Inverter grid-connected system

Abstract

The utility model discloses an inverter grid-connected system. According to the system, the input end of an inverter is connected with a power generation system, the output end of the inverter is connected with a grid-connected power grid system through a controllable switch, and the control end of the controllable switch is connected with a dry contact of the inverter; the output end of the inverter is also provided with a load and a generator; a switch of the generator is connected with a dry contact of the inverter; the power detection circuit is arranged between the load and the generator and used for detecting the output power of the generator. The problems that in the prior art, a grid-connected system of a photovoltaic inverter is prone to being affected by a power grid, under the condition that the quality of the power grid is poor, working stability is poor, and photovoltaic power generation energy is prone to being wasted are solved.

Description

Technical Field

[0001] This application relates to the technical field of inverter control, and more particularly, to an inverter grid-connected system. Background Art

[0002] In the related art, with the increasing global demand for clean energy, photovoltaic power generation, as an important renewable energy source, has been more and more widely used. An inverter is a key device in a photovoltaic power generation system, which can convert the direct current generated by the photovoltaic into alternating current for grid connection operation.

[0003] However, in some places, the grid quality is poor and power outages often occur. Since the grid-connected inverter does not have an energy storage system, its output power is greatly affected by the light intensity and cannot ensure the normal operation of the load. At this time, the grid-connected inverter needs to stop running, thus wasting a large amount of photovoltaic power generation. Existing control methods often cannot make full use of photovoltaic power generation, which will affect the economic benefits of photovoltaic power generation.

[0004] It can be seen that the grid-connected system of the photovoltaic inverter in the related art is easily affected by the grid. In the case of poor grid quality, the working stability is poor, and it is easy to waste photovoltaic power generation energy. Summary of the Utility Model

[0005] The main purpose of this application is to provide an inverter grid-connected system to solve the problems that the grid-connected system of the photovoltaic inverter in the related art is easily affected by the grid, has poor working stability in the case of poor grid quality, and is easy to waste photovoltaic power generation energy.

[0006] According to one aspect of this application, an inverter grid-connected system is provided, including an inverter, a generator, and a power detection circuit; the input end of the inverter is connected to a power generation system, the output end of the inverter is connected to a grid-connected power grid system through a controllable switch, and the control end of the controllable switch is connected to a dry contact of the inverter; a load and the generator are further arranged at the output end of the inverter, and the switch of the generator is connected to the dry contact of the inverter; the power detection circuit is arranged between the load and the generator for detecting the output power of the generator.

[0007] As an optional embodiment, the power detection circuit includes a processor, a current sampling circuit, a voltage sampling circuit, and an electric meter; the current sampling circuit is arranged on the circuit between the generator and the load and is connected to the processor; the voltage sampling circuit is arranged on the circuit between the generator and the power grid and is connected to the processor; the electric meter is arranged on the circuit of the power grid and is connected to the inverter and the processor through a preset communication interface.

[0008] As an alternative embodiment, an amplifier is provided between the current sampling circuit and the voltage sampling circuit and the processor; the processor is connected to the electric meter through an electric meter communication circuit.

[0009] As an alternative embodiment, the current sampling circuit includes a current transformer and two current sampling resistors disposed at both ends of the current transformer; the current transformer is serially disposed on the circuit of the object to be sampled, and the current transformer is connected to the inverter through the preset communication interface; the voltage sampling circuit includes two voltage sampling resistors connected in parallel across the object to be sampled.

[0010] As an alternative embodiment, the processor includes an ARM processor and a DSP processor; the current sampling circuit and the voltage sampling circuit are connected to the ARM processor, and the electric meter is connected to the ARM processor; the ARM processor is connected to the DSP processor, and the DSP processor is connected to the inverter.

[0011] As an alternative embodiment, a signal relay is provided at the dry contact of the inverter; the signal relay is connected to the processor of the power detection circuit.

