Distributed hierarchical control method and system for multi-converter series-parallel microgrid

Abstract

The present invention proposes a distributed hierarchical control method and system for a multi-converter series-parallel microgrid. In the multi-converter series-parallel microgrid system, each converter module communicates only with its corresponding neighbor converter module, and the constructed communication architecture does not need to be configured with a central controller, effectively avoiding the adverse effects of central controller failure on system operation performance. On the basis of the established communication architecture, the active and reactive power of each converter module is accurately distributed and the AC output voltage amplitude is stably controlled, and it is suitable for both resistive-inductive loads and resistive-capacitive loads; when a partial communication line fails, it will not affect the accurate distribution of active and reactive power and the stable control of AC output voltage amplitude, and the system operation reliability is significantly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of renewable energy power generation and microgrid system control, and in particular to a distributed hierarchical control method and system for a multi-converter series-parallel microgrid. Background Art

[0002] The statements in this section merely provide background information related to the present invention and do not necessarily constitute prior art.

[0003] Renewable energy generation has obvious advantages such as large reserves, clean and environmentally friendly, and pollution-free, and has become an important measure to solve the global energy crisis and environmental pollution problems. However, subject to the influence of natural environmental conditions such as light and temperature, the output power of renewable energy generation is seriously random, intermittent and volatile, causing a series of problems such as low power generation efficiency and poor power quality, which brings great challenges to the safe operation of the power grid. Microgrids have become an ideal solution to solve the above problems by organically combining different renewable energy power generation units and designing collaborative operation control strategies.

[0004] Among different types of microgrid systems, multi-converter series-parallel microgrids use H-bridge power converters as basic modules, which are connected in series to form series subnets to increase the voltage level, and then the series subnets are connected in parallel to increase the current level. This can realize the direct integration of new energy power generation units such as photovoltaics and energy storage, without the need to configure bidirectional DC / DC power converters, reducing power conversion links, reducing system volume and cost, and improving system efficiency and reliability. Therefore, multi-converter series-parallel microgrids have great development prospects and research value.

[0005] The inventors found that the multi-converter series-parallel microgrid system contains a large number of converter modules, which makes it extremely difficult to design a system hierarchical control method, and the traditional droop control strategy cannot be directly applied; the system output load or grid operating conditions are complex, and the characteristics under different operating modes are very different. Most traditional methods use linear controllers, and the system dynamic performance is limited, which makes it difficult to meet the requirements of multi-scenario adaptive microgrid systems; the existing distributed control method only considers the active power and reactive power allocation targets, and cannot achieve stable control of the AC bus output voltage amplitude, which seriously reduces the power quality. Therefore, a distributed hierarchical control method suitable for multi-converter series-parallel microgrids needs to be studied urgently. Summary of the invention

[0006] In order to overcome the shortcomings of the above-mentioned prior art, the present invention provides a distributed hierarchical control method and system for a multi-converter series-parallel microgrid, which only relies on the communication between the converter modules corresponding to each leader and its neighbor converter modules to achieve accurate distribution of active power and reactive power and stable control of the AC output voltage amplitude, without the need to configure a central controller, thereby improving the system operation reliability.

[0007] To achieve the above-mentioned object, the first aspect of the present invention provides a distributed hierarchical control method for a multi-converter series-parallel microgrid, wherein the multi-converter series-parallel microgrid comprises a plurality of series subnets, each of which comprises a plurality of converter modules connected in series, and the output ends of each series subnet are connected in parallel at a common coupling point of the microgrid; in the series subnets, the first converter module in the series subnet is selected as a leader, and the remaining converter modules in the series subnet are selected as followers; each converter module communicates only with its neighbor converter modules; the distributed hierarchical control method comprises:

[0008] According to the normalized active and reactive power deviations between the converter modules corresponding to each leader and the converter modules adjacent to each leader, and the normalized active and reactive power deviations between the converter modules corresponding to each follower and the converter modules adjacent to the follower in the series subnet, the active and reactive power of each converter module is distributed;

[0009] The AC voltage amplitude of the microgrid common coupling point is controlled according to the AC voltage amplitude of the leader's corresponding converter module, the AC voltage amplitude of the series subnet where the leader's corresponding converter module is located, and the AC voltage amplitude of the series subnet where the leader's adjacent converter modules are located.

