Three-port electric energy metering device and metering method suitable for photovoltaic grid connection

Abstract

The invention relates to a three-port electric energy metering device suitable for photovoltaic grid connection and a metering method. The three-port electric energy metering device comprises a shell, and a control module, a measurement module, a clock module, a storage module, a display module, a power supply module and a communication module which are integrally mounted in the shell, the measuring module detects voltage and current of a power grid side, a photovoltaic side and a load side through a first port, a second port, a third port and a common port, and transmits detected data to the control module. The control module is used for processing measurement data and controlling the state of the electric energy meter. The clock module is used for providing time coordinates for the system; the storage module is used for storing various acquired and calculated data; the display module displays voltage, current, power and electric energy; the power supply module provides energy for normal work of the electric energy meter. And the communication module establishes communication with an upper computer. According to the invention, efficient, integrated, simple and accurate three-port electric energy metering is realized.

Description

Technical Field

[0001] This invention belongs to the field of electricity metering, and particularly relates to a three-port electricity metering device and metering method suitable for photovoltaic grid connection. Background Technology

[0002] With the rapid development of distributed photovoltaic (PV) systems, the number of low-voltage residential PV installations is increasing daily. Most residential PV systems adopt a self-consumption model with surplus power fed into the grid. Grid-connected distributed PV systems are typical three-port networks, with the three ports belonging to the grid side, the PV side, and the load side, respectively. To accurately measure the PV system's power generation, grid-connected power, and user consumption, a power metering installation scheme needs to be determined.

[0003] Currently, there are two main metering schemes: The first method involves installing metering devices at three ports to separately measure the energy exchanged with the grid, photovoltaic power generation, and user electricity consumption. This method offers intuitive and accurate metering, but it has the following drawbacks: installing meters at three ports occupies a large space, is costly, and is difficult and cumbersome to install and debug.

[0004] The second approach is to eliminate one of the meters. Based on Kirkov's current law, the current at the third port can be calculated from the current at two of the ports, thus determining the electrical energy at each port. This method significantly improves cost and maintenance, but it still presents the following problems: First, two meters measuring the same voltage point leads to duplicate metering, and there is redundancy in components such as the LCD display module and carrier communication module of the two meters. Second, the wiring between the meters is complex, prone to errors, and time-consuming, with high consumption of consumables such as wires. Third, both meters need to be debugged simultaneously, increasing the difficulty of system debugging and on-site maintenance. Fourth, to calculate the user's actual electricity consumption, the clocks of the two meters must be strictly synchronized, requiring high accuracy. Fifth, the meter box has high investment costs and occupies a large area, making on-site installation difficult. Summary of the Invention

[0005] This invention addresses the shortcomings of existing technologies by proposing a three-port power metering device and method suitable for photovoltaic grid connection. This solves the problems of high cost, complex wiring, and large footprint of existing metering schemes, thereby achieving efficient, integrated, simple, and accurate three-port power metering.

[0006] One of the above-mentioned objectives of the present invention is achieved by the following technical solution: A three-port electricity metering device suitable for photovoltaic grid connection includes a housing and a control module, a measurement module, a clock module, a storage module, a display module, a power supply module, and a communication module integrated and installed within the housing. The measurement module, clock module, storage module, and display module are all connected to the control module, and the power supply module is connected to the other modules. The measurement module detects voltage and current on the grid side, photovoltaic side, and load side through a first port, a second port, a third port, and a common port, and transmits the detected data to the control module. The control module controls the working state of the electricity meter, periodically activates the sampling circuit to acquire instantaneous voltage and current data, calculates power and electrical energy, and periodically updates the display on the display module. The control module also handles communication with the host computer and human-machine interaction requirements. The clock module provides the system with a time coordinate. The storage module stores the various data collected and calculated. The display module displays physical quantities such as voltage, current, power, and electrical energy. The power supply module provides energy for the normal operation of the electricity meter. The communication module establishes communication with the host computer.

[0007] Furthermore, the measurement module consists of one voltage measurement module and two current measurement modules. The voltage measurement module converts the high voltage to a low voltage through a series resistor voltage divider, and then outputs the voltage measurement signals at the grid connection points of the grid side, photovoltaic side, and load side after isolation by an operational amplifier. The two current measurement modules are installed at two of the three ports on the grid side, photovoltaic side, and load side, respectively, to measure the current signals flowing into the two ports. The current measurement modules convert the current into voltage signals for measurement through a shunt.

[0008] Moreover, the control module uses a microcontroller or a digital signal processor.

[0009] Moreover, the clock module uses a clock chip with a communication interface that can synchronize, correct, and keep time.

[0010] Furthermore, the storage module uses a flash memory.