[0012] As an alternative embodiment, the processor is connected to the signal relay through a MOS field effect transistor; the gate of the MOS transistor is connected to the processor, the drain of the MOS transistor is connected to the signal relay, and the source of the MOS transistor is grounded.

[0013] As an alternative embodiment, the signal relay includes an inductor and a normally open switch; the normally open switch is disposed between the positive and negative terminals of the dry contact; the inductor is disposed near the metal gate of the normally open switch, one end of the inductor is connected to the drain of the MOS transistor, and the other end of the inductor is connected to a DC power supply.

[0014] As an alternative embodiment, a diode and a zener diode are connected in parallel across both ends of the inductor of the signal relay; the input end of the diode is connected to the drain of the MOS transistor, the output end of the diode is connected to the output end of the zener diode, and the input end of the zener diode is connected to the DC power supply.

[0015] As an alternative embodiment, the controllable switch is an air switch.

[0016] In this application, a generator is provided on the circuit connecting the output side of the inverter to the power grid system. The generator and the power grid can supply power to the load selectively. The generator acts as the power grid when the power grid loses power. By controlling the generator, its power output can be increased when the power generation of the inverter is insufficient, and decreased when the power generation of the inverter is large. The switch of the generator is connected to the dry contact of the communication port of the inverter, enabling the inverter to control the start and stop of the generator through the dry contact of the communication port. When the power grid is powered off, the generator is automatically started to supply power to the load, improving the working stability of the grid-connected system for the load. A power detection circuit is used to detect the voltage and power of each part for corresponding control. When the power grid voltage drops, it is determined that the power grid is powered off, and the power grid is disconnected through a controllable switch using the dry contact of the inverter, realizing the automatic control of the grid-connected system. The above power detection circuit can also monitor the power of the motor and the load to control the output power of the inverter, thereby realizing the utilization of the energy of the power generation system according to the actual usage requirements and achieving the purpose of saving electric energy. Furthermore, it solves the problems that the grid-connected system of the photovoltaic inverter in the related technology is easily affected by the power grid, has poor working stability under the condition of poor power grid quality, and is prone to wasting photovoltaic power generation energy. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The drawings described herein are used to provide a further understanding of the present application and form a part of the present application. The schematic embodiments of the present application and their descriptions are used to explain the present application and do not constitute an improper limitation to the present application. In the drawings:

[0018] Figure 1 is a schematic diagram of an inverter grid-connected system of a photovoltaic inverter disclosed in the present application;

[0019] Figure 2 is a schematic diagram of the power detection circuit disclosed in the present application;

[0020] Figure 3 is a schematic diagram of the connection circuit between the dry contact of the inverter and the processor disclosed in the present application.

[0021] Figure 4 is a schematic diagram of the working process of the grid-connected system disclosed in the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other. The present application will be described in detail below with reference to the drawings and in combination with the embodiments.

[0023] It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular forms are also intended to include the plural forms. In addition, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they specify the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0024] Unless otherwise specifically stated, the relative arrangements of components and steps, numerical expressions, and values set forth in these embodiments do not limit the scope of the present application. At the same time, it should be understood that, for the sake of convenience of description, the dimensions of the various parts shown in the drawings are not drawn in actual proportional relationships. Technologies, methods, and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and devices should be regarded as part of the authorization specification. In all the examples shown and discussed here, any specific value should be construed as merely exemplary and not as a limitation. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that like reference numerals and letters denote like items in the following drawings, and thus, once an item is defined in one drawing, it does not need to be further discussed in subsequent drawings.

[0025] See Figures 1 to 3 As shown, the present application provides an inverter grid-connected system, including an inverter, a generator, and a power detection circuit; the input end of the inverter is connected to the power generation system, the output end of the inverter is connected to the grid-connected power grid system through a controllable switch, and the control end of the controllable switch is connected to the dry contact of the inverter; a load and a generator are also arranged at the output end of the inverter, and the switch of the generator is connected to the dry contact of the inverter; the power detection circuit is arranged between the load and the generator and is used to detect the output power of the generator.