[0010] A second aspect of the present invention provides a distributed hierarchical control system for a multi-converter series-parallel microgrid, wherein the multi-converter series-parallel microgrid includes a plurality of series subnets, each of which includes a plurality of converter modules connected in series, and the output ends of each of which are connected in parallel to a common coupling point of the microgrid; in the series subnets, the first converter module in the series subnet is selected as a leader, and the remaining converter modules in the series subnet are selected as followers; each converter module communicates only with its neighbor converter modules; the distributed hierarchical control system includes:

[0011] Power allocation module: according to the normalized active and reactive power deviations between the converter modules corresponding to each leader and the adjacent converter modules of each leader, and the normalized active and reactive power deviations between the converter modules corresponding to each follower and the adjacent converter modules of the follower in the series subnet, the active and reactive power of each converter module is allocated;

[0012] AC voltage amplitude control module: controls the AC voltage amplitude of the microgrid according to the AC voltage amplitude of the microgrid common coupling point obtained by the leader's corresponding converter module, the AC voltage amplitude of the series subnet where the leader's corresponding converter module is located, and the AC voltage amplitude of the series subnet where the leader's adjacent converter module is located.

[0013] The third aspect of the present invention provides a computer device, comprising: a processor, a memory and a bus, wherein the memory stores machine-readable instructions executable by the processor, and when the computer device is running, the processor and the memory communicate through the bus, and when the machine-readable instructions are executed by the processor, a distributed hierarchical control method for a multi-converter series-parallel microgrid is executed.

[0014] A fourth aspect of the present invention provides a computer-readable storage medium having a computer program stored thereon, wherein the computer program, when executed by a processor, executes a distributed hierarchical control method for a multi-converter series-parallel microgrid.

[0015] One or more of the above technical solutions have the following beneficial effects:

[0016] In the present invention, in a multi-converter series-parallel microgrid system, each converter module communicates only with its corresponding neighbor converter module, and the constructed communication architecture does not require a central controller, effectively avoiding the adverse effects of central controller failure on system operating performance.

[0017] In the present invention, based on the established communication architecture, according to the normalized active and reactive power deviations between each leader and each leader's adjacent converter module, and the normalized active and reactive power deviations between each follower and the follower's adjacent converter module in the series subnet, the active and reactive power of each converter module is accurately distributed; according to the AC voltage amplitude of the common coupling point of the microgrid and the AC voltage amplitude of the series subnet where the leader's corresponding converter module is located, and the AC voltage amplitude of the series subnet where the leader's adjacent converter module is located, the AC output voltage amplitude is stably controlled, and it is applicable to both resistive-inductive loads and resistive-capacitive loads. Failure of some communication lines will not affect the accurate distribution of active and reactive power and the stable control of the AC output voltage amplitude, thereby improving the reliability of system operation.

[0018] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0020] Figure 1 This is a circuit structure diagram of a multi-converter series-parallel microgrid system in Embodiment 1 of the present invention;

[0021] Figure 21 is a circuit topology diagram of an H-bridge power converter module in Embodiment 1 of the present invention;

[0022] Figure 3 Schematic diagram of the communication architecture of the distributed hierarchical control method in the first embodiment of the present invention;

[0023] Figure 4 is a control block diagram of a distributed hierarchical control method in Embodiment 1 of the present invention;

[0024] Figure 5(a)-Figure 5(d) The simulation waveform diagram of the system output terminal connected to the resistive-inductive load under the first simulation condition in the first embodiment of the invention;

[0025] Figure 6(a)-Figure 6(d) The simulation waveform diagram of the system output terminal connected to the resistive and inductive load under the second simulation condition in the first embodiment of the invention;

[0026] Figure 7(a)-Figure 7(d) The simulation waveform diagram of the system output terminal connected to the resistive and inductive load under the third simulation condition in the first embodiment of the invention;

[0027] Figure 8(a)-Figure 8(d) The simulation waveform diagram of the system output terminal connected to the resistive and capacitive load under the first simulation condition in the first embodiment of the invention;

[0028] Figure 9(a)-Figure 9(d) The simulation waveform diagram of the system output terminal connected to the resistive and capacitive load under the second simulation condition in the first embodiment of the invention;

[0029] Figure 10(a)-Figure 10(d) It is a simulation waveform diagram of the system output end connected to the resistive and capacitive load under the third simulation condition in the first embodiment of the invention. DETAILED DESCRIPTION

[0030] It should be noted that the following detailed descriptions are exemplary and are intended to provide further explanation of the present invention. Unless otherwise specified, all technical and scientific terms used herein have the same meanings as those commonly understood by those skilled in the art to which the present invention belongs.

