phase three-level converters.

[0005] This invention solves the above-mentioned technical problems through the following technical means: a robust distributed control method for a low-communication three-level DC microgrid, which adopts a sparse communication cooperative control network layer and a converter local control layer. The converter local control layer is placed between the sparse communication cooperative control network layer and the physical layer of the multi-node DC microgrid. In the sparse communication cooperative control network layer, each consistent distributed secondary controller interacts with adjacent consistent distributed secondary controllers according to a preset communication topology. At the same time, the communication topology is an undirected connected communication topology, and it is not necessary to establish a fully connected communication relationship with all consistent distributed secondary controllers. Adjacent consistent distributed secondary controllers only exchange normalized output current and control status information to realize the consistent distributed secondary control function.

[0006] As a further optimization solution, the selected communication topology adopts an undirected connected graph corresponding to the DC microgrid topology.

[0007] As a further optimized technical solution, the consistent distributed secondary controller includes a current distribution layer, a voltage balancing layer, and a state coordination layer for the DC microgrid. The current distribution layer is used to ensure that each converter distributes current equally according to its rated current ratio. The voltage balancing layer, based on the deviation between the point of common coupling voltage and the reference voltage, and in conjunction with the coordination state generated by the current distribution layer, restores the voltage of each node in the DC microgrid to near the reference voltage under a weighted average. The state coordination layer, based on the control state variables, achieves dynamic coupling between the current distribution layer and the voltage balancing layer, and then further calculates the coordination control law through the current distribution layer, the voltage balancing layer, and the state coordination layer. Finally, the coordination control law is output to the current command generation layer to further complete the overall function of the consistent distributed secondary controller.

[0008] As a further optimized technical solution, the current command generation layer unifies the distributed secondary control function with the voltage outer loop of the primary control of the three-phase three-level converter, so that the output of the secondary control can be directly converted into the dq current inner loop reference command.

[0009] As a further optimized technical solution, the converter local control layer includes multiple converter local controllers. Each converter local controller receives the secondary coordination quantity and reference current information output by the corresponding upper-layer sparse communication cooperative control network layer's consistent distributed secondary controller current command generation layer.

[0010] As a further optimized technical solution, the converter local controller receives the current command value output from the consistent distributed secondary controller and synchronously samples local operating information, including AC side voltage and current, DC output voltage and current, and DC side capacitor voltage. Then, it further completes dq current inner loop PI control, midpoint potential control, and modulation signal generation, and outputs drive pulse signals through SPWM modulation based on zero-sequence component injection to complete the control of the three-phase three-level converter itself.

[0011] As a further optimized technical solution, in the physical layer of the multi-node DC microgrid, the DC node voltage of the i-th PCC point is... The output current of the i-th three-phase three-level converter is The consistent distributed secondary controller current command generation layer is based on the DC node voltage. Output current Reference voltage and the law of coordination and control Output d-axis current reference value And set the q-axis current reference value to 0.

[0012] As a further optimized technical solution, the first i A three-phase three-level converter obtains the dq-axis modulation reference voltage through PI control of the dq current inner loop. This voltage is then converted via dq / abc conversion to obtain the three-phase modulation reference signal. The midpoint potential difference is defined as... ,in The voltage across the capacitor on the DC side. The voltage across the capacitor on the DC side, and the potential difference at the midpoint. The input P controller completes the midpoint potential control, and finally obtains the midpoint potential compensation amount. Injecting SPWM based on zero-sequence component injection makes the voltages of the upper and lower capacitors on the DC side of the converter tend to be balanced. Finally, the SPWM modulation based on zero-sequence component injection receives the three-phase modulation voltage and the injected midpoint potential compensation amount. This generates corresponding switching drive pulses to complete the control of the three-phase three-level converter.

