DESC:FIELD OF THE INVENTION
The present invention relates to a Power Converter Topology and more particularly, to a unique Integrated Power Converter Topology which includes a Grid Tie Inverter and battery storage functionality, powered by the grid and/or a green energy power source.
BACKGROUND OF THE INVENTION
Power electronic converter topology refers to the arrangement of electronic components in a converter circuit that transforms electrical energy from one form to another. The topology determines the specific configuration of the components, such as transformers, power devices, resistors, capacitors, and inductors, used in the power converter circuit.
CN116094362A describes a double buck bidirectional inverter and a grid-connected system. The double buck full-bridge inverter-based power supply is improved and comprises a direct current power supply, an alternating current power supply, a first branch, a second branch, a third branch and a fourth branch, and has two working modes of grid-connected inversion and rectification. When the double buck bidirectional inverter is in a rectification working mode, the independent freewheeling diode replaces the body diode of the switching tube, so that the path of current flowing through the body diode is eliminated, and the effect of reducing common mode interference is achieved. Meanwhile, the double buck bidirectional inverter has no power switch bridge arm direct-connection problem, and can effectively improve reliability.
Such Prior Art consists of separate converters for the grid tie, charger/discharger, battery storage, and solar inverter parts of the system. Consequently, such prior art uses a higher number of switches in the topology. Consequently, such prior art carries drawbacks of increased cost and lower reliability inherent to the higher number of switches utilized in the Topology.