[0031] It should be noted that the terms used herein are for describing specific embodiments only and are not intended to be limiting of exemplary embodiments according to the present invention.

[0032] In the absence of conflict, the embodiments of the present invention and the features of the embodiments may be combined with each other.

[0033] Embodiment 1

[0034] Figure 1The circuit structure diagram of the multi-converter series-parallel microgrid system. The entire system contains M series subnets, each of which contains N H-bridge power converter modules. The DC input side of each H-bridge power converter is connected to a DC power supply, and the AC output side is connected to a group of LC output filters. Among them, each series subnet contains multiple H-bridge power converter modules connected in series, and the output ends of different series subnets are connected in parallel to the system common coupling point (Point of Common Coupling, PCC), which jointly provide high-quality power to the grid or load. ij (i=1,2,...;j=1,2,...) is the line impedance. SW is the grid-connected switch. When the grid-connected switch (SW) is closed, the system operates in the grid-connected mode; otherwise, the system operates in the island mode. In the island mode, the power grid cannot provide support for the system, and the difficulty of accurate power distribution between different power converter modules increases dramatically. For this reason, the method of this embodiment mainly conducts theoretical analysis on the island mode and designs a control method.

[0035] Figure 2 The circuit topology diagram of the H-bridge power converter module is composed of 4 power switch tubes. Pulse Width Modulation (PWM) is used to control the opening and closing of each power switch tube. It can be understood that the power switch tube is an insulated gate bipolar transistor (IGBT); the power switch tube can also be implemented by other forms of transistors.

[0036] This embodiment discloses a distributed hierarchical control method for a multi-converter series-parallel microgrid. Figure 3 This is a schematic diagram of the communication architecture, including:

[0037] According to the normalized active and reactive power deviations between the converter modules corresponding to each leader and the converter modules adjacent to each leader, and the normalized active and reactive power deviations between the converter modules corresponding to each follower and the converter modules adjacent to the follower in the series subnet, the active and reactive power of each converter module is distributed;

[0038] The AC voltage amplitude of the microgrid is controlled according to the reference value of the AC voltage amplitude of the microgrid common coupling point, the AC voltage amplitude of the series subnet where the leader's corresponding converter module is located, and the AC voltage amplitude of the series subnet where the leader's adjacent converter module is located.

[0039] Without loss of generality, Figure 1 Taking the M×N multi-converter series-parallel microgrid system shown as an example, that is, the entire system contains M series subnets, each of which contains N H-bridge power converter modules, the principles and steps of the method of this embodiment are analyzed and given in detail:

[0040] Step (1): Distributed controller communication architecture and rules

[0041] Establish the distributed controller communication architecture and rules to provide a basis for the design of distributed hierarchical control strategies. Figure 4 Schematic diagram of distributed controller communication architecture, where DG#ij represents the controller inside the jth H-bridge power converter module in the i-th series subnet (i=1,2,...,M; j=1,2,...,N). Specifically, the controller inside the first H-bridge power converter in each series subnet is designated as the leader, and the controllers inside other H-bridge power converters are designated as followers. A ring communication architecture is adopted, and the communication rules are as follows: between different series subnets, the leader node can communicate with the leader node of its neighboring nodes; within the series subnet, the leader or follower node can only communicate with its neighboring nodes to achieve data interaction.

[0042] Step (2): Distributed one-layer control strategy

[0043] For the leader node and follower node of each series subnet, a distributed one-layer control strategy is designed to achieve accurate distribution of active power and reactive power.

[0044] Specifically, a simplified finite-time regulator is designed to adjust the normalized active power deviation between different neighbor nodes to obtain the reference angular frequency correction value of different H-bridge power converter modules; a simplified finite-time regulator is designed to adjust the normalized reactive power deviation between different neighbor nodes to obtain the reference voltage amplitude correction value of different H-bridge power converter modules.

[0045] Specifically, the reference angular frequency correction value of the converter module corresponding to the leader node in the i-th series subnet is:

[0046]

[0047] Among them, sign(·) is the sign function, P i1 , P i1,rated is the active power and rated value of the first converter module in the ith series subnet, N i1,s is the set of serial neighbor nodes of the ith serial subnet leader node, N i1,p is the set of parallel neighbor nodes of the i-th series subnet leader node, λ i1 and λ i2 is the control parameter of the simplified finite-time regulator, α i1,a is the communication weight coefficient between the leader node of the ith series subnet and its series neighbor nodes, α i1,bis the communication weight coefficient between the leader node of the i-th series subnet and its parallel neighbor nodes.

