Distributed micro-inverter cooperation system and method based on wireless communication

Abstract

The invention discloses a distributed micro inverter cooperation system and method based on wireless communication, relates to the field of new energy, and is used for realizing strict synchronization of alternating current output voltage, phase and frequency of a large number of distributed micro inverters connected in parallel. The distributed micro inverter units are in communication connection with the control center through the Internet of Things communication unit, and the control center generates, broadcasts and issues reference signals to the micro inverter units, so that the micro inverter units synchronize output voltage, phase and frequency according to instructions of the reference signals. The control center is further provided with main and standby center controllers to prevent single-point failure. Under the condition that extra wiring is not added, strict synchronous cooperation of the alternating current output by a large number of parallel micro inverter units in voltage, phase and frequency is achieved, and the method is suitable for a grid-connected or independently-networked distributed power generation station.

Description

Technical Field

[0001] The present invention relates to the field of new energy, and in particular to a distributed micro-inverter cooperation system and method based on wireless communication. Background Art

[0002] In a distributed micro-inverter system, the power output by a single micro-inverter is very small, and multiple micro-inverters need to be connected in parallel on a single-phase or three-phase AC bus to output a larger power to meet the power requirements of the grid or load. However, this requires multiple micro-inverters to achieve strict AC voltage equality (voltage sharing), frequency and phase synchronization of voltage and current, otherwise not only will they not be able to generate more power, but they may also cause each other's output power to cancel each other out.

[0003] The traditional modular inverter parallel solution requires physical voltage or current control circuits between multiple inverter modules to achieve voltage and current balancing and voltage and current phase synchronization between multiple modular inverters.

[0004] This solution can only be applied when multiple inverter modules are in the same physical chassis or physically close to each other. In a wide-area photovoltaic power generation system, the physical distance between the distributed micro-inverters at the panel level is far and scattered, and adding additional voltage and current control lines is costly, and additional control lines also greatly increase system complexity and failure points.

[0005] Another common method for synchronizing the output voltage and phase of multiple micro-inverters is to use a distributed control method, such as a droop control method, but this method has stability issues and is difficult to support precise control and stable output under parallel regulation of a large number (such as more than ten) of micro-inverters. In centralized large-scale photovoltaic power generation sites or other new energy power plants, the system requires dozens, hundreds or even thousands of micro-inverters to achieve precise AC output synchronization and collaboration. The above solutions cannot meet the synchronization requirements of distributed power stations. Summary of the invention

[0006] The object of the present invention is to provide a distributed micro-inverter cooperation system and method based on wireless communication to solve the above-mentioned problems, so as to achieve strict synchronization of the AC output voltage, phase and frequency of a large number of distributed micro-inverters connected in parallel.

[0007] The technical solution adopted by the present invention is as follows:

[0008] A distributed micro-inverter cooperation system based on wireless communication, comprising a plurality of micro-inverter units arranged in a distributed manner, wherein the micro-inverter units are used to access the direct current generated by the new energy power generation module; each of the micro-inverter units is respectively connected to a control center through an Internet of Things communication unit;

[0009] The control center is configured to: generate a reference signal indicating synchronization of output voltage, phase and frequency, and send the reference signal to each micro-inverter unit by broadcasting;

[0010] The micro inverter unit is configured to: invert the input direct current to output alternating current; and, in response to receiving the reference signal, synchronize the output voltage, phase and frequency according to the instruction of the reference signal.

[0011] Furthermore, the reference signal is an analog signal, which is obtained by modulating a sinusoidal wave signal for voltage and current synchronization by using amplitude modulation, phase modulation or frequency modulation on a predetermined analog carrier.

[0012] Furthermore, the reference signal is a digital signal, which carries digital information for voltage and current phase synchronization.

[0013] Furthermore, the control center also performs spread spectrum, scrambling or encryption on the generated reference signal.

[0014] Furthermore, the control center generates the reference signal according to a received upper-level power grid instruction.

[0015] Furthermore, the control center is also configured to adjust the reference signal according to the voltage, phase and frequency of the AC power on the AC busbar to which each of the micro-inverter units is connected in parallel.

[0016] Furthermore, the control center generates the reference signal according to a local clock.