Accordingly, there is potential benefit in an Integrated Power Converter Topology which combines the functionality of a Grid Tie Inverter and battery storage functionality, powered by the Grid as well as a green energy source, as such an Integrated Power Converter Topology would overcome the above-mentioned drawbacks in the prior art.
SUMMARY OF THE INVENTION
Accordingly, the present invention presents an Integrated Power Electronic Converter (“Integrated PEC”). The Integrated PEC comprises of a low-frequency inductor unit and high-frequency inductor unit, a coupling multi-secondary power transformer, a bidirectional inverter unit, a buck-boost chopper circuit, a unidirectional device, an external (or internal) battery bank, and a control circuit, powered by an external AC source such as a grid and additionally and optionally, by an external DC Power Source such as, but not limited to a Renewable Power Source such as a Solar Panel Array. The design of the Integrated PEC is based on two-level technology, which maintains the DC bus voltage greater than typically 1.5 times of AC secondary voltage from the coupling multi-secondary power transformer. This DC voltage is maintained by the control circuit by monitoring the DC bus voltage feedback level. Hence, the Integrated PEC is seamlessly capable of bidirectional Power Flow, wherein the power may flow from (a) the Grid to the Integrated PEC in Converter mode, or alternatively, (b) From the Integrated PEC to the Grid, during Inverter mode, wherein the converter circuit sends power back to the grid. The inverter mode may be activated by several functional needs, such as (but not limited to) using the stored energy in the battery bank to discharge power into the Grid, or using the Renewable Power Source, when it is available, to charge the Battery. This bidirectional power flow maintains the level of DC voltage in the converter circuit throughout the operation cycle.
The unidirectional device prohibits reverse current flow from the DC link voltage produced by the bidirectional inverter unit. In the case where the DC voltage from the Renewable Power Source is greater than the DC link voltage, the batteries are charged from the Renewable Power Source. In the case where the DC voltage from the Renewable Power Source is less than the dc link voltage, the batteries are charged from the Grid. The battery bank is used for energy storage, regardless of it is charged from the Renewable Energy Source or from the Grid. Alternatively, the Integrated PEC is usable for Formation of Batteries during the battery production process, wherein they are formed by means of a charge / discharge sequence through the chopper circuit. During discharge, the battery energy is regenerated to the grid through the bidirectional inverter unit.
The multiport configuration at the secondary side of the coupling multi-secondary power transformer offers sufficient galvanic isolation as well as the possibility to connect a medium voltage source. This makes it possible to operate the Integrated PEC with regeneration into a low or medium voltage grid up to 36000Vac and power levels going up to multiple megawatts.
While using in grid tie mode, the multiple secondary windings make it possible to include multiple renewable energy sources.
OBJECT OF THE INVENTION
An object of the present invention is to integrate Grid Tie Inverter functionality and battery charge / discharge functionality in an Integrated Power Converter Topology.
Another objective is to incorporate the possibility for the Converter to be powered by any Renewable Energy power source in a power grid network.
Yet, another object of the present invention is to facilitate the functionality of charging/discharging/forming batteries using the grid as well as Renewable Energy power sources simultaneously and re-generate excess energy to the grid.
Yet, another object of the present invention is to utilize the bidirectional inverter unit as a captive energy source, employing multiple inverters connected in parallel through a multi-secondary power transformer.
Yet, another object of the present invention is to implement a grid tie with fewer power electronic switches, resulting in fewer losses, and allowing for configurable inverter operation in any mode.
BRIEF DESCRIPTION OF THE DRAWINGS
The objects and advantages of the present invention will become apparent when the disclosure is read in conjunction with the following figures, wherein
Figure 1 shows the detailed block diagram of a integrated power electronic converter including grid tie and battery storage functionalities in accordance with the present invention.
DETAILED DESCRIPTION OF THE INVENTION:
The foregoing objects of the invention are accomplished, and the problems and shortcomings associated with prior art techniques and approaches are overcome by the present invention described in the present embodiments.
The present invention provides an integrated power electronic converter that provides grid tie and battery storage functionalities. The integrated power electronic converter includes a grid tie inverter and a battery bank that can be powered by AC power source and/or a renewable energy source.
The present invention is illustrated with reference to the accompanying drawings, throughout which reference numbers indicate corresponding parts in the various figures. These reference numbers are shown in brackets in the following description and in the table below.
Ref No. Components Ref No. Components
10 AC source 60
Bidirectional inverter unit
20 Breaker 65 Chopper circuit
30 Coupling transformer 100 Unidirectional Device
35 Low-frequency inductor unit 110 Battery bank
40 Capacitor bank 120 Renewable power source
45 LC circuit 130 Controller
50 High-frequency inductor unit 200 Integrated Power Electronic Converter
Referring to figure 1, an Integrated Power Electronic Converter (200) (hereinafter referred as “Integrated PEC (200)”) is shown in accordance with the present invention.
The Integrated IPC (200) comprises an external AC source (10), a low-frequency inductor unit (35) and high-frequency inductor unit (50), a coupling transformer (30), a bidirectional inverter unit (60), a chopper circuit (65), a unidirectional device (100), an external or internal battery bank (110), an external renewable power source (120), and a controller (130).
The AC source (10) in a specific embodiment of the present invention is a three phase 50/60Hz AC source with a voltage range between 110V-36000V AC. The voltage range is selected based on the grid specifications of the electric network, and a breaker (20) circuit used for isolating the AC source (10) to the coupling transformer (30). In an embodiment of the present invention, the coupling transformer (30) is a multioutput secondary power transformer. The breaker (20) circuit is configured for coupling the AC source (10) to the bidirectional inverter unit (60) and by turning on/off the power supplied to the coupling transformer (30).
The coupling transformer (30) having electrical isolation between each of the secondary winding inside the housing. In the embodiments, the number of secondary windings and the size of the coupling transformer (30) varies according to network power ratings, and each of the secondary windings may be either in step-down or step-up configuration based on the power ratings of the circuit. In an exemplary embodiment, the coupling transformer (30) is at least one of a plurality secondary power transformer connected thereto. In another exemplary embodiment, a plurality of Integrated PECs (200) can be connected to a plurality of secondary coupling transformers.