[0048] The reference angular frequency correction value of the converter module corresponding to the jth (j≠1) follower node in the i-th series subnet is:

[0049]

[0050] Among them, sign(·) is the sign function, P ij , P ij,rated is the active power and rated value of the jth converter module in the i-th series subnet, N ij,s is the set of serial neighbor nodes of the ith serial subnet follower node j, and λ ij is the control parameter of the simplified finite-time regulator, α ij,c is the communication weight coefficient between follower node j of the ith series subnet and its series neighbor nodes.

[0051] The reference voltage amplitude correction value of the converter module corresponding to the leader node in the i-th series subnet is:

[0052]

[0053] Among them, sign(·) is the sign function, Q i1 , Q i1,rated is the reactive power and rated value of the first converter module in the ith series subnet, N i1,s is the set of serial neighbor nodes of the ith serial subnet leader node, N i1,p is the set of parallel neighbor nodes of the i-th series subnet leader node, μ i1 and μ i2 is the control parameter of the simplified finite-time regulator, α i1,d is the communication weight coefficient between the leader node of the ith series subnet and its series neighbor nodes, α i1,e is the communication weight coefficient between the leader node of the i-th series subnet and its parallel neighbor nodes.

[0054] The reference voltage amplitude correction value of the converter module corresponding to the jth (j≠1) follower node in the i-th series subnet is:

[0055]

[0056] Among them, sign(·) is the sign function, Q ij , Q ij,rated is the reactive power and rated value of the jth converter module in the i-th series subnet, Nij,s is the set of serial neighbor nodes of the ith serial subnet follower node j, and μ ij is the control parameter of the simplified finite-time regulator, α ij,r is the communication weight coefficient between follower node j of the ith series subnet and its series neighbor nodes.

[0057] Step (3): Distributed Layer 2 Control Strategy

[0058] For the leader node of each series subnet, a distributed two-layer control strategy is designed to achieve stable control of the system AC output voltage amplitude. The leader node of the ith series subnet samples the AC output voltage at the common coupling point and calculates its amplitude (denoted as V pcc,i ), and then send it to the neighboring node in a low-bandwidth communication mode; at the same time, it can receive the corresponding AC voltage amplitude sent by the neighboring node. Using the proportional-integral controller, the AC voltage amplitude compensation is obtained as:

[0059]

[0060] Among them, k p,V and k i,V are the parameters of the proportional-integral controller, is the reference value of the AC voltage amplitude at the common coupling point of the microgrid, V pcc,i 、V pcc,ne1 、V pcc,ne2 They are respectively the actual amplitudes of the AC output voltages of the i-th series subnet, the series subnet where neighbor node 1 is located, and the series subnet where neighbor node 2 is located.

[0061] Step (4): Generate instantaneous reference voltage signal

[0062] Based on the reference angular frequency correction value, the reference voltage amplitude correction value and the AC voltage amplitude compensation value of each converter module, an instantaneous reference voltage signal is generated as an input quantity of the voltage-current dual closed-loop control.

[0063] Specifically, the instantaneous reference voltage signal of the leader node is constructed by using the reference angular frequency correction value and reference voltage amplitude correction value of the converter module corresponding to the leader node obtained in step (2) and the AC voltage amplitude compensation amount obtained in step (3). The instantaneous reference voltage signal of the leader node in the i-th series subnet is:

[0064]

[0065] in, is the rated reference voltage amplitude of the first H-bridge power converter in the i-th series subnet (i=1,2,...,M), and the setting rule is shown in formula (7); ω* is the rated angular frequency, which is set to 2π×50rad / s.

[0066]

[0067] Specifically, the instantaneous reference voltage signal of the follower node is constructed by using the reference angular frequency correction value and reference voltage amplitude correction value of the converter module corresponding to the follower node obtained in step (2) and the AC voltage amplitude compensation amount obtained in step (3). The instantaneous reference voltage signal of the jth (j≠1) follower node in the i-th series subnet is

[0068]

[0069] in, is the rated reference voltage amplitude of the jth H-bridge power converter in the i-th series subnet (i=1,2,...,M; j=2,3,,N), and the setting rule is shown in formula (9); ω* is the rated angular frequency, which is set to 2π×50rad / s.