[0017] Furthermore, the control center includes a main central controller and at least one backup central controller.

[0018] Furthermore, the power generation units connected to the micro-inverter units are all configured with distributed energy storage units.

[0019] A collaboration method based on the above-mentioned distributed micro-inverter collaboration system based on wireless communication, comprising:

[0020] The control center generates a reference signal indicating synchronization of output voltage, phase and frequency, and sends the reference signal to each micro-inverter unit by broadcasting;

[0021] Each of the micro-inverter units receives the reference signal and synchronizes the output voltage, phase and frequency according to the instruction of the reference signal.

[0022] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0023] 1. For distributed power generation sites, without adding additional wiring, the present invention realizes strict synchronization and coordination of the voltage, phase and frequency of the AC power output by a large number of parallel micro-inverter units without any delay effect.

[0024] 2. The present invention is equipped with a primary and backup central controller to avoid single point failure.

[0025] 3. The present invention not only supports the synchronous coordination of AC voltage, phase and frequency of micro-inverters according to the instructions of the upper power grid under grid-connected conditions, but also supports the self-implementation of the adjustment of the AC voltage, phase and frequency of the micro-inverter output under independent networking. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present invention will now be described by way of example with reference to the accompanying drawings, in which:

[0027] Figure 1 is a structural diagram of a distributed power generation unit in one embodiment.

[0028] Figure 2 is a structural diagram of a distributed micro-inverter cooperation system in one embodiment.

[0029] In the figure, 200 is an Internet of Things communication unit, 201 is a new energy power generation module, 202 is a power optimizer, 203 is a distributed energy storage unit, 204 is a micro inverter unit, 300 is a distributed power generation unit, 301 is a control center, 302 is a transformer, and 303 is a power quality controller / power regulation device. DETAILED DESCRIPTION

[0030] All features disclosed in this specification, or steps in all methods or processes disclosed, except mutually exclusive features and / or steps, can be combined in any manner.

[0031] Any feature disclosed in this specification (including any additional claims and abstract), unless otherwise stated, may be replaced by other equivalent or alternative features having similar purposes. That is, unless otherwise stated, each feature is only an example of a series of equivalent or similar features.

[0032] The distributed generation station includes a large number of distributed generation units 300, such as Figure 1As shown, each distributed power generation unit 300 includes a new energy power generation module 201, and the new energy power generation module 201 includes at least one new energy power generation unit, the so-called new energy power generation unit, that is, a minimum power generation unit such as a photovoltaic panel, a wind turbine, etc. Each distributed power generation unit 300 is configured with a micro inverter unit 204. Preferably, each distributed power generation unit 300 is also configured with a distributed energy storage unit 203. The new energy power generation module 201 is respectively connected to the distributed energy storage unit 203 and the micro inverter unit 204. The micro inverter unit 204 and the distributed energy storage unit 203 are connected to each other. The direct current generated by each new energy power generation module 201 is connected to the corresponding micro-inverter unit 204, and is converted into alternating current by the micro-inverter unit 204. The low-voltage alternating current output by each micro-inverter unit 204 is connected in parallel to the AC bus to increase the output power, and the excess generated electric energy is transmitted to the distributed energy storage unit 203 for storage; when the electric energy generated by the new energy power generation module 201 is insufficient to support the load or the grid needs, the distributed energy storage unit 203 supplements the electric energy. In addition, due to the design of the distributed energy storage unit 203, when the micro-inverter unit 204 implements the adjustment of the power quality index of the low-voltage alternating current output by the inverter, if the electric energy provided by the new energy power generation module 201 is insufficient, the distributed energy storage unit 203 can also be used to supply power, or to assist the new energy power generation module 201 in supplying power. Figure 2 As shown, the AC bus is connected to the transformer 302, and the control center 301 can obtain the power quality indicators at the transformer 302, such as voltage, current, phase, frequency, active power, reactive power and harmonic components, and adjust the voltage, phase and frequency of each micro inverter unit 204 according to the power quality indicators. The control center 301 can also adjust the power quality indicators of the AC power output by the transformer 302 through the power quality controller / power adjustment device 303.