[0026] By arranging a generator on the output side of the inverter, the generator and the power grid can supply power to the load selectively. The switch of the generator is connected to the dry contact of the communication port of the inverter, so that the inverter can control the start and stop of the generator through the dry contact of the communication port. When the power grid is powered off, the connection between the inverter and the power grid is disconnected through the control of the controllable switch, and the generator is automatically started to supply power to the load. The generator acts as the power grid function when the power grid is powered off. Controlling the generator can increase the power output when the power generation of the inverter is insufficient and reduce the output when the power generation of the inverter is large. Improve the working stability of the grid-connected system for the load.

[0027] Use the power detection circuit to detect the voltage and power of each part and perform corresponding control. When the power grid voltage drops, it is determined that the power grid is powered off, and the power grid is disconnected through the controllable switch using the dry contact of the inverter, realizing the automatic control of the grid-connected system.

[0028] The above power detection circuit can also monitor the motor and load power to control the output power of the inverter, so as to realize the invocation of the energy of the power generation system according to the actual usage requirements, achieving the purpose of saving electric energy.

[0029] The power generation system connected to the above inverter can be a green power generation system such as a photovoltaic power generation system, a wind power generation system, a hydraulic power generation system, etc. Especially for a photovoltaic power generation system, it can be constructed by individual household users and connected to the power grid through an inverter. The electric energy generated by the photovoltaic power generation system can be used by household loads, and the surplus can also be fed into the power grid for use.

[0030] However, considering the different stabilities of the power grid in different regions and localities. For example, the stability of the urban power grid is higher than that of the rural power grid, and the stability of the power grid in developed regions is higher than that in underdeveloped regions. Especially during the peak electricity consumption period, the power grid with poor stability is prone to frequent power outages. However, the input of the power generation system to the power grid by the inverter depends on the operation of the inverter. In the case of a power grid outage, since the grid-connected inverter is greatly affected by the photovoltaic power generation, the method of solely supplying power to the load by the inverter cannot ensure the stable operation of the load. Therefore, to reduce the impact on the load when the load operates in an unstable power supply system, when the power grid is powered off, the inverter stops working and the load cannot operate normally.

[0031] Therefore, in this embodiment, the input end of the above inverter is connected to the power generation system, the output end of the inverter is connected to the power grid system through a controllable switch to achieve the grid-connected state, and the control end of the controllable switch is connected to the dry contact of the inverter. In the case of a power grid power failure, the path to the power grid can be quickly cut off through the controllable switch, and at the same time, a generator is connected and started. The generator can replace the power grid to maintain and ensure the normal operation of the load, avoiding the waste of photovoltaic energy caused by the inverter stopping working.

[0032] In theory, an energy storage device can also be set at the load end. In the case of a power outage and when the power of the power generation system is higher than the power of the load, the electric energy can be stored in the energy storage device. In the case where the power of the power generation system is insufficient to support the operation of the load, the electric energy is retrieved from the energy storage device to supply power to the load. In fact, the above energy storage device can also be understood as a kind of load.

[0033] In addition, the power of the power generation system will fluctuate, and the loads of individual households will also fluctuate. When the power grid is powered off, it is difficult to avoid the situation where the power of the power generation system is insufficient to support the operation of the load. Moreover, large-scale energy storage devices have high costs and poor safety, and are not suitable for the scenarios of individual household users.

[0034] To this end, a load and a generator are further arranged between the inverter and the power grid in this embodiment. The switch of the generator is connected to the dry contact of the inverter. When the power of the power generation system cannot meet the operation of the load, the generator can be turned on to supply power to the load to ensure the stable and effective operation of the load.

[0035] The above-mentioned control of the controllable switch and the generator by using the dry contact of the inverter can be carried out by manual operation. However, considering the long delay and poor reliability of manual operation, this embodiment adopts an automatic control method for circuit control.