[0013] As a further optimized technical solution, in the... i The information exchanged between a consensus distributed secondary controller and its neighboring consensus distributed secondary controllers includes: and control state variables ,in, j Indicates the relationship with the first i The numbers of adjacent consistent distributed secondary controllers. For the first jThe output current of the three-phase three-level converter is its rated current. Control state variables These represent the communication topology edge state variables, output current auxiliary tracking state variables, and voltage balance control state variables, respectively.

[0014] This invention also provides a system employing the robust distributed control method for low-communication three-level DC microgrids described in any of the above schemes, comprising a sparse communication cooperative control network layer and a converter local control layer. The converter local control layer is located between the sparse communication cooperative control network layer and the physical layer of the multi-node DC microgrid. In the sparse communication cooperative control network layer, each consistent distributed secondary controller interacts with adjacent consistent distributed secondary controllers according to a preset communication topology. Simultaneously, this communication topology is an undirected connected communication topology, and it is not necessary to establish a fully connected communication relationship with all consistent distributed secondary controllers. Adjacent consistent distributed secondary controllers only exchange normalized output current and control status information to realize the consistent distributed secondary control function.

[0015] The advantages of this invention are: This invention will reduce the communication burden of distributed secondary control in DC microgrids. Each consistent distributed secondary controller does not need to exchange DC common coupling point voltage and DC node voltage to obtain estimated values, but only needs to exchange normalized output current and control state variables, thereby reducing the number of communication links and the amount of communication data required.

[0016] This invention enables voltage balance and proportional current sharing in multi-node DC microgrids. Through a consistent distributed secondary controller, each three-phase three-level converter can share the load current according to its rated capacity, while keeping the DC node voltage within a reasonable range.

[0017] This invention is applicable to three-phase three-level AC / DC converter interface type DC microgrids. The method does not directly output the duty cycle like a DC / DC converter, but unifies the distributed secondary control with the voltage outer loop of the three-phase three-level converter. Compared with droop control microgrids, it effectively reduces the control steps.

[0018] The midpoint potential control scheme based on the proportional controller (P controller) of this invention is very simple, but it has the effect of consistent midpoint balance through zero-sequence injection of charge balance, which can improve the reliability of converter operation.

[0019] Furthermore, this invention exhibits good robustness and scalability. Even under conditions of load variations, uncertain line parameters, and changes in the connection status of some physical lines, the method can still maintain good dynamic performance and stability. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of a robust distributed control method and system for a low-communication three-level DC microgrid according to the present invention; Figure 2 A diagram showing the consistent distributed secondary control of the microgrid constructed using the three-phase three-level converter of the present invention and the local control structure of the converter; Figure 3 This is a schematic diagram showing the topology of the three-phase three-level converter of the present invention and its connection via resistive-inductive power distribution lines; Figure 4 For a by A three-phase three-level converter passes through A DC microgrid topology formed by connecting several power distribution lines; Figure 5 For the reason and Figure 4 The diagram shows a sparse communication topology for a sparse communication cooperative control network layer that is isomorphic to the DC microgrid topology. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Example 1 like Figure 1 As shown, it illustrates in detail the complete control framework of the multi-node DC microgrid constructed by the multi-three-phase three-level converter of the present invention. This control framework mainly includes a sparse communication cooperative control network layer, a converter local control layer, and a multi-node DC microgrid physical layer. Figure 3 The diagram shows the topology of a three-phase three-level converter and its connection via resistive-inductive power distribution lines. Each three-phase three-level converter includes a three-phase power grid, an RL filter, the converter body, upper and lower DC capacitors, and corresponding resistive-inductive power distribution lines connected in sequence.

