WO2014192015A2

WO2014192015A2 - Method and system for a multiport modular pv inverter

Info

Publication number: WO2014192015A2
Application number: PCT/IN2014/000298
Authority: WO
Inventors: Madhuwanti Joshi
Original assignee: Indian Institute Of Technology Bombay
Priority date: 2013-05-03
Filing date: 2014-05-02
Publication date: 2014-12-04
Also published as: WO2014192015A3

Abstract

The proposed invention is a multiport modular PV inverter providing offering an option for switching between grid connected mode and off the grid mode along with storage. The system comprises at least an inverter module coupled with a PV module, a storage module, an AC grid module and a load. The inverter module arranged to switch between islanded mode and grid tied mode using a physical disconnect device. It is arranged to operate in microgrid and grid connected mode also communicates with a control center and other inverters using a remote control and monitoring device along with one of a wireless and wired communication link.

Description

TITLE:

Method and System for a multiport modular PV inverter FIELD OF THE INVENTION:

Present invention describes a modular solar power system which offers an option for switching between grid connected mode and off the grid mode along with storage.

BACKGROUND OF THE INVENTION:

A typical solar plant consists of the solar panels and an inverter to convert DC voltage generated from the solar panel into an AC voltage. This AC voltage is either compatible with the grid voltage in grid connected systems or it is just designed to be suitable for local loads in an off-grid system.

A solar system design has three important considerations: The first consideration is whether the system needs to be grid connected or not. Most of the large scale solar power plants in operation are grid connected. In such systems grid serves as an infinite reservoir.

The second consideration is whether the solar system needs storage in the form of batteries or any other storage device. Energy storage for the solar power system is important because solar power is irregular in nature. This causes grid voltage and frequency fluctuations when installed in large capacities. Another problem with solar energy is that the amount of electrics] energy generated varies significantly over a period of time or duration. In order to achieve a minimum fliictuaiicii in energy supply, storage is essential especially during generation of higher energy; solar energy with higher storage capacity is not only necessary for remote areas but also different geological locations having climate fluctuations.

The third aspect of the solar power, system is the modularity and ease of installation. A modular system as proposed in the present invention is easily upgraded to the end user requirements. All the present day solar- systems are complicated to install for the end user. There are simple systems like micro- inverters and AC modules but however this system does not offer any provision for storage.

Two types of systems exist today. First type has a solar battery charger. This system is like an UPS. In this system battery is charged by solar energy or grid when the grid is available. In the absence of the grid the battery delivers power to the selected load. The transition between the grid and the battery is done by using an automatic switch.

The second system type is grid connected solar inverter. This solar inverter may be a string inverter with multiple solar panels connected in series or one inverter connected to a single panel and then connecting multiple inverters in parallel.

In the absence of grid, if a PV mic ogrid is required, the output of grid connected inverter needs to be synchronised with one of a separate battery inverter and any other island AC inverter. In such cases, there is a lot of electronics circuit which does not get used efficiently and optimally

OBJECTIVE OF THE INVENTION: 1. It is the primary objective of the invention to provide modular system so the user can design the system as they need. 2. It is another objective of the invention to provide optional modes in order to suit various energy needs. 3. It is another objective of the i ention to provide a system with ease of installation which reduces the overall p s'em cost significantly.

4. It is another objective of the invention to provide high reliability with multiple inverters connected in parallel to the system.

5. It is another objective of the invention to have maximum functionality with minimum electronics hardware configuration.

SUMMARY OF THE INVENTION:

The present invention is related to the field of solar inverter system topology. It describes a new product which enables user to have a modular solar power system. The system comprises at least an inverter module coupled with a PV module, a storage module, an AC grid module and a load. This system offers an option for switching between the grid connected mode and off the grid mode while offering storage. The inverter module circuits comprises a bidirectional DC to AC converter circuit for converting the DC voltage and DC current of the PV module in to AC voltage and AC current as required by the load and also to use the storage device to store the energy from the AC grid, a bidirectional DC to DC converter for storing the energy in a storage device and also support the load in absence of said PV module which is further coupled to said bidirectional DC to AC converter, a control circuit to operate and control said bidirectional DC to DC converter, said bidirectional DC to AC converter and said switching circuit which is coupled to said bidirectional DC to DC converter, at least a communication circuit to establish communication between plurality of inverters and also with outside world which is coupled to said control circuit a switching circuit to physically disconnect between the load and the AC grid and an energy metering and monitoring circuit. The inverter module arranged to switch between islanded mode and grid tied mode using a physical disconnect device. It is arranged to operate in microgrid and grid connected mode also communicates with a control center and other inverters using a remote control and monitoring device along with one of a wireless and wired commu ication link.