[0036] Automatic control requires detecting the current, voltage, etc. of each circuit part in the grid-connected system. To this end, this embodiment also provides a power detection circuit, which is arranged between the power grid and the generator and is used to detect the output power of the inverter and the generator.

[0037] It should be noted that power is the product of voltage and current. The above power detection circuit also includes at least a current detection part and a voltage detection part. The specific circuit will be described later.

[0038] As an optional embodiment, the power detection circuit includes a processor, a current sampling circuit, a voltage sampling circuit and an electric meter; the current sampling circuit is arranged on the circuit between the generator and the load and is connected to the processor; the voltage sampling circuit is arranged on the circuit between the generator and the power grid and is connected to the processor; the electric meter is arranged on the circuit between the generator and the power grid and is connected to the inverter and the processor through a preset communication interface.

[0039] The power detection circuit mainly includes a voltage sampling circuit, a current sampling circuit, and a processor. The voltage sampling circuit samples the voltage, the current sampling circuit samples the current, and the processor performs operations to calculate the power.

[0040] As Figure 2 shown, the AC alternating voltage is sampled through the sampling resistors R1 and R2, and the current collected by the CT is sampled through the sampling resistors R5 and R6. That is, the voltage sampling circuit can include the sampling resistors R1 and R2, which are respectively connected in parallel at both ends of the object to be sampled. The current sampling circuit includes a current transformer CT connected in series on the circuit of the object to be sampled, and the sampling resistors R3 and R4, which are respectively connected in parallel at both ends of the current transformer CT.

[0041] The above-mentioned electric meter has the same function as the current transformer, both of which are used for current detection. The difference is the object of detection. The current transformer can be set on the circuit of the specific object to be sampled, while the electric meter can be set on the circuit of the power grid, connected to the inverter and the processor through a preset communication interface, detect the current at the end of the grid-connected system inputting to the power grid, and then can collect the current and voltage of the power grid. Further, it is judged whether the current and voltage of the power grid are abnormal to determine whether the power grid is powered off, such as Figure 4 shown.

[0042] As an optional embodiment, amplifiers are provided between the current sampling circuit and the voltage sampling circuit and the processor; the processor is connected to the electric meter through the electric meter communication circuit.

[0043] Considering that the signals directly sampled by the voltage sampling circuit and the current sampling circuit are very small and may not be recognized when transmitted to the processor, therefore, the sampled signals can be amplified by the amplifier so that the processor can effectively receive the data of the sampled signals.

[0044] The above-mentioned electric meter communication circuit can be an RS485 communication circuit, which can directly transmit data such as current, voltage and power.

[0045] As an optional embodiment, the current sampling circuit includes a current transformer and two current sampling resistors arranged at both ends of the current transformer; the current transformer is connected in series on the circuit of the object to be sampled, and the current transformer is connected to the inverter through a preset communication interface; the voltage sampling circuit includes two voltage sampling resistors connected in parallel at both ends of the object to be sampled.

[0046] As Figure 1 and Figure 2 shown, that is, the voltage sampling circuit can include sampling resistors R1 and R2, which are respectively connected in parallel at both ends of the object to be sampled. The current sampling circuit includes a current transformer CT connected in series on the circuit of the object to be sampled, and sampling resistors R3 and R4, which are respectively connected in parallel at both ends of the current transformer CT. Thus, effective current sampling and voltage sampling are carried out on the generator, the load and the inverter.

[0047] The current transformer CT is arranged on the circuit between the generator, the load, the inverter and the power grid, and the current transformer is connected to the inverter through a preset communication interface. The preset communication interface is also Figure 1 the CT / Meter in, which can be understood as the current transformer communication interface / electric meter communication interface and can communicate directly with the current transformer or the electric meter. In this embodiment, it can be an RS485 communication interface, and the corresponding RS485 communication circuit is used for communication. It can directly transmit data such as current, voltage and power.