[0011] Furthermore, the display module can be a liquid crystal display screen.

[0012] Furthermore, the power module employs an AC / DC rectifier.

[0013] Furthermore, the communication module can employ communication methods such as power line carrier, RS485, and infrared.

[0014] The second objective of this invention is achieved through the following technical solution: A metering method based on the above-mentioned three-port electricity metering device suitable for photovoltaic grid connection includes the following steps: Step 1: Obtain the instantaneous voltage values ​​at the grid connection points of the grid side, photovoltaic side, and load side. u Instantaneous values ​​of the inflow current at the first and third ports i 1. i 3; and calculate the instantaneous value of the current flowing into the second port according to Kirkowski's Current Law: i 2 = - ( i 1+ i 3); Step 2: Based on the phase-locked loop (PLL) module of the control module, obtain the system frequency f and the signal period T=1 / f.

[0015] Step 3: Calculate the active power of the signals acquired at the first, second, and third ports. According to the definition of active power, active power P refers to the average value of instantaneous power (p=u*i) over one period T. Therefore, the active power of the signals acquired at the three ports... P x The calculation formula is:

[0016] in, N The number of sampling points within one period T. n Sampling time ( n =1,..., N ), u n The instantaneous value of the grid connection point voltage at each sampling time. i xn For the first x port( x =1,2,3) The instantaneous current value at each sampling time.

[0017] Step 4: Calculate the active energy of the signals acquired at the first, second, and third ports. According to the definition of active energy, active energy W refers to the integral value of instantaneous power over a certain period of time. The active energy injected from the three ports is the electrical energy. W x The calculation formula is:

[0018] in, W 0 represents the previously accumulated active electrical energy. W x For the first x port( x =1,2,3) Current total active electrical energy.

[0019] Step 5: Calculate the effective values ​​of voltage and current according to the definition of effective value. U , I 1. I 2. I 3; The formula for calculating the grid connection point voltage is:

[0020] No. x Port current Ix ( x The formula for calculating (=1,2,3) is:

[0021] in, u xn For the first x port( x =1,2,3) in n time( n =1,..., N The measured voltage across the shunt, R This is the resistance value of the shunt.

[0022] Step 6: Calculate the power factor and apparent power of the three ports according to the definition of apparent power. S x ( x The formula for calculating (=1,2,3) is:

[0023] Step 7: Calculate the power factor angles of the three ports. x ( x =1,2,3), the calculation formula is:

[0024] Step 8: Calculate the reactive power at the three ports. Q x The calculation formula is: .

[0025] The advantages and positive effects of this invention are as follows: 1. This invention combines the measurements of the three ports, improving the original one voltage measurement unit and one current measurement unit in the energy meter to one voltage measurement unit and two current measurement units. The energy data of each of the three ports can be calculated through the control and calculation module. This greatly simplifies the metering scheme. Taking a single-phase system as an example, the device only needs 4 external terminals. Compared with the first scheme of 3 energy meters and 12 terminals and the second scheme of 2 energy meters and 8 terminals, the number of terminals can be greatly reduced.

[0026] 2. This invention is applicable to three-port metering scenarios such as distributed photovoltaic self-consumption and surplus electricity fed into the grid. Compared to current data acquisition schemes that require at least two meters, its advantages are: First, it eliminates the need for one energy metering device, efficiently reusing clock, display, and communication modules, simplifying metering; second, it reduces the number of connecting wires between meters, lowering the possibility of incorrect wiring and saving consumables; third, it standardizes data acquisition, facilitating unified on-site installation and system debugging; fourth, it uses the same clock, eliminating the need to consider clock differences and facilitating energy calculation across the three ports; and fifth, it has a small footprint and high user acceptance. After general promotion, this invention can be applied to common three-port metering scenarios. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of an existing metering scheme that uses three metering devices; Figure 2 This is a schematic diagram of an existing metering scheme that uses two metering devices; Figure 3 This is a schematic diagram of the metering scheme of the metering device of the present invention; Figure 4 This is a structural diagram of the measuring device of the present invention; Figure 5 This is a circuit diagram of the voltage measurement module of the present invention; Figure 6 This is a circuit diagram of the current measurement module of the present invention; Figure 7 This is a flowchart of the energy calculation process of the three-port energy meter of the present invention; Figure 8 This is a flowchart of the sampling process for the three-port energy meter of the present invention. Detailed Implementation

[0028] The structure of the present invention will be further described below with reference to the accompanying drawings and embodiments. It should be noted that these embodiments are descriptive and not limiting.