[0033] Typically, each distributed power generation unit 300 is also equipped with a power optimizer 202 (such as an MPPT controller), which is connected to the new energy power generation module 201 to output the electric energy generated by the new energy power generation module 201 at the highest power. When the power optimizer 202 is configured, the new energy power generation module 201 outputs the generated electric energy to the power optimizer 202, and the power optimizer 202 performs power optimization and then outputs the power, which is respectively connected to the micro inverter unit 204 and the distributed energy storage unit 203.

[0034] Each distributed power generation unit 300 is equipped with an Internet of Things communication unit 200, which supports Internet of Things communication protocols, such as WIoTa, NB-IoT, LoRa, etc. The Internet of Things communication unit 200 is connected to the control center 300 and wirelessly communicates with it. The Internet of Things communication unit 200 serves as a bridge for communication between each distributed power generation unit 300 and the control center 301. In addition to being connected to the micro-inverter unit 204 in the distributed power generation unit 300, the Internet of Things communication unit 200 can also be connected to other units and modules, such as the new energy power generation module 201, the power optimizer 202 and the distributed energy storage unit 203. These units / modules can report their respective working parameters, and the control center 300 can also remotely control the working status of these units / modules.

[0035] Since a large number of distributed power generation units 300 are connected in parallel to output AC power, the AC power output by these distributed power generation units 300 (micro inverters) needs to achieve strict voltage balancing, and the phase and frequency of voltage and current need to be synchronized. In this regard, on the basis of realizing the distributed control of a large number of micro inverter units 204 by the control center 301, the control center 301 is configured to: generate a reference signal indicating the synchronization of output voltage, phase and frequency, and send the reference signal to each micro inverter unit 204 by broadcasting. Correspondingly, each micro inverter unit 204 synchronizes the output voltage, phase and frequency according to the instruction of the reference signal in response to receiving the reference signal.

[0036] Since each micro-inverter unit 204 communicates wirelessly with the control center 301 through the Internet of Things communication unit 200, each micro-inverter unit 204 can be configured with a device ID to achieve unique identification, or these micro-inverter units 204 can be grouped, and the micro-inverter units 204 in each group are respectively configured with the same group ID to achieve group management, so that the control center 301 can broadcast, groupcast / multicast and unicast the micro-inverter unit 204. The control center 204 adds a broadcast header to the reference signal to achieve synchronous transmission of the reference signal. In single-point communication / multicast communication, for example, when the control center 301 needs to shut down a certain or part of the distributed power generation unit 300, by configuring the device ID (or group ID) of the target micro-inverter unit 204 in the header, single-point communication / multicast communication with the target micro-inverter unit 204 can be achieved.

[0037] The reference signal can be in one of two forms:

[0038] 1) Analog signal: The analog signal is obtained by modulating a sinusoidal wave signal for voltage and current synchronization by amplitude modulation, phase modulation or frequency modulation on a predetermined analog carrier.

[0039] 2) Digital signal: The digital signal is obtained by periodically / non-periodically transmitting a digital phase reference on a predetermined digital channel. The digital phase reference uses the timing information for synchronizing the phases of voltage and current as a reference. The digital signal carries digital information for synchronizing the phases of voltage and current. In addition, the digital phase reference can also be spread spectrum, frequency modulated, scrambled, encrypted, etc. in a digital manner to prevent external attacks.

[0040] There are two types of networking for distributed power generation sites: one is connected to the power grid, and the other is an independent local network.

[0041] For the first networking mode, the control center 301 generates the reference signal according to the received upper power grid instruction, that is, the upper computer issues corresponding synchronization instructions to adjust the voltage, phase and frequency of each micro inverter unit 204 in the distributed power generation station. The upper computer can also adjust the issued synchronization instructions, and correspondingly, the reference signal generated by the control center 301 also needs to be adjusted accordingly.

[0042] For the independent networking mode, there is no need to consider other distributed power generation sites, so the relevant parameters for generating the reference signal may be pre-configured in the control center 301 .

[0043] Regardless of the networking form, the control center 301 generates the reference signal according to the local clock. In this way, for a large number of distributed power generation sites, since there can be multiple control centers 301, the control center 301 generates the reference signal locally, which can avoid the delay introduced by the host computer directly sending the reference signal, causing the control center 301 to forward the reference signal to the micro inverter unit 204, resulting in a phase delay.