A capacitor bank (40) along with the low-frequency inductor unit (35), and the high-frequency inductor unit (50) act as an LCL filter for the bidirectional inverter unit (60). LCL (35, 40, 50) filter is used for boosting the DC bus voltage. In another exemplary embodiment, the LCL filter boosts the DC bus voltage at any voltage level or specifically 1.5 times the secondary AC voltage from the transformer. In another exemplary embodiment, any other configuration can be used for boosting the DC bus voltage. The LCL filter (35, 40, 50) is further configured to reduce high-frequency AC current ripples and to help wave shaping of the current waveform.
In the embodiment, the switch unit (60a&60b) comprises a plurality of switches (Q1- Q6) that are connected in a three-phase bridge configuration to form a bidirectional inverter unit (60). The switching condition of each of the switches (Q1-Q6) is decided by a space vector modulation technique from the controller (130). In an exemplary embodiment, the switching of Q1-Q6, along with LCL filter (35,40,50) ensures the bidirectional power flow, keeping the current harmonic distortion THDi below 5%, similarly maintaining power factor (Cos Phi) at the secondary of multi-secondary power transformer better than 0.99.
The bidirectional inverter unit (60) is connected with the chopper circuit (65) via capacitor (C2) across thereto. In an exemplary embodiment, the bidirectional inverter unit (60) is configured as a captive energy source with multiple inverters connected in parallel through the coupling transformer (30). This connection is achieved with a fewer number of power electronic switches, and hence with lower losses as compared to Prior Art.
In a specific embodiment, the chopper circuit (65) is a buck-boost chopper. The chopper circuit (65) includes at least two insulated-gate bipolar transistors (IGBT) (Q7-Q8) with an inbuilt diode across the switch. The inbuilt diode works as a free-wheeling diode for inductor energy. The chopper circuit (65) is electrically coupled to the battery bank (110) via an LC circuit (45) comprising an inductor (L7) and a capacitor (C3). The switching frequency of the chopper circuit (65) is decided by the controller (130) and the series inductor (L7) in the LC circuit (45) by maintaining desired rms ripple current going in the batteries during charging.
The unidirectional device (100) is connected between the chopper circuit (65) and the renewable power source (120). In an embodiment, the unidirectional device (100) is a semiconductor diode (D1) that acts as a blocking device by conducting voltage in one direction and blocking voltage in reverse polarity. In an exemplary embodiment of the present invention, the renewable power source (120) is any renewable power source such as solar panel array. In an embodiment, the unidirectional device (100) is configured for connecting renewable power source unidirectionally to the chopper circuit (65) to charge the battery bank (110) and regenerate power to the grid through the bidirectional inverter unit (60).
The controller (130) is connected to the bidirectional inverter unit (60) and the chopper circuit (65). The switching of bidirectional inverter unit (60) and switching frequency of the chopper circuit (65) is decided by the controller (130). In an exemplary embodiment, the switching of the bidirectional inverter unit (06) is decided by a space vector modulation technique from the controller (130). The space vector modulation is responsible for generating pulse width-modulated signals to control the IGBTs of an inverter.
In another aspect of the present invention, the method of operation of an embodiment of the bidirectional inverter unit (60) is explained with respect to figure 1. The design of the Integrated PEC is based on two-level technology, which maintains the DC bus voltage greater than typically 1.5 times of AC secondary voltage from the coupling transformer (30). This DC voltage is maintained by the controller (130) by monitoring the DC bus voltage feedback level. Hence, the Integrated PEC acts as a bidirectional means, the power may flow from (a) the Grid to the Integrated PEC in Converter mode, or alternatively, (b) From the Integrated PEC to the Grid, during Inverter mode, wherein the converter circuit sends power back to the grid. The inverter mode may be activated upon two conditions, a. when the battery bank (110) is discharging during formation process, or b. when renewable energy source is available for charging battery bank (100) along with regenerating power to grid. This bidirectional current flow keeps a DC voltage maintained in Integrated PEC throughout the operation cycle. In the embodiment, the Capacitor (C2) is a dc link capacitor for transient suppression requirements (snubber). The LCL filter formed by low and high frequency inductor (35&50) and the capacitor bank (40) ensures the power factor at the grid above 0.99 and total current harmonics (THDi) less than 5% at rated operation of the converter circuit. Further, the battery ripple voltage is reduced by the capacitor (C3) in the LC circuit (45). The battery bank (110) is configured to be charged through the chopper circuit (65). The batteries can be charged through the mains network grid voltage simultaneously by the green energy source through the unidirectional device (100).
The unidirectional device (100) prohibits reverse current flow from the DC link voltage produced by the inverter. The unidirectional device (100) facilitates energy storage in the battery bank (110) from the renewable power source (120). In an exemplary embodiment of the present invention, in case of availability of renewable energy, if the voltage of the renewal energy source is greater than DC link voltage, the batteries are charged through the renewable energy, and when the voltage is less than the DC link voltage then the batteries are charged through the grid. The battery bank (110) is used for energy storage, they are charged from the renewable energy source or from grid. Alternatively, the Integrated PEC is usable for Formation of Batteries during the battery production process, wherein they are formed by means of a Charge / discharge sequence through the chopper circuit (65). During discharge, the battery energy is regenerated to the grid through the bidirectional inverter unit.
The battery bank (110) comprises a plurality of storage batteries specifically powered by the renewable power source (120) connected to the unidirectional device (100). The sizing of these cells is done according to the power rating of the inverter and the selection of a number of cells depends upon the DC link voltage of the bidirectional inverter unit (60). Typically, the range is 1.4 times the DC voltage.
The controller (130) monitors the grid voltage, current, dc-link voltage, battery voltage, and current and provides PWM signals to respective IGBTs. The switching frequency of the IGBTs is in a range of 0 - 500KHz based on the selection and switching speed and type of power semiconductor devices such as IGBTs, MOSFETs or SiC technology-based semiconductors.
Further, the unidirectional device (100) permits the connectivity to the renewable energy source in the Integrated PEC (200). The multiport configuration at the secondary side of the coupling transformer (30) offers sufficient galvanic isolation as well as the possibility to connect a medium voltage source. While using in grid tie mode, the multiple secondary windings make it possible to include a plurality of the renewable energy sources. In an exemplary embodiment, the bidirectional inverter unit (60) is configured to work in any mode:
1. Grid tie capability with multiple converters connected in parallel, as a captive energy source.
2. Battery storage with charging through renewable energy or grid in case of non-availability of the renewable energy.
3. Battery charger/discharger/battery formation rectifier device.