[0070]

[0071] (5) Voltage-current dual closed-loop control strategy

[0072] The reference voltage signal obtained in step (4) is used as the command signal to sample the capacitor voltage and inductor current of the LC output filter of each converter module, and a voltage-current dual closed-loop control scheme is constructed, where the outer loop and the inner loop are the capacitor voltage closed loop and the inductor current closed loop, respectively. The output of the inner loop regulator is used as a modulation wave, compared with the carrier, and a corresponding PWM drive signal is generated to control the opening and closing of the power switch tube, thereby controlling the operation of the multi-converter series-parallel microgrid system.

[0073] Without loss of generality, taking a 4×4 multi-converter series-parallel microgrid system as an example (i.e., the entire system contains 4 series subnets, each of which contains 4 H-bridge power converter modules), the simulation results and analysis of the method of the present invention are analyzed in detail:

[0074] Figure 5(a)-Figure 5(d) The simulation waveform diagram of the system output end connected to the resistive inductive load under the first simulation condition, including the active power (p ij ; i = 1, 2, 3, 4; j = 1, 2, 3, 4), reactive power (q ij ; i = 1, 2, 3, 4; j = 1, 2, 3, 4), frequency (f ij ; i = 1, 2, 3, 4; j = 1, 2, 3, 4), PCC point voltage (vpcc ) and its amplitude (V pcc ). The first simulation condition is set as follows: the power distribution ratio of different series subnets is equal; before the simulation time t=4s, the system control strategy only adopts distributed layer one control; when the simulation time t=4s, the distributed layer two control is started; before the simulation time t=6s, in the first series subnet, the power distribution ratio of the four H-bridge power converters is 1:1.04:1.13:1.17; in the second series subnet, the power distribution ratio of the four H-bridge power converters is 1:1.04:1.18:1.22; in the third series subnet, the power distribution ratio of the four H-bridge power converters is 1:1.05:1.23:1.27; in the fourth series subnet, the power distribution ratio of the four H-bridge power converters is 1:1.05:1.28:1.33. When the simulation time t = 6s, the power distribution ratio of different converter modules in each series subnet is switched from unequal to equal (i.e. 1:1:1:1). It can be seen that the active power and reactive power of different series subnets are equal, and the active power and reactive power distribution ratio of each H-bridge power converter module in different series subnets is equal to the corresponding set value; when only distributed first-layer control is adopted, the system AC output voltage amplitude is lower than the given value; when the distributed second-layer control is enabled, the system AC output voltage amplitude is equal to its given value (i.e. 311V), which verifies the effectiveness of the method of the present invention.

[0075] Figure 6(a)-Figure 6(d) The simulation waveform diagram of the system output end connected to the resistive inductive load under the second simulation condition, including the active power (p ij ; i = 1, 2, 3, 4; j = 1, 2, 3, 4), reactive power (q ij ; i = 1, 2, 3, 4; j = 1, 2, 3, 4), frequency (f ij ; i = 1, 2, 3, 4; j = 1, 2, 3, 4), PCC point voltage (v pcc ) and its amplitude (V pcc). The second simulation condition is set as follows: the power distribution ratio of different series subnets is equal; the system control strategy adopts distributed first-layer control + distributed second-layer control; when the simulation time t=4s, the load step increases. Before the simulation time t=6s, in the first series subnet, the power distribution ratio of the four H-bridge power converters is 1:1.04:1.13:1.17; in the second series subnet, the power distribution ratio of the four H-bridge power converters is 1:1.04:1.18:1.22; in the third series subnet, the power distribution ratio of the four H-bridge power converters is 1:1.05:1.23:1.27; in the fourth series subnet, the power distribution ratio of the four H-bridge power converters is 1:1.05:1.28:1.33. When the simulation time t=6s, the power distribution ratio of different converter modules in each series subnet is switched from unequal to equal (i.e. 1:1:1:1). It can be seen that: when the load step increases, the active power and reactive power of different converter modules in each series subnet increase accordingly, and the set power distribution ratio can be maintained, and the frequency is 50Hz; the system AC output voltage amplitude is equal to its given value.