[0048] As an alternative embodiment, the processor includes an ARM (Advanced RISC Machine) processor and a DSP (Digital Signal Processing) processor; the current sampling circuit and the voltage sampling circuit are connected to the ARM processor, and the electricity meter is connected to the ARM processor; the ARM processor is connected to the DSP processor, and the DSP processor is connected to the inverter.

[0049] Adopting the dual-processor mode of ARM and DSP can not only achieve electrical isolation to ensure circuit safety, but also improve the efficiency of data processing and calculation efficiency.

[0050] The sampled current and / or voltage signals are transmitted to the ARM, and the ARM then sends the collected data and the data such as voltage, current, power, and phase transmitted by the electricity meter to the DSP, and the DSP processes the data to obtain the grid-connected power input by the grid-connected system to the power grid, the output power of the inverter, and the power generated by the generator. Then, through power loop control, a suitable duty cycle is output to the inverter circuit to adjust the output power of the inverter through the inverter circuit.

[0051] As an alternative embodiment, a signal relay is provided at the dry contact of the inverter; the signal relay is connected to the processor of the power detection circuit.

[0052] As Figure 3 shown, a signal relay is provided between the positive and negative poles of the dry contact of the inverter. When the signal relay is closed, the positive and negative poles of the dry contact are connected, forming a short circuit between the positive and negative poles, which can control the generator switch to close to start the generator, or close the controllable switch to turn on the controllable switch.

[0053] Conversely, when the signal relay is opened, the positive and negative poles of the dry contact are disconnected, forming an open circuit between the positive and negative poles, which can control the generator switch to open to turn off the generator, or disconnect the controllable switch to turn off the controllable switch.

[0054] The signal relay is connected to the processor and is controlled by the processor, thereby realizing the automatic control of the generator and the controllable switch, improving the control efficiency, and further being more energy-saving and operating more safely and reliably.

[0055] As an alternative embodiment, the processor is connected to the signal relay through a MOS (Metal Oxide Semiconductor) field-effect transistor; the gate of the MOS transistor is connected to the processor, the drain of the MOS transistor is connected to the signal relay, and the source of the MOS transistor is grounded.

[0056] The above MOS transistor can be a PMOS transistor or an NMOS transistor. Taking the PMOS transistor as an example, the processor is connected to the signal relay through the PMOS transistor Q1; the gate of the PMOS transistor is connected to the processor, the drain of the PMOS transistor is connected to the signal relay, and the source of the PMOS transistor is grounded. The processor can use the output high and low level signals to control the on / off of the PMOS transistor, and then control the DC power supply DC, the inductor on the primary side of the signal relay, and the on / off of the loop of the PMOS transistor to charge and discharge the inductor.

[0057] When there is current passing through the inductor, a magnetic field is generated around it, attracting the metal gate of the normally open switch on the secondary side of the signal relay, causing the positive and negative poles of the dry contact to be short-circuited. When there is no current passing through the inductor, the magnetic field around it disappears, and the metal gate of the normally open switch on the secondary side of the signal relay automatically disconnects, causing the positive and negative poles of the dry contact to be open-circuited.

[0058] As an alternative embodiment, the signal relay includes an inductor and a normally open switch; the normally open switch is arranged between the positive and negative terminals of the dry contact; the inductor is arranged near the metal gate of the normally open switch, one end of the inductor is connected to the drain of the MOS transistor, and the other end of the inductor is connected to the DC power supply.

[0059] The ARM processor controls the IO port to send a high level, driving the PMOS transistor Q1 to conduct. The 12V DC power supply DC flows through the inductor on the primary side of the signal relay and the PMOS transistor Q1, generating excitation. The normally open switch on the secondary side of the signal relay closes, short-circuiting the positive and negative poles of the dry contact.