[0023] In this system, a sparse communication cooperative control network layer is located at the upper layer. This layer consists of a system-level information interaction network composed of multiple consistent distributed secondary controllers and communication links. Each consistent distributed secondary controller interacts with its neighboring consistent distributed secondary controllers according to a preset communication topology. This communication topology is undirected and does not require establishing full connectivity with all consistent distributed secondary controllers. Adjacent consistent distributed secondary controllers only exchange normalized output current and control status information to achieve consistent distributed secondary control functionality. It should be noted that, in this embodiment, for ease of understanding, the selected communication topology adopts an undirected connected graph corresponding to the DC microgrid topology. For example, in... Figure 4 Under the aforementioned DC microgrid topology, the communication topology of the sparse communication cooperative control network layer is selected as follows: Figure 5 The undirected connected sparse communication topology shown has the same edge set as the other two.

[0024] The converter local control layer is situated between the sparse communication cooperative control network layer and the multi-node DC microgrid physical layer. This converter local control layer comprises multiple converter local controllers. Each converter local controller receives secondary coordination quantities and reference current information output from the corresponding upper-layer sparse communication cooperative control network layer's consistent distributed secondary controller, such as... Figure 2 As shown. According to Figure 2 The upper-level consistent distributed secondary controller includes a current distribution layer, a voltage balancing layer, and a state coordination layer for the DC microgrid. The current distribution layer ensures that each converter can share the current proportionally according to its rated current. The voltage balancing layer, based on the deviation between the voltage at the point of common coupling (PCC) and the reference voltage, and in conjunction with the coordinated state generated by the current distribution layer, restores the voltage of each node in the DC microgrid to near the reference voltage under a weighted average. The state coordination layer, based on the control state variables, achieves dynamic coupling between the current distribution layer and the voltage balancing layer. The coordinated control law can then be further calculated through the current distribution layer, voltage balancing layer, and state coordination layer. Finally, the coordinated control law is output to the current command generation layer to further complete the overall function of the consistent distributed secondary controller. This consistent distributed secondary controller differs from traditional distributed controllers in that it omits primary control, i.e., the traditional voltage outer loop control, and combines the functions of secondary and primary control. Figure 2 The converter was also showcased. iThe local controller receives the current command value output from the current command generation layer of the consistent distributed secondary controller, and synchronously samples local operating information, including AC side voltage and current, DC output voltage and current, and DC side capacitor voltage. Then, it further completes the dq current inner loop PI control, midpoint potential control and modulation signal generation, and outputs drive pulse signals based on SPWM modulation of zero-sequence component injection to complete the control of the three-phase three-level converter itself.

[0025] The physical layer of a multi-node DC microgrid represents the electrical connections between each three-phase three-level converter and its DC-side PCC point. Specifically, the physical layer of a multi-node DC microgrid includes n distributed converter units, denoted as follows: Each distributed converter unit includes, in sequence, a three-phase AC power supply or grid, an AC-side filter inductor, a three-phase three-level converter, a PCC point, and a local load. Each common coupling point is interconnected via power distribution lines (resistive-inductive). Each converter local controller synchronously collects local sampling information, and the corresponding converter local controller is connected to the corresponding consensus distributed secondary controller in the sparse communication cooperative control network layer to receive coordination quantities and reference current information from the consensus distributed secondary controller. In the physical layer of the multi-node DC microgrid, the DC node voltage of the i-th PCC point is... The output current of the i-th three-phase three-level converter is Its rated current is .

[0026] In the sparse communication cooperative control network layer, the consensus distributed secondary controllers communicate according to a preset undirected connected communication topology and exchange limited information with adjacent consensus distributed secondary controllers, such as... Figure 5 As shown. In the first i The information exchanged between a consensus distributed secondary controller and its neighboring consensus distributed secondary controllers includes: and control state variables .in, j Indicates the relationship with the first i The adjacent consistent distributed secondary controllers are numbered. For the first j The output current of the three-phase three-level converter is its rated current. Control state variables These represent the communication topology edge state variables, output current auxiliary tracking state variables, and voltage balance control state variables, respectively. By exchanging only these variables, this invention can reduce the number of communication links and the amount of communication data while maintaining consistent control performance. It avoids exchanging the common coupling point voltage, DC node voltage, or their estimates, thereby reducing the impact of communication delays, packet loss, and communication failures on system control performance.