[0076] Figure 7(a)-Figure 7(d) The simulation waveform diagram of the system output end connected to the resistive and inductive load under the third simulation condition, including the active power (p ij ; i = 1, 2, 3, 4; j = 1, 2, 3, 4), reactive power (q ij ; i = 1, 2, 3, 4; j = 1, 2, 3, 4), frequency (f ij ; i = 1, 2, 3, 4; j = 1, 2, 3, 4), PCC point voltage (v pcc ) and its amplitude (V pcc ). The third simulation condition is set as follows: the power distribution ratio of different series subnets is equal; the communication line between converter module 3 and module 4 in the four series subnets fails; before the simulation time t=4s, the system control strategy only adopts distributed layer 1 control; when the simulation time t=4s, the distributed layer 2 control is started; when the simulation time t=6s, the load step increases. It is not difficult to see that: when part of the communication line fails, the method of the present invention can still achieve accurate distribution of active power and reactive power and stable control of the AC output voltage amplitude, thereby improving the reliability of system operation.

[0077] Figure 8(a)-Figure 8(d) The simulation waveform diagram of the system output end connected to the resistive and capacitive load under the first simulation condition, including the active power (p ij ; i = 1, 2, 3, 4; j = 1, 2, 3, 4), reactive power (q ij ; i = 1, 2, 3, 4; j = 1, 2, 3, 4), frequency (fij ; i = 1, 2, 3, 4; j = 1, 2, 3, 4), PCC point voltage (v pcc ) and its amplitude (V pcc ). The first simulation condition is set as follows: the power distribution ratio of different series subnets is equal; before the simulation time t=4s, the system control strategy only adopts distributed layer one control; when the simulation time t=4s, the distributed layer two control is started. Before the simulation time t=6s, in the first series subnet, the power distribution ratio of the four H-bridge power converters is 1:1.04:1.13:1.17; in the second series subnet, the power distribution ratio of the four H-bridge power converters is 1:1.04:1.18:1.22; in the third series subnet, the power distribution ratio of the four H-bridge power converters is 1:1.05:1.23:1.27; in the fourth series subnet, the power distribution ratio of the four H-bridge power converters is 1:1.05:1.28:1.33. When the simulation time t = 6s, the power distribution ratio of different converter modules in each series subnet is switched from unequal to equal (i.e. 1:1:1:1). It can be seen that the active power and reactive power of different series subnets are equal, and the active power and reactive power distribution ratio of each H-bridge power converter module in different series subnets is equal to the corresponding set value; because the system output end is connected to the resistive and capacitive load, the reactive power is negative. When only the distributed first-layer control is adopted, the system AC output voltage amplitude is lower than the given value; when the distributed second-layer control is enabled, the system AC output voltage amplitude is equal to its given value (i.e. 311V), which verifies the effectiveness of the method of the present invention.

[0078] Figure 9(a)-Figure 9(d) The simulation waveform diagram under the second simulation condition with the resistive and capacitive load connected to the output end of the system, including the active power (p ij ; i = 1, 2, 3, 4; j = 1, 2, 3, 4), reactive power (q ij ; i = 1, 2, 3, 4; j = 1, 2, 3, 4), frequency (f ij ; i = 1, 2, 3, 4; j = 1, 2, 3, 4), PCC point voltage (v pcc ) and its amplitude (V pcc). The second simulation condition is set as follows: the power distribution ratio of different series subnets is equal; the system control strategy adopts distributed first-layer control + distributed second-layer control; when the simulation time t=4s, the load step increases. Before the simulation time t=6s, in the first series subnet, the power distribution ratio of the four H-bridge power converters is 1:1.04:1.13:1.17; in the second series subnet, the power distribution ratio of the four H-bridge power converters is 1:1.04:1.18:1.22; in the third series subnet, the power distribution ratio of the four H-bridge power converters is 1:1.05:1.23:1.27; in the fourth series subnet, the power distribution ratio of the four H-bridge power converters is 1:1.05:1.28:1.33. When the simulation time t=6s, the power distribution ratio of different converter modules in each series subnet is switched from unequal to equal (i.e. 1:1:1:1). It can be seen that: when the resistive and capacitive load steps increase, the active power and reactive power of different converter modules in each series subnet increase accordingly, and the set power distribution ratio can be maintained, and the frequency is 50Hz; the system AC output voltage amplitude is equal to its given value.