[0060] As an alternative embodiment, a diode and a voltage stabilizing diode are connected in parallel at both ends of the inductor of the signal relay; the input end of the diode is connected to the drain of the MOS transistor, the output end of the diode is connected to the output end of the voltage stabilizing diode, and the input end of the voltage stabilizing diode is connected to the DC power supply.

[0061] When the ARM controls the IO port to send a low level, the PMOS transistor Q1 closes. The energy on the inductor on the primary side of the signal relay forms a loop through the diode D1 and the voltage stabilizing diode D2, quickly releasing the energy. The normally open switch on the secondary side of the signal relay reconnects, opening the positive and negative poles of the dry contact.

[0062] As an alternative embodiment, the controllable switch is an air switch.

[0063] The air switch combines control and multiple protection functions. In addition to being able to complete the contact and disconnection of the circuit, it can also protect against short circuits, severe overloads, and undervoltage that occur in the circuit or electrical equipment. At the same time, it can also be used to start the motor infrequently.

[0064] Considering that both the power grid and the inverter output are alternating current, therefore, this embodiment can use an AC air switch to enable normal control of the circuit.

[0065] It should be noted that this embodiment also provides an alternative implementation manner, which will be described in detail below.

[0066] This embodiment provides an inverter system equipped with a generator, and the main contents are as follows:

[0067] 1. The combined use of the inverter and the generator: The inverter and the generator are used in combination. The output side of the inverter, the commercial power grid, is connected to the generator. The generator switch is connected to the dry contact of the communication port of the inverter. The inverter can control the start and stop of the generator. At the same time, a controllable AC circuit breaker is connected to the incoming side, and the control signal is connected to the dry contact signal of the inverter. The inverter can control the generator and the circuit breaker connected to the commercial power grid.

[0068] 2. The use of multiple electric meters and CTs: A CT and an electric meter are connected to the inverter. The electric meter is located between the generator and the commercial power grid, and the CT is located between the generator and the load. The electric meter communicates directly with the inverter through 485 and can transmit data such as voltage and power. This usage method can monitor the working status of the generator and the inverter in real time, facilitating fault diagnosis and repair.

[0069] 3. Optimized control method: By controlling the output power of the inverter, effective control of the generator can be achieved, thereby reducing the output power of the generator, improving the operation efficiency of photovoltaic power generation, and reducing the losses of the generator. Make full use of the photovoltaic power generation amount and improve the economic benefits of photovoltaic power generation.

[0070] Thus, effectively solve the problems such as low operating efficiency of the generator, complex communication wiring between the inverter and the generator, and the existing control methods being unable to make full use of the photovoltaic power generation amount.

[0071] The sampling circuit and the power control circuit are as Figure 2 shown. This circuit samples the AC voltage of the power grid and the CT current using the corresponding sampling circuits. Then, after proportional amplification, it is transmitted to the ARM. The ARM then sends the collected data and the voltage, current, power, phase and other data transmitted by the electric meter to the DSP, and the DSP processes the data to obtain the grid-connected power input by the grid-connected system to the power grid, the output power of the inverter and the power generation power of the generator. Then, through power loop control, an appropriate duty cycle is output to the inverter circuit, and the inverter circuit is used to adjust the output power of the inverter.

[0072] Specifically, the AC alternating voltage is sampled through sampling resistors R1 and R2, transmitted into the amplifier, combined with resistors R3 and R4, and the sampled voltage signal is amplified using the DC voltage source DC, and then transmitted to the ARM. Similarly, for the current collected by the CT, it is sampled through sampling resistors R5 and R6, transmitted into the amplifier, combined with resistors R7 and R8, and the sampled voltage signal is amplified using the DC voltage source DC, and then transmitted to the ARM.

[0073] The dry contact control circuit is as Figure 3 shown. Through this circuit, the ARM can control the start and stop of the generator and the opening and closing of the air switch according to the grid voltage collected by the electric meter and the sampling circuit. Specifically, through this circuit, the ARM can control the open circuit and short circuit of the dry contact ± according to the grid voltage collected by the electric meter and the sampling circuit, so as to control the start and stop of the generator and the opening and closing of the air switch.