[0027] After completing local sampling, each converter's local controller first outputs the coordinated control law from the consistent distributed secondary controller to the current command generation layer. This current command generation layer unifies the distributed secondary control function with the voltage outer loop of the three-phase three-level converter's primary control, enabling the secondary control output to be directly converted into the dq current inner loop reference command. Specifically, the consistent distributed secondary controller current command generation layer generates the current command based on the DC node voltage. Output current Reference voltage and the law of coordination and control Output d-axis current reference value Furthermore, to maintain unity power factor operation, the q-axis current reference value is set to 0. Further, the... i A three-phase three-level converter obtains the dq-axis modulation reference voltage through PI control of the dq current inner loop. This voltage is then converted to a dq / abc signal to obtain the three-phase modulation reference signal. The midpoint potential difference is defined as... ,in The voltage across the capacitor on the DC side. The voltage across the capacitor on the DC side, and the potential difference at the midpoint. The input to the P controller completes the midpoint potential control. The final obtained midpoint potential compensation amount is... Injecting SPWM based on zero-sequence component injection makes the voltages of the upper and lower capacitors on the DC side of the converter tend to be balanced. Finally, the SPWM modulation based on zero-sequence component injection receives the three-phase modulation voltage and the injected midpoint potential compensation. This generates corresponding switching drive pulses to complete the control of the three-phase three-level converter.

[0028] like Figure 1 As shown, a robust distributed control method for a low-communication three-level DC microgrid specifically includes the following steps: Step (1) Sparse communication topology design and control objective determination: Assume that there are n connected three-phase three-level converters in the DC microgrid system, where the AC side of the i-th three-phase three-level converter is connected to a three-phase AC power supply or AC grid, and the DC output side of the three-phase three-level converter is connected to the corresponding point of common coupling (PCC). iThe common coupling points are interconnected via DC distribution lines containing line impedance and line reactance, forming a multi-node DC microgrid. Let... and The three-phase voltages and currents on the AC side of the three-phase three-level converter are respectively calculated. Then, the voltages and currents are transformed by dq transformation, and the grid angular frequency is obtained through a phase-locked loop. This allows us to obtain the voltage and current in the dq coordinate system. The dq transformation is as follows:

[0029] Among them, the definition and These are the d-axis and q-axis components of the three-phase voltage, respectively. and These represent the d-axis and q-axis components of the three-phase current, respectively. Therefore, under this DC microgrid, the local model can be expressed as:

[0030] in, i Indicates the first i The serial number corresponding to the three-phase three-level converter; and This refers to the filter inductor and its corresponding parasitic resistance; and These are the d-axis components of the three-phase current. and q-axis components The differential form; and These are the d-axis and q-axis components of the three-phase grid voltage, respectively. and The modulation reference voltage for the output of the inner loop PI control of the dq current; This is the equivalent capacitance value on the DC side; and Let be the DC output voltage and current of the converter, respectively, and let the differential form of the DC output voltage be... ; The load impedance; and The resistance and inductance of the power distribution line; Let be the current in line k, and Its differential form. The direction of the current in the power distribution line is arbitrarily chosen. The physical electrical topology correlation matrix of a DC microgrid can be constructed using the following formula:

[0031] Therefore, this DC microgrid topology is composed of an correlation matrix. Description, its first ik The elements are For example, such as Figure 4 The topology shown is as follows: Communication topology with undirected connectivity. Figure 5 The associated Laplace matrix can then be expressed as ,in .

[0032] In the secondary control of DC microgrids, one of the main control objectives is to achieve demand-based current sharing, namely:

[0033] in, Indicates the sampling time. For converter i and j The rated current value. According to this formula, achieving proportional current sharing is equivalent to making... An agreement was reached.

