WO2020068024A2

WO2020068024A2 - The smart circuit breaker for grid connected residential photovoltaic systems

Info

Publication number: WO2020068024A2
Application number: PCT/TR2019/050800
Authority: WO
Inventors: Gokay BAYRAK
Original assignee: Bursa Teknik Universitesi
Priority date: 2018-09-27
Filing date: 2019-09-27
Publication date: 2020-04-02
Also published as: WO2020068024A3

Abstract

The invention provides an electronic circuit for carrying out at least three measurements, comprising at least one controller (10), at least three current sensors (54), at least three voltage sensors (55), and at least three relays (211). The smart circuit breaker (K) is used for the protection of photovoltaic systems, characterized in that it comprises at least one web connection unit (12), the circuit breaker control card (20), which triggers said circuit breaker (21), which provides detection of island mode, voltage collapse, and voltage jump.

Description

THE SMART CIRCUIT BREAKER FOR GRID CONNECTED RESIDENTIAL

PHOTOVOLTAIC SYSTEMS

TECHNICAL FIELD

The invention relates to a smart circuit breaker, which enables the circuit breakers to be opened in the required conditions using real-time control and comparison of the inverter output, local load, and grid through appropriate communication in a distribution system.

In particular, the invention relates to a low-cost, high-response, high-speed smart circuit breaker capable of detecting island-mode operation (IMO), voltage collapse, and voltage jump failures in grid-connected photovoltaic (PV) systems.

PRIOR ART

Especially with the increase in the use of renewable energy sources and the widespread use of unlicensed electricity in the world, the number of small producers is increasing in production networks. The analysis of energy quality and the safekeeping of distribution systems increase its importance.

In case of a failure in the electricity grids, the generation facility connected to the grid, in the event of a failure in the grid, in the event of a grid interruption or case of a failure in the transmission line, it is called island mode operation (IMO). When island mode operation occurs, the distribution system becomes obligatory to be disconnected from the electricity grid as soon as possible due to the system going out of the specified operating voltage and frequency.

The IEEE 929-2008 standard states that when an island-mode operation occurs, the distribution system must be separated from the existing system. The IEEE 1547-2003 standard states that an undesired island mode operation is detected within a maximum of 2 seconds, and all distribution systems that energize the distribution line will face various problems if they do not leave the distribution line. For this reason, it is important to detect island mode operation in the shortest time and accurately. Especially in PV systems, changes in grid impedance caused instability of inverters operating parallel to the grid.

The island mode detection systems applied in the prior art are divided into local and remote monitoring methods. Local techniques are divided into passive, active, and hybrid. In cases where power imbalances are high in passive methods, IMO can be easily determined. The point of common coupling (PCC) refers to the connection point between the load and the transformer. In passive methods, system parameters such as voltage, frequency, harmonic distortion at the connection point are measured. However, if active and reactive power imbalances are small depending on the characteristics of the load in the system, IMO cannot be detected, and NDZ (non-detection zone) occurs. Active methods are evaluated according to normalized capacitor and coil values calculated based on RLC load values to prevent this situation. Especially in a PV system, the detection of IMO is quite difficult if the production is equal to the drawn load.

In active methods, by adding disturbing signals to the system, when IMO occurs in the distribution system, the disturbance signals added to the PCC point between the load and the inverter in the system cause a big change in the system parameter, and the detection of IMO can be achieved. In this structure, changes in the voltage or frequency parameters in PCC are detected and transferred to the circuit breaker with feedback so that the system can be disconnected from the network. Active methods include reactive power flow level, impedance meter, or phase or frequency shift.

As an alternative to independent and ineffective active and passive methods, hybrid methods that are used together with both methods and detection of the NDZ region, which passive methods cannot detect are used as the third detection method known in the literature. However, an alternative method has been developed due to the small amount of NDZ involved in the active methods and the degradation of the power quality of the active methods.

The most effective but cost-effective methods used in the known technique for the detection of IMO are remote monitoring methods. In remote monitoring methods, a communication platform is established between the network and the distribution system. A signal generator in the transmission system sends a signal to the distribution feeders in the existing power line. In the event of an IMO, the signal is interrupted, and detection occurs due to the opening of the circuit breakers between the transmission and distribution system. An alternative method for remote monitoring methods is based on the monitoring and analysis of all breakers and disconnectors that may cause IMO in the distribution system with the SCADA system. The application cost of this method is quite high. In particular, the need for high-cost measuring instruments and sensors and high- quality communications infrastructure leads to high operating costs. For this reason, remote methods are preferred, especially in high capacity systems.