[0029] Please refer to the following for a three-port power metering device suitable for photovoltaic grid connection. Figures 1-8 The invention comprises a housing and integrated within the housing are a control module, a measurement module, a clock module, a storage module, a display module, a power module, and a communication module. The measurement module, clock module, storage module, and display module are all connected to the control module, and the power module is connected to other modules.

[0030] The measurement module detects the voltage and current on the grid side, photovoltaic side, and load side through a first port, a second port, a third port, and a common port, and transmits the detected data to the control module. The measurement module consists of one voltage measurement module and two current measurement modules. The voltage measurement module converts the high voltage to a low voltage using a series resistor divider, and then outputs the voltage measurement signal at the grid connection point of the grid side, photovoltaic side, and load side after isolation by an operational amplifier. Since the grid side, photovoltaic side, and load side are connected in parallel, the voltage signal at the grid connection point is the common voltage signal of the grid side, photovoltaic side, and load side. The two current measurement modules are installed at two of the three ports on the grid side, photovoltaic side, and load side, respectively, to measure the current signals flowing into the two ports. The current measurement modules convert the current into a voltage signal for measurement through a shunt.

[0031] The control module is used to control the working status of the electricity meter, start the sampling circuit at regular intervals to obtain instantaneous voltage and current data, calculate physical quantities such as power and energy according to the corresponding formulas, and update the display on the display module periodically. The control module also needs to handle application requirements such as communication with the host computer and human-computer interaction. The control module can be a microcontroller or a digital signal processor.

[0032] The clock module is used to provide time coordinates for the system. The clock module can be a dedicated clock chip with a communication interface that can synchronize, correct, and keep time.

[0033] The storage module is used to store various data collected and calculated, and the storage module may be a flash memory.

[0034] The display module is used to display physical quantities such as voltage, current, power, and electrical energy. The display module may be an LCD screen.

[0035] The power module is used to provide energy for the normal operation of the electricity meter, and the power module may be an AC / DC rectifier.

[0036] The communication module is used to establish communication with the host computer. The communication module can use communication methods such as power line carrier, RS485, and infrared.

[0037] When the electricity meter is working, it acquires system voltage and three-port current data at fixed intervals. Through coordinate transformation and calculation, it obtains the effective values ​​of voltage and current, as well as physical quantities such as active power and reactive power. Combined with the current time, the data is stored in the storage module. The data in the storage module is periodically transmitted to the display module to display the current data in rotation.

[0038] For a metering method based on the above-mentioned three-port energy metering device suitable for photovoltaic grid connection, please refer to [link to relevant documentation]. Figure 6 and Figure 7It includes the following steps: Step 1: Obtain the instantaneous voltage values ​​at the grid connection points of the grid side, photovoltaic side, and load side. u Instantaneous values ​​of the inflow current at the first and third ports i 1. i 3; and calculate the instantaneous value of the current flowing into the second port according to Kirkowski's Current Law: i 2 = - ( i 1+ i 3); Step 2: Based on the phase-locked loop (PLL) module (a phase-locked loop is a control algorithm implemented in the control module), obtain the system frequency f and the signal period T = 1 / f; Step 3: Calculate the active power of the signals acquired at the first, second, and third ports. According to the definition of active power, active power P refers to the average value of instantaneous power (p=u*i) over one period T. Therefore, the active power of the signals acquired at the three ports... P x The calculation formula is:

[0039] in, N The number of sampling points within one period T. n Sampling time ( n =1,..., N ), u n The instantaneous value of the grid connection point voltage at each sampling time. i xn For the first x port( x =1,2,3) The instantaneous current value at each sampling time.

[0040] Step 4: Calculate the active energy of the signals acquired at the first, second, and third ports. According to the definition of active energy, active energy W refers to the integral value of instantaneous power over a certain period of time. The active energy injected from the three ports is the electrical energy. W x The calculation formula is:

[0041] in, W 0 represents the previously accumulated active electrical energy. W x For the first x port( x =1,2,3) Current total active electrical energy.

[0042] Step 5: Calculate the effective values ​​of voltage and current according to the definition of effective value. U ,I 1. I 2. I 3; The formula for calculating the grid connection point voltage is:

[0043] No. x Port current I x ( x The formula for calculating (=1,2,3) is:

[0044] in, u xn For the first x port( x =1,2,3) in n time( n =1,..., N The measured voltage across the shunt, R This is the resistance value of the shunt.

[0045] Step 6: Calculate the power factor and apparent power of the three ports according to the definition of apparent power. S x ( x The formula for calculating (=1,2,3) is:

[0046] Step 7: Calculate the power factor angles of the three ports. x ( x =1,2,3), the calculation formula is:

[0047] Step 8: Calculate the reactive power at the three ports. Q x The calculation formula is: .