ADVANTAGES OF THE INVENTION

1. A reduced number of semiconductor switches and interconnections, thereby having lower losses, lower power consumption, and a higher reliability as compared to Prior Art.
2. Inherent capability to perform Battery charging/discharging/forming/storage from a Renewable Energy power source.
3. Inherent capability to regenerate the Excess Renewable Energy, over and above what is needed for battery charging/forming/storage, into the grid.
4. Inherent capability to regenerate the Battery discharge Energy
5. Inherent capability to act as a Grid Tie Inverter, where the Renewable Energy Power Source grid tied through multi secondary transformer, providing isolation.
6. Multi-secondary power transformer ensures the possibility of connecting medium voltage grid with galvanic isolation.
7. Lower cost due to reduced number of Power Semiconductor Switches.

The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the present invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated. It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the scope of the present invention.

,CLAIMS:We Claim:

1. An Integrated Power Electronic Converter (200) topology for a grid tie comprising:
a coupling transformer (30) electrically coupled to an AC source (10) and a bidirectional inverter unit (60);
a chopper circuit (65) connected to the bidirectional inverter unit (60);
a renewable power source (120) connected to the chopper circuit (65);
a unidirectional device (100) connected between the chopper circuit (65) and the renewable power source (120), the unidirectional device (100) is configured to block voltage in reverse polarity;
a battery bank (110) electrically coupled to the chopper circuit (65) and the renewable power source (120);
a controller (130) communicatively coupled to the bidirectional inverter unit (60) and the chopper circuit (65);
wherein the power flow from the AC source (10) to the battery bank (110) in converter mode and the current flow back to the grid in inverter mode;

2. The Integrated Power Electronic Converter (200) as claimed in claim 1, includes a breaker (20) circuit that connects the AC source (10) to the coupling transformer (30) via a power ON/OFF arrangement.
3. The Integrated Power Electronic Converter (200) as claimed in claim 1 includes a LCL (35,40,50) filter configured between the coupling transformer (30) and the bidirectional inverter unit (60) that boost the DC bus voltage, reduce high-frequency AC ripple and wave shaping of the current passing therethrough.
4. The Integrated Power Electronic Converter (200) as claimed in claim 1, wherein the bidirectional inverter unit (60) is configured by connecting a plurality of switches (Q1- Q6) in three-phase bridge configuration.
5. The Integrated Power Electronic Converter (200) as claimed in claim 1, wherein the controller (130) is configured with a space vector modulation technique for deciding switching condition of each of the switches (Q1-Q6).
6. The Integrated Power Electronic Converter (200) as claimed in claim 1, wherein the chopper circuit (65) is a buck-boost chopper.
7. The Integrated Power Electronic Converter (200) as claimed in claim 6, wherein the chopper circuit (65) includes at least two insulated-gate bipolar transistors (IGBT) (Q7 - Q8) with an inbuilt diode across a switch thereof.
8. The Integrated Power Electronic Converter (200) as claimed in claim 1 includes a LC circuit (45) configured for electrically coupling the battery bank (110) to the chopper circuit (65).
9. The Integrated Power Electronic Converter (200) as claimed in claim 6, wherein the switching frequency of the chopper circuit (65) is decided by the controller (130) and the LC circuit (45) by selecting desired DC current, reduced rms ripple current going in the battery bank (110) during charging.
10 The integrated power electronic converter (200) as claimed in claim 1 includes a capacitor (C2) configured across the bidirectional inverter (60) for transient suppression requirement.
11. The Integrated Power Electronic Converter (200) as claimed in claim 1, wherein the unidirectional device (100) is configured for connecting renewable power source unidirectionally to the chopper circuit (65) to charge the battery bank (110) and regenerate power to the grid through the bidirectional inverter unit (60).
12. The Integrated Power Electronic Converter (200) as claimed in claim 1, wherein the AC source (10) is three phase 50/60Hz AC source with voltage ranges between 110V-36000V AC.
13. The Integrated Power Electronic Converter (200) as claimed in claim 1, wherein the coupling transformer is at least one of a plurality secondary power transformer connected thereto.
14. The Integrated Power Electronic Converter (200) as claimed in claim 1, wherein the renewable power source (120) is a green energy DC power source.
15. The Integrated Power Electronic Converter (200) as claimed in claim 1, wherein the grid tie and the battery storage are integrated together to facilitate charging, discharging, or forming of the battery bank (110) with the grid and renewable energy simultaneously and re-generate excess energy to the grid.