In JPO document publication JP3725285, it is mentioned that phase-to-phase measurement of synchronous generators through AVR and reactive power calculation. The system in question is intended to detect island mode and is not sufficient for the detection of the NDZ region in the prior art. Also suitable for use in these AVR synchronous generator configurations and not for PV systems.

USPTO patent publication US6810339 discloses the island mode blocking method. In this embodiment, the detection of voltage, frequency, and phase information is provided in the case of IMO. In this embodiment, the NDZ situation cannot be prevented completely.

Consequently, all the problems mentioned above have made it necessary, an improvement in the art.

OBJECT OF THE INVENTION

The present invention makes it necessary to eliminate the problems mentioned above and to make a technical innovation in the related field.

The main object of the invention is to minimize the NDZ zone occurring in PV systems to a minimum and to provide a compact smart breaker structure that provides security of the system.

Another object of the invention is to provide remote monitoring of the system by simultaneously measuring the power, voltage, current, frequency, frequency difference, and phase difference data.

It is another object of the invention to provide remote monitoring of the system by simultaneously measuring active power, reactive power, and apparent power data.

Another object of the invention is to provide remote monitoring of the grid current, load current, and inverter current data simultaneously. Another object of the invention is to provide an economical circuit breaker structure that provides monitoring, remote monitoring of all parameters in the system, and protection when necessary.

It is a further object of the invention to eliminate the problem of NDZ with a more economical application without relying on a single parameter.

BRIEF DESCRIPTION OF THE INVENTION

The present invention is a smart breaker for residential photovoltaic systems connected to the network, to achieve all of the objectives mentioned above and the following detailed description.

The invention includes at least one controller, at least three current sensors, at least three voltage sensors, at least three electronic circuitry, at least three relays, circuit breaker control card for triggering said circuit breaker, relates to a smart breaker for detecting island mode, used for the protection of photovoltaic systems, characterized in that it comprises at least one web link unit.

The invention is a method of detecting IMO that allows remote monitoring of the PV system containing at least one local load, which is suitable for placement at the network connection point, characterized by positive peak voltage, negative peak voltage and RMS voltage, positive peak current, negative peak voltage at the inverter output, load input and network. It is characterized in that the PV system is disconnected from the grid in 10-100 ms by calculating the active power, reactive power and apparent power of the system, measuring and calculating the current and RMS current, measuring the frequency of the grid and the frequency of the inverter and calculating the frequency difference.

In another preferred embodiment of the invention, the relay comprises a low response time.

In another preferred embodiment of the present invention, the smart circuit breaker (K) for detecting island mode, which is used for the protection of photovoltaic systems according to claim 1 , comprising a circuit-breaker (21 ) with a solid-state relay (21 1 ). In another preferred embodiment of the present invention, the smart breaker (K) for detecting island mode for use in the protection of photovoltaic systems according to claim 1 , comprising a controller (10) with FPGA processor.

In a further preferred embodiment of the invention, the inverter comprises a measuring card-1 for measuring the current, voltage, and frequency at the output of the inverter.

In a further preferred embodiment of the present invention, the measurement card-2 is provided for measuring current, voltage, and frequency in the load line.

In another preferred embodiment of the present invention, the measurement card-3 is provided for measuring the current, voltage, and frequency in the grid line.

In a preferred another embodiment of the invention, the output of inverter owned systems, the grid load, and the positive peak voltage comprise a negative peak voltage and RMS voltage, and the controller calculates the following.

In a preferred another embodiment of the invention, the output of the inverter to have the system grid and the load current of the positive peak, negative peak current, and RMS current comprises calculating and slave controller.

In another preferred embodiment of the invention, the system comprises a controller which calculates the phase difference.

In another preferred embodiment of the invention, the active power pressed into the grid comprises a controller that calculates reactive power and apparent power.

In another preferred embodiment of the present invention, the controller comprises a controller that measures the frequency of the grid and the frequency of the inverter and calculates and monitors the frequency difference.

In another preferred embodiment of the invention, the inverter comprises at least one relay for each of the load and network.

In another preferred embodiment of the invention, the inverter comprises at least one relay for each phase of the load and grid.