BRIEF DESCRIPTION OF THE DRAWINGS:

Figure- 1 shows the proposed system concept in accordance with an aspect of the present invention.

Figure-2 shows the block diagram of rmiitiport inverter in the grid connected mode used for one panel with an aspect of the present invention.

Figure-3 shows the block diagram o multiport inverter in the micro-grid mode used for one panel with an aspect of the present invention.

Figure-4 shows the block diagram of the multiport inverter with an aspect of the present invention. . Figure -5 shows the multiple system operating in parallel with an aspect of the present invention.

Figure -6 shows the communication between the inverters and the remote control and monitoring device with an aspect of the present invention.

DETAIL DESCRIPTION OF THE INVENTION:

The system and method of the proposed multiport modular grid tied PV solar inverter module is explained below with reference to the accompanying drawings in accordance with an embodiment of the present invention. The present invention relates to a solar system which can operate in grid tied and off the grid mode. It also has a battery charging port for charging the batteries. This unique concept of having multiple ports for grid, load, battery and PV makes the hardware very much modular.

A block diagram of the PV solar inverter (11) is illustrated in Figurel . The solar inverter has four ports, namely PV (10), AC grid (12), load (13) and battery (14).There are two possibilities of using this type of inverter. In the first type, PV input is given as a series and/or parallel combination of multiple PV module DC output. In the second type, the mverter can simply be module integrated microin verier or per panel inverter. Fig. 2 and Fig. 3 gives a general idea of this system from a common man's perspective if used as a per panel inverter. In this system, each solar panel is independent from each other. If used in the grid connected mode,the output of the inverter can be directly connected to any common power outlet in a typical household. If it is used in microgrid mode, the load circuit can be separated from the grid as shown in Fig. 3. The inverter can work in grid connected or standalone mode with the battery support. The inverter supports a remote control and monitoring device (15). The communication between the inverter and the remote control and monitoring device (15) is on a wireless link. The remote control and monitoring device (15) has the capability of adding multiple solar systems and displaying the energy generated by the system.

The system consists of six essential circuits, the first is the bi-directional DC-DC converter^ 8) for charging the storage module i.e. battery(14) or any other storage device, second is a bi-directional DC to AC converter or inverter(19) , the third one is the physical disconnect switch (20) between AC grid module (12) and the load (13), fourth one the control circuit (17) to operate and control DC-DC converter (18), DC-AC converter (19) and the disconnect device (20), fifth is the energy metering or monitoring circuit ( 1) and the last one is the communication circuits(16) for communication between the two inverters and also with the outside world. The communication itself can be wired or wireless. The control of the physical disconnect device helps the inverter operate in grid tied and off the grid modes. Figure 4 shows a block diagram of this multiport inverter.

The two systems are designed to operate in five operating modes: PV Grid tied mode:

In this mode, the battery gets charged either from the solar panel or the grid. The inverter delivers solar power to the grid. The inverter supports bi-directional ·■· power flow. When multiple inverters are connected in parallel, they all follow the - grid voltage and frequency.

No PV Grid tied inverter:

In this mode, the battery may get charged from the grid or support grid imbalance by providing reacting power.

PV Off the grid mode:

In this mode, part of the solar energy i s used for charging the battery and part of it is used to support the local loads. If the battery is completely charged and the load on the inverter is not sufficient then either the inverter is operated in simple voltage and current control mode or the excess power generated is reused in any other ways. Some of the ways of using this energy could be water heating, water pumping etc. When there are multiple inverters connected in parallel, first inverter acts as a master inverter setting the reference voltage and frequency and the other inverters follow the master. Battery operated off the grid mode:

In this mode, the inverter simply acts as regular battery inverter providing back up power. When there are multiple inverters connected in parallel, first inverter acts as a master inverter setting the reference voltage and frequency and the other inverters follow the master.

Micro-grid operation: In this mode, when the main power grid has failed and the electricity is being generated by local generator (different from PV source) e.g. diesel, all the solar inverters follow the local generator voltage and frequency. Multiple systems : operating in parallel is shown in fig. 5. Micro grid operation is also possible when the multiple inverters are operated in parallel and are operating in the off the grid mode.