[0034] The second objective is to regulate the PCC voltage to a given reference value under steady-state conditions. ,Right now However, on-demand current sharing does not allow for this type of voltage regulation mode. Therefore, as an alternative, the weighted average of the voltage signal at the PCC point can be adjusted to a value similar to the voltage at the PCC point in steady state. If the weighted averages are consistent, then the voltage smoothing objective can be expressed as:

[0035] Step (2) Design of a distributed secondary controller with low communication consistency: For multi-node DC microgrids constructed using the aforementioned three-phase three-level converter, a novel consensus distributed secondary controller based on a sparse communication network is designed. Compared to existing distributed secondary controllers, it requires fewer communication links. Furthermore, this novel consensus distributed secondary controller combines the voltage outer loop of the secondary control with that of the primary control. Therefore, the output of this consensus distributed secondary controller does not rely on a droop control mechanism, unifying the primary and secondary control. The novel consensus distributed secondary controller comprises a four-layer control structure with cross-layer interactions. The communication network of this consensus distributed secondary controller is based on an unweighted undirected communication graph with n nodes and k edges, where... .

[0036] First, the first-level current allocation layer of this consistent distributed secondary controller is responsible for achieving the proportional current allocation target, and its structure is as follows:

[0037] in, and All are controller parameters greater than 0; and , ; This is the differential form of the communication topology edge state vector of the consistent distributed secondary controller. This layer ensures proportional current sharing because of its position on the current vector. An correlation matrix is ​​introduced into the feedback loop. Meanwhile, under steady state, due to All elements are equal ( Current vector If the steady-state value is obtained, it can be inferred that the system can achieve steady-state proportional flow equalization.

[0038] Secondly, the structure of the second-layer voltage balancing layer of this consistent distributed secondary controller is as follows:

[0039] in, And all of them are controller design parameters; ; and Both are two state vectors of the proposed consistent distributed secondary controller. The second layer guarantees the voltage balancing objective. Note the additional terms in the above equation. It does not change the steady-state conditions (equal current distribution and voltage balance); however, this term can improve the dynamic response of the distributed system by generating consistent oscillations.

[0040] Next, the third state coordination layer of this consistent distributed secondary controller can be expressed as follows, namely, the coordination control law vector. :

[0041] in, and These are design parameters used to ensure closed-loop stability, and their values ​​are related to the last layer of the distributed controller. It is important to note that... It is a vector synthesized by combining the coordinated control laws obtained from the calculations of all consistent distributed secondary controllers, i.e. The third layer is for obtaining current commands that can be used for local current loop control.

[0042] Finally, the last layer of this consistent distributed secondary controller is used to obtain current commands, which are expressed as follows:

[0043] in, This represents a consistent distributed secondary controller. For equivalent damping, denoted as the equivalent time constant of the inner-loop PI control of the dq current. This is the equivalent time constant coefficient, typically taking a value of 5 to 10. For a consistent distributed secondary controller i The output is a coordinated control law. The equivalent time constant can be determined based on the time required for the current to reach 63.2% of its final steady-state value. It is important to note that the design parameters of the third layer of the consistent distributed secondary controller must meet certain requirements. , , .

[0044] Furthermore, since converter control is generally based on unity power factor, the q-axis current command of the inner loop of the dq current is... If the value is 0, then the instantaneous active power on the AC side is approximately: When losses are ignored, the DC-side power satisfies Therefore, the current command for the inner loop of the dq current can be obtained as follows:

[0045] Ultimately, and By inputting the current into the inner loop of dq, the modulation reference voltage can be further obtained, and the control of the three-phase three-level converter can be completed via SPWM based on zero-sequence component injection.

[0046] As can be seen from the above, this consistent distributed secondary controller does not need to exchange the PCC point voltage, the converter DC node voltage and their estimated values. It only needs the local variables of the converter and the corresponding state vectors. The amount of data to be exchanged is less, and the two can transmit their own relevant information to each other only through the physical power line connection. Therefore, as long as the basic communication topology is kept connected, this distributed secondary control scheme is robust to line faults.