In a further preferred embodiment of the present invention, the controller comprises a circuit breaker which is triggered by the output ports to separate the PV system and local load from the grid. In another preferred embodiment of the present invention, it has a protection unit that protects the circuit breaker, emergency deactivation and which has an emergency opening switch and fuse group.

In another preferred embodiment of the invention, the control board comprises at least one power supply for supplying the control card.

The scope of protection of the invention is outlined in the claims and is not to be limited to those described for purposes of illustration in this brief and detailed description. It will be apparent to one skilled in the art that, without departing from the main theme of the invention, similar embodiments can be achieved in light of the preceding.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 shows the flow diagram showing the measurement.

Figure 2 shows the diagram showing the decision tree after the measurement.

Figure 3 is a representative top view of the smart circuit breaker.

Figure 4 shows a diagram showing the operation of the smart circuit breaker.

Figure 5 shows a comparison of the measuring units.

DESCRIPTION OF THE REFERENCE NUMBERS IN THE FIGURES

10. Controller

11. Output pins of the controller

12. Web connection unit

20. The smart breaker controller card 21. Circuit breaker 30. Protection unit 40. Power supply 51. Measuring Board-1

511. Inverter connection terminal 52. Measuring Board-2

521 . Grid connection terminal

53. Measuring Board-3

531 . Load connection terminal

54. Current sensor

55. Voltage sensor

DETAILED DESCRIPTION OF THE INVENTION

In this detailed description, the smart circuit breaker for the grid-connected residential photovoltaic systems of the present invention is illustrated only by examples which will have no limiting effect to understand better the subject matter.

In a distribution system according to the invention, the inverter output relates to the smart circuit breaker (K), which enables the switching of the circuit breakers in the necessary conditions by real-time control and comparison of the local load and the grid with the appropriate communication method.

The invention provides an electronic circuit for performing at least three measurements, comprising at least one controller (10), at least three current sensors (54), at least three voltage sensors (55), and at least three relays (21 1 ). The circuit breaker (21 ) comprises at least one web connection unit (12), the circuit breaker control board (20), which triggers the mentioned circuit breaker (21 ).

Figure 3 is a representative top view of the breaker K according to the invention. Said breaker (K) comprises at least one controller (10). Said controller (10) comprises at least one port unit (1 1 ). By the software installed in control (10), the controller (1 1 ) is provided to simultaneously control the ports in the port unit (1 1 ).

The invention comprises at least one breaker control board (20), and using said breaker control board (20), the relays (21 1 ) on the circuit breaker (21 ) are triggered. The circuit breaker (21 ) comprises at least one relay (21 1 ), said relay (21 1 ) being preferably solid- state. In the preferred embodiment of the invention, there is at least one relay (21 1 ) structure for the phase connections of each unit to be controlled.

In the preferred embodiment of the present invention, the response time of the relays (21 1 ) on the circuit breaker (21 ) is preferably about 20-30 ms. In the preferred embodiments of the present invention, relays (21 1 ) having different response times may be used. In the IEEE 929-2008 standard, the response time of a breaker (K) is required to be 2 seconds. Relay (21 1 ) of the relays (21 1 ) on the circuit breaker (21 ), which allows the circuit breaker (K) of the present invention to open the circuit fully, may vary in response to these conditions.

The breaker (K), according to the invention, comprises at least one protection unit (30). Within said protection unit (30), there is at least one fuse for each controlled channel and includes at least one protection switch to shut down the system.

Breaker (K) comprises a power supply (40). The controller (10), circuit breaker (21 ), measuring board-1 (51 ), measuring board-2 (52), measuring board-3 (53), current sensors (53), and voltage sensors (K) are included in the circuit breaker (K). (55) is supplied by the said power supply (40).

The breaker (K) according to the invention, at least one inverter connection terminal (51 1 ) for connecting the output terminals of the inverter, the grid connection terminal (521 ) for connecting the system with the grid, and the load connection terminal (531 ) for the connection of the system with the load. The invention includes a metering card for each of said connections, and on said metering cards comprises a current sensor (54) and a voltage sensor (55). Figure 5 shows current sensors (54) and voltage sensors (55), the voltage measurement, current measurement, power measurement, and frequency measurements.

The invention comprises at least one metering card-1 (51 ) for measuring the output of the inverter, at least one metering card-2 (52) for measuring the grid, and at least one metering card-3 (53) for measuring the local load. Communication is provided between said measuring cards and the input ports of the controller (10).