[0074] The specific working state is as follows: The ARM controls the IO port to send a high level, driving the MOS transistor Q1 to conduct. The 12V power supply flows through the primary side of the signal relay and the MOS transistor Q1, generating excitation, and the secondary side of the signal relay closes, short-circuiting the dry contact ±; The ARM controls the IO port to send a low-level instruction, the MOS transistor Q1 closes, and the energy on the inductor of the primary side of the signal relay forms a loop through the diode D1 and the voltage regulator diode D2 to quickly release the energy, and the secondary side of the signal relay disconnects, opening the dry contact ±.

[0075] The grid-connected system is composed of the following: Module 1: An inverter with an RS485 communication interface for communicating with the electric meter. Module 2: A generator with two modes of manual start and automatic start. Connect the switch of the generator to the dry contact of the communication port of the inverter, so that the inverter can control the start and stop of the generator through the dry contact signal. Module 3: A qualified controllable AC air switch is placed on the grid side, and the control signal is connected to the inverter. The inverter can control its switch through the dry contact. Module 4: A current transformer (CT) and an electric meter for real-time monitoring of the working states of the generator and the inverter. The CT is used to measure the output current of the generator.

[0076] Connect all modules according to the wiring method of the system Figure 1 When the grid power is cut off, the electric meter detects that the grid voltage is 0, and the data is transmitted to the inverter. The inverter is disconnected from the grid, and then the AC air switch is disconnected from the grid through the dry contact, and the generator is controlled to start. The inverter operates in parallel with the grid based on the output voltage of the generator. The power output of the inverter and the generator is monitored through CT sampling, and the power output of the inverter is adjusted to reduce the generator loss, thereby improving the utilization rate of photovoltaic power generation, reducing the generator loss, and enhancing the efficiency of the entire system.

[0077] After the power grid supplies power, the power grid side meter reads that the grid voltage is normal and transmits the information to the inverter. The inverter controls the generator to shut down, the AC switch on the power grid side is turned on, and the inverter operates in parallel with the grid normally. The control logic is as follows Figure 4 shown. The grid voltage is collected by the meter to determine whether the grid voltage is normal. If it is normal, it means that the grid is stable and working properly, and the inverter can be directly connected to the grid for operation. If the grid voltage is abnormal, it can be considered that there is a fault in the grid and a power outage occurs. The inverter controls the controllable AC switch to disconnect the circuit between the grid-connected system and the grid, and starts the generator to use the electric energy converted by the generator system in combination with the inverter.

[0078] The CT is used to detect whether there is current in the circuit between the load and the generator. If there is current, it means that the load is working, and the corresponding power adjustment strategy needs to be adopted to adjust the power of the inverter. If there is no current, it means that the load is not working, and the power of the inverter does not need to be adjusted temporarily.

[0079] Specifically, the above power detection circuit can be used to detect the power of the load and the generator to compare whether the output power of the motor can meet the load demand. If it can meet the demand, the output power of the inverter can be reduced or even turned off. If it does not meet the demand, the output power of the inverter can be increased to cooperate with the output power of the generator to provide stable power supply for the load.

[0080] In this embodiment, a CT and a meter are connected to the inverter. The meter is located between the generator and the mains power grid, and the CT is located between the generator and the load. The meter and the inverter communicate directly through 485 to transmit data such as voltage and power. This usage method can monitor the output power of the generator and the inverter in real time. Both the CT and the meter can be replaced by other sampling periods. The inverter can control the AC switch and the start and stop of the generator to achieve automatic switching and reduce the load power outage time. The power consumption of the generator can be reduced by controlling the output power of the inverter, the utilization rate of photovoltaic clean energy can be improved, the loss of the generator can be reduced, and the efficiency of the entire system can be improved.