[0047] Step (3) Neutral point potential control of three-phase three-level converter: For a three-phase three-level converter, neutral point potential balance is crucial. First, based on the preceding information, assume the DC output voltage of a single converter is... ,in The voltage across the capacitor on the DC side. Let the voltage across the capacitor on the DC side be the voltage across the capacitor. Then the voltage difference between the upper and lower capacitors (the imbalance) is:

[0048] Assuming the capacitance values ​​of the upper and lower capacitors are... ,and It is constant. Midpoint current. If the flow from the midpoint is positive, then its relationship with the capacitor current is:

[0049] Furthermore, the switching function These correspond to the P, O, and N output levels, respectively. Current flows through the midpoint only in the O level state; therefore, the instantaneous midpoint current is...

[0050] The modulation scheme studied employs SPWM based on zero-sequence component injection. For carrier SPWM, within one switching cycle, if the normalized modulated wave is... In the ideal case, there is

[0051] in, These represent the duty cycles of the phase in the P, O, and N states, respectively. Therefore, based on the midpoint current in the O state, its average value can be written as...

[0052] Substitution , can be obtained

[0053] However, due to the three-phase three-wire system Then there is

[0054] This indicates that the midpoint current is determined by the duration of the zero-level operation in each phase and the phase current. Therefore, a further midpoint potential compensation amount is set. The new modulated wave is Because all three phases are superimposed with the same midpoint potential compensation. Therefore, the line voltage reference will not change: Therefore, the midpoint potential compensation amount It is a zero-sequence component, which theoretically will not change the fundamental frequency of the three-phase voltage, but will change the duty cycle of the 0-level voltage. Therefore, the midpoint current becomes Midpoint potential compensation amount Linearize around 0: Therefore, the average midpoint current can be rewritten as .

[0055] Furthermore, the dynamic equation for the voltage difference between the upper and lower capacitors can be written as follows: The sign of this expression depends on the direction of the midpoint current; if the current direction is defined in the opposite way, the expression needs to be inverted. Substituting into the approximate midpoint current expression:

[0056] The aforementioned midpoint controller has already been designed That is, the midpoint potential compensation amount If we temporarily ignore the disturbance of the natural midpoint current... Then there is .when hour, This will cause exponential decay, and the voltages of the upper and lower capacitors on the DC side will tend to balance. Therefore, the designed proportional controller (P controller) constructs a negative feedback loop: when... ,have ,but Change, further It will change, then The size will decrease. Ultimately, the control of each three-phase three-level converter is achieved through an SPWM modulation strategy based on zero-sequence component injection.

[0057] Matters not covered in this invention are common knowledge.

[0058] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A robust distributed control method for a low-communication three-level DC microgrid, characterized in that: A sparse communication cooperative control network layer and a converter local control layer are adopted. The converter local control layer is placed between the sparse communication cooperative control network layer and the physical layer of the multi-node DC microgrid. Each consistent distributed secondary controller in the sparse communication cooperative control network layer performs limited information interaction with adjacent consistent distributed secondary controllers according to a preset communication topology. At the same time, this communication topology is an undirected connected communication topology, and it is not necessary to establish a full connection communication relationship with all consistent distributed secondary controllers. Adjacent consistent distributed secondary controllers only exchange normalized output current and control status information to realize the consistent distributed secondary control function. The consistent distributed secondary controller comprises a current distribution layer, a voltage balancing layer, and a state coordination layer for the DC microgrid. The current distribution layer ensures that each converter distributes current proportionally to its rated current. The voltage balancing layer, based on the deviation between the point of common coupling voltage and the reference voltage, and in conjunction with the coordination state generated by the current distribution layer, restores the voltage of each node in the DC microgrid to near the reference voltage under a weighted average. The state coordination layer, based on the control state variables, achieves dynamic coupling between the current distribution layer and the voltage balancing layer, and further calculates the coordination control law through the current distribution layer, voltage balancing layer, and state coordination layer. Finally, the coordination control law is output to the current command generation layer to complete the overall function of the consistent distributed secondary controller.