Figure 4 shows a diagram showing the operation of the breaker (K). As can be seen in the figure, the connection to the circuit breaker control card (20) constituting the circuit breaker unit of the system is realized using the inverter connection terminal (51 1 ), grid connection terminal (521 ) and load connection terminal (531 ). The controller (10) communicates with the measuring cardl (51 ), the measuring card-2 (52), and the measuring profit-3 (53) and simultaneously checks the condition of the line.

In a further preferred embodiment of the invention, different connection applications can be realized in place of the inverter connection terminal (51 1 ), the grid connection terminal (521 ), and the load connection terminal (531 ).

In a preferred embodiment of the invention, the controller (10) is an FPGA processor. In this way, the measurement can be carried out simultaneously and quickly. In other preferred embodiments of the invention, it is possible to use different microprocessors.

The measurement steps of the circuit breaker K are shown in Figure 1 . These measurements are carried out in parallel and in real-time simultaneously.

The measurement made by the measurement cards is followed by the controller (10), and the necessary calculations are performed. Measurement, frequency and frequency change follow-up, grid voltage change follow-up, current measurement by measuring power values, and phase differences are monitored as follows.

Active power, reactive power, and apparent power of the system are measured while monitoring power values during these measurements.

Similarly, the output current and voltage of the inverter, the load current, and the voltage sag on it, the grid current, and the voltage are regularly measured simultaneously.

As is known, in PV systems, PV panels are connected to the inverter after the DC / DC converter. The inverter enables the electricity generated by the panels to be transferred to the grid. In this system, there is a local load between the output of the inverter and the grid connection, where generation is primarily consumed. Figure 4 illustrates this embodiment and the addition of the breaker (K) to this system.

Output terminals of the inverter on the inverter connection terminal (51 1 ) on the measuring board-1 (51 ) of the circuit breaker (K), grid connection terminals (521 ) on the grid connection terminal (521 ) on the measuring board (2) and on the load connection terminal (531 ) located on the measuring board-3 (53) to the load are fixed. In this way, the power output from the inverter, the power to the load can be controlled by the power breaker (K) supplying from the grid or not. At this point, the breaker (K) acts as a bridge. The current sensor (54) and the voltage sensor (55) are provided for measuring the current and voltage, the phase angle, on each measuring board of the circuit breaker (K). The measured data is transmitted to the controller (10), and the data received from the sensors is processed by the pre-configured program blocks in the memory unit of the controller (10).

Following the data received from the sensors, the controller (10) calculates by the flow diagram given in Figure 5. Within the scope of voltage measurement, positive peak voltage, negative peak voltage, and RMS voltage values are calculated. Flowever, current measurement is performed simultaneously, and positive peak current, negative peak current, and RMS current values are calculated within the scope of the current measurement. With the current and voltage data, phase angle and phase difference are calculated instantly.

The power is measured by the data received from the current sensor (54) and the voltage sensor (55). Active power, reactive power, and apparent power are measured instantly. All measurements made in this context are made for inverter, load, and grid, and the previous data are compared with the previously set variables simultaneously.

Furthermore, instantaneous frequency measurements are carried out employing the breaker (K). In this context, the frequency of the network and the inverter is measured continuously, and the frequency difference is measured accordingly.

The controller (10) of the present invention comprises at least one FPGA. Concurrent measurements enable the relay (21 1 ) on the circuit breaker (21 ) to be tripped without delay in case of failure.

In another preferred embodiment of the invention, a high-frequency processor capable of parallel processing may be used.

In a real-time or real-time controlled system with a delay of 1 -10 ms, continuously read parameters are compared with each other to ensure the operation of the system within the scope of fault tolerances. The smart circuit breaker (K) can thus detect faults such as island mode operation, voltage collapse, voltage rise.

In a preferred embodiment of the invention, a web link unit (12) comprises a configuration. Employing said web connection unit (12), all measured parameters of the system could be accessed remotely. The weblink unit (12) comprises at least one CAT link socket or wi-fi card. This interface allows for remote access to data and remote control of the breaker (K) by connecting to the grid. High-speed controller voltage utilizing current, the frequency parameters are controlled simultaneously, NDZ of only the breaker used for these parameters by power data due to being assayed simultaneously (K) relay (211 ) is restricted to response time.