[0044] In addition, in order to avoid single point failure, each control center 301 is equipped with a main central controller and at least one backup central controller, and the functions of each central controller are exactly the same. In this way, even if the main central controller fails, the backup central controller can immediately continue to complete the subsequent tasks.

[0045] Example 2

[0046] This embodiment proposes a distributed micro-inverter cooperation method, which is based on some or all of the design features of the distributed micro-inverter cooperation system based on wireless communication proposed in Embodiment 1.

[0047] The collaborative approach includes the following steps:

[0048] The control center 301 generates a reference signal indicating synchronization of output voltage, phase and frequency, and sends the reference signal to each micro inverter unit 204 by broadcasting.

[0049] Each micro inverter unit 204 receives the reference signal and synchronizes the output voltage, phase and frequency according to the instruction of the reference signal.

[0050] The reference signal generated by the control center 301 may be based on the instructions of the superior power grid command, or may be generated based on the voltage, phase, frequency and other parameters configured locally, and the selection is made based on the networking mode and corresponding requirements. For example, the relevant parameters may be configured locally, and the reference signal is generated by the locally configured voltage, phase, frequency and other parameters by default, but the superior power grid command has the highest priority, and the reference signal is generated based on the superior power grid command when the superior power grid command is received.

[0051] The present invention is not limited to the above-mentioned specific embodiments, but extends to any new features or any new combination disclosed in this specification, as well as any new method or process steps or any new combination disclosed.

Claims

1. A distributed micro-inverter cooperation system based on wireless communication, comprising a plurality of distributedly arranged micro-inverter units, wherein the micro-inverter units are used to access the direct current generated by the new energy power generation module; characterized in that: Each of the micro-inverter units is respectively connected to the control center through an Internet of Things communication unit; The control center is configured to: generate a reference signal indicating synchronization of output voltage, phase and frequency, and send the reference signal to each micro-inverter unit by broadcasting; The micro inverter unit is configured to: invert the input direct current to output alternating current; And, in response to receiving the reference signal, synchronizing the output voltage, phase and frequency according to the instruction of the reference signal.

2. The distributed micro-inverter cooperation system based on wireless communication according to claim 1, characterized in that: The reference signal is an analog signal, which is obtained by modulating a sinusoidal wave signal for voltage and current synchronization by using amplitude modulation, phase modulation or frequency modulation on a predetermined analog carrier.

3. The distributed micro-inverter cooperation system based on wireless communication according to claim 1, characterized in that: The reference signal is a digital signal, which carries digital information for voltage and current phase synchronization.

4. The distributed micro-inverter cooperation system based on wireless communication according to claim 3, characterized in that: The control center also performs spectrum spreading, scrambling or encryption on the generated reference signal.

5. The distributed micro-inverter cooperation system based on wireless communication according to claim 1, characterized in that: The control center generates the reference signal according to the received superior power grid instruction.

6. The distributed micro-inverter cooperation system based on wireless communication according to claim 1, characterized in that: The control center adjusts the reference signal according to the voltage, phase and frequency of the AC power detected on the AC busbar to which the micro inverter units are connected in parallel.

7. The distributed micro-inverter cooperation system based on wireless communication according to claim 1, characterized in that: The control center generates the reference signal according to a local clock.

8. The distributed micro-inverter cooperation system based on wireless communication according to claim 1, characterized in that: The control center includes a main central controller and at least one backup central controller.

9. The distributed micro-inverter cooperation system based on wireless communication according to claim 1, characterized in that: The power generation units connected to the micro-inverter units are all equipped with distributed energy storage units.

10. A collaborative method for a distributed micro-inverter collaborative system based on wireless communication according to any one of claims 1 to 9, characterized in that: include: The control center generates a reference signal indicating synchronization of output voltage, phase and frequency, and sends the reference signal to each micro-inverter unit by broadcasting; Each of the micro-inverter units receives the reference signal, and adjusts or synchronizes the output voltage, phase and frequency according to the instruction of the reference signal.

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