The control and communication of the inverter system is digitally programmable and can be configured to change the priorities and preferences of different operating modes. Various types of controls are implemented in this system. They are discussed as below:

, MPPT (Maximum Power point Tracking) control:

In this mode the inverter itself operates with either a module level MPPT program if it is a microinverter or a string level MPPT program if the inverter is a string inverter and tracks the maximum power of the solar panel.

Topology based control: In this mode, the inverter operates with closed loop control regulating the output voltage and current of the inverter. In the grid tied mode, the inverter acts a current source and in the off the grid mode, the inverter acts as voltage source. Grids connected/off the grid control:

In this mode, the inverter has control circuit to detect the grid voltage and synchronize with it. It also has the control program to operate in the off the grid mode using the built in switching network. In this mode the inverter controller detects if there is any other source on the load line and if there is none, then it becomes the master and staits generating power. The grid and the load are separated by a physical disconnect device.

Master slave control:

In this mode, the inverter has control software to run in master slave configuration when multiple units are connected.

Metering and monitoring:

In this mode, the inverters are able to measure the energy generated by them and either communicate it to the outside world or display on a local meter.

Communication:

In this mode, the inverters are able to communicate between them and also with a remote control and monitoring device (15).This communication can be a wired one or wireless depending on the application. The inverter will have the possibility of both the types of communication. Fig. 6 shows a communication structure between the inverters. Functions such as smart metering may be added to the inverter using this communication.

Battery charge control: In this mode, the inverter has advanced control software to charge the battery using battery charger circuit. The inverter has complete software to detect the battery health.

In conclusion there are Ihree unique features:

1. Hard ware to support grid tied, off the grid and battery charging mode;

2. Control algorithms to operate between grid tied and off the grid mode;

3. High modularity;

4. Lower system cost than the state of the art inverter design.

5. Communication between the inverters and a remote control and monitoring device (15)

This invention is a type of solar inverter. It is designed for low power solar ^! systems ha ving power rating in the range of a few kW. Such systems are typically installed on the rooftops of residential or commercial buildings.

The above description along with the accompanying drawings is intended to be illustrative and should not be interpreted as limiting the scope of the invention.

Those skilled in the art to which the invention relates will appreciate that many variations of the described example implementations and other implementations exist within the scope of the claimed invention.

Claims

What is claimed is:

1. A system for multiple modular PV inverter comprising of: at least an inverter module coupled with a PV module, a storage module, an AC grid module and a load; wherein said inverter module circuits comprising: a bidirectional DC to AC converter circuit for converting the DC voltage and DC current of the PV module in to AC voltage and AC current as required by the load and also to use the storage device to store the energy from the AC grid; a bidirectional DC to DC converter for storing the energy in a storage device and also support the load in absence of said PV module which is further coupled to said bidirectional DC to AC converter; a control circuit to operate and control said bidirectional DC to DC converter, said bidirectional DC to AC converter and said switching circuit which is coupled to said bidirectional DC to DC converter; at least a communication circuit to establish communication between plurality of inverters and also with outside world which is coupled to said control circuit; a switching circuit to physically disconnect between the load and the AC grid; an energy metering and monitoring circuit; and wherein the inverter module arranged to switch between islanded mode and grid tied mode using a physical disconnect device, the inverter module arranged to operate in micro grid and grid connected mode, the inverter module arranged to communicate with a control center and other inverters using a remote control and monitoring device along with one of a wireless and wired communication link and further the inverter module supports metering of the used power over the communication link;

2. The system for multiple modular PV inverter as claimed in claim 1, where the system is used as a portable roof top PV installation kit comprising at least an inverter module coupled with a PV module, a storage module, remote monitoring and controlling devices.

3. The system for multiple modular PV inverter as claimed in claim 1 , wherein said inverter module is one of a first type and second type.

4. The system for multiple modular PV inverter as claimed in claim 1, wherein said storage device can be a battery, a fuel cell, a flywheel storage and any other storage mechanism;

5. The system for multiple modular PV inverter as claimed in claim 2, wherein said first type inverter comprising the PV module is given as one of a series and parallel combination of multiple PV panel for DC output.

6. The system for multiple modular PV inverter as claimed in claim 2, wherein the said inverter can be one of a module integrated and per panel inverter in said second type inverter.

7. The system for multiple modular PV inverter as claimed in claim, 1 , wherein said inverter is one of single switching stage and two switching stage.

8. The system for multiple modular PV inverter as claimed in claim 1, wherein said inverter module supports bidirectional power flow between AC grid and the storage device connected on the PV side.