In a preferred embodiment of the present invention comprises the solid-state relay (211 ). In the preferred embodiment, the response time of the relays (211 ) is in the range of 20- 30 ms. Since the speed of the controller (10), which performs the parameter control and the necessary calculations, is much higher than the response time of the relays (211 ), the controller becomes independent of the NDZ region. In other preferred embodiments of the invention, the NDZ can be further reduced by using a relay (211 ) with higher response time. The NDZ response time of the inventive, smart breaker, is in the range of 10-200 ms. The mandatory NDZ time in 2008 is 2 seconds, according to IEEE-929-2008.

Claims

1. Smart breaker (K) for detecting island mode, used for protection of photovoltaic systems, characterized in that said smart breaker (K) comprises

- at least one controller (10),

- at least three current sensors (54),

- electronic circuit comprising at least three voltage sensors (55) conducting at least three measurements,

- circuit breaker (21 ) comprising at least three relays (211 ),

- breaker control card (20) provides triggering of said circuit breaker (21 ),

- at least one web link unit (12).

2. Smart breaker (K) for detection of island mode for use in the protection of photovoltaic systems according to claim 1 comprising relay (211 ) having low response time.

3. Smart breaker (K) for detection of island mode for use in the protection of photovoltaic systems according to claim 1 comprising a circuit breaker (21 ) having a solid-state relay (211 ).

4. Smart breaker (K) for detection of island mode for use in the protection of photovoltaic systems according to claim 1 comprising controller (10) having FPGA processor.

5. Smart breaker (K) for detection of island mode for use in the protection of photovoltaic systems according to claim 1 comprising measuring card-1 (51 ) providing measurement of current, voltage, and frequency at the inverter output.

6. Smart breaker (K) for detection of island mode for use in the protection of photovoltaic systems according to claim 1 comprising measuring card-2 (52) for providing measurement of current, voltage, and frequency in the load line.

7. Smart breaker (K) for detection of island mode for use in the protection of photovoltaic systems according to claim 1 comprising measuring card-3 (53) for providing measurement of current, voltage, and frequency in the grid line.

8. Smart breaker (K) for detection of island mode for use in the protection of photovoltaic systems according to claim 1 comprising controller (10) which calculates and monitors the positive peak voltage, negative peak voltage and RMS voltage of the grid and load at the output of the inverter owned by the system.

9. Smart breaker (K) for detection of island mode for use in the protection of photovoltaic systems according to claim 1 comprising controller (10) which calculates and monitors the positive peak voltage, negative peak voltage and RMS current of the grid and load at the output of the inverter owned by the system.

10. Smart breaker (K) for detection of island mode for use in the protection of photovoltaic systems according to claim 1 comprising controller (10) which calculates phase difference in the system.

11. Smart breaker (K) for detection of island mode for use in the protection of photovoltaic systems according to claim 1 comprising controller (10) which calculates and monitors active power, reactive power, and apparent power transferred to the grid.

12. Smart breaker (K) for detection of island mode for use in the protection of photovoltaic systems according to claim 1 comprising a controller (10) which measures frequency of the grid and the frequency of the inverter, and monitors the frequency difference by calculating it.

13. Smart breaker (K) for detection of island mode for use in the protection of photovoltaic systems according to claim 1 comprising at least one relay (211 ) for each of the inverter, load, and grid.

14. Smart breaker (K) for detection of island mode for use in the protection of photovoltaic systems according to claim 1 comprising at least one relay (21 1 ) for each phase of the inverter, load, and grid.

15. Smart breaker (K) for detection of island mode for use in the protection of photovoltaic systems according to claim 1 comprising circuit breaker (21 ) which is to be triggered through the controller output ports (1 1 ) to separate PV system and local load from the grid.

16. Smart breaker (K) for detection of island mode for use in the protection of photovoltaic systems according to claim 1 comprising protection unit (30) having emergency opening switch and fuse group, protecting circuit breaker (K), enables it to be deactivated in case of emergency.

17. Smart breaker (K) for detection of island mode for use in the protection of photovoltaic systems according to claim 1 comprising at least one power supply (40) for supplying the control card (20).

18. IMO detection method, which allows remote monitoring of the PV system consists of at least one local load, and which suitable for placement at the grid port characterized by

- measuring and calculating the positive peak voltage, negative peak voltage, and RMS voltage, positive peak current, negative peak current and RMS current at the inverter output, load input, and grid,

- measuring the frequency of the grid and inverter, and calculating the frequency difference in the system,

- disconnecting the PV system from the grid in 10-100 ms by calculating the active power, reactive power and apparent power of the system.