2. The robust distributed control method for a low-communication three-level DC microgrid as described in claim 1, characterized in that: The selected communication topology adopts an undirected connected graph corresponding to the DC microgrid topology.

3. The robust distributed control method for a low-communication three-level DC microgrid as described in claim 1, characterized in that: The current command generation layer unifies the distributed secondary control function with the voltage outer loop of the primary control of the three-phase three-level converter, so that the output of the secondary control can be directly converted into the dq current inner loop reference command.

4. The robust distributed control method for a low-communication three-level DC microgrid as described in claim 3, characterized in that: The converter local control layer includes multiple converter local controllers. Each converter local controller receives secondary coordination quantities and reference current information output by the corresponding consistent distributed secondary controller current command generation layer in the corresponding upper-layer sparse communication cooperative control network layer.

5. The robust distributed control method for a low-communication three-level DC microgrid as described in claim 4, characterized in that: The converter local controller receives the current command value output from the consistent distributed secondary controller and synchronously samples local operating information, including AC side voltage and current, DC output voltage and current, and DC side capacitor voltage. Then, it further completes the dq current inner loop PI control, midpoint potential control, and modulation signal generation, and outputs the drive pulse signal through SPWM modulation based on zero-sequence component injection to complete the control of the three-phase three-level converter itself.

6. The robust distributed control method for a low-communication three-level DC microgrid as described in claim 1, characterized in that: In the physical layer of the multi-node DC microgrid, the DC node voltage of the i-th PCC point is The output current of the i-th three-phase three-level converter is The consistent distributed secondary controller current command generation layer is based on the DC node voltage. Output current Reference voltage and coordination control law Output d-axis current reference value And set the q-axis current reference value to 0.

7. A robust distributed control method for a low-communication three-level DC microgrid as described in claim 6, characterized in that: No. i A three-phase three-level converter obtains the dq-axis modulation reference voltage through PI control of the dq current inner loop. This voltage is then converted via dq / abc conversion to obtain the three-phase modulation reference signal. The midpoint potential difference is defined as... ,in The voltage across the capacitor on the DC side. The voltage across the capacitor on the DC side, and the potential difference at the midpoint. The input P controller completes the midpoint potential control, and finally obtains the midpoint potential compensation amount. Injecting SPWM based on zero-sequence component injection makes the voltages of the upper and lower capacitors on the DC side of the converter tend to be balanced. Finally, the SPWM modulation based on zero-sequence component injection receives the three-phase modulation voltage and the injected midpoint potential compensation amount. This generates corresponding switching drive pulses to complete the control of the three-phase three-level converter.

8. A robust distributed control method for a low-communication three-level DC microgrid as described in claim 1, characterized in that: In the i The information exchanged between a consensus distributed secondary controller and its neighboring consensus distributed secondary controllers includes: and control state variables ,in, j Indicates the relationship with the first i The numbers of adjacent consistent distributed secondary controllers. For the first j The output current of the three-phase three-level converter is its rated current. Control state variables These represent the communication topology edge state variables, output current auxiliary tracking state variables, and voltage balance control state variables, respectively.

9. A system employing the robust distributed control method for low-communication three-level DC microgrids according to any one of claims 1 to 8, characterized in that: The system includes a sparse communication cooperative control network layer and a converter local control layer. The converter local control layer is located between the sparse communication cooperative control network layer and the physical layer of the multi-node DC microgrid. In the sparse communication cooperative control network layer, each consistent distributed secondary controller interacts with adjacent consistent distributed secondary controllers according to a preset communication topology. At the same time, the communication topology is an undirected connected communication topology, and it is not necessary to establish a full connection communication relationship with all consistent distributed secondary controllers. Adjacent consistent distributed secondary controllers only exchange normalized output current and control status information to realize the consistent distributed secondary control function.

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