[0048] Although embodiments and drawings of the present invention have been disclosed for illustrative purposes, those skilled in the art will understand that various substitutions, variations and modifications are possible without departing from the spirit and scope of the present invention and the appended claims. Therefore, the scope of the present invention is not limited to the contents disclosed in the embodiments and drawings.

Claims

1. A three-port power metering device suitable for photovoltaic grid connection, characterized in that: It includes a housing and integrated control module, measurement module, clock module, storage module, display module, power module and communication module installed in the housing. The measurement module, clock module, storage module and display module are all connected to the control module, and the power module is connected to other modules. The measurement module detects voltage and current on the grid side, photovoltaic side, and load side through a first port, a second port, a third port, and a common port, and transmits the detected data to the control module. The control module controls the working state of the energy meter, periodically activates the sampling circuit to acquire instantaneous voltage and current data, calculates power and electrical energy, and periodically updates the display on the display module. The control module also handles communication with the host computer and human-machine interaction applications. The clock module provides the system with a time coordinate. The storage module stores the various data collected and calculated. The display module displays voltage, current, power, and electrical energy. The power module is used to provide energy for the normal operation of the electricity meter; The communication module is used to establish communication with the host computer.

2. The three-port power metering device suitable for photovoltaic grid connection according to claim 1, characterized in that: The measurement module consists of one voltage measurement module and two current measurement modules. The voltage measurement module converts the high voltage to a low voltage through a series resistor voltage divider, and then outputs the voltage measurement signals at the grid connection points of the grid side, photovoltaic side, and load side after isolation by an operational amplifier. The two current measurement modules are installed at two of the three ports on the grid side, photovoltaic side, and load side, respectively, to measure the current signals flowing into the two ports. The current measurement modules convert the current into voltage signals for measurement through a shunt.

3. The three-port power metering device suitable for photovoltaic grid connection according to claim 1, characterized in that: The control module uses a microcontroller or a digital signal processor.

4. The three-port power metering device suitable for photovoltaic grid connection according to claim 1, characterized in that: The clock module uses a clock chip with a communication interface that can synchronize, correct, and keep time.

5. The three-port power metering device suitable for photovoltaic grid connection according to claim 1, characterized in that: The storage module uses a flash memory.

6. The three-port power metering device suitable for photovoltaic grid connection according to claim 1, characterized in that: The display module can be a liquid crystal display screen.

7. The three-port power metering device suitable for photovoltaic grid connection according to claim 1, characterized in that: The power module uses an AC / DC rectifier.

8. The three-port power metering device suitable for photovoltaic grid connection according to claim 1, characterized in that: The communication module can use power line carrier, RS485, or infrared communication methods.

9. A metering method for a three-port power metering device suitable for photovoltaic grid connection based on any one of claims 1-8, comprising the following steps: Step 1: Obtain the instantaneous voltage values ​​at the grid connection points of the grid side, photovoltaic side, and load side. u Instantaneous values ​​of the inflow current at the first and third ports i 1. i 3; and calculate the instantaneous value of the current flowing into the second port according to Kirkowski's Current Law: i 2=-（ i 1+ i 3）； Step 2: Based on the phase-locked loop module in the control module, obtain the system frequency f and the signal period T = 1 / f; Step 3: Calculate the active power of the signals acquired at the first, second, and third ports. According to the definition of active power, active power P refers to the average value of instantaneous power over one period T. Therefore, the active power of the signals acquired at the three ports... P x The calculation formula is: ； in, N The number of sampling points within one period T. n Sampling time, n =1,..., N , u n The instantaneous value of the grid connection point voltage at each sampling time. i xn For the first x The instantaneous current value at the port at each sampling time; Step 4: Calculate the active energy of the signals acquired at the first, second, and third ports. According to the definition of active energy, active energy W refers to the integral value of instantaneous power over a certain period of time. The active energy injected from the three ports is the electrical energy. W x The calculation formula is: ； in, W 0 represents the previously accumulated active electrical energy. W x For the first x The port currently has a total active power. Step 5: Calculate the effective values ​​of voltage and current according to the definition of effective value. U , I 1. I 2. I 3; The formula for calculating the grid connection point voltage is: ； No. x Port current I x The calculation formula is: ； in, u xn For the first x The port is n The voltage across the shunt measured at constant time, n =1,..., N , R This is the shunt resistor value; Step 6: Calculate the power factor and apparent power of the three ports according to the definition of apparent power. S x， The calculation formula is: ； Step 7: Calculate the power factor angles of the three ports. x The calculation formula is: ； Step 8: Calculate the reactive power at the three ports. Q x The calculation formula is: 。

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