[0079] Figure 10(a)-Figure 10(d) The simulation waveform diagram of the system output end connected to the resistive and capacitive load under the third simulation condition, including the active power (p ij ; i = 1, 2, 3, 4; j = 1, 2, 3, 4), reactive power (q ij ; i = 1, 2, 3, 4; j = 1, 2, 3, 4), frequency (f ij ; i = 1, 2, 3, 4; j = 1, 2, 3, 4), PCC point voltage (v pcc ) and its amplitude (V pcc ). The third simulation condition is set as follows: the power distribution ratio of different series subnets is equal; the communication line between converter module 3 and module 4 in the four series subnets fails; before the simulation time t=4s, the system control strategy only adopts distributed layer 1 control; when the simulation time t=4s, the distributed layer 2 control is started; when the simulation time t=6s, the load step increases. Obviously, when the method of the present invention is adopted, the failure of some communication lines does not affect the precise distribution of active power and reactive power and the stable control of the AC output voltage amplitude, and the system operation reliability is significantly improved.

[0080] Embodiment 2

[0081] The purpose of this embodiment is to provide a distributed hierarchical control system for a multi-converter series-parallel microgrid, wherein the multi-converter series-parallel microgrid includes a plurality of series subnets, each of which includes a plurality of converter modules connected in series, and the output ends of each series subnet are connected in parallel to a common coupling point of the microgrid; in the series subnets, the first converter module in the series subnet is selected as a leader, and the remaining converter modules in the series subnet are selected as followers; each converter module communicates only with its neighbor converter modules; the distributed hierarchical control system includes:

[0082] Power allocation module: according to the normalized active and reactive power deviations between the converter modules corresponding to each leader and the adjacent converter modules of each leader, and the normalized active and reactive power deviations between the converter modules corresponding to each follower and the adjacent converter modules of the follower in the series subnet, the active and reactive power of each converter module is allocated;

[0083] AC voltage amplitude control module: controls the AC voltage amplitude of the microgrid according to the AC voltage amplitude of the microgrid common coupling point obtained by the leader's corresponding converter module, the AC voltage amplitude of the series subnet where the leader's corresponding converter module is located, and the AC voltage amplitude of the series subnet where the leader's adjacent converter module is located.

[0084] Embodiment 3

[0085] The purpose of this embodiment is to provide a computing device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor implements the steps of the above method when executing the program.

[0086] Embodiment 4

[0087] The purpose of this embodiment is to provide a computer-readable storage medium.

[0088] A computer-readable storage medium stores a computer program, which executes the steps of the above method when executed by a processor.

[0089] The steps involved in the apparatuses of the above embodiments 2, 3 and 4 correspond to the method embodiment 1, and the specific implementation methods can refer to the relevant description part of embodiment 1. The term "computer-readable storage medium" should be understood as a single medium or multiple media including one or more instruction sets; it should also be understood to include any medium that can store, encode or carry an instruction set for execution by a processor and enable the processor to execute any method in the present invention.

[0090] Those skilled in the art should understand that the modules or steps of the present invention described above can be implemented by a general-purpose computer device, or alternatively, they can be implemented by a program code executable by a computing device, so that they can be stored in a storage device and executed by the computing device, or they can be made into individual integrated circuit modules, or multiple modules or steps therein can be made into a single integrated circuit module for implementation. The present invention is not limited to any specific combination of hardware and software.

[0091] Although the above describes the specific implementation mode of the present invention in conjunction with the accompanying drawings, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A distributed hierarchical control method for a multi-converter series-parallel microgrid, wherein the multi-converter series-parallel microgrid comprises a plurality of series subnets, each of which comprises a plurality of series-connected converter modules, and the output ends of each series subnet are connected in parallel at a common coupling point of the microgrid, wherein: In the series subnet, the first converter module in the series subnet is selected as a leader, and the remaining converter modules in the series subnet are selected as followers; Each converter module communicates only with its neighbor converter modules, and the distributed hierarchical control method includes: For the leaders and followers of each series subnet, the active power and reactive power of different converter modules are accurately distributed based on the distributed one-layer control strategy, specifically: According to the normalized active and reactive power deviations of the converter modules corresponding to each leader and the adjacent converter modules of each leader in the series subnet, based on the simplified finite time regulator, a first reference angular frequency correction value and a first reference voltage amplitude correction value of the converter modules corresponding to each leader are obtained; According to the normalized active and reactive power deviations of the converter modules corresponding to each leader and the adjacent converter modules in the grid-connected relationship of each leader, based on the simplified finite time regulator, a second reference angular frequency correction value and a second voltage amplitude correction value of the converter modules corresponding to each leader are obtained; According to the normalized active and reactive power deviations between the converter modules corresponding to each follower and the adjacent converter modules of each follower in the series subnet, a reference angular frequency correction value and a voltage amplitude correction value of the converter modules corresponding to each follower are obtained based on a simplified finite time regulator; For the leaders of each series subnet, based on the distributed two-layer control strategy, the system AC output voltage amplitude stability control is achieved, specifically: according to the actual AC output voltage amplitude of the series subnet where each leader is located and the actual AC output voltage amplitude of the series subnet where the adjacent converter modules of each leader are located, the AC voltage amplitude compensation amount is determined by using a proportional integral controller; Determining the instantaneous reference voltage of each converter module according to the reference angular frequency correction value, the reference voltage amplitude correction value, the AC voltage amplitude compensation amount and the rated reference voltage amplitude of each converter module; According to the obtained instantaneous reference voltage of each converter module, a PWM driving signal is generated based on voltage-current dual closed-loop control to control the operation of each converter module.