[0081] For ease of description, spatial relative terms such as "above", "over", "on the upper surface", "upper" etc. may be used herein to describe the spatial positional relationship of one device or feature to other devices or features as shown in the figures. It should be understood that the spatial relative terms are intended to encompass different orientations in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is inverted, a device described as "above" or "over" other devices or structures will then be positioned "below" or "under" the other devices or structures. Thus, the exemplary term "above" can include both orientations of "above" and "below". The device may also be positioned in other different ways (rotated 90 degrees or in other orientations), and the corresponding explanations for the spatial relative descriptions used herein will be made accordingly.

[0082] In addition, it should be noted that the use of terms such as "first", "second" etc. to limit components is only for the convenience of differentiating the corresponding components. Without additional statements, the above terms have no special meanings, and thus should not be construed as limiting the protection scope of the present application.

[0083] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, various changes and modifications can be made to the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. An inverter grid-connected system, characterized in that: Including inverter, generator, power detection circuit; The input end of the inverter is connected to the power generation system, the output end of the inverter is connected to the grid-connected power system through a controllable switch, and the control end of the controllable switch is connected to the dry contact of the inverter; The output end of the inverter is also provided with a load and the generator, and the switch of the generator is connected to the dry contact of the inverter; The power detection circuit is arranged between the load and the generator, and is used for detecting the output power of the generator.

2. The inverter grid-connected system according to claim 1, characterized in that: The power detection circuit includes a processor, a current sampling circuit, a voltage sampling circuit and an electric meter; The current sampling circuit is arranged on the circuit between the generator and the load, and is connected to the processor; The voltage sampling circuit is arranged on the circuit between the generator and the power grid, and is connected to the processor; The electric meter is arranged on the circuit of the power grid and is connected to the inverter and the processor via a preset communication interface.

3. The inverter grid-connected system according to claim 2, characterized in that: An amplifier is provided between the current sampling circuit and the voltage sampling circuit and the processor; The processor is connected to the electric meter via an electric meter communication circuit.

4. The inverter grid-connected system according to claim 2, characterized in that: The current sampling circuit includes a current transformer and two current sampling resistors arranged at two ends of the current transformer; The current transformer is arranged in series on the circuit of the object to be sampled, and the current transformer is connected to the inverter via the preset communication interface; The voltage sampling circuit includes two voltage sampling resistors connected in parallel at two ends of an object to be sampled.

5. The inverter grid-connected system according to claim 2, characterized in that: The processor includes an ARM processor and a DSP processor; The current sampling circuit and the voltage sampling circuit are connected to the ARM processor, and the electric meter is connected to the ARM processor; The ARM processor is connected to the DSP processor, and the DSP processor is connected to the inverter.

6. The inverter grid-connected system according to claim 1, characterized in that: The dry contacts of the inverter are provided with signal relays; The signal relay is connected to the processor of the power detection circuit.

7. The inverter grid-connected system according to claim 6, characterized in that: The processor is connected to the signal relay via a MOS tube; The gate of the MOS tube is connected to the processor, the drain of the MOS tube is connected to the signal relay, and the source of the MOS tube is grounded.

8. The inverter grid-connected system according to claim 7, characterized in that: The signal relay includes an inductor and a normally open switch; The normally open switch is arranged between the positive terminal and the negative terminal of the dry contact; The inductor is arranged near the metal gate of the normally open switch, one end of the inductor is connected to the drain of the MOS tube, and the other end of the inductor is connected to a direct current power supply.

9. The inverter grid-connected system according to claim 8, characterized in that: A diode and a voltage regulator diode are connected in parallel at both ends of the inductor of the signal relay; The input end of the diode is connected to the drain of the MOS tube, the output end of the diode is connected to the output end of the voltage regulator diode, and the input end of the voltage regulator diode is connected to the DC power supply.

10. The inverter grid-connected system according to any one of claims 1 to 9, characterized in that: The controllable switch is an air switch.

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