9. The system for multiple modular PV inverter as claimed in claim 1, wherein said communication circuit further comprising of a transmitter module, a receiver module connected over one of wired and wireless link and a metering device to keep the account of energy generated by the system.

10. A method for multiple modular PV inverter comprising steps of: a plurality of operating modes; and a plurality of control modes;

1 1. The method for multiple modular PV inverter as claimed in claim 9, wherein said plurality of operating modes comprising of: a PV grid tied mode; a PV off the grid mode; a storage device operated off the grid mode; and a micro-grid operation mode;

12. The method for multiple modular PV inverter as claimed in claim 10, wherein the storage device stores the energy from PV and also the grid.

13. The method for multiple modular PV inverter as claimed in claim 11, wherein the PV inverter delivers a solar power in the grid in said PV grid tied mode.

14. The method for multiple modular PV inverter as claimed in claim 12, wherein plurality of the PV inverters follow the grid voltage and frequency when multiple inverters are connected in parallel in said PV grid tied mode.

15. The method for multiple modular PV inverter as claimed in claim 10, wherein a first part of the solar energy is used for charging the battery and a second part of the energy is used to support the local loads in said PV off the grid mode.

16. The method for multiple modular PV inverter as claimed in claim 14, wherein a first inverter acts as a master inverter setting a reference voltage and frequency and other inverters follow the master inverter in said PV off the grid mode.

17. The method for multiple modular PV inverter as claimed in claim 10, wherein the inverter acts as regular battery inverter providing a backup power in the off the grid mode.

18. The method for multiple modular PV inverter as claimed in claim 10, wherein the first inverter acts as a master inverter setting a reference voltage and frequency and other inverters follow the master inverter in said battery operated off the grid mode.

19. The method for multiple modular PV inverter as claimed in claim 10, wherein an electricity is generated by a local generator when main power grid has failed in said micro-grid operation.

20. The method for multiple modular PV inverter as claimed in claim 10, wherein an electricity is generated by operating multiples of inverters in micro-grid.

21. The method for multiple modular PV inverter as claimed in claim 9, wherein said plurality of control modes comprising of: a MPPT(Maximum Power point Tracking) control mode; a topology based control mode; a grid tie and grid off control mode; a master slave control mode; a communication control mode; and a battery charge control mode;

22. The method for multiple modular PV inverter as claimed in claim 18, wherein the inverter system is digitally programmed and configured to change the priorities and preferences of different operating mode;

23. A method for multiple modular PV inverter as claimed in claim 18, wherein the inverter itself operates with one of a module level MPPT program if the inverter is a micro-inverter and a string level MPPT program if the inverter is string inverter and further tracks the maximum power of the solar panel in said MPPT control mode.

24. The method for multiple modular PV inverter as claimed in claim 18, wherein the inverter operates with closed loop control regulating a output voltage and current of the inverter in said topology based control mode.

25. The method for multiple modular PV inverter as claimed in claim 20, wherein the inverter acts as a current source in said grid tied mode and the inverter acts as a voltage source in said off the grid mode.

26. The method for multiple modular PV inverter as claimed in claim 18, wherein the inverter in said grid tie and off grid control mode further comprising of: a control circuit to detect the grid voltage and synchronized with it; and a control program to operate in the off the grid mode using build in V said switching network;

27. The method for multiple modular PV inverter as claimed in claim 22, - wherein the inverter controller detects if there is any other source on the load line in said grid tie and grid off control mode.

28. The method for multiple modular PV inverter as claimed in claim 23, wherein the grid tie and grid off control mode if the inverter controller does not detects any other source then it becomes the master or slave and starts generating power.

29. The method for multiple modular PV inverter as claimed in claim 18, wherein the inverter has control software to run in the master slave configuration when multiple units are connected in said master slave control mode.

30. The method for multiple modular PV inverter as claimed in claim 18, wherein the inverters are able to communicate between themselves over one of a wireless link or wired link and with said remote control and said monitoring device,

31. The method for multiple modular PV inverter as claimed in claim 18, wherein the inverters has an advanced control software to charge the the storage device using said battery charger circuit in said battery charge control mode.

32. The method for multiple modular PV inverter as claimed in claim 27, wherein the inverters has complete software to detect the battery health in said battery charge control mode.

Dated 02^πα of May 2014

MAHUA ROY CHOWDHURY IN/PA- 496

(Authorized Patent Agent for the Applicant)