2. The distributed hierarchical control method for a multi-converter series-parallel microgrid according to claim 1, characterized in that: The inductor current of the converter module LC output filter is used as the inner loop control, the capacitor voltage of the converter module LC output filter is used as the outer loop control, and the output of the inner loop control is used as the modulation wave, which is compared with the carrier to generate a corresponding PWM drive signal.

3. The distributed hierarchical control method for a multi-converter series-parallel microgrid according to claim 1, characterized in that: The rated reference voltage amplitude of the converter module corresponding to the leader is specifically: the product of the ratio of the reactive power rating of the converter module corresponding to the leader to the sum of the reactive power ratings of all converter modules in the series subnet where the leader is located, and the amplitude of the AC voltage at the common coupling point of the microgrid.

4. The distributed hierarchical control method for a multi-converter series-parallel microgrid according to claim 1, characterized in that: The rated reference voltage amplitude of the converter module corresponding to the follower is specifically: the product of the ratio of the reactive power rating of the converter module corresponding to the follower to the sum of the reactive power ratings of all converter modules in the series subnet where the follower is located, and the amplitude of the AC voltage at the common coupling point of the microgrid.

5. A distributed hierarchical control system for a multi-converter series-parallel microgrid, wherein the multi-converter series-parallel microgrid comprises a plurality of series subnets, each of which comprises a plurality of series-connected converter modules, and the output ends of each series subnet are connected in parallel at a common coupling point of the microgrid, characterized in that: In the series subnet, the first converter module in the series subnet is selected as a leader, and the remaining converter modules in the series subnet are selected as followers; Each converter module communicates only with its neighbor converter modules; The distributed hierarchical control system comprises: Power distribution module: For the leaders and followers of each series subnet, based on the distributed one-layer control strategy, the active power and reactive power of different converter modules are accurately distributed, specifically: According to the normalized active and reactive power deviations of the converter modules corresponding to each leader and the adjacent converter modules of each leader in the series subnet, based on the simplified finite time regulator, a first reference angular frequency correction value and a first reference voltage amplitude correction value of the converter modules corresponding to each leader are obtained; According to the normalized active and reactive power deviations of the converter modules corresponding to each leader and the adjacent converter modules in the grid-connected relationship of each leader, based on the simplified finite time regulator, a second reference angular frequency correction value and a second voltage amplitude correction value of the converter modules corresponding to each leader are obtained; According to the normalized active and reactive power deviations between the converter modules corresponding to each follower and the adjacent converter modules of each follower in the series subnet, a reference angular frequency correction value and a voltage amplitude correction value of the converter modules corresponding to each follower are obtained based on a simplified finite time regulator; AC voltage amplitude control module: For the leaders of each series subnet, based on the distributed two-layer control strategy, the system AC output voltage amplitude stability control is realized, specifically: according to the actual AC output voltage amplitude of the series subnet where each leader is located and the actual AC output voltage amplitude of the series subnet where the adjacent converter modules of each leader are located, the AC voltage amplitude compensation amount is determined by using a proportional integral controller; Dual closed-loop control module: Generates PWM drive signals based on voltage-current dual closed-loop control according to the instantaneous reference voltage of each converter module, and controls the operation of each converter module.

6. A computer device, characterized in that: include: A processor, a memory and a bus, wherein the memory stores machine-readable instructions executable by the processor, and when the computer device is running, the processor and the memory communicate through the bus, and when the machine-readable instructions are executed by the processor, the distributed hierarchical control method for a multi-converter series-parallel microgrid is performed.

7. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores a computer program, and when the computer program is executed by a processor, the distributed hierarchical control method for a multi-converter series-parallel microgrid as claimed in any one of claims 1 to 4 is executed.

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